Lecture 6 Flashcards
(26 cards)
What does DNA store?
DNA is a stable storage form of genetic information
Is DNA static?
NO- DNA metabolism includes replication, repair, and recombination
What is the most important requirement of DNA metabolism?
Accuracy- if you change the blueprint, you change the causing sequence, changing the protein structure/function
Why are repair mechanisms required?
Multiple damaging reactions can and do occur
RNA has a 2’ hydroxyl group which could deprotenate and do what…
It makes the oxianion a nucleophile right in proximity with an electrophile and it hydrolyzes the phosphodiester backbone in RNA.
-Eventually RNA degrades itself bc of nucleophile
Evolution has made which one more stable? DNA vs. RNA
DNA-more stable storage form to store information than RNA
Bacterial Genes are written in…
lower case italics, usually 3 letters (ispA, ispB)
Proteins are usually written in…
Roman type and first letter is capitalized (IspA, ISPB)
What makes accurate replication of genetic material possible?
Specific pairing of DNA bases
Semiconservative
DNA is semiconservative because each strand can act as a template for the synthesis of a perfect copy of the other strand
DNA polymerases
Enzymes responsible for replication. Polymerize 5’->3’
Template Runs from…
3’->5”
Phosphate Atoms during DNA replication
DNA Catalyzes nucleophillic attack.
- Oxygen acts as a nucleophile
- Attacks the ALPHA phosphorous atom and make phosphate be the leaving group
- Phosphodiester bond forms
- Polymerase CANNOT continue on (DNTP)
- Can be hydrolyzed by inorganic phophotase to thermodynamically make favorable
Meselson and Stahl Hypothesis
Each new DNA molecule consists of one old strand and one new strand
Meselson and Stahl Grew E.coli Cells in…
15N labeled NH4CL and determed the DNA density.
Meselson & Stahls Experiment
After groing e.coli in 15N NH4CL
- moved cells to media with 14N NH4Cl and let them double once
- Isolated DNA was lighter
- After second doubling, they showed there were 2 bands of DNA- confirming semi conservative DNA.
Ultracentrifugation
Meselson-Stahl Experiment:
- set up in salt gradient - set up a density gradient and ended up with not very dense at top and dense at bottom - Put DNA at top and spun it
DNA Polymerase uses…
Single strand DNA templates and adds nucleotides to a growing chain in the 5’-3’ direction
Replication bubbles suggest that…
theres a seperation of 2 strands of DNA acompanied by synthesis of complementary strand
*important for lucidation of DNA replications- A-T rich origin replication because easier to break.
Origin of Replication
Replication always begins at this unique point
Replication Fork
- Branch point in a replication bubble
- Bidirectional
DNA Polymerases work in what direction?
5’ to 3”
During Polymerization, the new DNA base is added to…
the 3’ OH of the previous added base
Evidence suggests that both strands of DNA are replicated…
Simultaneously- which is a problem because this means both strands cannot be synthesized continuously
