Amino acids and proteins Section 13.10 (pages 326-329)

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Amino acids and proteins Section 13.10 (pages 326- 329)

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Transcript of Amino acids and proteins Section 13.10 (pages 326-329)

Polymer Properties by Design

Amino acids and proteinsSection 13.10 (pages 326-329)Amino acidsAmino acids contain at least one amino group and one carboxylic acid group (they are an example of bifunctional compounds)-amino acids are particularly important in living systems.

-carbonNaming the amino acidsAmino acids are usually referred to by their trivial names as this is usually shorter than the systematic name. (see sheet)Thinking about amino acidsWeve just said that they have (generally) one amino group and one carboxylic acid.What can you tell me about each of these functional groups?The amino group is basic.The carboxylic acid is acidic.

A quick recap on acids and basesWe think of them as proton acceptors and donators.

Thinking about amino acidsSo what?The ends can react with each other and we get :

This is called a zwitterion (the name for a particle containing both +ve and ve charged groups)

Physical properties of amino acidsHave you ever seen a sample of amino acids?They are crystalline solidsThey area also highly soluble in water because they are effectively ionicAnd (unless there is another ionisable group) they are neutral in aqueous solutionAmino acids in solutionThey form what we call buffer solutions. (?)A buffer solution is a solution that can withstand the addition of small amounts of acid or alkali with little change to the pH.

HO- + H3N+-CHR-COO- H2O + H2N-CHR-COO- H3O+ + H3N+-CHR-COO- H2O + H3N+-CHR-COOH

Peptides (or poly peptides)An amines can react with a carboxylic acid to form a secondary amide.Water is eliminated so this is a condensation reactionWhen this happens between amino acids we call the secondary amide group a peptide link

Read from N terminus9The structure of proteinsThe Primary structure is the unique sequence of amino acids (residues).Most proteins have a precise shapeSecondary structure refers to the initial folding. Two common arrangements are sheets and helices

Read from N terminus10The () helixEach carbonyl (C=O) forms a hydrogen bond with an N-H group 4 peptide links along.

Read from N terminus11The (- pleated) sheetChains lying along side each other

Read from N terminus12Tertiary structureAfter regions of secondary structure have formed many proteins fold further to give their final shape, the tertiary structure.As well as Hydrogen bonds the following are also very importantInstantaneous dipole-induced-dipoleIonic bondsCovalent bonding

Read from N terminus13HydrolysisThis can be done by heating in in a moderately concentrated acid or alkali solutionIn living organisms this hydrolysis is catalysed by enzymesChromatography can be used to identify individual amino acids present in a polypeptide.

Read from N terminus14SummaryAmino acids exist as zwitterions.Protein structure has three levels.There are four kinds of bonding involved in protein structure: what are they?