enzymes

what type of protein are enzymes

globular

why are enzymes known as biological catalysts

they increase the rate of a chemical reaction without being used up in the reaction themselves

what two categories can enzymes be grouped into

intracellular and extracellular enzymes

define intracellular enzymes

enzymes that act within the cell that produces them

define extracellular enzymes

enzymes that act outside the cell that produces or secretes them

give an example of an intracellular enzyme and state its function

catalase- catalyses the breakdown of hydrogen peroxide into oxygen and water. (hydrogen peroxide is toxic)

given two examples of extracellular enzymes and state their function

1. amylase- secreted by the salivary glands, pancreas and small intestine to break down starch into maltose.

2. trypsin- secreted by the pancreas into the small intenstine to break down proteins into smaller polypeptides.

where is the extracellular enzyme amylase secreted from

salivary glands, pancreas and small intestine

where is the extracellular enzyme trypsin secreted from

secreted from the pancreas into the small intestine

name the stages of an enzyme breaking down a substrate

1. due to a unique tertiary structure which determines the shape of the enzymes ative site, the active site is complementary to the substrate.

2. the substrate binds to the active site to form an enzyme-substrate complex.

3. temporary bonds form between the R groups within the active site and the substrate. These bonds lower the activation energy to help break down the substrate into products.

4. the products are released from the active site, leaving the enzyme free to be used again.

what structure determines the shape of the enzymes active site

tertiary structure

what is it called when an enzyme binds with a substrate

enzyme-substrate complex

what is the lock and key model

in the model, the substrate fits erfectly into the enzyme’s active site in the same way a key fits into a lock

what is the induced fit model

the substrate ddoes not fit perfectly into the enzyme’s active site. As the substrate enters the enzyme, the active site changes shape slightly. This puts a strain on the substrate’s bonds which lowers the activation energy.

in the induced fit model, what happens when the active site changes shape slightly to fit the substrate

it puts a strain on the substrate’s bonds which lowers the activation energy

what are the steps for an enzyme becoming denatured

drastic temperature increase or pH change causes bonds to break within the enzyme, changing the enzyme’s tertiary structure and its active site shape. This means the substrate no longer fits, and no enzyme-substrate complexes can be formed.

what 4 factors affect the rate of enzyme controlled reactions

1. temperature

2. pH

3. substrate concentration

4. enzyme concentration

how does kinetic energy affect the rate of an enzyme controlled reaction

1. molecules with more kinetic energy have more collisions and more enzyme-substrate complexes form.

2. too much kinetic energy causes the active site to change shape and the enzyme denatures

what does the temperature coefficient (Q10) show

how much the rate of reaction changes when the temperature is increased by 10*C

what is the formula for Q10

Q10= R2/R1

R2= the rate of reaction at the higher temperature

R1= the rate of reaction at the lower temperature

how do acidic conditions affect enzyme action

in acidic conditions, H+ ions break ionic/hydrogen bonds and denature enzymes.

how do alkaline conditions affect enzyme action

in alkaline conditions, OH- ions break ionic/hydrogen bonds and denature enzymes

explain how substrate concentration affects the rate of an enzyme controlled reaction

1. as substrate concentration increases, there are more substrate molecules to form more enzyme-substrate complexes (rate of reaction increases)

2. at the saturation point, all active sites are occupied by a substrate, and enzyme concentration becomes the limiting factor (rate of reaction plateaus (levels off))

explain how enzyme concenration affects the rate of an enzyme controlled reaction

1. as enzyme concentration increases, there are more enzyme molecules to form more enzyme-substrate complexes.

2. once all substrate molecules available are being acted upon and substrate concentration becomes the limting factor, the rate of reaction plateaus (levels off)

define an inhibitor

molecules that bind to enzymes to reduce their activity

state the difference between reversible and irreversible inhibitors

reversible inhibitors form weak bonds (e.g hydrogen or ionic) with the enzyme, whereas irreversible inhibitors form strong bonds (e.g covalent) with the enzyme.

where do competitive inhibitors bind

to the active site

where do non-competitive inhibitors bind

away from the active site (allosteric site)

how do non-competitive inhibitors work

1. they bind away from the active site (allosteric site)

2. this binding changes the tertiary structure of the enzyme, causing the active site to change shape.

3. the active site is no longer complementary to the substrate, so the substrate and enzyme cannot bind.

4. less enzyme-substrate complexes are formed

5. rate of the enzyme-catalysed reaction decreases.

why can non-competitive inhibitors not be overcome by increasing substrate concentration

non-competitive inhibitors do not compete with the substrate to bind to the active site.

define cofactors and give an example

non-protein substances that bind to enzymes to increase their activity. Cl- is a cofactor for the enzyme amylase.

what are the two types of cofactors

coenzymes and prosthetic groups

define coenzymes

organic cofactors that are usually derived from vitamins

define prosthetic groups

cofactors that are tightly bound to enzymes e.g. Zn 2+ is a prosthetic group for the enzyme carbonic anhydrase

how do competitive inhibitors work

1. they have a similar shape to the substrate, so they can bind to the active site of the enzyme.

2. this prevents the substrate from binding, and reduces the formation of enzyme-substrate complexes.

3. decreases the rate of the enzyme-catalysed reaction

how can competitive inhibitors be overcome

by increasing the substrate concentration