Primary structure

Proteins• Proteins contain Carbon (C), Hydrogen (H), Oxygen,

Nitrogen (N) and sometimes Sulphur (S)

• The monomer units of proteins are called Amino Acids

• Single Amino Acids can be joined together by a Peptide bond to form a Dipeptide

• Long chains of amino acids are called Polypeptides

• Proteins are formed by one or more polypeptides.

Secondary structure

• Hydrogen bonds form because O has a weak negative charge and H has a weak positive charge……if they get close then a Hydrogen bond (a H bond) forms.

• Individually hydrogen bonds are weak, but because the molecule has A LOT of them, collectively they are strong

Secondary structure

Tertiary structure The Tertiary structure of a protein is held

together by 3 different types of bonding:

1) Hydrogen bonding between R groups.

2) Ionic bonding (between positively and negatively charged R groups).

3) Disulphide bonds (between R groups containing sulphur)

Bonds Holding Tertiary Structure

Hydrogen Bonds H OH

Ionic Bonds + -

Disulphide Bonds S S

Tertiary structure

GLOBULAR PROTEINS

• Their overall tertiary structure (3d shape) is important for their function

• They may contain more than one type of secondary structure

QuaternaryStructure

of Insulin – a Globular

protein

Characteristics of Globular Proteins:

• They are soluble

• Their function depends on their overall shape – the protein will fit other molecules with a specific complementary shape.

Good Examples of Globular Proteins:

• Enzymes, Receptor proteins on membranes, Channel proteins and Carrier proteins in membranes, Cell recognition proteins.

• Globular proteins have “biochemical” roles

REMEMBER

• THE FUNCTION OF ALL PROTEINS DEPENDS ON THEIR SHAPE.

• THIS IS DETERMINED BY THE ORDER OF AMINO ACIDS IN THE PRIMARY STRUCTURE.

Write this & don’t forget it!• It is the primary structure of a protein (the

sequence of amino acids) that determines what its overall shape will be.

• Any change in the sequence of these amino acids may change the position of the hydrogen/ionic/disulphide bonds that hold the tertiary structure together.

• This may then have the effect of changing the tertiary shape of the protein, so that…..

• …..now the protein can no longer function!

FIBROUS PROTEINS

• Secondary structure can be α helix or β pleated sheet

• There may be several polypeptide strands associated together and with H bonding between them.

CHARACTERISTICS

• Insoluble.

• Tough fibres and strong, flexible sheets.

• eg Keratin (in hair and nails), Collagen (in skin, tendons, bones, teeth), spider web silk.

Collagen - A fibrous protein

• ¼ of all of the protein in the human body is collagen

• Collagen is a major structural protein, that strengthens tendons and supports the skin and internal organs

• Bones and teeth are formed from collagen bonded to other minerals

Collagen - A fibrous protein• Collagen is composed of three chains,

wound together in a tight triple helix

• Each chain is 1000+ amino acids long (only 20 are shown on the next slide)

• A repeated sequence of three amino acids forms this sturdy structure (every third amino acid is glycine

This is what collagen looks like

return

Fibrous (Quaternary)

Structure of Collagen

Collagen - A fibrous protein

TASKS TO DO:1) Do Q5 p45 textbook.

2) Now mark answers from p45 Q1-5 using p244 section 3.2

3) Mark answers to Q1,3,4 p49 using p244 section 3.3

4) Do Q1 p67 peach box

5) Check answers to Q1 p67 on p245 section 3.10

6) Do Exam Q4 on p119