1.4 Proteins

Question 1

Describe the composition of proteins. (4 points)

Answer 1

Proteins are composed of chains of amino acids.

A typical protein is about 400 amino acids long.

As there are 20 different types of naturally occurring amino acids, many different proteins can be made.

Different proteins are made of different combinations ofamino acids.

Question 2

How is the shape of a protein determined?

Answer 2

The sequence of amino acids in the chain determines how the chain will fold up to make the protein, so different proteins have different three-dimensional shapes.

Question 3

What determines the FUNCTION of a protein and how?

.

Answer 3

The three-dimensional shape of a protein determines its function. This is because proteins form attachments and interact with many other molecules and structures inside organisms.

Question 4

How does the shape of a protein affect its interactions?

Answer 4

The shape of a protein determines what it can interact with, just like the shape of a key determines which locks it can operate.

Question 5

What are the four categories of proteins?

Answer 5

1. Structural
2. Enzymes
3. Hormones
4. Antibodies

Question 6

STRUCTURAL proteins

Describe the function and give examples.

Answer 6

Function -
Forms supporting frameworks inside cells and forms body structures

Examples -
Tubulin: forms spindle fibres during mitosis and
Keratin: the protein that makes up hair and nails

Question 7

ENZYMES

Describe the function and give examples.

Answer 7

Function -

Catalyse biological reactions

Examples -

ATPase: catalyses the breakdown of ATP

Cellulose synthase: catalyses the formation of cellulose from glucose molecules

Question 8

HORMONES

Describe the function and give examples.

Answer 8

Function -

Communication between different parts of the body.

Examples -

Hormones are released from endocrine glands and are transported in the blood to target cells

Insulin: released from pancreas, stimulates liver cells to take up glucose from the blood

Glucagon: released from pancreas, stimulates liver cells to release glucose into the blood

Question 9

ANTIBODIES

Describe the function and give examples.

Answer 9

Function -

Part of the immune system. They are produced by white blood cells and can bind to specific bacteria and viruses to label them for destruction by other types of white blood cells

Examples -

Your body produces around one million different types of antibody

Question 10

Why is speed an important factor in enzyme function?

Answer 10

Thousands of different chemical reactions must happen inside every cell, every second in order for them to function.

If these cellular reactions happen too slowly the cell may die. If the cell is part of a multicellular organism then this might also harm the whole individual.

Question 11

Give an example of the need for speed in enzyme function related to the liver.

Answer 11

For example, in liver cells the toxic chemical hydrogen peroxide must be broken down into harmless products, water and oxygen.

If this reaction happens too slowly then hydrogen peroxide can build up and poison the cell.

Question 12

How does temperature affect cellular reactions?

Refer to both laboratory and body conditions.

Answer 12

The rate of a chemical reaction can be increased in the laboratory by increasing the temperature. This gives more molecules sufficient energy to react with each other. However, in the body high temperature cannot be used to speed up reactions as this would damage cell proteins and prevent them from functioning.

Question 13

How do living cells speed up cellular reactions? Try to give 3 points.

Answer 13

Living cells solve this problem by producing proteins calledenzymes.

Enzymes speed up cellular reactions at body temperature by providing a more favourable environment for the reacting molecules to meet in.

They also remain unchanged by cellular reactions and therefore can be reused by the cell.

Question 14

What are substrates?

Answer 14

The chemicals that enzymes act upon are calledsubstrates.

Question 15

The chemicals produced by the action of an enzyme are calledwhat?

Answer 15

Products.

Question 16

Describe the process of liver cells speeding up the breakdown of hydrogen peroxide.

Answer 16

For example, liver cells produce the enzyme catalase to speed up the breakdown of hydrogen peroxide.

In this example the enzyme catalase acts on the substrate hydrogen peroxide and the products are water and oxygen.

Question 17

Describe the structure of enzymes.

Answer 17

Enzymes are proteins. Their amino acids fold into three-dimensional structures that can be represented by simple shapes.

Question 18

How do enzymes catalyse biological reactions?

Answer 18

Enzymes act on substrates by attaching to them. The part of an enzyme that one or more substrates molecules can attach to is called theactive site.

Question 19

Describe (and draw a diagram) DEGRADATION and SYNTHESIS of substrates.

Answer 19

The diagram should show how an enzyme catalyses thedegradation(breakdown) of one substrate into two products.

Enzymes can also catalyse thesynthesis(joining together) of two substrates to form one product.

Question 20

What makes different each enzyme type different/specific?

Answer 20

Each different type of enzyme will usually catalyse one biological reaction.

Enzymes are specific because different enzymes have different shaped active sites.

The shape of an enzyme’s active site is complementary to the shape of its specific substrate or substrates. This means they can fit together.

Question 21

What do proteins consist of?

Answer 21

Proteins consist of combinations of amino acids.

Question 22

What enzymes do body proteins include?

Answer 22

1. structural proteins
2. enzymes
3. hormones
4. antibodies

Question 23

What is the effect of the shape of an enzyme?

Answer 23

The shape of an enzyme allows it to speed up a biological reaction.

Question 24

What does ‘optimum comditioms’ mean in relation to enzymes?

Answer 24

The conditions under which a particular enzyme is most active are called the optimum conditions.

Question 25

How does the rate of activity of an enzyme affect a biological reaction?

Answer 25

When an enzyme is most active the rate of the biological reaction it catalyses is highest.

Question 26

What is the effect of temperature on enzyme activity?

Answer 26

Temperature is a measure of how much kinetic energy molecules have.

As the temperature is increased enzyme activity increases to a maximum value at the optimum temperature (around 37oC for most human enzymes).

As the temperature is increased above the optimum temperature enzyme activity decreases.

Question 27

What happens to enzyme activity at low temperatures?

Answer 27

At low temperatures enzyme activity is low because the enzyme and substrate molecules have less kinetic energy so there are fewer collisions between them.

Question 28

What happens to enzyme activity at optimum temperature?

Answer 28

At the optimum temperature, the kinetic energy in the substrate and enzyme molecules is ideal for the maximum number of collisions.

Question 29

What happens to enzyme activity at high temperature?

Answer 29

At high temperatures the shape of the enzyme is altered so that it is no longer complementary to its specific substrate. This effect can be permanent and irreversible and is calleddenaturation.

Question 30

What is DENATURATION?

Draw a diagram.

Answer 30

At high temperatures the shape of the enzyme is altered so that it is no longer complementary to its specific substrate. This effect can be permanent and irreversible and is calleddenaturation.

Question 31

What does pH measure?

Answer 31

pH is a measure of how acidic or alkaline a solution is.

Question 32

How does pH affect enzyme activity?

Answer 32

Enzyme activity is at its maximum value at the optimum pH.

As the pH value is increased above or decreased below theoptimumpH the enzyme activity decreases.

Question 33

How does very acidic pH affect enzyme activity?

Answer 33

At very acidic and alkaline pH values the shape of the enzyme is altered so that it is no longer complementary to itsspecificsubstrate.

This effect can be permanent and irreversible and is called denaturation.

Question 34

Give the working pH range for pepsin, catalase or other enzymes.

Answer 34

The enzyme pepsin breaks down proteins in the acidic conditions of the stomach.

Pepsin has an optimum of pH 2.5 and a working range of between pH 1-4.

Catalase has an optimum pH of 9 and a working range of between pH 7-11.

Most other enzymes function within a working pH range of about pH 5-9 with neutral pH 7 being the optimum