F214 - Respiration

Question 1

Energy

Definition

Answer 1

The ability to do work

Question 2

What do organisms require energy for?

Answer 2

• active transport
• endocytosis / exocytosis
• anabolic reactions
• movement of cilia, flagella etc.
• spindle formation
• activation, lowering the energy required for a reaction to take place

Question 3

Structure of ATP

Answer 3

Ribose sugar, adenosine bonded to adenine and a chain of three phosphates

Question 4

ATP - Universal Energy Currency

Answer 4

• used in all cells
• energy rich compound that can easily be hydrolysed to release energy
• can be broken down gradually to release small packets of energy
• an immediate energy source for biological processes

Question 5

Oxidation

Definition

Answer 5

Reactions involving the loss of electrons

Question 6

Reduction

Definition

Answer 6

Reactions involving the gain of electrons

Question 7

Coenzymes - NAD

Answer 7

• organic non protein molecule
• helps dehydrogenase enzymes to carry out oxidation reactions
• when one molecule of NAD has accepted two hydrogen atoms it is reduced

Question 8

Coenzymes - Coenzyme A

Answer 8

• carries acetate/ethanoate groups
• made from pantothenic acid, adenosine, 3 phosphates and cysteine
• carries acetate groups formed from pyruvate, fatty acids and some amino acids from the link reaction to the kerbs cycle

Question 9

Where does glycolysis take place?

Answer 9

Cytoplasm

Question 10

Glycolysis

Description

Answer 10

• glucose converted to glucose 6-phosphate, requires 1 ATP
• glucose 6-phosphate rearranged to form isomer fructose 1-phosphate
• fructose 1-phosphate converted to hexose 1, 6-bisphosphate, requires 1 ATP
• hexose bis phosphate splits to form two molecules of triose phosphate
• each triose phosphate molecule converted to one molecule of pyruvate, one NAD reduced and one ATP produced per pyruvate

Question 11

Glycolysis

Net Production

Answer 11

2 pyruvate
2 ATP
2 reduced NAD

Question 12

What happens to pyruvate at the end of glycolysis?

Answer 12

Actively transported into mitochondria

Question 13

Mitochondria

Inner Membrane

Answer 13

Different lipid composition to outer membrane
Impermeable to most small ions including protons
Folded to form cristae to increase surface area
Many electron carrier proteins and ATP synthase enzymes

Question 14

Mitochondria

Outer Membrane

Answer 14

Similar lipid composition to other organelle membranes
Contains enzymes
Channels / carriers for pyruvate

Question 15

Mitochondria

Matrix

Answer 15

Mitochondrial DNA coding for enzymes and other proteins
Mitochondrial ribosomes
Enzymes to catalyse link reaction and Kreb’s cycle
Molecules of coenzyme NAD

Question 16

Where does the Link Reaction take place?

Answer 16

Mitochondrial matrix

Question 17

The Link Reaction

Description

Answer 17

• pyruvate is dehydrogenated (reducing NAD) and decarboxylated (releasing 1CO2) to form 1 molecule of acetate
• acetate group combined with coenzyme A to form acetyl coenzyme A
• coenzyme A carries acetate group to the Kreb’s cycle

Question 18

The Link Reaction 
Net Production (per pyruvate)

Answer 18

1 acetyl coenzyme A
1 carbon dioxide
1 reduced NAD

Question 19

Where does the Kreb’s Cycle take place?

Answer 19

Mitochondrial matrix

Question 20

The Kreb’s Cycle

Description

Answer 20

• acetyl coenzyme A combined with oxaloacetate to form citrate, coenzyme A released
• citrate decarboxylated and dehydrogenated to form alpha-ketoglutarate, releasing 1 CO2 and reducing 1 NAD
• alpha-ketoglutarate is decarboxylated and dehydrogenated to form oxaloacetate, releasing 1 CO2, reducing 2 NAD and 1 RAD, and substrate level phosphorylation produces 1 ATP

Question 21

The Kreb's Cycle 
Net Production (per cycle)

Answer 21

2 carbon dioxide
3 reduced NAD
1 reduced FAD
1 ATP

Question 22

Where does oxidative phosphorylation take place?

