Enzymes and Biological Reactions Flashcards
Name two metabolic pathways and what they do:
Anabolic reactions, building up molecules
Catabolic reactions, breaking molecules down
What protein is an enzyme?
Globular (tertiary structure)
Why are enzymes referred to as a biological catalyst?
They are made up of living cells
What are some properties of enzymes that make them a good catalyst?
Speed up reactions
They are not used up
They do not change shape
They have a high turn-over number
What makes enzymes soluble?
Has a hydrophilic R group on the outside of the molecule
What three bonds can an amino acid make with each other that is determined by the R group?
Hydrogen bonds
disulphide bridges
ionic bonds
What are the three distinct sites where enzymes act and what do they do? Also give an example of what they catalyse at that site.
Extracellular-> Secreted from cells by exocytosis and catalyse extracellular reactions. Bacteria secrete amylases, lipases and proteases on to their food, which helps the organism absorb the product
Intracellular, in solution-> Act in solution inside cells. Enzymes that catalyse glucose breakdown in glycolysis ( a stage of respiration)
Intracellular, membrane-bound-> May be attached to membranes, for example on the cristae of mitochondria where they transfer electrons and hydrogen ions in ATP formation
When a substrate binds to the enzyme, what does it create?
Enzyme substrate-complex
What does ‘enzyme specificity’ mean?
An enzyme is specific for its substrate.
What does the ‘induced fit model’ mean?
That an enzyme is slightly flexible to accommodate the substrate.
Give an example of the ‘induced fit model’:
Lysozyme is an enzyme found in human saliva, the active site is a groove, and the sugars of the bacterial cell wall fit into it. The enzyme can change it shape to fit around the sugars and hydrolyses the bonds.
What is the definition of activation energy?
The minimum amount of energy needed for molecules to react.
How does temperature effect enzyme action?
The more temp the more kinetic energy the enzyme and substrate has meaning there is more chance of collision, however this only increases up to 40 degrees for most enzymes as the bonds within the tertiary structure breaks and alters the shape of the active site. The enzyme has denatured
Too little temperature will cause the enzyme to be inactivated as there is little kinetic energy, but the shape is unchanged.
How does pH effect enzyme action?
Small pH changes at the optimum will lower the rate of reaction but it is reversible changes, big pH changes can denature the enzyme. The active site of the enzyme is effected by hydrogen ions and hydroxide ions, low pH causes an excess of H+ ions which is attracted to negative charges and neutralises them, OH- ions do the same with positive charges
How does concentration of substrate/enzyme effect rate of reaction?
At low substrate concentration the enzyme molecules will only have a few substrate molecules to collide with not engaging the empty active sites. It is a limiting factor as the substrate is controlling the rate of reaction. When all the active sites are full the enzyme is said to be saturated
Enzyme concentration can be much less than substrate concentration as enzymes can be reused so only a small number can catalyse a large amount, as it increases the more active sites are available and therefore the rate of reaction increases.
What is a competitive inhibitor?
A molecule that is complimentary to the active site and similar to a substrate, so they compete for the active site. The more concentration of substrate will reduce the amount of inhibitors binding to the enzyme.
What is a non-competitive inhibitor?
They bind to the enzyme at a ‘allosteric site’ so they do not compete with the substrate. The inhibitor will affect bonds within the enzyme changing its overall shape along with the active site meaning no enzyme substrate-complexes can form. Some are irreversible and some are reversible.
What are immobilised enzymes?
Enzymes which are fixed, bound or trapped on an inter matrix. Enzymes will be in the beads or active site on the beads surface and as the substrate diffuses in it will bind to create the product. They do not contaminate the products.
What are advantages of immobilised enzymes?
Increased stability and function over a wider range of temp and pH than enzymes in free solution
Products arent contaminated with the enzyme
Enzymes are easily recovered for reuse
A sequence of columns can be used to accommodate several enzymes with different optima
Enzymes can be easily added or removed, giving more control over the reaction.
Uses of immobilised enzymes:
Lactose free milk= milk is passed through the column containing immobilised lactase, the lactose binds to it and the is hydrolysed into glucose and galactose
Biosensors
High-fructose corn syrup manufacture.
