B4 - Enzymes Flashcards
1
Q
What are enzymes?
A
- globular proteins that interact with substrate molecules
- they act as catalysts to metabolic reactions in living organisms
2
Q
What is a metabolic reaction?
A
- it is the sum of an anabolic (building up) and a catabolic (breaking down) reaction
- can only take place as a result of the control/order imposed by enzymes
3
Q
Example of an anabolic reaction
A
- cellulose forming the walls of plant cells
- long protein molecules forming contractile filaments of muscles in animals
4
Q
Example of a catabolic reaction
A
- growth (living processes)
- energy released from large organic molecules (glucose) in metabolic pathways
5
Q
What is ‘Vmax’?
A
- maximum initial velocity of the enzyme catalysed reaction
- enzymes can only increase the rates of reaction up to this point
6
Q
What are intracellular enzymes?
A
- a type of enzyme that aids the metabolic processes inside the cells that secreted them
7
Q
What is an example of an intracellular enzyme?
A
- catalase ensures that hydrogen peroxide is broken down into oxygen and water
- benefits = it is time efficient so it minimizes the risk of damage
8
Q
What are extracellular enzymes?
A
- a type of enzyme that works outside of the cell that secreted them
- cells require substrates (raw materials) to make products needed by the organism
- the nutrients are often in forms of large molecules and need to be broken down
- enzymes are released from the cells to break down these large nutrient molecules
9
Q
What are examples of extracellular enzymes?
A
- amylase (salivary glands/pancreas) is a digestive enzyme that breaks down starch polymers into maltose
- maltose is then broken down into glucose by maltase
- trypsin (protease) catalyses the digestion of proteins into smaller peptides
- produced in pancreas and released into small intestine
- amino acids are produced and absorbed into the bloodstream
10
Q
What are the properties of enzymes?
A
- tertiary structure (interactions between R-groups)
- active site is complementary to the shape of substrate molecule
- have the ability to reduce the activation energy required for a reaction to occur
- activity is affected by temp., pH, enzyme conc. and substrate conc.
11
Q
What is the lock and key hypothesis?
A
- idea that only a specific substrate will fit the active site of an enzyme
- forms an enzyme-substrate complex
- the substrates react and form an enzyme-product complex (products are then released)
- the right atom-groups and the R-groups (within active site) will react/interact with the substrate, forming temporary bonds
12
Q
What is the induced-fit hypothesis?
A
- recent research evidence has shown that the active site of an enzyme slightly changes its shape as substrate enters
- the initial interaction is relatively weak but they rapidly induce changes in the enzyme’s tertiary structure
- this weakens a bond/bonds in the substrate and lowers the activation energy
13
Q
What factors affect enzyme activity?
A
- temperature
- pH
- substrate/enzyme conc.
14
Q
How does temperature affect enzyme activity?
A
- increase = increases K.E. of particles which causes them to collide more frequently (increases rate of reaction)
-
Q10 is a measure of how much the rate of reaction increases with a 10 d.C. rise
- denaturation:
- at extremely high temperatures bonds holding the protein together vibrate
- this increases until they strain/break causing a change in the tertiary structure
- the change in shape means they have denatured so the active site is no longer complementary to the substrate
- optimum:
- highest rate of activity takes place
- human body = 40 d.C
- ** once enzymes have denatured past the opt. temp., the decrease in rate of reaction is rapid **
- extremes:
- cold = enzymes controlling metabolic activities of organisms
- they tend to have more flexible structures and are less stable than enzymes working at higher temps.
- thermophiles = organisms adapted to living in very hot environments
- enzymes are much more stable as they have an increased no. of bonds (H and S)
- their active sites and shapes are more resistant to temp. rises
15
Q
How does pH affect enzyme activity?
A
- change in pH = change in hydrogen ion conc.
- acidic = more
- alkaline = less
- this causes a change in the hydrogen and ionic bonds between the amino acid R-groups
-
optimum pH = active site is in the right shape
- renaturation = when pH returns to opt. and protein/active site resumes its normal shape to catalyse the reaction again
- a more significant change will irreversibly alter the structure and enzymes will become denatured
- low/high pH = less R-group interaction
- enzyme will only function within a narrow pH range
