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13: Chemoorganotrophy - Biology

13: Chemoorganotrophy - Biology


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Chemoorganotrophy is a term used to denote the oxidation of organic chemicals to yield energy. The process can be performed in the presence or absence of oxygen, depending upon what is available to a cell and whether or not they have the enzymes to deal with toxic oxygen by-products.

Aerobic Respiration

To start, let us focus on the catabolism of organic compounds when it occurs in the presence of oxygen. In other words, oxygen is being used as the final electron acceptor. When the process utilizes glycolysis and the tricarboxylic acid (TCA) cycle to completely oxidize an organic compound down to CO2, it is known as aerobic respiration. This generates the most ATP for a cell, given the large amount of distance between the initial electron donor (glucose) and the final electron acceptor (oxygen), as well as the large number of electrons that glucose has to donate.

Organic Energy Sources

In chemoorganotrophy, energy is derived from the oxidation of an organic compound. There are many different organic compounds available to a cell, such as proteins, polysaccharides, and lipids. But cellular pathways are arranged in such a way to increase metabolic efficiency. Thus, the cell funnels reactions into a few common pathways. By convention, glucose is used as the starting molecule to describe each process.

Glycolysis

Glycolysis is a nearly universal pathway for the catabolism of glucose to pyruvate. The pathway is divided into two parts: part I, which focuses on modifications to the 6-carbon sugar glucose, and part II, where the 6-carbon compound is split into two 3-carbon molecules, yielding a bifurcated pathway. Part I actually requires energy in the form of 2 molecules of ATP, in order to phosphorylate or activate the sugar. Part II is the energy conserving phase of the reaction, where 4 molecules of ATP are generated by substrate-level phosphorylation, where a high-energy molecule directly transfers a Pi to ADP.

The net yield of energy from glycolysis is 2 molecules of ATP for every molecule of glucose. In addition, 2 molecules of the carrier NAD+ are reduced, forming NADH. In aerobic respiration, these electrons will ultimately be transferred by NADH to an electron transport chain, allowing the cell to capture more energy. Lastly, 2 molecules of the 3-carbon compound pyruvate are produced, which can be further oxidized to capture more energy for the cell.

Glycolysis.

Tricarboxylic acid (TCA) cycle

The tricarboxylic acid (TCA) cycle picks up at the end of glycolysis, in order to fully oxidize each molecule of pyruvate down to 3 molecules of CO2, as occurs in aerobic respiration. It begins with a type of connecting reaction before the molecules can enter the cycle proper. The connecting reaction reduces 1 molecule of NAD+ to NADH for every molecule of pyruvate, in the process of making citrate.

The citrate enters the actual cycle part of the process, undergoing a series of oxidations that yield many different products, many of them important precursor metabolites for other pathways. As electrons are released, carriers are reduced, yielding 3 molecules of NADH and 1 molecule of FADH2 for every molecule of pyruvate. In addition, 1 molecule of GTP (which can be thought of as an ATP-equivalent molecule) is generated by substrate-level phosphorylation.

Taking into account that there were two molecules of pyruvate generated from glycolysis, the net yield of the TCA cycle and its connecting reaction are: 2 molecules of GTP, 8 molecules of NADH, and 2 molecules of FADH2. But where does the ATP come from? So far we only have the net yield of 2 molecules from glycolysis and the 2 molecules of ATP-equivalents (i.e. GTP) from the TCA cycle. This is where the electron transport chain comes into play.

TCA at the End of Glycolysis.

Oxidative Phosphorylation

The synthesis of ATP from electron transport generated from oxidizing a chemical energy source is known oxidative phosphorylation. We have already established that electrons get passed from carrier to carrier, in order of their standard reduction potential. We have also established that some carriers accept electrons and protons, while others accept electrons only. What happens to the unaccepted protons? And how does this generate ATP for the cell? Welcome to the wonderful world of the proton motive force (PMF) and ATP synthase!

Proton Motive Force

Protons that are not accepted by electron carriers migrate outward, to line the outer part of the membrane. For bacteria and archaea, this means lining the cell membrane and explains the importance for the negative charge of the cell.

As the positively charged protons accumulate, a concentration gradient of protons develops. This results in the cytoplasm of the cell being more alkaline and more negative, leading to both a chemical and electrical potential difference. This proton motive force (PMF) can be used to do work for the cell, such as in the rotation of the bacterial flagellum or the uptake of nutrients.

