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The Central Dogma and
Transcription
Chapter 17: Sections 17.1-17.3
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Today’s Exit TicketThe bonds creating the primary structure of a protein are called 1) peptide bonds and form between a 2) C atom in one amino acid and a 3) N atom in another amino acid.
The bonds creating the secondary structure of a protein are called 4) hydrogen bonds and form between 5) the backbone molecules of amino acids (NOT R-groups).
The bonds creating the tertiary structure of a protein can be covalent, ionic, or hydrogen bonds, and form between 6) R-groups.
7) Describe the quaternary structure of a protein.Quaternary structure is the interaction of different polypeptide
subunits to make a larger molecule.
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Unit 4• Proteins• Transcription (DNA to mRNA)• Translation (mRNA to tRNA to proteins)• Gene expression/regulation (turning genes on and off)• Viruses
3
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The Central Dogma and
Transcription
Chapter 17: Sections 17.1-17.3
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How do we get from DNA to traits?
• Gene expression = DNA directs the synthesis of proteins
TWO STEPS: (1) transcription (2) translation
All organisms do this!All organisms do this!
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Outline
1. Basic principles of transcription & translation2. Transcription in detail3. RNA processing in Eukaryotes4. The genetic code
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Fig. 5.26
Information flowfrom geneticinformation
encoded as DNAblueprint (genes)
to RNA copies
mRNA
Synthesis ofmRNA in thenucleus
DNA
NUCLEUS
mRNA
CYTOPLASM
Movement ofmRNA into cytoplasmvia nuclear pore
1
2
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What’s the difference between DNA and RNA??
• 3 Major Differences: DNA RNA– Different sugars: deoxyribose ribose– Different bases: C & G, A & T C & G, A & U– Structure: double-stranded single-stranded
(usually)
DNA & RNA provide information to make proteins• DNA and RNA = both nucleic acids• Both are made of nucleotide monomers
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and on to synthesis of proteins.
Fig. 5.26
Information flowfrom geneticinformation
encoded as DNAblueprint (genes)
to RNA copies
mRNA
Synthesis ofmRNA in thenucleus
DNA
NUCLEUS
mRNA
CYTOPLASM
Movement ofmRNA into cytoplasmvia nuclear pore
Ribosome
AminoacidsPolypeptide
Synthesisof protein
1
2
3
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Transcription vs. Translation
DNA RNA Proteins
Transcription:• Like copying info from a
book in the reserved section of the library
• Using the same language
Translation:• Literally translating between
two different languages
• Take the copied info from the library and translate it
into French/Spanish/Mandarin
สวั�สดี�เพื่�อนHello, friend
Hullo,
mate
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Videos of Gene Expression:
Hank’s Transcription and Translation Crash Course
http://www.youtube.com/watch?v=itsb2SqR-R0
http://www.youtube.com/watch?v=D3fOXt4MrOM
From DNA to Protein
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1. Overview of transcription and translation1. Overview of transcription and translation
Genes are nucleotide sequences, hundreds or thousands of nucleotides long
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THE CENTRAL DOGMA:
DNA RNA PROTEIN
1. Overview of transcription and translation1. Overview of transcription and translation
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1. Overview of transcription and translation1. Overview of transcription and translation
PROTEINPROTEIN
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1. Overview of transcription and translation1. Overview of transcription and translation
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Outline
1. Easing in: basic principles of transcription and translation
2. Transcription in detail3. RNA processing in Eukaryotes4. The genetic “code”
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Transcription vs. Translation
DNA RNA Proteins
Transcription:• Like copying info from a
book in the reserved section of the library
• Using the same language
Translation:• Literally translating between
two different languages
• Take the copied info from the library and translate it
into French/Spanish/Mandarin
สวั�สดี�ครั�บHello Hello
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Fig. 17-4 2. Transcription in detail2. Transcription in detail
Successful transcription requires 3 basic processes:
1. Initiation2. Elongation3. Termination
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Fig. 17-4 2. Transcription in detail2. Transcription in detail
Successful transcription requires 3 basic processes:
1. Initiation • Find the location where we start reading DNA• Actually begin making mRNA
To achieve this, we need some kind of signal on or in the DNA that says “START TRANSCRIBING HERE”
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2. Transcription in detail2. Transcription in detail
a) Initiationa) Initiation
“Upstream” of the gene is a promoter• whole promoter = several dozen nucleotides
example of DNA that is essential but is not transcribed
where the gene is
the “start here” signal
Now we know WHERE to initiate, but HOW do we initiate?Now we know WHERE to initiate, but HOW do we initiate?
Transcription Unit:
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2. Transcription in detail2. Transcription in detail
a) Initiationa) InitiationHOW: With an enzyme, as usual!HOW: With an enzyme, as usual!
