PL - kinetics *02

Question 1

what are enzymes?

Answer 1

biological catalysts

speed up essential chemical reactions in the body

proteins, also have non-protein components

Question 2

how do enzymes work?

Answer 2

have an area called an active site

this is the part that the substrate fits into so that it can interact with the enzyme

active site is 3-D and part of the tertiary structure

Question 3

are enzymes specific?

Answer 3

enzymes have high specificity, they only work for specific substrates

this is because for the enzyme to work the substrate needs to fit into the active site.

Question 4

Lock and key model

Answer 4

when the substrate fits into the active site

substrate held in place my temporary bonds (H bonds and ID-ID), which form between the substrate and R-groups of the enzymes amino acids

Question 5

enzymes and pH

Answer 5

enzymes only work well in a narrow range of pH

there is an optimum pH at which the enzyme works best and the reaction rate is at its max.

at too high or too low pHs the reaction rate drops dramatically because enzyme becomes denatured

Question 6

enzymes and temperature

Answer 6

enzymes only work well in a narrow range of temperature

there is an optimum temperature at which the enzyme works best and the reaction rate is at its max.

at low temps. the reaction is slow because the reactant molecules have low kinetic energy

at higher temps. (too high) the reaction drops off dramatically because the enzyme becomes denatured

Question 7

what does it mean when an enzyme denatures?

Answer 7

when the shape of the active site changes (because the bonds that define the shape are broken), this changes the tertiary structure. So active site no longer correct shape for the substrate to fit into.

HAPPENS BECAUSE: temp. too hot, pH too high or low

Question 8

what are competitive inhibitors and how do they work?

Answer 8

molecules that are a similar shape to the substrate

they compete with the substrate to bond with the active site, but no reaction follows. This blocks the active site - the substrate cannot bind/fit it

Question 9

What effects how much inhibition takes place?

Answer 9

how much inhibition happens depends on the relative concentrations of competitive inhibitor and substrate

eg. if a lot more competitive inhibitor it’ll take up most of the active sites and very little substrate will be able to get to the enzyme

also affected by how strongly the inhibitor bonds to the active site

Question 10

techniques and procedures involving enzymes

Answer 10

change pH, temp., substrate or enzyme conc.

gas syringe, mass balance, titrations

Question 11

shape of rate/substrate conc. graph for enzyme catalysed reaction - and why?

Answer 11

FIRST ORDER when substrate conc. is low, graph is straight

as substrate conc. increases graph levels off until horizontal

• because substrate conc. is greater than enzyme conc. all the active sites are involved in catalysis at any moment and so rate has reached max.
• so the rate is no longer affected by the conc. of the substrate, ZERO ORDER