ATP synthase

The PMF can also be used to synthesize ATP, with the help of an enzyme known as ATP synthase (or ATPase). This large enzyme has two components, one that spans the membrane and one that sticks into the cytoplasm and synthesizes the ATP. Protons are driven through the membrane-spanning component, generating torque that drives the rotation of the cytoplasmic portion. When the cytoplasmic component returns to its original configuration it binds Pi to ADP, generating a molecule of ATP.

Aerobic Respiration Summary

After all that, what did the cell end up with, from using aerobic respiration? Using substrate-level phosphorylation the cell generated 2 net molecules of ATP during glycolysis, in addition to 2 molecules of ATP-equivalents from the TCA cycle. For reduced carriers, there were 2 molecules of NADH generated during glycolysis, in addition to 8 molecules from the TCA cycle or its connecting reaction. There were also 2 molecules of FADH2 from the TCA cycle. All of those electrons were passed on to the ETC (and eventually to oxygen), in order to develop a PMF, so that ATP synthase could generate ATP. How much ATP is generated?

Research indicates that the process is not completely efficient and there is some “leakage” that occurs. Current estimates are that 2.5 ATP are generated for every molecule of NADH, while 1.5 ATP are generated for every molecule of FADH2. Using these values would allow the cell to synthesize 25 molecules of ATP from all the NAD+ that was reduced in the process, in addition to 3 molecules of ATP from the FAD+ that was reduced. This would bring the grand total of maximum ATP produced to 32 (counting the GTP in that figure).

ATP Generation.

Anaerobic Chemoorganotrophy

Certainly oxygen is a wonderful final electron acceptor, particularly when paired with glucose as an initial electron donor. It is part of the lowest redox couple on an electron tower, with an extremely positive standard electron potential. But what does a microbe do, if oxygen is not available or it lacks the protections necessary from toxic oxygen by-products? Let us focus on the generation of energy in the absence of oxygen, using a different electron acceptor, when an organic chemical is still being used as the initial electron donor. Examples of anaerobic chemoorganotrophy include anaerobic respiration and fermentation.

Anaerobic Respiration

Anaerobic respiration starts with glycolysis as well and the pyruvate can be shunted off to the TCA cycle, just like in aerobic respiration. In fact, oxidative phosphorylation is used to generate most of the ATP, which means the use of an ETC and ATP synthase. The key difference is that the final electron acceptor will not be oxygen.

There are a variety of possible final electron acceptors that can be used in anaerobic respiration, allowing microbes to live in a wide variety of locations. The best electron acceptor will be the one that is lowest down on the electron tower, in an oxidized form (i.e. on the left-hand side of the redox couple). Some common electron acceptors include nitrate (NO3-), ferric iron (Fe3+), sulfate (SO42-), carbonate (CO32-) or even certain organic compounds, like fumarate.

How much ATP is generated by anaerobic respiration? That will depend upon the final electron acceptor being used. It will not be as much as is generated during aerobic respiration, since we know that oxygen in the best possible electron acceptor. Selection of an electron acceptor other than oxygen pushes an organism up the electron tower, shortening the distance between the electron donor and the acceptor, reducing the amount of ATP produced.

Fermentation

No matter what they might teach you in a biochemical class, fermentation and anaerobic respiration are not the same thing, at least not to a microbiologist.

Fermentation is catabolism of glucose in the absence of oxygen as well and it does have some similarities to anaerobic respiration. Most obviously, it does not use oxygen as the final electron acceptor. It actually uses pyruvate, an organic compound. Fermentation starts with glycolysis, a process which we have already covered, that also starts off both aerobic respiration and anaerobic respiration. What does it yield? Two net molecules of ATP by substrate-level phosphorylation and 2 molecules of NADH. Organisms doing either aerobic or anaerobic respiration would then utilize oxidative phosphorylation in order to increase their ATP yield. Fermenters, however, lack an ETC or repress synthesis of their ETC when oxygen is not available, so they do not use the TCA cycle at all.

Without the use of an ETC (or a PMF or ATP synthase), no further ATP is generated beyond what was synthesized during glycolysis. But organisms using fermentation cannot just stop with glycolysis, since eventually all their molecules of NAD+ would become reduced. In order to re-oxidize this electron carrier they use pyruvate as a final electron acceptor, yielding a variety of fermentation products such as ethanol, CO2, and various acids.

Lactate Fermentation. By Sjantoni (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Fermentation products, although considered waste products for the cell, are vitally important for humans. We rely on the process of fermentation to produce a variety of fermented foods (beer, wine, bread, cheese, tofu), in addition to using the products for a variety of industrial processes.

