primary structure of proteins is constituted by its sequence of amino acids the first amino acid...

• Primary structure of proteins is constituted by its

sequence of amino acids

• The first amino acid makes the amino end, while

the last amino acid of the stretch makes the

carboxyl end. The primary structure is read from

the NH2-- terminal to the --COOH terminal.

• This forms a -N-C-C-N-C-C-N-C-C- backbone to

the molecules. Each amino acid is identified by its

specific R group.

How proteins are structured: 1º structureHL


•The primary structure of a polypeptide has group projecting from the N-C-C

backbone. These groups can attract each other and through hydrogen bonding

cause a folding of the amino acid chain.

•There are three noted forms of secondary structure:

•Alfa Helix

•Beta pleated sheet

•Open loops

Alpha Helix:

Formed from Hydrogen Bonds

There are 3.6 amino acid residues per turn of the helix.

This is drawn as a helix that follows the -N-C-C-N-C-

backbone of the polymer


Beta-pleated sheets:

The polypeptide chain is much more

stretched out in comparison to the

alpha helix.

This 'sheet' often has twists that

increase the strength and rigidity of

the structure.

HL

•Tertiary structure is the three-dimensional conformation of a polypeptide.

•In other words there are folds in a polypeptide chain.

•The shape is a consequence of the interaction of R-groups with one another and

with the surrounding water medium.

•The shape is maintained by intra-molecular bonds

• Hydrogen bonds

• Ionic Bonds

• Disulphide Bridges

How proteins are structured: 3º structure

HL

The structure of a protein is held together by 3 types of chemical bonds:

1. Hydrogen bonds

Between some H atoms and some O or N atoms in the polypeptide chain.

Attraction of opposite charges.

These bonds are weak but the large number of them maintains the molecule in a 3D-

shape.

2. Ionic bonds

Between any charged group that are not joined together by a polypeptide join.

They are stronger than hydrogen bonds but they can broken by changes in the pH and T.

3. Disulphide bridges

Between the S atoms of amino acids that are close together, (cysteine, methionine).

They are very strong and contribute to the strength of structural proteins such as keratin

and collagen.

4. The Hydrophobic effect helps some proteins to maintain their structure.

Disulphide bridge > Ionic bonds > Hydrogen Bonds

3º Structure: Protein bonding

A number of tertiary polypeptides joined together.

• Haemoglobin is a quaternary structure.

• It is composed of four different polypeptide chains.

• Each chain forms a tertiary structure called a haem group

Prosthetic groups: A tightly-bound non-peptide component of a protein.

• Lipids,

• Carbohydrates,

• Metal ions (e.g., iron in hemoglobin)

• or inorganic groups such as phosphates

HL

Conjugated Protein is a protein that functions in interaction

with other chemical groups attached by covalent bonds

or by weak interactions.

How proteins are structured: 4º structure

How proteins are structured HL

Fibrous proteins are water insoluble, long and narrow proteins.

They are associated with providing strength and support to

tissues.

• Collagen is the basis of the connective tissue and is

composed of three left handed helices.

• This is the most common protein in animals.

• Keratin is another common fibrous protein which is

composed of seven helices.

• Keratin is the major protein in hair and nail structure.

7.5.2 Fibrous and Globular proteins HL

Globular proteins are near soluble (colloids). They have more compact and

rounded shapes.

They are associated with functions such as:

• Pigments and transport proteins( haemoglobin, myoglobin, lipoproteins)

• Immune system (Immunoglobulins)

7.5.2 Fibrous and Globular proteins HL

Cell membrane proteins:

Polar aa –

positioning of proteins on surface of cell membrane

lining of the channel- diffusion of charged molecules and ions

Non-polar aa –

to site within the phospholipid bilayer.

7.5.3 Polar and non polar aa in protein structures

HL

7.5.4 Proteins function HL

primary structure of proteins is constituted by its sequence of amino acids the first amino acid...

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