Post on 25-Jan-2022
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