PROTEINS: SECONDARY

AND TERTIARY STRUCTURE

Lesson 5

SUCCESS CRITERIA Explain the term secondary structure Explain the term tertiary structure

STARTER Draw the structure of a protein and label

it in as much detail as you can

KEY TERM: SECONDARY STRUCTURE The coiling and pleating of parts of the

polypeptide molecule

SECONDARY STRUCTURES Alpha Helix or Beta Pleated Sheet Hydrogen bonds hold the structure in

place Hydrogen bonds form between oxygen

and hydrogen atoms Although hydrogen bonds are quite

weak, as many bonds are formed they add stability to the structure of the protein

ALPHA HELIX Right hand coil, where

hydrogen bonds form between oxygen and hydrogen atoms bought into close proximity

Stabilises the protein

Alpha helix

HYDROGENBOND

BETA PLEATED SHEET Amino acid chain folds

up on itself forming anti-parallel chains

O and H atoms bought in close proximity to each other form hydrogen bonds

Stabilises the protein

Beta pleated sheet

TASK Make plasticene models of alpha helix

and beta pleated sheet Describe the structures to the person

next to you

KEY TERM: TERTIARY STRUCTURE The overall 3D structure of the protein

molecule

TERTIARY STRUCTURE The final 3D shape of the protein is

formed when the polypeptide chain with the coils and pleats fold themselves

The 3D shape is held in place byHydrophobic and hydrophilic interactionsDisulphide bonds Ionic interactions

Primary

Secondary

TertiaryQuaterna

ry

LEVELS OF PROTEIN STRUCTURE

TASK In groups of 4 each person gets a

quarter of an OHT to explain one of the following:Tertiary structureHydrophobic and hydrophilic interactionsDisulfide bonds Ionic interactions

You will then present to the class

HYDROPHOBIC AND HYDROPHILIC INTERACTIONS Many hydrophobic R groups tend to

cluster towards the interior of the protein molecule forming Hydrophobic Interactions

Hydrophilic R Groups tend to be found on the outside of proteins

DISULPHIDE BONDS R groups of two amino acids

contain sulphur atoms (e.g. cysteine)

If these atoms are in close proximity they form DISULPHIDE BONDS

IONIC INTERACTIONS Many of the carboxylic acid and

amino groups form charged groups in solution. Oppositely charged groups form IONIC BONDS

TERTIARY STRUCTURE The proteins shape is vital to each

function Three examples are

EnzymeHormone ReceptorCollagen

Why is shape important in these three cases?

ANSWERS Enzyme: fit of the active site to its

specific substrate Hormone receptor: hormone won’t bind

unless specific shape Collagen: shaped for strength

3D PROTEIN SHAPES Globular

Ball structureHydrophobic amino acids turn inwards and

hydrophilic interactions turn outwards making them water soluble

E.g. enzymes Fibrous

Form fibresRegular repetitive amino acid sequencesUsually insolubleE.g. collagen

SUCCESS CRITERIA Explain the term secondary structure Explain the term tertiary structure

PLENARY Draw the structure of a protein and label

it in as much detail as you can

HOMEWORK Complete the next part of the summary

table