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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
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Proteins: A General Overview
• Biological roles: enzymes, structural components, hormones, immune function, storage, transport, muscle contraction
• Monomer = amino acid
• Polymer = polypeptide chain (protein)
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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
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Classes/Categories of Amino Acids
• The R group determines the class/category of an amino acid
• General categories:– Nonpolar– Polar– Positively Charged– Negatively Charged
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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
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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
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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
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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
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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
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Quaternary Structure (4°)
• Interaction between two or more polypeptide chains.
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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
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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
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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
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Nucleotide Components• Consist of 3 parts:
• Phosphate group
• 5 carbon (pentose) sugar
• Nitrogenous base– A, T, C, G, U (RNA
only)