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Proteins & 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
R group
Carboxyl
components
group
Amino
R
attached to a
group
O
central carbon
H N C C OH
• There are 20
different amino
H H
acids
Central
hydrogen
• the R group for each amino
carbon
acid is different determines
its properties
Classes/Categories of Amino Acids
• The R group determines the class/category
of an amino acid
• General categories:
–
–
–
–
Nonpolar (contains only nonpolar bonds)
Polar (contains polar bonds)
Positively Charged
Negatively Charged
Hydrophobic
Hydrophilic
Ionic
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?
Peptide bond
– Dehydration synthesis reaction
R
H
N
C
H
H
O
C
R
OH + H
N
C
H
H
O
C
R
OH
H
N
C
H
H
O
C
R
N
C
H
H
+ H2 O
O
C
OH
Four Levels of Protein Structure
•
•
•
•
Primary
Secondary
Tertiary
Quaternary
ALL proteins have
primary, secondary and
tertiary structure
– Only proteins with multiple chains will have
this level of 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 terminus
(amino
group end)
C terminus
(carboxyl
group end
Secondary Structure (2°)
• Local helical coiling
(alpha helix) or pleated
sheet (beta sheet)
formations in the chain
• Patterned formations
based on hydrogen
bonds between nonadjacent amino acids
Tertiary Structure (3°)
• The way the polypeptide
chain is folded three
dimensionally.
• Is brought about through the
following interactions
between R groups:
– Disulfide bridges (between
Cysteines)
– Ionic interactions
– Hydrophobic interactions
– Hydrogen bonds
Quaternary Structure (4°)
• Interaction between two or more
polypeptide chains.
• What types of interactions form this
level of structure?
– The same ones that form tertiary structure
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 b 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
O
O
P
N H O
N
H2 C
N
O
P
O
H N
N
N
O
N
O
O
CH2
O
O
P
O
H
O
O
N
H2 C
N
O
H
O
O
O
CH2
H
O
H
O
H2 C
O
N H
N
P
N
N
O
O
N
N
O
CH2
O
O
O
P
H
O
H2 C
O
O
O
P
N
N
N
O
O
O
O
N
O
O
O
N
H
P
O
O
P
N
N H
O
O
O
N
N H
N
O
– DNA
– RNA
O
H
O
O
H
O
N
H N
H N
H
P
O
O
N
N
O
CH2
O
O
P
O
Nucleotide Components
• Consist of 3 parts:
• Phosphate group
• 5 carbon (pentose)
sugar
• Nitrogenous base
– Purines: A, G
– Pyrimidines: C, T,
U