Molecular Biology DNA

Question 1

What is the simplest subunit in DNA?

Answer 1

nucleotide

Question 2

What is a nucleotide composed of?

Answer 2

• 5 carbon sugar (deoxyribose)
• A phosphate (PO4-)
• a nitrogen base (ATCG)
• backbone is made of alternating PO4 and deoxyribose
• teeth made by one of four n-bases
• all held together by covalent bonds
• h-bonds hold n-bases together

Question 3

The two strands of DNA are..

Answer 3

• complimentary because the n-bases bond with each other according to Chargoff’s rule

Question 4

Why should DNA have the ability to create an exact duplicate of itself?

Answer 4

• grow
• replace old/damaged cells

Question 5

DNA replication:

Answer 5

replication: single strand of nucleotides acts as a template for the formation of a complimentary strand

1) starts at replication origin
2) helicase enzyme unzips the hydrogen bonds between n-bases in double helix
3) DNA gyrase/topoisomerase decrease helical strain ahead of helicase activity, stabilize single strands
4) unzipped DNA held apart of single-strand binding proteins (SSBs) serves as template for new bases
5) exposed bases attract free-floating bases from nucleotides from foods that have complimentary bases to template strand, attached to chain by DNA polymerase III
6) short segment called RNA primer attached to template and guides DNA polymerase III to starting point (adds nucleotides 5’ to 3’ direction only) (made by RNA primase)
7) this results in one strand made continuously, called the leading strand
8) other strand called lagging strand, synthesized in short DNA Okazaki fragments
9) to complete replication, RNA primers cut out of DNA polymerase I and replaced by appropriate nucleotides
10) DNA ligase “glues” together the sugar-phosphate backbone and DNA fragments together