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Lesson 4 – Proteins Amino Acid Structure and the Peptide Bond. Heteropolymers. Proteins are heteropolymers . The amino acids they are made of are similar but different from each other. There are only ______ different amino acids that human proteins are made from. 20. Amino Acid Structure.

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slide2

Heteropolymers

Proteins are heteropolymers. The amino acids they are made of are similar but different from each other.

There are only ______ different amino acids that human proteins are made from.

20

slide4

Isomerism in Amino Acids

Like carbohydrates, amino acids also exist as D-form and L-form isomers. The L-form is found exclusively in proteins.

slide6

Ionised Forms

If the pH of the solution is neutral (like in a biological system) any amino acids in solution will be ionised.

slide7

R- Groups

The R-groups give the amino acids their unique chemical properties.

There are 4 classifications of R groups:

Acidic, Basic,Uncharged polar and Nonpolar

slide8

Amino Acid Classes

Copy the table below and complete with the information from the slides that follow.

slide9

Acidic R Groups

Of the 20 amino acids there are 2 that are acidic. They both have carboxyl groups that ionise to make them acidic.

-COOH

Aspartic Acid

Glutamic Acid

Asp

D

Glu

E

slide10

Acidic R Groups

Both acidic amino acids are hydrophilic.

On your desks list the 2 acidic amino acids. Include their 3 letter abbreviation and single letter code.

Aspartic Acid

Glutamic Acid

Asp

D

Glu

E

slide11

Basic R Groups

There are 3 different amino acids with basic R groups. All have additional amino groups that ionise to NH3+. All are hydrophilic. Lysine is an example of a basic amino acid.

-(CH2)4NH2

Lysine

Lys

K

slide12

Uncharged Polar Groups

There are 5 amino acids which are uncharged and polar. All are hydrophilic. These all have different functional groups most containing at least one –OH group. We will learn 2 – serine and asparagine.

Serine

Ser

S

Asparagine

Asn

N

slide13

Non-polar

There are 10 amino acids which are non-polar. All are hydrophobic. Their R groups are hydrocarbons. We need to know 3 of these: glycine, alanine and cysteine.

Cysteine

Cys

C

Glycine

Gly

G

Alanine

Ala

A

slide14

Peptide Bonds

Amino acid monomers are linked together to make a polypeptide through dehydration synthesis (condensation reaction).

The –OH from one amino acid bonds to the -H from the -NH2 group on another amino acid.

slide15

Test Yourself

On your desk draw the structure of an amino acid (just include a generic R group).

Now change the R group to make it an acidic amino acid and name the one you have drawn.

Now change the R group make it a basic amino acid and name the one you have drawn.

Same to uncharged polar.

Finally for nonpolar.

slide16

Your Task- Amino Acids

Past Paper Questions

You will need to access these in the department. Please DO NOT TAKE past papers home – we have limited numbers.

2002 MC Q4

2004 MC Q13

2. Complete Scholar activities on amino acids.

3. Read and make notes on pages 30-35

4. Make sure your glossary is up to date.

DUE Monday

(November 19th)