Proteins.Proteins.

Function of proteins.Function of proteins.

Proteins are very important in living Proteins are very important in living organisms and take on a variety of forms organisms and take on a variety of forms and functions:and functions:

Enzymes.Enzymes. Antibodies.Antibodies. Actin and myosinActin and myosin Collagen.Collagen. KeratinKeratin antigensantigens

The structure of proteins.The structure of proteins.

Proteins are made up of carbon, Proteins are made up of carbon, hydrogen, oxygen and nitrogen. hydrogen, oxygen and nitrogen. Sometimes sulphur is present.Sometimes sulphur is present.

Proteins are polymers made up of Proteins are polymers made up of the monomers called amino acids.the monomers called amino acids.

There are 20 different amino acids.There are 20 different amino acids. Amino acids can join up in any order Amino acids can join up in any order

and form an infinite number of and form an infinite number of protein molecules.protein molecules.

Amino acids.Amino acids.

Amino acids contain an amino group Amino acids contain an amino group (-NH (-NH²) and a carboxylic acid group ²) and a carboxylic acid group (-COOH). (-COOH).

Each amino acid has an R group.Each amino acid has an R group. There are 20 different R groups and There are 20 different R groups and

this is the reason for there being 20 this is the reason for there being 20 different types of amino acids.different types of amino acids.

Structure of an amino acid.Structure of an amino acid.

Carboxylic acid group

Amino group

R Group

How do two amino acids join How do two amino acids join together ?together ?

Two amino acids join together by Two amino acids join together by condensation to form a dipeptide .condensation to form a dipeptide .

A peptide bond is formed and this results in a dipeptide

What is a polypeptide?What is a polypeptide?

A chain of amino acids is known as a A chain of amino acids is known as a polypeptide.polypeptide.

Proteins can be divided into Proteins can be divided into groups.groups.

Globular proteins. These are Globular proteins. These are molecules that are often spherical in molecules that are often spherical in shape and have a chemical function shape and have a chemical function eg enzymes.eg enzymes.

Fibrous proteins . These have a Fibrous proteins . These have a structural role . They give strength or structural role . They give strength or elasticity to a particular tissue eg elasticity to a particular tissue eg keratin in hair.keratin in hair.

Four levels of structure.Four levels of structure.

Primary structure. A sequence of Primary structure. A sequence of amino acids in a polypeptide chain.amino acids in a polypeptide chain.

Secondary structure. The chain of Secondary structure. The chain of amino acids bend and twist and amino acids bend and twist and forms a stable structure that is held forms a stable structure that is held in position by hydrogen bonds. A in position by hydrogen bonds. A helix is the most common secondary helix is the most common secondary structure.structure.

Tertiary structure. The secondary Tertiary structure. The secondary structure folds to give a more three structure folds to give a more three dimensional shape. The shape is dimensional shape. The shape is maintain by hydrogen bonds and the maintain by hydrogen bonds and the stronger disulphide bridges which form stronger disulphide bridges which form between the sulphur containing amino between the sulphur containing amino acids molecules.acids molecules.

Such proteins are often called globular Such proteins are often called globular proteins. their shape is vital to their proteins. their shape is vital to their function. Eg enzymes.function. Eg enzymes.

Quaternary structure- the protein Quaternary structure- the protein consists of more than one consists of more than one polypeptide. The different polypeptide. The different polypeptide chains bind together polypeptide chains bind together to form a whole molecule. Eg to form a whole molecule. Eg insulin is made up of two insulin is made up of two polypeptide chains whilst polypeptide chains whilst haemoglobin is made up of four.haemoglobin is made up of four.

Haemoglobin is made up of 4 different polypeptide chains.

Keratin is a secondary structure protein. it has a spiral shape and is held in position by hydrogen bonds.

Haem group

Haemoglobin molecule

Globular proteins.Globular proteins.

Globular proteins have the following Globular proteins have the following characteristics:characteristics:

Irregular amino acid sequenceIrregular amino acid sequence Sequence is highly specific and never varies Sequence is highly specific and never varies

between 2 examples of the same protein.between 2 examples of the same protein. Polypeptides fold into a spherical shape.Polypeptides fold into a spherical shape. Relatively unstable structure.Relatively unstable structure. Metabolic functions.Metabolic functions. Egs enzymes, hormones and haemoglobin.Egs enzymes, hormones and haemoglobin.

Enzymes.Enzymes.

Structure and function of Structure and function of globular proteins.globular proteins.

The shape of a globular protein is very The shape of a globular protein is very delicate and vital to it’s function.delicate and vital to it’s function.

An enzyme has a precise tertiary structure An enzyme has a precise tertiary structure that provides it with it’s active site. Any that provides it with it’s active site. Any change in the shape of the active site will change in the shape of the active site will stop the enzyme from working.stop the enzyme from working.

High temperatures make the molecules High temperatures make the molecules vibrate and this causes the weak hydrogen vibrate and this causes the weak hydrogen bonds to break and as a result the shape bonds to break and as a result the shape changes. The enzyme is denatured and changes. The enzyme is denatured and will not work.will not work.

Denaturation of proteins.Denaturation of proteins.

The three dimensional shape of The three dimensional shape of proteins is maintained by hydrogen proteins is maintained by hydrogen bonds and ionic bonds which are fairly bonds and ionic bonds which are fairly weak.weak.

Any agent such as heat, acids or Any agent such as heat, acids or alkalis will break these bonds and alkalis will break these bonds and cause a change in shape.cause a change in shape.

With a change in shape the protein With a change in shape the protein can no longer carry out it’s function.can no longer carry out it’s function.

Questions.Questions.

1 Describe the general structure of an 1 Describe the general structure of an amino acid.amino acid.

2 With the aid of a diagram , show the 2 With the aid of a diagram , show the results when two amino acids are results when two amino acids are joined together.joined together.

3 Proteins may be described as having: 3 Proteins may be described as having: 4 Primary, secondary, tertiary or 4 Primary, secondary, tertiary or

quaternary structures. Explain the quaternary structures. Explain the meanings of these terms when applied meanings of these terms when applied to proteins. to proteins.

5 Describe the characteristics of a 5 Describe the characteristics of a globular protein.globular protein.

6 How is the structure of a globular 6 How is the structure of a globular protein related to it’s function?protein related to it’s function?

7 What is meant by the term 7 What is meant by the term denatured?denatured?

8 Explain how a protein may become 8 Explain how a protein may become denatured.denatured.