Key Words

chemoorganotrophy, aerobic respiration, glycolysis, substrate-level phosphorylation, tricarboxylic acid (TCA) cycle, GTP, oxidative phosphorylation, proton motive force (PMF), ATP synthase/ATPase, anaerobic respiration, fermentation.

Study Questions

  1. What is chemoorganotrophy?
  2. In glycolysis, what’s the starting compound? How many molecules of ATP (total and net) are produced? How molecules of NADH are reduced?
  3. What is substrate level phosphorylation?
  4. How do organisms reoxidize NADH, after the breakdown of glucose to pyruvate? Why is it important for them to reoxidize the NADH?
  5. During the TCA cycle and connecting reaction, what is glucose broken down to? How many molecules of ATP/ATP equivalents are formed by substrate phosphorylation? How many molecules of NAD and how many molecules of FAD are reduced?
  6. What does the cell get from the TCA cycle, in terms of energy & intermediates?
  7. In aerobic respiration, how is NADH reoxidized? What is the maximum ATP’s per NADH or FADH formed during this reoxidation? What is the final electron acceptor?
  8. What components are involved in electron transport? What is a proton motive force and what role does it play in energy generation?
  9. What is oxidative phosphorylation? Where specifically is energy given off in electron transport and how is that energy conserved?
  10. How does ATP synthase work to harvest the conserved energy?
  11. How many ATPs are formed when glucose is completely broken down in bacterial aerobic respiration and where do they come from? What other products are formed?
  12. How is anaerobic respiration similar and different from aerobic respiration? How does the energy yield compare? Why?
  13. How is fermentation similar and different to aerobic & anaerobic respiration? How does the energy yield compare? Why? What are the end products of fermentation?
  14. For each type of metabolism in this chapter, what is the initial electron donor? What is the final electron acceptor? What processes are used to generate energy? What is the energy yield?

Lactate Fermentation. By Sjantoni (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Fermentation products, although considered waste products for the cell, are vitally important for humans. We rely on the process of fermentation to produce a variety of fermented foods (beer, wine, bread, cheese, tofu), in addition to using the products for a variety of industrial processes.

Key Words

chemoorganotrophy, aerobic respiration, glycolysis, substrate-level phosphorylation, tricarboxylic acid (TCA) cycle, GTP, oxidative phosphorylation, proton motive force (PMF), ATP synthase/ATPase, anaerobic respiration, fermentation.

Study Questions

  1. What is chemoorganotrophy?
  2. In glycolysis, what’s the starting compound? How many molecules of ATP (total and net) are produced? How molecules of NADH are reduced?
  3. What is substrate level phosphorylation?
  4. How do organisms reoxidize NADH, after the breakdown of glucose to pyruvate? Why is it important for them to reoxidize the NADH?
  5. During the TCA cycle and connecting reaction, what is glucose broken down to? How many molecules of ATP/ATP equivalents are formed by substrate phosphorylation? How many molecules of NAD and how many molecules of FAD are reduced?
  6. What does the cell get from the TCA cycle, in terms of energy & intermediates?
  7. In aerobic respiration, how is NADH reoxidized? What is the maximum ATP’s per NADH or FADH formed during this reoxidation? What is the final electron acceptor?
  8. What components are involved in electron transport? What is a proton motive force and what role does it play in energy generation?
  9. What is oxidative phosphorylation? Where specifically is energy given off in electron transport and how is that energy conserved?
  10. How does ATP synthase work to harvest the conserved energy?
  11. How many ATPs are formed when glucose is completely broken down in bacterial aerobic respiration and where do they come from? What other products are formed?
  12. How is anaerobic respiration similar and different from aerobic respiration? How does the energy yield compare? Why?
  13. How is fermentation similar and different to aerobic & anaerobic respiration? How does the energy yield compare? Why? What are the end products of fermentation?
  14. For each type of metabolism in this chapter, what is the initial electron donor? What is the final electron acceptor? What processes are used to generate energy? What is the energy yield?

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Advances in Bacterial Respiratory Physiology

Marianne Guiral , . Marie-Thérèse Giudici-Orticoni , in Advances in Microbial Physiology , 2012

6 Concluding Remarks

A. aeolicus , an extreme chemolithotroph isolated from a marine hydrothermal environment, possesses outstanding properties. It has a special phylogenetic position and grows at the highest temperature known for a bacterium. Some of the proteins isolated from this microorganism are thus extraordinarily stable, that is, able to function under harsh conditions of temperature. The molecular basis for adaptation of these proteins to such extreme conditions has met an enhanced knowledge in the last few years. These findings have also attracting issues toward biotechnological devices, which are currently envisaging for health or environmental applications. In particular, hydrogenases from A. aeolicus present high efficiency toward hydrogen oxidation in addition to resistance to oxygen and CO. Consequently, they are viewed as excellent catalysts for H2/O2 biofuel cells, in replacement of platinum catalysts. Nowadays, the research faces great improvements in enzyme connection to electrode interfaces that promise development of biofuel cells able to power hundreds of μW cm − 2 devices in a very close future.

