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MolBio and Genetics I > 2. DNA structure and Genetic Code > Flashcards

2. DNA structure and Genetic Code Flashcards

1
Q

What are the 4 principles DNA structure should fit?

A
  1. provide a means for its own replication
  2. be able to encode the genetic information
  3. direct cell function
  4. accomodate changes caused by mutations
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2
Q

Why did Watson move to Cambridge

A

learn X-Ray diffration/crystalography

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3
Q

What can we learn from the analysis of difracted x-rays?

A

yields structural information. Based on the angles they defract, we can trace the structure

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4
Q

What were Erwin Chargaff’s rules?

A

DNA of any species always had equal concentrations of A&T and G&C bases suggesting a fixed relationship

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5
Q

What did Rosalind E Franklin discover?

A

DNA could exist in dehydrated ‘A Form’ and a fully hydrated ‘B form’

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6
Q

What are important things Franklin deduced from the first X-ray diffraction image?

A
  1. DNA was helical and most likely a double helix consisting of 2 anti parallel strands
  2. phosphates were on the outside of the helicies with the bases on the inside
  3. distance between bases, the length of the period and the rise of the helix
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7
Q

Are the base tautomersiin DNA most likely Keto or Enol form?

A

They are Keto form

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8
Q

What are important characteristics of the two complimentary DNA strands?

A
  • have directionality as they are polarized polymers that run antiparallel to each other
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9
Q

is phosphate bonded to the 5’ or 3’ carbon pf the deoxyribose sugar?

A

5’ phosphate group

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10
Q

is hydroxyl group bonded to the 5’ or 3’ carbon pf the deoxyribose sugar?

A

3’ hydroxyl group

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11
Q

What DNA replication theories were there?

A

Semi-conservative, conservative, dispersi ve

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12
Q

How did Meselson-Stahl test the DNA replication theories?

A
  • mixed heavy isotope 15Nitrogen (radioactive) and normal 14 Nitrogen
  • followed the sedimentation characteristics of DNA after each cell division
  • shows semiconservative replication
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13
Q

Describe Meselson and Stahl’s experiment

A
  1. DNA that contained radioactive (15 N) nitrogen was grown in a medium with 14 N (normal nitrogen)
  2. samples were spun rapidly to form a concentration gradient
  3. two separate regions were found (14 N and 15N region)
  4. After one generation, hybrids were found
  5. second generation showed, hybrid and pure normal nitrogen DNA
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14
Q

How did they crack the genetic code?

A

Only when using labelled phenylalanine, did the poly-uracil RNA lead to the production of radioactive protein

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15
Q

Which amino acids only have one codon?

A

methionine and tryptophan

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16
Q

What are mutations?

A

variations in the DNA sequence eg single base pair substituition
- influence the functionality of protein

17
Q

What percentage of the human DNA genome directly encodes amino acids?

A

only 1.5%

18
Q

how long is a bacterial DNA? and how large is a bacteria?

A

DNA: 1 mm while Bacteria is only 1 micrometer

19
Q

What are Topoisomerases

A

enzymes that insert or remove supercoils

20
Q

What does topoisomerase I do?

A

type I: break only one strand -> relaxing or twisting of the helix

21
Q

What does topoisomerase II do?

A

Type II breaks both strands and pass another part of the double helix through the gap

22
Q

How many giant supercoiled loops in the DNA does a typical bacterial chromosome consist of?

A

50

23
Q

What proteins does Eukaryotic DNA have?

A

Histones

24
Q

What ordered structures in eukaryotic DNA results in chromosomes

A

Chromatins and nucleosomes

25
Q

What is the sequence of a starting codon?

A

ATG

26
Q

How much shorter is the DNA due to folding?

A

10,000 fold shorter

27
Q

What is the eukaryotic chromatin hierchal structure?

A
  1. at simplest level, chromatin is just a double helix
  2. DNA is complexed with histones form nucleosomes
  3. 8 histones make up one nucleosome
  4. a chromosome consists of a nucleosome plus H1 histone
  5. the nucleosomes fold up to loops to produce fibers
  6. these are coiled into loops again to make even larger fibers
  7. tight super coiling of fibers produces the chromatid of the chromosome

MolBio and Genetics I (9 decks)

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