Introduction and Revision of DNA.

Question 1

What did Frederick Griffith suggest in 1928? Which bacteria?

Answer 1

Frederick Griffith suggested that bacteria were capable of transferring genetic information through a process called transformation. Pneumococcus.

Question 2

Name the three men which discovered that DNA was the material causing bacteria transformation. Which enzyme proved that it was DNA that caused the bacterial transformation?

Answer 2

Avery, McCarty, and McLeod. DNase. They checked RNase, DNase, Lipase, Protease, and Carbo-ase.

Question 3

Hershey and Chase confirmed what in 1952? What did they use?

Answer 3

They confirmed that DNA was genetic material using bacteriophage T2. One with a sulphur labeled protein coat, the other with a phosphorous labeled DNA core.

Question 4

What is the structure of DNA?

Answer 4

It is a linear, unbranched polymer.

Question 5

What is a sugar, base and phosphate called?

Answer 5

Nucleotide.

Question 6

What is a sugar and base called?

Answer 6

Nucleoside.

Question 7

Name the three components of a nucleotide.

Answer 7

1 - 2’ deoxyribose (sugar). Which is where the OH on carbon 2 has been replaced by a H.

2 - In DNA, the base is either Cytosine, thymine (single ring pyrimidines) or adenine, guanine (double ring purines).

3 - 1,2 or 3 phosphate units attached to the 5’carbon of the sugar. These are designated either alpha, beta or y.

Question 8

How is the base of a DNA molecule attached to the sugar.

Answer 8

The base in a pyrimidine(C and T) is attache to 1’ carbon of sugar by a beta-glycosidic bond to N no.1. Bonded to N no.9 of purine.

Question 9

Cells can contain how many phosphates? What is their names?

Answer 9

1, 2 or 3. Can be called nucleoside, nucleoside monophosphate, diphosphate or triphosphate.

Question 10

Which nucleosides act as substrates for DNA synthesis?

Answer 10

Nucleoside Triphosphates.

Question 11

What is the first names of the nucleotides that polymerise to make DNA. 2’ ……5’ triphosphate.

Answer 11

deoxyadenosine
deoxycytidine
deoxyguanosine
deoxythymidine

Question 12

How are polynucleotides nts linked together. Between the 3’ OH on the sugar (first nt) and the 5’ phosphate of the next nt in the chain.

Answer 12

Via phosphodiester bonds.

Question 13

After condensation of the nucleotides what are free.

Answer 13

The new di-nucleotide has a free 5’ phosphate and a free 3’ OH.

Question 14

Where does the polynucleotide grow?

Answer 14

From the point of the 3’ OH.

Question 15

Which is the order that the polynucleotide extends.

Answer 15

5’ - A - T - G - 3’.

Question 16

What are the two structural differences between DNA and RNA?

Answer 16

Sugar in RNA is ribose. OH

RNA contains uracil instead of thymine.

Question 17

What are 4 the nucleotides of RNA? …. 5’ triphosphate.

Answer 17

adenosine, cytodine, guanosine and uridine.

Question 18

What is the order of the RNA strand?

Answer 18

A, C, G, U

Question 19

Two facts about the structure of RNA and its conformations/bonding.

Answer 19

Is usually single stranded and does not form helical structures. Globular conformations formed via intramolecular hydrogen bonding.

Question 20

What are the two types of DNA double helixes that are right handed.

Answer 20

B and A.

Question 21

What is the type of DNA double helix that is left handed?

Answer 21

Z.

Question 22

What makes up the outside backbone of the helix?

Answer 22

sugar-phosphate.

Question 23

What is the orientation of the double helix strands.

Answer 23

(top) 5’ to 3’ orientation. Intrinsic orientation between the two strands.

Question 24

Who confirmed the orientation of the double helix strands? B- DNA

Answer 24

Watson and Crick.

Question 25

How are the strands of the DNa double helix joined? What type of bonding?

Answer 25

They are joined non-covalently by hydrogen bonding.

Question 26

What does Chargaff’s Rules State?

Answer 26

1:1 ratio. A to T 2 Hydrogen bonds. G to C 3 hydrogen bonds.

Question 27

What are the 3 main characteristics of B-DNA?

Answer 27

10.5 bp per turn
well defined minor and major grooves
Bp lie flat on the helix axis and are perpendicular to it.

Question 28

What are the 3 main characteristics of A-DNA?

Its helix is often formed from DNA and RNA hybrids.

Answer 28

Is right handed.
11bp per turn
Bp are tilted from the axis.
A-DNA is wider and more compressed than B-DNA.

Question 29

What are the conditions for a A-DNA to be adapted?

Answer 29

Reduction in relative humidity. Certain purine stretches around the helix.

Question 30

What are the conditions for a Z-DNA to come about?

Answer 30

Where there is alternating pyrimidine - purine nucleotides.

Question 31

What are the 3 main characteristics of Z-DNA?

Answer 31

12 bp per turn.
Left handed
Narrower than B-DNA
Little difference between the minor and major grooves.

Question 32

What are the 4 defining factors on the properties of nucleic acids?

Answer 32

Stability, Effect of an acid, Effect of an alkali and thermal denaturation.

Question 33

State three facts about the stability of nucleic acids?

Answer 33

DNA is more stable than RNA. This is due to the stacking interactions between the base pairs in the double helical structures and the hydrophobic nature of the bases.

Question 34

What does the effect of a strong acid and an elevated temperature have on the properties of nucleic acids?

Answer 34

A strong acid and a temp of over 100C means that the nucleic acids with become completely hydrolysed.

Question 35

What does the effect of a dilute acid have on the effects of nucleic acids?

Answer 35

The glycosidic bond between the purine and the sugar become apurinic sites (DNA damage)

Question 36

What does the effect of an alkali have on DNA?

Answer 36

A Tautomeric shift affects the hydrogen bonding between the base pairs resulting in the double stranded structure breaking down and the DNA becoming denatured.

Question 37

What does the effect of an alkali have on RNA?

Answer 37

RNA hydrolysis. (Chemical breakdown of a compound due to a reaction with water)

Question 38

What is the term called when a DNA sample is heated and comes apart?

Answer 38

This is known as DNA denaturation or melting.

Question 39

What is the melting temperature of DNA, Tm?

Answer 39

The temperature at which half the DNA strands are denatured is the melting temperature.

Question 40

At what absorbance in a melting curve analysis is the amount of strand separation measured?

Answer 40

Solution at 260nm.

Question 41

What is the term when the two strands separate?

Answer 41

A hyperchromic shift.

Abs rises 30-40%

Question 42

The higher the G and C content the higher the?

Answer 42

Tm.

Question 43

Name two other ways to denature DNA?

Answer 43

By using an organic solvent such as dimethyl sulphoxide formamide. Low salt. High pH.

Question 44

What is the term of unification of two strands after denaturation?

Answer 44

Annealing. Renaturation.

Question 45

Name three factors that affect renaturation efficiency and how they affect it.

Answer 45

1 - Temp: 25C below Tm.
2 - DNA concentration: higher the concentration the faster the annealing. (more to work with)
3- Time: the longer the time the more annealing.

Question 46

What is Hybridisation?

Answer 46

This involves putting two strands from different nucleic acids together. For efficient hybridisation, the strands for hybridising should be complementary or nearly complementary.