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Genetics And Evolution > Molecular genetics > Flashcards

Molecular genetics Flashcards

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1
Q

What structural aspect of DNA helps allow you to see it

A

It’s lined up and compacted

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2
Q

What did the transforming principle investigate

A

Wether proteins or DNA holds the genetic information

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3
Q

Roughly, what was the transforming principle experiment

A

R and S strains in mice. R = non-virulent, S = virulent.
R survives, S dies, heat activated S survives, R + heat activated S dies
Then
Protein from S + R = survives, DNA from S + R = dies
= DNA holds genetic information

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4
Q

What element would you use to label a protein and DNA with

A

Sulfur for proteins and phosphorus for DNA - they have these in their composition

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5
Q

How did Hershey and chase determine where genetic material lies

A

Radioactively labelled 2 phages - one protein and one DNA.
Centrifugation and mixed with a cell.
Protein phage - radioactivity found outside cell in supernatant
DNA phage - radioactivity found inside the cell

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6
Q

What was X-ray crystallography used for

A

Solving the structure of several materials - like the structure of DNA crystal fibers

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7
Q

What was discovered of the structure of DNA after X-ray crystallography

A

DNA is an antiparallel double helix.
Zig-zag pattern with a specific angle.
Spacing of sorts determines separation.
Empty spaces indicated helical structure.

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8
Q

How does X-ray crystallography work

A

X-ray beam shines from the source onto a crystal, which diffracts the x-rays.
Detector picks up x-rays and forms a diffraction pattern.
Use this is deduce the structure.

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9
Q

How are base pairs paired up - concerning purine and pyramidine and why

A

Purine + pyramidine = perfect, matches x-ray data
Purine + purine = too wide
Pyramidine + pyramidine = too narrow

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10
Q

Is A, T, C and G a purine or pyramidine

A

A + G = purine

C + T + U = pyramidine

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11
Q

What components make up a DNA strand

A

Nitrogen base.
Phosphate group.
Deoxyribose group.
Phosphodiester bonds.

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12
Q

Elements of the double helix

A 
Two antiparallel strands.
Complementary base pairing.
Helical structure.
Polymerisation biochemistry.
Replication mechanism.
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13
Q

How did Meselson conduct the semi-conservative experiment

A

Grew E.Coli with NH4Cl (as a source of nitrogen) to control isotopes induced in DNA.
Grew E.Coli with 15NH4Cl.
Added excess 14NH4Cl to culture.
Observed the different generations.

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14
Q

Features of DNA replication

A

Semi-conservative.
Fast process.
Accurate but not perfect.
Highly regulated.

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15
Q

Where on the DNA is replication initiated

A

At the origin

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16
Q

Names of the two strands that come off the replication fork and the direction they move in

A

Leading and lagging strands.
Leading - replicated continuously in the same direction
Lagging - replicated in the opposite direction, in Okazaki fragments

17
Q

Name 4 essential enzymatic activities in DNA replication

A

DNA polymerase.
DNA primases.
DNA helicase.
Topoisomerases.

18
Q

What occurs at the end of the DNA strand

A

DNA polymerase encounters RNA primer

DNA polymerase and ligaments finish the job

19
Q

What is a problem with linear eukaryotic chromosomes and what is the effect of this

A

The last RNA primer of the lagging strand can’t be made into DNA. Thus the single strand overhangs due to incomplete replication, shortening the chromosome with each round of cell division

20
Q

What process is in place to correct any errors made in DNA replication

A

Proof-reading enzymes

21
Q

What part of DNA replication is most likely to cause a mutation

A

Polymerase mistakes.
DNA damaged due to tension from the forks.
Resulting in a change in the sequence

22
Q

What is the central dogma and what concepts did crick grasp from it

A

DNA -> RNA -> Proteins

  • the role of nucleic acids is to inform synthesis of protein
  • flow of info in unidirectional
  • info is a sequence
23
Q

Why was the central dogma only a speculative idea

A
  • nobody knew what RNA or ribosomes did

- idea of 20 fixed amino acids hadn’t been discovered

24
Q

How did beadle and Tatum show that genes controlled biochemical reactions

A

Already knew: X-ray’s induce mutants.
Used neurosphora fungus and found X-ray induced mutants.
Generated the 3 mutants by putting them in different mediums, can’t grow vitamins.
Reproduced fungus sexually.
Saw the mutants had Mendelian inheritance.
Characterised mutants with race tube assay.

25
Q

What problems occurred when trying to figure out how codons worked

A

DNA is linear but proteins are 3D.
4 bases need to code for 20 amino acids.
Proteins are synthesised in the cytoplasm but DNA resides in the nucleus.

26
Q

What is protein finger printing used for

A

The digestion of proteins and separation of resulting peptides through electrophoresis and chromatography

27
Q

How did Ingram use protein fingerprinting

A
  1. Cutting protein with enzymes, in the same place - sequence specific
  2. Making 2D, reproducible, protein-specific patterns
  3. Digested haem in a few large peptides, digested 4 peptides again
  4. Repeated with mutant peptides, discovered an amino acid change
28
Q

Why did Ingram perform protein fingerprinting, what was he trying to discover/did he discover

A

That a DNA sequence determines protein sequence

29
Q

What experiment was performed to determine that codons are triplets

A

Used T4 phage and insertion and deletion mutagens

30
Q

Explain the experiment used to determine that codons are triplets - using T4, insertion and deletion mutagens

A
  1. One round of mutagenesis with T4 - isolated phage that can’t grow in K strain
  2. Grew a mutagen in strain B - generated a new mutant and tested with K strain
  3. Some mutants now grow in K strain
  4. Used physical mapping to see what happened
    Results: one insertion can be corrected with a deletion elsewhere.
    Affects amino acids between mutations but corrects displacement.
31
Q

Method used to determine which codon coded for which amino acid

A
  1. Lyse e.coli without destroying ribosomes
  2. Synthesis RNA and incubate them with ribosomal extracts
  3. Follow production of substance
  4. Determine what the triplet corresponds to
32
Q

6 key features of the genetic code

A 
Continuous 
Non-overlapping 
Degenerate 
Unambiguous 
Special codons (start and stop)
Universal
33
Q

What is the start codon

A

AUG/ATG

34
Q

What are the stop codons

A

UAG
UAA
UGA

35
Q

What is the important of the 5’ and 3’ untranslated regions

A

5’ UTR = after initiation codon, helps in binding the ribosome and initiating translation
3’ UTR = after termination codon, regulates activity and stability of mRNA

36
Q

Why does the wobble effect work

A

It doesn’t interfere with the protein complex as it only occurs in synonymous codons.
Provides versatility - some ribosomes don’t have tRNA for all synonym codons = more efficient

Genetics And Evolution (7 decks)

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