5.7 respiration Flashcards
Why do living organisms need to respire?
Respiration releases energy from respiratory substrates such as glucose, but it does not create or make energy
Why is it inacurate to say respiration creates energy
Because it releases energy from respiratory substances. That energy is used to synthesise molecules of ATP from ADP and Pi
Define anabolic reactions
metabolic reactions where large molecules are synthesised from smaller molecules
Define catabolic reactions
Hydrolysis of larger molecules to smaller ones
Describe the structure of ATP
It is a phosphorylated molecule which consists of an adenosine nitrogenous base a ribose sugar and 3 phosphate molecules
What bonds join the phosphate molecules in atp
Phosphoanhydride bonds
Why is the stability of ATP useful in the molecule
It doesn’t break down easily when in solution but rather needs to be hydrolysed by enzymes.
This makes it easily transportable around the cell
Why is ATP produced and energy is not just released in the body
Cells can obtain the energy they need for a process in a small manageable way that will not cause damage or be wasteful
How is some of the waste energy released from the hydrolysis of ATP used?
Some heat is released may seem inefficient and wasteful; however, it helps keep the living organisms warm and enables enzyme-catalysed reactions to proceed near or at their optimum
Describe the chemical energy released from the hydrolysis of ATP
the first hydrolysis of ATP to ADP releases 30.5Kj/mol of energy and so does the second hydrolysis to AMP
The last hydrolysis to adenosine releases 13.8Kj/mol
define glycolysis
It is the first stage of respiration; a 10 stage metabolic pathway that converts glucose to pyruvate
Where does glycolysis occur
the cytoplasm
What co enzyme helps in glycolysis
NAD
What are the 3 steps in glycolysis
phosphorylation of glucose to hexose bisphosphate
splitting each hexose bisphosphate into 2 triose phosphate molecules
oxidation of the triose phosphate to pyruvate
Describe the role of NAD during glycolysis
NAD is a non-protein molecule that helps dehydrogenase molecules carry out oxidation reactions - NAD oxidises substrate molecules during glycolysis, the link reaction and krebs cycle
Reduced NAD carries the protons and electrons to the cristae of mitochondria to be used in oxidative phosphorylation
Describe how NAD is recycled during respiration
When reduced NAD gives up the protons and electrons that it had previously accepted and can be reused to oxidise more substrate and becomes reduced again
Describe the structure of NAD
it contains 2 ribose sugars an adenine group and 2 phosphate molecules with an oxygen between them
one of the ribose contains nicotinamide which is a pyrimidine that can accept 2 hydropgen atoms to become reduced NAD
Describe phosphorylation - the first step of glycolysis
One molecule of ATP is hydrolysed, and the released phosphoryl group is added to make hexose monophosphate, and this is repeated to make hexose bisphosphate
What stops the hexose sugar being phosphorylated from being transported out of the cell
the energy from the hydrolysed ATP molecules activates the hexose sugar and prevents it from being transported out the cell
Describe the splitting of the hexose bisphosphate molecule
it is split into 2 triose phosphate molecules
Describe the oxidation of the triose phosphate
the process is anaerobic
dehydrogenase enzymes aided by NAD remove hydrogens from the triose phosphate molecules
the 2 molecules accept the hydrogen atoms and become NADH
4 molecules of ATP are made for every triose phosphate molecules undergoing oxidation
if 4 ATP molecules are made in glycolysis, why is it that there is only a net production of 2 ATP per glucose molecule in ATP
This is because 2 ATP are spent in the phosphorylation of the glucose at the start
what are the products of glycolysis
2 molecules of ATP
2 molecules of NADH
2 molecules of pyruvate
What are the stages of aerobic respiration
glycolysis
the link reaction
the Krebs cycle
oxidative phosphorylation
how does the last stage of glycolysis differ under aerobic and anaerobic conditions
under aerobic conditions pyruvate is actively transported into the mitochondria for the link reaction
in the absence of oxygen pyruvate in the cytoplasm is converted to lactate or ethanol and the NADH are reoxidised so that glycolysis can continue to run
what is the purpose of the cofactor in the electron carrier proteins
the iron ion can accept and donate electrons
What can carrier proteins also be called
oxido-reductase enzymes
How are protons pumped from the matrix into the intermembrane space
using energy released from the electrons the electron carrier proteins can pump the protons from the mitochondrial matrix to the intermembrane space
describe the structure of ATP synthase
It is an enzyme that is large and protrudes from the inner membrane into the matrix and protons can pass through them
define decarboxylation
removing a carboxyl group from a molecule
define dehydrogenation
removal of hydrogen from a substrate molecule
