Cellular Metabolismrefers to the sum of thousands of chemical reactions that occur constantly in each living thing.

2 Types:

Anabolic: atoms or molecules are joined together to make a more complex molecule. Energy is required (endothermic).

Catabolic: Break down complex molecules into simpler substances, releasing energy (exothermic).

ATP = energy moleculeAdenosine triphosphate (ATP) is the universal energy carrier for cells.

It is similar to a nucleotide, composed of adenine, ribose and three phosphate groups.

The phosphate groups are joined by high energy covalent bonds.

H HH H

OHOH

OCH2

N

C HC

CNC

NCH

NH2

N

OP

O

O-

O- OP

O

O-

OP

O

O-

Phosphate groups

Adenine

Ribose

The chemical structure of adenosine triphosphate

(ATP), and a space filling molecule (right).

Phosphate groupsRibose

Adenine

The Role of ATP in Cells

ATP (a high energy molecule) can release its energy by releasing a single phosphate group to become ADP (a low energy molecule)

ADP returns to the mitochondria where it gains more energy through cellular respiration to reattach a free phosphate group.

ATP

PPii

ATPase

Inorganicphosphate

PPADP +

Metabolism = Redox Reactions

Oxidation – the substance that loses electrons (fuels, fats, sugars, etc.) to become CO2

Reduction – the substance that gains electrons (an electronegative atom, eg. oxygen) to become H2O

Once the fuel breaks its (C-H) bonds and transfers its electrons to oxygen, energy is released in the form of heat

In a fire (combustion), fuels are oxidized rapidly to produce water and carbon dioxide.

Cellular Respiration & Redox

C6 H12O6 + 6 O2 --> 6 CO2 + 6 H2O + energy

reduction

oxidation

In biological systems, it’s not useful to produce only heat energy from the oxidation of glucose

Cellular Respiration & Redox

It’s not 100% efficient, creating some body heat

The oxidation of glucose is performed in a series of controlled steps to avoid combustion

Instead of the electrons reducing oxygen in one step, they are being used elsewhere to perform useful work (ie. make ATP)

Electron carriers (eg. NAD+) are used to transfer electrons which help to generate ATP

NAD+ and NADHNAD+ (nicotinamide adenine dinucleotide) is a coenzyme used in cellular respiration.

NAD+ is an electron acceptor, carrying electrons from one reaction to another.

E.g. When glucose molecules are broken down (oxidized) they lose electrons, these are then picked up by the NAD+ which is reduced to form NADH. The NADH then transports the electrons to where they are needed.

(high energy)

Aerobic Respiration

Cell cytoplasm

Mitochondrion

4. Electron transport chain Location: mitochondrial cristaeProcess: H2 is oxidised to water using oxygen. Energy is released as ATP.

Electron transport chain

Krebs Cycle

3. Krebs cycle Location: mitochondrial matrixProcess: A series of reactions producing carbon dioxide, ATP and hydrogens.

2. Transition reactionLocation: mitochondrial matrixProcess: Formation of acetyl coenzyme A from pyruvate.

Transition Reaction

Glycolysis1. Glycolysis Location: cytoplasmProcess: Glucose is broken down into two molecules of pyruvate.

Aerobic respiration can be separated into 4 stages.