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Question 1

enzyme kinetics

Answer 1

rate at which an enzyme works

• when and why it works best
• factors that affect activity (inhibitors)

Question 2

km (michaelis menten constant)

Answer 2

the substrate concentration at which the enzyme reaction velocity is half of its maximal rate.
-i.e substrate concentration required for significant catalysis to occur

Question 3

turnover

Answer 3

the number of molecules of substrate converted to product per second.
turnover is directly related to vmax

Question 4

what does km represent in terms of bonding strength

Answer 4

• the affinity of the enzyme for the substrate
  high km- weak binding
  low km- strong binding

km = [(k-1)+k2]/k1
when (k-1) > k2, Km allows the strength of the binding of the substrate to be estimated.

Question 5

Problems with the M-m equation

Answer 5

the graph looks like y= sqrt(x)

thus vmax is approached asymptotically, which is difficult to measure as km = vmax/2

Question 6

linewaver-burk plots

Answer 6

• double reciprocal of m-m plots
  1/V vs 1/[S]
  where the x-int: -1/km
  and y-int: 1/vmax

Question 7

kinetically perfect enzyme

Answer 7

an enzyme at which its catalytic rate is only limited by the rate at which it encounters the substrate.
Example of perfect enzyme: triosephosphate

Question 8

competitive inhibition

Answer 8

• inhibitor binds to the active sites of enzymes competing with the binding substrate, thus reducing rate of catalysis
• degree of inhibition depends on the concentration of substrates or inhibitor

Question 9

kinetics of competitive inhibition

Answer 9

-fixed amount of inhibitors present
- apparent km is higher
- disassociation constant for complex is:
Ki = [E][I]/[EI]

Question 10

non-competitive inhibition

Answer 10

• inhibitor binds to another site of the enzyme which alters the structure of the active site, affecting the capacity of the enzyme to convert substrates to products
• does not compete with binding of the substrate

Question 11

kinetics of non-competitive inhibition

Answer 11

• concentration of functional enzyme has effectively been lowered but is still able to work at the same velocity
• increases in substrate concentration have no effect

Question 12

allosteric enzymes- inhibition

Answer 12

allosteric enzymes are enzymes that change their structure upon binding with an effector which reduces catalysis at an active site

• contain regulatory sites in which small molecules can bind to
• some enzymes show feedback inhibition, often the products formed are their own inhibitors or the first enzyme in a pathway

Question 13

allosteric enzymes- cooperativity

Answer 13

• allosteric enzymes have multiple sites

- activity at one site increases the activity at others.

Question 14

allosteric enzymes and mm kinetics

Answer 14

• contains distinct regulatory and active sites; displays a property of cooperativity where regualtory/ active sites situmlate the activity of adjacent active sites. Therefore it is m-m kinetic; consists of 2 states (relaxed and tense- one for enzyme with low km and the other with a high km).

Question 15

zymogens

Answer 15

inactive precursors of enzymes. they allow proteins to only be active where they are required. I.e. proteolytic enzymes are only activated in the digestive tract.

Question 16

enzyme regulation of phosphorylation

Answer 16

• phosphorylation serves as a molecular switch, can turn enzymes on or off. It occurs on Serine, Threonine and Tyrosine
• phosphorylation adds two negative charges to a protein, this can alter its structure and function