5.2.2 Respiration Flashcards
what are the 4 stages of aerobic respiration
glycolysis
link reaction
Krebs cycle
oxidative phosphorylation
how are the stages of respiration grouped
- first 3 stages are a series of reactions, and the products from these reactions are used in the final stage to produce lots of ATP
what is the structure of mitochondria
- inner and outer mitochondrial membrane
- matrix found inside
- inner membrane folds, forming cristae, increasing the SA
- mitochondrial DNA (able to synthesise specific enzymes for respiration)
where do the stages of respiration take place
- glycolysis: occurs in the cytoplasm of the cell
- link reaction and Krebs cycle take place in the matrix of the mitochondria
- oxidative phosphorylation takes place in the inner mitochondrial membrane
what do cells use to respire
- all use glucose
- but can also break down other complex organic molecules to be respired
- e.g. fatty acids and amino acids
what is the overview of glycolysis
- the splitting of one molecule of glucose (6C) into two smaller molecules of pyruvate (3C)
- occurs in the cytoplasm of cells
what is special about glycolysis, as opposed to the other three steps
- it is the first stage of both aerobic AND anaerobic respiration
- doesn’t need oxygen to take place (so can be called an anaerobic process)
what are the two stages of glycolysis
- first: ATP is used to phosphorylate glucose into triose phosphate
- then: triose phosphate is oxidised and releases ATP
what happens during glycolysis
PHOSPHORYLATION:
1) glucose (6C) is phosphorylated by adding 2 phosphates from two molecules of ATP
2) this creates 1 molecule of hexose bisphosphate (6C) and 2 molecules of ADP
3) then, hexose bisphosphate is split into 2 molecules of triose phosphate (2x3C)
OXIDATION:
4) the triose phosphate are oxidised (lose H), and form 2 pyruvate molecules (2X3C)
5) the NAD collects the H+ ions, and forms 2 reduced NAD
6) 4 ATP are produced during this stage
- NET GAIN OF 2 ATP, as 2 used in first stage, and 4 formed in the second
what are the products of glycolysis
- 2 ATP
- 2 reduced NAD
- 2 pyruvate molecules
what happens with the products of glycolysis
- the 2 molecules of reduced NAD go to the last stage of respiration (oxidative phosphorylation)
- the 2 pyruvate molecules are actively transported into the matrix of the mitochondria for the link reaction
what is an overview of the link reaction
- conversion of pyruvate into acetyl coenzyme A
- takes place in the mitochondrial matrix
what happens during the link reaction
1) the pyruvate (3C) is decarboxylated, and one carbon is removed from it to form a molecule of CO2 (1C)
2) NAD is reduced to NADH, as it collects a hydrogen from pyruvate, changing it to acetate (2C)
3) the acetate (2C) combines with coenzyme A (CoA) to form acetyl coenzyme A (shortened to acetyl CoA) (2C)
how much ATP is produced in the link reaction
NONE
how many times does the link reaction occur for every molecule of glucose
TWICE
- as 2 pyruvates are made for every 1 glucose molecule that enters glycolysis
- so the link reaction (and the Krebs cycle) both happen twice for every glucose molecule
what are the products of the link reaction
- 2 molecules of acetyl CoA
- 2 CO2 molecules
- 2 molecules of reduced NAD
how are the products of the link reaction used
- the 2 molecules of acetyl CoA go into the Krebs cycle
- the 2 molecules of NADH go to the last stage of respiration (oxidative phosphorylation)
- the 2 molecules of CO2 are released as a waste product of respiration
what is an overview of Krebs cycle
- a series of oxidation-reduction reactions, forming reduced coenzymes and ATP
- takes place in the matrix of the mitochondria
- happens once for every pyruvate, so twice for every glucose molecules
what is the first step of the Krebs cycle
1) the acetyl group from acetyl CoA (2C) (produced in the link reaction) combines with oxaloacetate (4C) to produce citrate (citric acid) (6C) [step is catalysed by citrate synthase]
- the coenzyme A goes back to the link reaction to be used again
what is the second step of the Krebs cycle
2) the citrate molecule (6C) is converted into a 5C molecule
- this is via decarboxylation, where CO2 is removed
- dehydrogenation also occurs, where a hydrogen is removed and is used to form NADH from NAD
what is the third step of the Krebs cycle
3) the 5C molecule is then converted into a 4C molecule (some intermediates are formed during this conversion, but don’t need to know)
- decarboxylation and dehydrogenation (three times) occurs, producing one molecule of reduced FAD and 2 molecules of reduced NAD
- ATP is also produced, via the direct transfer of a phosphate group from an intermediate compound to ADP
- example of SUBSTRATE LEVEL PHOSPHORYLATION
- citrate (6C) had been converted back to oxaloacetate (4C)
what is substrate level phosphorylation
when a phosphate group is directly transferred from one molecule to another
what are all the products of the Krebs cycle PER CYCLE
- 1 coenzyme A
- oxaloacetate
- 2 CO2
- 1 ATP
- 3 reduced NAD
- 1 reduced FAD
- ALWAYS TIMES 2 FOR A MOLECULE OF GLUCOSE
what are the products of the Krebs cycle used for
- coenzyme A: reused in the next link reaction
- oxaloacetate: regenerated for use in the next Krebs cycle
- CO2: released as a waste product of respiration
- ATP: used for energy
- NADH: to oxidative phosphorylation
- FADH: to oxidative phosphorylation
what is an overview of oxidative phosphorylation
- where the energy carried by electrons from reduced coenzymes is used to make ATP
- all the previous stages have led up to making NADH and FADH for this final stage
- takes place in the inner mitochondrial membrane
describe the placement of components of oxidative phosphorylation
- NADH and FADH are found in the matrix of the mitochondria, near the inner mitochondrial membrane
- electron carriers are found on the inner mitochondrial membrane
- the H+ ions travel inside to the intermembrane space
- and pass out through enzyme ATP synthase, found after the electron carriers in the inner mitochondrial membrane
what is the process of oxidative phosphorylation
1) hydrogen atoms are released from NADH and FADH as they are oxidised to NAD and FAD (these regenerated coenzymes are reused in the Krebs cycle)
2) the hydrogen atoms split into H+ and e- (protons and electrons)
3) the electrons move along the electron transport chain, ade ofr 3 electron carriers), and lose energy at each carrier
4) this energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space
5) this means that the concentrations of protons is now higher in the intermembrane space than in the mitochondrial matrix, forming an electrochemical gradient (a concentration gradient of ions)
6) protons move down this electrochemical gradient, back into the mitochondrial matrix, via ATP synthase
7) this movement drives the synthesis of ATP from ADP and inorganic Pi
8) CALLED CHEMIOSMOSIS, described by the chemiosmotic theory
9) in the matrix, at the end of the transport chain, protons (out of ATP synthase), electrons (from the third electron carrier) and O2 (from the blood) combine to form water [1/2 O2 + 2H+ + 2e- → H2O]
10) oxygen is said to be the FINAL ELECTRON ACCEPTOR
what is chemiosmosis
the process of ATP production driven by the movement of H+ ions across a membrane (due to electrons moving down an electron transport chain)
why is cristae and important structure for oxidative phosphorylation
- the electron transport chain is located in the inner mitochondrial membrane
- this membrane in folded int structures of cristae
- they are able to INCREASE surface area of the membrane and maximise respiration
what is oxygen said to be in respiration
the final electron acceptor
how many ATPs can be produced from one molecule of glucose, and why
32
- as each NADH makes 2.5 ATP
- as each FADH makes 1.5 ATP
- GLYCOLYSIS: 2 ATP and 2 NADH = 7
- LINK REACTION: 2 NADH = 5
- KREBS: 2 ATP, 6 NADH, 2 FAD = 20
what is anaerobic respiration
respiration that doesn’t use oxygen
what stages does anaerobic respiration not include
link reaction, Krebs cycle, oxidative phosphorylation
what are the two types of anaerobic respiration
alcoholic fermentation
lactate fermentation
how do the two types of anaerobic respiration differ, and be the same
- similar as both take place in the cytoplasm
- similar as both start with glycolysis, which produced pyruvate
- differ in which organisms they occur in
- differ in what happens with the pyruvate produced
what organisms does lactate fermentation occur in
mammals
- and some bacteria
what occurs in lactate fermentation
- glycolysis as normal
- the reduced NAD from glycolysis transfers hydrogen to pyruvate to form lactate and NAD
- the NAD can be reused again in glycolysis
why is lactate regenerating NAD so important
- the production of lactate regenerates NAD
- glycolysis needs NAD to take place
- this means that glycolysis can still take place even when there isn’t much oxygen around
- means a small amount of ATP can still be produced to keep some biological processes going
what happens to the lactate produced in lactate fermentation
- our cells can tolerate a high level of lactate (and the levels of low pH it causes) for a short period of time
- e.g. during short periods of hard exercise, cells can’t get enough ATP from aerobic respiration
- HOWEVER: too much lactate is toxic
- is removed from cells into the bloodstream
- the liver takes up the lactate from the bloodstream
- converts it back into glucose
- process called GLUCONEOGENESIS
where does alcoholic fermentation take place
in yeast cells
- as well as plants
what happens during alcoholic fermentation
- glycolysis as normal
- CO2 is removed from the pyruvate to produce ethanal (decarboxylation)
- reduced NAD (from glycolysis) transfers a hydrogen to ethanal to form ethanol and NAD
- the NAD is then reused in glycolysis
- this regeneration of NAD is important for glycolysis to continue when there isn’t much oxygen around
why does anaerobic respiration produce so much less ATP than aerobic
- ONLY glycolysis is taking place
- which only produces 2 ATP molecules per glucose
- the other energy releasing reactions of Krebs and oxidative phosphorylation both require oxygen, so can’t occur during anaerobic respiration
what is a respiratory substrate
any biological molecule that can be broken down in respiration to release energy
- e.g. glucose, but also other carbohydrates
- also lipids and proteins, which enter respiration at the Krebs cycle
what is different about different respiratory substrates
different respiratory substrates release different amounts of energy when they are respired
what are the different energy values of different respiratory substrates
- lipids have the highest value
- then proteins
- then carbohydrates
why do lipids release the most amount of energy when respired
- most ATP is made during oxidative phosphorylation
- this process requires hydrogen atoms from reduced NAD and reduced FAD
- so the respiratory substrate containing the most hydrogen atoms per unit of mass cause more ATP to be produced when respired
- lipids contain the most hydrogen atoms per unit of mass (the long hydrocarbon chain), then proteins, then hydrocarbons
what is the respiratory quotient RQ
the volume of carbon dioxide produced when that substrate is respired, divided by the volume of oxygen consumed, in a set period of time
how do you work out RQ
vol. of CO2 produced / vol. of O2 consumed
- can be found in an equation, by using the number of molecules of CO2 and O2
what are the RQ values of respiratory substrates
CARBS: 1.0 (6 and 6 molecules)
PROTEINS: 0.9
LIPIDS: 0.7
why do proteins and lipids have a lower RQ value that carbohydrates
more oxygen is needed to oxidise fats and lipids than to oxidise carbohydrates
what does the RQ value of an organism tell you
- what kind of respiratory substrate an organism is respiring
- what type of respiration it is using (aerobic or anaerobic)
what is the typical RQ value of humans, under normal conditions
- between 0.7 and 1.0
- shows that some fats (lipids) are being used for respiration, as well as carbohydrates such as glucose
- protein is not normally used by the body for respiration
- unless there is nothing else
what is a very rare respiratory substrate
- proteins, so dont usually include when considering
- only during starvation or strenuous exercise
- always say this one is not usually used
what does an RQ of higher than 1 showcase
- an organism is short of oxygen
- having to respire anaerobically
- as well as aerobically
why do plants usually have very low RQ
- the CO2 released in respiration
- is used for photosynthesis
- so not measured
what gives an indication that yeast is respiring
- CO2 production
