1.4 Proteins (general properties)

Question 1

What are the different functions of proteins?

Answer 1

1. Structural function eg myosin in muscles
2. Enzymes are made of proteins
3. Some hormones are proteins eg insulin
4. Antibodies involved in the immune response are made from protein
5. Protein receptors eg receptor for insulin
6. Transport proteins eg carrier and channel proteins in plasma membranes
7. Antigens eg recognition of the cell as self and non self

Question 2

How are proteins used as structural components?

Answer 2

In making new calls for growth and repair

Question 3

What is an amino acid?

Answer 3

Monomers that make up proteins

Question 4

What elements do amino acids contain?

Answer 4

Carbon, hydrogen, oxygen and nitrogen (sometimes sulphur)

Question 5

How many types of naturally courting amino acids are there?

Answer 5

20

Question 6

What is the general structure for amino acids?

Answer 6

Question 7

How are dipeptides formed?

Answer 7

Condensation reaction occurs between a carboxylic acid group of one amino acid and the amine group of another to form a strong covalent bond called a peptide bond.
Molecules formed are dipeptide and a water molecule

Question 8

What are the 4 levels of protein structure?

Answer 8

1. Primary
2. Secondary
3. Tertiary
4. Quaternary

Question 9

What is the primary structure of a protein?

Answer 9

The sequence of amino acids held together by peptide bonds. The primary structure determines the secondary and tertiary structure and therefore the final 3D shape of the protein

Question 10

What is the secondary structure of a protein?

Answer 10

The folding of the primary structure- the polypeptide chain either coils to form an alpha helix or folds to form a beta pleated sheet.
They are both held together by many weak hydrogen bonds which overall make the structure

Question 11

What is the tertiary structure of a protein?

Answer 11

Further folding of the polypeptide chain to give a more complex 3D shape which is closely related to the function of a particular protein (eg if it’s going to be an enzyme, hormone etc)

Question 12

What is the tertiary structure stabilised by?

Answer 12

• Hydrogen bonds - weak bonds between the R groups - easily broken by temperature and pH
•Ionic bonds - between positively and negatively charged R groups of amino acids (stronger than hydrogen bonds and can be broken by a change in pH)
• Disulphide bonds - strong covalent bonds formed between sulphurs in the R group of the amino acid cysteine (strongest bond)
• Hydrophobic interactions - between non polar R groups which tend to cluster together towards the centre of the molecule
- R groups that are not charged ( hydrophobic), would be tucked away in the centre of the protein
- R groups that are charged (hydrophilic), are found on the outside

Question 13

What are van der waals?

Answer 13

Forces between atoms

Question 14

What is the quaternary structure of a protein?

Answer 14

Proteins that are made up of more than one polypeptide chain eg haemoglobin

• haeomoglobin consists of 4 polypeptide chains - 2 alpha and 2 beta.

Question 15

What are the 2 main groups the 3D shape of molecules can be divided into?

Answer 15

• Fibrous proteins
• Globular proteins

Question 16

Describe the term fibrous protein

Answer 16

Fibrous proteins form long fibres. They have regular, repetitive sequences of amino acids and are usually insoluble in water. They tend to have structural roles in living organisms eg keratin in hair

Question 17

Give and explain an example of a fibrous protein

Answer 17

Example: collagen
(found in skin, bones and ligaments)

• made from three identical left handed helix polypeptide chains wound around each other to form a triple helix (quaternary)
• every third amino acid is glycine (which is small so it allows 3 polypeptides to pack closely together leading to high tensile strength)
• 3 chains are held together by hydrogen bonds
• collagen molecules cross link through covalent bonds to form fibres which give collagen it’s great strength

Question 18

Describe the term globular protein

Answer 18

• They fold up into a compact ball like shape (think “glob” is like “blob”).
• Tend to have a metabolic role in living organism eg enzymes, antibodies and plasma proteins all have globular structures
• tend to be more water soluble than fibrous proteins due to hydrophobic R groups on amino acids being turned inwards towards the centre of the protein
and hydrophilic R groups being on the outside
• have a wide range of amino acid sequence in their structure because they need to have a very specific 3D shape to carry out there function

Question 19

Give an example of a globular protein

Answer 19

Haemoglobin because it has a compact ball shape

Question 20

What is a polypeptide?

Answer 20

A chain of amino acids covalently bonded by peptide bonds

Question 21

What reaction links amino acids together?

Answer 21

Condensation

Question 22

What reaction breaks amino acids apart?

Answer 22

Hydrolysis