1. Transcription and Translation
From Gene to Protein
Transcription and Translation

2. Black Urine Started it All
Archibald Garrod hypothesized that genes code for enzymes
Phenotypes are expressed via different chemical reactions in the cell
Alkaptonuria = lack of an enzyme to break down alkapton

3. The Importance of Enzymes
Eye color is determined by pigments- which are made by enzymes
Most organic molecules are created and destroyed by chemical processes involving enzymes
Led to one gene- one enzyme hypothesis

4. One Gene – One Polypeptide
Almost right
Each gene codes for one sub-unit of a protein
Many are components of enzymes
Requires 4 genes!

5. RNA (Ribonucleic Acid)
RNA contains ribose sugar, and A,C,G,U nucleotides
Almost always single stranded
Can fold and pair with itself (not always linear)

6. Transcription Overview
mRNA is “transcribed” from DNA
DNA serves as a template to make a strand of messenger RNA (mRNA) that is complementary to the DNA strand

7. Translation Overview
“Translation” of the mRNA blueprint into a functional polypeptide
Takes place in ribosomes

8. These Processes
All organisms ever studied use the same process of coding
It evolved very early on, before our ancestors diverged
We can use bacteria to synthesize human proteins
Tobacco plant expressing firefly protein

9. Transcription

10. Initiation
RNA Polymerase binds to a region of the DNA called the promoter with the help of transcription factors
Ensures we only transcribe the necessary gene

12. RNA Elongation
RNA polymerase makes an mRNA strand complementary to the DNA
Only one strand is used

13. Termination
A terminator signal in the DNA causes the end of transcription
The polymerase breaks away and the mRNA is released

14. Eukaryotic Cells Modify RNA
The product of transcription is called pre-RNA or primary transcript
Gets modified or processed before leaving the nucleus

15. Alteration of mRNA ends
The 5' end (beginning of RNA strand) has a “guanine cap” added to it
Protects mRNA and attaches to ribosomes
The 3' end receives a poly A tail ( A nucleotides)
Facilitates leaving of nucleus, as well as protection for the end of the strand

16. RNA Splicing
Long, noncoding sequences of RNA that are not necessary called introns are removed
Coding segments called exons are spliced together

17. Accomplished by a complex of molecules called a spliceosome
Splicing continued
Accomplished by a complex of molecules called a spliceosome

18. What is the Purpose of Introns?
Different segments of the gene can be expressed at different times (some segments may be introns at times, and exons at other times)
Some parts of the protein, or domains, function independently. Introns provide an opportunity for new combinations of segments
Allows multiple proteins to be made from one gene instructions

19. Nucleotide Triplets
mRNA molecules can be viewed as a “sentence” of nucleotide triplets
Called a codon
Each codon will code for 1 amino acid

20. Codons form Reading Frames
…UCAUGGCAGUCAGUC…
Could be read as
…UCA UGG CAG UCA GUC… Or
…U CAU GGC AGU CAG UC… OR
…UC AUG GCA GUC AGU C…

21. The Start Codon sets the reading frame
…UCAUGGCAGUCAGUC…
Translation starts at the start codon, to ensure the correct reading frame
So the mRNA should be read as
AUG GCA GUC AGU C…

22. Translation

23. Translation, The Synthesis of Polypeptides
Messenger RNA carries code to ribosomes
Transfer RNA or tRNA carries amino acids to the ribosomes
Amino acids are assembled into a polypeptide

24. Unique Proteins Each amino acid has slightly different properties
The sequence of amino acids thus creates proteins with different structures and functions

25. Transfer RNA
tRNA carries an amino acid on one end and an anticodon on the other
The anticodon is complementary to codons on the mRNA
e.g. anticodon UAC will bond to AUG (the start codon)

26. tRNAs carry the corresponding amino acid for each mRNA codon

27. Ribosomal Binding Sites
mRNA bonding site
P site holds the growing polypeptide
A site holds the next amino acid to be added
E is the exit site for tRNA
Ribosomes connect mRNA and tRNA

28. Translation Initiation
Small ribosomal subunit binds to mRNA
tRNA carrying Met binds to AUG (start codon)
Large ribosomal subunit attaches

31. Termination STOP Codons do not code for amino acids
When they are reached, polypeptide is released

32. Protein Structure Depends on More than Genes
Genes determine the primary structure (sequence of AAs)
Chaperone proteins may help form particular structures
Also can be modified by enzymes before becoming functional

33. Transcription/Translation Song!
Option 1
Option 2
Work alone or with one partner
Make a song parody explaining transcription and translation
Read it or sing it to the class
Work in a group of 3-5 people
Make a song parody explaining transcription and translation
Make a music video and present it to the class