1. Transcription and Translation
From Gene to Protein

2. Central Dogma
How might DNA serve as the genetic code for the synthesis of our proteins?
This chain occurs in all living things
Our question for the day…

3. RNA Distinctions from DNA Three types Ribose sugar
Uracil instead of thymine
Usually single-stranded
Three types
mRNA (messenger) – formed complimentary to a strand of DNA (stay tuned!)
rRNA (ribosomal) – ribosome formation
tRNA (transfer) – transport amino acids during translation
Think of our worksheet, DNA is double stranded!

6. Transcription We’re still in the nucleus!
Synthesizes a strand of mRNA from the DNA template
mRNA is the basis for making proteins
Helicase unzips the DNA template
RNA polymerase binds and brings the nucleotides to form the mRNA strand
Reads in 3’ to 5’, new strand is created 5’ to 3’
Non-template strand
Finished mRNA enters cytoplasm via nuclear pores
That’ll change come Monday

8. RNA Processing
Final mRNA code is significantly shorter than the DNA template – why?
Introns and Exons – explain the “missing pieces”
Introns – sequences “spliced” out of the original mRNA (before entering cytoplasm)
Exons – sequences that code for proteins
Addition of cap to 5’ end (for recognition)
Addition of poly-A tail to 3’ end
Found huge gaps in the sequences that are not in the final mRNA
Poly-A – many adenines! Unclear purpose.
Cap – recognition by the ribosomes

10. Translation
mRNA transcript is split into groups of three base pairs called codons
Each codon corresponds to an amino acid
More than one codon can indicate the same amino acid
STOP codons – UAA, UGA, UAG
START codons - AUG
Scientists knew these things

12. Translation Processed mRNA moves to the Ribosome
tRNA molecules act as the interpreters of the mRNA codon sequence
What is a codon? (Three letters)
On each tRNA there is an anticodon
Codon is read 5’ to 3’
tRNA has respective amino acid attached to it
Stop codons
Amino acids are linked by peptide bonds to form proteins

14. So what is going to bind at the promoter?

16. Gene Regulation and Mutations
Chapter 12, Sections 4-5
Depending on time?

17. Prokaryotic Gene Regulation
Ability of an organism to control which genes are transcribed in response to changes in the environment
Remember introns?
Operon – section of DNA that contains the genes for the proteins needed for a specific metabolic pathway.

18. Lac Operon Lac – lactose used by E. coli as an energy source!
Repressor
Lactose is an energy source!
Trp is another repressor operon

19. Eukaryotic Gene Regulation
Transcription factors – ensure the right time and right amount for expression.
Homeobox (Hox) genes – controls the differentiation of cells (in development).
Code for certain transcription factors
RNAi (interference) – double-stranded RNA is cut/modified, eventually binds mRNA preventing translation

20. Mutations Gene mutations Point(s) mutations Frameshift mutations
Missense substitution – wrong amino acid
Nonsense substitution – stops sequences early
Can also be silent
Frameshift mutations
Insertion
Deletion

21. Mutations (continued)
Chromosomal mutations
Deletion – of more than just one base
Duplication – of a segment
Inversion – part of sequence is flipped
Translocation – segments are exchanged between DNA strands (like crossing over…but not on homologous chromosomes)