Transcript Document

Honors
Biology
Ch. 12
Molecular Genetics
CH. 12 Molecular Genetics
I.DNA: The Genetic Material
- DNA: The Chemical
Basis of Heredity that
forms the universal
genetic code of cells
A. Discovery of the Genetic
Material
- In the early 1900’s scientists
were debating what was the
genetic material:
DNA vs. Protein.
1. Griffith
- In 1928 Griffith showed that a
heat killed, but lethal strain of
pneumonia bacteria could
‘transform’ a harmless
strain of pneumonia.
Can the Genetic Trait of Pathogenicity Be
Transferred between Bacteria?
EXPERIMENT Bacteria of the “S” (smooth) strain of Streptococcus pneumoniae are pathogenic because they
have a capsule that protects them from an animal’s defense system. Bacteria of the “R” (rough) strain lack a capsule
and are nonpathogenic. Frederick Griffith injected mice with the two strains as shown below:
Living S
(control) cells
Living R
Heat-killed
(control) cells (control) S cells
Mixture of heat-killed S cells
and living R cells
RESULTS
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells
are found in
blood sample.
CONCLUSION
Griffith concluded that the living R bacteria had been transformed into
pathogenic S bacteria by an unknown, heritable substance from the dead S cells.
2. Avery
- In 1944 Avery isolated DNA,
proteins, and lipids from the heatkilled, lethal bacteria,
and concluded that
DNA was the
transforming
agent.
3. Hershey and Chase
- In 1952 Hershey and Chase used
bacteria-infecting viruses containing
either radioactively label S or P to
show that DNA was the genetic
material.
Phage
head
Viruses Infecting
a Bacterial Cell
DNA
Bacterial
cell
100 nm
Tail
Tail
fiber
Is DNA or Protein the Genetic Material
of Phage T2?
EXPERIMENT
In their famous 1952 experiment, Alfred Hershey and Martha Chase used radioactive sulfur
and phosphorus to trace the fates of the protein and DNA, respectively, of T2 phages that infected bacterial cells.
1
2 Agitated in a blender to 3
Mixed radioactively
separate phages outside
labeled phages with
the bacteria from the
bacteria. The phages
bacterial cells.
infected the bacterial cells.
Phage
Centrifuged the mixture 4 Measured the
so that bacteria formed
radioactivity in
a pellet at the bottom of
the pellet and
the test tube.
the liquid
Radioactivity
(phage protein)
in liquid
Radioactive Empty
protein
protein shell
Bacterial cell
Batch 1: Phages were
grown with radioactive
sulfur (35S), which was
incorporated into phage
protein (pink).
Batch 2: Phages were
grown with radioactive
phosphorus (32P), which
was incorporated into
phage DNA (blue).
DNA
Phage
DNA
Centrifuge
Radioactive
DNA
Pellet (bacterial
cells and contents)
Centrifuge
Pellet
Radioactivity
(phage DNA)
in pellet
RESULTS Phage proteins remained outside the bacterial
cells during infection, while phage DNA entered the cells.
When cultured, bacterial cells with radioactive phage DNA
released new phages with some radioactive phosphorus.
CONCLUSION Hershey and Chase concluded that DNA,
not protein, functions as the T2 phage’s genetic material.
B.DNA Structure
- The structure of DNA was discovered by
James Watson and Francis Crick in 1953.
Watson and Crick
with Their DNA Model
- Rosalind Franklin used X-Ray
diffraction to discover the shape
and dimensions of DNA.
Rosalind Franklin
Franklin’s X-ray diffraction
Photograph of DNA
1.Components of DNA
(3 Main Parts)
a. Sugar
(Deoxyribose)
b. Phosphate
c. Bases
c. Bases
(1) Adenine (A)
Guanine (G)
(2) Cytosine (C)
Thymine (T)
2. Nucleotide:
- a subunit of a
nucleic acid
containing a sugar,
a phosphate,
and a base
3.DNA Shape:
- double helix
a. backbone - sugars
and phosphates
b. paired bases form
on the inside
c. Base Pairing Rule:
A : T , C : G
Link to an interview
with James Watson
(1:42)
The Watson-Crick Model of
DNA Structure
II. Replication of DNA :
- process by which DNA makes an
exact copy of itself
- occurs before mitosis during
interphase
A.Semiconservative Replication
- DNA strands separate and serve
as templates for rebuilding the
other half.
