Chapter 5: Structure and Function of Macromolecules

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Chapter 5Structure and Functionof
Macromolecules
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Polymers Most macromolecules are polymers

• Definition Large molecule consisting of many
  identical or similar subunits connected together
• Monomer Subunit or building block molecule of a
  polymer
• Macromolecule Large organic polymer 4
  classes carbohydrates, lipids, proteins, nucleic
  acid

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D. Making and breaking polymers
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1. Polymerization reactions

• Chemical reactions that link two or more small
  molecules to form larger molecules with repeating
  structural units

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2. Condensation reactions (dehydration synthesis)

• polymerization reactions during which monomers
  are covalently linked, producing a net removal of
  a water molecule for each covalent linkage
• One monomer losses OH, the other one loses H
• Requires energy and enzymes

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3. Hydrolysis

• A reaction that breaks covalent bonds between
  monomers by the addition of water molecules
• One monomer gains OH, the other gains H
• Digestive enzymes catalyze hydrolytic reactions

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Linking Molecules Together
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Carbohydrates

• Organic molecules made of sugars and their
  polymers

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A. Monosaccharide - Simple sugar in which C, H, O
occur in ratios of CH2O, carbons 3-7

• Major nutrient for cells, especially glucose
• Produced through photosynthesis store energy
  from the sun
• Aldehyde terminal carbon forms a double bond
  with oxygen
• Ketone carbonyl group within the carbon
  skeleton
• Ring and linear forms in aqueous solutions,
  many monosaccharides form rings. Chemical
  equilibrium favors ring structure

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B. Disaccharides - Double sugar that consists of
two monosaccharides joined by a glycosidic linkage

• Glycosidic linkage Covalent bond formed by a
  condensation reaction btwn 2 sugar monomers
• Maltose (glucose glucose)
• Lactose (glucose galactose)
• Sucrose (glucose fructose)

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C. Polysaccharides- Polymers of a few hundred or
thousand monosaccharides

• Storage Polysaccharides cells hydrolyze storage
  polysaccharides into sugars as needed, alpha 1,4
  linkages
• Starch Glucose polymer, plant storage
• Stored in granules in plastids
• Amylase, unbranched
• Amylopectin, branched
• Glycogen glucose polymer, animal storage
• Large polymer, highly branched
• Stored in muscle and liver vertebrates

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Polysaccharides cont.

• Structural polysaccharides
• Cellulose linear unbranched polymer of
  D-glucose in beta 1,4 linkages (-OH of C1 in up
  position)
• Major structural component of plant cell walls
• Chitin amino sugar polymer
• Exoskeleton in arthropods
• Found in cell walls of some fungi

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Lipids Nonpolar
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A. Fats - Macromolecules constructed from

• Glycerol 3 carbon alcohol
• Fatty Acid (carboxylic acid)
• Carboxyl group (head) at one end functions as
  an acid
• Hydrocarbon carbon (tail) at other end,
  nonpolar, usually 16-18 Cs long
• Ester linkage Bond formed between the hydroxyl
  of glycerol and the carboxyl of fatty acid by
  condensation
• Triacylglycerol A fat composed of three fatty
  acids bonded to one glycerol by ester linkages
  (triglyceride)

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5. Characteristics of fat

• Insoluble in water due to hydrophobic fatty acid
  chains
• Variation among fat molecules due to fatty acid
  composition
• Fatty acids may all be the same or different
• Fatty acids vary in length

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Characteristics of fat cont.

• Saturated fat
• No double bonds between Cs in the tail
• Cs bonded to maximum number of Hs (saturated)
• Usually solid at room temperature
• Most animal fats
• Unsaturated fat
• One or more double bonds between Cs in tail
• Tail kinks at each CC. So molecules do not pack
  closely enough to solidify at room temperature
• Usually liquid at room temperature
• Most plant fats (oils)

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Characteristics of fat cont.

• Functions
• Energy storage (9 Cal/g)
• Cushions vital organs in mammals (kidneys)
• Insulates against heat loss

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6. Phospholipids - glycerol, 2 fatty acids,
phosphate group

• Hydrophilic head (phosphate group)
• Hydrophobic tail (fatty acids)
• Major constituents of cell membranes

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Phospholipid bilayer separates the inside of
the cell from the outside of the cell, only water
and small ions can pass through
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7. Steroids - four fused carbon rings with
various functional groups attached

• Cholesterol
• Precursor to many other steroids including
  vertebrate sex hormones and bile acids
• Component of animal cell membranes
  stabilization and rigidity
• Can contribute to atherosclerosis

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Proteins

• Molecular tools for most cellular function
  Consists of one or more polypeptide chains folded
  and coiled into specific conformations

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Polypeptide Chains polymers of amino acids
that are arranged in a specific linear sequence
and are linked by peptide bonds
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B. Function

• Structural Support
• Storage (of amino acids)
• Transport (e.g. hemoglobin)
• Signaling (chemical messengers)
• Cellular response to chemical stimuli (receptor
  proteins)
• Movement (contractile proteins)
• Defense against foreign substances and disease
  causing organisms (antibodies)
• Catalysis of biochemical reactions (enzymes)

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C. Properties

• Abundant 50 or more of cellular dry weight
• Vary extensively in structure unique 3D shape
  (conformation)
• Made up of 20 amino acid monomers in different
  amounts and combinations

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D. Amino Acids - building block molecules of a
protein

• Structure Asymmetric carbon, alpha carbon,
  bonded to
• Hydrogen atom
• Amino group
• Carboxyl group
• Variable R group (side chain) specific to each aa

