GCSE revision

• Click on the hyperlink to see the movie

• Respiration.wmv

• http://www.youtube.com/watch?v=jJvAL-iiLnQ&sns=em

• Please take notes of the important concepts

• Revise GCSE science to refresh your memory about the fundamental concepts

Cellular Respiration

Cellular respiration is the metabolic process by which cells harvest the energy of food molecules and store it in molecules of ATP.

Respiration is the only metabolic process that occurs in all living cells and is the most efficient catabolic pathway for the production of ATP

Organic food molecules are broken down in series of reactions

Cellular Respiration In cellular respiration, electrons are transferred

from glucose to coenzymes such as NAD+ and finally to oxygen

The energy released by this relocation of electrons is used to make ATP. Carbon dioxide and water are given off as by-products.

ATP provides an immediate source of energy for various forms of biological work.

Cellular RespirationThere are 3 separate processes in cellular respiration:

1. Glycolysis

2. Krebs Cycle

3. Electron Transfer

The first stage of cellular respiration occurs in the cytoplasm, while the second and third stages occur in mitochondria.

This allows the cell to keep the metabolites separate, and to control the stages more easily

Glycolysis

Glycolysis is a series of steps in which a glucose molecule is broken down into two molecules of pyruvate

As the chemical bonds in glucose are broken, electrons (and hydrogen ions) are picked up by NAD+, forming NADH (or reduced NAD)

But most of the energy released by the breakdown of glucose is carried by the electrons attached to NADH

Glycolysis1. Glucose enters the cell by facilitated diffusion (using a

specific carrier molecule)

2. ATP provides energy and a phosphate group to form 2 molecules of triose phosphate in a process called PHOSPHORYLATION

3. Each molecule of triose phosphate is converted into a molecule of pyruvate.

• This releases energy as ATP is formed from ADP• This produces 2 molecules of ATP for each triose

phosphate• This is an OXIDATION reaction and involves the

transfer of hydrogen to a carrier molecule (NAD)• The carrier molecule is a coenzyme and is REDUCED

Link Reaction

Occurs inside the mitochondrial matrix

This is a step between glycolysis and the Krebs Cycle and is referred to as the ‘Link Reaction’

Pyruvate still contains chemical potential energy1. Pyruvate is combined with coenzyme A to

produce Acetylcoenzyme A and release a molecule of CO2

2. This is another OXIDATION reaction and produces another molecule of reduced NAD

3. The CO2 diffuses through the mitochodrial and cell membranes into the tissue fluid

Krebs Cycle

The second major step of cellular respiration

Chemical cycle that completes the breakdown (oxidation) of glucose molecule to CO2

The hydrogen given off by the oxidation reactions are used to reduce these coenzymes which are then carried into the final part of respiration, the Electron Transfer Chain

Occurs within the mitochondrial matrix

Krebs Cycle1. The 2 –carbon Acetyl from the link reaction is

combined with oxaloacetate (4 carbons) to produce citrate (6 carbons)

2. Citrate is gradually broken down (in several steps) to reform oxaloacetate.

• This produces 2 molecules of CO2 released as a waste gas

• Again these are OXIDATION reactions and the hydrogens are taken up by NAD and another coenzyme, FAD to produce reduced coenzymes

• The conversion of citrate back to oxaloacetate produces one molecule of ATP

Electron Transport Chain

Occurs within the inner mitochondrial membrane utilising integral membrane proteins

Hydrogen atoms from NADH gradually release all their energy to form ATP, and are finally combined with oxygen to form water.

A sequence of electron carrier molecules (membrane proteins) that shuttle electrons during redox reactions that release energy used to make ATP

Electron Transport Chain1. Hydrogen is released from the reduced coenzyme

and split into H+ and electrons (e-)

2. The NAD and FAD then return to the earlier stages of respiration to collect more hydrogens

3. The electrons move down the chain of proteins releasing a small amount of energy at each step

4. The released energy is used to pump the H+ ions out into the inter membrane space

5. As they cross back into the mitochondrial matrix (flowing through ATP synthase) their potential energy is released and used to create ATP

6. The last molecule of the chain is oxygen which combines with the electron and the H+ to produce water in a process called OXIDATIVE PHOSPHORYLATION

Anaerobic Respiration• Without oxygen the final step of the electron

transport chain cannot take place; this stops any further reactions taking place in ETC and the Krebs Cycle

• The only process that can continue ANAEROBICALLY is glycolysis

• However, anaerobic respiration is nowhere near as efficient as aerobic respiration, producing only 2 ATP molecules

• It does, however, allow organisms to survive where there are low concentrations of oxygen

Anaerobic Respiration

• In aerobic respiration all the reduced NAD is converted back to NAD by transferring its H+ ions to oxygen

• This cannot occur in anaerobic respiration and glycolysis cannot continue without supplies of NAD

• This is overcome by converting the pyruvate in glycolysis into another substance and in the process converting reduced NAD back into NAD allowing glycolysis to continue