5.2 Respiration Flashcards
Does condensation trap or release energy?
Traps!
Does hydrolysis trap or release energy?
Release!
Which part of respiration is glucose involved in?
Glycolysis
Which part of respiration is oxygen involved in?
It is the final electron acceptor of the electron transport chain during oxidative phosphorylation
Which part of respiration is CO2 involved in?
Link reaction & Krebs cycle
Which part of respiration is water involved in?
Waste from the electron transport chain during oxidative phosphorylation
What are the 3 ways in which ATP is produced?
- Photophosphorylation: LDR
- Oxidative phosphorylation: respiration in mitochondria
- Substrate-level phosphorylation: no ATP synthase (enzymes) required (i.e. phosphate group directly transferred from one molecule to another)
What is NAD?
Nicotinamide adenine dinucleotide: it’s an electron carrier and an important co-enzyme
It accepts hydrogen atoms from molecules that are being oxidised, becoming reduced NAD.
What are the waste products of anaerobic respiration in humans and yeast?
Humans: lactic acid
Yeast: ethanol and CO2
Where does each stage of respiration take place?
- Glycolysis: cytoplasm (all the required enzymes are there!)
- Link reaction: mitochondria
- Krebs cycle: mitochondria (matrix)
- Oxidative phosphorylation/e- transport chain: mitochondria (cristae)
In glycolysis, glucose molecules are oxidised to form…
pyruvate
Is glycolysis an aerobic or anaerobic process?
Anaerobic
Compare mitochondria outer & inner membrane
Outer: smooth & permeable to several small molecules
Inner: folded (cristae), less permeable, site of e- transport chain & location of ATP synthase
2 features of the mitochondrial intermembrane space
- low pH due to high concentration of H+
- conc. gradient across inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis
Glycolysis in a nutshell
Glucose → phosphorylated glucose → 2x triose phosphate → 2x pyruvate
Glycolysis stage 1
1 molecule of glucose is phosphorylated using 2 ATP molecules to form an unstable 6-carbon intermediate (phosphorylated glucose).
This intermediate undergoes lysis (splits) to form 2 molecules of triose phosphate.
Glycolysis stage 2
Oxidation of triose phosphate to pyruvate
Hydrogen is removed from each triose phosphate molecule and transferred to coenzyme NAD to form 2 molecules of reduced NAD.
The phosphates from triose phosphate are used to produce 4 ATP through substrate-level phosphorylation
What are the overall products of glycolysis per glucose molecule?
NET GAIN: +2 ATP, +2 pyruvate, +2 reduced NAD
What happens during the link reaction (in a nutshell?)
Pyruvate becomes acetate, producing CO2 in the process.
Acetate reacts with coenzyme A to form acetyl coenzyme A, which then enters the Krebs cycle.
What is produced in the Krebs cycle?
3 reduced NAD
2 CO2
1 reduced FAD
1 ATP
What are the technical terms for what happens to each pyruvate molecule in the link reaction?
Each pyruvate molecule is decarboxylated and oxidised, enabling NAD to be reduced.
What are the roles of reduced NAD and FAD?
Electron carriers
How many times do the link reaction and Krebs cycle occur for every glucose molecule?
Twice
Krebs Stage 1
Acetyl coenzyme A (2C) from the link reaction combines with oxoloacetate (4C) to form citrate (6C).
Coenzyme A is released and returns to the link reaction.
Krebs Stage 2
Citrate (6C) is converted to a 5C intermediate molecule.
Decarboxylation occurs - CO2 removed/produced.
Dehydrogenation (oxidation) occurs - hydrogen is removed, enabling one NAD to be reduced.
Krebs Stage 3
5C molecule converted back to oxoloacetate (4C).
Decarboxylation and dehydrogenation (oxidation) occur, producing 1 reduced FAD and 2 reduced NAD.
ATP is produced through substrate-level phosphorylation.
What happens to reduced NAD and reduced FAD in oxidative phosphorylation?
They become oxidised!
Reduced NAD → NAD + e- + H+
Reduced FAD → FAD + e- + H+
Describe chemiosmosis
H+ diffuse from an area of high conc to area of low conc via ATP synthase. This generates large quantities of ATP from ADP and Pi.
Oxidative phosphorylation stage 1
Reduced NAD and reduced FAD are oxidised, releasing hydrogen atoms.
The hydrogen atoms split into protons and electrons.
Oxidative phosphorylation stage 2
The electrons move down the electron transport chain, losing energy at each carrier.
This energy is used by the electron carriers to pump protons from the matrix to the intermembrane space.
Oxidative phosphorylation stage 3 (ATP production)
The concentration of protons is higher in the intermembrane space than in the matrix.
Protons diffuse down the electrochemical gradient back into the matrix via ATP synthase. This drives the synthesis of ATP from ADP and Pi.
Oxidative phosphorylation stage 4 (oxygen!)
In the mitochondrial matrix, at the end of the electron transport chain, the protons, electrons and O2 (from the blood) combine to form water. Oxygen is the final electron acceptor.
2 pieces of evidence for chemiosmosis in the mitochondria
- Low pH in the intermembrane space
- mV charge distribution: more +ve in spaces compared to the matrix
What are other respiratory substrates apart from glucose?
Breakdown products of lipids & amino acids - these enter the Krebs cycle
What happens to fatty acids?
Broken into two carbon compounds which enter the Krebs cycle
What happens to glycerol?
Phosphorylated and converted to triose phosphate, which enters glycolysis
What happens to amino acids?
Deaminated (amino group removed)
Remaining molecule enters Krebs cycle
In aerobic respiration, how does pyruvate from glycolysis enter the mitochondrial matrix?
Via active transport
What DOESN’T happen in anaerobic respiration?
- No final electron acceptor from electron transport chain
- No ATP production via oxidative phosphorylation
- Reduced NAD & FAD aren’t oxidised by an electron carrier
- Krebs cycle stops
What happens to the reduced NAD produced during glycolysis in anaerobic respiration?
It is oxidised by some cells, so it can be used for further hydrogen transport
What does the oxidation of reduced NAD in anaerobic respiration mean for the rest of the process?
Glycolysis can continue and small amounts of ATP are still produced
What are the 2 different ways in which reduced NAD is oxidised in anaerobic respiration?
Ethanol fermentation: done by yeast & microorganisms
Lactate fermentation: done by mammalian muscle cells
Describe ethanol fermentation
OVERALL: Reduced NAD transfers its hydrogen to ethanal to form ethanol
- Pyruvate is decarboxylated to ethanal: this produces CO2
- Ethanal is reduced to ethanol by alcohol dehydrogenase
Describe lactate fermentation
OVERALL: Reduced NAD transfers its hydrogens to pyruvate to form lactate
- Pyruvate is reduced to lactate via lactate dehydrogenase
- Pyruvate is the hydrogen acceptor
- Lactate can be further metabolised
What 2 things can happen after lactate is produced?
- It can be oxidised to pyruvate which is then channelled into the Krebs cycle for ATP production
- It can be converted to glycogen for storage in the liver
