5.7 Respiration Flashcards
What is the need for respiration?
- release energy stored in organic molecules which is used to synthesise ATP
What is ATP used for?
- hydrolysed to release a small quantity of energy for use in cells -> no damage or waste
- drive processes such as transport, protein synthesis, DNA replication, cell division, movement
What is the structure of ATP? Is it stable in solution?
- adenine, ribose, 3 phosphates (phosphoanhydride bonds)
- stable in solution but is readily hydrolysed by enzyme catalysis.
How are mitochondria adapted to perform their function?
- inner membrane: less permeable to smaller ions. CRISTAE gives large SA for electron carriers + enzymes such as the ATP synthase stalked particles.
- outer membrane allows pyruvate in for example
- inner + outer = envelope
- intermembrane space involved in oxidative phosphorylation
- matrix -> contains enzymes, NAD, FAD, oxaloacetate, DNA, ribosomes.
- ETC: electron carrier proteins are oxido-reductase enzymes -> iron ions are cofactors and can accept and donate electrons
Explain the process of glycolysis
- Glucose is activated via phosphorylation. 2 ATPS are hydrolysed into 2ADP and 2 phosphates and energy is released, preventing transport out of the cell. This results in hexose bisphosphate which is unstable.
- Each 6 carbon molecule is split into two TP molecules.
- Oxidation of the TP’s occurs, where NAD coenzymes accept hydrogens to become reduced NAD
- Substrate-level phosphorylation also forms 2ATP per TP.
- This forms two pyruvate molecules per molecule of glucose. Net gain 2ATP. Two reduced NAD.
Where does glycolysis happen?
- cytoplasm of the cell
What is NAD? What is its role? What is it synthesised from?
- non-protein coenzyme
- oxidation of substrate
- synthesised from nicotinamide (B3 vitamin), ribose, adenine, and 2 phosphates.
- carries protons and electrons to cristae
Where does the link reaction and Krebs cycle take place?
the mitochondrial matrix
will not occur in absence of oxygen
Describe the process of the link reaction. What are the products?
- each pyruvate is decarboxylated and dehydrogenated (NAD becomes reduced NAD), catalysed by pyruvate dehydrogenase.
- CoA then binds, forming acetyl CoA.
- NO ATP, 2xCO2 and 2 NADH for EACH GLUCOSE.
Describe the Krebs cycle
- formation of citrate from the acetyl group of acetyl CoA and oxaloacetate (CoA is released and reused in link reaction)
- citrate is decarboxylated and dehydrogenated (NAD -> NADH), forming a 5C compound
- this 5C compound is decarboxylated and dehydrogenated also (NAD -> NADH)
- the resulting 4C compound combines temporarily with and is released from coenzyme A
- substrate phosphorylation occurs, forming 1 ATP and a different 4C compound
- this compound is dehydrogenated, reducing FAD to FADH2 this time.
- this compound is dehydrogenated also (NAD -> NADH), catalysed by an isomerase enzyme, reforming oxaloacetate.
products: for EACH GLUCOSE there is 2 turns. therefore 4 CO2 is produced, 2 ATP, 2 FADH2, and 6 NADH
How is pyruvate transported into the matrix?
- pyruvate H+ symport
Where does oxidative phosphorylation occur?
matrix, cristae and intermembrane space
Describe the process of oxidative phosphorylation, including the chemiosmotic theory
- reduced NAD and reduced FAD are reoxidised, releasing 2 hydrogens for each coenzyme.
- these 2 hydrogens are split into 2 electrons and 2 H+ ions.
- the electrons travel down the electron transport chain through proteins containing an iron ion co factor, through a series of redox reactions.
- Hydrogen ions are pumped from the matrix to the intermembrane space using energy transferred by these electrons.
- this establishes an electrochemical gradient and proton-motive force, causing the H+ ions to diffuse down through the stalked particle and ATP synthase = CHEMIOSMOSIS
- ADP + Pi -> ATP
- 4 electrons, 4 H+ ions and oxygen from the blood are combined to form 2 water molecules . oxygen acts as the FINAL ELECTRON ACCEPTOR.
