Nucleic Acids

Question 1

What is the main purpose of nucleic acid?

Answer 1

Informational macromolecule - primary sequence of polypeptides

Question 2

Explain central dogma theory?

Answer 2

DNA > mRNA > Proteins

Question 3

What is DNA?

Answer 3

Deoxyribonucleic acid - genetic material - stores info on its own replication & order in which AA go to form protein

Question 4

What is RNA?

Answer 4

Ribonucleic Acid - messenger RNA, transfer RNA, ribosomal RNA - needed to convert info. on DNA into protein sequence

Question 5

Difference between nucleotide & nucleoside?

Answer 5

Nucleotide - pentose sugar, nitrogenous base, phosphate(s)

Nucleoside - pentose sugar & nitrogenous base

Question 6

Sugars in nucleic acid?

Answer 6

RNA - ribose
DNA - deoxyribose

Question 7

What are purines?

Answer 7

2-ring shaped structures (6&5 C membered) - adenine & guanine

Question 7

What are pyrimidines?

Answer 7

Single 6 membered ring - cytosine, thymine, uracil

Question 8

Where are the sugar & base bonded to the pentose sugar?

Answer 8

Phosphate to C5
Nitrogenous base to C1

Question 9

Where is the dehydration in DNA?

Answer 9

C2

Question 10

Explain the bonding between nucleotides?

Answer 10

Phosphate group of 1 nucleotide binds to C3 of another nucleotide releasing water - phosphodiester bond

Question 11

What is a polynucleotide?

Answer 11

Multiple nucleotides bound together - linear - “strand” - backbone of phosphate & sugar - bases project from one side

Question 12

How many strands does RNA have?

Answer 12

1

Question 13

Explain DNA structure?

Answer 13

Double stranded -double helix configuration - 2 strands run antiparallel - held together by H bonds between purines & pyrimidines (A-T, G-C)

Question 14

What is B-form DNA?

Answer 14

Double helix - Watson, Crick, & Franklin - right handed helix - major & minor grooves visible, bases project inwards & are perpendicular to backbone - 10.5bp/turn, 3.4nm between bp, 2nm wide

Question 15

What is A-form DNA?

Answer 15

Occurs in reduced relative humidity & at purine stretches - right hand helix, 2.3nm wide, bp are tilted from axis, 11bp/turn - occurs in DNA/RNA hybrids

Question 16

What is Z-form DNA?

Answer 16

Altering purine-pyrimidne - left-handed helix - 12bp/turn, 1.8nm wide

Question 17

Explain DNA’s stability?

Answer 17

Very stable -stacking interactions between base pairs & hydrophobic bases held inwards

Question 18

What happens to DNA in acidic conditions?

Answer 18

Strong acid & high temp. = hydrolysed completely
Dilute acid - glyosidic bonds between purine & sugar broken resulting in apurinic sites

Question 19

What happens to DNA in alkali conditions?

Answer 19

Tautomeric shift(bases change to structures that aren’t complementary) - H bonds break - double helix lost (denaturation) - single strands

Question 20

What happens to RNA in alkali conditions?

Answer 20

Intramolecular H bonds broken & hydrolysis

Question 21

Explain thermal denaturation/melting?

Answer 21

2 strands of DNA separate (H bonds break) - hyperchromic shift (Increased absorbance @260nm [U.V. series] - purines especially adenine being exposed & less quenching - rises by 30-40%

Question 22

What is the melting temperature?

Answer 22

Temperature @ which 1/2 the strands of DNA are denatured - G-C content raises Tm due to more H bonds

Question 23

Other methods of denaturing DNA?

Answer 23

Organic solvents (dimethyl sulphoxide & formamide), high pH, low salt conc.

Question 24

What is Renaturation/Annealing?

Answer 24

Re-uniting of 2 strands of DNA - 25° below Tm, conc. DNA, time - probe(small pieces of DNA used to test for specific genes can be added at this time)

Question 25

What is hybridisation?

Answer 25

2 strands of different nucleic acid together - complementary/non-complementary DNA