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DNA and RNA
Ch. 12 and 13
Griffith’s Experiments
• They were done to
determine whether
genes are made up of
DNA or protein.
• He injected bacteria
into mice in four
separate experiments.
His results..
• S bacteria caused
pneumonia and death
when injected.
• R bacteria had no visible
effect.
• Heat killed S bacteria did
no harm.
• Heat killed S and live R
were injected and the
mouse died of pneumonia.
• Streptococcus
pneumonia bacteria
were used.
• S strain was smooth
and caused
pneumonia.
• R strain was rough and
did no harm.
What can we conclude?
• If the mice died with S
and heat-killed S and R,
but not when S was heatkilled or R by itself, then
there had to be some
transforming material that
was transformed from the
heat-killed S to living R
changing it into S bacteria.
• What was this
transforming material?
• DNA
Oswald Avery
• Repeated Griffith’s experiment.
• Discovered that it is the nucleic acid DNA stores and
transmits the genetic information from one generation
of an organism to the next.
Hershey and Chase’s Experiment
• 2 experiments.
• Used bacteriophages
(viruses) that injected
radioactive material
into bacteria. They
they looked to see if
the bacteria became
radioactive.
1.
2.
Phages with green
radioactive DNA 32-P
injected it into bacteria
and the bacteria became
radioactive.
Phages with green
radioactive protein 35-S
injected it into bacteria
and it did not become
radioactive.
What can we conclude?
DNA Structure
• Remember that the
structure of a molecule
is related to its
function, so knowing
what a molecule looks
like gives researchers
insight into how DNA
works.
• What do you know
about DNA?
•
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•
•
•
Deoxyribonucleic acid
Double Helix
5’C sugar, Deoxyribose
Phosphate Group
4 Nitrogen Bases
Nucleotide
• First double helix
structure built by Watson
and Crick
• Published in 1953
Purines and Pyrimidines make up
the 4 N bases
• Purines- larger
– Adenine and Guanine
• Pyrimindines- smaller
– Cytosine and Thymine
Pairing of the bases in the DNA structure:
Chargaff’s Rule
(amount of A = amount of T and amount of C =amount of G
A—T
C—G
Discovery of DNA: X-Ray evidence
• Rosalind Franklin
used X-ray diffraction
to reveal the shape of
DNA.
•The X-shaped pattern shows
that the strands of DNA are
twisted around each other.
Double Helix
• The shape of DNA is that
of a “twisted ladder”.
• The P group is attached to
the sugar and that forms the
backbone.
• The “rungs” of the DNA
are the pairing of the bases.
• Watson and Crick
DNA Replication Semi-conservative
1.
2.
3.
The DNA unzips.
Enzymes split apart the
base pairs and unwind
the DNA.
Free nucleotides in the
cell find bases to pair up
with on each side along
the “open” DNA via
DNA polymerase.
The sugar-phosphate
backbone completes the
2 new DNA strands.
DNA Replication Simulation
• Each strand has a new and old
strand.
In depth DNA Replication
1. Antiparallel strands. Replication is 5’ to 3’
2.Topoisomerase (DNA gyrase) relieves superhelicity
downstream of replication fork.
3. Helicase unwinds ds DNA.
4. Primase synthesizes the RNA primers for lagging strand,
complexes with helicase. (not shown)
5. Ssb proteins keep DNA from reannealing.
6. DNA pol III polymerizes leading and lagging strand.
7. Lagging strand- okasaki fragments
8. DNA pol I- removes RNA primers and replaces with
DNA.
9. DNA ligase seals gaps
Cloning
Clone the Mouse
• A clone is a member
of a population of
genetically identical
cells produced from a
single cell.
• In 1997, Dolly the
sheep was the first
clone of an adult
mammal. It took over
500 tries.
Human Cloning?
Why or Why not?
Protein Synthesis
• Process when the
organism’s genotype
is translated into it’s
phenotype.
• Remember that
proteins are made up
of chains of Amino
Acids.
• How many a.a. are
there?
•
2 Processes
1. Transcription- DNA
to RNA
2. Translation- RNA
Protein
1.26 The genetic material in DNA molecules provides the
instructions for assembling proteins. This works the same in
nearly all life forms.
DNA vs. RNA
DNA
Double Stranded
Base Pairs (A-T, G-C)
Deoxyribose sugar
RNA
Single Stranded
Base Pairs (A-U, G-C)
Uracil is used instead
of Tymine
Ribose Sugar
Transcription
1. RNA polymerase unwinds • It occurs in the
a section of DNA
nucleus.
2. RNA polymerase binds
unattached RNA
• Tutorial
nucleotides to
complementary DNA
strand at promoter region.
3. A new strand of mRNA
(messenger RNA) is made.
4. DNA will signal RNA pol
to leave and transcription
stops.
RNA splicing
• Before mRNA can
• Introns- non-coding regions
leave the nucleus,
of DNA or RNA.
RNA must be spliced.
• Exons-coding regions
• It gets rid of introns
and exons are spliced
together.
• mRNA now leaves the
nucleus and into the
cytoplasm where it
finds a ribosome.
Things to Know before we go on.
• Codon- 3 base
sequence of mRNA
that codes for an
amino acid.
• Anti-codon:
complementary 3 base
sequence to mRNA on
a tRNA.
• rRNA- ribosome
where amino acids are
put together.
• tRNA (transfer RNA)matches up anticodons
to codons to make
amino acids that form
proteins.
Translation
1. rRNA attaches to first
codon on mRNA.
