Module 5 Section 6: Respiration Flashcards
4 stage of respiration
Glycolysis, the link reaction, krebs cycle, oxidative phosphorylation
How do the 4 stages of respiration interact and link together
First three stages are a series of reactions.
The products from these reactions are used in the final stage to produce ATP
Where do the stages of photosynthesis take place
Glycolysis happens in the cytoplasm of cells
Link reaction, Krebs cycle and oxidative phosphorylation take place in the mitochondria.
Structure of mitochondrion
What can the glucose that is respired be replaced by
All cells use glucose to respire, but organisms can also break down other complex organic molecules (e.g. fatty acids, amino acids), which can then be respired
What does stage one of respiration create
Glycolysis Makes Pyruvate from Glucose
Overview of glycolysis
Glycolysis involves splitting one molecule of glucose (with 6 carbons - 6C) into two smaller molecules of pyruvate (3C)
The process happens in the cytoplasm of cells.
Glycolysis is the first stage of both aerobic and anaerobic respiration and doesn’t need oxygen to take place - so it’s an anaerobic process
Process of glycolysis
Phosphorylation:
Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP.
This creates 1 molecule of hexose bisphosphate and 2 molecules of ADP.
Then, hexose bisphosphate is split up into 2 molecules of triose phosphate.
Oxidation:
Triose phosphate is oxidised (loses hydrogen), forming 2 molecules of pyruvate.
NAD collects the hydrogen ions, forming 2 reduced NAD.
4 ATP are produced, but 2 were used up in stage one, so there’s a net gain of 2 ATP
Draw process of glycolysis
What is reduced NAD also called
NADH
What happens to the products of glycolysis
The two molecules of reduced NAD go to the last stage (oxidative phosphorylation)
The two pyruvate molecules are actively transported into the matrix of the mitochondria for the link reaction
Where does the link reaction take place
In the mitochondrial matrix
Process of link reaction
Pyruvate (3C) is transported to the matrix of the mitochondria
Pyruvate is decarboxylated removing a single carbon as CO2
NAD is reduced to NADH — it collects hydrogen from pyruvate, changing pyruvate into acetate
Acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA).
Draw diagram of link reaction
How many cycles of link reaction does one glucose molecule provide
For every glucose molecule, 2 pyruvate is made in glycolysis so link reaction can cycle twice meaning:
Two molecules of acetyl coenzyme A go into Krebs cycle
Two CO2 molecules are released as waste product of respiration
Two molecules of reduced NAD are formed and go to last stage (oxidative phosphorylation)
Stage 1 of Krebs cycle: citrate formed
Acetyl group from acetyl CoA (produced in link reaction) combines with oxaloacetate to form citrate (citric acid) which is a 6C compound
This is catalysed by citrate synthase
Coenzyme A goes back to the link reaction to be used again
Stage 2 of Krebs cycle: citrate turned into 5C molecule
The 6C citrate molecule is converted to a 5C molecule (intermediate)
Decarboxylation occurs where CO2 is removed
Dehydrogenation also occurs where hydrogen is removed
The hydrogen is used to produce reduced NAD from NAD
Stage 3 of Krebs cycle: oxaloacetate reformed
The 5C molecules is then converted to a 4C molecule
(There are some intermediates compounds formed during this conversion but don’t need to know them)
Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two reduced NAD
ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP
When a phosphate group is directly transferred from one molecule to another its called substrate level phosphorylation
Citrate has now been converted into oxaloacetate
Draw Krebs cycle
Products per cycle of Krebs cycle
3 reduced NAD
1 reduced FAD
1 АТР
2 CO2
Products per glucose molecule for Krebs cycle
6 reduced NAD
2 reduced FAD
2 АТР
4CO2
Where does Krebs cycle occur
Mitochondrial matrix
Full process of oxidative phosphorylation
Hydrogen atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD. The H atoms split into protons (H+) and electrons (e-).
The electrons move along the electron transport chain (made up of three electron carriers) in the inner mitochondrial membrane
They lose energy at each carrier
This energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space
The concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix — this forms an electrochemical gradient
Protons move down the electrochemical gradient, back into the mitochondrial matrix, via ATP synthase.
This movement drives the synthesis of ATP from ADP and inorganic phosphate (Pi)
This process of ATP production driven by the movement of H+ ions across a membrane (due to electrons moving down an electron transport chain) is called chemiosmosis
In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and O2 (from the blood) combine to form water.
Oxygen is said to be the final electron acceptor.
Where does 1 coenzyme A go after Krebs cycle
Reused in next link reaction
Where does oxaloacetate go after Krebs cycle
Regenerated for use in next Krebs cycle
Where does the 2 CO2 go after Krebs cycle
Released as a waste product
Where does the 1 ATP go after Krebs cycle
Used for energy
Where does the 3 reduced NAD produced go after Krebs cycle
To oxidative phosphorylation
Where does the 1 reduced FAD go after Krebs cycle
To oxidative phosphorylation
What is oxidative phosphorylation
Oxidative phosphorylation is the process where the energy carried by electrons, from reduced coenzymes (reduced NAD and reduced FAD), is used to make ATP.
The point of the previous stages is to make reduced NAD and reduced FAD for the final stage
Where does oxidative phosphorylation take place
Takes place in the inner mitochondrial membrane
How many ATP molecules can be made from one glucose molecule over the whole of respiration
32 ATP
How many molecules of ATP are made from each coenzyme in oxidative phosphorylation
In oxidative phosphorylation 2.5 ATP are made from reduced NAD and 1.5 ATP are made from each reduced FAD
What doesn’t anaerobic respiration require
Oxygen
Doesn’t use link reaction, Krebs cycle or oxidative phosphorylation
Two types of anaerobic respiration
Alcoholic fermentation and lactate fermentation
Similarities and differences between alcoholic fermentation and lactate fermentation different
Both take part in the cytoplasm and both start with glycolysis
Differ in which organisms they occur in and what happens to pyruvate
Process of lactate fermentation
Reduced NAD (from glycolysis) transfers hydrogen to pyruvate to form lactate and NAD.
NAD can then be reused in glycolysis.
How does lactate fermentation still fuel some biological processes
The production of lactate regenerates NAD.
Glycolysis needs NAD in order to take place.
This means glycolysis can continue even when there isn’t much oxygen, so a small amount of ATP can still be produced to keep some biological process going.
What happens when lactate starts to build up
Our cells can only tolerate a high level of lactate (and the coinciding low pH conditions) for short periods of time.
E.g. during short periods of hard exercise, when they can’t get enough ATP from aerobic respiration
However, too much lactate is toxic and is removed from the cells into the bloodstream.
The liver takes up lactate from the bloodstream and converts it back into glucose in a process called gluconeogenesis
In what organisms does lactate fermentation occur
Mammals and bacteria
Process of alcoholic fermentation
CO2 is removed from pyruvate to form ethanal.
Reduced NAD (from glycolysis) transfers hydrogen to ethanal to form ethanol and NAD.
NAD can then be reused in glycolysis
How does alcoholic fermentation still fuel some biological processes
The production of ethanol also regenerates NAD so glycolysis can continue when there isn’t much oxygen around
In what organisms does alcoholic fermentation occur
Yeast cells and plants
What else can cells respire
Cells respire glucose as well as carbohydrates, lipids and proteins
Cells can respire different substrates
Any biological molecule that can be broken down in respiration to release energy is called a respiratory substrate
Where do lipids and proteins enter respiration
The Krebs cycle
How to tell how suitable something is to be respired
Different respiratory substrates release different amounts of energy when they’re respired
What has the best energy value and why
Lipids release the most energy followed by proteins and then carbohydrates
Lipids contain the most hydrogen atoms per unit of mass, followed by proteins and then carbohydrates.
Respiratory substrates that contain more hydrogen atoms per unit of mass cause more ATP to be produced when respired.
Because most ATP is made in oxidative phosphorylation, which requires hydrogen atoms from reduced NAD and reduced FAD.
What is a respiratory quotient (RQ)
This is what can be worked out when an organism respires a specific respiratory substrate
The RQ is the volume of carbon dioxide produced when that substrate is respired, divided by the volume of oxygen consumed, in a set period of time
Equation for respiratory quotient
How to work out the RQ for cells that only respire glucose
Equation for respiration:
C6H12O6 + 6O2 -> 6CO2 + 6H2O
RQ of glucose = molecules of CO2 released / molecules of O2 consumed
6/6 = 1
Explain the values in the table of RQs for carbohydrates, proteins and lipids
Lipids and proteins have an RQ value lower than one because more oxygen is needed to oxidise them than to oxidise carbohydrates
What information can RQs provide
RQ for an organism says what kind of respiratory substrate an organism is respiring
Says type of respiration it’s using (aerobic or anaerobic).
E.g. under normal conditions the usual RQ for humans is 0.7-1.0.
An RQ in this range shows that some fats (lipids) are being used for respiration, as well as carbohydrates (glucose)
Protein isn’t normally used by the body for respiration unless there’s nothing else
What do high RQs tell you
High RQs (greater than 1) mean that an organism is short of oxygen, and is having to respire anaerobically as well as aerobically.