All the A. aeolicus energy-generating mechanisms are not elucidated however, it seems clear that A. aeolicus presents a versatile metabolism. It can use, through a flexible respiratory system, reduced and oxidized sulfur species, in addition to hydrogen and oxygen as energy substrates. This probably allows the bacterium to adapt to fluctuations of nutrients available in its native habitats. Its potential to gain energy from various substrates and the use of the energy-efficient rTCA cycle for carbon assimilation (low energy demand compared to the Calvin–Benson–Bassham cycle) are probably an advantage over other microorganisms ( Hügler, Gärtner, & Imhoff, 2010 ). The challenge in studying the energy metabolism of A. aeolicus comes from the fact that the bacterium requires the three energy compounds, hydrogen, oxygen, and sulfur, at the same time for growth, at least in batch cultures, greatly restricting the possibility of metabolic conditions and electron donor/electron acceptor combinations to be studied. Moreover, this leads to energy conservation pathways with many interconnections that require considering the energy metabolism as a whole. No genetics tools are available for this microorganism preventing deletions and in vivo studies, and objectives are thus to develop alternative approaches to describe this complex energy metabolism. Further works are in progress to clarify the physiology of this hyperthermophilic bacterium, particularly the requirement in oxygen supply which may be a key parameter in regulation and functioning of the various respiratory chains. The interconnection between all the electron transfer routes is the next step to understand.


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Chapter 13 Metabolic Diversity of Microorganisms,100% CORRECT

