Respiration Flashcards
What is the purpose of cellular respiration?
Allows energy stored in organic molecules in cells (e.g. glucose) to be released to make ATP, which is then hydrolysed to provide the energy needed for active processes in cells
What is the balanced equation for respiration?
C6H12O6 = 6O2 —> 6CO2 + 6H2O + ENERGY
What is metabolism?
Refers to all of the reactions that occur inside an organism
What are anabolic reactions?
Metabolic reactions that build up large molecules from smaller ones
- Net requirement for energy
What are catabolic reactions?
Metabolic reactions that break down large molecules into smaller ones
Is respiration an anabolic or catabolic reaction?
Catabolic Substrates (usually glucose) are broken down, releasing energy
Why is ATP such a useful immediate source of energy?
- The hydrolysis of ATP releases small quantities of energy, in manageable amounts, to drive single reactions
- This prevents wastage and cell damage
- Single step reaction - a quick and easy way to release energy
What are the 4 stages in aerobic respiration?
1- Glycolysis
2- The link reaction
3- The krebs cycle
4- Oxidative phosphorylation
Where does glycolysis occur?
Cytoplasm
Where do the last 3 stages of aerobic respiration take place?
Mitochondria
Is glycolysis an anaerobic or aerobic process?
Can be both
Describe the steps in glycolysis
- Phosphorylation of glucose, involves 1 ATP molecule, into glucose phosphate (6C)
- Glucose phosphate is phosphorylated into hexose bisphosphate (6C) using 1 ATP
- Hexose bisphosphate splits into 2xTP (hydrolysis)
- 2xTP are oxidised to 2x pyruvate (3C)
- A single TP molecule produces 2xATP and 1xNADH through dehydrogenation
- Dehydrogenation - TP loses H+, NAD coenzymes accept the removed hydrogens - they are reduced, forming 2 NADH
What are the end products of glycolysis?
Net gain of:
- 2 ATP (2 used up, 4 made)
- 2x NADH
- 2x pyruvate
What is NAD?
- Coenzyme
- A non-protein organic molecule which helps the enzymes in the last part of glycolysis to work
What is substrate level phosphorylation?
Formation of ATP without the involvement of an electron transport chain
What is the purpose of phosphorylating glucose?
Makes the original glucose molecule more reactive
How is glycogen converted into glucose molecules?
Breaking 1,4 glycosidic bonds via hydrolysis
Enzymes and water are needed
Where does the link reaction occur?
Mitochondrial matrix
Is the link reaction an aerobic or anaerobic process?
Aerobic
What may happen to the CO2 produced after the link reaction?
- Diffuse away and be removed from organism as metabolic waste
- In autotrophic organisms, it may be used as a raw material in PHS
Describe the steps in the link reaction
- Pyruvate enters matrix by active transport via specific carrier proteins
- Pyruvate is decarboxylated and dehydrogenated to acetyl (2C)
- CO2 is produced as a by-product, NAD is reduced to NADH
- Acetyl combines with Co-A to produce acetyl-coenzyme A
What is the net gain from the link reaction?
- 1 CO2
- 1 NADH
Why does the link reaction happen twice?
2 pyruvate molecules were formed from glycolysis
Where does the kreb’s cycle take place?
Mitochondrial matrix
Describe the steps in the Kreb’s cycle
1- Acetyl group (2c) + oxaloacetate (4c) = citrate (6c)
2- Citrate is decarboxylated + dehydrogenated = 5c compound, 1 CO2 + NADH
3- 5c is decarboxylated & dehydrogenated = 4c compound, 1 CO2 + NADH
4- 4c compound dehydrogenated = NADH + FADH2
5- Regeneration of oxaloacetate
Where do the reduced co-enzymes carry the H atoms to?
Cristae of mitochondria
What step of aerobic respiration happens on the cristae?
Oxidative phosphorylation
What does oxidative phosphorylation mean?
Adding inorganic phosphate (Pi) to ADP in the presence of O2, to make ATP indirectly, via a chain of electron carriers
What is the advantage of oxidative phosphorylation occuring in the cristae?
