Week 2.1: Biology of DNA

Question 1

Nucleotide components

3

Answer 1

• a deoxyribose (5-carbon sugar)
• a nitrogenous base (nucleobase)
• a phosphate group

Question 2

DNA nitrogenous bases

Pyrimidines

Answer 2

One ring
Cytosine (C)
Thymine (T)

Question 3

DNA nitrogenous bases

Purines

Answer 3

Two rings
Guanine (G)
Adenine (A)

Question 4

Polynucleotide Formation

sugar-phosphate backbone

phosphodiester bond

Answer 4

the -OH on the 3’ carbon of the previous nucleotide’s ribose bonds with the phosphate group on the 5’ carbon of the next nucleotide’s ribose
5’ phosphate head, 3’ -OH tail

Question 5

Watson-Crick Model

DNA traits

structural and functional

Answer 5

double-stranded helix
anti-parallel orientation: strands go in opposite directions
right-handed: railing on right side going upstairs
base-pairing specificity
semiconservative replication

Question 6

DNA structure

nucleotide component attachment points

Answer 6

nucleobase attached to ribose at carbon 1
phosphate group attached to ribose at carbon 5

Question 7

DNA structure

nucleoside

Answer 7

nucleobase and ribose (no phosphate group)
eg answer triphosphate

Question 8

DNA structure

DNA base pairings

Answer 8

Adenine and Thymine (2 hydrogen bonds)
Cytosine and Guanine (3 hydrogen bonds)

Question 9

histones

4

Answer 9

• histones form H2A/H2B and H3/H4 heterodimers
• DNA strands wrap around octamer anchor
• linker histone H1 binds and changes DNA exit path from nucleosome
• histone fold region and N-terminal tail that extends out from DNA-histone core.

Question 10

nucleosome

4

Answer 10

• nucleosome = core particle + linker DNA
• core particle = ~147 DNA bp wrapped in little less than two 2 turns around protein core (8 histone proteins)
• linker DNA = 10-80 bp depending on species and tissue types
• Most eukaryotic cells have characteristic average nucleosome spacing of ~190 bp = 45 bp linker

Question 11

chromatin

Answer 11

• unraveled, condensed structure of DNA, packaged by histones in nucleus
• structure tightly linked with gene expression regulation
• interphase: chromatin exists as long, thin, tangled threads in nucleus so that individual chromosomes cannot be easily distinguished
• interphase: 30nm fiber
• unfolded: beads on a string (nucleosome)

Question 12

chromosomes

Answer 12

• separate molecules of DNA/genomes
• can be circular or linear