Nucleic Acids

How is DNA described?

DNA is a double helix made of 2 antiparallel strands (5’ to 3’) (3’ to 5’). Sugar phosphate backbones on the outside bases pair internally by hydrogen bonds. A-C (2 bonds) C-G (3 bonds)

Hershey and Chase

used bacteriophages to show DNA is hereditary and not proteins

Chargaff

showed A=T and C=G, base pairs

Wilkens and Franklin

x-ray diffrac

Watson and Crick

build the double helix model j

Arthur Kornberg

discovered DNA synthesis requires 4 components: -

1. nucleotides

2. DNA template

3. DNA polymerase

   1. Mg2+ cofactor

Meleson and Stahl

demonstrated semiconservative replication (DNA has one old and one new strand)

What makes up a DNA nucelotide

• phosphate group

• nitrogenous base 

  • sugar

What are the four nitrogenous bases?

Adenine, Guanine, Cytosine, thymine

How do purines and pyrimidines differ?

purines: A, G (double-ring)

pyrimidines: T, C (single ring)

What do telomeres do?

noncoding, repeating sequences at the end of chromosomes. postpone the erosion of genes during replication

What stabalizes DNA as they unwind?

single-stranded binding proteins (SSBPs). coat and stabalize unwound DNA

What is the role of ligase in DNA replication?

connects the 3’ end of the second fragment to the 5’ end of the first fragment.

joins Okazaki fragments on the lagging strand

What is the role of primase in DNA replicaiton 

synthesizes short RNA primers to start DNA replication, provides direction for polymerase to put nucleotides down

• on leading strang: one primer

  • on lagging strand: multiple primers (fragments)

What is the role of helicase in DNA replication?

unwinds the double helix at replication forks

What is the role of DNA polymerase III

adds nucleotides to new DNA strand in 5’ to 3’ direction

builds continuouslly on the leading strand and discontinuously on the lagging strand.

proofreads new DNA and corrects errors

Telomerase

extends telomeres by adding repetitive DNA to chromosome ends.

active in gametes, stem cells and cancer cells

What structures are found only on lagging strands?

okazaki fragments

multiple RNA primers

polymerase I

When does DNA replication occur?

during S phase of interphase. 

what is the pairing pattern of nucleotide bases?

A=T C=G

What causes DNA mutations?

• UV damage

• radiation

• chemical mutagens

• errors in proofreading