Respiration

Question 1

Why do we need to respire?

Answer 1

We need energy to drive biological processes; this energy is provided by respiration

Question 2

Define metabolism

Answer 2

All the reactions that take place within an organism

Question 3

Define anabolic

Answer 3

Metabolic reactions that build large molecules

Question 4

Define catabolic

Answer 4

Metabolic reactions that break down large molecules in hydrolysis. Often releases heat that helps organisms maintain necessary temperatures for enzymes

Question 5

What metabolic processes need energy?

Answer 5

Active transport; Secretion (exocytosis); Endocytosis; Anabolic reactions; DNA replication; Movement

Question 6

Describe the structure of ATP

Answer 6

Full name: adenosine triphosphate
Purine (2 rings) nitrogenous base adenine attached to 5 carbon sugar ribose which has 3 phosphates attached to it. If adenine is attached to carbon 1, the phosphates are attached to carbon 3.

Question 7

What is the function of ATP

Answer 7

Provides the immediate source of energy for biological processes

Question 8

Why are coenzymes needed in respiration?

Answer 8

There are many redox reactions in respiration with removal of hydrogens by dehydrogenase enzymes. Enzymes aren’t so great at catalysing redox reactions, so the hydrogen ions are combined with NAD that carries the H until needed. Coenzyme A is needed to carry acetate groups to the Krebs cycle.

Question 9

Where does glycolysis take place?

Answer 9

In the cytoplasm

Question 10

Describe the stages in glycolysis

Answer 10

ATP is hydrolysed, and a phosphate attaches to carbon 6 of glucose, making glucose 6-phosphate
Glucose 6-phosphate is changed to fructose 6-phosphate
ATP is hydrolysed and a phosphate attaches to carbon 1 making fructose 1,6-bisphosphate
Energy from the ATP activates the sugar, and prevents it from being transported out of the cell
Hexose bisphosphate is split into 2 molecules of triose phosphate
Triose phosphate is oxidised by the removal of 2 hydrogen atoms, aided by coenzyme NAD, becoming NADH. 2 molecules of ATP are formed
Triose phosphate is transformed into pyruvate, making 2 more molecules of ATP

Question 11

What are the products of glycolysis?

Answer 11

2 molecules of ATP were used; and 4 molecules of ATP were created: net gain of 2 ATP
2 molecules of NADH were produced
2 molecules of pyruvate were formed

Question 12

What happens to the pyruvate produced at the end of glycolysis in anaerobic respiration?

Answer 12

Actively transported into the mitochondria

Question 13

What are the 3 ways ATP can be produced?

Answer 13

Photophosphorylation; Oxidative phosphorylation and Substrate level phosphorylation

Question 14

How big are mitochondria?

Answer 14

2-5um long; 0.5-1um in diameter

Question 15

How is the matrix of the mitochondria designed to carry out its function?

Answer 15

Matrix is where the link and Krebs cycle occurs.
Has enzymes to catalyse the stages of these reactions
Molecules of NAD
Oxaloacetate
Mitochondrial DNA (coding for mitochondrial enzymes and other proteins)
Mitochondrial ribosomes for making of these proteins

Question 16

How is the outer membrane of the mitochondria designed to carry out its function?

Answer 16

Composed of phospholipids with proteins which form channels or carriers that allow passage of molecules such as pyruvate

Question 17

How is the inner membrane of the mitochondria designed to carry out its function?

Answer 17

Folded into cristae for large SA for oxidative phosphorylation
Many electron carriers and ATP synthase enzymes embedded
Impermeable to small ions

Question 18

Describe the structure and function of the electron transport chain in mitochondria

Answer 18

Each electron carrier is an oxidoreductase enzyme associated with a cofactor - a haem group. The haem group can accept and donate electrons because the iron atoms can be oxidised and reduced (Fe2+ or Fe3+)
Some also have a coenzyme that uses the energy of passing electrons to pump proton into the intermembrane space (inner membrane is impermeable to small ions); build up of protons

Question 19

Describe the structure and function of ATP synthase enzymes

Answer 19

Protrude from inner membrane into the matrix
Allow passage of protons down the proton concentration gradient (chemiosmosis)
The flow drives a rotation that converts ADP + P(i) to ATP

Question 20

Where does the link reaction take place?

Answer 20

In the mitochondrial matrix

Question 21

Describe the link reaction

Answer 21

Pyruvate dehydrogenase removes hydrogen atoms from pyruvate, reducing NAD, forming NADH
Pyruvate decarboxylase removes a carbon group, forming CO2
Left with acetate which is accepted by coenzyme A, giving acetyl coenzyme A which is then transported to the link reaction

Question 22

What are the products of the link reaction per molecule of glucose?

Answer 22

2 NADH; 2 CO2; 2 acetyl coenzyme A

Question 23

Where does the Krebs cycle take place?

Answer 23

The mitochondrial matrix

Question 24

Describe the Krebs cycle

Answer 24

Acetate is offloaded from coenzyme A and binds to 4 carbon oxaloacetate, making 6 carbon citrate
Citrate is decarboxylated and dehydrogenated, forming CO2 and NADH and a 5 carbon compound
This is decarboxylated and dehydrogenated forming CO2, NADH and a 4 carbon compound
The 4 carbon compound is changed into another 4 carbon compound, and ADP is phosphorylated to produce ATP in substrate level phosphorylation
This is transformed into another 4 carbon compound, removing hydrogens and reducing FAD to FADH
This is dehydrogenated, reducing NAD to NADH, forming oxaloacetate again.

Question 25

What are the products of the Krebs cycle a) in one turn b) per molecule of glucose?

Answer 25

a) 3 NADH; 1 FADH; 2 CO2; 1 ATP

b) 6 NADH; 2FADH; 4 CO2; 2 ATP

Question 26

Describe the process of oxidative phosphorylation; electron transfer chain

Answer 26

NADH and FADH are oxidised with the removal of hydrogen
The electron carrier chain in the mitochondrial cristae (inner membrane) accepts the electron, and the proton goes into the mitochondrial matrix
The first electron acceptor is NADH - coenzyme Q reductase (also known as NADH dehydrogenase)
Oxygen acts as the final electron acceptor, with an oxygen molecule receiving 4 H+ and 4 e- to form water
As electrons move down the chain, energy is released which is used to pump protons into the inner membrane space at electron carries 1, 3 and 4

Question 27

Describe the process of oxidative phosphorylation; chemiosmosis

Answer 27

As electrons move down the chain, energy is released which is used to pump protons into the inner membrane space at electron carries 1, 3 and 4
A proton gradient is formed (also a pH and electrochemical gradient)
Protons diffuse back through inner membrane via ion channels in chemiosmosis. Channels are associated with ATP synthase enzymes.
As protons flow through the enzyme, a rotation is driven which aids the combination of ADP and P(i) to ATP. Voila.

Question 28

Why is the maximum yield of ATP in aerobic respiration (approx. 30 molecules per molecule of glucose) rarely achieved?

Answer 28

Some protons leak across the mitochondrial membrane, reducing the number of protons to generate the proton motive force
Some ATP produced is used to actively transport pyruvate into the mitochondria
Some ATP is used for the shuttle to bring hydrogen from reduced NAD made during glycolysis, in the cytoplasm, into the mitochondria

Question 29

Define proton motive force

Answer 29

The force of the kinetic energy of the flow of protons down their concentration gradient

Question 30

Why does anaerobic respiration have a much lower yield of ATP than aerobic respiration?

Answer 30

If there is insufficient oxygen, the only stage of respiration that can occur is glycolysis. This produces 2 molecules of ATP, so can sustain the concentrations needed for a while; however it also requires NAD. So, we need to oxidise NADH. This process of oxidation doesn’t produce any ATP, resulting in a much lower yield.

Question 31

Describe anaerobic respiration in mammals

Answer 31

Pyruvate formed in glycolysis acts as a hydrogen acceptor, converting one molecule of NADH into NAD, producing lactate (lactic acid) as a by-product. The lactate then goes to the liver where it can be converted back into pyruvate or converted into glucose/glycogen when more oxygen is available. The NAD goes back to glycolysis, where ATP is produced.

Question 32

Describe anaerobic respiration in yeast

Answer 32

Pyruvate formed in glycolysis looses a carbon dioxide molecule, forming ethanal. This is catalysed by enzyme pyruvate decarboxylase
Ethanal accepts hydrogen atoms from reduced NADH, being reduced to ethanol (catalysed by ethanol dehydrogenase). The NADH becomes NAD to go back to glycolysis

Question 33

Define respiratory substrate

Answer 33

An organic substance that can be used for respiration

Question 34

Why do lipids release more energy than proteins, which release more energy than carbohydrates in aerobic respiration?

Answer 34

In aerobic respiration, the majority of the ATP is produced in chemiosmosis, involving protons. Therefore, the more hydrogen ions a molecule has, the more protons it will release and the more ATP will be produced due to the flow of protons through ATP synthase. Lipids have more hydrogen atoms than proteins which have more hydrogen atoms than carbohydrates. Therefore, lipids release the most ATP and carbohydrates the least. Note: only for aerobic respiration, as lipids and proteins can’t undergo glycolysis.