1.3 - Proteins

Question 1

Explain briefly what proteins are

Answer 1

A diverse group of large complex polymers made up of amino acids (after water, they are the most abundant molecules in the body)

Question 2

What type of functions do proteins have? (hint - there are 5)

Answer 2

• Structural
• Catalytic
• Signalling
• Transport & storage
• Defense

Question 3

What is the structural function of a protein?

Answer 3

Proteins are the main component of body tissues (e.g muscle, skin, ligaments & hair)

Question 4

What is the catalytic function of a protein?

Answer 4

All enzymes are proteins, catalysing many biochemical reactions - used for speeding up certain chemical reactions

Question 5

What is the signalling function of a protein?

Answer 5

Many hormones & receptors are proteins

Question 6

What is the transport & storage function of a protein?

Answer 6

Proteins are a major element in the transport & storage of certain molecules

Question 7

What is the defense function of a protein?

Answer 7

Protection against disease - all antibodies are proteins

Question 8

Name the main parts in the general structure of a protein

Answer 8

• Amino group
• Carboxyl group
• Side chain a.k.a R group (only part of an amino acid that differs between each - defines an amino acid)

Question 9

Describe how a peptide bond is formed

Answer 9

• From a condensation reaction
• The -OH from carboxyl group of one amino acid & -H from the other amino acid’s amine group
• Form covalent (peptide) bond
• Release a water molecule

Question 10

Name the structural order of proteins

Answer 10

Primary structure -> Secondary structure -> Tertiary structure -> Quaternary structure

Question 11

Describe the primary structure of a protein

Answer 11

• unique sequence of amino acids

- determined by inherited genetic info

Question 12

Describe the secondary structure of a protein

Answer 12

• Found in most proteins

- Consists of coils & folds in the polypeptide chain from H bonding between parts of the polypeptide backbone

Question 13

Name the two types of secondary structure of a protein

Answer 13

• Alpha helix (coiled)

- Beta pleated sheet (folded)

Question 14

Describe the tertiary structure of a protein

Answer 14

• Elements of secondary structure come together to form a 3D fold
• Overall shape of a polypeptide, results mainly from interactions between R groups
• Interactions include: H bonds, ionic bonds, hydrophobic interactions, Van Der Waals interactions & disulphide bridges

Question 15

What are disulphide bridges?

Answer 15

Strong covalent bonds that may reinforce protein structure

Question 16

Describe the quaternary structure of a protein

Answer 16

When two or more polypeptide chains form one subunit

Question 17

Name two common examples of proteins that have quaternary structure

Answer 17

• Collagen

- Haemoglobin

Question 18

Name the 5 factors that affect the protein structure

Answer 18

• Primary structure

Physical & chemical conditions e.g:

• Changes in pH
• Salt concentration
• Temperature
• Other environmental factors that can cause protein to unravel

Question 19

What does it mean when a protein has denatured?

Answer 19

• The protein has lost its original structure & has become biologically inactive

Question 20

Describe the general structure of a globular protein & how this affects its function

Answer 20

• Usually have a spherical shape caused by tightly folded polypeptide chains
• Chains are usually folded so that hydroPHOBIC groups are on the INside, while hydroPHILIC groups are in the OUTside
• This allows many of them to be soluble in water

Question 21

What are the 3 main functions of globular proteins?

Answer 21

Transport:

• Proteins
• Enzymes
• Hormones

Question 22

Give an example of a globular transport protein & where they are found

Answer 22

• E.g haemoglobin & myoglobin

- These proteins are embedded in membranes

Question 23

Give an example of a globular enzyme

Answer 23

• Lipase

- DNA polymerase

Question 24

Give an example of a globular hormone

Answer 24

• Oestrogen

- Insulin

Question 25

Describe the general structure of a fibrous protein & how this affects its function

Answer 25

• Formed from parallel polypeptide chains held together by cross-links
• These form long, rope-like fibres w/ high tensile strength
• Generally insoluble in water

Question 26

Name 3 common examples of fibrous proteins

Answer 26

• Collagen
• Keratin
• Silk

Question 27

Give the use of collagen

Answer 27

Main component of connective tissue (e.g ligaments, tendons, cartilage)

Question 28

Give the use of keratin

Answer 28

Main component of hard structures (e.g hair, nails, claws & hooves)

Question 29

Give an example of the use of enzymatic proteins

Answer 29

In digestion, to hydrolyse bonds in food molecules

Question 30

Give an example of the use of storage proteins

Answer 30

• Casein (protein of milk) is the main source of amino acids for a baby
• Plants have storage proteins in their seeds. Ovalbumin (protein of egg white) is used as an amino acid source for the developing embryo

Question 31

Give an example of the use of defensive proteins

Answer 31

Antibodies inactivate & help destroy pathogens

Question 32

Give an example of the use of transport proteins

Answer 32

• Haemoglobin (iron-containing protein & found in blood) transports O2 from lungs to other parts of body
• Other transport proteins transport molecules across membranes