How many NADH and FADH2 are made in respiration?
- 10 NADH and 2FADH2
- these then convert to 10NAD and 2FAD during oxidative phosphorylation
What happens if O2 isnt present?
- cannot act as final electron acceptor
- [protons] in matrix increases and oxidative phosphorylation ceases
- reduced NAD cannot be reoxidised
- Krebs cycle stops
what are the 2 pathways by which anaerobic respiration can occur?
lactate fermentation (mammals) and ethanol fermentation (fungi and plants)
What occurs during ethanol fermentation? What enzyme catalyses this?
- pyruvate is decarboxylated to form ethanal
- ethanal is then hydrogenated ( NADH + H+ becomes NAD+) to form ethanol. This is catalysed by ethanol dehydrogenase.
- NAD + is then reused in glycolysis.
What occurs during lactate fermentation?
- pyruvate is hydrogenated (oxidation of NADH), to form lactate. Catalysed by lactate dehydrogenase
What happens to lactate?
- if lactic acid were formed this would inhibit enzymes, so it is carried to the liver to be converted to pyruvate and enter Krebs, or recycled to glucose and glycogen.
What are respiratory substrates?
- organic substances that can be oxidised in respiration, releasing energy to make ATP
How can carbohydrates other than glucose be used in respiration?
- disaccharides can be digested to monosaccharides
- these can be changed by isomerase enzymes to glucose
- glycogen and starch can be hydrolysed to glucose
Fatty acids and amino acids can only be respired ………
aerobically
What are the mean energy values for carbs, lipids and proteins?
CARBS: 15.8
LIPID: 39.4
PROTEIN: 17.0
Why do lipids have a higher mean energy value?
- higher proportion of H atoms
- more NADH
- more protons for chemiosmosis
- more ATP
- more O2 also needed
How do you calculate Rq? What are the values you must memorise?
CO2 produced/ O2 consumed
Carb: 1
Fatty Acid: 0.7
Amino Acid: 0.8-0.9
Greater than 1 = anaerobic = glucose.
Which applies to NAD or FAD?
- Is a prosthetic group
- Is reduced in the link reaction
- Oxidises molecules in ETC
- FAD
- NAD
- NEITHER
A teacher told his students that the human body makes the equivalent of its own mass in
ATP every day.
Explain why, at the end of the day, only a small proportion of the students’ mass was
ATP.
because ATP is , broken down / hydrolysed (to ADP)
ATP is constantly recycled
ATP used to provide energy for , (named) metabolic reactions / processes
ATP is , not stored long term / used immediately
Explain why early eukaryotes were able to grow more quickly than cells that did not
possess mitochondria.
1 would be able to respire aerobically
2 (this) produces more ATP
3 ATP needed for , active transport / cell division /protein synthesis / DNA replication
4. more ATP allows faster metabolic ,
processes / reactions
Describe how the student could use the graph of rate of respiration vs rate of gas production to calculate the rate of respiration for each
type of sugar.
1 rate of respiration is proportional to
rate of gas production
2 use a tangent
3 calculate gradient (of each line)
4 volume of gas (collected) divided by time
5 compare the same , time / period (between sugars)
Explain why mitochondria produce CO2 when incubated with pyruvate, but do not produce CO2 when incubated with glucose.
glucose cannot enter mitochondria but pyruvate does.
CO2 produced during link reaction and Krebs, both in matrix, using pyruvate initially.
Explain why lactate is not produced by mitochondria incubated with pyruvate
Lactate is product of anaerobic respiration which doesn’t occur in mitochondria
Explain why, when cyanide is present, lactate is produced but not carbon dioxide.
Cyanide inhibits oxidative phosphorylation so aerobic stops
Anaerobic respiration occurs instead to oxidise NAD -> lactate pathway
This does not produce CO2. Glycolysis can continue where no decarboxylation occurs
