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DNA and RNA
Chapter 12
12-1: DNA
DNA Structure
 DNA is made up of monomers called
nucleotides
 each nucleotide is made up of three parts:
1. 5-carbon sugar (deoxyribose)
2. phosphate group
3. nitrogenous base
 FOUR types of nitrogenous bases
adenine (A) & guanine (G) – purines
cytosine (C) & thymine (T) – pyrimidines
Nitrogenous bases
 purines
(A & G):
two rings
 pyrimidines
(C & T):
one ring
Chargaff’s Rules
 # of A = # of T
 # of G = # of C
 # of purines = # of pyrimidines
DNA “double helix”
 discovered by Watson & Crick
 two strands are wound around each other
like a spiral staircase or twisted ladder
DNA “double helix”
 base pairing explains Chargaff’s Rules
 A always bonds with T (“points”) – double bond
 C always bonds with G (“curves”) – triple bond
So if you have one side of
DNA that has these bases,
 Cytosine (C)
 Adenine (A)
 Thymine (T)
 Guanine (G)
 Guanine (G)
 Thymine (T)
--(G) Guanine
--(T) Thymine
--(A) Adenine
--(C) Cytosine
--(C) Cytosine
--(A) Adenine
These bases will make the other side.
DNA Origami
Two types of FOLDS
Step 1
Cut the white border off the top, bottom, and
sides of the template.
Step 2
Fold all solid lines going
lengthwise down the
page into “mountain
folds”.
Step 3
Fold all dashed lines
going lengthwise down
the page into “valley
folds”.
Check Yourself
Your paper should look like this:
Step 4
Bring the two sides of the model together, similar
to an “I” beam.
Step 5
Look for the words ‘front’ and ‘back’ at the top of
your model. Hold the model with the ‘front’ side
facing you.
Step 6
Fold the two sides of the DNA model so the
‘front’ side is flat.
Step 7
Crease each solid, horizontal line into a
mountain fold (away from you).
Step 8
Flip the model to the ‘back’ side. Crease each
solid diagonal line into a mountain fold (away
from you).
Check Yourself
Your model should look like this.
Step 9
Fold ALL of the creases together in the directions
of the folds made in steps 7 and 8. Your model
will fold up like an accordion. While you are
folding, pinch the middle of the model to keep it
together to make a cylindrical shape.
Step 9
Step 10
Release the model. You
should be able to see the
shape of a double helix.
Step 11
Straighten out the sides of the
DNA model (the DNA
“backbones”) to make them
perpendicular to the creases in
the middle.
You’re DONE! 
Bell Work 2/22/10
 A scientists is researching the effect long-term
exposure to sunlight has on cell reproduction.
Which scenario extends the current understanding
of this relationship?
– A) a culture of liver cells exposed to different pH levels
over a 10-day period
– B) a culture of muscle cells exposed to different nutrients
over a 30-day period
– C) a culture of skin cells exposed to different
temperatures over a 50-day period
– D) a culture of brain cells exposed to different electrical
impulses over a 75-day period
12-2: Chromosomes
and DNA Replication
DNA and Chromosomes
 prokaryotes have a SINGLE, circular
chromosome in the cytoplasm containing
their DNA
DNA and Chromosomes
 prokaryotes have a SINGLE, circular
chromosome in the cytoplasm containing
their DNA
 eukaryotes have
MANY chromosomes
in the nucleus
containing their DNA
Chromosome Structure
 DNA is very tightly packed
 DNA is wound around histones (proteins) to form nucleosomes
 nucleosomes wind into coils and supercoils to ultimately form
chromosomes
tightly wound DNA is called
chromatids
Flashback!
What happens during the S
phase of the cell cycle?
DNA replicates (copies) itself!
DNA Replication
DNA Replication
 to make a copy of itself, DNA “unzips”
C—G
G---C
T-A-G-G--
--A
--T
--C
--C
DNA Replication
 new bases come in to make a new
complementary strand
C—G
G--C
G --C
T--A
T--A
A--T
A--T
G--C
G--C
G--C
G--C
Notice these strands are the same.
Your turn
 copy and complete the DNA strand
C-G-G-T-A-A-C-G--
Does it look like this?
C--G
G--C
G--C
T--A
A--T
A--T
C--G
G--C
“Unzip” and copy it!
C—G
G---C
G---C
T---A
A---T
A---T
C---G
G---C
Does it look like this?