- as produced during both aerobic and anaerobic respiration
PRACTICAL: how can you investigate the rate of CO2 production in yeast, in aerobic conditions
1) put a known volume and concentration of substrate solution, e.g. glucose, in a test tube
2) add a known volume of buffer solution to keep pH constant, and choose the optimum for the yeast you’re using
3) place the test tube in a water bath set to 25°C, to make sure the temperature stays constant throughout the experiment, and leave for 10 minutes for temp. of substrate to stabilise
4) add known mass of dried yeast to test tube and stir for 2 minutes
5) after yeast has dissolved, put bung with the tube attached to gas syringe, which should be set to 0
6) start stop watch straight away
7) yeast respires, and CO2 enters gas syringe
8) at regular timed intervals, record the volume of CO2 in the syringe for set amount of time
9) set up a control, with no yeast, should see no CO2 is formed
10) repeat 3 times, discard anomalies, and calculate mean
- ensure it is anaerobic, as eventually O2 will be used up in the tube, so if you need to repeat it for longer, use a conical flask that can hold more O2
PRACTICAL: how would you measure the rate of CO2 production of yeast respiring anaerobically
same as before, but once yeast has dissolved, trickle liquid paraffin down the inside of the test tube, letting it settle on and cover the surface of solution, and then repeat as normal
PRACTICAL: how can you tell if your results from the yeast practical were accurate
look up published results about the rate of respiration of yeast, and compare with yours
PRACTICAL: what other variables can you test the rate of respiration of yeast on
- temperature (water bath)
- substrate concentration
- different respiratory substrates (e.g. sucrose)
PRACTICAL: what is a respirometer used to show
- the rate of aerobic respiration
- measures the amount of oxygen used up by an organism over a period of time
- used on woodlice, other small organisms, plant seeds, peas
PRACTICAL: how do you set up a respirometer
- 2 test tubes, one is control, and other is the test one
- connect with a manometer [ a capillary tube filled with coloured fluid and a calibrated scale]
- in both, add potassium hydroxide solution, or soda lime
- add woodlice on a gauze in test tube, and glass beads in control
- add a syringe as well on the bung of the first tube
PRACTICAL: what is the point of the potassium hydroxide solution in the respirometer
absorb CO2 produced in respiration, so the only gas changes you notice are the O2 consumption
PRACTICAL: what is the point of the control tube of the respirometer
is set up in the same way, but has glass beads instead of woodlice (similar mass), to make sure any results are due to the woodlice respiring only
PRACTICAL: what is the point of the coloured fluid in the manometer
- via dipping the ends of the capillary tube in a beaker of the fluid
- via capillary action, the fluid will move into the tube
- syringe is used to set the fluid to a known level
PRACTICAL: what will happen during the respirometer practical
1) leave apparatus for 20 minutes
2) in the test tube, the volume of air will decrease
3) due to the O2 consumption
4) this decrease in volume will reduce the pressure in the tube
5) so the coloured liquid in the manometer will move towards the test tube
6) measure the distance moved by liquid in a given time
7) can calculate the volume of O2 taken in by the woodlice per minute, via diameter
8) CONTROL ALL VARIABLES, e.g. volume of potassium hydroxide in each tube
- more precise results, repeat experiment, and calculate mean volume
PRACTICAL: what are the limitations of the respirometer practical
difficult to accurately read the meniscus of the fluid in the manometer
PRACTICAL: what technology can be used instead of the respirometer practical
- respirometer is set up with an electronic oxygen sensor
- measures the oxygen concentration inside the respirometer chamber
- at set intervals
- also has a data logger to automatically record the set data
- can be put into a data analysis software, which helps to analyse and draw conclusions from experiment
PRACTICAL: why is using technology useful in the respiration practical
reduces the chances of human error in recording the data
