Respiration Flashcards
Respiration produces what?
ATP
What are the 2 types of respiration?
Aerobic and anaerobic
What is aerobic respiration?
requires oxygen
- produces carbon dioxide, water and much ATP
What is anaerobic respiration?
- takes place in absence of oxygen and produces lactate (in animals) or ethanol and CO2 (in plant and fungi) but only little ATP (in both cases)
Aerobic respiration can be divided into what four stages?
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation
Glycolysis is the initial stage of what?
aerobic and anaerobic respiration
What takes place during the process of cellular respiration?
formation of ATP from the breakdown of glucose
Where does glycolysis occur?
And briefly state what happens in it
- cytoplasm of all living cells
- a hexose (6C) sugar (usually glucose) is split into 2 molecules of 3-carbon —- PYRUVATE
Describe glycolysis process
- Glucose is double phosphorylated via 2 ATP molecules
- becomes glucose phospahte (6C) (after first phosphorylation)
- becomes hexose biphosphate (6C) - The double phosphorylated molecule (Hexose biphosphate) splits into 2 TP (triosephosphate) molecules
- Each TP (3C) oxidised - loses H and transferred to hydrogen-carrier (NAD) to form 2 reduced NAD
- enzyme-controlled reactions convert each TP into pyruvate (3C)
In process, 2 molecules of ATP are regenerated from ADP
In anaerobic respiration pyruvate is converted into what? and why does this have to happen?
lactate or ethanol
- this has to happen to re-oxidise the NAD so that it can be re-used in glycolysis
- small amount of ATP will still be produced
Respiration equation
C6H12O6 + 6O2 –> (equil..) 6H2O + 6CO2 (+energy)
Energy yields from glycolysis
- 2 molecules of ATP (four produced but 2 used in initial phosphorylation of gluocse and so net increase is 2)
- 2 molecules of reduced NAD
- 2 molecules of pyruvate
Why is glycolysis indirect evidence for evolution?
because it’s a universal feature of every living organism
Briefly - what happens in the link reaction?
- the 3-carbon pyruvate molecules enter into series of reactions which lead to formation of acetylcoenzyme A, a 2-carbon molecule
Reduced NAD also written as?
NADH
Is Glycolysis aerobic or anaerobic?
doesn’t need oxygen - so it’s an anaerobic process
2 main stages of glycolysis and describe?
phosphorylation + oxidation
- ATP used to phosphorylate glucose to triose phosphate (TP)
- TP oxidised, releasing ATP
Overall net gain: 2 ATP and 2 reduced NADand 2 pyruvate molecules
Similarities between aerobic and anaerobic respiration
Both produce ATP (anaerobic much less though)
Both start with glycolysis ( but differ afterwards)
Briefly state what happens in Link reaction
- link reaction converts pyruvate to Acetyl Coenzyme A
Where does link reaction occur?
mitochondrial matrix
Describe Link reaction process
1 pyruvate (3C) is decarboxyled (one C atom removed from pyruvate in the form of CO2)
2 pyruvate oxidised (dehydrogenated) to form acetate(2C) and NAD reduced to form reduced NAD
3 Acetate combined with Coenzyme A (CoA) to form acetyl Coenzyme A (Acetyl CoA)
4 allowing it to enter krebs cycle (NO ATP PRODUCED)
Overall equation of link reaction
pyruvate + NAD + CoA –> acetyl CoA + reduced NAD + CO2
How many times does link reaction and krebs cycle occur and why?
occurs twice for every glucose molecule because 2 pyruvate molecules are produced in glycolysis
Products from link reaction for each glucose molecule ?
- 2 molecules of acetyl CoA go into krebs cycle
- 2 CO2 molecules released as waste product of respiration
- 2 molecules of reduced NAD formed and go into oxidative phosphorylation
Briefly describe what happens in Krebs cycle?
- krebs cycle produces reduced coenzymes and ATP
Krebs cycle takes place where?
matrix of mitochondria
Krebs cycle happens how often?
once for every pyruvate molecule so twice for every glucose molecule
What are coenzymes?
- not enzymes
- molecules that some enzymes require to function
Role of coenzymes in photosynthesis and respiration?
-carry H atoms from 1 molecule to another
Examples of Coenzymes
NAD - important throughout respiration
FAD - important in krebs cycle
NADP - important in photosynthesis
In respiration what is the most important carrier and why?
