5.7 respiration

Question 1

Why do living organisms need to respire?

Answer 1

Respiration releases energy from respiratory substrates such as glucose, but it does not create or make energy

Question 2

Why is it inacurate to say respiration creates energy

Answer 2

Because it releases energy from respiratory substances. That energy is used to synthesise molecules of ATP from ADP and Pi

Question 3

Define anabolic reactions

Answer 3

metabolic reactions where large molecules are synthesised from smaller molecules

Question 4

Define catabolic reactions

Answer 4

Hydrolysis of larger molecules to smaller ones

Question 5

Describe the structure of ATP

Answer 5

It is a phosphorylated molecule which consists of an adenosine nitrogenous base a ribose sugar and 3 phosphate molecules

Question 6

What bonds join the phosphate molecules in atp

Answer 6

Phosphoanhydride bonds

Question 7

Why is the stability of ATP useful in the molecule

Answer 7

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

Question 8

Why is ATP produced and energy is not just released in the body

Answer 8

Cells can obtain the energy they need for a process in a small manageable way that will not cause damage or be wasteful

Question 9

How is some of the waste energy released from the hydrolysis of ATP used?

Answer 9

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

Question 10

Describe the chemical energy released from the hydrolysis of ATP

Answer 10

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

Question 11

define glycolysis

Answer 11

It is the first stage of respiration; a 10 stage metabolic pathway that converts glucose to pyruvate

Question 12

Where does glycolysis occur

Answer 12

the cytoplasm

Question 13

What co enzyme helps in glycolysis

Answer 13

NAD

Question 14

What are the 3 steps in glycolysis

Answer 14

phosphorylation of glucose to hexose bisphosphate

splitting each hexose bisphosphate into 2 triose phosphate molecules

oxidation of the triose phosphate to pyruvate

Question 15

Describe the role of NAD during glycolysis

Answer 15

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

Question 16

Describe how NAD is recycled during respiration

Answer 16

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

Question 17

Describe the structure of NAD

Answer 17

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

Question 18

Describe phosphorylation - the first step of glycolysis

Answer 18

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

Question 19

What stops the hexose sugar being phosphorylated from being transported out of the cell

Answer 19

the energy from the hydrolysed ATP molecules activates the hexose sugar and prevents it from being transported out the cell

Question 20

Describe the splitting of the hexose bisphosphate molecule

Answer 20

it is split into 2 triose phosphate molecules

Question 21

Describe the oxidation of the triose phosphate

Answer 21

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

Question 22

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

Answer 22

This is because 2 ATP are spent in the phosphorylation of the glucose at the start

Question 23

what are the products of glycolysis

Answer 23

2 molecules of ATP

2 molecules of NADH

2 molecules of pyruvate

Question 24

What are the stages of aerobic respiration

Answer 24

glycolysis
the link reaction
the Krebs cycle
oxidative phosphorylation

Question 25

how does the last stage of glycolysis differ under aerobic and anaerobic conditions

Answer 25

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

Question 26

what is the purpose of the cofactor in the electron carrier proteins

Answer 26

the iron ion can accept and donate electrons

Question 27

What can carrier proteins also be called

Answer 27

oxido-reductase enzymes

Question 28

How are protons pumped from the matrix into the intermembrane space

Answer 28

using energy released from the electrons the electron carrier proteins can pump the protons from the mitochondrial matrix to the intermembrane space

Question 29

describe the structure of ATP synthase

Answer 29

It is an enzyme that is large and protrudes from the inner membrane into the matrix and protons can pass through them

Question 30

define decarboxylation

Answer 30

removing a carboxyl group from a molecule

Question 31

define dehydrogenation

Answer 31

removal of hydrogen from a substrate molecule

Question 32

Define substrate level phosphorylation

Answer 32

production of ATP from ADP and Pi during glycolysis and the Krebs cycle

Question 33

What happens to pyruvate after glycolysis

Answer 33

it is transported across the outer and inner mitochondrial membranes via a pyruvate-H+ symport and into the matrix

