Topic 5 A: Respiration Flashcards
When is ATP broken down?
The breakdown of ATP, from glucose, occurs during respiration.
Glycolysis simple summary?
- splits one molecule of glucose into smaller molecules of pyruvate
- doesn’t require oxygen - its an anaerobic process
- takes place in cytoplasm of cells because glucose cannot cross the outer mitochondrial membrane
Stage one of glycolysis?
Phosphorylation of glucose:
- 2 phosphate molecules added to glucose to form fructose biphosphate (or glucose phosphate), which is unstable.
- 2 ATP molecules hydrolysed to allow this to occur.
Stage two of glycolysis?
Production of triosephsophate:
- splitting occurs because glucose phosphate is unstable ( due to 6C) into 2 triosephosphate molecules with 3C and 1 phosphate.
Stage three of glycolysis?
Oxidation of triosephosphate:
- one NAD (coenzyme) gains hydrogen from each TP molecule (2 in total)
- TP is oxidised (lost hydrogen) and NAD is reduced (NADH+)
- (2) pyruvate molecules created
Final products of glycolysis?
- 2 pyruvate
- 2 NADH
- 2 ATP (net gain - used 2 at the beginning)
Exam question : Describe the process of glycolysis? (4)
- phosphorylation of glucose occurs using ATP
- splits into 2 TP and is oxidised to form pyruvate
- NADH created
- net gain of 2 ATP
How does pyruvate reach the link reaction?
Actively transported into mitochondrial matrix for this stage (using transport protein)
Overall function of the link reaction?
Converts 2 pyruvate molecules into acetyl co-enzyme A (acetyl Co-A)
Overall equation of the link reaction?
pyruvate + NAD + CoA = acetyl Co-A + reduced NAD + CO2
Link reaction process?
- pyruvate oxidised (lost H) into acetate, H lost is picked up by NAD x2 (reduced)
(the loss of hydrogen is known as dehydrogenation) - pyruvate is a 3C molecule, acetate is 2C. Pyruvate loses one C in form of CO2 (decarboxylation)
- acetate converts into acetyl Co-A by reacting with co enzyme A
Krebs cycle process - Part one - The creation of citrate
- acetyl CoA comes from link reaction
- acetyl CoA reacts with oxaloacetate to create six-carbon citrate
- citrate then converted back into oxaloacetate through series of small reactions, cycle repeats
- CoA back into link reaction after citrate is formed
- the purpose of acetyl CoA is to bring acetate into the krebs cycle
Krebs cycle process - Part two - Formation of 5 carbon compound
- citrate converted into 5C compound
- this happens because decarboxylation (loss of CO2) and dehydrogenation occurs (NAD to NADH)
- intermediate compound (5C) formed.
Krebs cycle process - Part three - Regeneration of 4 carbon compound
- decarboxylation and dehydrogenation of intermediate compound occurs
- one molecule of reduced FAD is produced from FAD
- two molecules of reduced NAD is produced from NAD
Krebs cycle process - Part four - Production of ATP
- produced by the direct transfer of a phosphate group
- direct transfer known as substrate-level phosphorylation
Products of the krebs cycle?
- 1 CoA
- 1 oxaloacetate
- 2 CO2
- 1 ATP
- 3 reduced NAD
- 1 reduced FAD
Where does oxidative phosphorylation take place?
- in the cristae
Oxidative phsophorylation simple definition?
- when energy carried by electrons and reduced co-enzymes (NAD and FAD) are used to make ATP
Part one of oxidative phosphorylation?
- reduced NAD and FAD lose hydrogen atoms (oxidised)
- hydrogen atoms split into protons (H+) and electrons (e-)
Part two of oxidative phosphorylation?
- electrons are embedded within the inner membrane
- they then pass along electron transfer chain, and every time an electron moves to the next protein, it releases enough energy to transport a proton to the inner membrane space
- this occurs via active transport
- the movement of H+ ions from low to high creates electrochemical gradient
Part three of oxidative phosphorylation?
- protons move back down the electrochemical gradient from inner membrane to the matrix via ATP synthase.
- this occurs through facilitated diffusion
- this drives ATP synthesis (ADP+Pi)
Why is this process described as being oxidative?
- protons + electrons + oxygen = water
- oxygen = final electron acceptor
What would happen if oxygen wasn’t present?
- reduced co-enzymes cannot be oxidised to regenerate NAD and FAD
- protons wouldnt be transported across the membrane and no electrochemical gradient will form
- no more electrons would be able to move down the chain
- ATP not synthesised
ATP reference point for aerobic respiration processes?
- 2.5 ATP made from each reduced NAD
- 1.5 ATP made from each reduced FAD
How much ATP made during glycolysis?
product = 2 ATP & 2 NADH
- 7 ATP
How much ATP made during link reaction?
product = 2 NADH
- 5 ATP
How much ATP made during krebs cycle?
product = 2 ATP & 6 NADH & 2 FADH
- 20 ATP
How much ATP made during oxidative phosphorylation?
- 28 ATP
Total molecules of ATP within aerobic respiration?
- around 32
What else can be used as respiratory substances?
Lipids and proteins.
Hydrolysis if lipids and proteins?
lipids = glycerol and fatty acids
proteins = amino acids
Energy of lipids compared to glucose?
lipids release more than double the amount of energy than glucose.
Respiration and lipids?
- fatty acids are broken down into acetyl coA which enters krebs cycle
- glycerol is phosphorylated and then converted into triose phosphate, then enters through glycolysis into krebs cycle.
Respiration and proteins?
- amino acid group is removed, this is called deamination, 3C compounds converted into pyruvate.
- four and five carbon compounds converted to immediate compounds.
Where does anaerobic respiration occur?
- in the cytoplasm
Steps of anaerobic respiration?
- glycolysis
- fermentation (yeast or lactate)
Main purpose of anaerobic respiration?
- to release small amounts of ATP and to oxidise NAD
- this is crucial because we have to ensure the NAD can be reused in glycolysis again
Total energy formed in anaerobic respiration?
2 ATP
- Ethanol fermentation process?
- glycolysis (glucose into pyruvate)
- pyruvate loses CO2 (decarboxylation)
- reduced NAD (from glycolysis) transfers hydrogen to ethanal to form ethanol.
- ethanal is reduced to ethanol by enzyme, alcohol dehydrogenase
- ethanal is the final hydrogen acceptor
Ethanol fermentation equation?
pyruvate + reduced NAD = ethanol + CO2 + oxidised NAD
- Lactate fermentation process?
- glycolysis (glucose to pyruvate)
- reduced NAD (from glycolysis) transfers hydrogen to pyruvate to from lactate
- pyruvate is reduced to lactate by the enzyme lactate dehydrogenase
- pyruvate is the final hydrogen acceptor
Lactate fermentation equation?
pyruvate + reduced NAD = lactate + oxidised NAD
What happens to the lactate after?
- further metabolised back into pyruvate or converted into glycogen
Exam question: Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring
cell.
- less coenzymes / fewer electrons removed
- oxygen is final electron acceptor
Exam question: In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production
of ATP by anaerobic respiration.
- oxidises reduced NAD
- so glycolysis continues
