Introduction and Revision of DNA. Flashcards
What did Frederick Griffith suggest in 1928? Which bacteria?
Frederick Griffith suggested that bacteria were capable of transferring genetic information through a process called transformation. Pneumococcus.
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?
Avery, McCarty, and McLeod. DNase. They checked RNase, DNase, Lipase, Protease, and Carbo-ase.
Hershey and Chase confirmed what in 1952? What did they use?
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.
What is the structure of DNA?
It is a linear, unbranched polymer.
What is a sugar, base and phosphate called?
Nucleotide.
What is a sugar and base called?
Nucleoside.
Name the three components of a nucleotide.
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 Which is where the OH on carbon 2 has been replaced by a H.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.
How is the base of a DNA molecule attached to the sugar.
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.
Cells can contain how many phosphates? What is their names?
1, 2 or 3. Can be called nucleoside, nucleoside monophosphate, diphosphate or triphosphate.
Which nucleosides act as substrates for DNA synthesis?
Nucleoside Triphosphates.
What is the first names of the nucleotides that polymerise to make DNA. 2’ ……5’ triphosphate.
deoxyadenosine
deoxycytidine
deoxyguanosine
deoxythymidine
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.
Via phosphodiester bonds.
After condensation of the nucleotides what are free.
The new di-nucleotide has a free 5’ phosphate and a free 3’ OH.
Where does the polynucleotide grow?
From the point of the 3’ OH.
Which is the order that the polynucleotide extends.
5’ - A - T - G - 3’.
What are the two structural differences between DNA and RNA?
Sugar in RNA is ribose. OH
RNA contains uracil instead of thymine.
What are 4 the nucleotides of RNA? …. 5’ triphosphate.
adenosine, cytodine, guanosine and uridine.
What is the order of the RNA strand?
A, C, G, U
Two facts about the structure of RNA and its conformations/bonding.
Is usually single stranded and does not form helical structures. Globular conformations formed via intramolecular hydrogen bonding.
What are the two types of DNA double helixes that are right handed.
B and A.
What is the type of DNA double helix that is left handed?
Z.
What makes up the outside backbone of the helix?
sugar-phosphate.
What is the orientation of the double helix strands.
(top) 5’ to 3’ orientation. Intrinsic orientation between the two strands.
Who confirmed the orientation of the double helix strands? B- DNA
Watson and Crick.
How are the strands of the DNa double helix joined? What type of bonding?
They are joined non-covalently by hydrogen bonding.
What does Chargaff’s Rules State?
1:1 ratio. A to T 2 Hydrogen bonds. G to C 3 hydrogen bonds.
What are the 3 main characteristics of B-DNA?
10.5 bp per turn
well defined minor and major grooves
Bp lie flat on the helix axis and are perpendicular to it.
What are the 3 main characteristics of A-DNA?
Its helix is often formed from DNA and RNA hybrids.
Is right handed.
11bp per turn
Bp are tilted from the axis.
A-DNA is wider and more compressed than B-DNA.
What are the conditions for a A-DNA to be adapted?
Reduction in relative humidity. Certain purine stretches around the helix.
What are the conditions for a Z-DNA to come about?
Where there is alternating pyrimidine - purine nucleotides.
What are the 3 main characteristics of Z-DNA?
12 bp per turn.
Left handed
Narrower than B-DNA
Little difference between the minor and major grooves.
What are the 4 defining factors on the properties of nucleic acids?
Stability, Effect of an acid, Effect of an alkali and thermal denaturation.
State three facts about the stability of nucleic acids?
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.
What does the effect of a strong acid and an elevated temperature have on the properties of nucleic acids?
A strong acid and a temp of over 100C means that the nucleic acids with become completely hydrolysed.
What does the effect of a dilute acid have on the effects of nucleic acids?
The glycosidic bond between the purine and the sugar become apurinic sites (DNA damage)
What does the effect of an alkali have on DNA?
A Tautomeric shift affects the hydrogen bonding between the base pairs resulting in the double stranded structure breaking down and the DNA becoming denatured.
What does the effect of an alkali have on RNA?
RNA hydrolysis. (Chemical breakdown of a compound due to a reaction with water)
What is the term called when a DNA sample is heated and comes apart?
This is known as DNA denaturation or melting.
What is the melting temperature of DNA, Tm?
The temperature at which half the DNA strands are denatured is the melting temperature.
At what absorbance in a melting curve analysis is the amount of strand separation measured?
Solution at 260nm.
What is the term when the two strands separate?
A hyperchromic shift.
Abs rises 30-40%
The higher the G and C content the higher the?
Tm.
Name two other ways to denature DNA?
By using an organic solvent such as dimethyl sulphoxide formamide. Low salt. High pH.
What is the term of unification of two strands after denaturation?
Annealing. Renaturation.
Name three factors that affect renaturation efficiency and how they affect it.
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.
What is Hybridisation?
This involves putting two strands from different nucleic acids together. For efficient hybridisation, the strands for hybridising should be complementary or nearly complementary.
