Biology 8.3 DNA and Chromosomes

HideShow resource information
  • Created by: Anna
  • Created on: 11-04-13 15:14

Two types of cell:

  • prokaryotic (e.g. bacteria) - DNA molecules smaller, form a circle, not associated with protein molecules, do not have chromosomes.
  • eukaryotic cells - DNA molecules larger, form a line (linear), occur in association with proteins to form chromosomes.

Chromosome structure.

- Only visible as distinct structures when cell is dividing, widely dispersed throughout cell the rest of the time.

- Appear as two threads, joined at single point (centromere).

- Each thread = chromatid.

- DNA in chromosomes held in position by proteins, length of DNA coiled and folded:

  • DNA is a double helix.
  • Helix is wound around proteins to fix it in position.
  • DNA-protein complex coiled.
  • Coil is looped and further coiled, then packed into the chromosome.

Chromosome contains just a single molecule of DNA that is very long - lots of DNA condensed into single chromosome.

Single DNA molecule has lots of genes along its length, each gene occupies a specific position along the DNA molecule.

Number of chromosomes same for individuals of a species but different for…


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA, genetics and evolution resources »