7.1 DNA Structure and Replication HL Flashcards
What did the Hershey-Chase experiment prove?
That DNA is the genetic material
What were the 2 batches made in the Hershey-Chase experiment?
2 batches of bacteriophage virus
One with radioactive phosphate (35P)
One with radioactive sulfate (36S)
What did the radioactive phosphate in the Hershey-Chase experiment do?
The radioactive phosphate is a radioatcive tag. It labeled the DNA so it was easy to determine what is transfered to the bacteria. Phosphate is only found in DNA and not in proteins
Why did the Hershey-Chase experiment use viruses (bacteriophages)
It was a simple model organism that injects substances into bacteria. Has a DNA core
This substance makes the bacteria produce more bacteriophages, meaning that it must contain the instructions for making a new virus.
What did the radioactive sulfur in the Hershey-Chase experiment do?
The radioactive sulfur was also a tag, and it labeled proteins in order to show if they were transferred to the bacteria. Sulfur is only found in proteins and not DNA.
Steps of Hershey-Chase experiment
1) Virus batches were allowed to infect a bacterial culture
2) In order to separate the bacteria from the viruses attached to their outside, they agitated in a blender to dislodge them.
3) The batches were centrifuged in order to fully separate the bacteria from the viruses, with the larger bacteria falling to the bottom of the centrifuge. The tags in each batch were then analyzed to see where (and if) they were transferred.
Results of the Hershey-Chase experiment
When the protein was monitored, most of the radioactivity remained with the virus and did not enter the bacteria. Less than 1% of the protein radioactivity from the viral parents was found in the newly replicated virus, so the protein was not being inherited.
When the phosphate was monitored, most of the radioactive DNA was injected into the bacteria with a lot being passed on to the new virus generation.
What did the cross in the center of the X-ray diffraction mean?
DNA had a helical shape
What did the angle of the cross in the center of the X-ray diffraction mean?
Showed the pitch of the helix (how long each turn of the DNA helix is)
What did the distance between the horizontal bars in the X-ray diffraction mean?
Meant the turns helix
What did the distance between middle of diffraction pattern and top
Repeating structures within the molecule
What did Linus Pauling do?
Demonstrated the concept of molecular modeling and came up with the incorrect Triple Helix DNA
What did Rosalind Franklin do?
x-ray diffraction, discovered the structure of DNA (regular helical pattern)
What did Edwin Chargaff discover?
Discovered base composition of equal A amounts to T and the same for C-G
What did Watson & Crick discover?
- TIght packing of DNA would occur if a pyrimindine and purine paired together
- DNA was antiparallel
- DNA is stable b/c AT and CG are electronically compatible
- AT has 2 hydrogen bonds and CG has 3 hydrogen bonds
Nucleosomes consist of
Octamer, Linker DNA, H1 histones
Octamer
8 proteins
2 copies of 4 different types of histones
Linker DNA
DNA that connects one nucleosome to the next
H1 histone
Bind DNA to the core
- facilitates further packing by creating the 30m fiber
How are nucleosomes beneficial in eukaryotes
- Adaption that facilites the packing of the large eukaryotic genomes, keeping the DNA small and helping to super coil DNA
Leading strand
Continuing the replicationg fork as it opens, only needs 1 primer
Lagging strand
- made in fragments moving away from the replication fork
- New fragments are created as the leading strand exposes more lagging strand
What does the lagging and leading have in common?
- Both add dNTPs 5’ -> 3’ but in opposite directions
- Both require primers, but lagging needs multiple while leading needs only one
Topoisomerase
- Releases the strand that develops ahead of helicase
Helicase
seperate the strands of DNA
Primase
- creates RNA primer
- RNA primer intiates activity of DNA polymerase.
- One primer on leading strand, many primers on lagging strand
Ligase
- Connects gaps between Okazaki fragments
DNA Polymerases
- Many functions
- adds complimetary nucleotides to growing chain
- Proof reading the DNA
- Removal of RNA Primers
Origins of replication
where DNA replication begins
How many origins of replication do eukaryotes have?
Many origins
How many origins of replication do prokaryotes have?
One origin
Coding sequences
code for the production of polypeptides
Non-coding sequences
Don’t code for polypeptides
But may
* be transcribed to produce tRNA and rRNA
* Regulate gene expression
Repetitive sequences
- non-coding
- represents 60% of DNA
Moderatively repetitive sequences
- long sequences (~300 bp) that are repeated
- occur less often than highly repetitive sequence
Highly repetitive sequence
- satellite DNA
- Short sequences (~5-100 bp) repeated thousands of times
- important for forensic work
Telomeres
Repetitive sequences found on the ends of eukaryotic chromosomes
Protective function of telomeres
- like plastic tips on shoelaces
- Prevent chromosome ends from fraying and sticking to each other, which would destroy or scramble an organisms genetic info
What happens when telomeres are reduce
As cells divide, telomeres get shorter since replication cannot occur at the very ends of chromosomes. This means that DNA is more likely to “scramble” without the protection of the telomeres.
What is VNTR?
Variable Number Tandem Repeat
* Short nucleotide sequence (6-100bp) that shows variations between individuals in terms of the number of times the sequence is repeated
* Each variety can be inherited as an allele, one from mom and one from dad.
What are VNTRs used for
DNA profiling in forensics and genalogly
Locus
Location of a heritable element on a chromosome
Allele
Variation of a gene
What is gel electrophoresis?
A device/technique that uses electric movement used to seperate DNA/RNA fragments by size (number of base pairs)
How do primers help identify VNTRs?
Annel to the sequences of DNA that flank VNTRs
idk if this is right
Function of restriction enzymes
Molecular scissors that cut DNA at specific locations to obtain smaller framents.
What fragments travel the farthest?
Shortest travel farthest b/c they can get through the fine holes in the gel
Which fragments travel the shortest?
Longest travel shortest because they have a harder time squeezing their way through the gel
