1. CENTRAL DOGMA OF BIOLOGY

3. Transcription & Translation
How do we make sense of the DNA message?
Genotype to Phenotype

5. Central Dogma of Cell Biology
DNA codes for DNA = REPLICATION
DNA codes for RNA = TRANSCRIPTION
RNA codes for protein = TRANSLATION

6. Replication vs. Transcription
DNA-DNA
Starts at replication origins
Unwinds with Helicase
DNA polymerase
Proofreads
Start with 1 DNA
End with 2 DNA:
½ new, ½ old
DNA-RNA
Starts at promoter regions
Does not need Helicase to unwind
RNA polymerase
No proofreading
Start with 1 DNA
End with same DNA and 1 RNA

7. Transcription Process of converting DNA to mRNA
Takes place in the nucleus
3 main steps:
INITIATION  RNA pol binds to the DNA
ELONGATION  nucleotide chain is built, complementary to the DNA message
TERMINATION  RNA pol stops transcribing

8. How do we know what to transcribe?
Promoter
Characteristic region of DNA that signals the start of a gene.
A sequence of letters that signals “gene ahead!”
“TATA box” and enhancers

9. How do we know what to transcribe?
Start and stop codons
What are codons?
Each 3 bases form a codon that codes for a particular amino acid
AUG  methionine amino acid, but also START
UAA, UGA, UAG  STOP

10. Transcription - Step One:
RNA Polymerase unwinds and unzips the DNA double helix.

11. Transcription: Step Two:
RNA polymerase adds on free-floating nucleotides
A, G, C, U
What does each bind with?
Stops at STOP codon
Releases RNA polymerase
releases mRNA
mRNA

12. How do we know what to translate?
Before the mRNA message leaves the nucleus, RNA editing & modifications occur
DNA & RNA contain sequences that do not code for proteins = INTRONS
INTRONS = IN (BETWEEN) RONS
Sequences that code for proteins are expressed = EXONS
EXONS = EX (PRESSED SEQUENCE) ONS

14. RNA Editing 5. While still in the nucleus: a. INTRONS are cut out, and
b. EXONS are spliced together
c. before the RNA sequence is sent to the cytoplasm for translation

16. Transcription animation
Transcription animation

17. Transcription  Translation

19. Translation A. Process The mRNA leaves the nucleus  cytoplasm
Message is read at the ribosome
1 Codon (3 letter message) is translated into 1 amino acid
tRNA molecule has one end (anticodon) that matches the mRNA . Each anticodon specifies an amino acid.
The amino acids are bonded together as peptide chains…which fold into proteins

20. The Genetic Code: 3 letters = 1 codon  1 amino acid

21. Animation of translation
Animation of translation

23. Practice with this sequence
DNA: TCGATGTTCCGCCGTACGTCGTAACCG
AGCTACAAGGCGGCATGCAGCATTGGC
Use the bottom strand as the complement to the mRNA. What’s that mean?
Hint: Look for where it starts. How do you know?
Once you’ve found the “reading frame”, write in triplets
mRNA 
Use your genetic code wheel to write the amino acid sequence. How will you know when to stop?

24. Try again without help DNA: CCGTCATGTTCGCGCTACAAATGAAATGA
GGCAGTACAAGCGCGATGTTTACTTTACT
mRNA:
Polypeptide: