Biochemistry & Cell Biology

PHR213 / Lecture – 03

Fall 2019

What Are Proteins?

Macromolecules

Made up of chains of amino acids

Are found in every cell in the body

Are involved in most of the body’s functions and life processes

The sequence of amino acids is determined by DNA

Elemental Composition of proteins

Major Elements: Carbon, Hydrogen, Oxygen, Nitrogen and sulfur

Other elements: P, Fe, Cu, l, Mg, Mn, Zn etc.

Structural classes of proteins

Based on the number of amino acids in a chain:

Peptides:

Proteins:

fewer than 50 amino acids

Dipeptides: 2 amino acids

Tripeptides: 3 amino acids

Polypeptides: more than 3 amino acids

more than 50 amino acids

Amino Acids

R

H

COOHH2N Cα

A central chiral carbon Four groups connected to the alpha carbon

Hydrogen

Side chain Varies with different AA

Acidic groupCarboxylic acid

Basic groupAmino group

The alpha carbon (Cα) in organic molecules refers to the first carbonatom that attaches to a functional group.

α-amino acids: In amino acids, the amino and carboxylate functionalgroups are attached to the same carbon, the so-called α–carbon.

Amino Acids

Properties Amino Acids

Solubility: soluble in water and insoluble in organic solvents

Melting points: above 200˚C

Melting points:Sweet - Gly, Ala, ValTasteless - LeuBitter - Arg, Ile

Optical properties: Optically active – except glycine

Properties Amino Acids

Ampholytes: can donate a proton or accept a proton

Zwitter ion: hybrid molecule - positive and negative ionic groups

Classification of Amino Acids

Classification based on Structure

Amino acids with aliphatic side chains

Amino acids containing hydroxyl group

Amino acids containing sulfur

Acidic amino acids

Basic amino acids

Aromatic amino acids

Classification of Amino Acids

Non-polar aliphatic R groups

Polar uncharged R groups

Positively charged R groups

Negatively charged R groups

Classification based on polarity

Classification of Amino Acids

Classification based on Nutrition

Essential or indispensable amino acids

Semi-essential amino acids

Non-essential or dispensable amino acids

Classification of Amino Acids

Essential or indispensable amino acids

cannot be synthesized by the body

supplied through the diet

required for proper growth and maintenance

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

Classification of Amino Acids

Semi-essential amino acids

can be synthesized by adults and not by growing children

Classification of Amino Acids

Non-essential amino acids

body can synthesize

alanine, aspartic acid, asparagine, glutamic acid, serine

Classification of Amino Acids

Glucogenic amino acids precursors for the formation of glucose or glycogenEx: Alanine, Aspartate

Ketogenic amino acids precursors for the formation of fatEx: Leucine, Lysine

Ketogenic amino acids precursors for glucose as well as fatEx: Phenylalanine, Tryptophan

Thank you