Lecture 2: Introduction to macromolecules

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Lecture 2Introduction to macromolecules
Read Section 2.5. Four types of biological
molecules (pages 42-62).
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Macromolecules - huge, highly organized
molecules that form the structure and carry out
the activities of cells. Macromolecules can be
divided into 4 major categories (Fig 2.11)
1. Lipids 2. Carbohydrates 3. Nucleic
acids 4. Proteins Carbohydrates, nucleic
acids and proteins are polymers. Polymers are
composed of a large number of low-molecular-weight
building blocks, or monomers.
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• 1. Lipids
• A. Introduction
• Small, diverse organic molecules that are
  insoluble in H2O but soluble in nonpolar organic
  liquids.
• Polar different parts of the molecule have
  net negative or positive charge
• b. Hydrophobic (water fearing) or contain
  significant hydrophobic regions.

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B. Biological roles of lipids a. Source of
energy in the diet and serve to store energy in
the body. e.g. fats and oils b. Some hormones
(chemical messengers) are lipids. e.g.
steroids and prostaglandins. c. Many vitamins
are lipids. e.g. vitamins A, D, E d. The
basic structural elements of biological
membranes. e.g. phospholipids
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C. Fatty acids (see Fig. 2.19) - unbranched
hydrocarbon chains with a carboxyl group at one
end. Karp Fig 2.19b Stearic acid - chains
are typically 14 to 20 carbons. - chain is
hydrophobic. - carboxyl group is hydrophilic. -
therefore fatty acids are amphipathic. - they
can form micelles in water (see. Fig. 2.20). -
they may be saturated or unsaturated.
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D. Phospholipids (see Fig. 2.22) - major
component of membranes of all types. - consist
of glycerol linked to two fatty acids. - all
phospholipids are amphipathic.
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E. Steroids (see Fig. 2.21) - includes
cholesterol, which is found in membranes. -
cholesterol needed for synthesis of sex
hormones. - male androgens (eg. testosterone)
and female estrogens (estrogen) K
arp Fig 2.9 - Cholesterol
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2. Carbohydrates A. Introduction - have general
formula (CH2O)n - includes simple sugars
(monosaccharides) and all larger molecules
constructed of sugar building blocks. 1.
monosaccharides (simple sugars) energy source
and source of carbon 2. oligosaccharides - 2 to
10 monosaccharide units linked together. when
attached to lipids - forms glycolipids. when
attached to proteins - forms glycoproteins 3.
polysaccharides - very long chains of
monosaccharide units.
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B. Ring structures of monosaccharides - only
very small amounts of monosaccharides are found
in open chain form. - most molecules are ring
structures.
Karp Fig 2.12 Formation of a ring sugar
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C. Polysaccharides 1. Nutritional
polysaccharides glycogen and starch a. Glycogen
(see Fig. 2.17a) - principal food reserve in
animals and fungi - usually stored in liver and
muscle of animals b. Starches (see Fig. 2.17b)
- principal food reserve in plants. - comes in 2
forms amylose and amylopectin. - amylose is an
unbranched polymer of glucose. - amylopectin has
same structure but is slightly branched.
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2. Structural polysaccharides a. Cellulose (see
Fig. 2.17c) - linear polymer of several
hundred to thousand glucose units. - an
insoluble, rigid structural polymer. - makes up
cell wall of plants. - we cannot digest links
between monomers of cellulose (the bonds differ
from those of starch)
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3. Nucleic acids
Nucleic acids polymers of nucleotides
Nucleotides consist of three units - a
nitrogenous base (ringed structured with an N) -
a pentose sugar (5 carbon sugar) - a phosphate
group (PO4)
Nucleotides are attached to each other through
the sugar-phosphate backbone
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Biological roles of nucleotides
Nucleotides are involved in 3 major cellular
functions

