Download 9/16

•Exam #1 is T 9/23
in class
(bring cheat sheet)
DNA is used to
produce RNA
and/or proteins,
but not all
genes are
expressed at the
same time or in
the same cells.
How do cells
control which
genes are
expressed?
Protein
Signal Transduction
External
Stimulus
Internal
Effector…
Effector
Effector
Effector
Perception
(by receptor)
Stimulus
Response
(change in cellular
components and/or
gene expression)
How do
cells
express
genes?
The relationship between DNA and genes
a gene
promoter
coding region
terminator
non-gene
DNA
Combinations of 3 nucleotides code for each
1 amino acid in a protein.
Fig 13.2
• Overview of transcription
Fig 12.2
Fig 9.8
Each nucleotide carbon is numbered
Fig 9.22
Each nucleotide is
connected from the 5’
carbon through the
phosphate to the next 3’
carbon.
Fig 9.22
Each nucleotide
is connected
from the 5’
carbon through
the phosphate to
the next 3’
carbon.
Fig 12.8
The relationship between DNA and RNA
Fig 12.8
What is so magic about adding nucleotides to
the 3’ end?
How does the RNA polymerase know which
strand to transcribe?
Fig 12.7
Reverse promoter, reverse direction and strand transcribed.
RNA
5’
3’
5’
3’
5’
Why do polymerases only add nucleotides to the 3’ end?
RNA
RNA
DNA
DNA
U
similar to Fig 11.11
Error
P-P
P
Error
P
P
P-P-P
The 5’ tri-P’s
can supply
energy for
repair
similar to Fig 11.11
Incoming
nucleotide
Error repair on
5’ end not
possible.
5’
U
3’
Need for error repair limits nucleotide additions to 3’ end.
RNA
RNA
DNA
DNA
U
similar to Fig 11.11
When to express a gene is critical
a gene
promoter
coding region
terminator
non-gene
DNA
Promoter sequences in E. coli
Fig 12.5
Transcription initiation in prokaryotes:
sigma factor binds to the -35 and -10 regions and then
the RNA polymerase subunits bind and begin
transcription
Fig 12.7
Transcription Elongation
Fig 12.8
Termination of Transcription
Fig 12.11
Fig 12.13
Eukaryotic promoters are more diverse and
more complex
in eukaryotes: transcription factors are needed
before RNA polymerase can bind
Fig 12.14
Fig 12.3
Transcription overview
RNA synthesis
Protein
Some genes
code for RNA
(tRNA, rRNA,
etc) mRNA is
used to code
for proteins
rRNA is transcribed by RNA polymerase I
tRNA is transcribed by RNA polymerase III
mRNA is transcribed by RNA polymerase II
mRNA is processed during transcription
and before it leaves the nucleus.
(transcribed from DNA)
Fig 12.23
Addition of the 5’ cap, a modified guanine
Addition of the 3’ poly-A tail
Fig 12.24
After the RNA sequence AAUAAA
enzymes cut the mRNA and add 150 to 200 A’s
What do the cap and tail do?
(transcribed from DNA)
Luciferase
Gene (from
fireflies)
Expressed in
a Plant
100%
4.7%
0.34%
0.22%
The cap and tail have overlapping
and distinct functions
5’ untranslated
region
Protects from degradation/
recognition for ribosome
3’ untranslated
region
Protects from degradation/
transport to cytoplasm
DNA Composition:
In humans:
•Each cell contains ~6 billion base pairs of
DNA.
•This DNA is ~2 meters long and 2 nm wide.
•~3% directly codes for amino acids
•~10% is genes
•In a single human cell only about 5-10% of
genes are expressed at a time.
Introns are spliced out of most mRNAs
before they leave the nucleus.
(transcribed from DNA)
• Conserved sequences related to intron splicing
Sequences shown in bold
are highly conserved
Serve as recognition sites for the
binding of the spliceosome
Splicing an
intron: intron
removal.
Fig 12.22
Splicing an
intron: reattach
exons.
Fig 12.22
Alternate splicing of introns/exons can lead to
different proteins produced from the same gene.
Fig 15.16
Complex patterns of eukaryotic mRNA splicing
(-tropomyosin)
Fig 15.16
Fruit fly DSCAM, a neuron guide,
115 exons over 60,000 bp of DNA
20 exons constitutively expressed
95 exons alternatively spliced
For over 38,000 possible unique proteins
Size and Number of Genes for Some
Sequenced Eukaryotic Genomes
RNA editing:
Some mRNAs
are changed
after
transcription
by guide RNA
Tbl 12.3
http://www.cc.ndsu.nodak.edu/instruct/
mcclean/plsc731/genome/genome9.htm
http://users.rcn.com/jkimball.ma.ultrane
t/BiologyPages/R/RNA_Editing.html
A processed mRNA ready for translation
5’ untranslated
region
3’ untranslated
region
•Exam #1 is T 9/23
in class
(bring cheat sheet)