3 - Respiration (C1) Flashcards
Where does glycolysis occur?
In the cytoplasm of cells
What are the products of glycolysis?
- 4 ATP (2 used, 4 produced = 2 ATP profit)
- 2 pyruvate
- 2 NADH
What is the process of glycolysis?
- 2 ATPs attach 2 phosphates to glucose, forming hexose biphosphate and 2 ADPs
- Hexose biphosphate splits into 2 triose phosphates
- Each triose phosphate is oxidised as NAD is reduced to NADH +H+
- 2 ADPs are phosphorylated, forming pyruvate
Where does the link reaction occur?
Matrix of mitochondria
What is the process of the link reaction?
- Each pyruvate molecule is oxidised (dehydrogenated) as NAD is reduced to NADH +H+
- CoA is added
- CO2 is removed (decarboxylation)
- Acetyl CoA is formed
What are the products of the link reaction?
Total of both pyruvate molecules:
- 2 acetyl coA
- 2 CO2
- 2 NADH
What happens in the Krebs cycle?
- Coenzyme A is removed from acetyl coenzyme A
- Acetate (2C) is picked up by oxaloacetate (C4) forming citrate (C6)
- Citrate has 2 CO2s removed, 1 ADP+pi is phosphorylated to ATP, 3 NADs are reduced to NADHs, 1 FAD is reduced to FADH
What happens to the energy released from C-H bonds in the Krebs cycle?
It’s transferred to the high energy electron carriers NAD and FAD
How do fatty acids enter the Krebs cycle?
- Via Beta oxidation
- Long chain fatty acid molecules are split into 2C acetate fragments and are fed into the Krebs cycle as acetyl co-enzyme A
How does glycerol enter the Krebs cycle?
It’s converted to triose phosphate
How do proteins enter the Krebs cycle?
- Protein is hydrolysed to amino acids which are deaminated in the liver
- The amino groups combine with CO2 making urea, which requires 2 ATPs
- The remains are converted to acetyl CoA, pyruvate or another Krebs cycle intermediate
What is the primary, secondary and final energy source?
1 - Carbohydrates
2 - Fat
Last resort - Body proteins
Why is it difficult to transfer fat in the blood?
As they’re non-polar
Why is it easy to transfer carbohydrates in the blood?
As they’re polar and soluble
Can fats be respired anaerobically?
No
Can carbohydrates be respired anaerobically?
Yes
Why do lipids yield twice the ATP of carbohydrates?
- The energy used to drive oxidative phosphorylation is in the electrons attached to the hydrogen atoms released by dehydrogenase enzymes
- Lipids have twice as many hydrogens as carbohydrates, so:
- 2x the hydrogens are released during respiration
- 2x the reduced NAD/FAD take hydrogen to the ETC
- 2x high energy electrons are passed down the carrier chain providing energy for proton pumps
- 2x protons are pumped into the intermembrane space
- 2x protons pass through ATP synthase to build ATP from ADP + Pi
What happens at the electron transport chain?
- NAD and FAD transport H+ to the ETC where it divides into high energy electrons and protons
- Electrons are passed backwards and forwards across the inner mitochondrial space by electron carriers
- Energy in electrons is used by H+/proton pumps which pump H+ into the inter-membrane space
- This builds an electrochemical gradient allowing ATP synthesis to occur by chemiosmosis as protons diffuse through ATPase
Why is oxygen the final electron and proton acceptor and what’s its role?
- As it combines with electrons and hydrogens forming H2O (oxidative phosphorylation / photophosphorylation)
- Maintains gradients as it removes e- and H+
What does reduction mean?
Gaining an electron
What does oxidation mean?
Losing an electron
What is the definition of respiration?
The breakdown of complex food molecules to release ATP
What are the 3 major types of respiration?
- Aerobic respiration of fat (at rest)
- Aerobic respiration of glucose (moderate exercise)
- Anaerobic respiration of glucose (violent exercise)
Where does the electron transport chain occur?
In the inner membrane of mitochondria
How many reduced NAD and FAD are produced from the complete oxidation of 1 glucose molecule?
- 10 reduced NAD
- 2 reduced FAD
How many ATPs are produced from the ETC from the oxidation of each reduced NAD and FAD?
- Each NAD - 3 ATPs, using 3 proton pumps
- Each FAD - 2 ATPs, using 2 proton pumps
What does pyruvate from glycolysis form in anaerobic respiration?
