Chapter 14: DNA and the Gene Flashcards
What did Alfred Hershey and Martha Chase study?
how T2 virus infects E.coli and whether genes were made of protein or DNA…whether viral genes consisted of DNA or protein
Viral genes consist of:
DNA
Viral coats consist of:
protein
Phosphorus is found in:
DNA, but not protein
Sulfur is found in:
protein, but not phosphorus
What were the results from the Hershey-Chase experiment? (need more info)
- all radioactive proteins were in the viral capsid
- all radioactive DNA was found inside the host cells
Who discovered that DNA was the hereditary material?
Alfred Hershey and Martha Chase
What experiment proved that DNA contained all the info for life?
the Hershey-Chase experiment
State why protein is not considered hereditary material.
ASK
Who were famous for their discovery for how DNA is synthesized?
Mathew Meselson and Franklin Stahl
What were the 3 potential mechanisms proposed by biologists for DNA synthesis?
1) Semi-conservative
2) Conservative
3) Dispersive
Semi-conservative
if parental strands of DNA are separated, each could be used as a template for the synthesis of new strands
Conservative
if bases turned outwards, complementary strands can serve as template for synthesis of an entirely new double at once
Dispersive
if parent helix was cut before being unwound, copied and put back together, then the old and new segments would alternate
The Meselson-Stahl experiment:
studied how E.coli DNA replicates
Berfore the Meselson-Stahl exp., what did they know?
- bacteria is small and grows quickly
- the population doubles ~every 20-30 minutes
Step 1 of M-S experiment
bacteria was grown in Nitrogen 15 isotope only
G (not)
parental generation
G1
new daughter strand
G2
new second gen. daughter strand
Step 2 of M-S experiment
grew remainder of bacteria in Nitrogen 14 only and extracted the DNA after cells divide
Step 3 of M-S experiment
let remainder of bacterial culture grow and isolate the DNA (still in N14)
Who discovered the mechanisms of DNA replication/synthesis?
Meselson and Stahl
State why DNA replication is not dispersive or conservative.
- If conservative, would result in 2 distinct DNA bands, a high and low density one
- if dispersion, who result in one single band of intermediate density
- however, found that there were 2 bands, but they were high and intermediate density (semiconservative)
What molecules are responsible for copying DNA (synthesis)?
1) DNA polymerase
2) dNTP
What do DNA polymerases do?
they polymerize deoxyribonucleotides to DNA
the 3 types of DNA polymerases in bacteria are:
DNA polmerase I and III (replication) and DNA polymerase II (DNA repair)
What are dNTP’s?
deoxyribonucleoside triphosphates (the N stands for any of the bases A,T,G,C)
In what direction is DNA replicated?
in a 5’ to 3’ direction
Origin of replication
the replication bubble formed at a specific sequence of bases
-produces a prepriming complex, making single stranded DNA available for replication
How many origins of replication do bacteria have?
only one
How many origins of replication can eukaryotes have?
multiple
replication fork
a Y-shaped region where the parent DNA double helix is split into 2 single strands which are then copied
What does helicase do?
breaks hydrogen bonds between the base pairs to open the double helix
MAIN: opening the double helix
Function of single stranded binding proteins
to stabilize the single stranded DNA to prevent recoiling
MAIN: opening double helix
Function of topoisomerase
to break and rejoins DNA double helix to RELIEVE tension caused b opening helix
Function of primase
to catalyze the synthesis of RNA primer on leading and lagging strands
Function of DNA polymerase III
to extend the leading strand and Okazaki fragment on lagging strand (replication)
Function of sliding clamp
to hold DNA polmerase III in place during replication
Function of DNA polymerase I
to remove RNA primer and replace with DNA
DNA ligase
joins the Okazaki fragments into a continuous strand
How are leading stranding synthesized?
continuously
How are lagging strands synthesized?
in Okazaki fragments…discontinuously
If DNA ligase were defective, what would the replicating DNA look like?
the lagging strand would remain in fragments
What is the purpose of the RNA primer?
to provide a free 3’ hydroxyl group, so that an incoming dNTP can form a phosphodiester bond to
replisome
…
The region (cap) at the ends of linear chromosomes are called?
telomeres
What results in the formation of an unreplicated end in dsDNA?
from that fact that there is not enough room for an RNA primer once the end of DNA strand is reached, therefore leaving behind an unreplicated region
What happens to this unreplicated region on the lagging strand?
gets degraded, resulting in the shortening of chromosome
Do telomeres contain genes that can be coded?
No.
What is the base sequence of telomeres?
contains a unique DNA sequence that is REPEATED thousands of times
The telomeres of humans contain the base sequence:
TTAGGG
What is telomerase?
an enzyme that replicates telomeres by catalyzing DNA from RNA, using the RNA as a template to lengthen chromosomal ends
Why do bacteria and archaea have this unreplicated region?
they have a single, CIRCULAR chromosome
How can the ends of chromosomes be prevented from getting shorter?
with telomerase (add DNA onto the ends)
In humans, where is telomerase mostly found?
in cells of reproductive organs, specifically cells that undergo meiosis to produce gametes (ie. ovaries, testes)
Where is telomerase not commonly found?
somatic cells
Genes that contain errors are:
defective
How can the enzymes involved in DNA replication be as precise as they are?
- DNA polymerase III is highly selective in matching complimentary pairs correctly (1 base in 100 000)
- DNA pol. III can also proofread (can catch mismatch pairs and correct them)–exonuclease activity (1 base in 10 million)
- mistakes after synthesis are removed and replaced with repair enzymes (1 base in a billion)
How does UV light damage DNA?
causes covalent bonds to form between adjacent pyrimidine bases, therefore resulting in a deformed secondary DNA structure (kink)
Exonuclease
enzyme that removes dNTP’s from end of DNA strands
How does the kink of the deformed structure affect the DNA?
- stalls the movement of the replication fork
- cell may die if not repaired
How is damage DNA caused by radiation repaired?
Nucleotide excision repair (NER)