• Nucleotides are monomeric units from which DNA
  and RNA are made
• (i.e. the molecules that encode the blueprints
  to life)
• 2. Second messengers in cell signalling (eg.
  cAMP)
• 3. Agents of energy transfer for metabolism
• Cleaving of phosphate groups releases energy
  (ATP)
• Co-enzymes in energy transfer reactions (NAD)
• NAD nicotinamide adenine dinucleotide
• Co-enzymes are non-protein compounds needed
• for enzyme action

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Ribonucleic acid (RNA)
Chain of ribonucleotides Sugar is ribose (5
carbon ring) 4 nitrogenous bases
Adenine Guanine Cytosine Uracil
RNA is usually single stranded
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Deoxyribonucleic acid - DNA
Chain of deoyribonucleotides Sugar is deoxyribose
(an oxygen atom is missing at the C2 carbon)
4 nitrogenous bases Adenine Cytosine Guanine Thym
ine(instead of uracil)
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DNA is double-stranded
DNA is a double-stranded helix
Two strands held together by hydrogen bonds
between bases
Hydrogen bonds are between complementary pairs of
purines and pyrimidines
Purines adenine and guanine Pyrimidines thymine
and cytosine
Pairing rules A-T G-C
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4 Proteins A. Overview of Proteins -
consist of one or more polypeptide chains. - a
polypeptide is a polymer of amino acids linked
together by peptide bonds. - our cells may have
as many as 10,000 different proteins. - proteins
have a diverse array of functions.
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B. Some general functions of proteins a. enzymes
protein catalysts. b. structural elements
e.g. tubulin c. contractile elements e.g.
myosin d. control activity of genes e.g.
transcription factors e. transport material
across membranes e.g. glucose transporter f.
carriers e.g. hemoglobin g. hormones e.g.
insulin h. antibodies
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C. Composition of Proteins 1. Amino Acids
(see Fig. 2.24 2.26, Karp, p. 53) - building
blocks of proteins. - organic acids that
contain an amino group General Structure

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D. R groups R side chain of variable
structure any of 20 different groups
- differences in R groups account for different
properties of amino acids and proteins. - R
groups can be broadly classified as i. polar
charged ii. polar uncharged iii. nonpolar iv.
R groups with unique properties
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E. Peptide bond or Amide linkage (see Fig. 2.24)
- Links amino group of one amino acid with
carboxyl group of adjoining amino acid. - the
linkage in dipeptides and in polypeptides. - R
groups are not involved.
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F. Structure of Proteins 1. Primary
Structure - the sequence of amino acids in a
polypeptide. - most polypeptides contain over
100 amino acids. - in a polypeptide chain, amino
acids are termed residues. 2. Protein
conformation - three dimensional structure of a
protein. - secondary, tertiary and quaternary
structure describes conformation. - primary
structure determines secondary, tertiary and
quaternary structure of proteins.
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• G. Secondary structure of protein
• - the local spatial arrangement of the atoms in
  the backbone of a polypeptide (fixed
  configuration of the polypeptide backbone)
• results from hydrogen bonding between the oxygen
  of one peptide group and the nitrogen of another
  peptide group (through the H attached to the
  nitrogen).
• - secondary structure is limited to a small
  number of
• conformations.
• - two common secondary structures.

Beta sheet
Alpha helix
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H. depiction of secondary structure (Fig.
2.32) - ? helices are represented by helical
ribbons. - ? sheets as flattened arrows. -
connecting segments as thin strands.
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I. Tertiary Structure - The way that regions
of secondary structure are oriented with respect
to each other. - Tertiary structure
predominates in globular proteins. - Monomeric
proteins consist of a single polypeptide chain
folded into its tertiary structure. - Tertiary
structure results from side chain interactions
(Fig. 2.36). - These are i. hydrogen bonds
ii. hydrophobic bonds iii. ionic bonds
iv. disulfide bond - covalent bond between
two cysteines
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J. Quaternary Structure (Fig. 2.40) -
multimeric proteins contain several polypeptide
subunits. - often the subunits can be
independently folded. - quaternary structure is
the spatial arrangement of these subunits