Lecture 17: DNA Discovery and Replication

Question 1

How can something be purified?

Answer 1

1. Separate a mixture into its components
2. Assay each component to see which has the desired property

Question 2

What is an assay?

Answer 2

-A way of measuring something
-Can measure a substance
-Or can measure a phenomenon such as memory

Question 3

Cis chromosome?

Answer 3

-Chromosome contains both dominant or both recessive alleles

Question 4

Trans chromosome?

Answer 4

-Chromosome contains one dominant and one recessive allele

Question 5

Semi-dominant trait?

Answer 5

Blending of two alleles that results in a third phenotype that is different from the parents(heterozygous is different)
ex. RR(white), rr(red), Rr(pink)

Question 6

Alleric Series

Answer 6

-More than two alleles per gene(R, r, r’)

Question 7

Multigenic/Polygenic

Answer 7

Multiple genes affect one phenotype

Question 8

Penetrance

Answer 8

Percentage of individuals of a given genotype that actually show the phenotype

Question 9

Expressivity

Answer 9

Degree to which a phenotype is expressed(mild symptoms vs severe)

Question 10

What three factors contribute to the continuous spectrum?

Answer 10

1. Alleric Series
2. Multigenic
3. Environmental effects(penetrance/exppresivity)

Question 11

How can DNA be purified?

Answer 11

1. Grind up fav organism
2. Extract the lipids and proteins of the organism with solvent
3. Precipitate with ethanol

Question 12

How was it determined that genetic material was actually genetic material?

Answer 12

It was thought that if you dip another organism in another organisms DNA that the organism should come out as the other organism

Question 13

For what organisms does dipping into DNA work?

Answer 13

1. Viruses
2. Bacteria

Question 14

What was Frederick Griffiths Experiment?

Answer 14

1. Injected S Strain bacteria into mice they would die.
2. Injected R strain bacteria into mice, they would live
3. Heated up the S strain bacteria and killed it and when he injected it into the mice they survived
4. Mixed dead S strain bacteria with living R strain bacteria the mice died

Question 15

What did Federico Griffith’s experiment prove?

Answer 15

-A chemical component of one cell is capable of genetically transforming another cell
- R strain bacteria inherited the S strains DNA

Question 16

How do phage infect bacteria?

Answer 16

-Phage bind to bacteria and inject them with their DNA
-The bacteria then replicates this DNA , producing phages that burst out of the bacteria and infect others

Question 17

What are phages made up of?

Answer 17

-Proteins
-DNA

Question 18

What was Hershey-chase experiment 1?

Answer 18

1. Labelled DNA of phages with radioactive phosphorus
2. Mixed the phages with the bacteria (allowed them to inject)
3. Left with a pellet full of radioactive phosphorus

Question 19

What did experiment 1 of hershey-chase conclude?

Answer 19

The DNA of phages was transferred into bacteria

Question 20

What was Hershey-chase experiment 2?

Answer 20

1. Labelled protein of phages with radioactive sulphur
   2.Mixed the phages with the bacteria
2. Radioactive sulphur/protein was on top of the bacteria (in the supernatant)

Question 21

What did experiment two of the Hershey-Chase experiment prove?

Answer 21

Phages protein does not enter bacteria

Question 22

What would have happened if Hershey-Chase labelled their phage with 14C?

Answer 22

Both the pellet and supernatant would be radioactive because proteins(amino acids) and DNA(deoxyribose) are made up of carbon

Question 23

Is there an equal amount of each nucleotide base in DNA?

Answer 23

No
- Varies amongst different organisms

Question 24

What is chargaff’s rule?

Answer 24

-The amount of nucleotide base A is equal to the amount of nucleotide base T
-The amount of nucleotide base C is equal to the amount of nucleotide base G

Question 25

How does crystallography work for DNA?

Answer 25

1. Shine light through purified DNA 2. The x-rays will deflect off of the atoms of the material 3. Deflection pattern is telling of the structure of the molecule your shining the light through

Question 26

What insight did crystallography give to the structure of DNA?(4)

Answer 26

1. DNA is made up of two strands 2. DNA is a double helix 3. There are phosphates on the outside 4. The strands run antiparallel

Question 27

What was Watson and Cricks structure for DNA?

Answer 27

- Phosphates negatively charged, hydrophilic want to interact with water -Nucleotide bases want to be in the middle as they are relatively hydrophobic -Chargaff’s rules: A pairs with T and G pairs with C -Proposed a correct structure!!

Question 28

What does it mean when we say DNA strands are reverse complements?

Answer 28

Reverse: Run anti-parallel to each other (read in opposite directions going 5’ to 3’) Complement: A on one strand corresponds to T on the other strand(same for G and C)

Question 29

What direction is DNA transcribed?

Answer 29

5' to 3'

Question 30

Why do G-C pair and A-T pair?

Answer 30

This combination forms the most H-bonds resulting in the most stable structure -Also the distance within the DNA double helix is constant since a purine( double ring) is always paired with a pyrimidine(single ring)

Question 31

How many H-bonds do G-C A-T A-C G-T

Answer 31

G-C: 3 H-Bonds A-T: 2 H-bonds A-C: 0 H-Bonds G-T: 1 H-Bond

Question 32

How many H-bonds does A-U form?

Answer 32

2 H-bonds principals are the same for when RNA creates a complementary strand

Question 33

Is DNA constrained to one sequence of letters?

Answer 33

NO

Question 34

What about DNA suggests that it is replicated?

Answer 34

The fact that the two strands encode for the same information in complementary form

Question 35

Three hypothesis for how DNA is replicated?

Answer 35

1. Semi-conservative replication 2.Conservative replication 3. Dispersive replication

Question 36

What is the semi-conservative hypothesis?

Answer 36

1. DNA double helix separates into two strands 2. Each strand is then replicated into a complementary new strand 3. Creates 2 double helix DNA each with one original strand and one new strand

Question 37

What is the conservative hypothesis?

Answer 37

1. You take the original DNA and use it to create two brand new strands 2. You then have 1 DNA molecule with both old strands and one with both new strands

Question 38

What is the dispersive hypothesis?

Answer 38

The DNA makes little pieces of new DNA and then recombines them. Now you have strands of DNA that are mixtures of old and new DNA.

Question 39

What experiment proved that DNA is replicated via semi-conservative replication?(Meselson and Stahl)

Answer 39

1. Scientists fed bacteria heavy nitrogen which was incorporated into their DNA 2. They spun the DNA in a centrifuge where heavy DNA would go to the bottom of the tube and light DNA would go to the top of the tube. 3. Heavy strand produced two strands intermediate in weight(one old, one new) 4. The intermediate strands then produced even lighter DNA (one old intermediate, one new)

Question 40

If replication were conservative, what would have been the result of the Meselson and Stahl experiment after two rounds of replication in light nitrogen?

Answer 40

-3/4 light, 1/4 heavy

Question 41

What did Friedrich Miescher do?

Answer 41

Figured out a way to isolate cell components

Question 42

What was the transforming principle from Frederick Griffiths muse experiemnt?

Answer 42

It was the substance from the S-strain that transformed the R-Strain(DNA)