Proteins & Amino Acids

Enzymes

Biological catalysts that accelerate chemical reactions in living organisms by lowering the activation energy. They are typically proteins and are specific to substrates.

They speeds up the reaction

Hormones

Released by endocrine cells ( like cells of our pituitary glands)

Insulin

is a hormone produced by the pancreas that regulates glucose levels in the blood.

They bind to cells in liver and facilitated uptake of glucose. Helps return blood sugar to normal.

Amino Acids

Monomers that make up the proteins.

They are organic compounds that combine to form proteins and contain an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain and an alpha carbon.

How many amino acids are commonly found in proteins?

20

pH 7.2-7.4

amino acids is protonated and bears a positive charge

Carboxyl group

deprotonated and bears a negative charge

What determines the identity of the Amino ACids?

the R group which varies for each amino acid and determines their chemical properties.

Negatively charged amino acids [ acidic]

Aspartic acid & Glutamic acid

Positively charged [ BASIC]

Histidine

Lysine

Arginine

Amino acids polar charged

include Serine, Threonine, Glutamine and Asparagine, which have side chains that can form hydrogen bonds with water.

Non-polar hydrophobic

Alanine

Valine

Proline

Leucine

Isoleucine

Methionine

Tryptophan

phenylalanine

glycine

Proline

Forming a ring structure

Causes bends or kinks in amino acid chains

Cysteine

contain a thiol ( SH) group

Peptide bonds

are covalent bonds that connect amino acids in proteins.

they form through dehydration ( condensation) reaction

-C^=O- NH

One end is N-terminus and other end is C-terminus

Amino acids that is not chiral

Glycine

All 20 amino acids have both their amino and carboxyl groups attached to the

alpha carbon

Aspartic acids

Asp, D

Glutamic acid

Glu, E

Lysine

Lys , K

Arginine

Arg, R

Histidine

His , H

Tryrosine

Tyr, Y ( polar, hydrophilic aromatic )

Phenalyanine

Phe, F ( non-polar, aromatic AA)

Tryptophan

Trp, W ( Hydrophic -aromatic )

Serine

Ser, S

Threonine

Thr, T

Cysteine

Cys, C

Asparagine

Asn, N

Glutamine

Gln, Q

Glycine

Gly, G

Alanine

Ala, A

Valine

Val, V

Leucine

Leu, L

Isoleucine

ILe, I

Methionine

Met, M ( thioether group)

Proline

Pro, P

Amino acids structure

Essential amino acids

Body cannot synthesize must be obtained from the diet.

• Histidine

• Leucine

• isoleucine

• lysine

• methionine

• phenylalanine

• threonine

• tryptophan

• valine

Non-essential amino acdids

Can be synthesized by the body

• Alanine

• asparagine

• aspartic acid

• glutamic acid

• serine

• arginine

• cysteine

• gkutamine

• glycine

• proline

• tyrosine

Post-translational modifications

• Phosphorylation:- addition of phosphate group (serine, threonine & tyrosine)

• Glycosylation:- attach carbohydrate groups, affect protein stability, folding and cell recognition

• Acetylation & Methylation:- On lysine residue

• Ubiquitination:- ubiquitin binds to lysine residues, taggs protein for degradation

Simplest level of protein structure

primary structure

sequence of amino acids in a polypeptide chain

sequence of a protein is determined by the DNA of the gene that encode the protein

T or F. A change in the gene’s DNA sequenece may lead to change in the amino acid sequence of protein

TRUE

Sickle cell diseasea

Sixth amino acid change from glutamic acid to valine

local folded structures that form within a polypeptide due to interactions between atoms of the backbone.

Secondary structure ( alpha helics & beta sheets )

Proline

Tertiary structures

Three dimensional folding due to side chain Interactions between the R groups of the amino acids that make up the protein.

Include hydrogen bonding, ionic bonding, dipole-dipole interactions and london dispersion forces.

Hydrophobic interactions

Disulfide bonds

quaternary structure

• Multiple polypeptide chains known as subunits

• An example :- hemoglobin, DNA polymerase

Denatured protein

When a protein loses its higher order structure ( secondary, tertiary, quaternary) but not its primary sequence

They are non- functional

Chaperones

Heat shock proteins

ensure correct protein folding

prevent aggregation

Reversible denatration

Protein can refold into its native structure upon removing the denaturing agent

Irreversible denaturation

Results loss of protein structure and function often due to covalent modifications or aggregation of denatured proteins

Chiral configuration that is found in the human body

L-form

L- configuration

NH2 on left side ( fischer)

D- configuration

on the R side

enantionmers

isomers