They are folded, giving a large SA for as much ATP to be made as possible
Describe steps involved in oxidative phosphorylation
- NADH/FADH2 re-oxidised back to NAD/FAD, releasing 2 protons/electrons
- The e- are transferred along ETC
- H+ accumulate me in space, creating proton gradient, builds up chemiosmotic potential
- Protons diffuse down conc- gradient through ATP synthase
- As protons flow through ATP synthase via protein channels, energy is released
- Energy converts ADP + Pi to ATP (chemiosmosis)
- O2 us the final electron acceptor, combining with e- to form H2O
What is the evidence for the process of chemiosmosis occuring?
pH difference across 2 sides of mitochondrial membrane - H+ ions create an acidic pH
Give 3 differences between NAD and FAD
- NAD accepts H from glycolysis/link/kreb’s
- FAD only accepts H from kreb’s
- Reduced NAD is re-oxidised at the start of ETC, whereas FAD is re-oxidised further along
What does the matrix contain?
- Enzymes that catalyse stages of link/kreb’s
- NAD/FAD
- Oxaloacetate
- Mitochondrial DNA
- Mitochondrial ribosomes
What does the outer membrane contain?
- Proteins
- Some of which form channels or carriers
- Allow passage of molecules, such as pyruvate, into mitochondrion
How does the lipid composition of the inner membrane differ from the outer membrane?
- Less permeable to small ions such as H ions than is the outer membrane
How would you investigate the effect of temperature on rate of respiration in yeast?
- 2cm3 of yeast and glucose solution
- X6 tubes the same
- Transfer to 6 thermostatic water baths (15-65°C)
- Leave for 5 mins before starting (acclimatise)
- 2 drops of methylene blue as an indicator
- Blue when oxidised
- Colourless when reduced
- As yeast respires, H released, splits into H+ & e-
- Go into ETC, picked up by methylene blue, reducing it
How do you convert time taken into rate?
1/time
Give 2 ways that anaerobic respiration occurs in the eukaryotic cells
1- Muscle cells (animals) - lactate fermentation
2- Fungi/Plant/Yeast- ethanol fermentation
How many ATP will be made per glucose respired in anaerobic respiration?
2 ATP
How does anaerobic respiration occur in mammalian muscle cells?
- Glycolysis
- Reduced NAD is re-oxidised to NAD, so it can be reused to accept more H
- Pyruvate is the H acceptor, allowing the NAD to be regenerated (pyruvate reduced)
- Requires enzyme lactate dehydrogenase
- Allows glycolysis to continue, generating enough ATP to sustain muscle concentration for a short time
Is anaerobic respiration in mammals reversible or irreversible?
Reversible as it’s a single step reaction and nothing is lost
What happens to the lactate in anaerobic respiration?
- Carried from the muscles to the liver
- When O2 is available it’s turned back into glucose
- Can either enter glycolysis l, be stored as glycogen or be converted to purity are and enter link reaction of respiration
Why is it so important that lactate is removed from the muscles quickly?
- It would reduce the pH of the muscle cells
- Inhibit enzymes in muscle cells
- Inhibit muscle contraction (requires enzymes)
How does anaerobic respiration occur in plants, fungi and yeast?
- Glycolysis
- Each pyruvate molecule is decarboxylated to form ethanal
- This is catalysed by enzyme pyruvate decarboxylase (which has a coenzyme attached)
- The ethanal accepts H from NADH (which is reoxidised) and the ethanal is reduced to ethanol using the enzyme ethanol dehydrogenase
Why are yeast cells described as facultative anaerobes?
It can live without oxygen, but if this continues for too long, it will die as the concentration of ethanol builds up (once it reaches 15%)
What is the benefit of anaerobic respiration?
Allows respiration to occur for a short time in difficult conditions, allowing an organism to continue functioning
Why is glycolysis the only source of ATP production in RBC?
- RBC don’t have mitochondria so cannot do links/kerbs/ETC
- Advantage = more room for harm of living to be stored so more O2 can be carried around the body by each RBC
Why is it useful that cardiac muscle is adapted to reduce the chances of anaerobic respiration ever being needed?
- Don’t want anaerobic respiration in heart/cardiac cells
- Lactic acid would stop muscle contracting properly
- Cause fatigue of heart muscle and reduction in blood pumped around body
- Dangerous
What biochemical adaptations do diving mammals have to spent lots of time underwater?
- Greater conc of haemoglobin and myoglobin - maximises O2 stores
- Higher tolerance to lactose - can respire anaerobically for longer
- Greater tolerance of high CO2 levels - effective blood buffering systems that prevent catastrophic rise in pH
What physiological adaptations do diving mammals have to spent lots of time underwater?
- Modified circulatory system - when diving, peripheral vasoconstriction occurs, so blood is shunted to brain, heart and muscles
- Heart slows by up to 85% (bradycardia) - reduces energy demand of heart muscles
- Exchange 80-90% of air in lungs when they breathe - high compared to humans at 15%
What physical adaptations do diving mammals have to spent lots of time underwater?
- Streamlining to reduce drag due to friction from water whilst swimming - reduces energy demand during a dive
- Libs of marine animals are fin shaped- maximises efficient use of energy in propulsion
Why will plants die if left in water-logged soil for too long?
There are no air pockets in waterlogged soil so the root cells done have access to oxygen
- Anaerobic respiration cannot be sustained for long
- Ethanol accumulates which is toxic to root cells
What is a respiratory substrate?
An organic molecule that can be used in respiration to release energy
How are polysaccharides and disaccharides respired?
Hydrolysed using enzymes into monosaccharides and then respired
Give an example of a polysaccharide that is hydrolysed into a monosaccharide in plants
Starch, hydrolysed into alpha glucose and then respired
Give an example of a polysaccharide that is hydrolysed into a monosaccharide in animals
Glycogen, hydrolysed into alpha glucose and then respired
Give 3 examples of disaccharides that are hydrolysed into monosaccharides
1- Sucrose, hydrolysed into glucose and fructose, then respired
2- Maltose, hydrolysed into 2x alpha glucose, then respired
3- Lactose, hydrolysed into glucose and galactose, then respired
What are lipids hydrolysed into?
Fatty acids and glycerol
What happens to glycerol when a lipid is being respired?
Can be converted to pyruvate and enter respiratory pathway
What happens to the fatty acids when a lipid is being respired?
Combine with co-A to form a complex, which is then carried into mitochondrial matrix, forming acetyl-co-A
Then enters Krebs cycle
Pathway = Beta-oxidation pathway
Why are proteins usually not respired?
- Amino acids are either used to make important protein structures in the body, or they are converted into urea for excretion
- Only respired if an organism undergoes fasting, starvation or prolonged exercise
Where can various amino acids enter the respiratory pathway?
1- Pyruvate
2- Acetyl CoA
3- 5C compound
Why do lipids release more than twice as much energy as carbohydrates and proteins when respired?
- Made up of glycerol and fatty acids
- Fatty acids consist of very long hydrocarbon chains = LOTS of H
What is a respiratory quotient (RQ)?
The ratio of CO2 produced by a respiring organism to O2 consumed in a given time
What is the equation for RQ?
CO2 released / O2 uptake per unit time
What can the RQ tell us?
What respiratory substrate is being metabolised by an organism and what type of respiration (anaerobic & anaerobic) is being employed
What always give an RQ value of 1 or less
Aerobic respiration
What does a RQ value of more than 1 suggest?
That anaerobic respiration is taking place because more CO2 is produced than O2 consumer
What is used to measure respiration rates and the factors affecting respiration?
Respirometer
How do you set up a respirometer?
1- Place the coloured liquid, that had one drop of detergent added, into manometer tube
2- Connect apparatus with taps open, enabling air in apparatus to connect with atmosphere
3- Measure mass of living organisms (g)
Place whole set up in a water bath for 10 mins until it reaches same temp
4- place syringe near the top of the scale in the syringe barrel and note it’s level
5- Mark levels of coloured liquid in manometer with felt too pen
6- Close taps and leave apparatus in water bath for 10 mins
7- Measure change in level of manometer liquid
8- Depress syringe barrel to reset apparatus
9- Calculate volume of O2 absorbed per min per gram of living organism
What is the net gain from the Kreb’s cycle?
- 2xATP
- 3xNADH
- 1xATP
- 1xFADH2
