1

Energy –capacity to do work or cause change

• Endergonic reactions – consume energy

• Exergonic reactions – release energy

2

Energy Transfer reactions catalyzed by enzymes

1. Oxidation-reduction reactions – transfer of electrons

2. Phosphotransferases – transfer phosphate groups, involved in energy transfer

3

Redox reactions

• always occur in pairs

• There is an electron donor and electron acceptor which constitute a redox pair

• The process salvages electrons & their energy.

• released energy can be captured to phosphorylate ADP or another compound

4

Electron carriers

• resemble shuttles that are loaded and unloaded with electrons and hydrogen

• most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain

5

Electron carriers

6

ATP

• 3 part molecule consisting of– adenine – a nitrogenous base– ribose – a 5-carbon sugar– 3 phosphate groups

• Removal of the terminal phosphate releases energy

7

ATP

8

Formation of ATP

1. substrate-level phosphorylation

2. oxidative phosphorylation

3. photophosphorylation

9

substrate-level phosphorylation

10

Catabolism of glucose

1. Glycolysis

2. Tricarboxylic acid cycle, Kreb’s cycle

3. Respiratory chain, electron transport

11

Metabolic strategies

Pathways

involved

Final e- acceptor ATP yield

Aerobic respiration

Glycolysis, TCA, ET

O2 38

Anaerobic respiration

Glycolysis, TCA, ET

NO3-, So4

-2, CO3

-3

variable

Fermentation Glycolysis Organic molecules

2

12

Overview of aerobic respiration

13

Overview of aerobic respiration

• Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C)

• TCA – processes pyruvic acid and generates 3 CO2 molecules

• Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation

14

Glycolysis

15

TCA cycle

16

Electron transport system

17

Chemiosmosis

18

Fermentation

• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

• Uses organic compounds as terminal electron acceptors

• Yields a small amount of ATP• Production of ethyl alcohol by yeasts acting on

glucose• Formation of acid, gas & other products by the

action of various bacteria on pyruvic acid

19

Fermentation

20

Products of fermentation

21

• Many pathways of metabolism are bi-directional or amphibolic

• Metabolites can serve as building blocks or sources of energy– Pyruvic acid can be converted into amino acids through

amination– Amino acids can be converted into energy sources

through deamination– Glyceraldehyde-3-phosphate can be converted into

precursors for amino acids, carbohydrates and fats

22

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