Download DNA Structure, Replication, and Repair

Genetic Tranmission
Warm up
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Group 1 – Griffith experiment (279)
Group 2 – Avery experiment (279)
Group 3 – Hershey-Chase (279-280)
Group 4 – Watson-Crick and Franklin (281-283)
Group 5 – Meselson-Stahl experiment (284-285)
Write out a brief summary and state the
significance of the experiment(s) on the
transparency
DNA structure
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Antiparallel
DNA replication
Origin of replication
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Bacteria chromosomes
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1 replication origin
Recognized by a specific sequence
Eukaryotic chromosomes
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Hundreds or thousands of replication origin
Multiple Replication “bubbles” occur
simultaneously
Elongation
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Elongation
ss binding proteins hold strands apart
Primase joins RNA nucleotides to template (primer)
DNA polymerase III joins DNA nucleotides to template
DNA polymerase I replaces primer
with DNA nucleotides
Elongation (more nuances)
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Nucleoside triphosphate links to backbone,
losing 2 phosphates (ENERGY!)
Lagging strand –
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Proceeds away from the replication fork
Requires new primer for every okazaki
fragment (100 – 200 nucleotides)
Fragments joined by ligase
DNA replication - summary
DNA replication summary
What is a gene? Beadle and Tatum
What is a gene?
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A DNA segment has information for
making the protein hemoglobin, which
carries oxygen in your red blood cells
One allele will give information for
producing normal hemoglobin
-Another allele (ONLY 1 base
different) produces hemoglobin with 1
different amino acid
This difference makes the hemoglobin
less soluble
When Oxygen levels are low, the
hemoglobin molecules start sticking
together, resulting in the red blood
cell’s “sickle-shape”
Having both defective alleles will lead
to multiple effects shown to the right
What is a gene?
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Having only 1 defective allele (heterozygous) will
not be fatal and actually beneficial!
Malaria is a disease spread by mosquitois that
infects red blood cells
Being heterozygous results in your body
destroying the red blood cells as well as the
Malaria, leaving enough of the normal blood cells.
What is a gene?
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Mendelian definition:
Morgan definition:
1 gene-1polypeptide definition:
What about noncoding region, non
translated RNA?
“Region of DNA whose final product is
either a polypeptide or an RNA molecule”
What do you think?
Genetic code
Genetic code
Transcription
1. Transcription initiation
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Prokaryotes - RNA
polymerase attaches to
the promoter (startpoint
and upstream nucleotides)
Eukaryotes –
Transcription factors bind
to TATA box region of
promoter  RNA
polymerase II binds to
promoter (transcription
initiation complex)
Transcription elongation and termination
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2. RNA polymerase
untwists DNA and joins
RNA nucleotides (DNA
rejoins as RNA strand
peels away)
3. Prokaryotes –
termination at a DNA
certain DNA sequence
Eukaryotes – RNA
polymerase goes beyond
termination sequence
(AAUAAA –
polyadenylation)
Eukaryotic RNA modification
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5’ end – modified GTP (protect from
degradation and is signal for ribosomes)
3’ end – poly(A) tail (same functions and
facilitates export from the nucleus)
RNA
splicing
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Post transcriptional
nuances
Some organism’s
intron RNA
catalyzes splicing
(ribozymes)
Introns may
perform regulatory
roles
Domains
tRNA structure and function
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There are 61
codon
combinations,
but only 45
different
tRNAs. Why?
Wobble
position (A or G )
Connecting a.a. to
the correct tRNA
Ribosome structure and function
Translation - initiation
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mRNA, tRNA, ribosomal subunits brought
together with help of initiation factors
1. Small ribosomal subunit binds to mRNA
and initiator tRNA
2. Large ribosomal subunit attaches
Translation - elongation
Translation - termination
Translation nuances
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Polyribosomes
Posttranslational modifications – chemical
modifications, removal of amino acids,
polypeptide cleaved, joining of 2
polypeptides (hemoglobin)
DNA repair
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Replication problems?
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Initial paring errors: 1/10,000 bases
However, completed DNA has only 1 error in
every 1,000,000,000 bases
DNA polymerase can’t add to the 5’ end of
daughter DNA strands (why don’t prokayrotes
have this problem?)
DNA repair – solutions!
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Mismatch repair: DNA polymerase
proofreads nucleotides as it is added and
corrects it immediately
Additional proteins perform mismatch
repair
Excision repair (already damaged DNA) –
nuclease removes DNA segment and DNA
polymerase and ligase fill in with correct
nucleotides
DNA repair – solutions!
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Telomeres (non coding repeated sequence –
TTAGGG)
Telomerase lengthens telomeres by
incorporating its own RNA as template for
new segment
Not found in most cells – only germ line
cells and cancerous cells
Mutations
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Make a mini concept map using MOST or
ALL of the following terms (feel free to
add more) : mutations, point mutations,
substitutions, insertions, deletions,
frameshift mutation, mutagens,
missense mutations, nonsense mutations,
wild type, codon, polypeptide, DNA
replication, recombination, DNA repair,
nondisjunction, aneuploidy, polyploidy,
duplication, inversion, translocation,
deletion