Macromolecules: proteins & nucleic acids

Building Blocksof Life

2007-2008

PROTEINS

• Most structurally/functionally diverse macromolecule group

• Involved in almost everything: • enzymes : pepsin, amylase, • structure : keratin, collagen• carriers & transport : hemoglobin, aquaporin• cell communication : insulin, hormones, receptors• defense : antibodies • movement : actin & myosin• storage : seed coat proteins

monomer = amino acids• 20 different amino acids

polymer = polypeptide

• amino acids bound together with covalent peptide bonds

• protein can be one or more polypeptide chains folded & bonded together

• large & complex 3D molecules

hemoglobin

H2O

Dehydration forms peptide bonds

Structure

Amino acids

• Central C & an H

• Functional groups:• amino group• carboxyl group (acid)

• R group (side chain)• Variable; different for each amino acid• confers unique chemical properties

to each amino acid

—N—H

HC—OH

||O

R

|—C—

|

H

R group determines molecule charge

charge affects polypeptide folding Ex: a point mutation in hemoglobin :

> changes the amino acid, > changes the charge > changes the protein shape > deforming the cell

R Group

Building proteins

Peptide bonds

• Covalent; via dehydration,• Between NH2 (amine) of

one amino acid & COOH (carboxyl) of another

• C–N bond formed

peptidebond

dehydration synthesis

H2O

Primary (1°) structure

Sequence of amino acids in chain• amino acid sequence

determined by gene (DNA)

• change in sequence can be a change in charge which can cause change in protein structure and function

sequence -> structure -> function

Secondary (2°) structure

• Folding and coiling along short sections of polypeptide (local folding)

• H bonding between

R groups of adjacent

amino acids

-helix

-pleated sheet

Tertiary (3°) structure

Interactions between distant amino acids

hydrophobic interactionscytoplasm is aqueous;nonpolar amino acids organize away from water

• H bonds, ionic bonds,

disulfide bridges

Finally, a Protein

Sulfur containing amino acids

disulfide bridges• covalent bonds between sulfhydryl groups (SH)

stabilizes 3-D structure

Keratin protein in hair has many disulfide bridges – keeps its shape

Quaternary (4°) structure

• 2+ polypeptides bonded and folded together

Collagen

skin & tendons

Hemoglobin

Fe containing protein that carries O2 in

blood

Recap: protein structure

amino acid sequence

peptide bonds

1°

determinedby DNA

R groupsH bonds

R groupshydrophobic interactions

disulfide bridges(H & ionic bonds)

3°multiple

polypeptideshydrophobic interactions

4°

2°

Protein denaturation

Unfolding a protein

• disrupt bonds & bridges

temperature • pH • salinity

• alters shape• destroys functionality

many cannot return to

functional shape

Nucleic Acids

2006-2007

Informationstorage

protein

DNAThe genetic material• stores information

Genes = template for proteins• DNA RNA proteins trait

• transfers informationtemplate for new cells

template for next generation

to

to

trait

• Structure• monomer = nucleotide• adenine, guanine, thymine, cytosine,

uracil

• Types• RNA (ribonucleic acid)

• single helix, ribose, uracil

• DNA (deoxyribonucleic acid)• double helix, deoxyribose, thymine RN

A

DNA

Examples

Nucleotides

3 parts • nitrogen base

• pentose sugar (5C)ribose in RNA

deoxyribose in DNA

• phosphate (PO4) group

I’m the A,T,C,G or U

Types of nucleotides

• purines• double ring N base • adenine (A)• guanine (G)

• pyrimidines• single ring N base • cytosine (C)• thymine (T)• uracil (U)

Purine = AG“Pure silver”

Nucleic acid

Dehydration synthesis -> covalent bond aka phosphodiester

between hydroxyl & phosphate groups polymer ‘backbone’

Base Pair rule

• H-bonds between DNA nucleotide N-bases• Base-pair rule:

• purine pairs with pyrimidine

A :: T2 H bonds

G ::: C3 H bonds

Copying the Code

o DNA helices are complementary • via base-pair rule • can replicate entire molecule

o To reproduce cell via mitosiso To make gametes via meiosis

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”

James Watson & Francis Crick 1953

. oCan build RNA complement• aka transcription of genes

• for eventual translation into protein

Copying the Code