DNA properties and replication Flashcards
How many hydrogen bonds are formed between adenine and thymine?
2.
How many hydrogen bonds are formed between cytosine and guanine?
3.
What is Tm?
In denaturation, the temperature at which half of the helical structure is lost. This varies according to the GC content.
What is a common term for renaturation?
Annealing
What are the four requirements for DNA to be genetic material?
Must carry information, must replicate, must allow for information to change (mutation) and must govern the expression of the phenotype.
What can DNA mutations result in?
Disease such as clotting factor IX can cause haemophilia if one base is changed, causing a stop codon to be coded for rather than another amino acid and the entire protein is shortened. They can also result in the risk of disease being increased such as the LDL receptor in coronary heart disease, meaning medications may no longer be effective.
What is DNA replication?
The replication of the entire genome prior to cell division.
What are the basic steps of DNA replication?
Initiation - proteins bind to DNA, open up the helix and prepare the DNA for complementary base pairing
Elongation - proteins connect the correct sequences of nucleotides into a continuous DNA strand
Termination - proteins release the replication complex
What are the basic rules of replication?
Semi-conservative, starts at the origin, can be uni or bidirectional, semi-discontinuous, synthesis always occurs in the 5’-3’ direction and RNA primers are required.
What does semi-conservative mean?
Half of the old strand and half of the new strand is present in the newly formed DNA molecule.
What experiments proved the semi-conservative theory?
Meselson-Stahl experiments with 14-N and 15-N in centrifugation.
Why does replication start at the origin?
Initiator proteins identify specific base sequences to start the replication.
What is the difference between initiation of replication in prokaryotes and eukaryotes?
Prokaryotes only have a single origin site whereas eukaryotes have multiple sites of origin.
What is semi-discontinuous replication?
Replication in which continuous and discontinuous replication occurs - the leading strand undergoes replication continuously whereas the lagging strand undergoes synthesis in fragments.
Why does the lagging strand undergo replication in fragments?
The RNA primer can only sequence from 5’ to 3’ so Okazaki fragments must be formed and joined together.
