HIGHER The structure of DNA

Question 1

Describe the structure of DNA

Answer 1

DNA is a double stranded helix made up of repeating units called nucleotides. Each nucleotide is composed of a phosphate, deoxyribose sugar and a base. There are four bases in DNA: (A) adenine, (T) thymine, (G) guanine and (C) cytosine. The backbone of each DNA strand is produced by strong sugar phosphate bonds.

Question 2

Describe the structure of a nucleotide

Answer 2

There is a base pairing (A-T and G-C) by hydrogen bonds between the two DNA strands. DNA is a double stranded antiparallel structure, with deoxyribose and phosphate at 3’ and 5’ ends of each strand respectively, forming a double helix. The base sequence of DNA forms the genetic code.

Question 3

Describe the structure of eukaryotes

Answer 3

Eukaryotes all have linear chromosomes, in the nucleus, which are tightly coiled and packaged with associated proteins called histones. Eukaryotes also contain circular chromosomes in their mitochondria and chloroplasts. Yeast is a special example of a eukaryote as it also has plasmids.

Question 4

Describe the structure of prokaryotes

Answer 4

Their DNA is found in the cytoplasm of the cell as a single circular chromosome and smaller circular plasmids.

Question 5

What cell type are animal, plant, yeast (fungus) and bacterium?

Answer 5

Animal - eukaryote
plant - eukaryote
Yeast (fungus) - eukaryote
bacterium - prokaryote