DNA and RNA
II
Sapling Chapter 6
short version
You are responsible for textbook material
covered by the worksheets.
CP Biology
Paul VI Catholic High School
DNA and RNA
CENTRAL DOGMA
DNA
RNA
PROTEIN
(Francis Crick 1956)
DNA and RNA
Information
flows from
the nucleus
to the
cytoplasm
DNA and RNA
DNA
TRANSCRIPTION
Information storage
RNA
Information
Carrier
PROTEIN
TRANSLATION
Active Cell Machinery
DNA and RNA
GENETIC CODE: Information for expressed
traits contained in the nucleotide
sequence of DNA.
CODONS: Sequence of 3 nucleotides
specifying a particular amino acid.
(Brenner & Crick 1961)
DNA and RNA
THE GENETIC CODE CONSISTS OF
•GROUPS OF 3 NUCLEOTIDES
•EACH SPECIFIES AN AMINO ACID
THE CODE IS READ IN A CONTINUOUS
FASHION WITHOUT SPACES OR
PUNCTUATION.
DNA and RNA
Triplet Code
specifies one
amino acid
DNA and RNA
GENETIC CODE IS PRACTICALLY
UNIVERSAL
Suggests ALL CELLS originate from
a common ancestor
Genes transcribed by one organism
can be translated by another
Mitochondrial & Chloroplast DNA are
exceptions
Animation
Please note that due to differing
operating systems, some animations
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DNA and RNA
TRANSCRIPTION: That process
of faithfully copying the information
from DNA to an RNA molecule, i.e.
Messenger RNA (mRNA)
1. Initiation
2. Elongation
3. Termination
DNA and RNA
TRANSCRIPTION
Transcription
Bubble
DNA and RNA
TRANSCRIPTION
Transcription Bubble
3’
3’
5’
DNA and RNA
TRANSCRIPTION:
1. INITIATION:
RNA Polymerase II binds to PROMOTER
Approx. 60 bp long
Located at beginning of gene
NOT transcribed
Eukaryote’s promoter = TATA BOX
named for code of TATAAAT
Represents “START” site for RNA
polymerase II
DNA and RNA
TRANSCRIPTION:
2. Elongation:
DNA Template strand read 3’→ 5’
mRNA synthesized 5’→ 3’
Process more complex in eukaryotes
Elongation proceeds to end of gene
sequence
DNA and RNA
TRANSCRIPTION:
3.Termination:
RNA Pol II recognizes a stop signal
termination sequence on DNA
Causes separation of enzyme from
both DNA and RNA
Mechanism different in prokaryotes
and eukaryotes
DNA and RNA
DNA and RNA
INTRONS:
Present in eukaryotes (not bacteria)
Segments of mRNA that do not code
“Intervening Segments”
Part of “Primary” mRNA (unedited)
Need to be “edited” prior to mRNA
leaving the nucleus
Introns 10-30X larger than EXONS
DNA and RNA
EXONS:
“Expressed Segments” of mRNA
Shorter sequences than “Introns”
Spliced together after removal of
Introns to form functional mRNA
Splicing occurs with “SPLICESOME”
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
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DNA and RNA
DNA and RNA
TRANSLATION:
Polypeptide chain synthesized
Each CODON specifies an AA in the
peptide chain or a “start” or “stop”
Translation includes
1. Initiation
2. Elongation
3. Termination
DNA and RNA
GENETIC CODE
64 Codons for
Individual AA
Similar diagram
Miller & Levine
Page 303
DNA and RNA
Transfer RNA (tRNA)
Synthesized by RNA Polymerase III
Two active sites:
Amino acid accepting end
Anticodon (complementary to
mRNA codon)
Approximately 45 different tRNA
“Wobble Hypothesis”
DNA and RNA
Always CCA
tRNA
DNA and RNA
Transfer RNA (tRNA):
Aminoacyl Transferase catalyzes the
addition of specific AA to tRNA
tRNA attaches to “A Site” of ribosome
No tRNA exists for
UAA
UAG
“STOP” CODONS
UGA
DNA and RNA
Anticodon
Initiation begins with assembly of ribosome
Using fMet tRNA at the “P site”.
DNA and RNA
DNA and RNA
DNA and RNA
DNA and RNA
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
DNA and RNA
TRANSLATION:
1. Initiation:
Initiation Factors become attached
to the small ribosomal subunit
Attach to the “Start” codon (AUG)
of the mRNA
Large ribosomal subunit binds to
the small creating a functional
ribosome
DNA and RNA
TRANSLATION:
2. Elongation:
tRNA with AA joins to “A Site”
of ribosome (Aminoacyl Site)
Ribosome moves from 5’ to 3’
PEPTIDE BOND forms between AA
TRANSLOCATION occurs
tRNA leaves from “E Site” (Exit Site)
DNA and RNA
TRANSLATION:
3. Termination:
“Stop” codon has no tRNA
Empty site filled with “Release Factor”
Release Factor catalyzes hydrolysis of
tRNA to peptide chain
Polypeptide released
DNA and RNA
DNA and RNA
DNA and RNA
POLYSOME (Polyribosome)
In prokaryotes, Transcription &
Translation may occur together
Multiple ribosomes may attach to
emerging mRNA
Multiple strands of identical protein
formed simultaneously
DNA and RNA
Polysomes
DNA and RNA
REGULATION OF GENES:
OPERON: CONSISTS OF
PROMOTER
OPERATOR
PROTEIN CODING GENES
DNA and RNA
REGULATION OF GENES:
REPRESSIBLE OPERONS:
“trp” Operon:
Normally “on”
Repressor protein
Allosteric inhibition
DNA and RNA
DNA and RNA
DNA and RNA
REGULATION OF GENES:
INDUCIBLE OPERONS:
“lac” Operon:
Normally “Off”
Repressor always active
Allosteric control of
repressor protein
DNA and RNA
DNA and RNA
DNA and RNA
Repressible Enzymes function
in Anabolic Pathways
Synthesize essential end-products
from raw materials
Inducible Enzymes function in
Catabolic Pathways
Break down nutrients to simpler
molecules
DNA and RNA
MUTATIONS:
A. CHROMOSOMAL MUTATIONS:
1. Deletions
2. Duplications
3. Inversions
4. Translocations
DNA and RNA
DNA and RNA
MUTATIONS;
B. POINT MUTATIONS:
1. Silent
2. Missense (Replacement)
3. Nonsense
4. Frameshift
DNA and RNA