5.18 - Respiration Flashcards
What is respiration?
The process by which organic molecules e.g. glucose are broken down into smaller inorganic molecules e.g. carbon dioxide and water.
This provides ATP for metabolic reactions
What is the site of respiration?
Mitochondria
Why do organisms need to respire?
To produce ATP as an energy currency for:
- active transport
- metabolic reactions
- muscle contraction
Releases heat energy for thermoregulation
What is the structure of a mitochondrion?
- outer mitochondrial membrane
- inner mitochondrial membrane, has projections called cristae
- intermembrane space between outer and inner membrane including the spaces in cristae
- matrix is the aqueous environment inside of the cell
What are the adaptations of a mitochondrion
- outer membrane for compartmentalisation, creates ideal conditions
- inner membrane contains ATP synthase and ETC, cristae increase surface area
- matrix contains enzymes for Krebs cycle and link reaction. mitochondrial DNA
- intermembrane space is small increase chemiosmotic gradient for H+
What are the stages of aerobic respiration?
- glycolysis
- link reaction
- Krebs cycle
- electron transport chain
What are the stages of anaerobic respiration?
- glycolysis
- fermentation
What happens during glycolysis?
- Phosphorylation - 2 phosphates released by 2ATP attach to glucose molecule forming hexose bisphosphate
- Lysis - hexose bisphosphate is unstable, so splits into 2 triose phosphate
- Phosphorylation - one phosphate group added to each TP forming 2 triose bisphosphate
- Dehydrogenation and ATP formation - oxidised by removal of hydrogen which NAD accepts (=NADH), 2 phosphates each accepted by 4ADP (=4ATP), forms 2 pyruvate molecules
Where do the stages of respiration occur?
- glycolysis = cytoplasm of cell
- link reaction = mitochondrial matrix
- Krebs cycle = mitochondrial matrix
- ETC = inner mitochondrial membrane
What happens during the link reaction?
- Pyruvate enters matrix by active transport
- Oxidative decarboxylation - CO2 is removed and hydrogen removed is accepted by NAD (=NADH)
- This forms a 2C acetyl group, which is bound to coenzyme A
- Acetyl CoA
What happens during the Krebs cycle?
- Acetyl CoA delivers acetyl group to Krebs cycle (still in matrix)
- 2C acetyl combines with 4C oxaloacetate to form 6C citrate (citric acid)
- Decarboxylation and dehydrogenation - releases CO2 and a H to reduce NADH, 5C compound formed
- Decarboxylation and dehydrogenation - CO2 released, 2NADH and FADH2 produced ATP reduced by substrate level phosphorylation
- This regenerates oxaloacetate
What happens during oxidative phosphorylation (ETC)?
- Hydrogen atoms collected by NAD and FAD delivered to ETCs in the cristae
- Dissociation - H atoms dissociate into H+ and electrons, highe energy electrons’ energy used for chemiosmosis
- H+ ions used to create proton gradient in chemiosmosis, then diffuse down ATP synthase to form ATP
- At end of ETC, electrons combine with the H+ and oxygen to form water
Oxygen is the final electron acceptor, so is an aerobic process
What happens in the electron transport chain/chemiosmosis
- Excited electron from dissociated hydrogen molecule moves through electron transport chain in the inner mitochondrial membrane.
- Energy released by electron is used to pump protons across the membrane from the matrix into the intermembrane space
- Protons move back down chemiosmotic gradient through hydrophilic protein channel ATP synthase. The flow of protons provide energy to phosphorylate ADP into ATP
- Oxygen acts as a final electron acceptor and also accepts H+ ions to form H2O
What is an obligate anaerobe?
An organism that cannot survive in the presence of oxygen (almost all are prokaryotes e.g. Clostridium, food poisoning, but some fungi)
What is a facultative anaerobe?
Organisms that synthesise ATP by aerobic respiration in oxygen is present, but can switch to anaerobic in the absence of oxygen e.g. yeast, human muscle cells
What are obligate aerobes?
Organisms that can only synthesise ATP in the presence of oxygen e.g. mammals (some cells such as muscles can be facultative anaerobe but only for short periods, oxygen is eventually requires)
What is fermentation
The process of breaking down complex organic molecules into simpler inorganic compounds without the use of oxygen or involvement of an electron transport chain. The organic compounds are not fully broken down, so less ATP is produced than in aerobic respiration.
What is the process of alcohol fermentation?
