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Unit 11: Protein Synthesis
11.5 Transcription Details
Begin working on Do-Now
Silently!
Transcription produces genetic
messages in the form of RNA
RNA
polymerase
RNA nucleotide
Direction of
transcription
Template
strand of DNA
Figure 10.9A
Newly made RNA
Differences between DNA and RNA
• Ask yourself, “R U
Single?”
– The sugar in RNA is
ribose, in DNA it is
deoxyribose
– RNA contains Uracil
(U) instead of Thymine
(T)
– DNA is doublestranded, RNA is mostoften single-stranded.
3 major types of RNA
Messenger RNA
Transfer RNA
Ribosomal RNA
copy of DNA message brings amino acid makes up ribosome
to the ribosome
with protein
Transcription Factors help get
things started…
• TFs are proteins that
control which genes
are turned on or off.
• They bind to DNA
and help recruit RNA
polymerase (the main
enzyme involved) to
bind to the DNA.
• In transcription, the
DNA helix unzips
– RNA nucleotides line
up along one strand
of the DNA following
the base-pairing rules
– The single-stranded
messenger RNA
peels away and the
DNA strands rejoin
Figure 10.9B
Transcription: at the
nucleus—from Promoter
to Terminator
RNA polymerase
DNA of gene
Promoter
DNA
Terminator
DNA
Initiation
1) RNA polymerase binds to
the promoter region of
DNA—before the gene
starts—initiation!
2) RNA polymerase begins
transcription—
initiation…coding for mRNA
complementary to the
DNA—elongation!
3) RNA polymerase reaches
the terminator and it
detaches from the gene.
The mRNA is released.
Elongation
Area shown
in Figure 10.9A
Termination
Growing
RNA
Completed RNA
RNA
polymerase
Eukaryotic RNA is processed before leaving
the nucleus
• Noncoding
segments called
introns are
spliced out
• A Guanine cap
and a PolyA tail
are added to the
ends (for
protection
against
degradation)
Figure 10.10
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM
transcription animation
How does RNA polymerase “know’ where to
start transcribing a gene into mRNA?
1. It starts at one end of the chromosome
2. Transfer RNA acts to translate the message
to RNA polymerase.
3. It starts at a certain nucleotide sequence
called a promoter.
4. The ribosome directs it ot the correct portion
of the DNA molecule
5. It looks for the AUG start codon.
20%
20%
20%
20%
20%
1
10
2
3
4
5
When RNA is being made, the RNA base ____
always pairs with the base ___ in DNA
10
1.
2.
3.
4.
5.
20%
20%
20%
20%
20%
1
2
3
4
U…T
T…G
U…A
A…U
T…A
5
A messenger RNA molecule for making a protein is
made in the nucleus and sent out to a ribosome. The
ribosome reads the mRNA message and makes a
protein containing 120 amino acids. The mRNA
consisted of at least how many codons?
1.
2.
3.
4.
5.
20%
20%
20%
20%
20%
1
2
3
4
30
40
120
360
480
5
10
Transcription in
animations
• In real-time!