Introducing the Genetic Code (A-level Biology)
Introducing the Genetic Code
Anatomy of a Gene
DNA is Packaged into Chromosomes
DNA is very long and needs to be packaged in order to fit inside the nucleus:
- DNA wraps around histone proteins. Histones are DNA-binding proteins. Strands of DNA wrap around histones to form a structure called a nucleosome.
- A chain of nucleosomes is called chromatin. The nucleosomes combine in a chain, and the chain of nucleosomes is further compacted into a structure called chromatin.
- Chromatin is wound up to form a single chromosome. A single chromosome is made up of the entire length of the double-stranded DNA that was used to make it. Humans have 23 pairs of chromosomes, giving a total of 46 chromosomes in the nucleus of every somatic (body) cell.
Chromosome Structure in Eukaryotes and Prokaryotes
Despite sharing a common genetic code, eukaryotic and prokaryotic chromosome structures are very different. Unlike eukaryotes, prokaryotes do not have true chromosomes:
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