1.1 The Structure Of DNA

Question 1

DNA stands for…

Answer 1

deoxyribonucleic acid

Question 2

the basic sub-unit for any nucleic acid is the…

Answer 2

nucleotide

Question 3

label the 3 parts of a DNA nucelotide

Answer 3

• phosphate
• deoxyribose sugar
• base

Question 4

describe ‘DNA’

Answer 4

DNA is a double-stranded molecule. Its shape is described as a double helix because it is made up of two strands and has a twisted shape. The two strands are antiparallel to each other.

In each strand, there are strong covalent bonds between the deoxyribose sugar of one nucleotide and the phosphate of the next (this forms the backbone). There are also weak hydrogen bonds between complementary base pairs.

There are 4 bases: adenine, thymine, cytosine and guanine.

The base pairing rule is that adenine pairs with thymine and cytosine pairs with guanine.

The base sequence of DNA forms the genetic code.

Question 5

describe ‘ the organisation of DNA in prokaryotes’

Answer 5

e.g. bacterial cells

• have no nucleus
• contain single circular chromosomes in the cytoplasm
• can also contain smaller circular plasmids
• have no membrane-bound organelles

Question 6

describe ‘the organisation of DNA in eukaryotes’

Answer 6

e.g. animal cells, plant cells and yeast cells

• contain a nucleus
• contain linear chromosomes tightly coiled with associated proteins (histones)
• mitochondria and chloroplasts also contain DNA as circular chromosomes

! yeast cells are eukaryotic but contain plasmids !