1. Transcription/ Translation
From Gene to Protein
(protein synthesis)

2. Transcription
Protein is made outside of the nucleus at the ribosome, but DNA can’t leave the nucleus.
Transcription - is the making of mRNA from DNA.
messenger RNA (Ribo Nucleic Acid) is a copy of DNA that can leave the
nucleus.

3. mRNA A-T-G C-G-G T-T-A DNA U-A-C G-C-C A-A-U mRNA
mRNA is single stranded
mRNA contains no T’s (thymine)
It replaces that T’s with U’s (uracil)
It can leave the nucleus.
It’s base pairs are read it sets of 3 called codons.
A-T-G C-G-G T-T-A DNA
U-A-C G-C-C A-A-U mRNA

4. Transcription in Three stages
The three stages of transcription:
Initiation – starting transcription
Elongation – laying down the mRNA nucleotides
Termination – finalizing the mRNA

5. Promoter
Promoter – the beginning of the DNA sequence to be copied. (RNA polymerase II attaches at the promoter)
TATA Box – the promoter begins with a sequence of DNA that includes the base pairs T and A.

6. Transcription Factors
Transcription Factors – Proteins that allow the RNA Polymerase II to bind to the promoter.

7. Transcription Initiation Complex
Transcription initiation complex – the promoter, RNA Polymerase II, and Transcription factors all combined and ready to start transcription.

8. RNA Polymerase
RNA Polymerase – enzyme that unwinds DNA and lays down RNA nucleotides.

10. Termination
A termination code caused the mRNA to be cut free from the DNA. (ex. AAUAAA)**
At this point the mRNA is pre-mRNA is needs a few modifications

11. Alteration of mRNA
The 5 end receives a modified 5 cap – a modified guanine nucleotide with 3 phosphate groups
The 3 end gets a poly-A tail – several adenine nucleotides in a row (50+)
These modifications have several functions:
They allow mRNA to leave the nucleus
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5 end

12. Eukaryotic RNA Splicing
Finally, the sections of the pre-mRNA that will not be used to code for the protein are cut out.
introns – section that are cut out of the pre-mRNA
exons –sections that are left in the finalized mRNA

13. exons spliced together Coding segment
Fig 5
Exon
Intron
Exon
Intron
Exon 3
Pre-mRNA
5 Cap
Poly-A tail 1 30 31
104
105
146
Introns cut out and
exons spliced together
Coding
segment
mRNA
5 Cap
Poly-A tail 1
146
Figure RNA processing: RNA splicing
5 UTR
3 UTR

14. Spliceosomes Spliceosomes – carry out RNA splicing Made of
ribonucleoproteins (snRNPs)
that recognize the splice sites

15. Ribozymes
Ribozymes -are catalytic RNA molecules that function as enzymes and can splice RNA (present in snRNP’s)
(ribozyme)

16. Alternative RNA splicing
alternative RNA splicing – choosing different regions of introns or exons from the same pre-mRNA sequence
So one gene can code for more than one protein.

17. tRNA t-RNA – Transfer RNA (single stranded) Each tRNA has an
anti-codon that matches
up with a codon on the
messenger RNA
Each tRNA also has a
particular amino acid
attached to it.

18. Amino Acids Each tRNA also has a particular amino acid attached to it.
aminoacyl-tRNA synthetase – enzyme that attaches amino acids to tRNA

20. Ribosomes
Ribosomes match the tRNA anticodons with mRNA codons in protein synthesis
The two ribosomal subunits are made of proteins and ribosomal RNA (rRNA)
small subunit holds mRNA
Large subunit holds the tRNA

21. Building a Polypeptide
A ribosome has three binding sites for tRNA:
A site- holds the tRNA that carries the next amino acid to be added to the chain
P site- holds the tRNA that carries the growing polypeptide chain
E site- is the exit site, where discharged tRNAs leave the ribosome.** P A

22. Translation initiation complex
Fig
Large
ribosomal
subunit 3 U C 5 A
P site
Met 5 A
Met U G 3
Initiator
tRNA
GTP
GDP E A
mRNA 5 5 3 3
Start codon
Figure The initiation of translation
Small
ribosomal
subunit
mRNA binding site
Translation initiation complex

23. GDP GDP Amino end of polypeptide E 3 mRNA Ribosome ready for
Fig
Amino end
of polypeptide E 3
mRNA
Ribosome ready for
next aminoacyl tRNA P
site A
site 5
GTP
GDP E E P A P A
Figure The elongation cycle of translation
GDP
GTP E P A

24. Polyribosomes
polyribosome (or polysome) -several ribosomes translate a single mRNA simultaneously, allowing a cell to make many copies of a protein very quickly
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

25. Completing the Protein
signal peptide – a short peptide added to the finished protein.**
signal-recognition particle (SRP) – attaches to the signal peptide that that it may enter the ER.

26. Predicting Proteins Predict the protein DNA = ATG CGG RNA = UAC GCC
Prot. = Tyr Ala