Enzymes

Question 1

What are catalysts?

Answer 1

A catalyst is a substance that can speed up a chemical reaction, without itself being chemically changed at the end of the reaction

Question 2

What are enzymes

Answer 2

They are proteins that function as biological catalysts. They can catalyse or speed up the rate of a chemical reaction and remain chemically unchanged at the end of the reaction

Question 3

How do they speed up rate of rxns

Answer 3

They provide an alternative pathway that requires lower eA

Question 4

what reactions do enzymes catalyse

Answer 4

amylase - digests starch to maltose
maltase - digests maltose to glucose
protease - digests proteins to polypeptides, the polypeptides to amino acids
lipase - digests fats to fatty acids and glycerol

some food molecukles are large and insoluble in water, and these molecules cannot diffuse thru cell membrane. thus enzymes are needed to break these large molecules and into simpler and smaller substances so that they are soluble in water and small enough to diffuse through cell membrane.

Question 5

How do enzymes work? with ref to lock-and-key hypothesis

Answer 5

1. According to the lock-and-key hypothesis,
2. An enzyme has a specific three dimensional shape and has a depression called the active site
3. Only a substrate with a 3D shape complementary to the active site of the enzyme can bind to the enzyme, forming an enzyme-substrate complex.
4. The enzyme is just like a lock and the substrate a key
5. While the substrate is attached to the active site of the enzyme, a chemical reaction occurs and substrate molecules is converted into product molecules
6. The product molecules leave the active site of the enzyme afterwards
7. Enzyme remains chemically unchanged and can catalyse another reaction after.

enzyme-substrate complex is a temporary molecule formed when a subsrate bidns to an enzyme

Question 6

What are the characteristics of enzymes

Answer 6

1. Enzymes speed up the rate of chemical reactions - by lowering activation energy needed to start the reaction
2. Enzymes are specific in nature - only substrates with a shape complementary to the active site of the enzyme, forming enzyme substrate complex. However, high temeprature, acids and alkali can affect the shape of enzyme and consequently its function
3. Enzymes are required in minute amounts and remain chemically unchanged at the end of a reaction - since they remain chem unchanged after, the same enzyme can be used repeatedly and a small amoutn of enzyme can catalyse a reaction for a large amount of substrate
4. Enzymes are protein in nature
5. Enzymes are affected by temperature - refer to next slides for more details
6. Enzymes are affected by pH - refer to next slides for more details

Question 7

What happens when enzymes are in a temperature lower than optimum

Answer 7

Tempature lower than optimum temperature - Enzymes are less active

Explanation : The kinetic energy of enzyme and substrate molecules are low. The rate of effective collision of substrate molecules colliding and binding to the active site of enszyme is decreased, decreasing the rate of enzyme-substrate complex formation, resulting in slower rate of product formation

Question 8

What happens when enzymes are in optimum temperature

Answer 8

Enzyme is the most active at its optimum temperature

Explanation: The optimum temperature of (state temperature from qn) provides sufficient kinetic energy for enzyme and subtrate molecules and rate of effective collision of substrate molecules colliding and binding to the active site of the enzyme is at its highest, forming enzyme substrate complex at the highest rate and resulting in fastest rate of product formation

Question 9

What happens to enzyme in temperature above optimum temperature

Answer 9

Enzyme denatured

Explanation: Active site of enzyme begins to lose its 3D shape and is no longer complementary to the shape of the substrate molecule

Question 10

Define denaturation

Answer 10

Denaturation is the change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such as acids or alkalis

Thus enzyme cannot carry out function after denaturation - as change in 3d shape can no longer bind to substrate and result in enzyme substrate complex and activation energy remains high, so enzymes cannot catalsye reaction

Question 11

Enzymes affected by pH. however, what happens if they are placed in pH conditions that vary from optimum?

Answer 11

Denaturation.

Some enzyems work best in alkali conditions while some work best in acidic conditions. However when there are extreme changes in pH such as from ph 7 to 1, enzyme is denatured.