Studied by 4 peopleRosalind Franklin
Performed X-Ray crystallography on DNA; found our dna is repetitive and regular
Edwin Chargaff
Amount of Adenine = Thymine
Amount of Cytosine = Amount of Guanine
Purine
Adenine, Guanine & DOUBLE RINGED
Pyrimidines
Cytosine, Uracil, Thymine & SINGLE RINGS
Base pairs have what?
Held by hydrogen bonds
Adenine and Thymine
2 Hydrogen bonds
Cytosine and Guanine
3 Hydrogen bonds
Watson and Crick combined the findings of _____ and ______ to create ______
Franklin (the helix shape); Chargaff (base pairing); the first 3D, double helix model of DNA
DNA STRUCTURE
backbone: sugar-phosphate
center: nucleotides pairing
5’ end
Phosphate group
3’ end
Hydroxyl group
What is the primary source of heritable info?
DNA; SOMETIMES RNA FOR VIRUSES
What happens to genetic info through DNA?
Genetic info is stored in and passed from one generation to the next through DNA
Eukaryote Cells
Dna in nucleus
Linear chromosomes
Prokaryote Cells
Dna in Nucleoid Region
Circular chromosomes
Prokaryotes (and some eukaryotes) contain plasmids:
Small, circular DNA molecules that are separate from chromosomes
Plasmids replicate how?
Independently
Plasmids are useful when?
They contain genes that may be useful to the prokaryote when it’s in a particular environment, but its not need for survival
Plasmids can be _______
Manipulated laboratories
Plasmids can be removed from _____
Bacteria, then a gene of interest can be inserted into the plasmid to form a recombinant plasmid DNA
When the _______ plasmid is inserted back into the bacteria the gene will be expressed
Recombinant
Bacteria can ________ ______ found on plasmids with neighboring bacteria
Exchanging genes
Once DNA is exchanged, the bacteria can _____ the genes fs
Express
Once plasmids go though with expressing DNA, then…
Plasmids help with the survival of prokaryotes
DNA replicates during which phase of the cell cycle?
Synthesis
3 models of DNA replication:
Conservative, Semi-conservative, Dispersive
Conservative
The parental strands direct synthesis of an entirely new double stranded molecule; the parent strands are fully “conserved”
Semi Conservative
The two parental strands each make a copy of itself; After one round of replication the two daughter molecules each have one parental and one new strand
Dispersive
The material in the two parental strands is dispersed randomly between the two daughter molecules; After one round of replication the daughter molecules contain a random mix of parental and new DNA
What experiment did Meselon and Stahl perform?
Using bacteria they cultured it with a isotope 15N, then transferred to a lighter isotope of 14N, then the DNA was centrifuged and analyzed after each replication
Results of the experiment of Meselon and Stahl
Semi-Conservation model was CORRECT🔥🗣🦅
DNA replication begins at sites called..
Origins of Replication
How to form a Replication fork?
Various proteins will attach to the origin of replication and open the DNA to form it
_______ will unwind the DNA strands at each ____________ ____
Helicase; Replication fork
To keep the DNA from Re-bonding w itself..
Proteins called Protein (SSBP) (single strand binding proteins) bind to the DNA to keep it open
What is Topoismerase?
It will help prevent strain ahead of the replication fork by relaxing supercoiling
Primase
Initiates replication by adding short segments of RNA (primers) to the parental DNA strand
The enzymes that synthesize DNA can only attach new DNA nucleotides to….
An existing strand of nucleotides
What serve as the foundation for DNA synthesis
Primers
DNAP 3
Attaches to each primer on the parental strand and moves in the 3’ to 5’ strand
As DNAP 3 moves…
It adds nucleotides to the new strand in the 5’ to 3’ direction
The DNAP 3 that follows helicase is known as the ______
Leading strand (only requires one primer)
The DNAP 3 on the other parental strand that moves away from the helicase is known as….
The lagging strand (requires many primers)
Okazaki fragments
Segments of the lagging strand
After DNAP 3 forms an ___________ fragment, DNAP 1 replaces _______ nucleotides with ______ nucleotides
Okazaki; RNA; DNA
DNA LIGASE
joins the Okazaki fragments forming a continuous DNA strand
Since DNAP 3 can only add nucleotides at the 3’ end, there is NO WAY to finish replication on the 5’ end of a…
Lagging strand
Over many replications mean
The dna would become shorter and shorter
How are genes on DNA protected from over replication?
Telomeres
Telemores
Repeating units of short nucleotide sequences that do not code for genes
Form DNA cap at the end of DNA to help postpone erosion
Telomerase adds telomeres to DNA
As DNA POLYMERASE adds nucleotides to the new DNA strand, it proofreads the bases added.
If errors still occur then,
Mismatch repair will take place and enzymes remove and replace the incorrectly paired nucleotide
If segments of DNA are damaged..
NUCLEASE can remove segments of nucleotides and DNA polymerase and ligase can replace the segments
Note
Flashcard