Lecture 2 - DNA (Genetic Material)

Question 1

Griffith experiment: What was the overview of the experiment and what was the knowledge produced by this experiment?

Answer 1

• Two types of bacteria: S-Virulent bacteria (killed mouse)-had protective capsule and R-strain bacteria (did not kill mouse) was killed my immune system.
• 4 parts:
  1. ) S-bacteria injected and killed the mouse
  2. ) R-bacteria injected and did not kill the mouse
  3. ) Heat-killed S-bacteria did not kill the mouse
  4. ) Heat-killed S-bacteria and R-bacteria KILLED the mouse
• Why? Theory of transformation-R-bacteria picked up DNA from S-bacteria resulting in transformation from R to S-virulent bacteria. R-bacteria now had the protective capsule.

Question 2

Avery, MacLeod, and McCarthy: What was the overview of the experiment and what was the conclusion?

Answer 2

Overview: Used heat killed S-bacteria and R-bacteria.
-5 Parts: Used specific enzymes to destroy certain molecules in heat-killed S-bacteria to see if transformation still occurred:
1.) RNA destroyes= transformation occurred
2.) Protein destroyed= transformation occurred
3.) Lipids destroyed= transformation occurred
4.) Carbs destroyed= transformation occurred
5.) DNA destroyed= NO transformation occurred!!
Conclusion: DNA is the hereditary factor that carries genetic information. 1st evidence

Question 3

Hershey and Chase: What is the overview of the experiment and overall conclusion?

Answer 3

Overview: Used two separate batches of T2 bacteriophage to see if DNA or protein was injected into the bacteria.

1. ) Used radioactive phosphorus to label the DNA in one batch of viruses and used radioactive Sulfur in the other viral batch.
2. ) Viruses infect E.Coli bacteria.
3. ) Heads are blended and sheared off the bacteria.
4. ) The centrifuge was implemented. (heavier objects end up at the bottom and light ones at the top)
5. ) Found the viral DNA in the infected E. Coli and bottom of test tube while the protein coat was supernatant.
   - Conclusion: DNA is the carrier of genetic information. Cemented Avery, MacLeod, and McCarthy experiment.

Question 4

Watson and Crick discovered what 6 aspects?

Answer 4

1. ) DNA is usually right-handed double helix. (Phosphate back-bone on the outside with nirtogenous bases on the inside.
2. ) Antiparrallel strands- one strand runs 5’ to 3’ and the other 3’ to 5’ (Opposite Polarity)
3. ) Nitrogenous bases are flat and perpendicular to the back-bone.
4. ) There are 10 N.B. per turn.
5. ) Complementary strands
   - A=T (2 H Bonds) and G=C (3 H Bonds)
6. ) Sequence on one stand dictates the sequence on the other strand.

Question 5

What were the three lines of evidence that directed the double helix model?

Answer 5

1. ) Levene: Discovered the chemical nature of DNA components= nucleotide building blocks.
2. ) Rosland Franklin: Used X-Ray deffraction to discover that DNA had a double helix shape.
3. ) Chargeoffs rule: discovered that Purines (A and G) = Pyrimidines (T and C) and that A=T and G=C.

Question 6

What is a nucleoside composed of?

Answer 6

A pentose sugar and a nitrogenous base.

Question 7

What is a nucleotide composed of?

Answer 7

A nucleoside + phosphate group.

Question 8

What are the two pentose sugars of nucleic acids and what is the main difference between them?

Answer 8

• Ribose in RNA and Deoxyribose in DNA.

- The main difference is that RNA has an OH group on its 2’ while DNA has an H group on its 2’.

Question 9

What are pyrimidines and purines? Structure?

Answer 9

1. ) Pyrimidines are Cytosine, Thymine, and Uracil.
   - Structure = a 6-sided ring
2. ) Purines are Adenine and Guanine.
   - Structure = a 6-sided ring + 5-sided ring.

Question 10

Are Nucleic Acids Macromolecules? If so, why?

Answer 10

Yes because they are composed of smaller nucleotide monomeric subunites that are covalently linked together.

Question 11

How are nucleotides bonded together?

Answer 11

Covalently bonded phosphodiester bonds. 5’ phosphate group bonds to 3’ OH.

Question 12

What is a minor groove and what is a major groove? And which groove do DNA binding proteins bind to?

Answer 12

Minor groove are the parts where sugar-phospate backbones are close together while major grooves are where the backbones are farther aparts. Proteins bind to the major groove.

Question 13

Denaturation vs. Renaturation of DNA double helix: What are they and how do you perform both?

Answer 13

Denaturation occurs when you heat DNA and the H-bonds between N.B. break. Renaturation is re-bonding the H-bonds of the single-stranded DNA back together by slowly-cooling the strands.

Question 14

What are the main differences of RNA from DNA? How does RNA form double-strands?

Answer 14

1. ) RNA has a hydroxyl group on its ribose sugars 2’ while DNA has an H on its 2’.
2. ) RNA contains Uracil while DNA contains Thymine.
   - RNA can have complementary sequences that overlap and pair with one another to create parts that have double strands.

Question 15

Chromosomes are made up of what two molecules?

Answer 15

DNA and protein are packaged together.

Question 16

How is Chromatin made?

Answer 16

Nucleosomes -> Nucleotides -> DNA -> wrapped round 8 histone proteins called nucleosomes -> H1 protein keep DNA attached to Histones called chromatosomes -> chromatosomes are wrapped and coiled together with Linker proteins to form Chromatin.

Question 17

What are the charges of DNA and Histone proteins?

Answer 17

DNA has a negative charge while Histones have a positive charge.

Question 18

How is gel electrophoresis used to separate DNA fragments?

Answer 18

Since DNA is negatively charged it is pulled from the - electrode to + electrode. The larger the DNA sequence, the more nucleotide base pairs present, the shorter the distance the DNA “bands” move. Smaller “bands” move the farthest.

Question 19

How is chromatin structured into chromosomes?

Answer 19

Chromatin after being made of nucleosomes is then folded into loops which start to create chromosomes.

Question 20

What is a covalent modification of histone tails? Effects?

Answer 20

• Alters to higher order chromatin structure.

- Can affect the way DNA is wrapped around them and thereby alter which genes are expressed or not.

Question 21

Difference between Heterochromatin and Euchromatin regions on chromosomes?

Answer 21

• Heterochromatin regions are more condensed DNA regions that are not very active in gene expression.
• Euchromatin regions are less condensed and are the genes here are active and expressed.