Flashcards in Respiration Deck (24)
why do plants, animals and microorganisms need to respire?
The process breaks down complex organic molecules to release energy as ATP, which acts as the immediate energy source for metabolic reactions vital to an organisms existence, such as active transport, DNA replication, synthesis of complex molecules from simpler ones (anabolic reactions)
describe the structure of ATP
ATP stands for adenosine triphosphate
It is made up of three phosphate groups, ribose (pentose sugar) and adenine and is therefore known as a phosphorylated nucleotide.
Why is ATP so unique/important?
- is a universal energy currency used by all cells and found in almost all organisms
- moved around the cell
- when hydrolysed to ADP + Pi energy is released - immediate energy source
- produced by substrate-level phosphorylation where energy is released (e.g. in krebs cycle) ADP + Pi + energy --> ATP
- energy released in small 'packets' of energy: 30kJ - in a rapid turnover
- couples catabolic and anabolic processes
explain the importance of coenzymes in the stages of respiration
Coenzymes are used in both glycolysis and the link reaction. In glycolysis coenzyme NAD acts as a hydrogen carrier, accepting H to become reduced and carrying this H to a later stage of respiration.
Following the link reaction coenzyme A carries an acetyl group to the site of the Krebs cycle (Acetyl CoA).
FAD and NAD are both used in the Krebs cycle, acting as hydrogen carriers - part of the yield of Krebs is 1redFAD and 3redNAD.
In oxidative phosphorylation these donate their hydrogens which are passed to hydrogen carriers on the cristae and split into H+ and e- the latter of which are passed down the electron transport chain generating the energy for phosphorylating ADP + Pi --> ATP
What are the four stages of respiration, in order, and where do they occur?
Do they take place in aerobic/anaerobic respiration?
1. Glycolysis - cytoplasm, common to aerobic and anaerobic respiration.
2. Link - matrix of mitochondria, aerobic respiration only
3. Krebs cycle - matrix of mitochondria, aerobic respiration only
4. Oxidative phosphorylation - cristae of mitochondria, aerobic respiration only
outline the process of glycolysis
1. Glucose is phosphorylated to form hexose bisphosphate (energy as well as phosphate group provided by hydrolysis of ATP to ADP + Pi),
2. Hexose bisphosphate is hydrolysed into two triose phosphate molecules
3. Triose phosphate is oxidised (enzyme - dehydrogenase) to form pyruvate, the H atoms that have been removed are picked up by NAD --> reduced NAD goes to the electron transfer chain
Overall, there is a net gain of 2ATPs (4 produced, two used as activation energy) and reduced NAD
Following glycolysis, what happens to pyruvate in aerobic respiration?
It is actively transported to the mitochondria where it takes part in the link reaction
outline the link reaction
1. Pyruvate is decarboxylated (decarboxylase enzymes)w and oxidised (dehydrogenase enzymes) to form acetate
2. The H is picked up by coenzyme NAD which becomes reduced NAD
3. acetate is combined with coenzyme A to be carried to the Krebs cycle
outline the Krebs cycle,
1. formation of citrate from acetate (carried over by Coenzyme A) and oxaloacetate
2. In the reconversion of citrate to oxaloacetate decarboxylation and dehydrogenation occur: coenzymes NAD and FAD are reduced so with each cycle 3 reduced NAD and 1 reduced FAD form, both of which carry H to the electron transfer chain
3. The cycle releases enough energy for substrate-level phosphorylation to occur during the cycle, forming 1ATP from ADP + Pi
outline the process of oxidative phosphorylation and chemiosmosis
1. reduced NAD/FAD diffuse to cristae and are oxidised by dehydrogenases
2. the removed H atoms are split into H+ and e-
3. the electrons are pumped along a series of electron carriers, releasing energy - some of which is used to pump H+ into the intermembranal space using proton pumps
4. This sets up a proton gradient, aka an electrochemical gradient (high conc H+ in intermembranal space, low conc. H+ in matrix), and protons diffuse down this gradient via ATP synthase, releasing energy in CHEMIOSMOSIS
5. The movement of H+ through ATP synthase (the proton motive force) causes the head of this enzyme to spin, causing phosphorylation of ADP + Pi --> ATP to occur
6. oxygen is known as the final H+ and electron acceptor, accepting H+ and e- to form H2O
what is known as the final electron acceptor in aerobic respiration?
evaluate the experimental evidence for the theory of chemiosmosis
pH in the intermembrane space lower than
Matrix (evidence of H ions being actively
chemicals e.g. dinitrophenol that inhibit active transport of H+ ions also stop ATP production. These chemicals act as carriers for H+ across membranes so the ions diffuse back and no proton gradient is created.
