5.2 - Respiration

Question 1

What is respiration?

Answer 1

Process by which organic molecules are broken down in a series of stages to synthesis ATP
Aerobic requires oxygen
Anaerobic takes place in absence of oxygen, producing lactic acid in animals, and ethanol & carbon dioxide in plants and yeast

Question 2

What is the symbol equation for respiration?

Answer 2

C6H1206 + 602 —> 6CO2 + 6H2O + 38 ATP

Question 3

What are the 4 stages of respiration?

Answer 3

1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Electron transfer chain

Question 4

Summarise the matrix of the mitochondria:

Answer 4

Aqueous solution within inner membranes of mitochondria
Contains ribosomes, enzymes & circular mitochondrial DNA

Question 5

Summarise the cristae of the *mitochondria:

Answer 5

Folds of inner membrane
Site of electron transport chain
Location of ATP synthase

Question 6

What is phosphorylation?

Answer 6

Addition of an inorganic phosphate group (Pi) to a molecule

Question 7

What 2 types of phosphorylation occur in respiration?

Answer 7

Substrate-level phosphorylation
- in glycolysis & krebs cycle
- single reaction
- transfer of phosphate group from donor molecule to ADP
Oxidative phosphorylation
- in electron transfer chain
- series of oxidation reaction
- provides energy to form ATP from ADP & Pi

Question 8

What are coenzymes?

Answer 8

Molecules that bind with a specific enzyme or substrate, helping catalyse a reaction.
Breaking bonds between coenzyme & product after reaction is crucial, otherwise coenzyme concentration will drop, limiting respiratory rate.

Question 9

What 3 main coenzymes are used in respiration?

Answer 9

NAD
CoA (coenzyme A)
FAD

Question 10

What is glycolysis?

Answer 10

1st stage of both aerobic & anaerobic respiration - as doesn’t require oxygen, so this stage is anaerobic
Occurs in cytoplasm

Question 11

What are the 2 stages of glycolysis:

Answer 11

1. Phosphorylation
2. Oxidation

Question 12

Summarise phosphorylation in glycolysis:

Answer 12

Glucose phosphorylated by adding 2 phosphates from 2 ATP molecules
Making it a more reactive molecule = hexose bisphosphate, which then splits to form 2 x 3C molecules of TP
Is substrate-level phosphorylation

Question 13

Summarise oxidation in glycolysis:

Answer 13

TP oxidised = looses hydrogen & phosphate, forming 2 x pyruvate
NAD collects hydrogen ions, forming 2 x reduced NAD

Question 14

What are the products of glycolysis for 1 glucose molecule?

Answer 14

2 x reduced NAD - goes to ETC
2 x pyruvate - actively transported into mitochondria for link reaction
2 x ATP - used for energy

Question 15

What is the link reaction?

Answer 15

2nd stage of respiration
Occurs in matrix of mitochondria
Links glycolysis to Krebs cycle
Converts pyruvate to acetyl CoA

Question 16

Summarise the link reaction:

Answer 16

Pyruvate from glycolysis is decarboxylated - one carbon atom is removed in the form of carbon dioxide
At the same time, pyruvate oxidised to form acetate (2C) and NAD, which is reduced to from reduced NAD
Acetate combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl coA)

Question 17

Why does this process require energy?

Answer 17

As pyruvate needs to be actively transported into mitochondrial matrix, if oxygen present.

Question 18

How many times does the link reaction occur per glucose molecule?

Answer 18

2 pyruvate molecules produced per glucose molecule
So link reaction & krebs cycle occur twice for every glucose molecule

Question 19

What are the products of the link reaction and what are they used for?

Answer 19

For one glucose molecule, so two link reactions:
- 2 acetyl CoA - to Krebs cycle
- 2 carbon dioxide - released as waste product
- 2 reduced NAD - to oxidative phosphorylation

Question 20

Where does the Krebs cycle occur?

