The Structure and Function of Macromolecules Proteins & Nucleic Acids.
The Structure and Function of Macromolecules
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Transcript of The Structure and Function of Macromolecules
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The Structure and Function of
MacromoleculesChapter 5
Biology – Campbell • Reece
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Polymers Polymers are large molecules
consisting of many identical or similar subunits connected together› Monomer – single building block
Macromolecules (large organic polymers)› Carbohydrates› Lipids*› Proteins› Nucleic acids
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Polymers in Nature
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Condensation Reaction Specifically a dehydration
reaction One monomer loses a hydroxyl and
the other loses a hydrogen This reaction is repeated as each
monomer is added Requires energy Requires enzymes
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Condensation Reaction
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Hydrolysis Process that breaks covalent bonds
between monomers by the addition of water molecules› Essentially the reverse of the dehydration
reaction› A hydrogen from the water bonds to one
monomer, and the hydroxyl bonds to another› Example: Digestive enzymes catalyze
hydrolytic reactions which break apart large food molecules into monomers that can be absorbed by the bloodstream
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Hydrolysis
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Carbohydrates Carbohydrates are organic
molecules made of sugars and polymers of sugars
Provide energy and act as building material
Building block molecules are simple sugars called monosaccharides
Classified by the number of simple sugars
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Monosaccharides Single sugar (CH2O) Major nutrients for cells (glucose
most common) Can be produced by photosynthetic
organisms from CO2, H2O and light Store energy in their chemical bonds
which is harvested by cellular respiration
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Monosaccharides Their carbon skeletons are raw
materials for other organic molecules
Carbon skeleton varies from 3 to 7 carbons
Can be incorporated as monomers into disaccharides and polysaccharides
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Monosacharides
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Dissaccharides A double sugar that consists of two
monosaccharides joined by a glycosidic linkage
Glycosidic linkage = covalent bond formed by a condensation reaction between two sugar monomers› Maltose (glucose + glucose)› Lactose (glucose + galactose)› Sucrose (glucose + fructose)
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Dissacharides
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Polysaccharides Polymers of a few hundred or thousand
monosaccharides Important biological functions:
› Energy storage (starch and glycogen) Starch = glucose polymer that is a storage
polysaccharide in plants Glycogen = glucose polymer that is a storage
polysaccharide in animals› Structural support (cellulose and chitin)
Cellulose = major structural component of plant cell walls
Chitin=carbohydrate used by arthropods for exoskeletons
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Storage Polysaccharides
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Lipids Generally not big enough to be
considered macromolecules Hydrophobic – little or no affinity for
water Consist mostly of hydrocarbons Includes waxes, pigments, fats,
phospholipids, and steroids
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Fats Main function is energy storage; also
provides cushioning and insulation Triacylglycerol or triglyceride Made of glycerol and 3 fatty acids
› glycerol = alcohol with three carbons› fatty acid = a long hydrocarbon chain with
a carboxyl group saturated = no double bonds between carbons
in the fatty acid tail (animal fats) unsaturated = one or more double bonds in the
fatty acid tail (vegetable and fish oils)
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Fat Molecules
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Phospholipids Make up cell membranes Similar to fats, but they have only
two fatty acids rather than three The hydrocarbon tail is hydrophobic
but the phosphate head is hydrophilic
Micelle = a phospholipid cluster with the phosphate heads facing outward and the hydrophobic tails inward
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Phospholipids
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Phospholipids When placed in water, they self-
assemble into a bilayer Phospholipid Bilayer = hydrophilic
heads are in contact with water, whereas the hydrophobic tails are in contact with each other and remote from water.
