Unit 4: respiration
Respiration is the process in which energy stored in complex molecules is used to make ATP (adenosine triphosphate)

Energy is the ability to do work, it exists as potential (stored) or kinetic (movement) energy, large organic molecules contain chemical potential energy.
Energy cannot be created or destroyed, only converted from one form to another.

The reactions that take place in the body are known collectively as metabolism, it is the sum total of all anabolic and catabolic reactions.
Anabolic reactions are reactions where larger molecules are synthesised from smaller molecules.
Catabolic reactions larger molecules are hydrolysed to produce smaller molecules.

Processes that need energy include • Active transport- moving ions against a concentration gradient • Secretion- exocytosis • Endocytosis- bulk movement of molecules into cells • Synthesis of molecules • DNA replication + organelle synthesis • Movement • Activation of chemicals

Where does energy come from?
Energy comes from photoautotrophs (plants) that use sunlight energy in photosynthesis to make glucose. Glucose contains chemical potential energy which consumers can use. Respiration releases energy which is used to phosphorylate ADP to make ATP.

Photosynthesis: 6CO2 +6H20 ( C6H12O6 + 6O2
Respiration: C6H12O6 + 6O2 ( 6CO2 +6H2O

The role of ATP
ATP is a high energy intermediate compound. It contains adenosine ( adenine + ribose sugar) + 3 phosphate groups. It can be hydrolysed to make ADP (adenosine di-phosphate) and a inorganic phosphate group and then further hydrolysed to make AMP (adenosine monophosphate) and another inorganic phosphate group.
It releases 30.6 kj of energy.
ATP is derived from RNA as it contains a ribose sugar and not a deoxyribose sugar.

the stages of respiration

There are 4 stages to respiration: • Glycolysis- happens in the cytoplasm of cells. It does not need oxygen, can take place aerobically or anaerobically. Glucose is broken down to pyruvate. • The link reaction- happens in the matrix of the mitchochondria. Pyruvate is dehydrogenated and decarboxylated to make acetate. Requires oxygen. • Krebs cycle- takes place in the matrix acetate is dehydrogenated and decarboxylated. Requires oxygen. • Oxidative phosphorylation- happens in the cristae (folded membrane) where ADP is phosphorylated to ATP. Requires oxygen.

Coenzymes
During the reaction hydrogen atoms are removed from molecules in oxidation reactions,they are catalysed by dehydrogenase atoms. Coenzymes help them carry out oxidation reactions, the hydrogen atoms are combined with coenzymes such as NAD or FAD, these carry hydrogen atoms which can later be split.

NAD is a organic molecule that helps dehydrogenase atoms carry out their job. Nicotinamide dineucleotide (NAD) is made from nicotineamide, 2x ribose sugar, adenine and 2 phosphate groups.
When NAD accepts 2 hydrogen atoms it is reduced to NADH.

Coenzyme A
Made from a pantothenic group,adenosine, 3x phosphates and cysteine, its function is to carry acetate, forming acetyl coenzyme A.

Glycolysis
Stage 1: substrate level phosphorylation: • One ATP molecule is hydolysed and the phosphate group attatches at carbon number 6 on the glucose molecule by hexokinase • Glucose is changed by isomerisation to fructose-6-phosphate by isomerase • Another ATP molecule is hydrolysed and the phosphate group is added to fructose-6-phosphate at carbon atom 1 by phosphofructokinase making fructose-1-6-biphospate • Two ATP’s are used for each glucose molecule

Stage 2: glucose splitting • Fructose 1-6-biphosphate isomerised by isomerase to 2x glyceralderhyde-3-phosphate (GAP) • GAP is hydrogenated by dehydrogenase enzymes aided by 2x NAD which accepts the protons forming 2x NADH