2. A tRNA brings an a.a.
to the rRNA with the
anti-codon and matches
it up with the codon.
3. A 2nd tRNA brings in the
next one and then a
peptide bond bonds the 2
a.a. together. It moves
over and the 1st one
leaves so the next one can
come in.
http://www.rothamsted.bbsrc.ac.uk/notebook/courses/guide/trad.htm
Starting and Stopping Translation
• AUG- Methionine is
the Start Codon.
• There are 3 Stop
Codons: UAA, UAG,
and UGA.
Protein synthesis
Frameshift mutations (Gene
mutation)
• When nucleotides are
deleted or added, it
changes the order or
code of the codons,
results in different a.a.
Point Mutations (Gene mutation)
• Occur when there is only one change in the
nucleotide. It only changes one a.a. coded for.
Jumping Genes (Transposons)
• Occurs when
a large
stretch of
DNA is
inserted into
the gene.
• Multicolored
corn
• 1.28b Genetic variation occurs from crossing over,
jumping genes and deletion and duplication of genes.
Mutations arise?
• 1. ionizing radiationgamma and X-rays
• 2. alkylating agentscarcinogens.
• If occur in somatic
cells- only affects that
cell.
• If occurs in gametepassed on.
Polyploidy
• When nondisjuction
occurs in all
chromosome pairs.
• Occurs often in plants
and can make them
“robust”.
Control over Genes
Ch. 14
Control Over Genes
• Regulatory proteins intervene before, during
or after gene transcription or translation. Ie.
Hormones, initiate changes in cell activities
when they dock at suitable receptors.
• Negative control- slow or stop gene action
(repressor protein)
• Positive control- promote or enhance it
(activator protein)
Promoters and Enhancers
• Promotors- noncoding
sequence that marks
where to start
transcription. RNA
polymerase hops on.
• Enhancers- binding
sites for activator
proteins.
Structure Determines Function
When genes are
changed, the proteins
they code for may
change and this can
affect cell structure
and function,which
changes a phenotype.
• The control of gene
expression (protein
synthesis), is different
in prokaryotes and
eukaryotes.
Gene Expression
• Prokaryotes
– Genes turn on and off
primarily in response to
changes in environmental
factors.
• 1.1b Different parts of the
genetic instructions are used
in the different kinds of cells
and are influenced by the
cell’s environment and past
history.
• Eukaryotes
– Gene regulation involves
several complex systems.
– Most eukaryotic genes are
controlled individually and
have regulatory sequences
that are much more
complex.
– TATA box
Operons
• A group of genes that operate together are
known as operons.
• In E.coli there are 4288 protein encoding
genes that are turned off and on together.
• Because the genes must be expressed in
order for the bacterium to be able to use the
sugar lactose as food, they are called lac
operon.
Gene Regulation in Prokaryotes
1. The regulatory gene
codes for production
of the repressor that
binds to DNA,
preventing RNA pol
from binding to the
promoter. Protein
synthesis can’t occur.
Lac genes (operon)- group of
genes that operate together.
The repressor is inactivated.
2. Enzymes bind to the
repressor and changes
it’s shape so it can’t
combine to DNA.
Now, RNA pol can
bind to promoter.
The Genes are On
3. RNA pol moves along
DNA where mRNA is
translated to produce
product. When there is
enough “product” in the
cell, the repressor takes
back original shape and
turns genes back off.
Was this negative or positive
control?
Analogy of Gene Regulation in
Prokaryotes
• An analogy to gene
control would be when
a house gets below a
certain temp. the
furnace kicks on and
when it is hot enough
it turns back off.
• What would the
promoter be?
Positive control
• The lac operon is controlled by activator
protein called CAP .
• RNA pol binds to promoter if CAP is there.
• CAP is first activated by cAMP.
• When glucose is scarce- CAP-cAMP complex
forms and turn on lactose metabolism genes.
• The lac operon is regulated by several factors
including the availability of glucose and of
lactose. Lactose can be degraded into glucose
for the cell to use. If you have glucose, you
don’t need to have lactose.
Gene Expression in Eukaryotes
• TATA box is about 30 bp long and helps
RNA polymerase to find position by marking
a point just before the point for transcription
to begin.
Eukaryotic Gene Controls
•
•
•
•
Controls before transcription
Controls of transcript processing
Controls at Translation
Controls after translation
• Can you think of activities that need to be
controlled at each of these points?
• Prokaryotic- transcription.
Development and Differentiation
• Differentiation- cells become specialized in
structure and function.
• Hox genes (Homeotic Genes)- control the
differentiation of cells and tissue in the
embryo. Clusters. A mutation can completely
change the organs that develop in specific
body parts. Legs instead of antennae on fruit
fly can grow on head.
Hox gene clusters
What do you recognize about where each gene controls in each
organism?
X-Chromosome Inactivation
• Barr Bodies are formed in females (inactivated X) because
one X is all that is needed in some cells and the other is
switched off randomly and forms a dense region in the
nucleus. Once an X chromosome is inactivated it will
remain inactive throughout the lifetime of the cell and its
descendants in the organism.
• Dosage compensation- process where one of the X on
females is shut down so that the remaining overall
expression of the remaining X is equivalent to the lone X of
the male.
X chromosome inactivation
• Cats
– You can tell if male or
female by spots because
genes that controls spots
is located on X
chromosome. Males will
have one color of spot
and females will have 2
colors. Why? What
happens if one of them is
a Barr Body?
Knock out genes