16 Cellular respiration Flashcards by Dawn Parker

what are the needs for ATP?

active transport

chemical activation

anabolic synthesis

cellular ultrastructure

bioluminescence

exocytosis

movement (e.g. of flagella and cilia)

homeostasis

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why is ATP considered to be the ‘universal energy currency’?

found in all living eukaryotic and prokaryotic cells

links energy-releasing and energy-consuming reactions

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where does glycolysis take place? why?

cytosol

requires specific enzymes only found there

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what is the function of glycolysis?

to oxidise glucose and split a 6C hexose into 2x 3C triose (pyruvate)

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what is required for glycolysis?

1 glucose molecule

2 ATP

2 NAD+

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what are the products of glycolysis?

2 pyruvate

4 ATP (gross)

2 red. NAD

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give each stage of the conversion from a. glucose to pyruvate

a. glucose

glucose phosphate

fructose phosphate

fructose bisphosphate

2 glyceraldehyde 3-phosphate

2 glycerate 1,3-bisphosphate

2 glycerate 3-phosphate

2 pyruvate

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what is phosphorylation? what is its use in glycolysis?

addition of a phosphate group, providing a -ve charge to the substrate (which prevents glucose diffusing out of the cel)

increases the CPE of glucose ∴ Ea of next reaction decreases

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where does the link reaction take place? why?

mitochondrial matrix

CoA and other enzymes only found here

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what substrates are required for the link reaction?

1 pyruvate

1 ATP

1 CoA

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how does pyruvate reach the mitochondrial matrix?

moves across mitochondrial envelope through specialised intrinsic protein carriers via active transport

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what are the three reactions involved in the link reaction?

decarboxylation

redox

dehydrogenation

[collectively oxidative decarboxylation}

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what are the components of coenzyme A (CoA)?

pantothetic acid (a vitamin B complex)

ADP

-SH group (joins acetyl group to CoA)

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what are the products of the link reaction?

CO(2)

acetyl CoA (aCoA)

red. NAD

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how can fats be converted into a CoA molecule?

B. oxidation occurs - 2C fragments hydrolysed from hydrocarbon tails of fatty acids

each fragment can make 1 CoA

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where does the Krebs cycle take place?

mitochondrial matrix

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what is the Krebs cycle controlled/limited by?

substrate concentration

allosteric (non-competitive) inhibitors

end-product inhibition

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KC: what is added to oxaloacetate to produce citrate?

an acetyl group from aCoA

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KC: what is added/removed to citrate to produce a 5C intermediate?

CO(2)

+ NAD+ (producing red. NAD)

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KC: what is added/removed to the 5C intermediate to produce a 4C intermediate?

CO(2)

+ NAD+ (producing red. NAD)

+ ADP + P(i) (producing ATP)

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KC: what is added to the 4C intermediate to produce another 4C intermediate?

+ FAD (producing red. FAD)

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KC: what is added to the second 4C intermediate to reform oxaloacetate?

+ NAD+ (producing red. NAD)

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what is produced in 1 turn of the Krebs Cycle?

1 ATP

2 CO(2)

1 red. FAD

3 red. NAD

what is the purpose of red. FAD and red. NAD?

co-enzymes

act as H carriers to the electron transport chain (eTC)

to allow production of ATP via oxidative phosphorylation

where does oxidative phosphorylation take place?

cristae of inner mitochondrial membrane

what molecules are involved in the eTC?

red. NAD red. FAD e- carriers O2

eTC: what are e- carriers?

specialised carrier globular proteins accept/donate e- have a quaternary structure (a prosthetic group: - Fe3+ + e- Fe2+)

eTC: what is the first e- carrier?

red. NAD dehydrogenase

eTC: how do e- carriers pump H+ across inner mitochondrial membrane?

e- cause conformational change to protein structure causes protein to pump H+ across membrane into the inter-membrane space

eTC: how does the pumping of H+ in the eTC result in the formation of ATP?

pumping creates an electrochemical H+ gradient --> proton motive force H+ diffuse back down gradient through ATP synthase channels into mitochondrial matrix E released forms ATP from ADP and P(i)

eTC: what is the role of oxygen?

to act as the final e- acceptor and combine with 2H+ and 2e- to form H(2)O

how many ATP molecules are produced in: - glycolysis - link reaction - krebs cycle - oxidative phosphorylation as substrate-level phosphorylation?

