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Ch. 12 Molecular Genetics
p. 325 - 349
Big Idea
DNA is the genetic material that
contains a code for proteins.
12.1 DNA: The Genetic Material
p. 326 - 332
Essential Question
 How did we come to find out
that DNA is the genetic code?
Main Idea
The discovery that DNA is the genetic code
involved many experiments
What are the 2 main
components of chromosomes?
  DNA and proteins
What did Griffith find from his
studies of Strepococcus
pneumoniae?
  That one strain could be transformed, or
changed into the other form
Which strain causes
pneumonia?
  The coated strain, or the smooth strain
Which strain does not cause
pnemonia?
  The noncoated strain, or the rough strain
Griffith’s Experiment
When Griffith isolated live
bacteria from the dead mouse,
what did that evidence suggest?
  That a disease-causing factor was passed
from the killed deadly bacteria to the live
harmless bacteria
What did Avery conclude?
  When the S cells were killed, DNA was
realeased, and some of the R cells were
exposed to the S cells, and then the S cells
turned into R cells
What were the published results
from Hershey and Chase?
  That DNA is the transforming factor
What technique did Hershey
and Chase use to trace the
DNA and protein?
  Radioactive labeling
What is a nucleotide?
  The subunits of nucleic acids
  Consist of a five-carbon sugar, a phosphate
group, and a nitrogenous base
What is a purine base?
  Guanine and adenine
  Double-ringed bases
What is a pyrimidine base
  Thymine, cytosine, and uriacil
  Single-ringed bases
What is Chargaff’s rule?
  C=G
  A=T
How did Rosalind Franklin
determine DNA was a double
helix shape?
  Using X-ray diffraction she took photo 51
that showed the double helix structure
Double Helix
  Twisted ladder shape
What were the three important
features of Watson and Crick’s
molecule?
1.  Two outside strands consist of alternating
deoxyribose and phosphate
2.  Cytosine and guanine bases pair to each
other by 3 hydrogen bonds
3.  Thymine and adinine bases pair to each
other by two hydrogen bonds
Compare a DNA molecule to a
twisted ladder
  The rails of the ladder are the sugar
phosphate backbone
  The steps of the ladder are the base pairs
In prokaryotes, where is the
DNA molecule located?
  Cytoplasm
How is DNA organized in
Eukaryotic organisms?
  Into individual chromosomes
Nucleosome
  DNA coiled around histones
What makes up the DNA
structure recognized as a
chromosome?
  Nucleosomes grouped together into
chromatin fibers, then supercoiled
Chromosome Structure
12.2 Replication of DNA
p. 333-335
Essential Question
How does DNA
replicate?
Main Idea
  DNA replicates by making a strand that is
complementary to each original strand
Semiconservative Replication
  Parental strands of DNA separate, sere as
templates, and produce DNA molecules that
have one strand of parental DNA and one
strand of new DNA
What are the stages of
semiconservative replication?
1.  Unwinding
2.  Base pairing
3.  Joining
What enzyme is responsible for
unwinding and unzipping the
double helix?
  DNA helicase
What does RNA primase do?
  Adds a short segment of RNA on each DNA
strand
DNA Polymerase
  An enzyme that catalyzes the addition of
appropriate nucleotides to the new DNA
strand
What is the leading strand?
  Is elongated and the DNA unwinds
  It is built continuously
What is the lagging strand?
  The strand that elongates away from the
replication fork
  It is built in small segments
Okazaki fragments
  Small segments of new DNA created on the
lagging strand
DNA Replication
What does DNA ligase do?
  Links the two sections
Comparing DNA Replication in
Eukaryotes and Prokaryotes
  Eukaryotic DNA unwinds in multiple
areas as DNA is replicated
  In prokaryotes, the circular DNA strand is
opened at one origin of replication
12.3 DNA, RNA, and Protein
p. 336-341
Essential Question
 What are the different
types of RNA?
 What is transcription and
translation?
Main Idea
  DNA codes for RNA, which guides protein
synthesis
What is the central dogma of
biology?
  DNA codes for RNA, which guides the
synthesis of proteins
RNA
  A nucleic acid similar to DNA
Comparison of DNA and RNA
  DNA
  Deoxyribonucleic acid
  Contains the bases C,
A, G, T (thymine)
  Double stranded
  RNA
  Ribonucleic acid
  Contains the bases C,
A, G, U (uricil)
  Single stranded
Types of RNA
  mRNA (messenger RNA) – formed
complementary to one strand of DNA
  rRNA (ribosomal RNA) – associates with
proteins to form ribosomes
  tRNA (transfer RNA) – transport amino
acids to the ribosome
Transcription
  DNA code is transferred to mRNA
Takes Place:
  In the nucleus
RNA polymerase
  An enzyme that regulates RNA synthesis
  Binds to a specific section where an mRNA
will be synthesized
Introns
  The code on the DNA is that is interrupted
Exons
  The remaining pieces of DNA that serve as
the coding sequences
Codon
  Three base code in DNA or mRNA
Translation
  Where the mRNA code is read and translated
to make proteins
Steps of Translation
1.  mRNA associates with the ribosomes
2.  tRNA’s add their amino acids as the mRNA
moves through the ribosome one codon at a
time until a stop codon is reached
3.  When a stop codon is reached, the poly
peptide chain (protein) made of amino
acids is released
12.4 Gene Regulation and
Mutation
p. 342 - 349
Essential Question
What are some common
types of genetic
mutations?
Main Idea
  Gene expression is regulated by the cell, and
mutations can affect this expression
Gene regulation
  The ability of an organism to control which
genes are transcribed in response to the
environment
Operon
  A section of DNA that contains the genes for
the proteins needed for a specific metabolic
pathway
Mutation
  A permanent change in a cell’s DNA
Types of Mutations
1.  Point mutations
2. Substitution
3. Missense
3. nonsense
1. Framshift mutations
2. Insertion
2. Deletion
Missense mutations
  DNA code is altered to it codes for the wrong
amino acid
  Ex: achondroplasia
Nonsense mutations
  Change a codon for an amino acid to a stop
codon
  Ex. Muscular Dystrophy
Deletion Mutations
  Loss of a nucleotide that causes a change in
the “frame” of the codon sequence
  ACG GGA CAG (delete the first C)
  AGG GAC AG_
  Ex. Cystic Fibrosis
Insertion
  Addition of a nucleotide
  ACG GGA CAG (add a 4th G)
  ACG GGG ACA G
  Ex. Chron's Disease