T
A
T
A
T
A
C
G
C
G
C
T
A
T
A
T
A
A
T
A
T
A
T
G
C
G
C
G
C
G
A
T
A
T
A
T
C
G
C
G
C
G
T
A
T
A
T
A
T
A
T
A
T
C
G
C
G
C
A
G
Free
Nucleotides
DNA
Replication
New
double
helix with
1 old &
1 new
strand
Parental
DNA
double
helix
1. Unwinding
- DNA helicase unwinds and unzips
DNA molecule.
- RNA primase adds a short segment
(RNA primer)
on each DNA
strand.
DNA Replication
Overall direction of replication
1 Helicase unwinds the
parental double helix.
2 Molecules of singlestrand binding protein
stabilize the unwound
template strands.
3 The leading strand is
synthesized continuously in the
5 3 direction by DNA pol III.
Leading
strand Origin of replication
Lagging
strand
Lagging
strand
Leading
strand
OVERVIEW
DNA pol III
Leading
strand
5
3
Parental DNA
Replication fork
Primase
DNA pol III
Primer
4 Primase begins synthesis
of RNA primer for fifth
Okazaki fragment.
5 DNA pol III is completing synthesis of
the fourth fragment, when it reaches the
RNA primer on the third fragment, it will
dissociate, move to the replication fork,
and add DNA nucleotides to the 3 end
of the fifth fragment primer.
4
DNA ligase
DNA pol I
Lagging
strand
3
6 DNA pol I removes the primer from the 5 end
of the second fragment, replacing it with DNA
nucleotides that it adds one by one to the 3’ end
of the third fragment. The replacement of the
last RNA nucleotide with DNA leaves the sugarphosphate backbone with a free 3 end.
2
1
3
5
7 DNA ligase bonds
the 3 end of the
second fragment to
the 5 end of the first
fragment.
2. Base Pairing
- DNA polymerase adds nucleotides
with the complementary base on
the 3’ end of each strand.
- The leading strand is synthesized
continuously by adding nucleotides
to 3’ end.
- The lagging strand is synthesized
from Okazaki fragments which are
later connected by DNA ligase.
3. Joining
- RNA primers are replaced by
DNA nucleotides
- DNA ligase connects the
fragments together.
Link to
DNA Replication
Video Clip (2:19)
A Summary of DNA Replication
Overall direction of replication
Lagging
Leading
strand Origin of replication strand
1 Helicase unwinds the
parental double helix.
2 Molecules of single- 3 The leading strand is
strand binding protein synthesized continuously in the
stabilize the unwound 5 3 direction by DNA pol III.
template strands.
DNA pol III
Lagging
strand
OVERVIEW
Leading
strand
Leading
strand
5
3
Parental DNA
4 Primase begins synthesis
of RNA primer for fifth
Okazaki fragment.
5 DNA pol III is completing synthesis of
the fourth fragment, when it reaches the
RNA primer on the third fragment, it will
dissociate, move to the replication fork,
and add DNA nucleotides to the 3 end
of the fifth fragment primer.
Replication fork
Primase
DNA pol III
Primer
4
DNA ligase
DNA pol I
Lagging
strand
3
6 DNA pol I removes the primer from the 5 end
of the second fragment, replacing it with DNA
nucleotides that it adds one by one to the 3’ end
of the third fragment. The replacement of the
last RNA nucleotide with DNA leaves the sugarphosphate backbone with a free 3 end.
2
1
3
5
7 DNA ligase bonds
the 3 end of the
second fragment to
the 5 end of the first
fragment.
Telomeres
1 µm
B. DNA Replication in Prokaryotes
- Prokaryotic chromosomes made
of one circular DNA strand
without proteins.
- DNA replication begins at a single
origin of replication and occurs
very quickly.
Origins of Replication
in Eukaryotes
Origin of replication
1 Replication begins at specific sites
where the two parental strands
separate and form replication
bubbles.
Bubble
Parental (template) strand
Daughter (new) strand
0.25 µm
Replication fork
2 The bubbles expand laterally, as
DNA replication proceeds in both
directions.