Define substrate level phosphorylation
production of ATP from ADP and Pi during glycolysis and the Krebs cycle
What happens to pyruvate after glycolysis
it is transported across the outer and inner mitochondrial membranes via a pyruvate-H+ symport and into the matrix
Where does the link reaction occur
the mitochondrial matrix
Outline what occurs inthe Link reaction
The carboxyl group of the pyruvate is removed and is the origin of some of the CO2
the decarboxylation and dehydrogenation of pyruvate produces an acetyl group
the acetyl group combines with the coenzyme A to become acetyl CoA
NAD becomes reduced
what is the equation that outlines what occurs in the link reaction
2 pyruvate + 2NAD +2CoA–> 2CO2 + 2NADH+2acetyl CoA
Where does the Krebs cycle occur
the mitochondrial matrix
Define the Krebs cycle
series of enzyme catalysed reaction that oxidise the acetate from the link reaction to 2 molecules of CO2 while conserving energy by reducing NAD and FAD
what are the products of the link reaction per glucose molecule
2 NADH
2CO2
2acetyl CoA
0 ATP
What are the products of the Krebs cycle
6 NADH
2 FADH
4 CO2
2ATP
What can be found in the mitochondrial matrix
enzymes
NAD
FAD
oxaloacetate
Mitochondrial DNA and ribosomes
how many steps are there in the Krebs cycle
6
Describe the first 2 steps of the Krebs cycle
The acetyl group released by acetyl CoA combines with the 4 carbon compound oxaloacetate to form a six carbon citrate
Citrate is decarboxylated and dehydrogenated producing a five carbon compound one molecule of CO2 and one molecule of reduced NAD
describe the 3rd and 4th steps of the Krebs cycle
the five carbon compound is further decarboxylated and dehydrogenated producing a four carbon compound one molecule of carbon dioxide and a molecule of reduced NAD
The four carbon compound combines temporarily with and is then released from CoA and substrate-level phosphorylation occurs producing one molecule of ATP
describe the 5th and 6th steps of the Krebs cycle
The 4 carbon compound is dehydrogenated producing a different 4 carbon compound and a molecule of reduced FAD
rearrangement of the atoms in the 4 carbon molecule catalysed by an isomerase enzyme followed by further dehydrogenation regenerates a molecule of oxaloacetate
at what steps in the Kreb cycle is FADH made
step 5
At what step in the Kreb cycle is ATP made
step 4
At what steps in the Kreb cycle is NADH made
step 2 3 6
How many turns of the Krebs cycle are there per one glucose molecule
2
what other substrates beside glucose can be respired aerobically
fatty acids
glycerol
amino acids
how are fatty acids respires
they are broken down to many molecules of acetate that can enter the Krebs cycle via acetyl CoA
How are glycerol’s respired
may be converted to pyruvate and enter the Krebs cycle via the link reaction
How are amino acids respired
they may be deaminated and the rest of the molecule can enter the Krebs cycle directly or be changed to pyruvate or acetyl CoA
Define chemiosmosis
flow of protons down their concentration gradient across a membrane through a channel associated with ATP synthase
define oxidative phosphorylation
the formation of ATP using energy released in the electron transport chain and in the presence of oxygen it is the last stage of aerobic respiration
What happens in the first stages of oxidative phosphorylation
NADH and FADH are reoxidised when they deliver the hydrogen atom to the electron transport chain
the hydrogen atoms released from the reduced co enzymes split into electrons and protons
The protons go into solution in the mitochondrial matrix
Describe what occurs at the electron transport chain during oxidative phosphorylation
The electrons from the hydrogen atoms enter the electron carrier proteins and passes along the chain. The iron ion at its core can gain and lose electron so it can donate an electron to the next iron ion in the electron carrier
As electrons pass in the chain some of their energy is used to pump protons across the mitochondrial membrane into the intermembrane space
Describe what happens once a proton gradient is created in oxidative phosphorylation
As protons accumulate in the intermembrane space a proton gradient forms across the membrane
Proton gradients cause chemiosmotic potential which is a source of potential energy and ATP is made using that energy
Protons diffuse through proton channels associated with ATP synthase enzymes and as protons diffuse down through their concentration gradient the flow of protons causes a conformational change in the ATP synthase that allows ADP +Pi to combine to form ATP
What is the final electron acceptor in oxidative phosphorylation
oxygen is the final electron acceptor
It combines with the electrons coming from the electron transport chain and with protons diffusing down the ATP synthase channel forming water
4H+ +4e- +O2 –> 2H20
What is chemiosmotic potential also known as
proton motive force
What happens if there is an absence of oxygen
Oxygen acts as the final electron acceptor so protons diffusing through ATP synthase are unable to fuse with it and form water