Occurs in yeast and some plant root cells, it is not a reversible process as atoms are lost
1. Pyruvate from glycolysis is converted into ethanal, releasing CO2. It is catalysed by pyruvate decarboxylase
2. Ethanal accepts a hydrogen atom from NADH, becoming ethanol
NAD can then continue to act as a coenzyme in glycolysis so the process can continue
What is the process of lactate fermentation in mammals?
- Pyruvate acts as a hydrogen acceptor, taking the hydrogen from NADH
- The pyruvate is converted into lactate (lactic acid) and NAD is regenerated
NAD can then be used in glycolysis, which generates a small amount of ATP through substrate level phosphorylation
Why can’t lactase fermentation occur indefinitely in mammals?
- the reduced quantity of ATP produced would not be enough to maintain vital processes for a long period of time
-the accumulation of lactic acid causes a fall in pH leading to proteins denaturing. Respiratory enzymes and muscle filaments will cease to function at a low pH
What is the net gain in glycolysis
2NADH and 2ATP per glucose
What is the net gain in the link reaction
1CO2 and 2NADH per pyruvate
What is the net gain in the Krebs cycle
2CO2, 3NADH, FADH2, 1ATP per acetyl group
Name the stages in respiration that produce ATP through substrate-level phosphorylation
- glycolysis
- Krebs cycle
What molecules can be used as an alternative respiratory substrate?
- protein (amino acids)
- lipids (glycerol and fatty acids)
What are some bacterial adaptations to low oxygen environments?
Different groups of bacteria have evolved to use different molecules as a final electron acceptor so they can live in zero oxygen environments. For example, bacteria in cows’ digestive system use CO2 as a final electron acceptor, creating methane.
What are some mammalian adaptations to low oxygen environments?
Marine mammals that dive for long periods
Biochemical:
Higher tolerance of lactic acid and CO2 levels, effective pH buffering system, less tissue damage
Physiological:
Bradycardia when diving to reduce energy demand of heart, can exchange more air when breathing
Physical:
Streamlining to reduce drag and therefore energy demand
Outline an investigation into respiration rates in yeast
Measuring the rate of anaerobic respiration/fermentation of yeast cells
1. Set up a vacuum (to control temperature) flask attached to a gas syringe with a solution of water, brewer’s yeast and carbohydrates.
2. cover solution with liquid paraffin wax to ensure anaerobic conditions
3. As the yeast respires, CO2 is released, moving the plunger of the gas syringe outwards.
4. The rate of respiration can be measured by dividing the increase in volume of the gas syringe by the time taken.
Outline an investigation into the factors affecting the rate of respiration using a respirometer
- The apparatus consists of two tubes, one containing germinating seeds and the other with glass beads to act as a control.
- Both tubes contain an alkali such as sodium hydroxide to absorb any carbon dioxide given off during respiration. This ensures that any volume changes measured in the experiment are due to oxygen uptake only.
- The reduction of volume (oxygen) in the tube increases pressure causing the coloured liquid to move toward the seeds
- The distance moved by the liquid in a given time is measured will provide the volume of oxygen taken in by the seed per minute.
To investigate temperature the experiment is repeated at different temperatures, eg 10, 15, 20, 25, 30°C.
Evaluate the benefits and drawbacks of a low carbohydrate diet
Benefits:
-relatively fast weight loss
- reduced diabetes risk
Drawbacks:
- risk of ketosis, which may cause blood pH to fall to dangerous levels (high levels of ketones which is CoA not taken into Krebs broken down by liver)
- can lead to muscle wastage as lean muscle in broke down so proteins can be used for respiration
What is a respiratory quotient (RQ)?
CO2 produced / O2 consumed
What can the respiratory quotient be used to determine?
- Respiratory substance present
(carbohydrate = 1.0, protein = 0.9, lipid = 0.7) - if organism is undergoing anaerobic respiration (values would then be larger)
What are the RQs of each respiratory substance?
carbohydrates = 1.0
proteins = 0.9
lipids = 0.7
Why do lipids have the lowest RQ and twice as much energy as carbohydrates?
Lipids contain a greater proportion of carbon-hydrogen bonds than carbohydrates and proteins, so they produce more ATP being broken down and release less carbon dioxide
What is a respirometer?
A respirometer is a piece of equipment that can be used to measure the rate of respiration by measuring the volume of oxygen taken in over a set period of time.
Why do proteins have a low net production of ATP?
They have to be hydrolysed into amino acids first and then the amino groups have to be deaminated (usually by pyruvate). This requires ATP, reducing the net gain.
