Respiration

Question 1

Glycolysis
Detail
Step 1

Answer 1

Occurs in cytoplasm
1. Phosphorylation of glucose to glucose phosphate: makes glucose more reactive, addition of two phosphate molecules, from the hydrolysis of 2 ATP, provides energy to activate glucose, lowers activation energy for following stages.

Question 2

Glycolysis
Detail
Step 2

Answer 2

Production of triose phosphate:
Each glucose molecule is split into 2 3-carbon molecules: triose phosphate

Question 3

Glycolysis
Detail
Step 3

Answer 3

Oxidation of triose phosphate:
Hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen carrier molecule called NAD (forms NADH)

Question 4

Glycolysis
Detail
Stage 4

Answer 4

Production of ATP:
enzyme controlled reactions convert each TP molecule into pyruvate (also 3C)
2 molecules ATP generated

Question 5

Glycolysis yields

Answer 5

2 ATP
2 NADH
2 Pyruvate

Question 6

Glycolysis stages
From the markschemes

Question 7

Link reaction

Answer 7

Pyruvate molecules actively transported into the matrix of the mitochondria
Pyruvate oxidised to acetate, 2C (decarboxylation and dehydrogenation- loses a CO2 and 2H)
Hydrogen released accepted by NAD
Acetate combines with coenzyme A to produce acetylcoenzyme A

Question 8

Overall equation for link reaction

Answer 8

Pyruvate + NAD +CoA —> acetyl CoA + NADH + CO2

Question 9

Krebs cycle

Answer 9

Occurs in matrix of mitochondria
Acetyl coenzyme A combined with 4C molecule to produce a 6C molecule, co enzyme A regenerated
Series of redox reactions occur
6C compound loses a CO2 and a hydrogen (accepted by NAD) to produce a 5C compound
5C compound loses a CO2, 2 hydrogens (accepted by 2 NAD), another hydrogen which is accepted by an FAD (generates reduced co enzymes) and one molecule of ATP is produced from, ADP+Pi (substrate level phosphorylation), 4C compound formed again to continue cycle

Question 10

Substrate level phosphorylation

Answer 10

Creation of ATP without ATP synthase
Phosphate is added to ADP from another molecule

Question 11

Krebs cycle yields

Answer 11

Reduced co enzymes (have potential to provide energy to produce ATP in OP)
One ATP
3 CO2

Question 12

Co enzymes

Answer 12

Molecules that some enzymes require in order to function
(Not enzymes themselves)
Carry hydrogen atoms from one molecule to another

Question 13

NAD

Answer 13

Works with dehydrogenase that catalyse the removal of hydrogen from, substrates and transfer them to other molecules involved in oxidative phosphorylation

Question 14

Significance of Krebs cycle

Answer 14

Breaks down macromolecules into smaller ones (pyruvate into CO2)
Produces hydrogen atoms that are carried by NAD to ETC (provided energy to produce ATP)
Regenerates 4C molecule that combines with acetyl co enzyme A which would otherwise accumulate
Source of intermediate compounds used by cells to manufacture fatty acids/ amino acids/ chlorophyll

Question 15

How can proteins and lipids also be respired aerobically?

Answer 15

Broken down into acetyl coenzyme A to join the kerbs cycle

Question 16

Krebs cycle from the mark scheme

Question 17

Link reaction from markschemes

Question 18

Oxidative phosphorylation
First two stages

Answer 18

NADH and FADH donate the electrons of the hydrogen atoms they are carrying to the first electron carrier molecule in the electron transfer chain.
The electrons pass along the chain in a series of redox reactions, releasing energy as they flow, causing the active transport of protons across the inner mitochondrial membrane and into the inter mitochondrial space.

Question 19

Oxidative phosphorylation
Next stages

Answer 19

These protons accumulate in the inter membranal space (conc grad) before diffusing back into matrix through ATP synthase channels embedded in the inner membrane of the mitochondria
At the end of the chain, the electrons combine with these protons and oxygen to form water
Oxygen is the final acceptor of electrons
This is chemiosmotic theory
Releases energy for ADP +Pi to form ATP?

Question 20

Importance of oxygen being the final electron acceptor

Answer 20

The protons would back up along the chain and prevent respiration occurring
(Conc grad?)

Question 21

How energy is released in small manageable amounts and why

Answer 21

If released all in one go, more lost as heat
More can be harvested
Electrons carried by NAD and FAD passed along series of electrons transfer carrier molecules, each of which is at a slightly lower energy level. Electrons move down an energy gradient, energy released gradually

Question 22

Respiration of lipids

Answer 22

Hydrolysed to glycerol and fatty acids
Glycerol phosphorylated d converted to triose phosphate (enters glycolysis)
Fatty acids broken down into 2 carbon fragments which are converted to acetyl co enzyme A which enters Krebs cycle
Hydrogen atoms produced by oxidation of lipids used to produce ATP during oxidative phosphorylation

Question 23

Respiration of protein

Answer 23

Hydrolysed into amino acids
Deamination (amino group removed)
Enter respiratory pathway at different points depending on number of carbons

Question 24

Why can’t krebs or oxidative phosphorylation occur in anaerobic conditions?

Answer 24

Soon all FAD and NAD will be reduced and there will be none left to take up the H+ produced by Krebs cycle

Question 25

What’s needed to keep glycolysis going?

Answer 25

Pyruvate and hydrogen (products of glycolysis) must constantly be removed
Hydrogen must be removed by NADH to regenerate NAD or glycolysis will stop.

Question 26

How is glycolysis continued in anaerobic conditions?

Answer 26

Pyruvate accepts hydrogen from NADH
NAD can then be used in further glycolysis

Question 27

Anaerobic glycolysis in mammals and bacteria

Answer 27

Pyruvate converted to lactate
Lactate eventually oxidised back to pyruvate
Can be converted to glycogen

Question 28

Anaerobic glycolysis in plants and yeast

Answer 28

Pyruvate converted to ethanol and carbon dioxide (produced as ethanal made first which is then turned into ethanol by oxidation of NADH)
(pyruvate decarboxylated first)

Question 29

Effects of lactate

Answer 29

Cramps and muscle fatigue when accumulated in muscles
Acidic so causes pH fluctuations with disrupt enzyme function