RESPIRATION

RESPIRATION

• This is the release of energy from food.• Different from gas exchange or breathing.• Respiration occurs in cells, in the

cytoplasm and the mitochondria.

SOURCES OF ENERGY

• We get energy from carbohydrates, lipids and proteins.

AN ANALOGY

• The energy in the food we eat is a $100 bill, if you tried to buy a box of matches or some gum, you would be asked for something smaller like a $5 bill.

• The glucose in the food we eat is the $100 and the smaller $5 is ATP (adenosine triphosphate).

ATP – THE UNIVERSAL ENERGY CARRIER

• This carries the energy to power all metabolic reactions in living things.

• ATP and ADP (Adenosine diphosphate) are very similar, ATP carries the energy, while ADP is an empty carrier.

• The energy is carried in the 3rd phosphate bond.

• When ATP gives up energy it loses a phosphate to become ADP.

ATP CONT

• The ADP then goes back into the cytoplasm and the mitochondria to be recharged.

THE ENERGY CYCLE

NAD – THE HYDROGEN CARRIER

• Most of the energy used to charge up ATP comes from the hydrogen in glucose.

• The carbon dioxide formed is a waste product which is exhaled.

• The Hydrogen from various steps needs to be carried to where it is needed, this is done by a hydrogen carrier NAD (nicotinamide adenine dinucleotide)

NAD – THE HYDROGEN CARRIER

NAD NADH2

H2

H2

NAD CONT

• NAD is a coenzyme, which uses one of the B complex vitamins in its structure. If this is missing from the diet, an animal will become deficient in NAD.

• Respiration will be affected and the animal will always be tired.

• In humans the deficiency disease is pellagra, symptoms include dermatitis, diarrhoea, mental disturbance, muscular weakness and fatigue.

FAD

• Flavin adenine dinucleotide.• Another hydrogen carrier involved in the

Kreb’s cycle.

CO-ENZYME A

• An acetyl group is formed in glycolysis.• This has to be carried to the next step by a

carrier called co-enzyme A.

Acetyl Co-A Co-A

Acetyl

Acetyl

AEROBIC RESPIRATION

• This requires oxygen.

C6H12O6 + 6O2 6CO2 + 6H2O + ATP

GLYCOLYSIS• Takes place in the cytoplasm.• Needs 2 ATP to kick start.• The process charges 4 ATP so there is a net

gain of 2 ATP.• Glucose is converted into 2 molecules of a 3C

pyruvate.

• 2 NADs pick up Hydrogen to become NADH2. These are carried off to the mitochondrial membranes and the electron transport chain.

• No oxygen is needed in glycolysis.

GLYCOLYSIS

Glucose

2 Pyruvate

2 ADP

2 ATP

NAD

NADH2

Aerobic pathway

To electron transport chain

Anaerobic pathway

Anaerobic

FORMATION OF ACETYL CO-ENZYME A

• The pyruvate loses a C (forming CO2) to become a 2C acetyl group.

• This is carried by Co-A to the Kreb’s Cycle.

• This takes place in the matrix of the mitochondria.

• The Co-A drops off the acetyl group, then goes back to the end of glycolysis to pick up more acetyl groups.

FORMATION OF ACETYL CO-ENZYME A

Pyruvate (C3)

Acetyl Co-A (C2)

Co-A

The Kreb’s Cycle

2NADH2

CO2

THE KREB’S CYCLE

• This takes place in the inner matrix of the mitochondria.

• In a complex series of chemical reactions, the acetyl group joins with other chemicals in a returning cycle.

• CO2 is released and a small amount of ATP is produced.

• Many NADs are charged to form NADH2, which are carried to the electron transfer system.

KREB’S CYCLE (CITRIC ACID CYCLE)

Acetyl Co-A (C2)

Citric Acid (C6)

C5

C4

CO2

CO2NAD

NAD

NADH2

NADH2

ADP

ATP

To electron transport

chain

To electron transport

chain

THE ELECTRON TRANSFER SYSTEM OR RESPIRATORY

CHAIN• This is located on the membranes or

cristae of the mitochondria.• The system consists of a row of

cytochromes, which pass hydrogen electrons down from one to the other.

• This results in a series of oxidation and reduction reactions which release about 3 ATPs for every hydrogen involved.

• One molecule of glucose can charge up to 38 molecules of ATP.

THE ELECTRON TRANSFER SYSTEM OR RESPIRATORY

CHAIN• Think of the cytochromes as a row of

springs, the electrons bounce down the springs.

• Each bounce gives off energy to help charge up ADP to form ATP.

• At the end of this stage the low energy hydrogen joins with oxygen and forms water.

ANAEROBIC RESPIRATION OR FERMENTATION

• If there is no oxygen, the electron transport system blocks up, the Kreb’s Cycle jams up and so on. Another acceptor has to be found for all the hydrogen.

• In the absence of oxygen, glycolysis can still occur.

• Different things happen in plants and animals.

ANAEROBIC METABOLISM IN PLANTS

• Ethyl alcohol and carbon dioxide are given off.

• The NAD is cleared to pick up some more hydrogen.

Pyruvate + NAHD2 ethanol + Carbon dioxide + NAD + 2 ATP

•Quite common in bacteria, fungi such as yeast, and the seeds of some plants e.g. peas

ANAEROBIC METABOLISM IN ANIMALS

• The hydrogen is passed to the pyruvate, and the end product is lactic acid.

• The NAD is cleared to keep this cycle of glycolysis going.

Pyruvate + NAHD2 lactic acid + NAD + 2 ATP

SUMMARISING ANAEROBIC

RESPIRATIONGlucose

Pyruvate

Lactic Acid

Ethanol + Carbon Dioxide

NADH2

NADH2

NAD NAD

2ADP2ATP

PlantsAnimals

FACTORS THAT CAN AFFECT RESPIRATION

• The process of respiration is run by enzymes, so anything which affects enzyme action will affect respiration.– Temperature– pH– Enzyme and substrate concentration– Can be poisoned

FACTORS THAT CAN AFFECT RESPIRATION

• An energy source is needed (glucose, fats or proteins.)

• Sufficient oxygen is needed• Carbon dioxide must not be allowed to

accumulate or it will slow respiration down.• With anaerobic metabolism, the ethanol

produced can poison off yeast cells.