The reduced NAD formed in glycolysis transfers the hydrogen to pyruvate, to form lactic acid in animals, and ethanol and CO2 in plants
What is the yield of ATP in anaerobic respiration?
- 2 ATPs in glycolysis (substrate-level phosphorylation)
- The 2 reduced NAD formed in glycolysis are oxidised when 2 pyruvates are reduced to a lactate
How many ATP molecules are formed per glucose molecule?
- 2 ATPs in glycolsis (substrate-level phosphorylation)
- 2 ATPs in Krebs cycle (substrate-level phosphorylation)
- 34 ATPs from oxidative phosphorylation (using chemiosmosis)
Why is the maximum yield of ATP molecules per glucose often not obtained?
- Due to leaky membranes
- ATP is used to move pyruvate, ADP, and reduced NAD and FAD across mitochondrial membrane
What is the definition of aerobic respiration?
The release of large amounts of energy as ATP from the breakdown of molecules, with O2 as the final electron acceptor
What is the definition of anaerobic respiration?
The breakdown of molecules in the absense of O2, releasing little energy and making a small amount of ATP by substrate-level phosphorylation
Why can’t glycolysis constantly continue during anaerobic respiration?
As NAD will run out if it is not being oxidised again (either by the ETC or fermentation)
Why is a build up of lactic acid in muscles bad?
As it causes muscle fatigue
What is lactic acid fermentation?
A series of anaerobic reactions in animal cells where pyruvate uses reduced NAD to form lactic acid (lactate) and NAD. This NAD can be reduced again in glycolysis.
What are the 2 different types of fermentation?
- Lactic acid fermentation
- Alcoholic fermentation
What is alcoholic fermentation?
- Anaerobic process in which cells convert pyruvate into CO2 and ethanol
- Pyruvate is broken down to ethabal by releasing a CO2 molecule
- The ethanal accepts the H+ from reduced NAD to form ethanol
- NAD can then be reduced again in glycolysis
- Happens in yeast and some plant cells
What is a disadvantage of alcoholic fermentation?
It’s irreversible and ethanol can build to toxic levels
Why is ATP needed for glycolysis?
To phosphorylate glucose, which lowers the activation energy needed and stops it diffusing out the cell
How does a camels hump produce metabolic water?
- Long, fatty acid tails are converted into many acetate, which are dehydrogenated and decarboxylated, producing lots of CO2 and reduced NAD
- Reduced NAD and FAD carry the hydrogen to the inner mitochondrial membrane where O2 is the final electron acceptor, forming H2O used by camel
Why does having a large number of proton pores in the inner mitochondrial membrane result in a person being less likely to gain weight?
- Larger number of proton pores means protons leak back into matrix
- This reduces yield of ATP from chemiosmotic gradients and so less ATP is made from oxidative phosphorylation
- This means food isn’t converted to ATP as efficiently and fats aren’t stored as well, so these people don’t gain as much weight
What is a metabolic pathway?
A sequence of reactions controlled by enzymes
Where does oxidative phosphorylation occur?
On the inner membranes of mitochondria in aerobic respiration
Where does photophosphorylation occur?
On the thylakoid membranes of the chloroplasts in the light-dependent stage of photosynthesis
Where does substrate-level phosphorylation occur?
When phosphate groups are transferred from donor molecules e.g. G3P to ADP to make ATP in glycolysis, or when enough energy is released for a reaction to bind ADP to inorganic phosphate
What are obligate aerobes?
Organisms that use aerobic respiration only, so can’t respire in the absense of O2
What are facultative anaerobes?
Microorganisms that respire aerobically, but can also respire anaerobically in the absense of O2
What are obligate anaerobes?
Some bacteria which use anaerobic respiration, and can’t respire in the presence of O2
What is a coenzyme?
A molecule required by an enzyme in order to function
What does cyanide, a non-competitive inhibitor, do in the ETC?
- It stops electrons and protons being transferred to water, so they accumulate and destroy the proton gradient
- ATP synthetase can’t operate and the cell dies quickly
What do longer fatty acid chains that enter the Krebs cycle have?
- More carbon atoms - so more CO2 is produced
- More hydrogen atoms - so more NAD is reduced, so more ATP is produced, also more H2O is produced
