macromolecules: proteins & nucleic acids building blocks of life 2007-2008
TRANSCRIPT
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Macromolecules: proteins & nucleic acids
Building Blocksof Life
2007-2008
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Quaternary (4°) structure
• 2+ polypeptides bonded and folded together
Collagen
skin & tendons
Hemoglobin
Fe containing protein that carries O2 in
blood
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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°
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Protein denaturation
Unfolding a protein
• disrupt bonds & bridges
temperature • pH • salinity
• alters shape• destroys functionality
many cannot return to
functional shape
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Nucleic Acids
2006-2007
Informationstorage
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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
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• 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
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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
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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”
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Nucleic acid
Dehydration synthesis -> covalent bond aka phosphodiester
between hydroxyl & phosphate groups polymer ‘backbone’
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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
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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
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. oCan build RNA complement• aka transcription of genes
• for eventual translation into protein
Copying the Code