enzymes questions Flashcards
Enzymes act as catalysts because they lower what?
activation energy by providing alternative transition state
An enzyme’s active site is made up of two parts called what?
Substrate Binding Site
Catalytic Site
Enzymes can show four different levels of specificity – name any two of them
absolute
bond
group
stereo
Define the initial reaction velocity of an enzyme catalysed reaction
Initial Reaction Velocity (t=0) = x/y
used to compare enzyme activities
Define 1 katal of enzyme activity
1 Katal of enzyme activity produces 1 mole of product per second
or utilises one mole of substrate per second
(1 Katal = 1 mole/sec)
Define the turnover number of an enzyme
the number of substrate molecules that can be converted to product by 1 enzyme molecule in 1 second (kcat)
State three factors which may result in pH changes decreasing the rate of enzyme reaction
- Overall 3-D structure of active site is altered
- Group involved in binding to substrate changes charge
- Group involved in the catalytic act changes charge
- Group on substrate involved in binding to enzyme changes charge
- Group on substrate involved in catalytic act changes charge
By what two effects does temperature affect an enzyme reaction?
kinetic
denaturing
What is the relationship between v (velocity) and [S] at low [S] if [E] remains constant?
The number of substrate molecules present [S] determines how fast the reaction takes place
What is the relationship between v and [S] at high [S] if [E] remains constant?
The number of enzyme molecules present [E] determines how fast the reaction takes place
What is the name given to the constant Km and what does it indicate?
michaelis constant
indicator of affinity of enzyme for its substrate
On a Lineweaver-Burk graph the intercept on the 1/v axis is equal to what?
y intercept = 1/Vmax
What are the two types of reversible inhibitors covered in lectures?
Competitive
non-competitive
How do irreversible inhibitors interact with the enzyme
- Bind irreversibly to enzyme
Usually bind via a covalent bond - Bind to an amino acid side chain at or near the active site
- Commonly bind to either Ser (-CH2-OH) or Cys (-CH2-SH) side chains
- Binding permanently inactivates the enzyme
- Usually prevents substrate binding
Give two characteristics of competitive inhibitors
- Reversible inhibitor
- Compete with substrate for access to active site
- Often have structure similar to substrate
- When bound to enzyme prevents binding of substrate
- Can be overcome by increasing [S] until it out-competes inhibitor
