Chapter 10: DNA and RNA Structure

What are the two types of nucleic acids?

• DNA

• RNA

What are the three major groups of a nucleotide?

1. Nitrogenous base

2. Pentose sugar

3. Phosphate group

What does the phosphodiester bond do? 

• Links two nucleotides together by joining the phosphate of one nucleotide to the 3’ carbon of the sugar of the next nucleotide, forming the backbone of DNA or RNA

Where is the glycosidic bond? 

• Connects the 1’ carbon of the sugar to the nitrogen of the base

How does a deoxyribonucleotide differ from a ribonucleotide? 

• Deoxyribonucloeitde: 2’ carbon has H 

• Ribose: 2’ carbon has OH

What is the name of the nucleotide that’s incorporated into DNA? How many phosphate groups does it have? How many of these phosphate groups actually end up in DNA? 

• Doexyribonucleoside triphosphates

• 3 phosphate groups 

• 1 photospahte group, the other two are released as pyrophosphate during polymerization

What overall charge does the phosphate give DNA?

• Negative charge

Which bases are found in DNA? Which are found in RNA? 

• DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

• RNA: Adenine (A), Uracil (U), Guanine (G), Cytosine (C)

 What are the three typical base pairs? How many hydrogen bonds are found between them?

• Adenine–Thymine (A–T): 2 hydrogen bonds

• Guanine–Cytosine (G–C): 3 hydrogen bonds

• Adenine-Uracil(RNA): 2 hydrogen bonds

What is Chargaff’s rule? What does it say about (A+G)/(T+C)?

• Chargaff’s Rule: In DNA, the amount of adenine = thymine, and the amount of guanine = cytosine.

• Therefore, (A + G) = (T + C)

• Purines = Pyrimidines in total

dsDNA has 40% Guanine. Calculate the percentage of Thymine.

• Total DNA = 100%

• G = 40% → C = 40% (G = C by Chargaff’s rule)

• Remaining = 100 − (G + C) = 100 − 80 = 20%

• A = T → T = 10%

• Answer: Thymine = 10%

What is melting temperature and how can it be calculated for DNA?

• Melting temperature (Tm): The temperature at which 50% of a DNA molecule becomes single-stranded (double helix “melts”).

• (Tm = 2(A+T) + 4(G+C)

The phosphodiester backbone is ___________ bonded, while the bases are held together by noncovalent hydrogen bonds.

• Backbone: Covalently bonded (phosphodiester bonds)

• Bases: Held together by hydrogen bonds

Descriptors of DNA

• Double-stranded 

• Antiparallel 

• Right-handed helix 

• Contains guanine

What is one characteristic that allows DNA replication to be semiconservative?

• Antiparallel double-stranded structure with complementary base pairing allows each strand to serve as a template for a new strand.