3 Eventually, the replication
bubbles fuse, and synthesis of
the daughter strands is
complete.
Two daughter DNA molecules
(a) In eukaryotes, DNA replication begins at many sites along the giant
DNA molecule of each chromosome.
(b) In this micrograph, three replication
bubbles are visible along the DNA of
a cultured Chinese hamster cell (TEM).
C. Chromosome Structure
- Chromosomes of eukaryotes are made of
DNA and proteins forming bead-shaped
nucleosomes which are coiled and folded to
form chromatin.
Structure of a
Eukaryotic
Chromosome
C. Chromosome Structure
- Chromosomes of eukaryotes are made of
DNA and proteins forming bead-shaped
nucleosomes which are coiled and folded to
form chromatin.
Link to
DNA Packaging
Video Clip (1:43)
III.DNA, RNA, and Protein
A. ‘Central Dogma’
- DNA codes for RNA which
guides protein synthesis.
1. Gene
- a specific sequence of bases in
DNA that determines the
sequence of amino acids in a
protein
2. Proteins
- composed of 50-20,000 amino acids
- 4 Levels of Structure:
a) Primary:
- sequence of amino acids
b) Secondary:
- either -helical or “β-pleated sheet”
c) Tertiary:
- globular (3-dimensional)
d) Quaternary:
- 2+ polypeptides combined
Illustration of Protein Structure
Primary
(Amino Acid
Sequence)
Tertiary
(Bending)
Quaternary
(Layering)
Secondary
(Helix)
B. RNA Structure:
- Nucleic acid
that makes
protein
B.RNA Structure:
Shape
Sugar
Base
Size
Location
Function
DNA
double helix
deoxyribose
thymine
very large
nucleus
- stores genetic
info
- replication
- makes RNA
RNA
single helix
ribose
uracil
smaller
cytoplasm
- makes
protein
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
Original DNA
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
DNA base
pairs separate
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
DNA half
‘transcribes’ RNA
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
Link to
Transcription
Video Clip
(1:54)
RNA released to
make protein
Transcription: First Two Steps
Transcription: Last Step
Three Types of RNA
mRNA
A G A U G C G A G U U A U G G
codons
Ribosome
contains rRNA
Met Amino
acid
tRNA
anticodon
Large
subunit
1 2
Small
subunit
tRNA
docking
sites
UGA
D. Messenger RNA (mRNA):
- carries the information for
making a protein from DNA
to the ribosomes
- acts as a template (pattern)
- contains codons:
triplets of bases that code
for a particular amino acid
- Start Codon:
(AUG) - marks the start of a polypeptide
- Stop Codon:
(UAA, UAG, UGA) - marks the end
E. Transfer RNA (tRNA):
- carries amino acid to specific
place on mRNA
- contains Anticodon:
triplet of bases complimentary
to mRNA codon
F. Ribosomal RNA (rRNA):
- combined with protein into
ribosomes (site of protein
synthesis)
IV. Translation:
- protein synthesis
- decoding the "message" of
mRNA into a protein
Link to
Translation
Video Clip
(2:05)
Information Flow:
DNA
RNA
Protein
Translation: Initiation
Translation: Elongation 1
Translation: Elongation 2
Translation: Elongation 3
Translation: Elongation 4
Translation: Elongation 5
Translation: Termination
V. Genetic Regulation and
Mutations
A. Prokaryotic Gene Expression
- Prokaryotic cells regulated gene expression
with a set of genes called an operon.
- An operon consists of
1. Operator
2. Promoter
3. Regulatory gene
4. Protein coding genes
Trp Operon: Inducible Operon
Regulation of a Metabolic Pathway
(a) Regulation of enzyme
activity
Precursor
Feedback
inhibition
(b) Regulation of enzyme
production
Enzyme 1
trpE Gene
Enzyme 2
trpD Gene
Enzyme 3
Regulation
of gene
expression
trpC Gene
–
Enzyme 4
trpB Gene
–
Enzyme 5
Tryptophan
trpA Gene
The trp operon: regulated synthesis
of repressible enzymes
trp operon
Promoter
Promoter
Genes of operon
trpD
trpC
trpE
trpR
DNA
trpB
trpA
Operator
Regulatory
gene
mRNA
3
RNA
polymerase
Start codon
Stop codon
mRNA 5
5
E
Protein
Inactive
repressor
D
C
B
A
Polypeptides that make up
enzymes for tryptophan synthesis
Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA
at the promoter and transcribes the operon’s genes.