Plants sometimes have a low RQ.
This is because the CO2 released in respiration is used for photosynthesis (so it’s not measured)
What dye to use to measure aerobic respiration
Methylene blue is a redox indicator dye that can take the place of electron acceptors in oxidative phosphorylation
Changes blue to colourless.
The rate of colour change shows the rate of respiration of the yeast.
Method of measuring aerobic respiration
Known volume and concentration of substrate solution (e.g. glucose) in a test tube.
Add known volume of buffer solution to keep the pH constant.
Place the test tube in a water bath set to 25°C.
This ensures that the temperature stays constant throughout the experiment (leave it there for 10mins to stabilise temperature)
Add known volume of yeast suspension to test tube and stir for 2mins
Add known volume of methylene blue and seal the tube with a bung.
Shake the test tube for set number of seconds (e.g. 10 seconds) and place it back in water bath.
Start a stopwatch immediately afterwards.
Record how long it takes for the solution in the test tube to change from blue to colourless.
Use control to compare colours
Repeat steps 1-5 three times and calculate mean time for the colour change to occur.
Calculate mean rate of respiration of the yeast using the following equation:
Mean rate of respiration = 1 / mean time for colour change to occur
Process behind measuring anaerobic respiration
Yeast produces CO2 when it respires anaerobically, so the rate at which CO2 is produced gives an indication of the yeast’s respiration rate.
Measured using gas syringe
Method to determine rate of anaerobic respiration
Known conc and volume of substrate solution in test tube, add known volume of buffer solution to test tube, place in 25° water bath, then add known volume of yeast suspension
Trickle liquid paraffin down inside of test tube so that it settles on and completely covers the surface of the solution.
This will stop oxygen getting in, which forces the yeast to respire anaerobically.
Put a bung, with a tube attached to a gas syringe, in the top of the test tube and start a stopwatch.
Set gas syringe to zero.
As the yeast respire, the CO2 formed will push gas into the syringe, which measures volume of CO2 released.
Record the volume of gas in the gas syringe at regular time intervals (every minute).
Do this for a set amount of time (10mins).
Repeat the experiment three times and calculate mean rate of CO2 production.
How to increase validity of aerobic respiration experiment
Set up test tube containing water (instead of substrate solution and buffer solution) to act as a control.
After the yeast and methylene blue is added, it shouldn’t decolourise as the yeast will not be respiring aerobically.
How to increase validity of anaerobic respiration experiment
A negative control experiment should also be set up, where no yeast is present.
No CO2 should be formed without the yeast
How to measure variables affecting both aerobic and anaerobic respiration
Repeat the same experiments but change certain variables e.g:
Substrate concentration: replace glucose with sucrose
Temperature: put test tubes in water baths of different temperatures
How are respirometers used
Used to indicate rate of aerobic respiration
Measures how much oxygen is consumed by an organism over a period of time
Can be used to measure respiration of small organisms like woodlice or seeds
How to set up respirometer
Each test tube contains KOH (potassium hydroxide), also known as soda lime, which absorbs CO2
Control tube set up in same way but without living organisms (may use glass beads which have same mass as organism but don’t respire)
Coloured fluid is added to the manometer through capillary action
Apparatus left for a set period of time (20mins)
How does a respirometer work
During the time you leave the respirometer to set there’ll be a decrease in volume of air in test tube
This is due to oxygen consumption by organism (CO2 produced is absorbed by soda lime)
Decrease in volume of air reduced pressure in the tube and cause the coloured liquid in manometer to move towards the test tube
Distance move by the liquid in a given time is measured
This can be used to calculate volume of oxygen taken in per min
Equation to measure the rate oxygen taken up per min in a respirometer
Volume calculated using:
πr^2h
Divide this by time taken
How to make sure the results from a respirometer are more accurate
Any variables which can affect the results are controlled
E.g. temperature, volume of KOH is kept the same
How to increase precision and validity of results from respirometer
Experiment is repeated and a mean volume of O2 is calculated
Use electronic oxygen sensor and data logger to record O2 conc at set intervals
Data is then put into data analysis software to help draw conclusions from experiment
Limitations of using a respirometer
Can be difficult to accurately read meniscus of the fluid in manometer
Adaptations of inner mitochondrial membrane for chemiosmosis to occur
Large surface area
Membrane mostly impermeable to H+, forcing it to travel through proteins
Contains ATP synthase to produce ATP from ADP and Pi