) The metabolic diversity of photosynthetic bacteria stems from different A) bacteriochlorophylls and pigments they contain. B) chlorophylls they can have and organic compounds they can produce. C) . light-harvesting complexes, electron donors, and organic compounds they produce. D) unrelated taxa capable of photosynthesis. 2) Whether an organism is classified as a photoheterotroph or a photoautotroph depends on its A) energy source. B) carbon source. C) oxygen requirements. D) carbon and energy sources. 3) In photosynthesis, NADH and NADPH are produced from NAD+ and NADP+ by A) oxidation reactions. B) reduction reactions. C) both oxidation and reduction reactions. D) neither oxidation nor reduction reactions. 4) Bacteriochlorophyll and chlorophyll contain ________ as a cofactor. A) iron (II) B) iron (III) C) magnesium D) manganese 5) In contrast to chlorophylls, carotenoids function A) as accessory pigments that enable absorption of energy from higher wavelengths. B) primarily as photoprotection (but they also transfer some absorbed energy into reaction centers). C) to convert reactive oxygen species into usable energy. D) to quench toxic oxygen species. 6) Proteomic analysis of a microbial community indicated an abundance of phycobiliproteins. Which phototrophic group is likely active and abundant in this community? A) cyanobacteria B) eukaryotic phototrophs C) green bacteria D) prochlorophytes 7) At some of the lowest light concentrations, ________ can still grow well due to their ________, which effectively harvest photons for energy. A) green bacteria / antenna pigments B) green bacteria / chlorosomes C) purple bacteria / antenna pigments D) purple bacteria / chlorosomes 8) Light energy passes from phycobiliproteins to reaction centers in A) cyanobacteria. B) green sulfur bacteria. C) purple bacteria. D) most photosynthetic bacteria. 9) Two separate photosystems involved in electron flow is a hallmark of A) anoxygenic phototrophs. B) green sulfur bacteria. C) oxygenic phototrophs. D) purple bacteria. 10) Intracytoplasmic membrane systems housing vesicles known as chromatophores, which function in photosynthesis, are commonly found in A) algae. B) green sulfur bacteria. C) most autotrophic organisms. D) purple phototrophic bacteria. 11) "Special pair" is the name given to the ________ in the photochemical complex of the purple bacteria. A) two bacteriochlorophyll a molecules B) two bacteriochlorophyll b molecules C) two quinones D) two reaction centers 12) What will happen to a cyanobacterium that has its photosystem II (PSII) blocked? A) Additional electron acceptors, such as NADP+, will be required to oxidize oxygen and overcome the lost PSII process. B) Anoxygenic photosynthesis only using photosystem I (PSI) could occur by using cyclic photophosphorylation and an alternative electron donor such as H2S. C) It will die from being unable to obtain energy for photosynthesis. D) Photons will generate excessive reactive oxygen species and the cyanobacterium will die as a consequence. 13) Which group of microorganisms would the Calvin cycle LEAST likely be found in? A) anoxygenic Bacteria B) chemolithotrophic Bacteria C) cyanobacteria D) hydrocarbon catabolizing Bacteria 14) The process by which electrons from the quinone pool are forced against the thermodynamic gradient to reduce NAD+ to NADH is called reverse A) proton motive force. B) reduction. C) electron transport. D) energy flow. 15) The path of electron flow in oxygenic phototrophs is referred to as the ________ scheme. A) E B) S C) Q D) Z 16) Plastocyanin is a A) membrane-bound sac found in certain bacteria. B) photosynthetic pigment found in some bacteria. C) copper-containing protein in photosystem II that donates electrons to photosystem I. D) blue-green bacterium known for its unusual photoreactive complex. 17) The Calvin cycle A) is responsible for the fixation of CO2 into cell material. B) utilizes both NAD(P)H and ATP. C) requires both ribulose bisphosphate carboxylase and phosphoribulokinase. D) uses CO2, NAD(P)H, and ATP to make biomass with ribulose bisphosphate carboxylase and phosphoribulokinase. 18) Regarding CO2 fixation mechanisms in the autotrophic green sulfur bacteria, A) Chlorobium uses the reverse citric acid cycle, and Chloroflexus uses the hydroxypropionate pathway. B) Chlorobium uses the hydroxypropionate pathway, and Chloroflexus uses the reverse citric acid cycle. C) both Chlorobium and Chloroflexus use the reverse citric acid cycle. D) both Chlorobium and Chloroflexus use the hydroxypropionate pathway. 19) In most cases, the final product of sulfur oxidation is A) hydrogen sulfide. B) elemental sulfur. C) sulfate. D) thiosulfate. 20) Identifying carboxysomes in a bacterium suggests it A) contains the reverse citric acid cycle. B) has a deficient Calvin cycle and accumulated CO2. C) is in a carboxylic acid rich environment and is storing excess quantities for potentially harsh conditions. D) will use the Calvin cycle convert the concentrated CO2 into biomass. 21) Ferrous iron (Fe2+) oxidation generally occurs in environments with A) alkaline conditions. B) high H+ concentrations. C) high oxygen content. D) little or no light present. 22) Alternative autotrophic routes to the Calvin cycle such as the reverse citric acid cycle and the hydroxypropionate pathway are unified in their requirement for A) CO2. B) coenzyme A. C) NAD(P)H. D) organic compound(s) formed. 23) The aerated upper layer of soil is likely to have ________ concentrations of H2 for aerobic H2-oxidizing Bacteria, so these bacteria likely ________. A) high / thrive in such conditions by not competing with chemoorganotrophs B) high / generate important reducing equivalents as byproducts for other microorganisms in the soil C) low / do not occur in such habitats D) low / will need a chemoorganotrophic way to grow as well 24) What metabolic advantage do cells have in storing the elemental sulfur byproduct from sulfide oxidation? A) The cells avoid producing transport energy waste to secrete the sulfur. B) The byproduct serves as an electron reserve for subsequent oxidation. C) Sulfur decreases the intracellular acidification for non-acid-tolerant sulfide oxidizers. D) The byproduct can be used for other biosynthetic pathways that use sulfur, such as Rieske Fe-S proteins. 