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Learning Outcome

• Protein folding • Explain how one strand of mRNA can give

rise to many proteins by ….– Pre-transplational modificayion (process of

alternative RNA splicing)– Post-translational modification (cutting, combining

polypeptide chains, addition of groups)

Why is shape important?

Protein shape and folding .....• A string of amino acids (polypeptide chain)• Charges on the amino acid causes hydrogen

bonding either folds of coils

Further interactions between side chains (R group on amino acids)

Amino acids linked by peptide bonds to form polypeptide and then chains form 3D shapes of protein

Amino AcidsPolypeptide (chain of aa)

Coils into helix

Beta sheets

Elastin proteins

Fibril proteins

Conjugated proteins

Globular proteinsFibrous proteins

Proteins have a wide variety of structures and shapes resulting in a wide range of functions!

Elastin proteins

Fibril proteins

Conjugated proteins

Globular proteins

Fibrous proteins

Enzymes

AntibodiesHormones & recpetors

Why is shape important?

Pre

-tra

nsla

tiona

l Mod

ifica

tion

Alte

rnat

ive

splic

ing

However, multiple introns may be spliced differently in different circumstances, for example in different tissues.

3 541 2

1 2 3 5Heart muscle

1 43 5Uterine muscle

Thus one gene can encode more than one protein. The proteins are similar but not identical and may have distinct properties. This is

important in complex organisms

Post-Translation Modification

2 main methods of modification;• Cutting/Cleavage• Addition

Cleavage

Cleavage and Cutting

• Some hormones are produced in an “immature” form, and require further cutting to get the active peptide hormone.

• Pro-hormones are cut into final form by peptidases (enzyme) in the Golgi apparatus.

• Cutting usually occurs at basic amino acids (lysine, arginine)

Inhibin alpha

Inhibin alpha

processing

Molecular Addition

• Modification by adding different groups such as carbohydrate component (eg. glycoprotein for membrane)and phosphate group (eg. regulatory proteins such as p53)

• p53 is a tumour repressor protein – only needs to be active (with a phosphate group) if the cell DNA becomes damaged. •When made for active form is needed phosphorylation occurs which adds a phosphate group. •p53 then can either repair the DNA, or if not able then it causes programmed cell death (apoptosis)

Demonstrate your knowledge by summarising .....

Separating Proteins

• Process called electrophoresis• Separates on charge and size• Useful for analysis/identification and purification

Charge Separation

Size Separation

Analyze

Identify

PurifyMixture of Charged

Molecules

Positive Molecules

Negative Molecules

Electrophoresis

Definition• Electro = Charge + Phorsesis=

Carry

• Electrophoresis = Separation of charged molecules by differences in their rate of migration in an electric field.

Agarose Gel

• Mesh of gel sepeartes size

• Electrical Charge then placed across to separate.

Name 5 functions of proteins;

Name 5 functions of proteins;

• Enzymes• Structural proteins • Hormones• Antibodies• Associations with other chemicals