4. Enzymes Section B Flashcards
pg 14 Fig. 1.1 shows two ways in which enzymes interact with their substrates, explain the difference between the two ways these enzymes interact with their substrates 2
Enzyme A uses “Lock & Key” hypothesis with an active site that’s complementary to the shape of its substrate
Enzyme B uses “Induced fit” hypothesis with an an active site that changes its shape to fit it’s substrate.
Explain why the shape of an active site of an enzyme is important 2
Active site of an enzyme is complementary to the shape of its substrate
so the substrate can temporarily bind with R-groups of amino acids
What is primary structure of protein made of?
Amino acids joined with peptide bonds
What is secondary protein structure made of? 2
Alpha helices
Beta Pleated sheets
What are Alpha Helices? 2
Tightly coiled structures
occur due to hydrogen bonds forming between amino acids 4 places apart
What are Beta Pleated sheets? 2
Looser, straighter structure is formed
Formed when bonding occurs between parallel polypeptide chains
What is tertiary protein structure? 2
Caused by bonds forming between R-groups on amino acids
that lie close to each other when chain starts to be folded & coiled
What is quaternary structure? 3
Not always present
composed of more than 1 polypeptide chain
contain same levels of bonding as tertiary proteins
2 c) i) Draw
Draw thibgy
What is activation energy
the energy level that must be overcome before a reaction can progress
What is Vmax?
The point at on y-axis which the line of enzyme reaction is horizontal
3 Fig 2.1, Determine the Vmax
3.4 uM min^-1
How do you calculate Km
1/2Vmax on y-axis & then find value on the X-axis
3 a) ii) Calculate the Km
3.4/2 =1.7, (look on graph for x-value where y=1.7)
=0.15 mM
3 b) fig 2.1 Describe & explain shape of curve 5
When substrate concentration is lower, rate of reaction is proportional to substrate concentration
This is because there are still some unoccupied active sites
At higher substrate concentrations, the increase in the rate of reaction is slower
& substrate concentration is no longer limiting factor, instead enzyme concentration is
because all active sites are occupied
3 c) in the functioning enzyme, these 3 amino acids are close together in the active site. Explain how protein structure makes this possible 2
coiling of polypeptide chain brings these amino acids closer together,
this is due to tertiary structure of trypsin that is caused by bonds between amino acids
When trypsin acts on a substrate, another substance is required as a reactant. Name this substance
H20
- a) describe the reaction catalysed by lactase, use fig 3.1 to help you & in your answer identify R & product S 4
The hydrolysis reaction changes disaccharides to monosaccharides
The glycosidic bond is broken
R is water & S is alpha glucose
4 b) suggest why product inhibition is useful in K.lactis when lactase is acting as an intracellular enzyme but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk 2
It’s an advantage when the enzyme is intracellular because in high quantities, the product has no requirement for use in cell respiration
But it’s a disadvantage in solution because of loss of product
How does immobilised lactase in a commercial application help to reduce the problem of product inhibition
The product and enzyme are separate and the product can be quickly removed
For a commercial application using an enzyme, the progress of the enzyme-catalysed reaction needs to be studied. Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally 4
Keep temperature & pH constant
Take samples of the amount of product formed at regular intervals
Plot a graph of product formation against time
Draw a tangent to determine initial rate of reaction
what does intracellular mean?
It works inside the cell