C—G
G--C
G--C
T--A
A--T
A--T
C--G
G--C
G--C
G--C
T--A
A--T
A--T
C--G
G--C
DNA Replication
 the main enzyme
involved in DNA
replication is
DNA polymerase
 RESULTS in two
identical DNA
molecules!
Bellwork 2/23/10
 When designing a scientific investigation,
which of the following should be identified
first?
– A) lab equipment needed
– B) appropriate sample size
– C) useful analysis software
– D) a testable hypothesis
12-3: RNA and
Protein Synthesis
RNA vs DNA structure
RNA
 sugar: ribose
DNA
 sugar: deoxyribose
 single-stranded
 double-stranded
 uracil (U) base
 thymine base
3 Types of RNA
RNA is mainly involved in PROTEIN SYNTHESIS
 messenger RNA (mRNA)
 ribosomal RNA (rRNA)
 transfer RNA (tRNA)
Protein Synthesis
1. Transcription
2. RNA Editing
3. Translation
Overview
Transcription
 DNA is “transcribed” into a RNA strand with
the help of RNA polymerase
Transcription
 how does RNA polymerase “know” where to
start and stop making the RNA copy of DNA?
 the promoter region of the DNA is the light
switch ON
 then the middle part is the coding region, or
the TV show you watch
 the RNA polymerase stops at the
termination sequence, the light switch OFF
RNA Editing
 like a writer’s 1st draft
 introns
(intervening sequences)
are removed
 exons
(expressed sequences)
are left to make up
the mRNA
Translation
 mRNA “translated” into amino acids (which
form proteins!)
 occurs in the RIBOSOME
How does the ribosome
“read” the mRNA?
 using the GENETIC CODE!
 this “code” only uses 4 letters:
A, U, C, G
 these 4 letters represent 20 different amino
acids
 the code is read 3 letters at a time (in triplicate)
– these are called codons
 example:
RNA sequence
UCGCACGGU
would be read
UCG CAC GGU
The Genetic Code
 each codon
represents an
amino acid
 there are
64 codons
that code for
20 amino acids
 1 start:
AUG
 3 stops:
UAA
UAG
UGA
Translation
 before translation starts, mRNA is transcribed in
the NUCLEUS
Translation
 then, in the cytoplasm, an mRNA molecule attaches to
a RIBOSOME
 translation starts at AUG, and the transfer RNAs come
in! (AUG = methionine)
Translation
 it’s a polypeptide “assembly line” of amino acids …
Translation
 … until a stop codon is reached
Protein Synthesis
Bell Work 2/26/10
 In 1928 Alexander Fleming observed the mold
Penicilium notatum growing in a Petri dish. Also in
the dish was the bacteria Staphylococcus aureus.
Fleming observed that no bacteria colonies were
found growing in the area where the Penicillium
notatum was. Which conclusion is BEST defended
by Fleming’s discovery?
–
–
–
–
A) P. notatum destroys all colonies of S. aureus
B) P. notatum prevents the growth of all bacteria
C) P. notatum inhibits the growth of S. aureus
D) P. notatum promotes the growth of certain bacteria
colonies
Bell Work 3/1/10
 A pesticide manufacturer claims that a new product will decrease
the pest population 15% more than the current pesticide for a 10week period. A population of 50 beetles of the same species is
exposed to the new pesticide for a 10-week period. A separate
population of the same species of beetle is exposed to the same
amount of the current pesticide for a 10-week period. The data
collected is sent to an independent research company to verify
the results. Which statement BEST explains how an independent
research company verifies data to ensure unbiased results.
 A) The company compares the data given to similar
investigations
 B) The company performs the same investigation and compares
results
 C) The company sends out the data to another researcher to
investigate
 D) The company tests many types of pesticides and draws its
own conclusion
12-4: Mutations
What is a mutation?
 any change in the DNA sequence
 two types:
1. gene mutations (changes in a single gene)
2. chromosomal mutations (changes in whole
chromosomes)
Gene Mutations
 POINT mutations
- mutations that affect ONE nucleotide
- mainly substituting one nucleotide for
another
 FRAMESHIFT mutations
- mutations that affect MULTIPLE
nucleotides and shift the “reading frame”
- adding/deleting a nucleotide
Gene Mutations
Gene Mutations
Chromosomal Mutations
 4 types:
deletion
duplication
inversion
translocation
MUTATIONS