Genetic discovery and processes Flashcards
Who discovered that DNA was used for genetic material instead of proteins?
Hershey and Chase
What virus was used in the Hershey-Chase experiment?
Bacteriophage/ phages, is a virus that infects bacteria by injecting it with DNA
What are the steps to the Hershey-Chase experiment?
- A phage was produced in a medium of 35S amino acid, which radioactively labeled the protein shell of the phage,
- When the phage injected its DNA into a bacteria, the phages that reproduced had no radioactive labeling
- The phage protein shells are removed from the outside of the cell by vigorous shaking
- A second phage was produced in a medium of 32P deoxyribonucleotides, this radioactively labeled the DNA,
- When this phage injected its DNA into the bacteria, the phage that reproduced had the same radioactive labeling,
- The phage protein shells are again shaken from the outside of the cell
- This proves that genetic information is stored in DNA
What is the basic structure of a phage?
- Protein shell
- Holds DNA inside
What are the two mediums the phages were produced in?
- 35s (protein)
- 32p (nucleotide)
What protein unwinds DNA and what bonds are broken?
Helicase breaks the hydrogen bonds between base pairs in a double helix
What is the enzyme that adds new nucleotides to DNA and where does it add them?
Polymerase adds DNA on a free 3’ end of a growing strand
What are the leading and lagging strands in DNA replication?
- Leading strand is added to a free 3’ end on a strand, DNA is placed from 5’ to 3’
- Lagging strand is also added to a free 3’ end of a strand, but because the template strand is read 5’->3’ polymerase cannot function continuously
How does DNA get placed on the 3’->5’ direction (lagging strand)?
- An RNA primer is placed further down the template strand by RNA primase
- Polymerase III then places DNA on the new RNA primers 3’ end towards OoR
- The new DNA placed and the RNA primer is called an Okazaki fragment
- A polymerase I replaces the polymerase III and places DNA where the RNA primer was placed in the previous cycle,
- DNA ligase then connects the new DNA placed by DNA polymerase III with the DNA placed by the DNA polymerase I using phosphodiester bonds
- The cycle restarts (DISCONTINUOUS)
What is the function of RNA primase?
An enzyme that places the RNA primer in DNA synthesis
What is the function of Polymerase III?
An enzyme that places DNA from the 3’ end of an RNA primer
What is the function of Polymerase I?
An enzyme that replaces polymerase III and then replaces RNA primer with DNA
What is the function of DNA ligase?
An enzyme that creates phosphodiester bonds between two fragments of DNA to make a single fragment
What strand of DNA synthesizes continuously?
The leading strand
What strand of DNA synthesizes discontinuously?
The lagging strand
How does the DNA unwind in DNA replication?
Helicase enzymes break the hydrogen bonds between bases and the strands of DNA straighten out and extend,
- One strand is a 3’ Carbon side
- The other is a 5’ Carbon side
What is DNA polymerase?
An enzyme that places DNA and connects individual nucleotides to each other to make a DNA molecule
What is the lagging strand in DNA synthesis?
A strand that is replicated in short fragments,
- MADE in the 3’ -> 5’ direction
- Parent is read in the 5’ -> 3’ direction
What is the leading strand in DNA synthesis?
A strand that is MADE continuously in the 5’ -> 3’ direction
- Parent strand is read in the 3’ -> 5’
What is an Okazaki fragment?
Small fragments of DNA produced on the lagging strand during DNA replication
- Includes RNA primer and newly placed DNA from polymerase III
- fragment between two RNA primers
What places the RNA primer?
Primase,
- Uses the parent strand as a template to make an RNA complementary fragment
What is RNA primer?
A short segment of RNA that acts as a starting point for a new DNA strand
What is the replication fork?
A Y-shaped region on a replicating DNA molecule where new strands are growing
What is the function of single-strand binding proteins in DNA replication?
A protein that binds to and stabilizes unwound DNA until it is used as a template
- Binds near the start of the replication fork
What is topoisomerase/gyrase?
Proteins that untangle DNA before the replication fork
- Does so by breaking the DNA and then repairing it once they untangle
What is the difference between topoisomerase and gyrase?
Topoisomerase is found in eukaryotes while gyrase is found in prokaryotes
What is the origin of replication (OoR)?
A segment of DNA where the reading of the parent strand begins bidirectionally
- Site where DNA replication starts
- Consists of specific nucleotide sequences
What is telomerase?
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells
What is nucleotide excision repair?
Enzymes cutting and replacing damaged stretches of DNA
What is nuclease?
An enzyme that cuts DNA or RNA
- Does this by removing a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides
