DNA Replication - MBM

Lecture 1

What are Nucleotides composed of?

Sugar, Phosphates, and Nitrogenous Bases.

What is a sugar?

A pentose that has 5 carbons

What is a sugar in RNA called?

A ribose and it has an OH group on 2’ carbon, distinguishing it from DNA.

What does 5’ and 3’ refer to?

The carbons on the sugars which are linked together by phosphodiester bonds to make nucleic acids.

How does the nitrogenous base attach to the 1’ carbon?

Via an N-glycosidic bond.

Nucleoside

sugar + nitrogenous base attached to the 1' carbon of the sugar, but without a phosphate group.

How many rings do Purines have?

Two Rings

How many rings do Pyrimidines have?

One Ring

What makes of Purine?

A purine comprises a six-membered and a five-membered nitrogen-containing ring, which are fused together. The two main purines in DNA and RNA are adenine and guanine.

What makes up a Pyrimidine?

Cytosine and thymine in DNA, cytosine and uracil in RNA

What is the difference between thymine and uracil?

There’s a methyl group (CH3) on thymine

What is Deamination?

spontaneous loss of an amine group from the nitrogenous base of a nucleotide, and is a common type of DNA damage

Why is it easy for DNA repair mechanisms to detect and repair the damage of deamination?

Most of the time, loss of the amine group makes a nitrogenous base that is not normally found in DNA so easy to identify: Cytosine becomes uracil, Adenine becomes hypoxanthine, and Guanine becomes xanthine.

What do these nitrogenous bases (cytosine, adenine, and guanine) have in DNA?

amine groups (NH2).

What mutations are the most common?

C to T transition mutations, or permanent change in DNA sequence because thymine is a normal nucleotide in DNA, so it’s a lot harder for the cell to detect it as damage.

What does DNA Methylation do?

DNA methylation changes how proteins interact with the DNA, influences its structure (indirectly), and plays an important role in regulation of gene expression.

What does the deamination of a methylated cytosine (5- methylcytosine, 5mC) result in?

It results in formation of thymine instead of uracil.