Unit 4
•
•
•
•
•
Proteins
Transcription (DNA to mRNA)
Translation (mRNA to tRNA to proteins)
Gene expression/regulation (turning genes on and off)
Viruses
1
Today’s Exit Ticket
The final product of transcription is mRNA. The template used for transcription is DNA. The first step of the process is called initiation
and involves transcription factors binding to the promoter region. This allows RNA polymerase to bind to the DNA and begin
transcribing, in a process called elongation. During that process, the enzyme reads from the 3’ to 5’ direction and builds the new strand
from 5’ to 3’. The last step of transcription is called termination. In eukaryotes, there is another step before translation. This is called
RNA processing and involves removing introns and adding a 5’ cap and 3’ poly-A tail.
2
Unit 4
•
•
•
•
•
Proteins
Transcription (DNA to mRNA)
Translation (mRNA to tRNA to proteins)
Gene expression/regulation (turning genes on and off)
Viruses
3
Today’s Agenda
• Transcription practice
• Translation in detail
• Mutations
4
The template strand of a given gene
includes the sequence
3′-G C C A C G T A T C A G-5′.
– What is the sequence of the non-template strand?
5’– C G G T G C A T A G T C – 3’
– What is the mRNA sequence made?
5’– C G G U G C A U A G U C – 3’
For each one, be sure to indicate 5′ and 3′ ends.
5
The template strand of a given gene
includes the sequence
3′-G C C A C G T A T C A G-5′.
Non-template strand:
5’– C G G T G C A T A G T C – 3’
mRNA sequence:
5’– C G G U G C A U A G U C – 3’
What is the amino acid
sequence produced
from this DNA?
Arg-Cys-Ile-Val
6
Today’s Agenda
•Transcription practice
• Translation in detail
• Mutations
7
Transcription vs. Translation
DNA
RNA
Proteins
สวัสดีครับ
Transcription:
• Like copying info from a
book in the reserved section
of the library
• Using the same language
Translation:
• Literally translating between
two different languages
• Take the copied info from
the library and translate it
into French/Spanish/Mandarin8
Translation
The major
players in
translation
U G G U U U G G C
9
Translation
Translation:
•The structure of tRNA
•The ribosome
i. initiate
ii. elongate
iii. terminate
10
11
Translation
a) tRNA
For accurate translation, the tRNA HAS to have the right amino acid!
1
20 different
synthetases
 20 different
amino acids
12
Translation
a) tRNA
2
3
13
Translation
a) tRNA
4
14
Translation
Translation:
•The structure of tRNA
•The ribosome
i. initiate
ii. elongate
iii. terminate
15
Translation
a) The ribosome
 What is a ribosome?
• Made of proteins and
rRNA (ribosomal RNA)
 Where are ribosomes?
A.
B.
C.
D.
E.
In the nucleus
Loose in the cytoplasm
On the Golgi body
On the ER
More than one of the above is correct
16
All those RNA molecules…
• RNA = ribonucleic acid
• pre-mRNA = the RNA transcript produced initially
during transcription in eukaryotes
• mRNA = messenger RNA = the (processed) RNA
transcript molecule that will actually be translated
• tRNA = transfer RNA = the RNA molecule that brings
amino acids to the ribosome
• rRNA = ribosomal RNA = RNA that forms the
structure of the ribosome
17
Translation
b) the ribosome
a) The ribosome
 What does it do?
•
Serves as the site of matching mRNA
codons with tRNA anticodons
•
Catalyzes formation of peptide bonds to form
proteins
18
Translation
b) the ribosome
Growing polypeptide
Next amino acid
to be added to
polypeptide chain
19
Translation
Translation:
•The structure of tRNA
•The ribosome
i. initiate
ii. elongate
iii. terminate
20
5. Translation
(i) Initiation of translation
• Small ribosomal
subunit binds
mRNA.
• Scans for start
codon (sets reading
frame).
• Initiator tRNA binds
to start codon.
AU G
21
Translation
b) the ribosome: initiation
AUG
 Final step of initiation: large ribosomal subunit binds.
