1. Protein Synthesis: Transcription & Translation
Chapter 12-3
DNA > mRNA > ribosome > protein 1

2. Learning Goals
1. Summarize the overall process of protein synthesis including the “central dogma”.
2. Describe Transcription in detail including where it takes places and the roles of introns and exons.
3. Describe Translation in detail including where it takes place, codons, anti-codons, tRNA, amino acids, and protein
4. Explain how gene expression works.

3. DNA > RNA > ribosome > protein
Protein Synthesis
Central Dogma Rule:
DNA > RNA > ribosome > protein 3

4. Protein Synthesis Overview
Two processes are required:
1. Transcription: DNA > mRNA
2. Translation: mRNA > protein 4

5. Transcription: DNA > mRNA
Process of making messenger RNA (mRNA) from a DNA template to take the DNA info outside of the nucleus 5

6. DNA can NOT leave the nucleus (too big)
Messenger RNA (mRNA) carries the info encoded in DNA out of the nucleus to the ribosomes located in the cytoplasm. 6

7. Steps of Transcription
1. DNA strands unwind & separate
2. DNA strand containing a specific gene serves as a template strand
3. RNA nucleotides are matched to complimentary DNA bases
4. mRNA molecule is complete and DNA rewinds

8. mRNA Processing
Introns: the mRNA contains extra info (junk) that must be removed (cut out)
Exons: the remaining pieces carry useful information are spliced (connected) together to make the complete mRNA 8

9. The bases of mRNA pair with DNA bases but RNA replaces T with U
DNA: C T G T A C G G A
---> Transcription
mRNA: G A C A U G C C U
DNA
RNA A U T G C
template strand 9

10. Check: Are there any T’s in your mRNA?
Now you try…
Based on the DNA template, create the matching mRNA strand:
DNA: C T A T G C A A A C T A T A G
mRNA: ______________________________
G A U A C G U U U G A U A U C
Check: Are there any T’s in your mRNA?
There shouldn’t be!!!

12. Translation: mRNA > protein
Process of making proteins from info on mRNA
mRNA travels out of nucleus to the ribosome, which “reads” the mRNA as a series of 3 letter words called codons 12

13. Codon: 3-base code on mRNA that codes for a specific amino acid
Ex. CGU = alanine
GUU = valine
The sequence of bases in DNA tell mRNA what order amino acids must join together to make a particular protein. 13

14. Codons found in mRNA
Second Base
First Base
Third Base 14

15. Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid
Each tRNA molecule has 3 unpaired bases called the anticodon that is complementary to one mRNA codon. 15

16. Each amino acid is added to a growing chain of amino acids
Protein = peptide bonds connecting amino acids
Many different types of proteins exist because the number and sequence of amino acids can be different

17. Codons found in mRNA Practice translating mRNA into amino acids:
First Base
Second Base
Third Base
Codons found in mRNA
Practice translating mRNA into amino acids:
mRNA: AUG AAA AGU UGU CUG GUU UAA
A.A: ______________________________________
Met - Lys – Ser - Cys – Leu – Val - Stop 17

18. How DNA determines proteins
DNA molecules serve as templates for making messenger RNA molecules
Messenger RNA molecules move to ribosomes
Transfer RNA molecules bring amino acids to the ribosome
Polypeptides (proteins) are formed as ribosomes move along the messenger RNA strand

19. Gene Expression DNA in all of your body cells is the same!
Ex: DNA in your eye cells is the same DNA that is in your skin cells.
Different types of cells express different genes.
Ex: Your eyes may be green, while your skin is brown.
Specialization of cells is due to different patterns of gene expression, rather than different genes themselves.
Liver cells express different genes than blood cells 19

20. ----Transcription----> mRNA: AUG AGG UCG CGU UGA
DNA: TAC TCC AGC GCA ACT
----Transcription---->
mRNA: AUG AGG UCG CGU UGA
----Translation--->
A.A.: met arg ser arg stop 20

21. Learning Goals
1. Summarize the overall process of protein synthesis including the “central dogma rule”.
2. Describe Transcription in detail including where it takes places and the roles of introns and exons.
3. Describe Translation in detail including where it takes place, codons, anti-codons, tRNA, amino acids, and protein
4. Explain how gene expression works.