Factors affecting enzyme activity

Question 1

What is meant by an endotherm?

Answer 1

An organism that relies on it’s metabolic processes to warm their bodies and maintain their own temperature.

Question 2

What are the four factors that affect enzyme activity?

Answer 2

• temperature
• pH
• enzyme conc.
• substrate conc.

Question 3

What is the effect of temperature on enzyme activity?

Answer 3

As temperature increases, molecular kinetic energy increases. Molecules move faster, leading to more successful collisions and more frequent ESC formations.

This continues up until the temperature reaches the enzyme’s optimum temperature.

Question 4

What happens once temperature exceeds the enzyme’s optimum temp?

Answer 4

The enzyme begins to be disrupted and lose stability:
- movement of the molecules continues to increase, causing them to vibrate which can break the weak hydrogen and ionic bonds in the tertiary structure.

This disrupts the active site, causing denaturation.

Question 5

In what context is denaturation reversible?

Answer 5

Thermal denaturation is usually irreversible, denaturation by pH can often be reversed.

Question 6

Define optimum temperature:

Answer 6

The temperature at which the rate of reaction is at it’ maximum. It varies according to the habitat to which an organism is adapted.

Question 7

What is meant by thermostable?

Answer 7

Organisms that have an optimum temperature of over 80°C.

Question 8

What is the temperature coefficient (Q10)?

Answer 8

The ratio between the activities of a process at two different temperatures.

For most enzyme-catalysed reactions, rate of reaction doubles for every 10°C increase. Temperature coefficient shows how much rate changes when temp is raised by 10°C.

Question 9

What is the equation for temperature coefficient?

Answer 9

temperature coefficient = rate of reaction at (x+10)°C / rate of reaction at x°C

Question 10

What is meant by pH being a “logarithmic scale”?

Answer 10

A change of 1 pH is equal to a x10 change in concentration of H+ ions.

Question 11

How do changes in pH affect bonds in enzymes?

Answer 11

Excess H+ ions will interfere with the hydrogen and ionic bonds that hold the tertiary structure of the enzyme together. This causes the active site to change shape.

Increasing H+ concentration also alters charges on the active site - more protons will cluster around negatively charged R groups. This can interfere with substrate binding.

Question 12

What is the site, optimum pH, enzymes and function of saliva?

Answer 12

• mouth / throat
• pH 7-8
• amylase
• starch –> maltose

Question 13

What is the site, optimum pH, enzymes and function of gastric juice?

Answer 13

• stomach
• pH 1-2
• pepsin
• proteins –> polypeptides

Question 14

What is the site, optimum pH, enzymes and function of pancreatic juice?

Answer 14

• small intestine
• pH 8
• trypsin, lipase, amylase, maltase
• breaks down proteins, triglycerides, starch & maltose –> glucose

Question 15

What is a buffer?

Answer 15

A buffer is a substance which resists changes to pH, donating or accepting H+ ions to maintain the pH.
- e.g. blood plasma - maintains pH of the blood within 7.35 and 7.45

Question 16

Describe the relationship between substrate concentration and enzyme rate of reaction:

Answer 16

• As substrate is added, rate of reaction increases as more enzyme-substrate complexes (and product) forms.
• Substrate concentration is the limiting factor of the reaction - at the Vmax all active sites are occupied, and adding substrate molecules will not increase the rate of reaction.

Question 17

What is meant by enzyme synthesis and degradation?

Answer 17

• synthesis - genes for synthesising particular enzymes can be switched on or off
• degradation - cells are continuously degrading enzyme molecules to synthesis new ones.

Question 18

What are the advantages of enzyme synthesis and degradation?

Answer 18

• Eliminates abnormally shaped proteins that may accumulate and harm the cell
• Regulates metabolism in the cell by eliminating any unused enzymes

Question 19

Describe the relationship between enzyme concentration and rate of reaction:

Answer 19

Increasing enzyme conc. means more active sites become available and more successful enzyme / substrate collisions can occur.

This makes enzyme conc. the limiting factor.

Question 20

What happens if enzyme concentration is increased, but substrate concentration is limited?

Answer 20

If substrate conc. is limited, then all substrate molecules will be occupying an active site - enzyme conc. is no longer the limiting factor and substrate conc. is.

Question 21

What happens at the initial rate of reaction?

Answer 21

• At the beginning of the reaction, there is a greater chance for enzyme / substrate collisions.
• Substrate conc. begins to drop, and so does the frequency of successful collisions - meaning initial reaction rate gives the maximum reaction rate.