Answer 20

In the mitochondrial matrix

Question 21

What is the Krebs cycle?

Answer 21

3rd stage of respiration
Aerobic process, but doesn’t directly require oxygen
Occurs once for every pyruvate molecule
Produces ATP & reduced coenzymes
Series of enzyme controlled oxidation - reduction reactions

Question 22

Summarise the Krebs cycle:

Answer 22

Acetyl coA (from link reaction) combines with 4C molecule to form citrate (6C)
Coenzyme A is recycled back to link reaction
Decarboxylation of citrate = looses a carbon dioxide
And dehydrogenation = looses a hydrogen
Forms a 5C molecule, hydrogen used to produce reduced NAD from NAD
Then converted into a 4C molecule - oxaloacetate - decarboxylation & dehydrogenation occur, producing 1 x reduced FAD, 2 x reduced NAD
ATP produced by substrate-level phosphorylation

Question 23

What are the products of the krebs cycle and what are they used for?

Answer 23

1 CoA - reused in link reaction
Oxaloacetate - regenerated (combines with acetyl coA) for use in next krebs cycle
2 carbon dioxide - released as waste product
1 ATP - used for energy
3 reduced NAD - to oxidative phosphorylation
1 reduced FAD - to oxidative phosphorylation

Question 24

What is oxidative phosphorylation?

Answer 24

• final stage of respiration
• occurs in inner membrane of mitochondria
• generates ATP

Question 25

What are the 2 processes involved in **oxidative phosphorylation**?

Answer 25

1. Electron transfer chain 2. Chemiosmosis

Question 26

Summarise **oxidative phosphorylation**:

Answer 26

- **reduced NAD & FAD** from glycolysis, link reaction & krebs cycle are **oxidised** to NAD & FAD, they release **hydrogen** atoms —> split into **protons** & **electrons** - **electrons** move down **ETC**, loosing energy at each carrier. - energy is used to actively transport **protons** from **matrix —> intermembrane space** of mitochondria, this creates an **electrochemical gradient** (chemiosmosis) - **protons** move back, down concentration gradient via **ATP synthase** (**facilitated diffusion**) —> ATP synthesised from ADP + Pi (chemiosmosis) - at end of **ETC**, in **matrix**, **protons, electrons & oxygen*** combine to form **water**. **oxygen** is **final electron acceptor**

Question 27

In what organisms does **ethanol fermentation** occur?

Answer 27

Plants & yeast

Question 28

Summarise **ethanol fermentation**:

Answer 28

- **pyruvate decarboxylated** to **ethanal** - producing CO2 - **ethanal reduced** to **ethanol** by enzyme **alcohol dehydrogenase**, so ethanal is final **hydrogen** acceptor - ethanol cannot be further metabolised = waste product

Question 29

In what organisms does **lactate fermentation** occur?

Answer 29

Animals & some bacteria

Question 30

Summarise **lactate fermentation**:

Answer 30

- **pyruvate reduced** to **lactate** by enzyme **lactate dehydrogenase**, pyruvate is hydrogen acceptor - **lactate** can be further metabolised

Question 31

Summarise the **metabolism of lactate**:

Answer 31

1. **oxidised** back to **pyruvate** —> Krebs cycle for ATP production OR 2. converted into **glycogen** —> stored in liver

Question 32

What is **oxygen debt**?

Answer 32

- extra oxygen needed for **oxidation** of **lactate** back to **pyruvate** - explains why animals breathe deeper & faster after exercise

Question 33

Why do **Krebs cycle** & **ETC** shut down in **oxygen absence**?

Answer 33

- oxygen is **final electron acceptor** at end of ETC, so if not available, electrons from last carrier protein cannot be accepted - **electrochemical gradient** not established, so **no ATP synthesised** - build-up of **reduced NAD & FAD** occurs as they aren’t able to give away electrons or protons, so no more oxidised NAD & FAD is cycled back to **krebs** cycle, so shuts down.