Metabolism / MB - 8.2 Aerobic Respiration (detail) (HL only)

Question 1

(Notes)

• Glycolysis
• The formation of co-enzyme A (the link reactions)
• Krebs cycle (or citric acid cycle)
• Electron transport system (or respiratory chain)

Answer 1

• Lucy’s notes (covers pages 20 and 21 of booklet)

Question 2

Oxidative phosphorylation - process. === chemiosmosis (occours in the cristae)

Answer 2

= the production of ATP from oxidised hydrogen carries (as opposed to substrate level phosphorylation

• E- are donated to electron transport chain (lose energy as they are passed between successive carrier molecules)
• Energy from e- is used to translocate H+ ions from the matrix to the inter-membrane space against the concentration gradient
• buildup of H+ ions creates an electrochemical gradient / H+ (proton motive force)
• Protons return to the matrix via a transmembrane enzyme called ATP synthase
• protons/H+ = release energy which is used to produced ATP (from ADP and Po)
• H+ ions and e- are combinded with oxygen to form H2O allowing the process to be repeated

Question 3

Mitochondria Structure and Function

Answer 3

Understanding: The structure of the mitochondrion is adapted to the function it performs
Skill: Annotation of a digram of a mitochondrion to indicate the adaptations to its functions

1) inner membrane
2) inter-membrane space
3) Matrix
4) Outer membrane

Question 4

1) inner membrane

Answer 4

Folded into cristae to increase surface area for electron transport chain

Question 5

2) inter-membrane space

Answer 5

Small space between inner and outer membranes for accumulation of protons (increases PMF)

Question 6

3) Matrix

Answer 6

Contains appropriate enzymes and a suitable pH for the Krebs cycle t occour - pH is very important!!

Question 7

4) Outer membrane

Answer 7

Contains appropriate transport proteins for shuttling pyruvate into the mitochondria

Question 8

LEO and GER + extras

Answer 8

OIL RIG – Oxidation Is Loss (of electrons) ; Reduction Is Gain (of electrons)
LEO goes GER – Loss of Electrons is Oxidation ; Gain of Electrons is Reduction
ELMO – Electron Loss Means Oxidation

Question 9

Aerobic Respiration

Answer 9

If oxygen is present, the pyruvate is transported to the mitochondria for further breakdown (complete oxidation)

This further oxidation generates large numbers of reduced hydrogen carriers (NADH + H+ and FADH2)

In the presence of oxygen, the reduced hydrogen carriers can release their stored energy to synthesise more ATP

Aerobic respiration involves three additional processes – the link reaction, krebs cycle and the electron transport chain

Question 10

Anaerobic Respiration (Fermentation)

Answer 10

If oxygen is not present, pyruvate is not broken down further and no more ATP is produced (incomplete oxidation)

The pyruvate remains in the cytosol and is converted into lactic acid (animals) or ethanol and CO2 (plants and yeast)

This conversion is reversible and is necessary to ensure that glycolysis can continue to produce small quantities of ATP

Glycolysis involves oxidation reactions that cause hydrogen carriers (NAD+) to be reduced (becomes NADH + H+)

Typically, the reduced hydrogen carriers are oxidised via aerobic respiration to restore available stocks of NAD+

In the absence of oxygen, glycolysis will quickly deplete available stocks of NAD+, preventing further glycolysis

Fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks)

Hence, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen

Question 11

Summary: Oxidative Phosphorylation

ALSO NOTES AND DIAGRAMS IN FOLDER

Answer 11

Hydrogen carriers donate high energy electrons to the electron transport chain (located on the cristae)
As the electrons move through the chain they lose energy, which is transferred to the electron carriers within the chain
The electron carriers use this energy to pump hydrogen ions from the matrix and into the intermembrane space
The accumulation of H+ ions in the intermembrane space creates an electrochemical gradient (or a proton motive force)
H+ ions return to the matrix via the transmembrane enzyme ATP synthase (this diffusion of ions is called chemiosmosis)
As the ions pass through ATP synthase they trigger a phosphorylation reaction which produces ATP (from ADP + Pi)
The de-energised electrons are removed from the chain by oxygen, allowing new high energy electrons to enter the chain
Oxygen also binds matrix protons to form water – this maintains the hydrogen gradient by removing H+ ions from the matrix

Question 12

Decarboxylation:

Answer 12

Carbon atoms are removed from the organic molecule (glucose) to form carbon dioxide
Aerobic respiration involves the complete combustion of glucose (6C) – so six CO2 molecules are produced

Question 13

Oxidation:

Answer 13

Electrons and hydrogen ions are removed from glucose and taken up by hydrogen carriers (NADH and FADH2)
The hydrogen carriers are in turn oxidised at the electron transport chain (where the energy is used to make ATP)
The electrons and hydrogen ions are then taken up by oxygen (reduction) to form water molecules
Twelve hydrogen carriers are produced and so six oxygen molecules are required (12 × O = 6 × O2)

Question 14

Phosphorylation:

Answer 14

Energy released from the breakdown of glucose is used to phosphorylate ADP to make ATP
A net total of four ATP molecules are produced directly via substrate level phosphorylation
The remaining ATP is produced indirectly via the electron transport chain (oxidative phosphorylation)