RNA polymerase• Reads one strand of DNA and builds the mRNA• Can’t bind to the promoter on its own (in eukaryotes) • Only binds when specific transcription factors are present
Promoter sequence
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Once RNA polymerase binds, it can only synthesize RNA in a 5’ to 3’ direction. Which of the two DNA strands shown here will it “read” as it makes RNA? a) Top oneb) Bottom onec) Both strands
Promoter sequence
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2. Transcription in detail2. Transcription in detail
a) Initiationa) Initiation
With transcription factors in place, RNA polymerase can now bind DNA at the right place to begin
transcription of the gene
With transcription factors in place, RNA polymerase can now bind DNA at the right place to begin
transcription of the gene
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Fig. 17-4 2. Transcription in detail2. Transcription in detail
Successful transcription requires 3 basic processes:
Initiation • Bind transcription factors, then RNA
polymerase to promoter region
2) Elongation• Make the full length mRNA transcript
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2. Transcription in detail2. Transcription in detail
b) Elongationb) ElongationRN
A Polym
erase
untwists
DN
A, m
akes m
RNA
RNA
Polymera
se untw
ists D
NA,
makes
mRN
A
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2. Transcription in detail2. Transcription in detail
b) Elongationb) Elongation
Summary of elongation in transcription:
1.RNA polymerase untwists and separates 10-20 base pairs of DNA at a time2.RNA nucleotides enter and pair with the DNA template (U, not T, pairs with A)3.RNA polymerase bonds nucleotides onto the 3’ end of the RNA molecule4.RNA polymerase moves along, the new RNA molecule peels away from the DNA, and the helix re-twists
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Fig. 17-4 2. Transcription in detail2. Transcription in detail
Successful transcription requires 3 basic processes:
Initiation
Elongation make the full length mRNA transcript
• Termination stop transcribing; mRNA completed
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2. Transcription in detail2. Transcription in detail
c) Terminationc) Termination
But how does it stop?
Bacteria: termination sequence in the DNA
Eukaryotes: a bit more complicated• enzymes cut the transcript free…among other things!
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Outline
1. Easing in: basic principles of transcription and translation
2. Transcription in detail3. RNA processing in Eukaryotes4. The genetic code
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3. RNA processing in eukaryotes
Observations: • Average human pre-mRNA transcript length: 27,000 nucleotides
• Each amino acid is coded by 3 nucleotides
• Average human protein: 400 amino acids requires only 1200 nucleotides
How does that work?How does that work?
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3. RNA processing in eukaryotes
Before RNA transcripts leave the nucleus, they are modified.
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3. RNA processing in eukaryotes
Before RNA transcripts leave the nucleus, they are modified.
Modified how?1.Alteration of ends2.Cutting out some of the middle
offers cell a way of controlling when and where proteins are produced
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3. RNA processing in eukaryotes
1. Alteration of ends
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3. RNA processing in eukaryotes
2. Cutting out some of the middle: RNA splicing
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3. RNA processing in eukaryotes
The sequence of DNA that codes for a eukaryotic
protein is NOT a continuous
sequence
Some introns are “self-splicing” catalyze their own excision!
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Ribozymes!
Thomas Cech• CU Professor • 1989 Nobel Prize winner, along with Sidney Altman• Discovered that RNA can sometimes splice itself!
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3. RNA processing in eukaryotes
1. Cutting out some of the middle: RNA splicing
Why do introns exist?
• Alternative splicing alternative mRNA multiple proteins from a single DNA sequence
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Outline
1. Easing in: basic principles of transcription and translation
2. Transcription in detail3. RNA processing in Eukaryotes4. The genetic code
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4. The genetic code4. The genetic code
Nucleotides: A, T, G, and C in DNA (A, U, G, and C in RNA)
Amino Acids 20 are commonly used by most organisms
The genetic code consists of 3-letter codons:• Sequence of 3 nucleotides = specification of amino acid• Each triplet of mRNA nucleotides is called a codon
The genetic code consists of 3-letter codons:• Sequence of 3 nucleotides = specification of amino acid• Each triplet of mRNA nucleotides is called a codon
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Fig. 17-4
DNAmolecule
Gene 1Gene 2
Gene 3DNA template strand
TRANSCRIPTION
TRANSLATION
mRNACodons
Protein
Amino acid
4. The genetic code4. The genetic code
note: either strand may serve as the template depending upon the particular gene
U U U U UG G G G C C A
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Math check:WAIT a second! • 4 nucleotides...in sets of 3... • Shouldn’t there be 43 codons??
YES!• Using just 4 nucleotides, DNA can make 64 different
codons
BUT... You just said there are only 20 amino acids!?!• Yes, friends, there are only 20.
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C
C
C
C
C
C
U
U
U
U
U
U
A
A
A
A
A
A
G
G
G
G
G
G
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Fig. 17-4 4. The genetic code4. The genetic code
Some notes on codons:
1.When we say “codon”, we are referring to RNA triplets
2.Codons are read in the 5’ to 3’ direction, because that is how they are read by the translation machinery
1.Codons don’t overlap (300 nucleotides encode 100 codons)
ACUUCCAAG
1 2 3
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Today’s Exit TicketThe final product of transcription is _(1)_. The template used for transcription is _(2)_. The first step of the process is called _(3)_ and
involves the _(4)_ binding to the _(5)_ region. This allows _(6)_ to bind to the DNA and begin transcribing, in a process called _(7)_.
During that process, the enzyme reads from the _(8)_’ to _(9)_’ direction and builds the new strand from _(10)_’ to _(11)_’. The last
step of transcription is called _(12)_. In _(13)_, there is another step before translation. This is called _(14)_, and involves removing
_(15)_ and adding a 5’ cap and 3’ poly-A tail.
WORD BANK (not all will be used, some are used more than once):
3 5 DNA elongation
eukaryotes exons initiation introns
mRNA prokaryotes promoter RNA polymerase
RNA processing termination transcription factors