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Section 4
Section 3-2 Notes
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Carbohydrates
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Carbohydrates: organic compounds composed of carbon, hydrogen, and
oxygen in a ratio of about 1 carbon to 2 hydrogen to 1 oxygen atoms.
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The number of carbon atoms in a carbohydrate varies.
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Some carb serves as a source of energy.
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Carb can exist as monosaccharides, disaccharides, or polysaccharides.
Monosaccharides
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Monosaccharides: a monomer of a carbohydrate (CH2O)N (N = 3 ~ 8)
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A monosaccharide or simple sugar contains C, H, O in a ratio of 1:2:1
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Most common monosaccharides: glucose, fructose, and galactose.
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Glucose: main source of energy for cells
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Fructose: found in fruits and sweetest of the monosaccharides.
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Galactose: found in milk
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Glucose, fructose, and galactose have the same molecular formula (C6H12O6)
but differ in structures (isomers).
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The different structures determine slightly different properties of the 3
compounds.
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Isomers: compounds that have the same formula but different structural
forms.
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Disaccharides and Polysaccharides
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Disaccharide: double sugar; combination of two monosaccharides by
condensation reaction. Ex:) mono fructose and glucose = disa sucrose.
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Polysaccharide: complex molecule composed of three or more
monosaccharides.
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Animals store glucose in the form of polysaccharide glycogen.
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Glycogen: consists of hundreds of glucose molecules strung together in a
highly branched chain.
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Glucose from food stored in liver, muscles glycogen, as quick energy.
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Plants store glucose molecules in the form of polysa starch.
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Starch molecules have two basic forms: highly-branched chains (similar to
glycogen), and long coiled unbranched chains.
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Plants also make a large polysa called cellulose.
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Cellulose: gives strength and rigidity to plant cells. Makes up 50% of wood.
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In a single cellulose molecule, thousands of glucose monomers are linked in
long straight chains. These tend to form H bonds with each other.
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The resulting structure is strong and can be broken down by hydrolysis only
under certain conditions.
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Proteins
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Proteins: organic compounds composed mainly of C, H, O, and N. Formed from
the linkage of monomers called amino acids.
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Amino Acids
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There are 20 different amino acids, and all share a
basic structure.
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Each amino acid contains a central carbon atom
covalently bonded to four other atoms or functional
groups.

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Single H atom: bonds at one site.
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Carboxyl group (COOH): bonds at second site.
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Amino group (NH2): bonds at third site.
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R group (side chain): bonds at fourth site.
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Pg. 56 last para
Dipeptides and Polypeptides
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Dipeptide : (Figure 3–8a) shows how two amino
acids bond to form a dipeptide. In this
condensation reaction, the two amino acids
form a covalent bond (peptide bond) and
release a water molecule.
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Polypeptides: long chains of amino acids.
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Proteins are composed of 1 or more
polypeptides.
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Para 2 on pg 57
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Enzymes
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Enzymes: RNA or protein molecules that act as biological catalysts.

Enzyme reactions depend on a physical fit between the enzyme molecule and
its specific substrate, the reactant being catalyzed.
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
Para last 2 pg 57.
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Enzyme might not work if its environment changed.
Lipids
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Lipids: large, non polar molecules. Includes triglycerides, phospholipids,
steroids, waxes, and pigments.
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Lipid molecules have a higher ratio of C and H atoms to O atoms than Carb.
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Since lipid molecules have larger numbers of carbon-hydrogen bond per gram
than any other organic compounds do, they store more energy per gram.
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Fatty Acids
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Fatty acids: unbranched carbon chains that make up most of lipids.

Para 2 of pg. 59
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In saturated fatty acids, each carbon atom is covalently bonded to four
atoms.
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The C atoms are in effect full, or saturated.
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Para 3 of pg. 59
Triglycerides
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Three classes of lipids important to living things containing fatty acids:
triglycerides (fats), phospholipids, and waxes.
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Triglyceride: composed of three molecules of fatty acid joined to one
molecule of the alcohol glycerol.
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More…
Phospholipids
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Phospholipids: have two rather than three fatty acids attached to a molecule
of glycerol.
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Lipid bilayer: the cell membrane that is made up of two layers of
phospholipids.
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More…
Waxes
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Wax: a type of structural lipid consisting of a long fatty-acid chain joined to
a long alcohol chain.
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Waxes are waterproof, protective layer/coating for animals and plants.
Steroids
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Steroid molecules are composed of four fused carbon rings with various
functional groups attached to them.
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One of the most familiar steroids in humans is cholesterol.
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Cholesterol is needed by the body for nerve and other cells to function
normally. It is also a component of the cell membrane.
Nucleic Acids
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Nucleic Acids: very large and complex organic molecules that store and
transfer important information in the cell.
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Two types: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
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DNA: contains information that determines the characteristic of an
organism and directs it cell activities.
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RNA: stores and transfers info from DNA that is essential for the
manufacturing of proteins.
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RNA can also act as enzymes.
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Both DNA and RNA are polymers, composed of thousands of linked
monomers called nucleotides.

Each nucleotide is made of three main components: a phosphate group, a
five-carbon sugar, and a ring-shaped nitrogenous base.