1. Transcription and Translation Mader Biology Chapter 14
Protein Synthesis
Transcription and Translation
Mader Biology Chapter 14

2. Protein synthesis = Central dogma= DNA To RNA TO protein
Transcription: DNA transcribes code to mRNA in nucleus
Translation: tRNA transports amino acids to mRNA on ribosome, builds polypeptide

3. 3 rna’s used to make proteins
mRNA – carries the “message” of DNA
Travels from nucleus to cytoplasm
Takes message to ribosome for protein synthesis
tRNA – transfer RNA – brings amino acids to ribosome for protein synthesis
rRNA – ribosomal RNA – what ribosome is made of

4. The tRNA molecule A G 3 5 Amino acid attachment site Anticodon
Symbol used
in some books
Amino acid
attachment site
Anticodon A G 3 5

5. Transcription and translation
In prokaryotes, occurs together
In eukaryotes, separated by nuclear envelope
(b)
TRANSCRIPTION
RNA PROCESSING
TRANSLATION
mRNA
DNA
Pre-mRNA
Polypeptide
Ribosome
Nuclear
envelope
(a)
TRANSLATION
TRANSCRIPTION
DNA
mRNA
Ribosome
Polypeptide

6. transcription
DNA mRNA

7. Transcription Transfer of genetic information from DNA to RNA (mRNA)
Similar to replication:
The DNA strands must separate
Nitrogen bases are paired with their opposite
Unlike replication:
Carried out by RNA polymerase
(not DNA polymerase)
Only 1 mRNA strand created, not 2
Leading strand only
Thymine  Uracil
Elongation
RNA
polymerase
Non-template
strand of DNA
RNA nucleotides
3 end C A T G U 3 5
Newly made
Direction of transcription
(“downstream”)
Template

9. More Transcription
Promoter- region where RNA polymerase attaches and initiates transcription
Often a sequence of TATA – known as the TATA box
Terminator- DNA sequence that signals the end of transcription

10. transcription
DNA mRNA

11. Translation mRNA  protein Takes place on ribosome in cytoplasm
TRANSCRIPTION
TRANSLATION
DNA
mRNA
Ribosome
Polypeptide
Amino
acids
tRNA with
amino acid
attached
tRNA
Anticodon
Trp
Phe
Gly A G C U
Codons 5 3
mRNA  protein
Takes place on ribosome in cytoplasm
Video here

12. Translation: Genetic Information is “read”
DNA = letters A, C, T, G (you know this!)
These bases are encoded as a sequence base triplets, or codons, each of which is translated into a specific amino acid
FOR EXAMPLE:
Theredfoxatetherat = the red fox ate the rat
AUGCCTUGUCGA = AUG CCT UGU CGA (easier, huh?)

13. Translation: Genetic information is “read”
Codons = genetic code
Translates to amino acids (proteins)
Codon chart is universal for all living organisms (see pink sheet)
So, let’s take the DNA sequence:
TACGGT
mRNA sequence?
Amino acid sequence?
*see chart

14. How does translation happen? 3 stage process

15. Translation initiation complex
Brings together mRNA, tRNA and ribosome
Begins at the start codon, AUG
Large
ribosomal
subunit
Initiator tRNA
mRNA
mRNA binding site
Small
Translation initiation complex
P site
GDP
GTP
Start codon
Met U A C G E 3 5

16. Peptide bond formation
2) Elongation
Amino end
of polypeptide
mRNA
Ribosome ready for
next aminoacyl tRNA E P A
GDP
GTP 2
site 5 3
TRANSCRIPTION
TRANSLATION
DNA
Ribosome
Polypeptide
Codon recognition 1
Peptide bond formation
Translocation. 3
Codon of mRNA and anticodon of tRNA complementary bond to one another
Peptide bond formation
Translocation-ribosome moves to next codon

17. 3) Termination mRNA stop codons - UAA, UAG, UGA Release factor Free
polypeptide
Stop codon
(UAG, UAA, or UGA) 5 3
When a ribosome reaches a stop
codon on mRNA, the A site of the
ribosome accepts a protein called
a release factor instead of tRNA. 1
The release factor hydrolyzes
the bond between the tRNA in
the P site and the last amino
acid of the polypeptide chain.
The polypeptide is thus freed
from the ribosome. 2 3
The two ribosomal subunits
and the other components of
the assembly dissociate.

19. Protein synthesis and mutation
Mutation = Permanent, (sometimes) heritable DNA change
Mutagens:
Chemical mutagens (alcohol, tobacco, drugs)
Increases rate to 1 in ,000)
Radiation
X rays, gamma rays break DNA, bases
UV light causes knots in DNA strand
Spontaneous mutations
Occurs in DNA replication (1 in 109 bp)
Polymerase makes mistakes

20. Protein Synthesis and Mutation
Point mutation (base substitutions)
Can have many effects:
Missense mutation
Nonsense mutation
Run-on
Silent mutation
Frameshift mutations (Insertions or deletions)
Dramatic change in amino acids
Run-ons, premature stops (nonsense mut.)

21. Point Mutation - Substitutions
A substitution of one base for another
This can have many different effects:
Missence
Nonsense
Run-on
Silent

22. Missense mutation
Changes an amino acid in the sequence

23. Nonsense mutation
Prematurely stops the amino acid sequence

24. Run-on mutation Continues the sequence that was supposed to end G C
Glu

25. Silent mutation
No effect on the amino acids G C

26. Frameshift Mutations – Insertions or deletions
THEBIGCATATETHERAT = THE BIG CAT ATE THE RAT
THEBIGCBATATETHERAT = THE BIG CBA TAT ETH ERA T

27. Summary: Mutations FRAMESHIFT:
POINT mutations-one base pair is changed
Substitutions
FRAMESHIFT:
Insertions (additions)
Deletions