molecular genetic ppt
TRANSCRIPT
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MOLECULAR
GENETICS
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I. THE CENTRAL DOGMA*http://www.mansfield.ohio-state.edu/~sabedon/biology.htm
*Coined by Francis Crick in 1958 (http://www.euchromatin.org/Crick01.htm#Published)
A. Explains how genetic informationmoves around a cell and from parentto offspring under normalcircumstances
Replication (S.H.)
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B. Exceptions to the Central Dogma
1. retroviruses have RNA, not DNA andthen their RNA is used as a template
to make DNA in the host cell
a. Enzyme called reverse transcriptase
catalyses the production of DNA from RNA
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(points b and c are from
http://en.wikibooks.org/wiki/IB_Biology/Nucleic_Acids_and_Proteins)
b. can make DNA from mature mRNA
(eg insulin) which can then bespliced into host's (eg bacteria) DNA without the introns. Then when thehost's DNA is transcribed, proteins
like insulin are made.
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i. important that the DNA created by
reverse transcriptase has nointrons, because the host does nothave the genes (and thereforeproteins) necessary to remove theintrons.
2. prions are misshapen proteins that
have the ability to make normalproteins become misshapen as welland thus cause disease
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Let's begin with a specific example of whatwe are trying to learn in this section:
http://learn.genetics.utah.edu/content/begin/dna/firefly/fireflymon8.swf
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II. Transcription A. the process of using a section of DNA
(known as a gene) as a template to
make a molecule of messenger RNA (mRNA)
1. each gene has the information forone polypeptide strand
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B. only one strand of the two strands is
transcribed
i. Called the template strand ornonsense or anti-sense strand or
non-coding strand
C. the strand that is not transcribed is
called the sense or coding or mRNA-like strand
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D. only about 2% of the 3 billion basepairs in human DNA are part of genes
1. in total, there are about 30 000genes
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transcription.htm l
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E. Requirements1. RNA polymerase
a. An enzyme
b. Many forms exist
i. In eukaryotes usually a form
called RNA polymerase II
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2. Raw Materials
a. 4 ribonucleoside triphosphates
i. ATP/adenosine triphosphateii. GTP/guanosine triphosphateiii. CTP/cytidine triphosphateiv. UTP/uridine triphosphate
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F. Steps (in Prokaryotes)
1. Initiation
a. RNA polymerase binds to thetemplate strand of the DNA at an area called thepromoter site
i. by convention, the promoter isindicated on the sense/coding/non-template strand
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b. RNA polymerase opens the DNA
molecule so that about 10 basepairs are separated
2. Elongation
a. Complementary base pairing of free nucleoside triphosphates
occurs with the exposednitrogenous bases of the templatestrand
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b. RNA polymerase binds the
nucleosides to each other
i. Two of the phosphates are
released in the process
c. The 5' end of a nucleoside isadded to the 3' end of the RNA molecule being made
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i. Means that the RNA is made in a5' to 3' direction
ii. Means that the template isbeing read in a 3' to 5' direction
d. As the RNA polymerase movesalong the DNA, it rewinds the
DNA that has been transcribedand unwinds the DNA that hasnot yet been transcribed
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3. Termination
a. RNA polymerase reaches atermination site or terminator
b. RNA polymerase releases themRNA strand
c. DNA rewinds completely
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G. Note that more than one RNA polymerase can be transcribing onegene at the same time
H. Other types of RNA are also made by
transcription
Here are 2 animations of transcription:http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591855 __
http://www.johnkyrk.com/DNAtranscription.html
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I. Transcription in Eukaryotes
Here is an animation of transcription in prokaryotes and also in eukaryotes. Pay attentionto the differences.