25) A cell that lacks sulfite oxidase but can still oxidize sulfur for energy could be identified by A) adenosine phosphosulfate reductase coupled with substrate-level phosphorylation. B) electrons being transferred to cytochrome c prior to shuttling them into the electron transport chain. C) identifying an alternative quinone, flavoprotein, or cytochrome. D) quantifying the release of sulfate byproduct. 26) The only organisms that perform photosynthesis are ones that produce some form of A) chlorophyll or bacteriochlorophyll. B) carotenoids. C) phycoerythrin. D) phycocyanin. 27) Which of the following are NOT found within the photosynthetic gene cluster of Rhodobacter (a purple phototrophic bacterium)? A) genes encoding reaction center and light-harvesting photocomplexes B) genes encoding proteins involved in phycobiliprotein biosynthesis C) genes encoding proteins involved in bacteriochlorophyll biosynthesis D) genes encoding proteins involved in carotenoid biosynthesis 28) Anammox is an anaerobic process that generates energy from ________ and forms N2. A) ammonia B) ammonium C) ammonia and nitrate D) ammonia and nitrite 29) What would likely occur if an anammox bacterium was unable to use ladderane lipids? A) Ammonium rather than ammonia would be used due to ammonia toxicity to other cellular processes. B) It would require a different source for carbon assimilation. C) Rates of anammox would be considerably slower due to a lack of localized metabolism. D) Reactive nitrogen species would kill the cell. 30) Which of the following reactions is classified as a heterofermentation? A) hexose 2 lactate + 2 H+ B) HCOOH H2 + CO2 C) glucose lactate + ethanol + CO2 + H+ D) fructose 3 acetate + 3 H+ 31) Glucose fermentation by Clostridium spp. produce ATP only when acetate and butyrate are produced. Why do these organisms produce acetone and butanol after strong initial activity of generating ATP with acetate and butyrate byproducts? A) Acetate and butyrate accumulation creates a deadly acidic environment, which acetone and butanol do not. B) Acetate and butyrate are no longer needed for biosynthetic pathways. C) Acetone and butanol serve as better sources for NAD(P)+ reduction. D) Acetone and butanol production is favored for stability to store intracellular carbon sources for potential nutrient poor conditions. 32) The foul-smelling putrescine byproduct suggests activity of A) amino acid fermentation by clostridia. B) secondary fermentation. C) sulfur-oxidizing bacteria. D) syntrophic carbohydrate metabolism. 33) A bacterium that catabolizes a compound by linking ion pumps to establish a proton or sodium motive force for energy A) can circumvent substrate-level and oxidative phosphorylation. B) makes insufficient energy to grow but enough for cellular maintenance to survive. C) requires a second bacterium to cooperatively drive the gradient. D) still requires another carbon substrate to provide a carbon source. 34) Which metabolic strategy’s existence suggests rapid growth is NOT always the best strategy to survive in the environment? A) anaerobic fermentation B) disproportionation C) methylotrophy D) syntrophy 35) Obligate anaerobes can often use ________ electropositive redox couples than facultative anaerobes, and ________ metabolism is most common in this group as well. A) lower / assimilative B) lower / dissimilative C) higher / assimilative D) higher / dissimilative 36) In Bacteria, the MOST common oxidized form of nitrogen is ________ and of sulfur is ________. A) nitrate / sulfate B) nitrate / sulfite C) nitrite / sulfate D) nitrite / sulfite 37) Anaerobic fermentation often provides CO2, which can be used by ________ as an electron acceptor for energy. A) acetogens B) methanotrophs C) methanogens D) acetogens and methanogens 38) How is ATP made by an acetogen during CO2 fixation? A) Electrons from metal cofactors energize the electron transport chain and drive the proton motive force to activate ATP synthase. B) Substrate-level phosphorylation of ADP occurs when coenzyme A is removed from acetyl-CoA. C) It is made by substrate-level phosphorylation and a Na+-translocating ATPase. D) The energized CO-CH3 complex during thioesterification drives a Na+-translocating ATPase. 39) A researcher lacked the necessary equipment to measure methane production so instead monitored CO2 concentration as the unknown archaeon grew and produced methane. Why might CO2 NOT decrease but methane still increase? A) An alternative carbon source such as methanol was used. B) CO2 is not a carbon source used by methanogens. C) CO2 was used an electron donor but not as a carbon substrate. D) Methanogenic Archaea containing carboxysomes likely made measuring small losses of CO2 difficult to conclude. 40) Methanogens that use methyl-CoM for biosynthesis use ________ as a substrate. A) acetate B) carbon monoxide C) methane D) methanol 41) The serine pathway and ribulose monophosphate pathway can both be used by ________ as a way to incorporate carbon into biomass. A) acetogens B) anoxygenic hydrocarbon fermenters C) methanogens D) methylotrophs 42) What products would be expected to form during anoxic degradation of the seven-carbon compound benzoate following reduction and cleavage of the aromatic ring? A) 1 three-carbon compound and 1 four-carbon compound B) 1 three-carbon compound and 2 two-carbon compounds C) 2 three-carbon compounds and CO2 D) 3 two-carbon compounds and CO2 43) Organisms that aerobically catabolize methane use the intermediate ________ for biosynthesis and produce ________ when oxidizing the substrate for energy. A) CH2O (formaldehyde) / CO B) CH2O (formaldehyde) / CO2 C) HCOO− (formate) / CO D) HCOO− (formate) / CO2 44) Which of the following is NOT a potential reason anoxic methane-oxidizing Archaea have not also acquired the ability to reduce sulfate? A) An individual electron acceptor such as sulfate is not always present where methane is. B) Minimizing the metabolic requirements of the archaeon's genome size provides flexibility to interact with other reducing bacteria, such as nitrate reducers. C) The archaeon-bacterium relationship yields more energy from methane oxidation/sulfate reduction when performed together than separately. D) The methane-oxidizing Archaea will not easily acquire this metabolic capability from the bacterial partner 45) What metabolism would be favored when there is a lack of electron acceptors? A) anaerobic fermentation B) anoxygenic photosynthesis C) anoxic ammonia oxidation D) acetogenesis True/False Questions 1) The conversion of light into chemical energy is called photoautotrophy. 