Transcription and Translation

1. Przeworski

2. Protein Synthesis
Instructions for proteins are stored as DNA in
the nucleus (one gene = one protein)
The ribosomes that actually make the proteins
are outside in the cytoplasm
DNA is too large to
exit through nuclear
pores… it requires a
messenger to send
the instructions

3. Ribosom
e

4. Transcription
In transcription, a copy of a protein recipe
called messenger RNA (mRNA) is made from
DNA
mRNA is half the width of DNA and can leave
the nucleus

5. Ribonucleic acid
Contains the sugar
ribose
Single-stranded
Bases are G, C, A, U
U = Uracil, replaces
Thymine
 G still pairs with C
 A pairs with U
DNA vs RNA
Deoxyribonucleic
acid
Contains the sugar
deoxyribose
Double-stranded
Bases are G, C, A, T
U
R
P
Uracil
Nucleotide
(RNA)
T
D
P
Thymine
Nucleotide
(DNA)

6. C
D
P
T
D
P
D
P
D
P
D
P
T
D
P
C
D
P
D
P
R
P
R
P
U
R
P
C
R
P
• The RNA bases are
slightly different.
• C still pairs with G
• A now pairs with U
(instead of T)

7. STEP ONE: INITIATION
RNA polymerase locates the section of DNA
(gene) that it wants to transcribe.
It attaches to the promoter region, causing DNA
to unzip with the help of a Helicase.
Polymerase and Helicase are enzymes (special
proteins!)

8. STEP TWO: ELONGATION
Once DNA is unzipped, the Polymerase
transcribes the DNA section
Free-floating RNA nucleotides attach
This is just like Replication, but with the base
uracil instead of thymine. (A-U and C-G)

9. STEP TWO: ELONGATION
For example, if the DNA strand read ACGT, then the
RNA would be UGCA.
This continues until the entire gene is transcribed,
ending with the Stop sequence.

10. STEP THREE: TERMINATION
Once the stop sequence is reached, the RNA
strand detaches
 It is then processed into mRNA by adding a 5’
cap and a poly-A tail (for protection)
Finally, the mRNA leaves the nucleus! (DNA rezips)

11. Ribosom
e

12. TRANSCRIPTION CLIP (REAL TIME)
 https://www.youtube.com/watch?v=5MfSYnItYvg

13. GROUP POSTER PROJECT
 In your groups of four (each table should work with the one
behind them, and turn your chairs around)
 You will be given a step of transcription or DNA vs RNA
 For your assigned topic, make sure there is:
A legible title
Large writing describing what occurs in the step (or
large writing that explains the differences between
DNA and RNA)
A large picture, colored. (All writing should be in
marker)

14. Translation - Overview
In translation, a ribosome uses an mRNA
recipe to select and put together a sequence of
amino acids
 mRNA is read 3 bases at a time (3 bases = 1 codon)
 Each codon = 1 amino acid
DNA template: A T A G A T C C A
mRNA: U A U C U A G G U
Amin
o Acid
1
Amin
o Acid
2
Amin
o Acid
3

15. DNA: A T A G A T C C A
mRNA: U A U C U A G G U
Tyrosine Glycine
Leucine

16. Special Codons
As a ribosome reads an mRNA transcript, special
codons tell it where to start and stop making a
protein
 START codon: A U G (must memorize!)
mRNA: A A G G U C A U G C C A C G U U A A
Amino Acid: Methionine Proline Arginine STOP

17. STEP ONE
The mRNA from the nucleus makes its way
through the cell to a free-floating ribosome and
attaches to it.

18. STEP TWO:
Each set of three RNA bases is called a
codon.
For this sequence: AUGCUA, AUG is a
codon and CUA is another codon.
Each codon codes for a single amino acid,
which is the building block of proteins.

19. STEP TWO:
At the ribosome, the codon of mRNA pairs
with its anti-codon (correct base pairs)
For our earlier codons, AUG would pair
with UAC and the anticodon for CUA is
GAU.

20. STEP TWO:
tRNA (transfer
RNA) translates
each codon into
one amino acid.
Amino Acids are
linked with
peptide bonds to
form a chain

21. STEP THREE:
Once the amino
acids are linked
with a PEPTIDE
BOND, the mRNA
strand moves like
an assembly line,
releasing the first
codon and
anticodon.

22. STEP FOUR
The chain of amino
acids (polypeptide
chain) will then form a
protein.
There are 20 different
amino acids, which are
the codes for all living
things!

23. WHEEL OF CODONS!!
Input the mRNA
codon, get out
the amino acid!
Special amino
acids:
AUG= start
UGA=stop

25. Types of RNA
Structure Function
mRNA
(messenger)
Single strand Takes copied DNA
recipe to ribosome
tRNA
(transfer)
Has anticodon on one
end, carries amino acid
on the other
Delivers amino acids to
ribosomes
rRNA
(ribosomal)
Folded into ribosome
shape
The ribosome itself is
made of this

26. Given the mRNA codon GCU, what is the amino
acid?

27. PRACTICE TIME!
Given mRNA codon of AUG, what is the amino
acid?

28. • The process of translation is further
divided into 3 steps
1. Initiation
2. Elongation
3. Termination

29. In initiation, there are 4 steps involved
1. Dissociation of 80S ribosomes into 40S
and 60S components
2. Formation of 40S pre-initiation complex
3. Formation of 40S initiation complex
4. Formation of 80S initiation complex

30. • The process of elongation is divided into
3 main steps
1. Binding of aminoacyle tRNA complex to
A site of ribosomes
2. Peptide bond formation
3. Translocation

31. Ribosomes
• In eukaryotes, ribosome is of 80S
• In prokaryotes, ribosome is of 70S
(S) is Swedberg unit or sedimentation
coefficient
(g) Is relative centrifugal force

32. 40S
60S
30S
50S
80S =
Prokaryotic Ribosome
Eukaryotic Ribosome
70S =
40S
60S

33. Transcription
5’
3’ 5’
3’
Coding Strand
Template Strand
During transcription, template strand gives rise mRNA which would be
the copy of this template
mRNA

34. • Every ribosome on mRNA will be involve
in synthesis of polypeptide which will be
same to other peptides being synthesized
by other ribosomes present on the same
mRNA
• The anticodon in tRNA will be red from 3’
to 5’ direction
• where as mRNA is red from 5’ to 3’
polarity

35. • During transcription, the mRNA produced
at first instance from template strand of
DNA is known as heterogeneous nuclear
RNA (hnRNA) because
• In this RNA, exact sequence are present
called exon and other segments which are
not complimentary to coding strand are
known as introns.
• DNA dependent RNA polymerases are
involve in synthesis of hnRNA.

36. • Splicing of introns takes place by means of
splicesomes. It consist of the primary
transcript and 5 small nuclear RNA which
are referred to as U1, U2, U4, U5 and U6
and unknown number of proteins.
• Splicesome remove introns from hnRNA.
(When ribosome nucleic acid act as an enzyme is called
ribozyme).

37. Translation
• Synthesis of protein from mRNA
Consist of 3 steps
1. Initiation
2. Elongation
3. Termination
The process of initiation consist of 4 steps

38. 1. Dissociation of 80S ribosome to 40S
and 60S subunits
How this process start? First of all, there are
two initiation factors. Overall, in whole
process of initiation, mRNA, tRNA, rRNA,
10 initiation factors, GTP , ATP and
aminoacids take part in the whole
initiation process.
Two factors
1. eIF-3
2. eIF-1A

39. • These factors binds to 40S subunit and
separation of 2 subunits takes place due to
binding of these 2 factors.
• Another factor eIF-3A binds to 60S subunit
40S
60S
eIF-3
eIF-1A
eIF-3A
40S
eIF-3
eIF-1A
40S
eIF-3

40. 2. Formation of 40S pre-initiation complex
Another factor eIF-2 binds to GTP and then
the complex binds to tRNA
eIF-1A 40S
eIF-3
eIF-2
GTP
eIF-1A
eIF-3
40S
eIF-1A
eIF-3
eIF-2
eIF-1A
eIF-3
40S
eIF-2
eIF-1A
eIF-3
GTP
40S
eIF-2
eIF-1A
eIF-3
GTP
40S
eIF-2
eIF-1A
eIF-3
GTP
eIF-2
40S
GTP
eIF-2
eIF-3
40S
GTP
eIF-2
eIF-1A
eIF-3
40S
GTP
eIF-2

41. 3. Formation of 40S initiation complex
The 5’ terminals of most mRNA are caped. This
cap facilitates the binding of mRNA to 40S pre-
initiation complex. This binding require
hydrolysis of ATP
eIF-1A
eIF-3
GTP
eIF-2
Caped
mRNA
40S

42. 4. Formation of 80S initiation complex
This step involves the hydrolysis of GTP
which is already bound to eIF-2 by means
of eIF-5. This reaction results in the
release of initiation factors bound to 40S
subunits. So finally 40S subunit re-
associate to 60S subunit.

43. Cap A U G
met
P-site A-site
U A C
80S initiation complex
40S
60S
mRNA
tRNA binds or present at
P-site and containing
methionine aminoacid.
So A-site is vacant to
accommodate new tRNA
containing another
appropriate aminoacid.

44. Elongation
It has 3 steps
1. Binding of aminoacyle tRNA complex
to A-site of ribosomes
In the complete 80S ribosome, A-site is free
whereas, P-site contains tRNA with
metheonine. The binding of appropriate
aminoacyl tRNA in A-site require proper
codon recognition.

45. • eEF-1α forms a complex with GTP and
entering aminoacyl tRNA. This complex
allows aminoacyl tRNA to enter A-site with
release of eEF-1α and GDP.
2. Peptide bond formation
The α-aminogroup of the amino acid in the
A-site carries out and attach on carboxyl
group of peptidal tRNA present in P-site.
This reaction is catalysed by peptidal
transferase.

46. O
NH-C linkage (peptidal linkage)
This enzymatic activity may also be perform
by some ribosomal RNA that’s why they
are known as ribozymes.
This results in the attachment of growing
peptide chain to the tRNA in the A-site.