- NAD
- works with dehydrogenase enzymes that catalyse removal of H atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation
Describe the four important roles of the Krebs cycle in cells of organisms
1 breaks down macromolecules into smaller ones (pyruvate into CO2)
2 produces H atoms carried by NAD to electron transfer chain and provide energy for oxidative phosphorylation - leads to production of ATP & provides metabolic energy for cell
3 regenerates 4-carbon molecule that combines with acetyl CoA, which would accumulate otherwise
- source of intermediate compounds used by cells in manafacture of other important substances like fatty acids, AAs and chlorophyll
Describe the Krebs Cycle Process
1 - CoA removed from acetyl CoA (2C) allowing acetyl to combine with oxaloacetate (4C) to form citrate (citric acid) (6C)
- CoA goes back to link reaction to be used again
2 - 6C citrate molecule converted to 5C molecule
- decarboxylation occurs, CO2 (1C) removed
- dehydrogenation, H removed to reduce NAD to NADH
3 5C molecule converted to a 4C molecule (OXALOACETATE)
- decarboxylation and dehydrogenation occur, producing 1 molecule of reduced FAD and 2 of reduced NAD
- ATP produced by substrate-level phosphorylation
- citrate now converted to oxaloacetate (4C) - marks end of krebs cycle
What is substrate-level phosphorylation?
Occurs in Krebs Cycle
-direct transfer of phosphate group from 1 molecule to another
What things generally happens to products of krebs cycle?
- some reused, some released and others used for next stage of respiration
Products of 1 krebs cycle? (so double these for 1 glucose molecule)
3 x reduced NAD 1 x reduced FAD 2 x CO2 1 x ATP oxaloacetate (4 Carbon molecule)
Where does coenzyme A go after 1 krebs cycle?
reused in next link reaction
where does oxaloacetate (4C sugar) go after 1 krebs cycle?
regenerated for use in next krebs cycle
where does CO2 (x2) go after 1 krebs cycle?
released as waste product
what is ATP used for after 1 krebs cycle?
used for energy
where does FAD (x1) and reduced NAD (x3) go after 1 krebs cycle?
to oxidative phosphorylation
Aim of oxidative phosphorylation
to make as much ATP as possible
What was the point of steps previous to oxidative phosphorylation ?
- to make reduced NAD and reduced FAD for final stage
Briefly describe what happens in oxidative phosphorylation?
process where energy carried by electrons, from reduced coenzymes (reduced NAD and FAD) is used to make ATP
- involves electron transport chain and chemiosmosis
Describe oxidative phosphorylation process (or ETC)
1 NADH and FADH become oxidised (H atom splits) releasing H+ (protons) and e- (electrons)
2 electrons enter ETC, moving through electron carriers, losing energy at each carrier. Energy released from this used to move H+ (protons) against conc gradient - from mitochondrial matrix to intermembrane space
3 conc of protons now higher in intermembrane space than mitochondrial matrix - establishing electrochemical gradient (conc of gradient ions)
4 H+ (protons) move down electrochemical gradient (across inter mitochondrial membrane & into mitochondrial matrix) through ATP synthase, catalysing reaction : ADP + Pi –> ATP
5 in mitochondrial matrix (at end of transport chain) oxygen (from blood) acts as a final electron acceptor combining with H+ & electrons to form water
1/2O2 + 2e- + 2H+ —> H2O
How does flow of protons in oxidative phosphorylation lead to ATP synthesis?
- flow of H+ (protons) causes a change of shape in protein ATP synthase and leads to ATP synthesis
What is chemiosmosis?
movement of ions across semi permeable membrane down their electrochemical gradient
e.g. process of ATP production driven by movement of H+ ions in oxidative phosphorylation
How does pyruvate enter mitochondrial matrix after glycolysis?
active transport
In anaerobic respiration pyruvate is converted to what? (refer to notes for equations)
ethanol (in plants + yeast) - alcoholic fermentation
lactate (in animal cells & some bacteria) - lactate fermentation
using reduced NAD
Benefit of production of ethanol or lactate for biological processes?
oxidised NAD is regenerated (in anaerobic respiration) - meaning glycolysis can continue when not much O2 around
- so small amount of ATP still produced to keep some biological processes going
Name two respiratory substrates apart from sugars
Lipids
Proteins
Describe the respiration of lipids
- lipids hydrolysed to glycerol+ fatty acids
- glycerol phosphorylated & converted to triose phosphate
- TP enters glycolysis - krebs pathway
- fatty acid broken down into 2C fragments of carbohydrates which are converted to acetyl coenzyme A - then enters krebs cycle.
