Molecular Biology

2.4 Proteins

Made of C, H, O and N Proteins are large molecules constructed of

many amino acids Most abundant organic compound found in living

cells

Most important macromolecule in the body… Proteins Rule Everything!

Functions? Structural parts

nails, hair, cell membrane, and cartilage

Pigments skin, eyes, and chlorophyll

Hormones and receptors Muscle contractions Immunity-Antibodies Enzymes

Cytoskeleton Blood clotting Transport of nutrients/gases Cell adhesion Cell membrane transport Packing of DNA

Total energy gain is 4 Calories/gram. (however, energy gain is not their main function).

Amino acids are linked together by condensation reactions to form polypeptides.

The building blocks of proteins are amino acids.

Amino Acids

Centre carbon atomBonded to: Hydrogen (H) Amine group (-NH2) Carboxyl group (-COOH) R- group (different in each amino acid)

Amino acids are linked together by condensation reactions to form polypeptides.

The amino acids are bonded together by peptide bonds to form proteins.

The bond that is formed from the acid group (COOH) and the amino group (NH2)

Water is eliminated = condensation reaction Proteins are frequently called polypeptides

(many peptide bonds).

The smallest polypeptide consists of 20 amino acids (less than that called an “oligopeptide) Insulin contains 2 polypeptides: 21 amino acids

and 30 amino acids Human titin has 34 350 amino acids

There are 20 different amino acids used by ribosomes to make polypeptides

Draw molecular diagrams to show the formation of a peptide bond:

Locate the Amine, Carboxyl, and R-groups Show the formation of a peptide bond between 2 amino acid Try to draw an oligopeptide with all 4

Serine Glutamic acid

Alanine

Glycine

Did you notice? The amine and carboxyl are used in the peptide bonds Chain of atoms linked with single bonds form backbone H attached to N by single bond O attached to C by double bond The R-groups remain

Serine Glutamic acid

Alanine

Glycine

The amine and carboxyl group are used in the condensation reaction

The R-groups give the polypeptide its character

The R-groups provide an amazing range of proteins

Some proteins contain amino acids not contained in the list of 20.

This is due to modification after a polypeptide has been made. Example: hydroxyproline in collagen

Patterns, trends, discrepancies: most but not all organisms assemble polypeptides from the same amino acids.

We can exclude the possibility that this trend is due to chance…

What reasons would account for almost all organisms using the same 20 amino acids?These were the ones produced before lifeThese are the idealAll life evolved from a single ancestral species

Amino acids can be linked together in any sequence giving a huge range of possible polypeptides

Calculate the possibilitiesNumber of Amino Acids in the Chain

Number of possible sequences

1 201

2 202 400

3 8000

4

64 000 000

Shapes – primary (linear) secondary (β-pleated sheets and α-helix) tertiary (bent-coiled) quaternary (compact with a specific structure).

You can unfold a protein (de-nature) by exposing the protein to heat, radiation or a change in pH. (i.e. frying an egg, baking a cake, UV exposure, x-rays).

Questions

1. What 2 functional groups do all amino acids have in common?

2. Draw a generic formation of a peptide bond. Identify the amino terminus, carboxyl terminus, and peptide bond.

3. Define primary structure.4. Name the 2 types of secondary structure.

What type of bond stabilizes this structure?5. Distinguish between polypeptide and protein.6. Why do proteins have more diverse functional

roles than carbohydrates?