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

3. DNA TO RNA TO PROTEIN
Transcription: DNA transcribes code to mRNA in nucleus
Translation: tRNA transports amino acids to mRNA on ribosome
Protein Synthesis-assembly of amino acids to polypeptides and, ultimately, proteins

4. 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 – brings amino acids to ribosome for protein synthesis
rRNA – what ribosome is made of

5. 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

6. Transcription and translation
In prokaryotes, occurs together
In eukaryotes, separated by nuclear envelope
Eukaryotic cell. The nucleus provides a separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
(b)
TRANSCRIPTION
RNA PROCESSING
TRANSLATION
mRNA
DNA
Pre-mRNA
Polypeptide
Ribosome
Nuclear
envelope
Prokaryotic cell. In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing.
(a)
TRANSLATION
TRANSCRIPTION
DNA
mRNA
Ribosome
Polypeptide

7. transcription
DNA mRNA

8. Transcription Transfer of genetic information from DNA to RNA (mRNA)
Similar to replication:
The DNA strands must separate.
Carried out by RNA polymerase (not DNA polymerase)
Other similar enzymes
Unlike replication:
Only 1 mRNA strand created, not 2
3 stages:
Initiation
Elongation
Termination
Elongation
RNA
polymerase
Non-template
strand of DNA
RNA nucleotides
3 end C A E G U T 3 5
Newly made
Direction of transcription
(“downstream”)
Template

10. 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

11. After Transcription – mRNA processing
DNA has many non-coding segments
Used to be called “junk” DNA (Not really junk)
In RNA splicing, the extra segments are cut out

12. After Transcription – mRNA processing
Introns = non-coding DNA that is removed – splicing
Exons = coding DNA segments that are kept and joined together

13. Mrna processing – cap and tail
mRNA also receives a G3P cap on the 5’ end
And a poly-a tail (many adenine’s in a row) on the 3’ end

14. transcription
DNA mRNA

15. Translation mRNA  protein Takes place on ribosome in cytoplasm Amino
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

16. 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?)

17. 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

18. How does translation happen? 3 stage process

19. 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

20. 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

21. 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.

22. summary TRANSCRIPTION RNA is transcribed from a DNA template. DNA RNA
polymerase
transcript
RNA PROCESSING
In eukaryotes, the
RNA transcript (pre-
mRNA) is spliced and
modified to produce
mRNA, which moves
from the nucleus to the
cytoplasm.
Exon
Poly-A
RNA transcript
(pre-mRNA)
Intron
NUCLEUS
Cap
FORMATION OF
INITIATION COMPLEX
After leaving the
nucleus, mRNA attaches
to the ribosome.
CYTOPLASM
mRNA
Growing
polypeptide
Ribosomal
subunits
Aminoacyl-tRNA
synthetase
Amino
acid
tRNA
AMINO ACID ACTIVATION
Each amino acid
attaches to its proper tRNA
with the help of a specific
enzyme and ATP.
Activated
amino acid
TRANSLATION
A succession of tRNAs
add their amino acids to
the polypeptide chain
as the mRNA is moved
through the ribosome
one codon at a time.
(When completed, the
polypeptide is released
from the ribosome.)
Anticodon A C U G E
Ribosome 1 5 3
Codon 2 3 4 5
summary

24. Protein Synthesis and Mutation
Mutation = Permanent, (sometimes) heritable DNA change
Point mutation (base substitutions)
Missense mutation
Nonsense mutation (premature stop)
Silent mutation
Frameshift mutations
Insertions or deletions
Dramatic change in amino acids
Run-ons, premature stops (nonsense mut.)

25. Protein synthesis and mutation
The Creation of Mutation (mutagenesis):
Spontaneous mutation
Occurs in DNA replication (1 in 109 bp)
Polymerase makes mistakes
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

26. Mutation: Some Definitions
A heritable change in the genetic material
Mutations may be neutral, beneficial, or harmful
Mutagen: Agent that causes mutations
Spontaneous mutations: Occur in the absence of a mutagen

27. Missense mutation
Changes an amino acid in the sequence

28. Nonsense mutation
Prematurely stops the amino acid sequence

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

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

31. Frameshift Mutations THEBIGCATATETHERAT = THE BIG CAT ATE THE RAT
Insertion or deletion – affects CODONS
THEBIGCATATETHERAT = THE BIG CAT ATE THE RAT
THEBIGCBATATETHERAT = THE BIG CBA TAT ETH ERA T

32. Summary: Mutations FRAMESHIFT:
POINT mutations-one base pair is changed
Substitutions
FRAMESHIFT:
Insertions (additions)
Deletions
Mutagens-physical and chemical agents that interact DNA to cause mutations—exp.: xrays