Why do lipids release x2 energy of same mass of carbohydrate?
oxidation of lipids produces 2C fragments of carbohydrates & many H atoms
- H atoms used to produce ATP during oxidative phosphorylation
- this is why lipids release double the energy of the same mass of carbohydrate
Describe the respiration of proteins
- first hydrolysed to AAs - amino group removed (deamination) before entering respiatory pathways (depending on how many C atoms they contain)
- 3C compounds converted to pyruvate
- 4C and 5C converted to intermediates in krebs cycle
Briefly describe why aerobic respiration can’t take place in the presence of no oxygen?
- neither krebs or ETC can continue because all FAD & NAD will soon be reduced
- no FAD or NAD available to take up H+ produced during krebs so enzymes stop working
- leaves only anaerobic process glycolysis as (potential) source of ATP
For glycolysis to continue, what must happen?
- its products (pyruvate & hydrogen) must constantly be removed - H must be removed from NADH to regenerate NAD
In anaerobic respiration, For gylcolysis to continue, its products must be removed, what will happen if this isn’t the case?
- already tiny supply of NAD in cells will entirely be converted to reduced NAD, leaving no NAD to take up newly produced H from glycolysis so gylcolysis stops
How is replenishment of NAD is achieved in glycolysis?
- by pyruvate molecules from glycolysis accepting hydrogen from reduced NAD
- oxidised NAD produced can then be used in further gylolysis
List reasons why aerobic can’t take place without oxygen?
1 O2 can’t act as final electron acceptor
2 no/fewer electrons move through ETC
3 H+ not moved against conc gradient (since no energy provided by movement of electrons)
4 No ATP made in oxidative phosphorylation
5 NADH & FADH not oxidised back into FAD & NAD
- therefore NAD & FAD not available to oxidise reactions in krebs cycle
- also link reaction stops because it relies on reduction of NAD to oxidise pyruvate
in absence of O2 very little ATP made.
In plants (and microorganisms e.g. yeast) pyruvate is converted to what?
ethanol and carbon dioxide
glucose —-> ethanol + carbon dioxide
In animals, pyruvate is converted to what?
lactate
glucose —-> lactate
Why can glycolysis continue in the absence of oxygen?
- allows NADH to be oxidised into NAD
- however net yield of ATP is much less than in aerobic respiration
Describe what happens to pyruvate after formed in anaerobic respiration (for fungi & plants)
(3C) pyruvate reduced to (2C)ethanol, CO2 released
while NADH is oxidised to NAD
and NAD recycled back to glycolysis
Describe what happens to pyruvate after formed in anaerobic respiration (in animals)
(3C) pyruvate reduced to (3C)lactate while NADH is simultaneously reduced to lactate
and NAD recycled back to gylcoysis
Summary equation of anaerobic respiration in plants
pyruvate + reduced NAD —> ethanol + carbon dioxide + oxidised NAD
summary equation of anaerobic respiration in animals
pyruvate + reduced NAD —> lactate + oxidised NAD
Describe what happens during streneous exercise?
- lacatate production in muscles causing muscle cramps
- oxygen used more rapidly than it’s supplied so oxygen debt occurs
additional info:
when O2 returns it will break down lactate into CO2 and water
Why are enzymes affected by lactate in body?
causes PH change which affects enzymes
give two ways in which aerobic respiration in yeast is similar to anaerobic respiration of glucose in muscle cell
- pyruvate is reduced
- reduced NAD is oxdidised to NAD which are both recycled to glycolysis
give two ways in which aerobic respiration in yeast is different to anaerobic respiration of glucose in muscle cell
- production of ethanol as opposed to lactate
- CO2 released by yeast but not muscle cell
Describe the energy yields from aerobic and anaerobic respiration
substrate-level phosphorylation in glycolysis and krebs cycle: direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP
oxidative phosphorylation in ETC: indirect linking of energy from phosphate to ADP to produce ATP involving energy from H atoms that are carried on NAD and FAD
(cells produce most of ATP this way)
Apart from respiration, give three uses of ATP in a liver cell
Active transport
Phagocytosis
Mitosis
Synthesis of protein
Describe the part played by the inner membrane of a mitochondrion in producing ATP.
Electrons transferred down electron transport chain;
Provide energy to take protons into space between membranes.
Protons/H+ pass back through membrane into matrix
Energy used to combine ADP and phosphate/to produce ATP
Give two advantages of ATP as an energy-storage molecule within a cell
Cannot pass out of cell
Quickly/easily broken down
Stores / releases small amounts of energy
