Download Ch 17 Protein Synthesis

Chapter 17
DNA – mRNA – Enzyme
Life
Almost
Chapter 17
DNA – mRNA – Protein
Life
Almost
Chapter 17
DNA – mRNA – Polypeptide
Life
Almost
Chapter 17
DNA – mRNA – Polypeptide
(most of the time)
Life
Yes really!
I. Eukaryotic Genome Review
Eukaryotes
I. Eukaryotic Genome Review
Eukaryotes
Multiple chromosomes
Linear chromosomes
Located in nucleus
Made of DNA
Small coding region (few exons, lots of introns)
Extranuclear DNA- Mitochondria, Chloroplasts
-Replicate independently
-Sometimes have plasmids
Picture
II. General flow of information
transcription
translation
DNA---------------→ mRNA ------------→ polypeptide
DNA
TRANSCRIPTION
mRNA
Ribosome
TRANSLATION
Polypeptide
(a)
Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
Nuclear
envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Ribosome
TRANSLATION
(b)
Polypeptide
Figure 17.3b
A. Prokaryotes can begin translation
during transcription - no nuclear envelope
B. Eukaryotes: separate transcription
(nucleus) and translation (ribosome)
C. One gene/ one polypeptide
1. however all genes are not fully
translated in polypeptides
2. DNA → tRNA
3. DNA → rRNA
III. DNA v RNA
DNA
RNA
III. DNA v RNA
DNA
RNA
Sugar, phosphate, base
Sugar, phosphate, base
3’ and 5’ ends
3’ and5’ ends
double stranded and
antiparallel
A,C,T,G
single stranded
deoxyribose sugar
ribose sugar
A,U,C,G
V. Transcription
Nucle
ar
envelo
pe
DN
A
TRANSCRIPT
ION
Pre-mR
NA
RNA
PROCESSING
mR
NA
Riboso
me
TRANSLAT
ION
Polypept
ide
Figure
17.3b
(
b
)
V. Transcription
A. Basics
1. occurs in the nucleus
2. DNA template is transcribed
into single strand pre- RNA using
comp. base pairing
3. A-U, C-G
4. requires energy
Transcription In Depth
B. In Depth
Initiation
1. Transcription factors help RNA
polymerase II bind to promoter upstream from
gene
2. Promoter region contains a TATA box
which indicates non-template strand
Elongation
3. no primer needed
4. RNA polymerase II unwinds and
assembles pre-mRNA from 5' -- 3'
Termination
5. polymerase transcribes
polyadenylation signal AAUAAA
6. polymerase falls off DNA after 100+
bases
• Animation please work!
• http://vcell.ndsu.edu/animations/transcripti
on/movie.htm
• http://media.pearsoncmg.com/bc/bc_camp
bell_biology_6/cipl/ins/17/HTML/source/14
.html
• http://www.stolaf.edu/people/giannini/flash
animat/molgenetics/transcription.swf
• Back up!
• Animation please work!
• http://vcell.ndsu.edu/animations/transcripti
on/movie.htm
• http://www.stolaf.edu/people/giannini/flash
animat/molgenetics/transcription.swf
• Back up!
V. Processing pre-mRNA
http://highered.mcgraw-hill.com/sites/00724
37316/student_view0/chapter15/animation
s.html#
V. Processing pre-mRNA
A.
5' cap: G-P-P-P
B. poly-A tail: 50- 250 adenines added to 3’
end
C. excision of introns
1. introns are cut out using a spliceosome
2. exons are joined together, ready to
leave nucleus
D. Importance of Introns
1. regulatory role (not all junk)
2. allow alternative RNA splicing: multiples
proteins from same exons
3. safe crossing over
E. Regulating transcription with RNAi
E. Regulating transcription with RNAi
1. RNAi bind to mRNA sequences
2. can increase or decrease level of
transcription → protein production
3. used to silence genes, role in
defense
VI. tRNA
VI. tRNA
Structure
Function
VI. tRNA
Structure
3 loops- but L shape
Function
match anticodon to mRNA
codon
VI. tRNA
Structure
3 loops- but L shape
amino acid attached to 3'
Function
match anticodon to mRNA
codon
pick up correct amino acid
VI. tRNA
Structure
3 loops- but L shape
amino acid attached to 3'
Function
match anticodon to mRNA
codon
pick up correct amino acid
anticodon on bottom loop transfer new amino acids
to growing polypeptide
VII. ribosomes
VII. Ribosomes
Structure
Function
VII. Ribosomes
Structure
Function
Built from rRNA (ribozyme) Catalyze peptide bond
and proteins
formation between new
amino acids
VII. Ribosomes
Structure
Function
Built from rRNA (ribozyme) Catalyze peptide bond
and proteins
formation between new
amino acids
Contain a small and large
subunit
Allow bonding of new aa
from tRNA
VII. Ribosomes
Structure
Function