- 4 - 0 - 2 - 0

how many ATP molecules are produced indirectly from: - 2 red. NAD from glycolysis - 2 red. NAD from link reaction - 6 red. NAD from Krebs cycle - 2 red. FAD from Krebs cycle?

- 4 - 4 - 18 - 4

why is the net gain of ATP always less than the theoretical gain?

used for active transport of pyruvate used to move ADP into matrix used to shuttle red. NAD from glycolysis into mitochondria some protons leak from the inter-membrane space ∴ reduced proton motive force ∴ less ATP made

what is anaerobic respiration?

when molecules other than oxygen are used as final electron acceptors

what is the purpose of anaerobic respiration?

to allow glycolysis to continue and produce 2 ATP

what type of anaerobic respiration takes place in skeletal muscles?

lactate fermentation | following vigorous exercise

outline the stages of lactate fermentation

H removed from red. NAD combines with pyruvate --> lactate NAD oxidised to NAD+ ==> NAD+ can accept more e- and glycolysis can continue

what can result from a build up of lactate?

inhibition of glycolysis cramp and fatigue in skeletal muscles lactic acidosis

what is the fate of lactate?

transported to liver in plasma oxidised back to pyruvate by lactate dehydrogenase forming red. NAD 1/5 = respired aerobically, producing ATP in the Krebs cycle 4/5 = converted to glucose-6-phosphate and then to glycogen in glycogenesis in liver cells

what type of anaerobic respiration takes place in yeast?

alcoholic fermentation

why is yeast considered a 'facultive anaerobe'?

it can survive in both anaerobic and aerobic conditions (although growth is faster in aerobic)

outline the stages of alcoholic fermentation

pyruvate is decarboxylated to ethanAl and CO(2) by pyruvate decarboxylase ethanAl acts as H+ acceptor and removes H+ from red. NAD forming ethanOl (catalysed by ethanOl dehydrogenase) oxidising red. NAD back to NAD+ ==> NAD+ can now accept more e- and glycolysis can continue

why is alcoholic fermentation considered wasteful for the yeast?

CPE is trapped in the ethanOl ∴ it is wasted

what is a respiratory substrate?

an organic molecule that can be oxidised in respiration to produce ATP

why do different respiratory substrates produce different amounts of ATP?

have different amounts of hydrogen ∴ different number of H+ that can be pumped into the IMS ∴ different proton motive forces generated ∴ different numbers of ATP molecules can be produced

name two cells that only use glucose as a respiratory substrate

brain cells erythrocytes

how are proteins converted and used as respiratory substrates?

excess amino acids are deaminated (removal of amino group --> converted to urea in ornithine cycle) remainder of molecule is converted to glycogen or lipids for storage during starvation, can be hydrolysed to release a.a.

how are lipids converted and used as respiratory substrate?

triglycerides hydrolysed to 3 fatty acids and 1 glycerol converted to glyceraldehyde then pyruvate and respired fatty acids broken down during B. oxidation to release acetyl groups --> join a CoA to form aCoA --> Krebs cycle

what is the respiratory quotient (RQ)?

the ration of the volume of carbon dioxide evolved to that of oxygen consumed by an organism, tissue or cell in a given time

what does the RQ indicate?

the type of respiratory substrate being used

how is RQ calculated?

mol/vol of CO(2) evolved / mol/vol of O(2) taken up

what is the RQ value for anaerobic conditions?

{infinitely large}

what is the RQ value for carbohydrates?

what is the RQ value for lipids?

0.70 - 0.72

what is the RQ value for proteins?

0.80 - 0.90

why is the RQ value for carbohydrates higher than proteins and lipids?

less oxygen is required to oxidise carbohydrates