Even if there is no electron transfer occurring ATP van still be produced in the crust as long as there is a proton gradient.
Isolated membranes can be made to produce ATP when put in a solution with a different pH to that in the membranes
explain how the structure of mitochondria enables them to carry out their functions
- mitochondrial envelope compartmentalises/isolates reactions from other reactions in the cytoplasm that could interfere
- envelope controls the entry or pyruvate, ADP, Pi and O2 and the exit of ATP, CO2 and NAD
- the matrix contains the necessary dehydrogenase and decarboxylase enzymes needed for the link reaction and krebs cycle, both of which occur here.
- small ribosomes in the matrix allow respiratory enzymes/membrane proteins to be synthesised here
- inner membrane is folded to form cristae to increase surface area for attachment of electron carriers and ATP synthase
- intermembrane space allows a proton gradient to be set up
- mitochondria are only 1um in diameter giving a short diffusion distance, but can vary in length to increase surface area : volume ratio
explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration
Glycolysis - 2ATP
Krebs cycle - 1ATP
Oxidative phosphorylation: 3ATP per redNAD, 2ATP per redFAD
= 38ATP per glucose molecule
In practise, some ATP is used to actively transport pyruvate from the cytoplasm into the mitochondria and to transport reduced NAD also from glycolysis into the mitochondria.
Some protons leak back across the mitochondrial membrane (dont go via ATP synthase) reducing the number of protons available to generate the proton motive force.
what are some specific roles of an ATP molecule?
- binding to a protein molecule, changing its shape and causing it to fold differently to produce movement - muscle contraction
- transferring a phosphate group to an enzyme making it active
- transferring a phosphate group to an unreactive substrate molecule so that it can react in a specific way
- binding to a trans-membrane protein so that active transport can take place
what is catabolism compared to anabolism?
catabolism - breaking down of complex molecules to simpler ones
anabolism - the building up of more complex molecules from simpler ones
anabolism + catabolism = metabolism: the total of all the biochemical reactions needed for an organisms to stay alive
describe anaerobic respiration in mammals
- following glycolysis pyruvate acts as hydrogen acceptor and is converted to lactate, releasing NAD
- the pathway is reversible by the Cori cycle
describe anaerobic respiration in yeast
- alcoholic fermentation occurs whereby pyruvate is decarboxylated to ethanal, which accepts hydrogen from red NAD and is reduced to ethanol, releasing NAD
what are the similarities and differences between anaerobic respiration in mammals and in yeast?
- both 'buy time' by providing H acceptors sp that NAD is released and glycolysis can continue
- both pathways are inefficient and wasteful in that the products have chemical bond energy that is untapped
- the ethanol and lactate produced os toxic and restricts the use of pathways
- there is a net gain of 2ATP molecules (from glycolysis) during anaerobic respiration
- lactate pathway is reversible by the Cori cycle, ethanol pathway is irreversible
- ethanol pathway produces CO2, decarboxylation occurs
- ethanal vs. pyruvate is reduced
- toxic in different ways: lactate lowers pH, ethanol dissolves phospholipids
define the term respiratory substrate
a molecule from which energy can be liberated to produce ATP in a living cell by respiration
how are carbs, proteins and fats respectively used in aerobic respiration?
Carbs are digested into glucose which enters glycolysis
Proteins are digested into amino acids which are deaminated in the liver and the remaining keto acids can be concerted into acetate or other krebs cycle intermediates
Fats are digested into glycerol and fatty acids. Glycerol can be converted to triose phosphate and enter glycolysis. Each fatty acid can be converted to many molecules of acetate and enter the krebs cycle.
explain the difference in relative energy values of carbohydrate, lipid and protein respiratory substrates
(Most energy kJg-1) lipids --> proteins --> (least energy kJg-1) carbohydrates
The more hydrogens there are in the structure of a molecule the greater the energy value
Aerobic respiration in mammals and yeast both involve a hydrogen acceptor after glucose. What are they?