3.3 Respiration

4 stages of respiration

Glycolysis
Link reaction
Krebs Cycle
Electron Transport Chain

3 stages of glycolysis

1. A glucose molecule is phosphorylated by the addition of two phosphate groups, using two molecules of ATP, making hexose bisphosphate

2. Hexose bisphosphate is split into two triose phosphate molecules

3. The triose phosphate molecules are dehydrogenated, oxidising them to pyruvate. The hydrogen atoms are transferred to NAD. These steps release enough energy to synthesise 4 ATP molecules

What does glycolysis produce

A net yield of 2 ATP produced by substrate level phosphorylation

2 molecules of reduced NAD

2 pyruvates

Full name for NAD

Nicotinamide adenine dinucleotide

Where does glycolysis occur

Cytosol/ cytoplasm

Does glycolysis require oxygen

no

Describe phosphorylated glucose

more reactive so less activation energy is required for the enzyme controlled reactions

More polar than glucose and therefore less likely to diffuse out of the cell

Why does glycolysis occur in the cytoplasm

Because glucose cannot pass through the mitochondrial membranes and enzymes for the breakdown of glucose are not present in the mitochondria

Where does the link reaction take place

Matrix of mitochondria

How is pyruvate transported to the matrix of the mitochondria

Diffusion

Describe the 3 stages of the link reaction

1. Pyruvate diffuses from the cytoplasm into the matrix

2. Pyruvate is dehydrogenated and decarboxylated

3. 2 carbon acetate group combines with coenzyme A which makes acetyl coenzyme A

Define dehydrogenation

The removal of one or more hydrogen atoms from a molecule

Define decarboxylation

The removal of a carboxyl group from a molecule releasing carbon dioxide

State what each turn of the krebs cycle produces

1 ATP produced by substrate level phosphorylation

3 NADH

1 FADH

2 molecules of carbon dioxide

State the full name of FAD

Flavin adenine dinucleotide

Describe the 4 stages of Krebs cycle

1. Acetyl coenzyme A enters the Krebs cycle by combining with a 4-carbon acid to form citric acid. Coenzyme A is regenerated

2. Citric acid is dehydrogenated and decarboxylated to make a 5-carbon acid

3. The 5-carbon acid is dehydrogenated and decarboxylated to regenerate the 4-carbon acid

4. The 4-carbon acid can combine with more acetyl coenzyme A to repeat the cycle

How many water molecules are used in reactions in the Krebs cycle

3

Where does the krebs cycle occur

matrix

Where is the electron transport chain located

cristae of the inner mitochondrial membranes

Describe the steps of the passage of electrons in the electron transport chain

1. NADH donates the electrons of the hydrogen atoms to the first of a series of electron carriers in the ETC

2. Electrons provide energy for the proton pump and protons from the hydrogen atoms are pumped into the inter membrane space

3. The electrons pass along the chain of carrier molecules providing energy for each of 3 proton pumps in turn

4. The electrons combine with protons and oxygen to form water

Describe the steps of the passage of protons in the electron transport chain

1. The inner membrane is impermeable to protons and so the protons accumulate in the inter membrane space.

2. The concentration of protons in the inter membrane space becomes higher than in the matrix so a gradient of concentration and charge is set up and maintained by the proton pumps

3. The enzyme ATP synthetase is associated with each channel. Protons diffuse back through these channels and as they do so their electrical potential energy produces ATP.

4. Protons combine with electrons and oxygen to form oxygen

Where is ATP synthetase located

Stalked particles on the cristae

What process produces ATP in the ETC

Oxidative phosphorylation

Define chemiosmosis

The flow of protons down an electrochemical gradient through ATP synthetase coupled with the synthesis of ATP from ADP and phosphate ion

NAD and FAD are electron carriers. Define electron carrier

A molecule required by an enzyme in order to function

Why is oxygen important in the ETC

Without oxygen NADH and FADH cannot by reoxidised and therefore made available to pick up more hydrogen atoms

How much ATP does NAD generate

3

How much ATP does FAD generate

2

How many turns of the kerbs cycle does glucose give

2

What is the total molecules of ATP per molecule of glucose respired

38

State the stage of respiration that can occur without respiration

glycolysis

How many proton pumps can NAD use

3

How many proton pumps can FAD use

2

Why can FAD only use 2 proton pumps

FAD passes the hydrogen atoms directly to the second proton pump

How many hydrogen atoms are needed to synthesise one ATP molecule

2

Describe lactic acid fermentation

Pyruvate is the hydrogen accepter and is reduced to lactate regenerating NAD

Describe alcoholic fermentation

Pyruvate is converted to carbon dioxide and to ethanal, a hydrogen accepter, by decarboxylase.

Ethanal is reduced to ethanol and NAD is regenerated

Is lactic acid fermentation reversible

yes

Is alcoholic fermentation reversible

no and it will accumulate in the cells and can rise to toxic concentrations

State the yield of ATP under anaerobic respiration

2 ATP by substrate level phosphorylation

What happens to triglycerides as a respiratory substrate

it is hydrolysed to glycerol and fatty acid chains

Glycerol is converted into triose phosphate

Fatty acid chains molecules are split into 2C fragments which enter the krebs cycle as acetyl coenzyme A

Gives the pros and cons of respiring fats

More carbon atoms so more carbon dioxide is produced. More carbon dioxide produced than could be removed quickly enough

More hydrogen atoms so more FAD and NAD are reduced so more ATP produced

More hydrogen atoms so more water is produced

What happens to proteins as a respiratory substrate

Proteins are hydrolysed into their constituent amino acids

When are proteins used as a respiratory substrate

starvation

What happens to amino acids as a respiratory substrate

The amino group is converted into urea

The residue is converted to acetyl CoA, pyruvate or some other Krebs cycle intermediate