http://highered.mcgraw-hill.com/olc/dl/120077/bio25.swf
1. initiation requires proteins called
transcription factors that RNA polymerase binds to
2. the promoter region has a sequence
called the TATA box
3. the promoter often includes a CAATsequence
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4. product is called pre-mRNA andmust be processed
a. Synthesis of a cap made of amodified guanine attached to the5' end
i. protects the RNA from enzymesthat work from the 5' end
ii. Assembly point for the proteinsneeded to attract the smallsubunit of the ribosome to begin
translation
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b. introns (highly repetitive
sequences that code for aminoacids that are not found in theactual polypeptide) are removed
i. Most begin with GU and endwith AG
c. what's left are sequences calledexons (they are expressed)
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i. joined together by spliceosomes
(made of 5 types of snRNA anda large number of proteinmolecules) in a process
called splicing
d. Synthesis of a polyA tail, a stretchof adenine nucleotides attachedto the 3' end
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e. After processing mRNA can leavethe nucleus
Here is an animation of spliceosomes atwork:
http://highered.mcgraw-hill.com/olc/dl/120077/bio30.swf
*alternative and trans splicing makes itpossible for a large number of proteins to be
made from a small number of genes formore information see the following:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transcription.html
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III. TRANSLATION
A. the process of producing apolypeptide chain using the sequenceof nitrogenous bases in mRNA as a
template
B. Requirements
1. Raw materials: amino acids
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2. energy
3. ribosomes consisting of twosubunits (small and large)
a. Are separate when not in use forprotein synthesis
i. Small subunit consists of 1 rRNA molecule and 33 differentprotein molecules in eucaryotes
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ii. Large subunit consists of 3different rRNA molecules and
about 45 different proteins ineucaryotes
4. mRNA with nitrogenous bases intriplets called codons
5. transfer RNA (tRNA) with asequence of nitrogenous basescalled an anticodon
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a. Will complementary base pair withcodons on the mRNA
b. Each tRNA can bind to one aminoacid
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPROTSYn.html#Table%20of%20Contents
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5. Wobble in anticodons
a. Theoretically, there should be 64types of tRNA's based oncomplementary base pairing with
the mRNA codons
b. Most organisms have between 31
and 40 tRNA's
c. One type of tRNA will bind tomore than one codon
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d. Third base of a codon is allowedto bind inexactly (this position isknown as the wobble position)
i. G can bind with U in the wobble
position
ii. Inosine (a modified G) can pair
with C, U or A in the wobbleposition
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C. The Triplet Code
1. the mRNA nitrogenous bases areread in groups of three calledcodons
2. each codon calls for a particularamino acid
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3. the code is degenerate meaning
that more than one codon can codefor the same amino acid
a. there are 64 different codonspossible but only 20 amino acids
b. some codons are stop codons andsignal the end of the polypeptide
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https://www.dna20.com/index.php?pageID=251
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http://www.accessexcellence.org/RC/VL/GG/genetic.php
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D. Steps
1. Initiation
a. Small subunit of ribosome binds
to mRNA and moves along themRNA until it reaches the startcodon AUG
b. Initiator tRNA binds at the P siteon the large subunit
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i. In eucaryotes, the start codon is
AUG
ii. Initiator tRNA has the anticodon
UAC and carries the amino acidmethionine
c. Lastly, large subunit of ribosomebinds
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http://kentsimmons.uwinnipeg.ca/cm1504/proteinsynth.htm
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2. Elongation
a. tRNA's that carry amino acids(charged tRNA's) diffuse to the A site on the ribosome
b. If the anticodon base pairs arecomplementary to the codon base
pairs, the tRNA will stay
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c. A peptide bond is formed between
the amino group of the incomingamino acid and the carboxyl groupof the amino acid or peptide heldat the P site
d. The tRNA at the P site is released
e. The growing polypeptide is on thetRNA located at the A site
f The ibosome mo es one codon
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f. The ribosome moves one codonforward from the 5' end to the 3'
end
i. The start codon is closer tothe 5' end than is the stop
codon
g. The tRNA with the growingpolypeptide is now at the P siteand the A site is empty
h. The steps from a to g repeat
h //k / 0 / h h
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http://kentsimmons.uwinnipeg.ca/cm1504/proteinsynth.htm
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3. Termination
a. Ribosome's A site reaches a stopcodon
b. A release factor binds to thestop codon on the mRNA
c. Polypeptide is released from thetRNA at the P site
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d. Ribosome releases the mRNA
and separates into 2 subunitshttp://kentsimmons.uwinnipeg.ca/cm1504/proteinsynth.htm
l h
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E. Polysomes occur when manyribosomes are translating the same
mRNA http://kentsimmons.uwinnipeg.ca/cm1504/proteinsynth.htm
H 2 i ti f t l ti d i t ti
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Here are 2 animations of translation and an interactivepractice of trascription and translation:
http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591858 _ _
http://www.johnkyrk.com/DNAtranslation.html
http://learn.genetics.utah.edu/content/begin/dna/transcribe/
E. Fate of Molecules
1. mRNA: can be translated by other
ribosomes or degraded and thenucleotides made available forreuse
2 tRNA: becomes charged again
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2. tRNA: becomes charged again
3. ribosomes: available for reuse
4. polypeptide:
a. Folds and coils into secondary andtertiary structures
b. Associate with other polypeptidesto form quaternary structures
c transported to its final destination
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c. transported to its final destinationbased on signal sequences
(sequence of amino acids atterminal end)
d. proteolysis: cutting polypeptideinto smaller fragments
e. glycosylation: addition of sugars
f. phosphorylation: addition of phosphate groups
IV Replication
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IV. Replication
A. the synthesis of a new DNA moleculeusing an existing DNA molecule as atemplate
B. semi-conservative because at end of replication, each new molecule is
made of one old strand plus one newstrand
C R i t
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C. Requirements
1. Raw materials
a. 4 deoxyribonucleoside triphosphates
i. deoxy-ATP/deoxyadenosine
triphosphateii. deoxy-GTP/deoxyguanosine
triphosphateiii. deoxy-CTP/deoxycytidine
triphosphateiv. deoxy-TTP/deoxythymidine
triphosphate
2 h li th t i d
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2. helicase: an enzyme that unwindsthe DNA double helix
3. DNA polymerase III: enzyme that
a. binds to DNA and incomingnucleotides
b. proofreads the growing newstrand
l dd l tid t th 3'
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c. can only add nucleotides to the 3'end of the growing chain
d. Two work at the same time, onefor each strand of DNA
3. RNA primase: enzyme that adds ashort strand of RNA that
complementary base pairs witheach strand of DNA
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a. initiates DNA replication by
producing a 3' end that DNA polymerase can add nucleotidesto
4. DNA ligase: links together shortchains of DNA called Okazaki
fragments
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5. DNA Polymerase I: enzyme that
removes RNA primers and replacesthem with DNA
a. can only add nucleotides to the 3'end of a nucleotide chain
6 telomerase: enzyme that replaces
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6. telomerase: enzyme that replacestelomeres
a. telomeres: region of DNA at theends of chromosomes that help to
prevent against DNA erosion
b. telomerase mostly found in
immortal cells and in thedeveloping organism
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D. Process
1. helicase unwinds the double helix
a. becomes unstable
b. open area is called a replicationbubble or fork
2 single-strand binding protein
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2. single strand binding proteinprevents the two strands from re-
joiningThe following diagram and all similar ones are from:http://www.scq.ubc.ca/breakfast-of-champions-does-replication/
http://kentsimmons.uwinnipeg.ca/cm1504/dnareplication.htm
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p // p g / / p
3. RNA primase puts a short strand of
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p pRNA that is complementary to each
strand of the separated DNA a. needed because the DNA
polymerase need a 3' end to add
nucleotides to
3 RNA primase puts a short strand of RNA
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3. RNA primase puts a short strand of RNA
that is complementary to each strand of
the separated DNA
a. needed because the DNA polymeraseneeds a 3' end to add nucleotides to
3. RNA primase puts a short strand of RNA
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p p
that is complementary to each strand of
the separated DNA a. needed because the DNA polymerase
needs a 3' end to add nucleotides to
b. Only 1 primer is needed for the
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y pDNA strand that ends with the 3'
end (leading strand)
i. because the primer will end with
a 3' end
c. Problem with the strand that endswith the 5' end (lagging strand) isthat the primer will end with the 5'end
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i. DNA polymerase cannot add
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nucleotides to the 5' end
ii. Must make short strands of DNA on the 3' end of the primer
iii. results in short strands of DNA called Okazaki fragments
4. DNA sequence is now copied but thenew nucleic acid is in short piecesand has many bits of RNA
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http://kentsimmons.uwinnipeg.ca/cm1504/dnareplication.htm
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5. DNA polymerase I finds the placesh RNA i d h t
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where an RNA primer and a short
strand of DNA are not joinedtogether
a. Begins from the 5' end and
removes the RNA primer
b. Leaves a 3' end at the end of the
DNA freec. Adds nucleotides to the free 3'
end
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6. the strands are still in bits
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7. ligase joins all the DNA bits together
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8. Now there are two new double-stranded molecules of DNA
9. in eucaryotes, replication occurssimultaneously at many sites on the
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simultaneously at many sites on the
DNA molecule
http://kentsimmons.uwinnipeg.ca/cm1504/dnareplication.htm
Here are animations of the replication process:
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p p
http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591852__
(there are two parts here)
http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swf
http://www.johnkyrk.com/DNAreplication.html
V. Mutations
A. mutation: heritable changes in DNA
1. somatic mutations are only passedon to daughter cells