Transcription and Translation (full version)

1. 12-3 RNA and protein synthesis
The Central Dogma

2. RNA and DNA
DNA RNA
Strands • Double helix strands • One strand
Sugar • Deoxyribose • Ribose
Base • A,T,C,G • A,U (uracil), C,G
Location • Nucleus • Cytoplasm & nucleus

3. DNA ( A T C G)
RNA (A U C G)

4. Three types of RNA
A. messenger RNA (mRNA)
B. transfer RNA (tRNA)
C. ribosome RNA (rRNA)

5. Steps from DNA to Proteins
A cooking
book in
French
Sequence of nucleotides
A cooking
book in
Chinese
Sequence of nucleotides
Sequence of
amino acids
The Central Dogma

6. Steps from DNA to Proteins
Nuclear
DNA membrane
Transcription
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein

7. Transcription
• Synthesize a mRNA molecule along one template
strand of DNA
– In nucleus
– Starts at promoter (TATA region of DNA)
– Ends at terminator
– Need enzyme RNA polymerase
– When complete, pre-mRNA is released.

8. DNA
A T C G T A C G A A G T C T A C G G G A C T A T C G
5 3
A C G A A G U C
T A G C G A T A G C
A T G C T T C A G A T G C C C T
mRNA
RNA polymerase
Direction of transcription

9. Transcription
• Steps
– DNA unzipped by RNA polymerase
– RNA polymerase builds RNA by base paring
RNA nucleotides to one strand of DNA
– U is used instead of T
– RNA is released and leaves the nucleus

12. Question
• What would be the complementary RNA
strand for the following DNA sequence?
• DNA: GCGTATG
RNA: CGCAUAC

13. Question
• What is the enzyme responsible for the
production of the RNA molecule?
• RNA Polymerase
– Separates the DNA molecule by breaking the H-
bonds between the bases.
– Then moves along one of the DNA strands and links
RNA nucleotides together.

15. RNA processing

16. RNA processing
Part of a DNA strand
exon intron exon intron exon
3’ 5’
transcription into pre-mRNA
poly-A tail
cap
5’ 3’
snipped out intron snipped out intron
5’ 3’
mature mRNA transcript

17. Translation
• Synthesize a polypeptide chain using the
genetic code on mRNA

18. Translation
• Key characters
– 1) mRNA : provide code
– 2) tRNA : bring building blocks
– 3) Ribosome (rRNA) : provide site

19. 1) mRNA
• A linear sequence of
nucleotides
• Three nucleotides make
a codon
– Codon : the genetic code
for a amino acid
– 64 codons
– AUG: start
– UAA, UAG, UGA: stop

21. 1) mRNA
start
codon
mRNA A U G G G C U C C A U C G G C G C A U A A
codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7
protein methionine glycine serine isoleucine glycine alanine stop
codon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds

22. 2) tRNA
• Delivers amino acids to
ribosomes
• One side attached with
amino acid
• Another side with
anticodon
– Anticodon: 3 nucleotides
that can pair with a
codon
– 20 different types of
amino acids

23. 2) tRNA
amino acid
attachment site methionine amino acid
U A C
anticodon

24. 3) rRNA
• Major component of
ribosomes
• Ribosome
• Place where amino acids are
made into proteins
• Small subunit + large subunit
• Large subunit has 2 sites for
tRNA

25. 3) rRNA
Ribosome
Large
subunit
P A
Site Site
mRNA
A U G C U A C U U C G
Small subunit

26. Translation
• Three Steps
1. initiation: start codon (AUG)
2. elongation:
3. termination: stop codon (UAG, UAA,
UGA)
• Let’s make a PROTEIN!!!!.

28. 1) Initiation
aa1
Large
subunit
P A
Site Site
1-tRNA
anticodon U A C mRNA
A U G C U A C U U C G
codon
Small subunit

29. aa2
aa1
2-tRNA
1-tRNA
G A U
anticodon U A C
hydrogen A U G C U A C U U C G A
bonds codon mRNA

30. 2) Elongation
peptide bond aa3
aa1 aa2
3-tRNA
1-tRNA 2-tRNA G A A
anticodon U A C G A U
hydrogen A U G C U A C U U C G A
bonds codon mRNA

31. aa1 peptide bond
aa3
aa2
1-tRNA
U A C 3-tRNA
(leaves)
2-tRNA G A A
G A U
A U G C U A C U U C G A
mRNA
Ribosomes move over one codon

32. peptide bonds
aa1 aa4
aa2 aa3
4-tRNA
2-tRNA 3-tRNA G C U
G A U G A A
A U G C U A C U U C G A A C U
mRNA

33. peptide bonds
aa1 aa4
aa2
aa3
2-tRNA
4-tRNA
G A U
(leaves) 3-tRNA G C U
G A A
A U G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon

34. peptide bonds aa5
aa1
aa2
aa4
aa3
5-tRNA
U G A
3-tRNA 4-tRNA
G A A G C U
G C U A C U U C G A A C U
mRNA

35. aa1 peptide bonds aa5
aa2
aa3
aa4
5-tRNA
3-tRNA U G A
G A A 4-tRNA
G C U
G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon

36. 3) Termination
aa5
aa4 aa199
aa3 primary aa200
structure
aa2 of a protein
aa1 terminator
200-tRNA
or stop
codon
A C U C A U G U U U A G
mRNA

37. 4) End Product
• The end products of protein synthesis is a primary
structure of a protein.
– A sequence of amino acid bonded together by peptide
bonds.
aa5
aa3 aa4
aa2 aa199
aa1 aa200

40. Question:
• The anticodon UAC belongs to a tRNA that
recognizes and binds to a particular amino acid.
• What would be the DNA base code for this amino
acid?

41. Answer:
• tRNA - UAC (anticodon)
• mRNA - AUG (codon)
• DNA - TAC