Nucleic Acids Flashcards

Question

What was Erwin Chargaffs experiment?

Answer 1

Measured the isolation, purification, and measurement of nucleic acids from living cells using many biochemical techniques. By this time it was already known that DNA contained a, c, g, and t

Answer 2

Relative proportions of base pairs suggested complementary base pairing. % adenine = % thymine % cytosine = % guanine This concept became known as chargaffs rule.

Answer 3

Built ball and stick models to draw together all the recent discoverys and observations. They tried to answer the questons how the two (or more) strands interacted, and an early hypothesis for this was that the strand interacts through phosphate-Mg++ crosslinks

Answer 4

Model building showed that this was incorrect.

Answer 5

Then built models with the Sugar-phosphate backbone on the outside Bases projecting toward each other Bases form H bonds with identical bases in the opposite strand ie., A - A, T - T, C - C, and G - G Model building revealed that this also was incorrect

Answer 6

Built ball-and-stick models with A - T and C - G pairing These were consistent with all known data about DNA structure

Answer 7

in the 5' to 3' direction

Answer 8

DNA is a polymer of nucleotides with a sugar phosphate backbone. The order of its nucleotides is known as the DNA sequence and runs in the 5' to 3' direction. DNA is double stranded and these strands are antiparallel to eachother

Answer 9

H bonds are relatively weak

Answer 10

G - C rich regions are more stable than A - T rich regions since they have more hydrogen bonds.

Answer 11

Two strands are twisted together around a common axis There are 10 bases per complete twist

Answer 12

The helix is right-handed It spirals away from you, moving in a clockwise direction This is called the B form of DNA

Answer 13

1. Major groove 2. Minor groove

Answer 14

Certain proteins can bind within these grooves and interact with a particular sequence of bases

Answer 15

However, under certain in vitro conditions, A-DNA and Z-DNA double helices can also form.

Answer 16

Right-handed helix 11 bp per turn Occurs under conditions of low humidity Little evidence to suggest that it is biologically important

Answer 17

Left-handed helix 12 bp per turn Its formation is favored by GC-rich sequences, at high salt concentrations Cytosine methylation, at low salt concentrations Evidence from yeast suggests that it may play a role in transcription and recombination

Answer 18

Human nuclear DNA is around 2m in length To fit within a living cell DNA must be extensively compacted Aided by DNA-binding proteins (such as histones)

Answer 19

Uracil is present instead of thymine. A binds with U instead of T

Answer 20

several hundred to several thousand nucleotides in length

Answer 21

1. SIngle stranded.

Answer 22

Different types of RNA secondary structures are common Short double-stranded regions can form due to complementary base pairing within one RNA strand

Answer 23

rRNA (ribosomal) tRNA (transfer) mRNA (messenger) siRNA* (si RNA) and others

Answer 24

Small (or short) interfering RNA (siRNA) is the most commonly used RNA interference (RNAi) tool for inducing short-term silencing of protein coding genes. siRNA is a synthetic RNA duplex designed to specifically target a particular mRNA for degradation.