Download Molecular Genetics

Unit 5
Molecular Genetics
DNA and RNA
I. DNA- deoxyribonucleic acid
A. History of DNA as Genetic Material “code of
life”
1. Griffith and Transformation
a. Frederick Griffith made discovery while
investigating bacteria known to produce
pneumonia
b. Griffith isolated two different strains of
bacteria
1). Disease causing strain- had (S) smooth edges.
When injected into mice caused pneumonia.
2). Harmless strain- grew with (R) rough edges.
3). When disease causing bacteria heatedmice survived when injected
4). Mixed the heated-killed bacteria and
harmless ones. When injected caused
pneumonia. Concluded that one strain had
been changed into another. Called
transformation (another organism takes up
outside DNA.).
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
Avery
 Identified the molecule that transformed
the R strain of bacteria into the S strain
 Concluded that when the S cells were
killed, DNA was released
 R bacteria incorporated this DNA into their
cells and changed into S cells.
 Concluded that DNA carries the genetic
code
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
Hershey and Chase
Showed conclusively that
DNA was molecule that
carried genetic code.
Studied viruses known as
Bacteriophages
(virus that infects bacteria)
Bacteriophage
Used different radioactive markers to label DNA
and proteins of bacteriophages
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
 Nucleotides
 Consist of a
five-carbon sugar
a phosphate group
a nitrogenous base
Base Groupings
Purines (Double ringed)
1. Adenine
2. Guanine
Pyrimidines (Single ringed)
1. Cytosine
2. Thymine
Backbone of DNA chain formed by sugar and
phosphate groups of nucleotides
sugar
phosphate
Chargaff’s Rule- ratio of guanine:cytosine and
adenine:thymine are equal
A=T
and
G=C
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
X-ray Diffraction
1950’s Rosalind Franklin used X-ray
diffraction to study structure of DNA molecule.
Concluded structure was coiled like a spring (helix)
 X-ray diffraction data helped solve the
structure of DNA
X-ray Diffraction cont’d…
 Indicated that DNA was a double helix
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
Watson and Crick
 After looking at Franklin and Wilkin’s work,
Watson and Crick constructed a model of
DNA molecule (1953)
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
 DNA often is compared to a twisted ladder.
 Rails of the ladder are represented by the
alternating deoxyribose and phosphate.
 The pairs of bases (cytosine–guanine or
thymine–adenine) form the steps.
Chapter
12
Molecular Genetics
12.1 DNA: The Genetic Material
Chromosome Structure
 DNA coils around histones to form nucleosomes,
which coil to form chromatin fibers.
Quick Molecular Genetic
Terminology
•
•
•
•
Replication= DNA DNA
Transcription= DNA RNA
Translation= RNA Amino Acids
Polypeptide= Chain of amino acids
• Adenine, cytosine, & guanine= DNA & RNA
• Thymine= DNA Only
• Uracil= RNA Only
Chapter
12
Molecular Genetics
12.2 Replication of DNA
Replication
 Parental strands of
DNA separate,
serve as templates,
and produce DNA
molecules that have
one strand of
parental DNA and
one strand of new DNA.
Chapter
12
Molecular Genetics
12.2 Replication of DNA
Unwinding
 DNA helicase, an enzyme, is responsible for
unwinding and unzipping the double helix.
 RNA primase adds a short segment of RNA,
called an RNA primer, on each DNA strand.
Chapter
12
Molecular Genetics
12.2 Replication of DNA
Joining
 DNA polymerase removes the RNA primer
and fills in the place with DNA nucleotides.
 DNA ligase links the two sections.
Chapter
12
Molecular Genetics
12.2 Replication of DNA
Comparing DNA in Eukaryotes and Prokaryotes
 Eukaryotic DNA located in cells nucleus in form
of a number of chromosomes
 In prokaryotes, the circular DNA strand is opened
at one origin of replication.
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
Central Dogma: DNA makes RNA makes protein
 RNA
 Contains the sugar ribose
and the base uracil
 Usually is single stranded
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
Messenger RNA (mRNA)
 Strands of RNA nucleotides that are
complementary to one strand of DNA
Ribosomal RNA (rRNA)
 Helps join the mRNA codons to the tRNA
anticodons in the ribosome
Transfer RNA (tRNA)
 Transport amino acids to the ribosome
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
Transcription
 DNA to mRNA
 DNA is unzipped in
the nucleus and RNA
polymerase binds to
a specific section where
an mRNA will be synthesized.
Animation
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
The Code
 DNA code is a three-base code.
 The three-base code in mRNA is called a
codon.
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
Translation
 RNA Amino Acid
 In translation, tRNA
molecules act as the
interpreters of the mRNA
codon sequence.
 Each anticodon (on tRNA)
is complementary to a
codon (on mRNA).
Codons
•64 possible codons
•20 different amino acids
Codons
Start Codon
• AUG
Stop Codons
• UGA
• UAA
• UAG
Molecular Genetics
Extra Facts
• Genes give instructions for making
proteins
• It is possible for more than one combo of
codons to code for the same amino acid
because there are 64 different types of
codons, but only 20 amino acids
• Takes 3 bases to code for 1 amino acid
Chapter
12
Molecular Genetics
12.3 DNA, RNA, and Protein
RNA Processing
 The code on the DNA is interrupted
periodically by sequences that are not in the
final mRNA.
 Intervening sequences are called introns.
are cut out by enzymes
 The portions of DNA molecules that actually
code for the production of proteins are
called exons.
parts of the mRNA that are kept and expressed
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
Mutations
 A permanent change that occurs in a cell’s
DNA
2 Main Types of Mutations:
Gene
Chromosomal
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
Causes of Mutation
 Can occur spontaneously
 Radiation such as UV rays, X rays and
gamma rays
 Chemicals – Mutagens & carcinogens
 Nondisjunction
 Viral Infection- HPV
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
Body-cell v. Sex-cell Mutation
 Somatic cell mutations are not passed
on to the next generation.
 Mutations that occur in sex cells are
passed on to the organism’s offspring and
will be present in every cell of the offspring.
Gene mutations
• Point mutations – mistakes with 1 nucleotide
– Substitution of the wrong nucleotide (nitrogen base) in
place of correct one
• Frameshift mutations – occur when a nucleotide is
either inserted or deleted, altering the codon
sequence
– More severe than point mutations because it affects all
of the amino acids in the protein
Chromosomal mutations
• Change in the number or structure of
the chromosomes
– Duplication
– Inversion
– Translocation
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation