RNA Structure/Synthesis Book notes
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- Review; what is TRANSCRIPTION?
- The process of copying DNA into mRNA.
- What is TRANSLATION?
- The process of making protein products out of the mRNA.
- What type of RNA gets translated? What types don't?
-
mRNA gets Translated.
tRNA, sRNA, and rRNA don't. - What is the central feature to remember about Transcription?
- It is highly SELECTIVE - some sequences are transcribed, but not ALL.
- How is it that Transcription is so selective?
- Very specific signals embedded in DNA tell where and when to start and stop transcription.
- List the 3 major types of RNA, state its % and complexity:
-
mRNA - 5% most complex
tRNA - 15%
rRNA - 80% least complex - How do most RNA molecules exist in the cell?
- As single strands - not a double helix like DNA.
- Where are rRNA molecules found?
- In RIBOSOMES
- What are Ribosomes?
- Complex structures - sites of protein synthesis.
- What are the 3 size species of rRNA in proks?
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-23S
-16S
-5S - What are the 4 rRNA size species in the eukaryotic cytosol?
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28S
18S
5.8S
5S - What is S?
- the Svedburg unit; relates mw and shape of the rRNA.
- Which type of RNA is smallest?
- tRNA.
- How many residues are commonly in tRNA?
- 74-95
- What are 2 unique qualities of tRNA?
-
-They have unusual bases
-Have extnsive intrachain base-pairing. - How many tRNA molecules are there?
- At least one specific type for each of 20 amino acids.
-
Which end of a tRNA molecule carries:
-The amino acid?
-The binding code for mRNA? -
3' end - amino acid
Anticodon loop - anticodon - What is the Major Function of mRNA?
- Carrying genetic information from the nuclear DNA to the cytosol for protein synthesis.
- What characteristics make eukaryotic mRNA unique from Prokaryotic?
-
-5'-5' CAP - 7methylguanosine
-3' PolyA Tail - What is a PROMOTER REGION?
- A sequence (at the beginning of a DNA sequence for transcriptn) that is recognized by RNA Pol
- What is a Termination Region?
- Similar to the promotor region but tells RNA Polymerase to stop transcription.
- In what direction is RNA sequenced during transcription?
- 5' -> 3'
- What are the subunits in the Core enzyme RNA Polymerase?
-
2 alpha
1 Beta
1 Beta'
1 w (omega) - What makes up the holoenzyme RNA Polymerase?
- The Core subunits + Sigma
- What is the function of the sigma subunit in RNA Pol?
- Confers specificity for recognizing various promotor regions of DNA.
- What is the function of the core portion of RNA Pol?
- Polymerization of the RNA.
- What TYPE of an enzyme is RNA polymerase?
- a Zinc Metalloenzyme - requires Zn2+.
- What is rho (p) factor?
- A termination factor in E. coli that signals transcription to stop.
- What are the 3 main Phases of transcription in E. coli?
-
1. Initiation
2. Elongation
3. Termination - What is a Promotor site again?
- The sequence where RNA Pol binds to start transcription.
- What is the Operator site?
- A site near the Promotor, but it has binding sites for activation or repression of the gene.
- What component of RNA Pol is responsible for binding the Promotor site again?
- Sigma.
- How many genes intended for translation are usually in the DNA being transcribed in bacteria?
- Many - polycystronic.
- What is an Operon?
- The combined name for the Promotor, Operator, and Structural genes in bacteria.
- What is the Pribnow box, really?
- The name for the Standard promotor found in bacterial genes.
- Where is the Pribnow box located?
- -10 nucleotides from the start of transcription.
- What is the Pribnow box sequence?
- TATAAT
- What key info should be remembered re: bacterial promotor regions?
- Consenses sequences are highly conserved - the promotors are very similar, but not identical allowing varied gene expression.
- Are all consenses sequences (promotors) recognized by the same sigma factor?
- No; there are different sigma factors for different operators.
- What other sequence is an important promotor in prokaryotes?
- -35