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CHAPTER 9
REPLICATION
TRANSCRIPTION
TRANSLATION
REGULATION
THE GENETIC
MATERIAL
LIKE DNA, RNA IS A LONG CHAIN OF NUCLEIC ACIDS BUT THERE
ARE SOME DIFFERENCES
•URACIL REPLACES THYMINE
•RIBOSE SUGAR REPLACES DEOXYRIBOSE
3’→5’
DNA is a DOUBLE helix
DNA REPLICATION
DNA polymerase
synthesizes DNA only in
the 5’ to 3’ direction.
This leads to continuous
replication on one strand
and short fragments on
the other.
DNA polymerase
requires a primer to
initiate synthesis. This is
a short segment of RNA
synthesized by RNA
primase (an RNA
polymerase)
THE RAW MATERIALS
FOR TRANSCRIPTION
AND TRANSLATION
LIKE DNA, RNA IS A CHAIN OF NUCLEIC
ACIDS BUT THERE ARE SOME
DIFFERENCES
•RNA IS SINGLE STRANDED
•RNA IS COPIED FROM A DNA TEMPLATE
•THERE ARE THREE MAJOR TYPES OF
RNA THAT ARE COPPIED FROM DNA
•messenger RNA (mRNA) is a copy of a gene
•transfer RNA (tRNA) carries an amino acid
•ribosomal RNA (rRNA) is part of the
ribosomes
Transfer RNAs
• Structure
• Copied from ca 20 genes, one/tRNA
• Charged by attaching to an amino acid.
• Each tRNA is charged with an amino acid
specific for its anticodon
• Pairs with mRNA on the ribosomes
attaches to an amino acid
that is specific for this
particular tRNA
pairs with messenger RNA
C. Ribosomal RNAS
• Location of rRNA in cell: nucleolus
• Ribosome subunits: 3 genes
tandomly repeated
• Combine with proteins to make
large and small subunit ribosomes
Chromosome
Genes
SSU Gene
5.8 S Gene
LSU Gene
Tandemly repeated sequence
5S Gene
Structure of the ribosomal RNA repeat unit
SSU Gene
5.8 S Gene
LSU Gene
5S Gene
Plus proteins
ribosome small subunit
Plus proteins
ribosome large subunit
Gene: A sequence of DNA that
encodes a polypeptide
Gene (blue) is on one strand of the DNA
double helix
Genes are segments of DNA along a strand of DNA. They have
a start code and a stop codon (codon = a three base DNA
sequence).
Chromosome
Genes
Gene - enlarged
Start
codon
Stop
codon
Exon = gene coding regions
Introns = non gene regions
Start
codon
Promoter
(RNA polymerase binds here)
Stop
codon
Poly A attachment site
TRANSCRIPTION
TRANSCRIPTION
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
Stop
codon
TRANSCRIPTION
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
Stop
codon
mRNA PROCESSING
PROCESSING
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
Stop
codon
Pre-mRNA
(Pre-messenger RNA)
PROCESSING
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
7MG
Stop
codon
PROCESSING
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
Stop
codon
7MG
INTRONS SPLICED OUT
Cut at poly A
recognition
sequence
PROCESSING
Poly A attachment site
Promoter (RNA polymerase binds here)
Start
codon
Stop
codon
AAAA
7MG
INTRONS SPLICED OUT
Poly A tail added
mRNA leaves the nucleus
mRNA MOVES TO THE
RIBOSOMES
Ribosomal
subunits
mRNA
AAA
nucleus
Cell membrane
mRNA
Ribosomal
subunits
AAA
nucleus
Cell membrane
mRNA
Ribosomal
subunits
AAA
nucleus
Cell membrane
mRNA
Ribosomal
subunits
AAA
nucleus
Cell membrane
mRNA IS TRANSLATED
INTO A PROTEIN
mRNA CODON CHART
1
3
2
A
4
5
6
A
POLYPEPTIDES ARE
SORTED
In prokaryotes, linked genes may be copied into a single
mRNA which is ten translated into different polypeptides
PROKARYOTE GENE
REGULATION
The operon system of gene regulation in prokaryotes
involves regulatory regions and linked genes that are coregulated. For example, the Lac operon
The Lac operon acts to import lactose into the cell and to
break down lactose into glucose + galactose. Glucose is
used in glycolysis and cellular respiration.
EUKARYOTIC GENE
REGULATION
Eukaryotic genes are not organized into introns
Instead, there are a number of regulatory regions, each
responding to a different signal.
protein “z”
protein “y”
xyz
za
xy
END
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