Key area 1: structure and organisation of DNA

Question 1

Name the molecules in a DNA nucleotide

Answer 1

Phosphate group, deoxyribose sugar and a nitrogenous base

Question 2

Name the type of bond on the back bone the DNA molecule

Answer 2

Nucleotides are linked by there deoxyribose sugars and phosphates to form a strand with a sugar-phosphate backbone

Question 3

Give the names of the 4 DNA bases

Answer 3

(A) adenine
(T) thymine
(G) guanine
(C) cytosine

Question 4

Describe the base pairing rule for DNA bases

Answer 4

Base are complementary to each other. The base adenine always pairs with thymine and guanine always pairs with cytosine.

Question 5

Describe the role of hydrogen bonds in the DNA structure

Answer 5

The chains of polynucleotides are joined together by the bases , by hydrogen bonds, to form a double helix

Question 6

State the name of the coiled structure adopted by DNA

Answer 6

Each DNA molecule is very long and has two strands coiled into the shape of a double helix

Question 7

Identify the positions of the 3’ and 5’ ends on a DNA strand

Answer 7

The double helix is describes as having two anti parallel chains of nucleotides because one side goes from 5’ to 3’ and the opposite side goes 3’ to 5’

Question 8

Prokaryote cells

Answer 8

Organisms lacking a nucleus. Usually have a single circulate double stranded chromosome And a plasmid. DNA us tightly packed with proteins to form a nucleoid

Question 9

Eukaryotes

Answer 9

Organisms with a nucleus containing several linear chromosomes. Also have small circular chromosomes within their mitochondria and within their chloroplasts.

Question 10

Similarities and differences between prokaryotes and eukaryotes

Answer 10

Prokaryote doesn’t have a nucleus while eukaryotes does. Eukaryotes have more than one chromosomes while prokaryote has one in the form of a plasmid. Eukaryotes are usually multicellular cells whereas prokaryotes are usually unicellular

Question 11

Describe the structure of a plasmid

Answer 11

Prokaryotes have a second chromosome which can carry extra non essential genes which is called a plasmid

Question 12

Mitochondrial DNA (mtDNA)

Answer 12

Circular double stranded DNA
Varies in size
Codes for transfer RNA (tRNA), ribosomal RNA and some proteins in the mitochondria

Question 13

Chloroplast DNA (cpDNA)

Answer 13

Circular double stranded DNA
Between 80000 and 600000 b in size. Chloroplasts can have multiple copies
Codes for rRNA, tRNA, proteins required for transcription, translation and photosynthesis

Question 14

DNA packaging in eukaryotes

Answer 14

Level 1: DNA is wrapped around his tone proteins forming nucleosomes. The piece of DNA between nucleosomes is known as linker DNA and is a constant length
Level 2: chain on nucleosomes folds into a thicker chromatid fibre
Level 3: folds again on a non-his tone protein scaffold to form looped fibres
Level 4: folded chromatid then fold further to produce a condensed chromosome