Answer 22

Inner mitochondrial membrane

Question 23

Oxidative Phosphorylation and Chemiosmosis

Description

Answer 23

• reduced NAD is oxidised forming NAD and hydrogen
• the hydrogen is split into electrons and protons
• the protons go into solution in the matrix and the electrons are passed along a four protein transport chain through a series of redox reactions that release energy
• FAD is also oxidised but electrons only enter the transport chain at electron carrier two
• the energy released is used to pump protons into the inter membrane space establishing proton concentration, electrochemical and pH gradients
• the protons diffuse back through the membrane down the gradient through ATP synthase which drives the rotation of part of the enzyme, ADP is joined to an inorganic phosphate forming ATP
• electrons are passed to the final electron acceptor, molecular oxygen, where they combine with protons from the matrix to form water

Question 24

Oxidative Phosphorylation

Definition

Answer 24

The formation of ATP, in the presence of oxygen, by chemiosmosis

Question 25

Chemiosmosis | Definition

Answer 25

The flow of hydrogen ions through ATP synthase enzymes | The force of this flow allows ATP to be produced

Question 26

Inefficiencies in Respiration

Answer 26

- some protons leak across the mitochondrial membrane reducing the proton motive force - some ATP is used to actively transport pyruvate into the mitochondria - some ATP is used as a shuttle to bring hydrogen from reduced NAD made during glycolysis in the cytoplasm into the mitochondria

Question 27

Anaerobic Respiration in Mammals

Answer 27

1. Glycolysis 2. Conversion of pyruvate to lactate catalysed by lactate dehydrogenase, this process oxidises one molecule of reduced NAD to NAD

Question 28

Anaerobic Respiration in Plants and Yeast

Answer 28

1. Glycolysis 2. Decarboxylation of pyruvate to form ethanal, catalysed by pyruvate decarboxylase, releases one molecule of carbon dioxide 3. Ethanal converted to ethanol, catalysed by ethanol dehydrogenase, oxidised one molecule of reduced NAD to NAD

Question 29

Why does anaerobic respiration produce a much lower yield than aerobic respiration?

Answer 29

If oxygen is absent then the electron transport chain cannot function as molecular oxygen is the final electron acceptor in oxidative phosphorylation The link reaction and Kreb's cycle stop Glycolysis is the only source of ATP in anaerobic respiration Anaerobic respiration recycles reduced NAD so that glycolysis can continue and small amounts of ATP can be produced

Question 30

Respiratory Substrate | Definition

Answer 30

An organic molecule that can be broken down to release energy in respiration

Question 31

Respiratory Substrates | Carbohydrates

Answer 31

- primary respiratory substrate is glucose - some mammalian cells (e.g. brain, red blood) can only respire glucose - glucose can be stored as glycogen in animals and starch in plants - starch and glycogen hydrolysed to form glucose - 15.8 kJ/g

Question 32

Respiratory Substrates | Lipids

Answer 32

- if carbohydrates run out, lipids respired instead - triglycerides hydrolysed by lipase to fatty acids and glycerol - glycerol converted to glucose and respired - fatty acids are combined with coenzyme A and transported to the matrix where they are split into two acetate groups which take part in the Kreb's cycle - 39.4 kJ/g

Question 33

Respiratory Substrates | Proteins

Answer 33

- excess amino acids from protein digestion can be deaminated, the rest of the molecule is converted to glycogen or fat - when an organism undergoes fasting, starvation or prolonged exercise protein from muscles can be hydrolysed to amino acids for respiration but this is a destructive process - 17.0 kJ/g

Question 34

Evidence for Chemiosmosis

Answer 34

- lower pH in intermembrane space than in mitochondrial matrix - more negative potential on the matrix side of the inner mitochondrial membrane - no ATP made in mitoblasts (mitochondria without outer membrane) - no ATP made if headpieces are removed form stalked particles (ATP synthase)

Question 35

Respiration | Definition

Answer 35

The breakdown of complex organic molecules in the presence of oxygen to release energy