MBG 2040 Lecture 2: MBG 2040 Ch. 11
3 Dec 2017
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MBG 2040
Chapter 11
Transcription and RNA Processing
The Central Dogma of Biology:
• Info stored in DNA is transferred to RNA molecules during transcription and to proteins during
translation
Transcription and Translation – Prokaryotes:
• Primary transcript is equivalent to mRNA molecule
• mRNA codons on mRNA are translated into an amino acid sequence by the ribosomes
Tr anslat ion
mRNA t ranscript cont aining t he
UUU t riplet specifies t he ami no
acid phenylalanine (Phe) in t he
polypept ide gene product
Tr anscript ion
DNA st r and cont aining t he
nucleot ide sequence AAA is
used as a t emplat e t o produce
t he complement ary sequence
UUU in t he RNA t ranscr ipt
Replicat ion
•
•
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Transcription and Translation – Eukaryotes:
• Primary transcript (pre-mRNA) is
precursor to mRNA
• Pre-mRNA is modified at both ends, and
introns are removed to produce mRNA
• After processing, mRNA is exported to
the cytoplasm for translation by
ribosomes
Types of RNA Molecules:
• Messenger RNAs (mRNAs) -
intermediates that carry genetic
information from DNA to the ribosomes
• Transfer RNAs (tRNAs) - adaptors
between amino acids and the codons in mRNA
• Ribosomal RNAs (rRNAs) - structural and catalytic components of ribosomes
• Small nuclear RNAs (snRNAs) - structural components of spliceosomes
• Micro RNAs (miRNAs) - short single-stranded RNAs that block expression of complementary mRNAs
KEY POINTS:
• The central dogma of molecular biology is that genetic information flows from DNA to DNA during
chromosome replication, from DNA to RNA during transcription, and from RNA to protein during
translation.
• Transcription involves the synthesis of an RNA transcript complementary to one strand of DNA of a
gene.
• Translation is the conversion of information stored in the sequence of nucleotides in the RNA
transcript into the sequence of amino acids in the polypeptide gene product, according to the
specifications of the genetic code
The Process of Gene Expression:
Overview:
Overview of Gene Expression
They also know t hat t he
number of genes in an
or ganism var ies over an
enormous range, wit h gene
number increasing wit h t he
devel opment al complexit y of
t he species
Genet icist s know t hat t he
phenot ype of an or ganism is
produced by t he combined
ef f ect s of all it s genes act ing
wit hin t he const r aint s imposed
by t he environment
•t (pre-mRNA) is a precursor to the mRNA
•fie
•
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• Evidence for an Unstable Messenger RNA: Synthesis of viral proteins in infected bacteria involved an
unstable RNA molecule synthesized from the viral DNA
o Information stored in the nucleotide sequences of genes is translated into the amino acid
sequences of proteins through unstable intermediaries called messenger RNAs (mRNAs)
General Features of RNA Synthesis:
• Similar to DNA Synthesis except
o The precursors are ribonucleoside triphosphates
o Only one strand of DNA is used as a template
o RNA chains can be initiated de novo (no primer required)
• The RNA molecule will be complementary to the DNA template (antisense) strand and identical
(except that uridine replaces
thymidine) to the DNA nontemplate
(sense) strand
• RNA synthesis is catalyzed by RNA
poleases ad poeeds i the 5→
direction
• RNA synthesis occurs by a mechanism
that is similar to that of DNA synthesis
except that:
o The precursors are
ribonucleoside triphosphates
rather than
deoxyribonucleoside
triphosphates
o Only one strand of DNA is used
as a template for the synthesis
of a complementary RNA chain
in any given region
o RNA chains can be initiated de
novo, without any requirement
for a preexisting primer strand
• Synthesis of RNA chains, like DNA chains, occurs in the
5’→3’ diretion, with the addition of ribonucleotides to the
- hydroxyl group at the end of the chain
• The reaction involves a nuleophili attak y the 3’- OH
on the nucleotidyl phosphorus atom of the ribonucleoside
triphosphate precursor with the elimination of
pyrophosphate
• This reaction is catalyzed by enzymes called RNA
polymerases
•
t
•ide
es
•ed
f a
y
•e
ant isense st rand
uridine replaces t hymi dine
•
5’→3’
3’
•
3’
•
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Info stored in dna is transferred to rna molecules during transcription and to proteins during translation. Dna st r and cont aining t he nucleot ide sequence aaa is used as a t emplat e t o pr oduce t he complement ar y sequence. Uuu in t he rna t r anscr ipt. Tr anslat ion mrna t r anscr ipt cont aining t he. Uuu t r iplet speci es t he amino acid phenylalanine (phe) in t he polypept ide gene pr oduct. Transcription and translation prokaryotes: primary transcript is equivalent to mrna molecule, mrna codons on mrna are translated into an amino acid sequence by the ribosomes. Transcription and translation eukaryotes: primary transcript (pre-mrna) is precursor to mrna, pre-mrna is modified at both ends, and introns are removed to produce mrna, after processing, mrna is exported to the cytoplasm for translation by ribosomes.
