5.1 Aerobic respiration

Question 1

Spec Points

Answer 1

i Know that cellular respiration yields ATP which is used as a source of energy
for metabolic reactions, and the process also generates heat.

ii Know the different stages in aerobic respiration, including:
● glycolysis in the cytoplasm
● link reaction
● Krebs cycle
● oxidative phosphorylation in mitochondria.

Question 1

Where does glycolysis take place ?

Answer 1

• Takes place in the cytoplasm

Question 2

What does glycolysis mean ?

Answer 2

Sugar - Splitting

Question 3

What does the process of glycolysis consist of ?

Answer 3

• The splitting of a 6 carbon glucose molecule into two 3 carbon pyruvate molecules

Question 4

What is the net gain of ATP molecules during glycolysis

Answer 4

• 2 ATP molecules

Question 5

How does the glucose molecule become trapped in the cytoplasm?

Answer 5

• It is too charged due to the adding of phosphates .

Question 6

Explain the stages of glycolysis

Answer 6

1 - 6C Glucose sub primed by 2 phosphate molecules on either side of 6C glucose

2 - 6C split into two 3GP molecules, phosphates still attached.

3 - Each GP is oxidised, realising 2 H molecules which are accepted by coenzyme NAD. Therefore reducing it

4 - 4 molecules of ATP is synthesized, this is done by removing the two phosphates at the start of the process and also getting two phosphates in the cytoplasm

Question 7

What are the alternative routes of pyruvate

Answer 7

• If there is insufficient oxygen, the pyruvate is converted into lactate in animals and ethanol in plants, this is used to regenerate NAD.

Question 8

Describe the link reaction

Answer 8

• Pyruvate reacts with Coenzyme A to form Acetylcoenzyme A + CO2
• Whilst this process occurs, oxidation of NADH occurs
• Remember, there are two link reactions which take place therefore two of each molecule produced

Question 9

Where does the krebs cycle take place

Answer 9

• Mitochondrial matrix

Question 10

Describe the process of the krebs cycle

Answer 10

• Acetyl-CoA combines with 4C compound in matrix to form 6C citrate
• Citrate is decarboxylated by removal of CO2
• Citrate is then oxidised by NADH
• 5C compound is then decarboxylated by the removal of CO2
• During the conversion of 5->4C, one molecule of ATP is synthesised
• 4C Compound is Oxidised 2x by NAD to produce 2xNADH and 1x by FAD to make FADH
• 4C Compound at the end is used to start the process again

Question 11

Where does the ETC take place

Answer 11

• Inner membrane of the mitochondria (Cristae)

Question 12

Explain the role of the Krebs Cycle

Answer 12

• Completely oxidises pyruvate, to release as much energy as possible
• To generate ATP directly
• To produce NADH and FADH

Question 13

Explain the electron transport chain step by step

Answer 13

• Reduced hydrogen carriers go to cristae and split to produce electrons and hydrogen ions
• Electrons are passed down the electron carriers as they move down each electron carrier
• Electrons lose energy as hydrogen ions are transported into inner membrane space via active transport
• H+ ions then travel down conc gradient into stalked particle (ATP Synthase) where they drive the rotation of ATP synthase to produce ADP+PI into ATP

Question 14

Why do the electrons lose energy as they are transported down the carriers

Answer 14

• As they provide energy for H+ ions to move into inter membrane space via

Question 15

How does FAD differ to NAD in regards to how they are received by electron carriers

Answer 15

• FAD joins the second electron carrier, where as NAD joins the first carrier

Question 16

Describe what happens to oxygen at the end of the electron transport chain

Answer 16

• Acts as an electron accepter
• Produces water

Question 17

What is chemiosmosis ?

Answer 17

• H+ Ions are actively transported into the intermembrane space , therefore this creates a concentration gradient (move back into matix)
• They are done this by moving into stalked particles, where the chemical gradient forces ATP synthase to rotate and produce ATP

Question 18

Explain why the conversion of hexose molecules to glycerate 3-phosphate requires the conversion of molecules of ATP to ADP+Pi

Answer 18

• The pi phosphorylates glucose
• Therefore molecule is trapped within cell membrane

Question 19

Why is so much more ATP produced in aerobic conditions ?

Answer 19

• Pyruvate fully oxidised aerbobic conditions
• More reduced enzymes are produced which go to the ETC

Question 20

Explain why hydrogen cyanide gas can kill an animal.

Answer 20

• Cyanide changes structure of active site
• Therefore transport of hydrogen ions stop
• So that less ATP is made