22
Translation
Translation:
•The structure of tRNA
•The ribosome
i. initiate
ii. elongate
iii. terminate
23
E, P, and A sites
• A site: where new aminoacyl tRNAs enter
• P site:
– Location of peptidyl tRNA
– Where peptide bonds are made
• E site: Exit site
24
Elongation
25
Termination
Also, don’t forgetHank’s crash
course on gene expression!
One more good video:
http://www.dnalc.org/resources/3d/16-translation-advanced.html
26
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
RNA:
5’ CGC 3’ = ___________
5’ UAU 3’ = ___________
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
27
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
RNA:
5’ CGC 3’ = ___ Arg ___
5’ UAU 3’ = ___ Tyr ___
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
28
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
DNA (template strand):
3’ TTG 5’ = ___________
3’ ACT 5’ = ___________
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
29
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
DNA (template strand):
3’ TTG 5’
RNA 5’ AAC 3’ = Asn
DNA 3’ ACT 5’
RNA 5’ UGA 3’ = Stop
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
30
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
Brain twister: DNA
NON-template strand:
5’ ATG 3’ = __________
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
31
USE THE GENETIC CODE TABLE
TO TRANSLATE 5 DIFFERENT
CODONS into AMINO ACIDS:
Brain twister: DNA
NON-template strand:
5’ ATG 3’ = _______
DNA template strand =
3’ TAC 5’ =
RNA 5’ AUG 3’ = Met (start)
NOTE: technically “Codon”
refers to the 3 letters in the
mRNA that are translated.
32
How DNA mutations can alter proteins
Mutations in protein coding DNA sequences (exons) can alter
protein structure and function in several ways.
33
Fanpop.com
5) How DNA mutations can alter proteins
5) Mutations in protein coding DNA sequences (exons) can alter
protein structure and function in several ways.
a) Substitution - Switching one nucleotide for another
b) Insertion/deletion- Adding or removing a nucleotide
 can create a frameshift
34
5) How DNA mutations can alter proteins
a) Substitution - Switching one nucleotide for another can cause
different amino acid to be attached.
A U G A A G U U U G G C U
A U G A A G
U U U
A G C U
A A
A A
35
5) How DNA mutations can alter proteins
a) Substitution- Switching one nucleotide for another can cause NO
CHANGE in the protein. How?
A U G A A G U U U G G C U
A A
36
5) How DNA mutations can alter proteins
a) Substitution- Switching one nucleotide for another can cause
NO CHANGE in the protein. How?
A U G A A G
U U U
G G C U
A A
37
5) How DNA mutations can alter proteins
b) Insertions or Deletions - Inserting an extra nucleotide, or deleting
a nucleotide causes a frameshift.
A U G
A U G
A A G
U U U
G G C U
U
G U U
U G G
A
A
A A
C U
A A
38
5) How DNA mutations can alter proteins
b) Insertions or Deletions - Inserting an extra nucleotide, or deleting
a nucleotide causes a frameshift.
A U G
A A G
U U U
G G C U A A
U
A U G
A A G
U U G
G C U
A A
39
5) How DNA mutations can alter proteins
b) Insertions or Deletions - Inserting an extra nucleotide, or deleting
a nucleotide causes a frameshift.
40
5) How DNA mutations can alter proteins
c) Gene duplications: a duplicate copy of an exon or whole gene
is created in the genome
 this is largely how NEW proteins arise in evolution: once a gene
has been duplicated, one copy can evolve, while the other one
maintains the original function.
Gene
DNA
mRNA
Exon 1 Intron Exon 2 Intron Exon 3
Exon 1
Exon 2
Exon 2
Exon 3
41
Today’s Exit Ticket
1)
Fill in the blanks in the
DNA/RNA chart below.
1)
What is the amino acid
sequence corresponding to the
DNA and RNA sequences
below?
Template DNA __’
C
Non-Template __’
mRNA 5’
G
T
A
A
G __’
T A
U
A
G
A
__’
3’
42