Question 34

Where does the link reaction occur

Answer 34

the mitochondrial matrix

Question 35

Outline what occurs inthe Link reaction

Answer 35

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

Question 36

what is the equation that outlines what occurs in the link reaction

Answer 36

2 pyruvate + 2NAD +2CoA--> 2CO2 + 2NADH+2acetyl CoA

Question 37

Where does the Krebs cycle occur

Answer 37

the mitochondrial matrix

Question 38

Define the Krebs cycle

Answer 38

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

Question 39

what are the products of the link reaction per glucose molecule

Answer 39

2 NADH 2CO2 2acetyl CoA 0 ATP

Question 40

What are the products of the Krebs cycle

Answer 40

6 NADH 2 FADH 4 CO2 2ATP

Question 41

What can be found in the mitochondrial matrix

Answer 41

enzymes NAD FAD oxaloacetate Mitochondrial DNA and ribosomes

Question 42

how many steps are there in the Krebs cycle

Answer 42

6

Question 43

Describe the first 2 steps of the Krebs cycle

Answer 43

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

Question 44

describe the 3rd and 4th steps of the Krebs cycle

Answer 44

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

Question 45

describe the 5th and 6th steps of the Krebs cycle

Answer 45

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

Question 46

at what steps in the Kreb cycle is FADH made

Answer 46

step 5

Question 47

At what step in the Kreb cycle is ATP made

Answer 47

step 4

Question 48

At what steps in the Kreb cycle is NADH made

Answer 48

step 2 3 6

Question 49

How many turns of the Krebs cycle are there per one glucose molecule

Answer 49

2

Question 50

what other substrates beside glucose can be respired aerobically

Answer 50

fatty acids glycerol amino acids

Question 51

how are fatty acids respires

Answer 51

they are broken down to many molecules of acetate that can enter the Krebs cycle via acetyl CoA

Question 52

How are glycerol's respired

Answer 52

may be converted to pyruvate and enter the Krebs cycle via the link reaction

Question 53

How are amino acids respired

Answer 53

they may be deaminated and the rest of the molecule can enter the Krebs cycle directly or be changed to pyruvate or acetyl CoA

Question 54

Define chemiosmosis

Answer 54

flow of protons down their concentration gradient across a membrane through a channel associated with ATP synthase

Question 55

define oxidative phosphorylation

Answer 55

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

Question 56

What happens in the first stages of oxidative phosphorylation

Answer 56

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

Question 57

Describe what occurs at the electron transport chain during oxidative phosphorylation

Answer 57

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

Question 58

Describe what happens once a proton gradient is created in oxidative phosphorylation

Answer 58

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

Question 59

What is the final electron acceptor in oxidative phosphorylation

Answer 59

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

Question 60

What is chemiosmotic potential also known as

Answer 60

proton motive force

Question 61

What happens if there is an absence of oxygen

Answer 61

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

Question 62

How can reduced NAD be oxidised again in the absence of oxygen

Answer 62

Fungi such as yeast use the ethanol pathway whereas mammals use the lactate pathway both take place in the cytoplasm of cells

Question 63

Describe the ethanol fermentation pathway

Answer 63

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

Question 64

Describe the lactate fermentation pathway

Answer 64

pyruvate + lactate dehydrogenase (NADH->NAD) --> lactate Pyruvate accepts hydrogen atoms from the NADH and is reduced to lactate

Question 65

What happens to the NAD after the ethanol and lactate pathways

Answer 65

It becomes oxidised and can accept more hydrogens from triose phosphatye so glycolysis can continue

Question 66

What is the fate of lactate

Answer 66

It will either be converted to pyruvate and enter the krebs cycle via the link reaction (in the liver) recycled to glucose and glycogen

Question 67

Why must lactate be removed

Answer 67

The pH of tissues could be lowered inhibiting enzyme activity

Question 68

What is the ATP yield of anaerobic respiration

Answer 68

1/15th of aerobic respiration

Question 69

Describe the process for calculating the rate of reproduction of yeast cells under aerobic and anaerobic conditions

Answer 69

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

Question 70

escribe a haemocytometer

Answer 70

it has a dipped square central chamber about 0.1mm thick and grooves on it

Question 71

How would you use a haemocytometer

Answer 71

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

Question 72

How do you calculate the number of yeast cells in a certain volume by using a haemocytometer

Answer 72

find the volume of the haemocytometer square for example if the depth is 0.1 and the lengths are 0.2 do 0.2*0.2*0.1= 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

Question 73

define respiratory substrate

Answer 73

An organic substance that can be oxidised using respiration releasing energy to make molecules of ATP

Question 74

What are some examples of respiratory substrates

Answer 74

carbohydrates lipids proteins

Question 75

Describe how carbohydrates can be used as respiratory substrates

Answer 75

disaccharides can be digested to monosaccharides for respiration monosaccharides such as galactose and fructose can be changed by isomerase enzymes to glucose for respiration

Question 76

Describe how lipids can be used as respiratory substrates

Answer 76

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

Question 77

Describe how proteins can be used as respiratory substrates

Answer 77

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

Question 78

What are the energy values of carbohydrates proteins and lipids

Answer 78

c - 15.8 l - 39.34 p- 17

Question 79

What is the respiratory quotient

Answer 79

co2 produced / co2 consumed

Question 80

What does a rq larger than 1 indicate

Answer 80

Some anaerobic respiration is taking place

Question 81

What are the rq values of glucose fatty acids amino acids

Answer 81

glucose = 1 fatty acid = 0.7 amino acid = 0.8

Question 82

What is a respirometer

Answer 82

Appararus used to measure the rate of respiration of living organisms

Question 83

Describe a respirometer

Answer 83

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

Question 84

how do you reset a respirometer

Answer 84

inject air using the syringe to get the liquid in the manometer to the starting position

Question 85

How do you calculate respiration rate using a respirometer

Answer 85

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.