The Structure and Function of Macromolecules

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The Structure and Function of Macromolecules

• Campbell
• Chapter 5

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Essential Questions

• How do various molecules support the functions of
  life?
• How do the structures of various molecules
  support their life enabling functions?

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Macromolecules

• 4 major classes
• carbohydrates, lipids, proteins, and nucleic
  acids.
• Large molecules are called polymers
• Made of several monomers

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Joining Monomers

• Monomers are connected by covalent bonds via a
  condensation reaction or dehydration synthesis.
• This process requires energy and is aided by
  enzymes.

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Breaking Polymers

• The covalent bonds connecting monomers in a
  polymer are disassembled by hydrolysis.
• Water is added.
• Hydrolysis reactions dominate the digestive
  process, guided by specific enzymes.

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• Each cell has thousands of different
  macromolecules
• Diversity comes from various combinations of the
  40-50 common monomers and other rarer ones.
• These monomers can be connected in various
  combinations

• Monomer/Polymer Video

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Carbohydrates

• Organic molecules, sugars and their polymers.
• Monomers-monosaccharides
• disaccharides, 2 monosaccharides linked together
• Polysaccharide, 3 ore more monosaccharides linked
  together

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Monosaccharides

• Monoone sacchar sugar
• Have the empirical formula (CH2O)
• Function
• nutrients for cells
• C skeletons used for other macromolecules
• Energy storage in their chemical bonds
• Structure and Support (particularly plants)

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Structure of Monosaccharides

• Ring and chain forms
• Chain forms contain a carbonyl group and a
  hydroxyl group
• Carbon skeleton varies from 3-7
• The most common are 3, 5, 6, triose, pentose
  and hexose respectively
• Several isomers exist
• Ring forms of monosaccharides occur when the
  sugar is placed in an aqueous solution

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Alpha Glucose
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Disaccharides

• Disaccharide video

• Literally 2 sugars
• 2 monosaccharides joined by a glycosidic linkage,
  covalent bond formed by a condensation reaction
  between 2 monosaccharides

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Condensation reactions to form Disaccharides
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Polysaccharides

• Polysaccharide Video
• Made of a few hundred or thousand monosaccharides
• Formed by enzyme-mediated condensation reactions
• Have 2 essential functions
• Energy Storage (starch and glycogen)
• Structural Support (cellulose and chitin)

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Storage Polysaccharides - Starch

• Glucose polymer ? storage molecule in plants
• Helical glucose polymer
• Stored in granules called plastids within plant
  cells
• Amylose, simplest starch, unbranched polymer
• Amylopectin, branched polymer

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Storage Polysaccharides - Glycogen

• Glycogen stores glucose in animals
• Large glucose molecule that is highly branched
• Stored in the muscle and liver of humans and
  other vertebrates

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Structural Polysaccharides - Cellulose

• Linear, unbranched polymer of glucose
• Major component of plant cell walls
• Differs from starch in its glycosidic linkages
• Starch - polymers of ? glucose
• Cellulose - polymers of ß glucose (1-4 linkages)
• The different isomers of glucose in starch and
  cellulose give each molecule unique 3-D shapes
  and properties
• Can we/ most organisms digest cellulose?

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Structural Polysaccharides - Chitin

• Polysaccharide that is a polymer of an amino
  sugar
• A sugar with an amine functional group
• Found in the exoskeletons of arthropods and in
  the cell walls of some fungi

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Lipids

• Lipid Video

• Diverse group
• Insoluble in water, nonpolar
• Will dissolve in other nonpolar solutions
• ex. ether, chloroform, benzene
• Important groups
• Fats
• Phospholipids
• Steroids

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Fats store large amounts of energy

• Dont really have monomers/polymers
• Fats are constructed from
• 1) Glycerol, a 3C alcohol
• 2) Fatty acid
• Composed of a carboxyl group at one end attached
  to a hydrocarbon chain (tail), hydrophobic
• Carboxyl end (head) is polar, hydrophilic
• Hydrocarbon chain has a long skeleton with a
  large (usually even) number of carbon atoms
  (usually 16-18)
• Nonpolar C-H bonds make the tails insoluble in
  water

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Fats (continued)

• One glycerol molecule can link with up to 3 fatty
  acids
• Ester linkage bond formed between a hydroxyl
  group and a carboxyl group
• Triglycerol a fat composed of 3 fatty acids
  bonded to one glycerol by ester linkages

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Characteristics of Fat

• Insoluble in water
• hydrophobic C-H chains
• Variation in fats is in the fatty acid
  composition
• May vary in length or number and location of CC

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• Saturated fats
• Most animal fats
• Solid at room temperature
• May lead to cardiovascular disease
  (atherosclerosis)
• Unsaturated fats
• Plant and fish fats, known as oils
• liquid at room temperature
• Trans-fats, mono or poly
• Trans versus cis configuration
• neither required nor beneficial for health

Hydrogenated oils- Peanut butter, margarine.
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Functions of Fats

• Energy storage
• One gram of fat stores twice as much energy as
  one gram of a carbohydrate.
• More energy rich C-H bonds in fats
• Less mass for energy storage for plants and
  animals
• starch is bulky
• Cushions vital organs in mammals
• Insulates against heat loss

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Types of Lipids -1 Phospholipids

• Structure
• A glycerol and 2 fatty acids.
• 3rd C of the glycerol is attached to a phosphate
  group.
• heads hydrophilic ? tails hydrophobic
• Cluster in water with philic heads towards the
  water and phobic tails away
• Ex micelle, cell membrane? phospholipids bilayer

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Types of Lipids -2 Steroids

• Four fused carbon rings with various function
  groups attached
• Ex cholesterol, important steroid
• Precursor to many other steroids like human sex
  hormones and bile acids
• Common component in animal cell membranes
• Can contribute to atherosclerosis

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Cholesterol
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Proteins the Molecular tool of the Cell

• Abundant, make up 50 or more of dry cellular
  weight
• Have varied and important functions within the
  cell
• structural support
• amino acid storage
• transport (hemoglobin)
• signaling (chemical messengering)
• Cellular responses to chemical stimuli
• Movement (contractile proteins)
• Defense, antibodies
• Biological catalysts, enzymes
• Vary extensively in structure depending on its
  function
• Made of combinations of 20 different amino acids.

