Lecture Notes: November 9, 2009
(Review)
Transcription – the copying of DNA into RNA so that proteins can be made and the cells can be made
-where transcription starts
- DNA must be unwound and unzipped at promoter sequence
-RNA binds at promoter sequence
Sigma factor- subunit of RNA polymerase that binds to DNA promoter
sequences
- Different sigma factors attach to diff promoter sequences
- Different sigma factors express under diff conditions
1. Initiation – is the start of transcription
a. Starts with interactions bw RNA polymerase with a specific sequence of bases on the DNA called the promoter sequence
i. RNA polymerase-enzyme that makes RNA copy of DNA strand
b. Sigma factor (sigma subunit) of RNA polymerase attaches specifically to the promoter sequences on the DNA
c. Different sigma factors that exist under different sequences/ bind to different promoter regions on the DNA
d. Different sigma factors are made in response to different environmental conditions
i. Ex. V. fischeri (gram negative have the genes for leiferase –gene for HSL
1. A sigma factor that is always on in v. Fisheri promoter sequence always on would be gene for receptor of HSL
a. Default sigma factor- gene for HSL and the homo serine lactone receptor which would intiate the transcription of DNA into RNA and the RNA will be translated into an aa transport chain
b. HSL is going to bind to the receptors and is going to lead to the production of light bc the HSL is going to trigger the production of another sigma factor
c. Chapter 8 in the online txt bood
d. Find similarities in the promoter sequences and variability in the promoter sequence (Table 8.4 D showing examples of different sigma factors and promoter sequences they bind to)
1. Initiation: Start of Transcription *DNA must be unwound, unzipped before it can be transcribed
a. This is b/c single DNA strand serves as a template for RNA copy
2. Elongation- process by which the RNA strand is going to be actively synthesized
a. RNA strand synthesized by pairing complementary RNA bases w/ DNA template strand and hooking those bases together w/ sugar phosphate backbone (sugar is ribose)
i. Also RNA has U Uracil instead of T thyamine
3. Termination – RNA polymerase reaches hairpin loop, can’t get past (b/c RNA polymerase can only move along ss (single strand DNA)
a. So RNA polymerase falls off DNA strand, releasing new ss RNA
b. “hairpin loop” DNA strand that’s folded back on itself b/c complementary to self= hairpin loop
Kinds of RNA:
mRNA: single strand of RNA transcribed off a single strand of DNA-
-single strand of DNA gene, will be translated to amino acid sequence
tRNA: (transfer RNA) involved in the translation of the messenger RNA into an aa sequence
- “cloverleaf” structure where transfer RNA is also a single strand of RNA but is base paired with itself
- Site that has amino acid attached
- Anitcodon: 3 bases that can pair with sets of 3 bases on mRNA
rRNA: (ribosomal RNA) the main component that makes up ribosomes –the site in the cell that actual translate mRNA into aa sequences
*mRNA tend to be short lived just existing in the cell for a few seconds if they aren’t be actively used
*tRNA and rRNA: long lived exist in cell for days and weeks at a time