2) The light-harvesting pigments in Bacteria are classified as bacteriochlorophylls. 3) Reaction centers ONLY indirectly receive photon energy via light-harvesting molecules. 4) Chlorosomes are present in purple bacteria but absent in green sulfur and nonsulfur bacteria. 5) Carotenoids are hydrophobic accessory pigments and vary widely in the color they can absorb. 6) Each chlorophyll and bacteriochlorophyll type is distinguished by its absorption spectrum. 7) Photooxidation reactions can lead to the production of toxic forms of oxygen and the destruction of the photosynthetic apparatus. 8) The Calvin cycle provides autotrophs the ability to convert inorganic carbon into biomass and generate energy during this process. 9) A bacterium that uses CO2 as an electron source but CANNOT use it as a carbon source is considered a mixotroph. 10) Phototrophic purple bacteria such as Rhodobacter species grow ONLY by photosynthesis, using bacteriochlorophylls to harvest light. 11) Despite being called the reverse citric acid cycle, it is currently identified as the most ancient autotrophic pathway. 12) Chemolithotrophs that obtain electrons from donors such as sulfide use the same electron transport chains to obtain energy as chemoorganotrophs. 13) Photosystem I is responsible for splitting a water molecule in the first step of oxygenic electron flow. 14) RubisCO converts ribulose bisphosphate and CO2 into two molecules of 3-phosphoglyceric acid (PGA). 15) Organisms grown with CO2 as its sole carbon source must have energy in the form of ATP as well as reducing power. 16) Iron-oxidizing bacteria grow better in alkaline environments where protons are less likely to abiotically convert Fe2+ into Fe3+. 17) Some sulfur-oxidizing bacteria can simultaneously reduce nitrate, which enables them to grow anaerobically. 18) Due to a chemical equilibrium, a syntrophic relationship can be disrupted if the product from the first partner's metabolism is removed too quickly. 19) Because H2 levels in oxic environments are transient, it is likely that aerobic hydrogen bacteria shift between chemoorganotrophy and chemolithotrophy depending on levels of organic compounds and hydrogen in their habitats. 20) Some anaerobic bacteria not only use organic compounds as a carbon source but can also use them for energy as well. 21) Heterofermentation CANNOT be differentiated from homofermentation based on the compound fermented. 22) A monooxygenase can always be distinguished from a dioxygenase by incorporating only one oxygen atom from O2 into the substrate rather than both. 23) Reductive dechlorination involves chlorinated organic compounds serving as electron donors and releasing the chloride in inorganic forms. 24) Fermentation of organic compounds, such as acetate, produces NADH and ATP. 25) The acetyl-CoA pathway is a primary route for carbon source utilization. 26) When elemental sulfur is provided externally as an electron donor, the organism must attach itself to the sulfur particle because of the extreme insolubility of elemental sulfur. 27) One result of the oxidation of reduced sulfur compounds is a rise in the pH of the medium. 28) Bacteria that are capable of oxidizing both iron and sulfur usually have a strong preference for sulfur oxidation because it yields more energy. 29) Beta-oxidation exclusively removes two carbons at a time to catabolize fatty acids regardless of the carbon chain length. 30) Bacteria that degrade aromatic compounds with reductions steps rather than oxygenase activity prior to ring fission are likely to be anaerobes. Essay Questions 1) Compare and contrast the prokaryotic and eukaryotic light-gathering machinery function and spatial organization. Why do various chlorophylls show different absorption spectra? 2) What is the difference between chlorophyll and bacteriochlorophyll, and which organisms contain each? 3) Explain the Calvin cycle process that produces a full molecule of glucose and regenerates the ribulose bisphosphate molecule. 4) In what types of organisms are carboxysomes found and what advantage do they provide for a cell? 5) Describe what occurs when elemental sulfur is provided externally as an electron donor and how energy is obtained. 6) Illustrate the reaction center of a purple bacterium with the following features highlighted: antenna pigments, the special pair, protein H, protein L, protein M, quinone pool, and ATPase. Also explain the importance of proximity for these components within a reaction center. 7) Explain why it is unlikely an iron-oxidizing bacterium would thrive in a cold stream with a neutral pH. Also propose an experiment that would test whether iron-oxidizing bacteria are present in the stream. 8) Propose why it would be advantageous for a photosynthetic microorganism to have more than one type of chlorophyll or bacteriochlorophyll. 9) Under what circumstances does oxygenic photophosphorylation use non-cyclic photophosphorylation and when does it use cyclic photophosphorylation? Also describe what occurs during each process. 10) Why does an organism that is able to respire both aerobically and anaerobically preferentially undergo aerobic respiration? 11) Explain why most iron-oxidizing bacteria are obligately acidophilic, and discuss some of the environments where these organisms are found. 12) Explain why the discovery of iron-oxidizing phototrophs has important implications for both understanding the evolution of photosynthesis and explaining the large deposits of ferric iron (Fe3+) found in ancient sediments on Earth. [Show More]


