Proteins!

ProteinsProteins account for more than 50% of the

dry mass of most cellsMonomer: amino acids

20 amino acids used in cellsCentral carbon atomOne hydrogen attachedAmine (NH2) and carboxylic acid (COOH)

groups attached to carbonOnly thing different is side chain…R-

group (side chain)Responsible for 3D shape of protein

Polymer: polypeptide chains (proteins)Link between monomers is called:

polypeptide bond or PEPTIDE bondMade by a dehydration reaction (between amine group of one aa and

carboxyl group of another aa)

Functions of ProteinsStructural support/strengtheningCatalysts (enzymes)StorageTransportCellular communicationsMovementDefense against foreign substances

Some famous proteins…

Essential components of cell membranes

Oxygen-carrying pigment hemoglobin (haemoglobin)

Antibodies which attack and destroy invading microorganisms

Enzymes!Collagen! (fibrous)

Amino Acids20 -23 major AA (others have been

synthesized in labs)STRUCTURE

Amino group on one end (-NH2)Carboxylic acid group on one end (COOH)HydrogenR-group/side chain (changes)

Glycine

Alanine

Peptide Bond When two amino acids (AA#1 and AA #2) join,

…AA #1 loses a hydroxyl group (-OH) from its

carboxylic acid (-COOH) sideAA #2 loses a hydrogen from its amine (NH2)

groupThe Carbon atom in the carboxyl group of AA#1

is now free to make ONE bond with the Nitrogen of the amine group in AA#2

This bond is called a PEPTIDE Bond H- and –OH removed…what is this???

WATER!!! Another condensation reaction

(dehydration) Dipeptide Molecule New molecule formed by joining 2 amino acids Polypeptide Molecule Molecule made up of many amino acids joined

by peptide bonds Polypeptide is the POLYMER (not protein) Complete protein may contain one polypeptide

chain, twisted and folded or two or more polypeptide chains interacting with each other

Polypeptide bonds

DEHYDRATION!!!

Where are amino acids linked?In living cell

Ribosomes!These reactions that

occur on the ribosomes are controlled by ENZYMES (more on this later)

How are polypeptides broken?

Hydrolysis ReactionsNaturally occurs in

stomach and small intestine

Protein in food is hydrolyzed into amino acids prior to being absorbed by the blood

Once in the blood, these AA can be restructured into polypeptides and then twisted and folded into functioning PROTEINS the cells in you body needs

Protein Structure Primary structure 1’ Order of amino acids in a polypeptide chain

Secondary structure 2’ Polypeptide chain folds because of interactions

between amino acids HYDROGEN BONDING

Tertiary Structure 3’ Gives proteins 3-D shape

VERY IMPORTANT to function of protein Beta pleated sheets and alpha helices fold based on

interactions between R-groups of a.a. Hydrogen bonds, polar/non-polar interactions,

acid/base interactions, disulfide bonds, van der Waals forces

Quaternary Structure 4’ the association of the polypeptide chains some proteins contain more than one polypeptide

chain Each polypeptide chain in the protein is called a

subunit Two or more subunits come together for a specific

function HEMOGLOBIN

On Red blood cells Its shape allows RBCs to carry oxygen all around your

body!

Practice Set 4(6 MC and 1 SAQ)

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