2.2 Proteins

Question 1

What are proteins formed from?

Answer 1

Amino acids

Question 2

How many different amino acids are there?

Answer 2

20

Question 3

What is the structure of amino acids ?

Answer 3

• consists of amine group ( N bonded to two H
• consists of carboxyl group ( C with a double bond to O and single bond to hydroxyl group, OH )
•R group which is different for each of the 20 amino acids

Question 4

What elements do amino acids contain?

Answer 4

Carbon, hydrogen, nitrogen and oxygen
•some amino acids also contain the element sulfur

Question 5

What bond is formed between two amino acids?

Answer 5

Peptide bond (Dipeptide)

Question 6

What is the first level of protein structure called ? And what is it?

Answer 6

Primary structure - the specific order of amino acids in a polypeptide

Question 7

What is the second level of protein structure called? And what is it?

Answer 7

Secondary structure - the coiled alpha helix shape or the beta pleated sheet shape formed due to hydrogen bonds

Question 8

What is the tertiary structure of protein?

Answer 8

The overall 3 dimensional shape of a polypeptide chain

Question 9

What is the quaternary structure of protein?

Answer 9

Shows how the individual subunits are arranged to form a larger 3 dimensional structure

Question 10

Do all proteins have a quaternary structure?

Answer 10

No, quaternary structure only applies to proteins with at least 2 subunits

Question 11

What do scientists call polypeptide chains ?

Answer 11

Subunits

Question 12

What are prosthetic groups?

Answer 12

non-protein molecules forming part of the quaternary structure (in conjugated proteins)

Question 13

What do prosthetic groups do? Give an example

Answer 13

Help the protein carry out its role
E.g. haemoglobin contains the prosthetic group haem which binds to oxygen

Question 14

What are proteins with a prosthetic group called?

Answer 14

Conjugated proteins

Question 15

What bonds are in proteins?

Answer 15

Hydrogen bonds
Ionic bonds
Disulphide bonds

Question 16

What are features of globular proteins?

Answer 16

•Tend to have a spherical shape
•soluble in water- have got hydrophilic amino acids on their surface—> the hydrophilic R groups can interact with water molecules
•hydrophobic amino acids in the centre of the protein

Question 17

What are hydrophilic amino acids?

Answer 17

Amino acids that have R groups which are attracted to water

Question 18

What are hydrophobic amino acids?

Answer 18

Amino acids that have R groups that are not attracted to water

Question 19

Globular protein- haemoglobin

Answer 19

•4 polypeptide subunits
-2 are called the alpha subunits and 2 are called the beta subunits
•Each subunit contains the prosthetic group haem ( haemoglobin is a conjugated protein)
• Each haem group contains an Fe2+ ion, this is where the oxygen binds
—-> One haemoglobin molecule can bind to four oxygen molecules

Question 20

Globular protein- insulin

Answer 20

•Consists of 2 polypeptide chains linked by disulfide bonds

Question 21

Globular protein- lysozyme

Answer 21

•Found in saliva and tears
•job is to catalyse the breakdown of a molecule in the bacterial cell wall, helps to defend the body against bacteria
•Consists of a single polypeptide chain, which folds to form a groove along the surface (active site)

Question 22

What are examples of globular proteins?

Answer 22

Insulin, haemoglobin and the enzyme lysozyme

Question 23

What are examples of fibrous proteins?

Answer 23

Collagen, keratin and elastin

Question 24

Features of fibrous proteins

Answer 24

•Often play a structural role
•Form long rope-like molecules
•Large proportion of amino acids with hydrophobic R groups —> fibrous proteins are INSOLUBLE in water

Question 25

Fibrous protein- collagen

Answer 25

•Found in tendons, ligaments and skin
•Strong molecule due to its structure—-> the polypeptide chains wrap tightly together to form a triple helix
•In collagen polypeptides, every third amino acid is glycine (R group of glycine is a hydrogen atom) Which means glycine has the smallest R group of any amino acid-> allows the collagen polypeptide to wrap tightly around each other, LOTS of hydrogen bonds helping to stabilise the quaternary structure

Question 26

Fibrous protein- keratin

Answer 26

•Found in hair, nails and the outer surface of skin
•Strong molecule
•Consists of long stranded molecules
•Contains high proportion of the amino acid cysteine-> large number of disulfide bonds

Question 27

What are disulfide bonds?

Answer 27

Strong covalent bonds

Question 28

Features of globular proteins

Answer 28

• often have spherical shape, any hydrophobic r groups r turned inwards towards tge centre of the molecule while hydrophillic groups r on other side SOLUBLE