GALILEO Open Learning Materials

This lab manual was created for Anatomy and Physiology I at the University of Georgia under a Textbook Transformation Grant and revised through a Scaling Up OER Pilot Grant.

  1. Introduction to Anatomy & Physiology
  2. Cells
  3. Histology – Epithelial & Connective Tissues
  4. Histology – Muscle & Nervous Tissues
  5. The Integumentary System
  6. Introduction to the Skeletal System
  7. Introduction Joints
  8. The Lower Limb – Bones
  9. The Lower Limb – Muscles
  10. The Lower Limb – Joints
  11. The Lower Limb – Nerves
  12. The Lower Limb – Movement
  13. The Upper Limb – Bones
  14. The Upper Limb – Muscles
  15. The Upper Limb – Joints
  16. The Upper Limb – Nerves
  17. The Upper Limb – Movement
  18. Muscle Physiology
  19. Axial Skeleton
  20. Axial Musculature
  21. Intervertebral Discs
  22. Central Nervous System – The Spinal Cord
  23. Central Nervous System – The Brain
  24. Motor Control
  25. The Senses – Vision
  26. The Senses - Hearing

Accessible files with optical character recognition (OCR) and auto-tagging provided by the Center for Inclusive Design and Innovation.


Biological Sciences

Our courses promote an understanding of modern biological principles, foster independent thinking, deepen the understanding of biology's relevance to modern societal issues and encourage personal growth in scientific writing and research. Many courses have internet components to improve the students analytical powers and information technology skills which are valuable for success in life beyond college.

Programs at Kingsborough Community College provide biology majors with an excellent foundation to transfer to four year colleges and universities, and to transfer to professional schools in the allied health sciences. With a wide variety of degree offerings and concentrations students have many ways to launch a career in the exciting and constantly expanding field of Biology. Please note our new program: A.S. Biotechnology


Most cases of trisomy 13 result from having three copies of chromosome 13 in each cell in the body instead of the usual two copies. The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 13.

Trisomy 13 can also occur when part of chromosome 13 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) or very early in fetal development. Affected people have two normal copies of chromosome 13, plus an extra copy of chromosome 13 attached to another chromosome. In rare cases, only part of chromosome 13 is present in three copies. The physical signs and symptoms in these cases may be different than those found in full trisomy 13.

A small percentage of people with trisomy 13 have an extra copy of chromosome 13 in only some of the body's cells. In these people, the condition is called mosaic trisomy 13. The severity of mosaic trisomy 13 depends on the type and number of cells that have the extra chromosome. The physical features of mosaic trisomy 13 are often milder than those of full trisomy 13.

Learn more about the chromosome associated with Trisomy 13


Abstract

Many of the α-proteobacteria establish long-term, often chronic, interactions with higher eukaryotes. These interactions range from pericellular colonization through facultative intracellular multiplication to obligate intracellular lifestyles. A common feature in this wide range of interactions is modulation of host-cell proliferation, which sometimes leads to the formation of tumour-like structures in which the bacteria can grow. Comparative genome analyses reveal genome reduction by gene loss in the intracellular α-proteobacterial lineages, and genome expansion by gene duplication and horizontal gene transfer in the free-living species. In this review, we discuss α-proteobacterial genome evolution and highlight strategies and mechanisms used by these bacteria to infect and multiply in eukaryotic cells.


Watch the video: ATP u0026 Respiration: Crash Course Biology #7 (December 2022).