Molecular genetics

Question 1

What structural aspect of DNA helps allow you to see it

Answer 1

It’s lined up and compacted

Question 2

What did the transforming principle investigate

Answer 2

Wether proteins or DNA holds the genetic information

Question 3

Roughly, what was the transforming principle experiment

Answer 3

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

Question 4

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

Answer 4

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

Question 5

How did Hershey and chase determine where genetic material lies

Answer 5

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

Question 6

What was X-ray crystallography used for

Answer 6

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

Question 7

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

Answer 7

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

Question 8

How does X-ray crystallography work

Answer 8

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.

Question 9

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

Answer 9

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

Question 10

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

Answer 10

A + G = purine

C + T + U = pyramidine

Question 11

What components make up a DNA strand

Answer 11

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

Question 12

Elements of the double helix

Answer 12

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

Question 13

How did Meselson conduct the semi-conservative experiment

Answer 13

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.

Question 14

Features of DNA replication

Answer 14

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

Question 15

Where on the DNA is replication initiated

Answer 15

At the origin

Question 16

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

Answer 16

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

Question 17

Name 4 essential enzymatic activities in DNA replication

Answer 17

DNA polymerase.
DNA primases.
DNA helicase.
Topoisomerases.

Question 18

What occurs at the end of the DNA strand

Answer 18

DNA polymerase encounters RNA primer

DNA polymerase and ligaments finish the job

Question 19

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

Answer 19

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

Question 20

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

Answer 20

Proof-reading enzymes

Question 21

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

Answer 21

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

Question 22

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

Answer 22

DNA -> RNA -> Proteins

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

Question 23

Why was the central dogma only a speculative idea

Answer 23

• nobody knew what RNA or ribosomes did

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

Question 24

How did beadle and Tatum show that genes controlled biochemical reactions

Answer 24

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.

Question 25

What problems occurred when trying to figure out how codons worked

Answer 25

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.

Question 26

What is protein finger printing used for

Answer 26

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

Question 27

How did Ingram use protein fingerprinting

Answer 27

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

Question 28

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

Answer 28

That a DNA sequence determines protein sequence

Question 29

What experiment was performed to determine that codons are triplets

Answer 29

Used T4 phage and insertion and deletion mutagens

Question 30

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

Answer 30

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.

Question 31

Method used to determine which codon coded for which amino acid

Answer 31

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

Question 32

6 key features of the genetic code

Answer 32

``` Continuous Non-overlapping Degenerate Unambiguous Special codons (start and stop) Universal ```

Question 33

What is the start codon

Answer 33

AUG/ATG

Question 34

What are the stop codons

Answer 34

UAG UAA UGA

Question 35

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

Answer 35

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

Question 36

Why does the wobble effect work

Answer 36

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