Enzymes Lesson 2 Need to Book - PowerPoint Presentation

Slide1

Enzymes

Lesson 2

Slide2

Need to Book

Repro

Enzyme question

Slides 17-22

Slide3

Specification

Slide4

Starter

Jot down the key ideas from last lesson on to some scrap/spare paper.

What were some of the key words and phrases?

Use them in a sentence/paragraph to describe what enzymes do...

Slide5

Cofactors

Some enzymes need the help of...

Slide6

Cofactors

Some enzymes can only work if another small,

non-protein

molecule is

attached

to them (non permanent).

The presence of cofactors such as certain

ions

may help the formation of the

enzyme-substrate complex

.

Some cofactors are

free and can even join with the substrate to make the correct, complementary shape required (co-substrates).Some cofactors change the charge distribution on the surface of the substrate or enzyme and make the temporary bonds in the ES-complex easier to form.e.g. Amylase will only digest starch in the presence of chloride ions

cofactor

enzyme

active site

substrate

Slide7

Prosthetic groups

Carbonic anhydrase with zinc ion permanently bound to its active site.

Found in red blood cells

Catalyses conversion of carbon dioxide and water to carbonic acid, which then breaks down into protons and hydrogencarbonate ions.

Important for the removal of CO

2

from respiring tissues to the lungs

Slide8

Coenzymes

Along with cofactors and prosthetic groups,

coenzymes

are another small molecule that helps the enzyme-substrate complex form.

Coenzymes bind

temporarily

to the

active site

of enzymes

.

Many vitamins act as coenzymes.

Vitamin C is a very important coenzyme.

Unlike prosthetic groups and other cofactors, coenzymes are

changed in a reaction

.

What’s the implication of this?

need to be recycled or need a source of more

Slide9

Question

Nicotinamide

(NAD) is a very important coenzyme needed by cells. The RDA for humans is 18mg.

The amount of NAD used in metabolic reactions is a great deal more than 18mg. Suggest why the RDA is so low.

The NAD is constantly recycled, which means that there is a always a supply of it. Therefore not much is needed in the diet.

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Inhibitors

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Competitive Inhibitors

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Competitive Inhibitor

Have a similar shape to that of the substrate

molecule

Complementary shape to the active site

Inhibitor

occupies

the active site, forming enzyme-inhibitor complexes

.

D

oes

not lead to the formation of products Most do not bind permanently They bind for a short period of time and then leave.Their action is described as reversible, as the removal of the inhibitor form the reaction mixture leaves the enzyme molecule unaffected.

Slide13

Competitive Inhibitors: Graph

The level of inhibition depends on the concentrations of inhibitor and substrate.

As the number of substrate

molecules is increased, the level of inhibition decreases because a substrate molecule is more likely than an inhibitor molecule to collide with the active site.

Slide14

Non-competitive Inhibitors

Slide15

Non-competitive inhibitors

Does

not compete with substrate molecules for a place in the active site.

Instead

, they attach

to the enzyme, molecule in a region away from the active site.

This distorts

the tertiary structure of the enzyme molecule, leading to the shape of the active site changing.

This means that

the

substrate no longer fits into the active site

Enzyme-substrate complexes cannot formThe reaction rate decreases.Most non-competitive inhibitors bind permanently to the enzyme molecule. The inhibition is irreversible

Slide16

N-C Inhibitors: Graph

The level of inhibition depends on the number of inhibitor molecules present.

If

there are

enough inhibitor molecules to bind to all of the enzyme molecules present, then the

enzyme controlled reaction will stop.

Changing the substrate concentration will have no

effect

Slide17

Examples

– Inhibitor poisons

Example 1

: Snake Venom

Inhibitor name

: A protein called

fasciculation

is found in snake venom.