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Phospholipid bilayer
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Steroids Lipids characterized
by a carbon skeleton consisting of four fused rings› Cholesterol is a
precursor from which other steroids (including sex hormones) are produced High levels may
contribute to atherosclerosis
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Proteins Account for more than 50% of the
dry mass of most cells Used for structural support, storage,
transport of other substances, cell communication, movement, defense against foreign substances, and catalysis (enzymes)
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Proteins Made up of 20 amino acids Polypeptides = polymers of amino acids Proteins consist of one or more
polypeptides folded and coiled into specific three-dimensional structures
Amino acids have a carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable group symbolized by R› The R group (or side chain) differs with each
amino acid
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Hydrophobic Amino Acids
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Hydrophilic Amino Acids
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Proteins Amino acids are joined by a dehydration
reaction (removal of water) forming a peptide bond between the carboxyl group of one amino acid and the amino group of the other
Each polypeptide has a unique sequence of amino acids
The sequence of amino acids in a protein is determined by inherited genetic information (DNA)
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Protein Structure A functional protein is one or more
polypeptides precisely twisted, folded, and coiled into a unique shape
Many proteins are roughly spherical (globular proteins)
Others are like long fibers (fibrous proteins)
A protein’s structure determines its function
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Primary Structure Basic sequence of amino acids The order is crucial to the function of
the protein › Sickle cell anemia results from the
substitution of one amino acid in hemoglobin
› Frederick Sanger discovered insulin’s primary structure in the late 1940’s
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Protein Primary Structure
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Secondary Structure Segments of the polypeptide chain are
repeatedly coiled or folded as a result of hydrogen bonds at regular intervals along the polypeptide backbone› Alpha (α) helix – delicate coil held together
by hydrogen bonding between every fourth amino acid (found in fibrous proteins)
› Beta (β) pleated sheet – parallel regions are held together by hydrogen bonds between adjacent polypeptides
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Secondary Structure
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Tertiary Structure The overall shape of a polypeptide
resulting from interactions between the R groups› Hydrophobic interaction – the nonpolar
side chains cluster at the core of the protein away from water (van der Waals interactions hold them together)
› Disulfide bridges – the sulfur of one cysteine amino acid binds to the sulfur of another (-S-S-)
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Tertiary Structure
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Quaternary Structure Some proteins
consist of two or more polypeptides
Structure in proteins that results from interactions between and among several polypeptide chains
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Denaturation of Proteins Denaturation is a process that alters
a protein’s native conformation and biological activity.
Occurs when:› Proteins are transferred to an organic
solvent (ex. ether or chloroform)› Chemical agents disrupt hydrogen
bonds, ionic bonds, and disulfide bridges
› Excessive heat disrupts weak interactions
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Denaturation of Proteins
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Predicting Protein Folding Predicting protein conformation based on
amino acid sequence is difficult because most proteins pass through intermediate stages in the folding process
Chaperone proteins (chaperonins) temporarily brace a protein while it folds spontaneously
Knowledge of protein folding would allow the design of proteins for specific purposes
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Nucleic Acids DNA - deoxyribonucleic acid
› Contains coded information that programs all cell activity
› Contains directions for its own replication› Is copied and passed from one generation of
cells to another› Found primarily in the nucleus in eukaryotic
cells› Makes up genes that contain instructions for
protein synthesis (direct the synthesis of mRNA)
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Nucleic Acids RNA - ribonucleic Acid
› Functions in the actual synthesis of proteins coded for by DNA
› Sites of protein synthesis are on ribosomes
› Messenger RNA (mRNA) carries encoded genetic message from the nucleus to the cytoplasm
› Flow of genetic information goes from DNA to RNA to protein
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Nucleotides Nucleic acids are polymers of nucleotides
1. A five carbon sugar (ribose or deoxyribose)2. A phosphate group 3. A nitrogenous base
Purines – adenine (A) and guanine (G) Pyrimidines – cytosine (C), uracil (U), and
thymine (T) Base Pairings: A-T, C-G (in DNA) and A-U,
C-G (in RNA)
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Nucleotides
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DNA - The Double Helix James Watson and Francis Crick
proposed the double helix structure of DNA in 1953› DNA consists of two nucleotide chains
held together by hydrogen bonds between paired bases and van der Waals attraction between stacked bases and wound in a double helix (twisted ladder)
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DNA