The concentration of protons in the matrix increases reducing the proton gradient across the membrane so oxidative phosphorylation ceases
Reduced NAD and FAD are unable to unload their hydrogen to be reoxidises
How can reduced NAD be oxidised again in the absence of oxygen
Fungi such as yeast use the ethanol pathway whereas mammals use the lactate pathway
both take place in the cytoplasm of cells
Describe the ethanol fermentation pathway
Pyruvate + pyruvate decarboxylase –> ethanal + ethanol dehydrogenase (NADH ->NAD)–> Ethanol
each molecule of pyruvate is decarboxylated to produce ethanal catalysed by pyruvate decarboxylase
The ethanal accepts hydrogen atoms from NADH to produce ethanol catalysed by ethanol dehydrogenase
Describe the lactate fermentation pathway
pyruvate + lactate dehydrogenase (NADH->NAD) –> lactate
Pyruvate accepts hydrogen atoms from the NADH and is reduced to lactate
What happens to the NAD after the ethanol and lactate pathways
It becomes oxidised and can accept more hydrogens from triose phosphatye so glycolysis can continue
What is the fate of lactate
It will either be converted to pyruvate and enter the krebs cycle via the link reaction (in the liver)
recycled to glucose and glycogen
Why must lactate be removed
The pH of tissues could be lowered inhibiting enzyme activity
What is the ATP yield of anaerobic respiration
1/15th of aerobic respiration
Describe the process for calculating the rate of reproduction of yeast cells under aerobic and anaerobic conditions
4 beakers of differing volumes are filled with 50cm3 of cider
a drop of yeast suspension is added (shake yeast thoroughly first)
cover with cheesecloth and leave in a warm place for about a week
Swirl and drop some of the fluid on a haemocytometer slide and count the number of yeast cells in the corner and cetral squares
escribe a haemocytometer
it has a dipped square central chamber about 0.1mm thick and grooves on it
How would you use a haemocytometer
Breathe onto the underside of the slip to moisten it
slide the coverslip whilst pressing gently you will know its in the correct place when you see 6 rainbow patterns so the depth of the central chamber is 0.1mm
place the pipette tip at the entrance to the groove and allow liquid to enter and leave for 5 minutes
Place the haemocytometer on the microscope stage with 40x-100x magnification
count the cells in the 4 corner squares
How do you calculate the number of yeast cells in a certain volume by using a haemocytometer
find the volume of the haemocytometer square for example if the depth is 0.1 and the lengths are 0.2 do 0.20.20.1= 0.004mm3
you counted 5 squares making the volume 5*0.004=0.02mm3
if you multiply the cells you counted by 50000 you will find the number of cells in 1cm3
define respiratory substrate
An organic substance that can be oxidised using respiration releasing energy to make molecules of ATP
What are some examples of respiratory substrates
carbohydrates
lipids
proteins
Describe how carbohydrates can be used as respiratory substrates
disaccharides can be digested to monosaccharides for respiration
monosaccharides such as galactose and fructose can be changed by isomerase enzymes to glucose for respiration
Describe how lipids can be used as respiratory substrates
triglycerids can be hydrolysed to glycerol which can be converted to triose phosphate and respired
fatty acids can be combined with coenzyme A and transported to the mitochondrial matrix and be broken down to 2 acetyl carbon groups attached to a CoA
This beta oxidation pathway generate NADH and FADH and then the carbons can enter th ekrebs cycle
Describe how proteins can be used as respiratory substrates
Deamination of amino acids produces a keto acid which can enter the respiratory pathway as pyruvate, acetyl CoA or a krebs cycle acid such oxaloacetic acid
What are the energy values of carbohydrates proteins and lipids
c - 15.8
l - 39.34
p- 17
What is the respiratory quotient
co2 produced / co2 consumed
What does a rq larger than 1 indicate
Some anaerobic respiration is taking place
What are the rq values of glucose
fatty acids
amino acids
glucose = 1
fatty acid = 0.7
amino acid = 0.8
What is a respirometer
Appararus used to measure the rate of respiration of living organisms
Describe a respirometer
The living organism uses oxygen and exhales co2 in respiration which is absorbed by a sodium hydroxide solution which decreases pressure as the volume of oxygen is large in the tube with no organism
this moves the fluid in the capillary containing tube towards the organism
how do you reset a respirometer
inject air using the syringe to get the liquid in the manometer to the starting position
How do you calculate respiration rate using a respirometer
Find the volume of the cylinder and check how much it has moved and you can use it to measure volume of oxygen absorbed in the time taken
Volume is given by volume of a cylinder V = π r 2 h , where is the distance moved by the coloured liquid. The unit of rate of respiration is cm 3/min.
