Proteins, Enzymes and Digestion

Question 1

How would you test to see if a food contained lipids?

Answer 1

By doing the emulsion test.

Add water and shake. If an emulsion forms, a protein is present.

Question 2

Why do lipids form an emulsion in water?

Answer 2

Because fats are soluble in ethanol but insoluble in water. So when you shake in water, the globules disputes forming a white emulsion.

Question 3

What’s the letter that denotes the variable group of an amino acid?

Answer 3

R

Question 4

What is the bond between amino acids in polypeptides called?

Answer 4

Peptide bonds.

Question 5

How does temperature affect enzymes?

Answer 5

1. The rise in temperature makes enzyme’s molecule vibrate more
2. If the temperature goes above a certain level, the vibration breaks the bonds that hold the enzymes in shape.
3. The active site changes shape and the enzyme and substrate no longer fit together.
4. At this point, the enzyme is denatured, so no longer functions as a catalyst.

Question 6

What happens if the enzyme goes above or below the optimum pH?

Answer 6

The H+ and OH- ions found in acids and alkalis can damage the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes the active site change, so the enzyme is denatured.

Question 7

How does enzyme concentration affect the rate of reaction?

Answer 7

The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form the enzyme substrate complex.
So increasing the concentration of the enzyme increases the rate of reaction.

Question 8

What happens if the amount of substrate is limited?

Answer 8

There is no further effect. Because there’s enough substrate to enzyme molecules, so adding more enzymes wouldn’t do anything.

Question 9

What happens if there is a greater amount of substrate concentration?

Answer 9

Higher substrate concentration = faster reaction. Because more substrate concentration means a collision between substrate and enzyme is more likely and so more active sites will be used.

Question 10

For substrate concentration, what happens after the saturation point is met?

Answer 10

There are so many substrate molecules that the enzymes have as much as they can cope with - all the active sites are full - so adding more makes no difference.

Question 11

How could you prevent the rate of reaction decreasing over time?

Answer 11

Add more substrate concentration.

Question 12

What do competitive inhibitors look like?

Answer 12

The molecule have a similar shape to that of substrate molecules.

Question 13

What do competitive inhibitors do?

Answer 13

They compete with the substrate molecules to bind the active site, but no reaction takes place. Instead, they block the active site so that no substrate molecule can fit in it.

Question 14

How much the enzyme is inhibited by a competitive inhibitor depends on…

Answer 14

The relative concentration of the enzyme and substrate.

High concentration of inhibitor = nearly all active sites take up. Not much substrate will reach the enzyme.

High concentration of substrate = increased ROR (up to a point) because there is a higher chance of substrate getting to an active site before the inhibitor does.

Question 15

How could you test to see if a food contains proteins?

Answer 15

Perform the biuret test.

Add biuret solution (sodium hydroxide and copper sulphate). If a protein is present, it would turn purple.

Question 16

What are the transport proteins?

Answer 16

Channel and carrier protein

Question 17

What does a channel protein do?

Answer 17

Carries small, charged molecules eg Na+

Question 18

What does a carrier protein do?

Answer 18

Carries large, polar molecules (ie have -ve and +ve areas). For example, glucose, glycerol, amino acids.

Question 19

What is the only difference between the 20 amino acids?

Answer 19

Their R group

Question 20

Enzymes are…

Answer 20

Globular proteins that act as catalysts

Question 21

What does the indicted fit model propose?

Answer 21

That the active site forms as the enzyme substrate interact. The proximity of the substrate (a change in the environment of the enzyme) leads to a change in the enzyme that forms a functional active site.

(Basically the enzyme is flexible and can mound itself around the substrate).

Question 22

What does the lock and key model propose?

Answer 22

A substrate will only fit the active site of one particular enzyme. The shape of the substrate (key) exactly fits the active site (lock) of the enzyme.

Question 23

What is the lock and key model supported by?

Answer 23

The observation that enzymes are very specific in the regions that they catalyse.

Question 24

Why are enzymes very specific and usually only catalyse 1 reaction?

Answer 24

Because they only have one complementary substrate which will fit into the active site.

Question 25

What is the active site of an enzyme determined by?

Answer 25

It’s tertiary structure (which is determined by its primary structure)

Question 26

Why do enzymes all have different shaped active sites?

Answer 26

Because each different enzyme has a different tertiary structure

Question 27

What happens if the tertiary structure of an enzyme is altered?

Answer 27

The active site will change shape, so the substrate won’t fit into the active site and an enzyme substrate complex won’t be formed.

Question 28

What can rage tertiary structure of an enzyme be altered by?

Answer 28

Changes in pH or temperature

Question 29

An increase in temperature increases the _______ ______ of molecules.

Answer 29

Kinetic energy

Question 30

In an enzyme-catalyst reaction, what would an increase in kinetic energy result in?

Answer 30

The molecules moving around more rapidly and colliding more often. This means that the enzyme and substrate molecules come together more often in a given time.

Question 31

How can an increase in temperature cause an enzyme to change its active site?

Answer 31

Because the temperature rise causes hydrogen bonds and other bonds in the enzyme to break. At first, this causes the substrate to fit less well into the active site.

Question 32

What happens if the temperature becomes too high in an enzyme-catalysed reaction?

Answer 32

The enzyme becomes denatured.

Question 33

What is the pH of a solution?

Answer 33

A measure of its hydrogen ion concentration.

Question 34

What does the optimum pH of an enzyme mean?

Answer 34

The pH at which it works fastest

Question 35

What does a change in pH mean in an enzyme-catalysed reaction?

Answer 35

A change in the pH alters the amino acids that make up the active site of an enzyme. As a result, the substrate can no longer become attached to the active site and the enzyme substrate complex cannot be formed.

Question 36

In an enzyme catalyse reaction, what can a significant change in pH cause?

Answer 36

The bonds maintaining the enzyme’s tertiary structure to break, so the active site changes shape.

Question 37

Increasing the enzyme concentration __________ the rate of reaction

Answer 37

Increases

Question 38

Why does increasing the enzyme concentration increase rate of reaction?

Answer 38

Because the more enzyme substances there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme substrate complex

Question 39

The higher the substrate concentration, the ______ the enzyme catalyst reaction.

Answer 39

Faster

Question 40

What happens after the saturation point of adding more substrate?

Answer 40

All the active sites are full and adding more substrate makes no difference.

Question 41

What is the shape of a competitive inhibitor?

Answer 41

They have a similar shape to that of substrate molecules

Question 42

What do competitive inhibitors do?

Answer 42

They compete with the substrate molecules to bind to the active site, but no reaction takes place. Instead, they block the active site so that no substrate molecule can fit in it.

Question 43

For competitive inhibitors, how much the enzyme is inhibited depends on…

Answer 43

The relative concentration of the inhibitor and the substrate. If there is a high concentration of the inhibitor, it’ll take up most of the active sites, so hardly any of the substrate will reach the enzyme.

Question 44

How do non-competitive inhibitors work?

Answer 44

• they bind to the enzyme, away from the active site.

- this causes the active site to change shape so the substrate can no longer bind to it

Question 45

Why don’t non-competitive inhibitors compete with substrate molecules to bind to the active site?

Answer 45

Because they are a different shape

Question 46

What does increasing the concentration of a substrate do with non-competitive inhibitors?

Answer 46

It makes no difference, enzyme activity will still be inhibited.