16 Cellular respiration Flashcards
what are the needs for ATP?
active transport
chemical activation
anabolic synthesis
cellular ultrastructure
bioluminescence
exocytosis
movement (e.g. of flagella and cilia)
homeostasis
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
where does glycolysis take place? why?
cytosol
requires specific enzymes only found there
what is the function of glycolysis?
to oxidise glucose and split a 6C hexose into 2x 3C triose (pyruvate)
what is required for glycolysis?
1 glucose molecule
2 ATP
2 NAD+
what are the products of glycolysis?
2 pyruvate
4 ATP (gross)
2 red. NAD
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
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
where does the link reaction take place? why?
mitochondrial matrix
CoA and other enzymes only found here
what substrates are required for the link reaction?
1 pyruvate
1 ATP
1 CoA
how does pyruvate reach the mitochondrial matrix?
moves across mitochondrial envelope through specialised intrinsic protein carriers via active transport
what are the three reactions involved in the link reaction?
decarboxylation
redox
dehydrogenation
[collectively oxidative decarboxylation}
what are the components of coenzyme A (CoA)?
pantothetic acid (a vitamin B complex)
ADP
-SH group (joins acetyl group to CoA)
what are the products of the link reaction?
CO(2)
acetyl CoA (aCoA)
red. NAD
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
where does the Krebs cycle take place?
mitochondrial matrix
what is the Krebs cycle controlled/limited by?
substrate concentration
allosteric (non-competitive) inhibitors
end-product inhibition
KC: what is added to oxaloacetate to produce citrate?
an acetyl group from aCoA
KC: what is added/removed to citrate to produce a 5C intermediate?
- CO(2)
+ NAD+ (producing red. NAD)
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)
KC: what is added to the 4C intermediate to produce another 4C intermediate?
+ FAD (producing red. FAD)
KC: what is added to the second 4C intermediate to reform oxaloacetate?
+ NAD+ (producing red. NAD)
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?
1
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
