Proteins & Nucleic AcidsProteins & Nucleic Acids

Images taken without permission from http://upload.wikimedia.org/wikipedia/de/4/4d/Protein_GFP_1EMA.png, http://cmgm.stanford.edu/biochem201/Slides/Protein%20Structure/Levels%20of%20Protein%20Structure.JPG, http://www.lakemichigancollege.edu/dept/Arts-Sciences/bio/pics/DNA.gif

Proteins: A General Overview

• Biological roles: enzymes, structural components, hormones, immune function, storage, transport, muscle contraction

• Monomer = amino acid

• Polymer = polypeptide chain (protein)

Monomer = amino acid• There are 4

components attached to a central carbon

• There are 20 different amino acids

R

C

H

C

OOHNH

H

Amino group

Central carbon

Carboxyl group

R group

• the R group for each amino acid is different determines its properties

hydrogen

Classes/Categories of Amino Acids

• The R group determines the class/category of an amino acid

• General categories:– Nonpolar– Polar– Positively Charged– Negatively Charged

Peptide Bonds• Formation of a protein occurs when amino

acids covalently bond through the formation of a peptide bond.

• What kind of reaction forms a peptide bond?– Dehydration reactionR

C

H

C

OOHNH

H

R

C

H

C

OOHNH

H

+

R

C

H

C

O

NH

H

R

C

H

C

OOHN

H

+ H2O

Peptide bond

Four Levels of Protein Structure

• Primary

• Secondary

• Tertiary

• Quaternary– Only proteins with multiple chains will have

this level of structure

All proteins have primary, secondary and tertiary structure

Primary Structure (1°)

• The sequence of amino acids

• All other structures are based on this level of structure

Primary Sequence of Hemoglobin Chain A: VLSPADKTNVKAAWGKVGAH......etc

N terminusC terminus

Secondary Structure (2°)

• Local helical coiling (alpha helix) or pleated sheet (beta sheet) formations in the chain

• Patterned formations based on hydrogen bonds between non-adjacent amino acids

Tertiary Structure (3°)

• The way the polypeptide chain is folded three dimensionally.

• Is brought about through the following interactions:– Disulfide bridges– Ionic interactions– Hydrophobic interactions– Hydrogen bonds

Quaternary Structure (4°)

• Interaction between two or more polypeptide chains.

Important Protein Concept

• Changes in protein structure can lead to disease

• Ex. Sickle cell anemia = disease caused by a single amino acid substitution in the chain of hemoglobin

Image taken without permission from http://www.sciencecollege.co.uk/SC/natural_selection/sickle_cell.jpg

Protein Folding

• Proteins are folded into the appropriate formation during or after protein synthesis

• Certain conditions such as temperature, pH, and salt concentrations can alter the shape of a protein

• Chaperonins assist to fold proteins correctly in the cell – Think “chaperones”

Denaturation = unfolding of protein

Nucleic Acids

• Biological roles = Store/carry genetic information, form part of ribosomes, energy carriers

• Monomer = Nucleotide (A, T, C, G)

• Polymer = Nucleic Acid– DNA– RNA

O

OO

O

O

O

O

OPO

O

O

N

NH2C

O

PO

O

OH2C

O OPOO

H2C

P

H2C

P

O

N

N

N

N

N

N

N

HH

N

H

H

N

O

N

O

H

H

N

H H

N

N

O

P

N

P

P

P

CH2

P

O

O

O

O O

O

O

OO

O

O

OO

O

O

O O

O

O

OO

NH

N

O

N

NHH

HH

N

N

N

N

N

NN

N N

NO

H

H

H

O

O

O

O

CH2

O

O

O

CH2

CH2

Nucleotide Components• Consist of 3 parts:

• Phosphate group

• 5 carbon (pentose) sugar

• Nitrogenous base– A, T, C, G, U (RNA

only)