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• Grouped by properties of side chains
• Nonpolar side groups hydrophobic
• Polar side groups hydrophilic
• Uncharged polar
• Charged polar
• Acidic side groups dissociated carboxyl group
  negative charge
• Basic side groups amino group w/extra proton
  positive charge

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E. Polypeptide Chains - polymers formed when
amino acids polymerize

• Peptide bond Covalent bond formed by a
  condensation reaction that links the carboxyl
  group of one amino acid to the amino acid group
  of another
• Backbone - N C C N C C N -

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F. Protein Conformation 3D shape of a protein
function is dependent on structure

• Protein Structure
• Primary
• Secondary
• Tertiary
• Quarterary

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Primary structure - Unique sequence of amino
acids

• Determined by genes
• Slight change can significantly affect
  conformation

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b. Secondary structure - Regular, repeated
coiling and folding of a proteins polypeptide
backbone

• Contributes to overall structure
• Stabilized by H bonds between peptide linkages in
  the protein backbone
• Alpha Helix helical coil stabilized by
  H-bonding between every 4th peptide bond
• Found in fibrous proteins (keratin, collagen) for
  most of their length and some portions of
  globular proteins
• Beta Pleated Sheets sheets of antiparallel
  chains folded into accordion pleats
• Make up dense core of globular protein and major
  portion of some fibrous proteins

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Hydrogen bonds
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c. Tertiary structure - Irregular contortions of
a protein due to bonding between side chains (R
groups) third level of protein structure
superimposed upon primary and secondary structure

• Weak interactions
• H-bonding between polar side chains
• Ionic bonds between charged side chains
• Hydrophobic interactions between nonpolar side
  chains in proteins interior
• Covalent linkages Disulfide bridges form
  between two cysteine monomers strong bond

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d. Quaternary structure - Structure that results
from the interaction among polypeptides in a
single protein
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Folding due to hydrophilic and hydrophobic amino
acids
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G. Denaturation - A process that alters a
proteins native conformation and biological
activity caused by

• Transfer to an organic solvent (nonpolar)
• Chemical agents can disrupt H bonds, ionic bonds,
  and disulfide bridges
• Excessive heat
• Inappropriate pH

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V. Nucleic Acids - Protein conformation is
determined by primary structure. Primary
structure is determined by genes (DNA sequences)
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A. DNA Deoxyribonucleic Acid

• Contains coded info that programs all cell
  activity
• Contains directions for its own replication
• Is copied and passed from 1 generation of cells
  to another
• In eukaryotic cells, found primarily in the
  nucleus
• Genes direct the synthesis of RNA

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B. RNA Ribonucleic Acid

• Functions in the actual synthesis of proteins
  coded for by DNA
• Sites of protein synthesis are on ribosomes in
  the cytoplasm
• mRNA carries genetic message from nucleus to
  cytoplasm

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C. Nucleotides building blocks of a nucleic
acid

• Pentose 5-carbon sugar (RNA/ribose
  DNA/deoxyribose)
• Phosphate group attached to a number 5 carbon of
  the sugar
• Nitrogenous base
• Pyrimidine six-membered ring made up of carbon
  and nitrogen atoms
• Cytosine (C)
• Thymine (T) found only in DNA
• Uracil (U) found only in RNA
• Purine 5 membered ring fused to a 6 membered
  ring
• Adenine (A)
• Guanine (G)

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Nucleotides cont.

• Function
• Monomers for nucleic acids
• Transfer chemical energy from one molecules to
  another (ATP)
• Are electron acceptors in enzyme controlled redox
  reactions (NAD)
• Phosphodiester linkages between phosphate of one
  nucleotide and sugar of the next

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DNA Structure

• Two nucleotide chains wound in a double helix
• Sugar-phosphate backbones are on the outside of
  the helix
• Nitrogenous bases are paired in the interior of
  the helix and held together by H bonds
• A-T and C-G pairing

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What You Need to Know About Ch.5
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The Principles of Polymers

• List the four major classes of macromolecules.
• Distinguish between monomers and polymers.
• Draw diagrams to illustrate condensation and
  hydrolysis reactions.

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Carbohydrates Serve as Fuel and Building Material

• Distinguish between monosaccharides,
  disaccharides, and polysaccharides.
• Describe the formation of a glycosidic linkage.
• Distinguish between the glycosidic linkages found
  in starch and cellulose. Explain why the
  difference is biologically important.
• Describe the role of symbiosis in cellulose
  digestion.

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Lipids are a Diverse Group of Hydrophobic
Molecules

• Describe the building-block molecules, structure,
  and biological importance of fats, phospholipids,
  and steroids.
• Identify an ester linkage and describe how it is
  formed.
• Distinguish between saturated and unsaturated
  fats.
• Name the principal energy storage molecules of
  plants and animals.

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Proteins have Many Structures and Many Functions

• Distinguish between a protein and a polypeptide.
• Explain how a peptide bond forms between two
  amino acids.
• List and describe the four major components of an
  amino acid. Explain how amino acids may be
  grouped according to the physical and chemical
  properties of the R group.
• Explain what determines protein conformation and
  why it is important.
• Explain how the primary structure of a protein is
  determined.
• Name two types of secondary protein structure.
  Explain the role of hydrogen bonds in maintaining
  secondary structure.
• Explain how weak interactions and disulfide
  bridges contribute to tertiary protein structure.
• List four conditions under which proteins may be
  denatured.

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Nucleic Acids Store and Transmit Hereditary
Information

• List the major components of a nucleotide, and
  describe how these monomers are linked to form a
  nucleic acid.
• Distinguish between
• pyrimidine and purine
• nucleotide and nucleoside
• ribose and deoxyribose
• 5 end and 3 end of a nucleotide
• Briefly describe the three-dimensional structure
  of DNA.