3.9. DNA REPLICATION AND GENETIC CODE Flashcards
What are the four requirements for DNA as a genetic molecule?
-Must carry information
-Must replicate
-Must allow for DNA to change (mutate)
-Must control phenotype, using protein synthesis
What are the DNA nitrogenous bases and when are they accessible?
Adenine, Thymine, Guanine, Cytosine.
Genes are mostly accessible when DNA is unwound (chromatin).
What is fidelity?
Degree of exactness when replicated.
Does DNA have high fidelity?
They have extreme accuracy to preserve the integrity of genome in successive generations.
In eukaryotes, DNA replication occurs during S phase of the cell cycle - slower than prokaryotes (highly fidelity).
What is semi conservative replication?
After one round of replication, every new DNA double helix would be a hybrid that consisted of one strand of old DNA bound to one strand of newly synthesized DNA.
What is conservative replication?
In conservative replication, two DNA copies are produced from one original DNA, which serves as a template. Out of these two, one is entirely new DNA, and the other is made of old DNA strands.
What is Dispersive replication?
DNA replication results in two DNA molecules that are mixtures, or “hybrids,” of parental and daughter DNA. In this model, each individual strand is a patchwork of original and new DNA.
What is the Meselson and Stahl experiment (1958)?
To begin with they used heavy nitrogen (N15) and extracted the DNA from it and placed it in caesium chloride. This was very dense and formed at the bottom of the test tube.
Then, they added N14 (light nitrogen) to this which caused the density to lower and the solution to rise.
After they continued this process which caused two DNA bands to float in the solution - two different types of DNA.
This shows semi - conservative replication.
Where does DNA replication begin?
At the origin (bacterial chromosomes have a single point of origin whereas eukaryotes have multiple origins)
What direction does DNA replication happen in?
5’ to 3’ direction (the template strand runs in a 3’ to 5’ direction)
What is DNA polymerase?
an enzyme that copies DNA.
It requires a free 3’ hydroxyl group on deoxyribose before synthesis can be initiated.
What does the term Discontinuous mean, referring to DNA replication?
The antiparallel strand is replicated by DNA Polymerase as a series of short fragments that are subsequently joined together (lagging strand).
What does the term Continuous mean, referring to DNA replication?
The template strand is replicated by DNA polymerase (leading strand).
What is the replication fork?
Helicase enzyme splits the (original) DNA strand into two separate strands. Here, DNA is forced to rotate.
What are Topoisomerases?
Enzymes that temporarily break strands of DNA, relieving tension by unwinding the two strands of DNA helix. This happens by adding negative supercoils in helix.