Built from rRNA (ribozyme) Catalyze peptide bond
and proteins
formation between new
amino acids
Contain a small and large
subunit
P-site:
Allow bonding of new aa
from tRNA
holds growing polypeptide
VII. Ribosomes
Structure
Function
Built from rRNA (ribozyme) Catalyze peptide bond
and proteins
formation between new
amino acids
Contain a small and large
subunit
P-site:
Allow bonding of new aa
from tRNA
holds growing polypeptide
A-site:
holds amino acid to be added
VII. Ribosomes
Structure
Function
Built from rRNA (ribozyme) Catalyze peptide bond
and proteins
formation between new
amino acids
Contain a small and large
subunit
P-site:
Allow bonding of new aa
from tRNA
holds growing polypeptide
A-site:
holds amino acid to be added
E-site:
discharges tRNA without
amino acid
VIII. Translation
A. Basics
1. Translation occurs at ribosomes
2. mRNA is translated into amino acid
sequence (polypeptide)
http://www.biostudio.com/demo_freeman_pr
otein_synthesis.htm
http://www.stolaf.edu/people/giannini/flashan
imat/molgenetics/translati
on.swf
http://highered.mcgraw-hill.com/sites/00724
37316/student_view0/chapter15/animation
s.html#
B. Codons
1. 3 base sequence on mRNA read
from 5' -- 3‘
2. 3 bases code for one amino acid
3. Start codons = AUG
Stop codons = UAA, UAG, UGA
4. Codons are redundant - 61 codons and
only 20 amino acids
5. Unambiguous- one codon never codes
for more than one amino acid
6. Genetic code is universal
a. must have been operating very
early in life
b. all descendents use the same
code
c. cells come from cells → all
organisms are related
C. Initiation
1. small ribosomal subunit binds to
mRNA upstream from the start codon
2. ribosome scans mRNA until it put
start codon (AUG) at the P-site
3. tRNA with Met hydrogen bonds to
start codon
4. large subunit attaches
5. driven by GTP hydrolysis
D. Elongation
1. codon recognition- tRNA with amino
acid bonds to complementary mRNA
codon at A (requires 2 GTP)
2. peptide bond formation: rRNA
catalyzes formation of peptide bond
between amino acid at the P site and A
site, polypeptide is now at the A site
3. translocation: ribosome moves
polypeptide at A-site to P-site, empty P
site tRNA moves to E-site, A-site is now
open for new aminoacyl- tRNA (requires
GTP)
http://www.biostudio.com/demo_freeman_pr
otein_synthesis.htm
http://www.stolaf.edu/people/giannini/flashan
imat/molgenetics/translati
on.swf
http://highered.mcgraw-hill.com/sites/00724
37316/student_view0/chapter15/animation
s.html#
E. Termination
1. stop codon signals a release factor
to bind to A-site
2. release factor adds water to
polypeptide which hydrolyses polypeptide
and tRNA
3. polypeptide leaves through tunnel in
large ribosomal subunit
4. ribosomal complex breaks apart
IX. Modifying and transporting
polypeptides
A. Modifications
1. amino acids cut
2. polypeptides merge
3. addition of cofactors
B. Protein destinations
1. RER→ Golgi→ lysosome or
cell membrane
2. Free ribosome→
cytoplasm
C. Protein function → phenotypes
(Life is all about proteins)
1. Enzymatic reactions: lactose intolerance
2. Transport by proteins: cystic fibrosis
(CTFR transport gene)
3. Synthesis: failure to produce myelin→
multiple sclerosis
4. Degradation: apoptosis → cell death
X. Mutations
A. Mutagens
1. mutagens- physical or chemical agents
causing changes in base pairs
a. base analogs pair incorrectly,
chemical insert themselves instead of
bases
b. UV light, X-rays
2. Whether or not a mutation is
detrimental, beneficial or neutral depends
on the environmental context. Mutations
are the primary source of genetic variation.
Types of mutations
DNA
ACGGCCGGCACTGCCTACTCCTACGG
TGCCGGCCGTGACGGATGAGGATGCC
RNA
ACGGCCGGCACUGCCUACUCCUACGG
AA
B. Point mutations- changes in one base
pair
1. substitution- incorrect base pair is
substituted
a. can have no effect (wobble on 3rd
base)
b. missense- codes for wrong amino
acid → usually nonfunctional
c. nonsense- codes for stop →
nonfunctional
2. insertions and deletions- addition of loss
of nucleotides
a. shirt reading frame of codons frameshift mutation
b. all nucleotides downstream are
affected
c. leads to missense followed probably by
nonsense