Function

: Inhibits

Acetylcholinesterase

which is an enzyme used to degrade a neurotransmitter called Acetylcholine (Serotinin is another example of a neurotransmitter that you should have heard of from GCSE).How: Fasciculation acts as a competitive inhibitor preventing the acetylcholine from being broken down by Acetylcholinesterase after an impulse transmission.Effect: In skeletal muscle fasciculations stop nerve impulses from being transmitted and hence stop muscle contraction. Eventually this will lead to flaccid paralysis.Normal (no venom)

After venom

Slide18

Examples

– Inhibitor poisons

Example 2

: Cyanide poisoning

Inhibitor name

: Potassium cyanide

Function

: Inhibits a vital respiratory enzyme called

cytochrome

oxidase

(found inside mitochondria)How: Cytochrome oxidase normally combines oxygen and hydrogen together to form water and allows ATP creation. Cyanide non competitively inhibits chytochrome oxidase changing the shape of its active site meaning no ATP creation.Effect: Any reactions requiring ATP are no longer supplied. The body eventually has no energy supply causing total cell failure … and death even though all products for respiration still present.

Slide19

Examples

– Medicinal inhibitors

Example 1

: HIV Protease inhibitors

Inhibitor name

: Protease inhibitors (many variations all under research)

Function

: Competitively inhibits HIV virus protease enzymes. Normally the virus uses this to cut viral RNA into smaller pieces so as into implant genes into the host cells DNA and hence replicate).

How

: The inhibitor binds specifically with the HIV protease enzymes active site preventing longer viral RNA pieces from bindings, as a result the RNA is not cut into smaller pieces so it cannot be implanted into the host cells DNA = no replication.

Effect

: A host cell can be infected by HIV but it cannot be ‘hijacked’ into making more HIV copies as a result of DNA implantation by the virusNormal(no inhibitor)

With protease inhibitor (red)

Slide20

Examples

– Medicinal inhibitors

Example 1

: Suspected antifreeze poisoning treatment

Inhibitor name

: Ethanol (alcohol!)

Function

: Ethylene glycol is found in antifreeze, if ingested can be broken down by alcohol

dehydrogenase

(liver) forming extremely toxic oxalic acid = death. Ethanol if taken as a treatment can prevent this.

How

: Ethanol competitively inhibits alcohol dehydrogenase so give the patient a massive dose of ethanol so as to prevent ethylene glycol from interacting with alcohol dehydrogenase.Effect: Less oxalic acid is produced allowing the harmless ethylene glycol to be excreted. Better to be drunk than dead!!Ethylene glycol

Broken down by alcohol dehydrogenase into Oxalic acid

Ethanol (inhibitor)

Massive ethanol dosage

Ethylene glycol excreted

Slide21

Examples: Product Inhibition

Product of an enzyme binds to the enzymes and inhibits its action

Way to regulate metabolism

Form of negative feedback

E.g. regulation

of ATP formation by phosphofructokinase (an enzyme in glycolysis)

ATP inhibits phosphofructokinase, so that when ATP levels are high, glucose is not broken

down

Slide22

Inactive Precursors

Some enzymes produced in inactive precursor form

E.g. Trypsin produced in the small intestine as Trypsinogen

After

they’re made some amino acids are

removed by another enzyme

Thus completing the shape/or exposing the active site

E.g. trypsinogen turned into trypsin

Slide23

Plenary

Discuss with a partner:

The difference between intracellular and extracellular enzymes, and examples of each.

The similarities and differences between:

Cofactors, Prosthetic Groups and Coenzymes.

Slide24

Success criteria

The role of enzymes in catalysing both intracellular and extracellular reactions

To include

catalase

as an example of an enzyme that catalyses intracellular reactions and amylase and

trypsin

as examples of enzymes that catalyse extracellular reactions.

The need for coenzymes, cofactors and prosthetic groups in some enzyme-controlled reactions

To include C

l – as a cofactor for amylase, Zn

2+

as a prosthetic group for carbonic anhydrase and vitamins as a source of coenzymes.