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Amino Acids

• Building blocks of proteins (monomers)
• Typically made of
• central carbon atom attached to an amine group, a
  carboxyl group and a H and a variable side chain
  (R)
• Carboxyl group acts as a weak acid and the amine
  works as a weak base depending on the solution
  they are in
• the amino acid can exist in a number of states
• 20 Amino Acids (pgs 72-73)

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Know the 20 Amino Acids

• some AA are nonpolar
• Hydrophobic R groups, less soluble in water

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Know the 20 Amino Acids

• some AA are uncharged polar
• Dissolve in water, R groups show an uneven
  distribution of charge
• serine, threonine, cysteine, tyrosine,
  asparagine, glutamine

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• some AA are polar and some are electrically
  charged

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Polypeptide chains

• formed when AAs link and form peptide bonds
• Condensation reaction? produces peptide bonds
  (polar)
• Carboxyl group of one AA links to the amino group
  of the other AA
• Range from a few AA to more than 1000

• Protein Intro Video

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Protein Structure

• Protein function depends on its specific
  conformation
• depends on ability to recognize and bind to some
  other molecule
• Important for binding sites
• Results from the amino acid sequence
• Produced when amino acids coil and fold in
  response to hydrophobic interactions
• Stabilized by chemical bonds and interactions
  with neighboring regions of the protein

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4 Levels of Protein Structure

• Primary Structure
• Secondary Structure
• Tertiary structure
• Quaternary Structure

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Primary Structure of Proteins

• Unique sequence of amino acids
• Determined by genes
• Slight alterations can change the conformation
  and function, i.e. sickle cell
• Can be determined in labs, genetic profiling

• Primary Structure Video

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Secondary Structure of Proteins

• Regular, repeated coiling and folding of a
  proteins backbone.
• Alpha helix
• Stabilize protein with H bonds
• Beta pleated sheet
• Compact protein

• Secondary Structure Video

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Tertiary Structure of Proteins

• 3-D shape of a protein
• Results from
• bonding among side chains
• interactions of R groups and the aqueous
  environment
• Stabilized by
• 1)The sum of weak interactions
• H bonds
• Ionic bonds between side chains
• Hydrophobic interactions
• 2) Disulfide bonds

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• Tertiary Structure of Proteins
• Quaternary Structure

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Quaternary Structure of Proteins

• Results from the interactions among peptide
  chains
• Influenced by environmental conditions
• pH, Temperature, chemicals
• Denaturation ? deformation of a protein
• Disruption of bonds that maintain the proteins
  shape
• usually irreversible
• Complex intramolecular interactions
• Many proteins are dynamic (have several forms)
• Most proteins appear to undergo several
  intermediate stages before reaching their
  mature configuration

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Review

• What are the functions of proteins?
• What are proteins made of?
• Structural Proteins
• Storage Proteins
• Transport Proteins
• Receptor Proteins
• Contractile Proteins
• Defensive Proteins
• Signal Proteins
• Enzymes
• Sensory Proteins
• Gene Regulatory

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Nucleic Acids Informational Polymers

• Nucleic Acids- store and transmit genetic
  information
• Contain information for the production of
  proteins
• Primary structure of proteins is determined by
  genes
• 2 types of Nucleic Acids
• DNA
• RNA

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Deoxyribonucleic Acid (DNA)

• Contains info for
• cell activity
• cell replication
• Is copied and passed from one cell to another
• Found in the nucleus of eukaryotic cells
• Makes up genes that control the direction of
  protein synthesis

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Ribonucleic Acid (RNA)

• Responsible for the production of proteins
• Makes up ribosomes
• Carries genetic information from the nucleus to
  the cytoplasm
• Sequence of information transmission
• DNA? RNA ? Protein

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Nucleic Acid Structure

• Nucleotides
• monomers of NAs
• Made of
• a sugar
• a phosphate
• nitrogenous base

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Nucleic Acid Structure The Sugar

• Pentose, 5-C sugar
• 2 found in nucleic acids ribose and deoxyribose

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NA Structure The Nitrogenous Base

• 2 families of nitrogenous bases
• Pyrimidines 6 membered ring of C and N
• Cytosine
• Thymine (DNA)
• Uracil (RNA)
• Purines 5 membered ring fused to a 6 membered
  ring
• Adenine
• Guanine

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• Nucleotides are held together by covalent bonds
  called phosphodiester linkages
• Between the phosphate of one nucleotide an the
  sugar of another
• Creates a sugar phosphate backbone
• Series of nitrogenous bases are attached to the
  S-P backbone
• These series create genes

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Inheritance and the Double helix

• 1953, Watson and Crick proposed the double helix
  model
• Based on the X-ray crystallograhy of Rosalind
  Franklin

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The Double Helix

• Strands of DNA are complimentary
• Base pairing
• A-T (U)
• C-G
• H bonds hold sides of the double helix together
• Universal genetic code
• No 2 people have the same DNA
• Most DNA molecules contain millions of base pairs

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What is the function of Nucleic Acids?
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Central DogmaThe Big Nucleic Acid Picture
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Organic MacromoleculesReview

• Carbohydrates
• Proteins
• Lipids
• Nucleic Acids