1. PROTEIN SYNTHESIS
THE DETAILS

2. The Central Dogma DNA rNA protein
States that DNA carries the genetic information which is transcribed to RNA and then translated to protein
DNA
rNA
protein

4. We already know about DNA Replication

5. Notes on RNA RNA - carrier of genetic information RNA is made with:
-ribose sugar
-uracil rather than thymine
RNA is single stranded

6. Types of RNA Messenger RNA (mRNA) end product of transcription
carries genetic code from nucleus to cytoplasm

7. Types of RNA Transfer RNA (tRNA) delivers aa’s to the ribosomes
Ribosomal RNA (rRNA)
binds with proteins to form ribosome
site for the assembly of polypeptides

8. OVERVIEW Transcription and Translation

9. DNA Template Strand Transcription mRNA Translation Protein
A T G G A C T T A 5’ 3’
5’ U A C C U G A A U 3’

10. The Genetic Code 4 bases found in mRNA -code for 20 amino acids
Codon-sequence of 3 bases found in mRNA that codes for a particular amino acid.
64 possible combinations (43=64)
(redundancy in genetic code-minimizes errors that may lead to mutations.

11. The Genetic Code
Start codon – signals initiation of polypeptide (AUG, methionine)
Stop codon – signals termination of polypeptide (UAA, UAG, UGA)

12. Figure 7 pg 240

13. TRANSCRIPTION: the details
INITIATION
RNA polymerase binds to promoter (sequence of DNA upstream of the gene to be transcribed) – opens up double helix
promoters contain base pair patterns rich in A’s and T’s ….Why???

14. RNA polymerase binds to DNA at promoter region
Pg 243
RNA polymerase binds to DNA at promoter region

15. DNA strand is unwound, double helix disrupted…exposing template strand
Pg 243
DNA strand is unwound, double helix disrupted…exposing template strand

16. ELONGATION
RNA polymerase starts building mRNA in the 5’ to 3’ direction
process similar to DNA replication – except…
no primer is used
only 1 strand of DNA is used -the template strand

17. DNA template is used to synthesize mRNA in 5’ to 3’
Pg 243
DNA template is used to synthesize mRNA in 5’ to 3’
(uracil complements adenine)

18. DNA that has already been transcribed rewinds into double helical form
Pg 243
DNA that has already been transcribed rewinds into double helical form

19. ELONGATION
unused DNA strand is called the coding strand
***mRNA is complementary to the template strand and identical to the coding strand (except it contains U)

20. RNA polymerase stops when it reaches a terminator sequence
TERMINATION
RNA polymerase stops when it reaches a terminator sequence
mRNA dissociates from the DNA template
RNA polymerase is free to transcribe another gene.

21. RNA polymerase reaches termination sequence at end of gene.
Pg 243
RNA polymerase reaches termination sequence at end of gene.

22. RNA synthesis ceases; mRNA and RNA polymerase are released
Pg 243
RNA synthesis ceases; mRNA and RNA polymerase are released

23. made to primary transcript 1) 5’ cap added
POSTTRANSCRIPTION MODIFICATIONS
made to primary transcript
1) 5’ cap added
7-methyl guanosine added to start
protects mRNA from digestion in cytoplasm
Plays a role in initiation of translation - binding to the ribosome

24. Pg 244

25. also known as capping or tailing animation
POSTTRANSCRIPTION MODIFICATIONS
2) Poly-A tail added
enzyme poly-A polymerase adds a string of adenine bases to end of mRNA to protect it from degradation later
also known as capping or tailing
animation

26. POSTTRANSCRIPTION MODIFICATIONS
3) Introns cut out
eukaryotic gene is made of coding regions called exons, and non-coding regions called introns
if non-coding regions are translated, the protein will not fold properly (so must remove!)

27. POSTTRANSCRIPTION MODIFICATIONS
3) Introns cut out
spliceosomes (particles made of RNA and protein) cut introns from mRNA and bind exon regions together

29. Final mRNA called mRNA transcript.
Unlike DNA replication, no quality control, therefore, there are more errors made during transcription than DNA replication….BUT…

30. Since a single gene is transcribed many times to produce 100’s of transcripts, errors are not as detrimental.
Errors in mRNA result in a protein being made that is susceptible to degradation.