AS-LEVEL AQA BIOLOGY NOTES 
TOPIC 2: structure of prokaryotic cells & viruses

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Eukaryotic cells are all cells which have a nucleus. All animal, plant, and fungi cells, for example, are eukaryotic. On the other hand, bacteria are prokaryotic: they have no definitive nucleus.

EUKARYOTIC	PROKARYOTIC
May have membranes within the cell which form part of encapsulated organelles, e.g. mitochondria and chloroplasts	Only one membrane: cell surface membrane
Plant cell wall made out of cellulose; fungal cell wall made out of chitin	Cell wall made out of peptidoglycan; also sometimes has a capsule surrounding the cell and might have flagellae
Ribosomes are 25-30nm in diameter	Ribosomes are 20nm in diameter
DNA stored as chromosomes within the nucleus	DNA is free in cytoplasm, in the form of a single loop called a ‘circular chromosome’ - as well as some smaller DNA loops called ‘plasmids’.
ATP production takes place in mitochondrial cristae (inner membrane folds).	ATP production takes place in the cell surface membrane
Cell diameter 10 –100 µm	Cell diameter 1 –10 µm
Strictly aerobic only	Sometimes capable of anaerobic respiration

Structure of a virus

• Acellular
  
• Non-living
  
• Contain genetic material (in the form of RNA)
  
• Capsid = protein coat that envelopes the RNA, similarly to the nuclear envelope
  
• Attachment proteins = glycoproteins project from membrane envelope