1.4 Enzymes Flashcards
Define metabolism
- all the organisms chemical processes, comprising anabolic and catabolic pathways
What is a metabolic pathway
A sequence of enzyme controlled reactions in which a product of one reaction is a reactant in the next
Define an enzyme
- biological catalyst
- globular protein made by cells that alters the rate of a chemical reaction without being used up itself
What structure are enzymes in?
Tertiary (globular)
Are enzymes soluble or insoluble?
- soluble as R groups of enzymes are hydrophilic
- active site is insoluble due to hydrophobic R groups
Extracellular enzymes
- secreted (exocytosis) from cell for outside action
- eg amylase made in salivary glands moves down duct ti the mouth
Intracellular (solution) enzymes
- act inside solution in cells ie cytoplasm
- eg enzymes that catalyse glycolysis (respiration stage in cytoplasm) or enzymes in stroma of plants that catalyse photosynthesis
Intracellular (membrane bound) enzymes
- attached to membranes
- eg cristae of mitochondria for ATP formation
What is the enzyme for hydrogen peroxide break down?
- catalase
- hydrogen peroxide damages dna in cell if not broken down
Explain the lock and key model
- enzyme and the active site are perfectly complimentary so each enzyme only catalyses one type of reaction
- active site does not change
- able to synthesise and split molecules
- temporary bonds form enzyme substrate complex
Explain the induced fit model
- active site flexible - alters slightly to accommodate substrate
- ie lysozyme in mucus and tears - groove molds to substrate
Define activation energy
- minimum energy that must be put into a chemical system for a reaction to occur
How do enzymes speed up chemical reactions?
- lower activation energy
- reactions can take place at lower temp
- modify substrate
How does temperature influence rate of reaction?
- increases as temp increases as more KE so greater rate of successful collision (therefore more enzyme-substrate complexes)
- rate falls after optimism as the enzyme/active site denatures
- optimum temp in mammals is 37.5
How does pH influence rate of reaction?
- anywhere away from optimum pH decreases the rate
- alters some of the charges in the active site which disrupts H bonds in tertiary structure - reversible but can become permanent
- extreme changes result in key bonds in tertiary breaking, altering the AS shape and therefore denatured enzyme
How does enzyme/substrate concentration influence rate of reaction?
- increase and then plateau once become saturated and no more substrates or enzymes left
- prevent plateau by adding more substrates/enzymes
Define turn over rate
- the number of substrate molecules an enzyme can catalyse in a given time
Define an inhibitor
A molecule/ion that binds to an enzyme and reduces the rate of reaction that an enzyme catalyses
Define competitive inhibition
Reduction of the rate of reaction of an enzyme controlled reaction by a molecule/ion that is complementary to the active site of an enzyme and so binds to it, preventing the substrate from binding
Define non-competitive inhibition
A molecule/ion that reduces the rate of reaction by binding to an enzyme at an allosteric site, altering its tertiary structure and therefore the shape of its active site, meaning that substrates can no longer bind
Define Vmax
Maximum rate of reaction of an enzyme controlled reaction when the reaction is concentrated with substrates
What are immobilised enzymes?
- enzyme molecules that bind to an inert material over which the substrate molecules move
- used in industrial processes like fermentation or making lactose free milk
- immobilising enzymes makes them more stable
Advantages of immobilised enzymes
- increased stability and function at range of pH and temp
- products are not contaminated
- enzymes easily recovered for reuse
- enzymes easily added or removed -> controlled reaction
- sequence of columns with different enzymes can be used
What is the difference between bacterial amylase and human amylase?
- diff optimum temps
- human is 37 whereas bacterial shows 100
Anabolic reactions
Synthesise molecules
Catabolic reactions
Break down molecules
Uses of immobilised enzymes in food industry
- pectinases break down pectin so a good quality fruit juice is obtained
- lactase breaks down lactose in milk to galactose and glucose so can be digested by lactose intolerant people
What are the 3 methods of immobilising enzymes?
- Entrapment - enzymes in a membrane bound structure ie alginate beads
- Carrier bound - bound to membrane by either adsorption or covalent bonds
- Cross linking
Why is there a tap on an immobilised enzyme column?
To regulate the flow rate ensuring that lactose is broken down
What are some properties of biosensors?
Rapid, sensitive and specific measurement of products
—> high turnover rate and specific to substrates
How does a blood glucose biosensor work?
- electrical probe w a specific immobilised enzyme in the membrane is placed in blood sample
- if glucose present it diffuses through membrane and forms enzyme substrate complex
- reaction produces a small electrical current which is detected by electrode and read by a meter which then displays the glucose reading
What causes the active sites of enzymes to do denature?
- temp: vibrations cause H bonds to break which alters the tertiary structure, leading to changed shape of active site
—> above optimum
Why do enzymes only catalyse 1 reaction?
- enzymes have specific active site for a substrate
- substrate and active site complimentary
- binds to form enzyme substrate complex
More … collisions lead to …
- successful
- more enzyme substrate complexes formed therefore more product
How do you reduce the effect of an inhibitor?
Increase the concentration of the substrate
Why would it be inappropriate to use a buffer in an experiment with a colorimeter?
- colour change is dependant on pH
- hydrolysis produces fatty acids which lower pH
- buffer would stabilise/control the pH
How can a diet high in cholesterol lead to a person developing heart disease?
- increase levels of LDL
- increase incidence of atheromas in the arteries
What is a biosensor?
A device that uses biological molecules (ie immobilised enzymes) to detect the presence of chemicals/molecules in a solutiom
