Enzyme Action

Question 1

What are enzymes?

Answer 1

proteins that are biological catalysts

recall: a catalyst helps speed up a reaction but is not chemically altered

Question 2

What are the functions of an enzyme? (2 POINTS)

Answer 2

to catalyse metabolic reactions in the body

(cellular and organism levels)

NO ENZYME - NO LIFE…

They are vital for life and serve a wide range of important functions in the body, such as aiding in digestion and metabolism.

GOOD VIDEO INTRODUCING ENZYMES

Question 3

Describe an enzyme (3 POINTS)

Answer 3

they are protein structures (tertiary shape)

they possess an active site - this has a particular shape for its target (substrate) molecules

enzymes are specific in the molecules they target for reaction

Question 4

What is the induced fit theory of enzymes?

Answer 4

An updated version of the ‘lock and key’ model of the action between an enzyme’s active site and the substrate target molecules

Basically, the induced fit model allows for the enzyme-substrate complex to change slightly

(in particular, the active site alters)

Question 5

How do enzymes work?

Answer 5

They lower the activation energy required for a reaction

• in so doing, the rate of reaction is sped up
• When two substrate molecules need to be joined, grabbing and holding them together makes the number of reactions taking place increase
• Similarly, long molecular chains are more likely to be broken down if something is grabbing them and splitting them!

Question 6

What structure do enzymes have? (1 POINT)

Answer 6

tertiary protein structure

Question 7

Why do we say that enzymes are ‘very specific’?

Answer 7

They only catalyse one reaction

maltase only breaks down maltose.

Why? only one substrate (key) will fit (the lock)

If the active site is altered by changes in pH or temperate, the substrate won’t fit any more

Question 8

What are the main factors affecting enzyme activity?

(5 POINTS)

Answer 8

“STEEP”

• Substrate concentration
• Temperature
• Enzume concentration
• Enzyme inhibitors
• pH

Question 9

How does temperature affect enzyme activity?

Answer 9

rise in temperature -> more kinetic energy -> increased chance of collision

more kinetic energy also implies increased collision energy

BUT

too high temperature -> collisions can break the enzyme’s own bonds -> active site changes shape -> enzyme is denatured

Question 10

How does pH affect enzyme activity?

Answer 10

A change in the pH value in the environment destroys the fragile ionic and hydrogen bonds that hold the tertiary structure in place -> denaturing

Note: most human enzymes prefer a pH neutral environent; pepsin loves pH2 as it’s in the stomach.

Question 11

How does enzyme concentration affect enzyme activity?

Answer 11

• The more enzymes, the more likely they’ll pick up their target molecules
• This is also dependent on the number of substrate (target) molecules around
• if the market’s quiet, there’s not much business to be had, regardless of the number of cafés!

Question 12

How does substrate molecule concentration affect enzyme activity?

Answer 12

The more, the merrier - higher collision rate, so increased rate of reaction

Up to a point - if the active sites are full, adding more substrates won’t affect the number being catalysed.

Just like a very busy market - the cafés become full and waiters at the active site can only fulfil a certain amount of orders

Question 13

How can enzyme activity be inhibited?

Answer 13

Enzyme inhibitors!

molecules that bind to the enzyme to stop production!

Just like the presence of gendarmes (police) at French cafés can reduce sales

Question 14

What are competitive inhibitors

Answer 14

They have a similar shape to the substrate molecules and bind to a reaction site -> no reaction takes place.

(sneaky infiltrators)

• by how much - depends on the relative concentration of inflitrating competitive inhibitors to substrates:
• high concentration of competitive inhibitors will deplete reaction rates

Question 15

What are non-competitive inhibitors?

Answer 15

Non-competitive inhibitors bind to the enzyme - but not on the active site.

This causes a change in the shape (deformation) of the active site though.

Just like if we carry a weight, any weight, we alter our shape.

Question 16

How can enzyme activity be measured?

Answer 16

1) measure how fast the products are made
2) how fast a substrate is broken down

Question 17

how can we measure the rate of products of hydrogen peroxide?

Answer 17

Catalase breaks down hydrogen peroxide into H₂O and O₂

It’s easy to measure the volume and rate of O₂ production using apparatus:

• put boiling tubes (with equal amounts of H₂O₂ + catalase) in different temperatures in a water bath

record the O2 produced drawn off into an upside down measuring cylinder in cm³ and time the rate in seconds. Units = cm³s^-1 or cm³/s (same thing)

VIDEO USING DIFFERENT METHOD - COOL TO SEE

Question 18

How can we measure the rate of substrates being broken down e.g., starch into maltose using amalyse enzymes?

Answer 18

Equal amounts of amylase and starch are mixed in test tube

Pippette takes out same amount from the tube at regular intervals;

Droplets are put onto a spotting tile which has iodine in potassium iodide at regular intervals and colour is observed

Browny orange = no starch

Blue-black = starch

Idea - you want to time how long it taks for the iodine solution to no longer change blue-black

QUICK VIDEO (he does speed it up!)

Question 19

Understand rates of reaction on a graph

Question 20

How understand rates of reaction -

Answer 20

Draw a tangent to a curve.

If the tangent is going up - it’s positive, down, it’s negative.

Look for these ideas:

“increasing at an increasing rate” I-I

“increasing at steady rate” I-S

“increasing at a decreasing rate” I-D

The image shows a reaction rate increasing at diminishing rates.

Answer 21

involved in the production of structures such as collagen and in cellular respiration