2- ICH - Proteins

Question 1

Elements that make up proteins?

Answer 1

Carbon

Hydrogen

Oxygen

Nitrogen

Sulphur

Question 2

Monomer of proteins?

Answer 2

Amino acids

Question 3

General structure of an amino acid?

What are the ends of the structure called?

Answer 3

Carboxyl end = C Terminal

Amine end = N Terminal

Question 4

Number of common amino acids?

Essential and non-essential?

Answer 4

20 common amino acids.

There’s 9 essential amino acids - Must be present in the diet.

There’s 11 non-essential acids - Can be synthesised from the essential amino acids.

Question 5

What does the R group determine?

Example of protein and it’s structure + R group?

Answer 5

R group determines the properties of the protein.

Glycine. R group is -H

Question 6

Name of reaction by which amino acids join together?

Name of bond formed?

Answer 6

Condensation reaction

Peptide bond

Question 7

Primary structure?

Answer 7

The sequence of amino acids in a polypeptide chain

Question 8

Secondary structure? 2 Types?

Answer 8

The folding of the primary structure.

• Alpha helix. Held together by hydrogen bonds. Easily broken by high temperatures and pH changes.
• ß Pleated sheet. Held together by hydrogen bonds into parallel flat sheets.

Question 9

Tertiary structure?

Answer 9

The folding of the secondary structure into even more complex shapes, often forming unique 3 dimensional structure which gives the protein its specific properties.

Many proteins consist of only one poypeptide chain and so the tertiary structure represents the working protein.

Question 10

Name the types of bonds/interactions in the tertiary structure. (4)

What do the bonds form between?

Answer 10

Disulphide bonds (also known as disulphide bridges) - Formed between sulphur atoms of 2 molecules of the amino acid cysteine. Very strong bonds (covalent).

Hydrogen bonds - Result from the attraction between electronegative oxygen on the -CO groups and the electropositive H atoms on either -OH or -NH groups. Relatively weak but will be provide strength if there’s many present.

Hydrophobic and Hydrophilic interactions - Weak interactions between polar and non-polar R groups.

Ionic bonds - Forms between oppositely charged R groups.

Question 11

Quaternary structure? Exmaple?

Answer 11

Protein may consist of 2 or more polypeptide chains combined to form the functioning protein. The way these polypeptide chains combine gives the protein describe its quaternary structure.

E.G.

Haemaglobin - Made of 4 linked polypeptide chains

Question 12

The 3 groups of proteins?

Answer 12

Fibrous, globular and conjugated

Question 13

Examples:

1. Fibrous proteins (3)
2. Conjucated protein (2)
3. Globular proteins (3)

Answer 13

1. Collagen, keratin and elastin
2. Haemaglobin, glycoproteins…
3. Enzymes (insulin), receptor protein, recognition protein

Question 14

Keratin

Protein type and where it’s found?

Answer 14

• Fibrous protein.
• Found in hair and finger nails

Question 15

Collagen

Protein type and where it’s found?

Answer 15

• Fibrous protein
• Found in the connective tissue. Found in skin, tensons, ligaments and nervous system.
• Made of 3 collagen polypoptides (alpha helicies) braided together

Question 16

Elastin

Protein type and where it’s found?

Answer 16

• Fibrous protein
• Found in walls of blood vessels and in the alveoli in the lungs. Give structures flexibility.

Question 17

What are fibrous proteins?

Answer 17

Protein molecules that form long chains or fibres which make them insoluble and useful for structure and support

Question 18

What are globular proteins?

Answer 18

Form a compact spherical mass with a specific 3 dimensional shape.

Usually soluble and play an important part in metabolism.

Question 19

What are conjugated proteins?

Answer 19

They are globular proteins that contain a non-protein component called a prosthetic group

Question 20

Name given to proteins that don’t contain any prosthetic group?

Answer 20

Simple proteins

Question 21

1^st class and 2^nd class protein?

Example?

Answer 21

1^st class = Contains all essential amino acids e.g. Meat

2^nd class = Doesn’t contain all essential amino acids e.g. plant based proteins

Question 22

What does amphoteric mean?

Answer 22

Both basic and acidic. Proteins are amphoteric.

Question 23

What is a buffer?

Answer 23

Buffers = Resistant to pH changes. They can help keep pH constant. Important in homeostasis

Question 24

What is a zwitterion?

Answer 24

Zwitterin (also called a double ion) = Both a cation and an anion

Question 25

What is the isoelectric point?

Answer 25

pH at which the zwitterion exists at

Question 26

What is a prosthetic group?

Example? (2)

Answer 26

A non-protein component.

e.g.

- Haem groups contain Fe²⁺

- Metal ions and molecules derived from vitamins also form prosthetic groups. These are called cofactors

Question 27

Compare Globular and fibrous proteins

• 3D feature
• Solubility in water
• Role
• Examples?

Answer 27

Question 28

Compare haemaglobin and collagen

Answer 28

Question 29

What are cofactors?

Answer 29

Metal ions and molecules derived from vitamins also form prosthetic groups.

Necessary for the proteins to carry out their functions.

Question 30

Test for a protein?

Answer 30

Biuret test

Add sample to a test tube.

Add 2cm³ dulite NaOH.

Then add 0.5cm³ CuSO_{<strong>4</strong>.}

Shake test tube well.

If proteins are present it will go:

Pale blue → Purple.

If no proteins are present then it remains pale blue.

Question 31

How to use chromatography to seperate biological solutions?

Answer 31

Can be used for seperating: proteins, carbohydrates, vitamins and nucleic acids.

E.g. Seperating Amino acids

1. Conduct a paper chromatography.
2. If solution is coclourless them spray with ninhydrin.
3. Caculate the Rf = Distance travelled by compound / distance travelled by solvent.