DNA & RNA Flashcards Preview

ESA 1 - MCBG > DNA & RNA > Flashcards

Flashcards in DNA & RNA Deck (17)
Loading flashcards...
1
Q

What are polynucleotide nucleic acids?

A

Linear polymers of nucleotides, i.e. DNA and RNA.

2
Q

What is the difference between a nucleotide and a nucleoside?

A
  • Nucleotide = sugar + base + phosphate

- Nucleoside = sugar + base

3
Q

Why are nucleic acid molecules (nucleotides) polar?

A

Negative charge on phosphate group.

4
Q

What are the 2 types of pentose sugars?

A
  • 2-deoxyribose (in DNA) - H linked to 2’ C

- ribose (in RNA) - OH linked to 2’ C

5
Q

How can nucleoside analogues be used as antiviral and anticancer drugs?

A
  • Phosphorylated nucleoside analogues are similar to nucleosides - can be incorporated into growing viral DNA strand - act as chain terminators and stop viral DPol.
  • Less selective analogues used as chemotherapy agents.
6
Q

Why are nucleosides rather than nucleotides used as antiviral/anticancer drugs?

A

Charged nucleotides can’t easily cross membranes

7
Q

What are the 2 types of nitrogenous bases?

A
  1. Purines
    • Adenine
    • Guanine
  2. Pyrimidines
    • Cytosine
    • Thymine (DNA only)
    • Uracil (RNA only)
8
Q

How are nucleotides joined together to form a DNA polymer?

A

Phosphodiester bond (phosphate to sugar

9
Q

Do DNA strands have polarity?

A

Yes: 5’ to 3’, with distinct 5’P and 3’OH

10
Q

How do nucleotides on different strands form complementary base pairs?

A
  • Each nucleotide has specific +/- charges.

- When one is flipped (as in the antiparallel arrangement of DNA strands), the charges attract to form hydrogen bonds.

11
Q

How many hydrogen bonds form between G-C and A-T (or A-U) base pairs?

A
  • Charges in G-C base pair are at the same distance so 3 bonds can form.
  • Charges in A-T base pair are at different distance so only 2 bonds can form.
12
Q

What are the characteristics of DNA double-strands?

A
  • Complimentary
  • Anti-parallel
  • Form a right-handed double helix containing major and minor grooves.
13
Q

Are major or minor DNA grooves more difficult for DNA-binding proteins to access and why?

A

Minor, due to steric hindrance.

14
Q

How wide and long is DNA?

A
  • 2nm width

- 2m total length/cell

15
Q

How does DNA fit in the nucleus?

A
  1. DNA is packaged using histones, forming complexes called nucleosomes (DNA wound 1.65x around 8 histones proteins).
  2. Nucleosomes fold up to form a 30nm solenoid chromatin fibre, which forms loops averaging 300nm in length.
  3. Chromatin fibres are compressed and folded to produce a 250nm-wide fibre, which is tightly coiled into the chromatid of a chromosome.
16
Q

What are histones?

A

Positively-charged proteins that strongly adhere to negatively-charged DNA.

17
Q

Give an example of a disease involving deficient DNA packaging/expression.

A
  • RETT’S DISEASE
  • Neurological development disorder (loss of hand coordination, mobility & speech).
  • Mutation in methyl-CpG-binding protein 2 (silences transcription of certain genes) - inability to bind to correct DNA regions, or inability to recruit histone binding complexes - modifying complexes can’t repress gene - abnormal gene activation.