DNA
No RNA made
mRNA
Active
repressor
Protein
Tryptophan
(corepressor)
Tryptophan present, repressor active, operon off. As tryptophan
accumulates, it inhibits its own production by activating the repressor protein.
B. Eukaryotic Gene Expression
- Eukaryotic cells regulate gene expression
using various transcription factors and
other processes.
Eukaryotic Gene Expression
Distal control
element
Activators
Enhancer
1 Activator proteins bind
to distal control elements
grouped as an enhancer in
the DNA. This enhancer has
three binding sites.
Promoter
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
2 A DNA-bending protein
brings the bound activators
closer to the promoter.
Other transcription factors,
mediator proteins, and RNA
polymerase are nearby.
Group of
Mediator proteins
RNA
Polymerase II
Chromatin changes
3 The activators bind to
certain general transcription
factors and mediator
proteins, helping them form
an active transcription
initiation complex on the promoter.
Transcription
RNA processing
mRNA
degradation
RNA
Polymerase II
Translation
Protein processing
and degradation
Transcription
Initiation complex
RNA synthesis
C. Mutations
- any change in the nucleotide sequence of
DNA
- usually recessive
- many are harmful
- some are neutral
- some beneficial (leads to evolution)
- Mutagens: cause mutations
1) Radiation- UV, X-rays, etc.
2) Chemicals (asbestos, etc.)
D. Types of Mutations:
1. Point Mutation
- change of a single base
- ex: sickle-cell anemia
AUG GGG CUU CUU AAU
AUG GGG CAU CUU AAU
Normal Red Blood Cells
Sickled Cells
Link to a Video
Clip about Sickle
Cell Disease(0:59)
2. Frameshift Mutation
- addition or deletion of a single base
AUG GGG CUU CUU AAU
AUG GGG CAU UCU UAA U
3. Chromosomal Mutation
- change in an entire chromosome or in
chromosome number within a cell
a) Translocation:
Normal
Translocation
b) Inversion:
Normal
Inversion
c) Insertion:
Normal
Insertion
d) Deletion :
Normal
Deletion
The End
(Cytoplasm)
DNA
(Nucleus)
1 Transcription
rRNA mRNA tRNA
+ Proteins
tRNA
Ribosomes
mRNA
tRNA-AA
2 Translation
Inactive
Protein
Active
Protein
3 Modification
4 Degradation
Substrate
Product
Amino
Acids
Overview of
Information Flow
Complementary Base Pairing
gene
G
C
A
T
G
G
G
A
G
T
template
DNA strand
T
(a) complementary
DNA strand
C
G
T
A
C
C
C
T
C
A
A
codons
(b) mRNA
G
C
A
U
G
G
G
A
G
U
U
anticodons
(c) tRNA
U
A
C
C
C
U
C
A
amino acids
(d) protein
Methionine
Glycine
Valine
A
Incorporation of a Nucleotide
into a DNA Strand
New strand
Template strand
Sugar
A
Base
Phosphate
3’ end
5’ end
3’ end
5’ end
T
A
T
C
G
C
G
G
C
G
C
A
T
A
P
OH
P
Pyrophosphate 3’ end
C
C
OH
Nucleoside
triphosphate
2 P
5’ end
5’ end
Structural Proteins
Horn
Hair
Spiderweb
Hair
Structure
Hair
Cell
Single hair
Microfibril
Protofibril
|
S
|
Hydrogen bonds
S
|
|
S
|
S
|
disulfide
bridges
Curling of Hair
S
|
|
|
S
|
|
S
S
|
|
|
S
|
S
S
|
|
|
S
|
Permanent
Wave
S
|
Naturally
Curly
Hair
|
S
|
S
|
|
S
Straight
Hair
LUX Operon Controls Light Production
Light Emitted
by Bacterial
Luciferase
Video Clip about how a single transcription
factor controls the LUX operon, which
contains five genes necessary to produce
bioluminescence in bacteria (2:26).