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Nucleic Acids
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AP Biology
2006-2007
NUCLEIC ACIDS
 Instructions for:
Traits
 Protein synthesis
 Enzymes

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NUCLEIC ACIDS
Elements
 Carbon
 Hydrogen
 Oxygen
 Nitrogen
 Phosphorous
Monomer
 Nucleotide
Phosphate
Nitrogenous
base
Sugar (5C)
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Monomer? Nucleotide = a yard!
Garage=nitrogen
base
Pool=phosphate
House= sugar
But what yard? 742 Evergreen Terrace!
Evergreen Terrace
Complementary: structurally
matching!
Whose rule?
Nucleic Acids
 Function:

store & transmit hereditary information
 Examples:
RNA (ribonucleic acid)
 DNA (deoxyribonucleic acid)

 Structure:

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monomers = nucleotides
RNA and DNA allow living organisms to reproduce their
complex components form one generation to the next
DNA--------> RNA-------> Protein
Protein synthesis
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We can use DNA and proteins as tape
measures of evolution
 Genes (DNA) and their products (proteins)
document the hereditary background of an
organism.
 Because DNA molecules are passed from
parents to offspring, siblings have greater
similarity than do unrelated individuals of
the same species.
 This argument can be extended to develop
a molecular genealogy between species.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Two species that appear to be closely-related based on fossil
and molecular evidence should also be more similar in DNA
and protein sequences than are more distantly related
species.


In fact, the sequence
of amino acids in
hemoglobin
molecules differ by
only one amino acid
between humans and
gorilla.
More distantly
related species have
more differences.
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Nucleotides
 3 parts
nitrogen base (C-N ring)
 pentose sugar (5C)

 ribose in RNA
 deoxyribose in DNA

phosphate (PO4) group
Are nucleic acids
charged molecules?
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RNA & DNA
 RNA

single nucleotide chain
 DNA

double nucleotide chain
 N bases bond in pairs
across chains

spiraled in a double helix
 double helix 1st proposed as structure of DNA
in 1953 by James Watson & Francis Crick
(just celebrated 50th anniversary in 2003!)
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Types of nucleotides
 2 types of nucleotides
different nitrogen bases
 purines

 double ring N base
 adenine (A)
 guanine (G)

pyrimidines
 single ring N base
 cytosine (C)
 thymine (T)
 uracil (U)
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Building the polymer
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Nucleic polymer
 Backbone
sugar to PO4 bond
 phosphodiester bond

 new base added to sugar of
previous base
 polymer grows in one direction

N bases hang off the
sugar-phosphate backbone
Dangling bases?
Why is this important?
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Pairing of nucleotides
 Nucleotides bond between
DNA strands
H bonds
 purine :: pyrimidine
 A :: T

 2 H bonds

G :: C
 3 H bonds
Matching bases?
Why is this important?
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Information polymer
 Function

series of bases encodes information
 like the letters of a book

stored information is passed
from parent to offspring
 need to copy accurately

stored information = genes
 genetic information
Passing on information?
Why is this important?
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G
C
T
A
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A
C
G
T
A
C
G
T
A
DNA molecule
 Double helix

H bonds between bases
join the 2 strands
 A :: T
 C :: G
H bonds?
Why is this important?
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Copying DNA
 Replication

2 strands of DNA helix are
complementary
 have one, can build other
 have one, can rebuild the
whole
Matching halves?
Why is this
a good system?
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When does a cell copy DNA?
 When in the life of a cell does DNA have
to be copied?

cell reproduction
 mitosis

gamete production
 meiosis
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DNA replication
“It has not escaped our notice that
the specific pairing we have
postulated immediately suggests a
possible copying mechanism for the
genetic material.”
James Watson
Francis Crick
1953
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1953 | 1962
Watson and Crick … and others…
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Maurice Wilkins… and…
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1953 | 1962
Rosalind Franklin (1920-1958)
Determined ladder
shape using x-ray
chrystallography
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This is DNA as seen from top of
double helix. Can you find the
phosphate/sugar backbone? The
base rungs?
X-ray Chrystallography
 Here’s a chandelier but
you cannot see the metal
structure. You can only
shine a light on it and see
it's shadow.
 So to figure out the details
of the chandelier, you
observe the shadows and
images cast on the walls
of the room.
 From that, you determine
the whole structure. This
is how protein structures
are figured out.
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Interesting note…
 Ratio of A-T::G-C
affects stability
of DNA molecule


2 H bonds vs. 3 H bonds
biotech procedures
 more G-C =
need higher T° to
separate strands

high T° organisms
 many G-C

parasites
 many A-T (don’t know why)
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Another interesting note…
 ATP
Adenosine triphosphate

modified nucleotide
 adenine (AMP) + Pi + Pi
+
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+
Macromolecule
Review
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2006-2007
Carbohydrates
 Structure / monomer

monosaccharide
 Function
energy
 raw materials
 energy storage
 structural compounds

glycosidic bond
 Examples

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glucose, starch, cellulose, glycogen
Lipids
 Structure / building block

glycerol, fatty acid, cholesterol, H-C chains
 Function
energy storage
 membranes
 hormones

 Examples

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ester bond (in a fat)
fat, phospholipids, steroids
Proteins
 Structure / monomer
amino acids
 levels of structure

 Function
enzymes
 transport
 signals

defense
 structure
 receptors

peptide bond
 Examples

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digestive enzymes, membrane
channels, insulin hormone, actin
Nucleic acids
 Structure / monomer

nucleotide
 Function

information storage
& transfer
 Examples

AP Biology
DNA, RNA
phosphodiester bond