DNA Replication & RNA Structure/Function Flashcards
What are the 3 proprosed models of DNA Replication Mechanism?
- Dispersive: breakage and reunion
- Semiconservative: unwind and replicate each
- Conservative: replication without unwinding
SEMICONSERVATIVE IS HOW IT ACTUALLY DOES IT
DNA is synthesized in what direction?
5’ to 3’
What are the 5 components required for synthesis of DNA?
- All four dNTPs (AT,GC)
- A fragment of DNA to act as a template
- DNA polymerase
- Mg 2+ (cofactor for DNA polymerase activity)
- A primer providing free 3’-OH group
What is the role of DNA polymerase?
- Catalyzes formation of phosphodiester bond between 3’ OH group and 5’ phosphate
- Needs a primer before it can start
- At each step is forms the complementary base on the template strande
- If it makes a mistake-it can repair it
- 3’ to 5’ proofreading exonuclease activity of DNA polymerase- clips off any unpaired residues
Function of DNA polymerase III?
Prokaryotic
Primary enzyme of DNA synthesis
Alpha subunit
DNA synthesis on the lagging strand is…?
3 steps
Discontinuous.
Has a series of short segments known as Okazaki fragments
1. DNA polymerase III synthesizes the Okazaki fragment
2. DNA polymerase I removes the RNA primer
3. DNA ligase joins the DNA gragments together (phosphodiester bond)
Helicase function
Unwinds helix
Single strand binding proteins
Prevent reattachment of original DNA strands
Primase function
Initiates attachment of new polynucleotide strand
DNA polymerase I function
Replacement of RNA primer with DNA
Ligase function
Joins Okazaki fragments of lagging strand
Topoisomerase function
Severs over-wound DNA then reattaches it
This is due to stress-it removes it
2 main differences between DNA synthesis and RNA synthesis?
- No primer needed for RNA
- Uracil instead of thymine in RNA
What are the three stages of transcription?
- Initiation
- Elongation
- Termination
The DNA sequence where RNA polymerase attaches to is called?
The promotor
What are the alterations of mRNA?
- 5’ prime end receives a 5’ cap
- 3’ end receives a poly A tail
- Excision of introns
Protect them from hydrolytic enzymes, help ribosomes attach
What removes introns?
RNA splicing (by spliceosomes)
Can 1 mRNA give rise to more than one protein?
YES, think about tropomyosin gene
What is RNA polymerase in bacteria composed of?
Core polymerase and sigma factor
RNA polymerase in eukaryotes (3)
- 5.8S, 18S, 28S
- All protein-coding genes (mRNA) and some snRNAs
- tRNA genes and some snRNAs
Eukaryotic promotors (5)
- GC Box
- CAAT Box
**3. BRE - TATA Box
- INR (initiator element)**
Bolded=core promotor
What does polycistrionic mean?
Can code for multiple proteins
Can RNA be edited after the final transcipt?
Yes-
Substitution ending
Insertion/deletion
What is the structure of tRNA?
Hydrogen bonds in between base pairs
Looks like a cloverleaf
