biology chapter 4

• The coagulation cascade is a series of successive enzyme activations in blood clotting.
• Living organisms need to be built and maintained, involving the synthesis of large polymer-based components like cellulose and long protein molecules.
• Cellulose forms the walls of plant cells and long protein molecules form the contractile filaments of muscles in animals.
• The different cell components are synthesised and assembled into cells, which then form tissues, organs, and eventually the whole organism.
• The chemical reactions required for growth are anabolic (building up) reactions and they are all catalysed by enzymes.
• Energy is constantly required for the majority of living processes, including growth.
• Energy is released from large organic molecules, like glucose, in metabolic pathways consisting of many catabolic (breaking down) reactions.
• Catabolic reactions are also catalysed by enzymes.
• These large organic molecules are obtained from the digestion of food, made up of even larger organic molecules, like starch.
• Digestion is also catalysed by a range of enzymes.
• Reactions rarely happen in isolation but as part of multi-step pathways.
• Metabolism is the sum of all of the different reactions and reaction pathways happening in a cell or an organism, and it can only happen as a result of the control and order imposed by enzymes.
• The speed at which different cellular reactions proceed varies considerably and is usually dependent on environmental conditions.
• The temperature, pressure, and pH may all have an effect on the rate of a chemical reaction.
• Enzymes can only increase the rates of reaction up to a certain point called the V (maximum initial velocity or rate of the enzyme-catalysed reaction).
• Many different enzymes are produced by living organisms, as each enzyme catalyses one biochemical reaction, of which there are thousands in any given cell.
• This is termed the specificity of the enzyme.
• Energy needs to be supplied for most reactions to start, this is called the activation energy.
• Sometimes, the amount of energy needed is so large that it prevents the reaction from happening under normal conditions.
• Enzymes help the molecules collide successfully, and therefore reduce the activation energy required.
• There are two hypotheses for how enzymes do this: the lock and key hypothesis and the induced-fit hypothesis.
• In the lock and key hypothesis, an area within the tertiary structure of the enzyme has a shape that is complementary to the shape of a specific substrate molecule, this area is called the active site.
• When the substrate is bound to the active site an enzyme-substrate complex is formed.
• The substrate or substrates then react and the product or products are formed in an enzyme-product complex.
• The product or products are then released, leaving the enzyme unchanged and able to take part in subsequent reactions.
• The substrate is held in such a way by the enzyme that the right atom-groups are close enough to react.
• The R-groups within the active site of the enzyme will also interact with the substrate, forming temporary bonds.
• These put strain on the bonds within the substrate, which also helps the reaction along.
• In the induced-fit hypothesis, the active site of the enzyme actually changes shape slightly as the substrate enters.
• This is called the induced-fit hypothesis and is a modified version of the lock and key hypothesis.
• Inorganic cofactors are obtained via the diet as minerals, including iron, calcium, chloride, and zinc ions.
• This leads to bonds breaking and the shape of the enzyme changing.
• Zinc ions (Zn?*) form an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.
• Respiration is a metabolic pathway resulting in the production of ATP.
• In some cases a change in conditions, such as pH or temperature, results in a change in tertiary
• When the levels of ATP are high, more ATP binds to the allosteric site on PFK, preventing the addition of the second phosphate group to glucose.
• Prosthetic groups are tightly bound and form a permanent feature of the protein.
• Sometimes the change in tertiary structure is brought about by the action of another enzyme, such as aprotease, which cleaves certain bonds in the molecule.
• Some enzymes need a non-protein 'helper' component in order to carry out their function as biological catalysts.
• When the cofactor is added and the enzyme is activated, it is called a holoenzyme.