Nucleic acids 1- Nucleic Acids and Chromosomes

Question 1

How are nucleotides joined?

Answer 1

linear chains of nucleotides are joined by phosphodiester bonds

Question 2

What is a nucelotide?

Answer 2

consists of a nitrogenous base, a sugar and one or more phosphate groups

Question 3

What is a nuceloside?

Answer 3

nitrogenous base and a sugar (NO PHOSPHATE)

Question 4

Whats the different between purine and pyrimidines and which bases fall under each category?

Answer 4

Purines (big): Adenine (A) and Guanine (G)
Consists of TWO aromatic rings

Pyrimidines (Small): Cytosine (C) and Thymine (T)/ Uracil (U)- in RNA Consists of ONE aromatic ring

Question 5

How are nitrogenous bases linked to pentose sugars?

Answer 5

beta-Glycosidic linkage

Question 6

Describe the structure of DNA? (4)

Answer 6

 a long chain of deoxyribonucleotide units linked by
phosphodiester links.
 The 3’ C-OH group on a sugar of one nucleotide is linked to phosphate group, which in turn is joined to 5’-OH of an adjacent sugar.
 On each deoxyribose there is a base.
 The chain has two ends, the 5’ end and the 3’ end. It is not symmetrical

Question 7

Describe the primary structure of DNA?

Answer 7

The primary sequence is the linear sequence of the bases. By convention, the nucleotide sequence is specified in the 5‟ to 3‟ direction.
 The bases carry genetic information, the sugar and phosphates perform a structural role.

Question 8

Describe the secondary structure of DNA? (6)

Answer 8

A right-handed double helix. The two chains in the helix run in opposite directions; antiparallel
 There are 10 base pairs per helical turn
 The deoxyribose and phosphate groups run along the outside of the helix, with the negative charges outside.
 The bases point inwards and the flat planes are perpendicular to the helix.
 There is a MAJOR GROOVE and a minor groove.
5’ end has a free phosphate group, 3’ end has a free hydroxyl group
 The two strands are complementary in their sequence due to the specificity of base-pairing. A pairs T. G pairs C
 A and T form 2 Hydrogen bonds, C and G, which forms 3 hydrogen bonds

Question 9

What is the genome?

Answer 9

The entire DNA coding for an organism constitutes its genome

Question 10

What is a karyotype?

Answer 10

A karyotype is an organised profile of someone’s chromosomes.
 A diploid human cell has 46 chromosomes
o 22 pairs of ‘normal’ chromosomes (autosomes) and
o 2 sex chromosomes (X and Y)

Question 11

Describe the packaging of eukaroytic DNA?

Answer 11

DNA is tightly packed forming a complex with proteins - the complex is called CHROMATIN

During interphase the DNA is extended and not visible, during mitosis the DNA condenses to form chromosomes.

Question 12

What are the two different levels of packaging of DNA?

Answer 12

1. NUCLEOSOMES, DNA wrapped around histones with linker DNA between histones. Roughly 200bp of DNA per nucleosome.
2. 30nm FIBER - the nucleosomes are further packed to generate a more compact structure with around 40 fold condensing of DNA.

Question 13

Give a method of separating and annealing strands

Answer 13

Heat or Low Salt = Melting or Denaturing

Cool or High Salt = Re-anneal or Hybridise