Bacteria are prokaryotic cells. They are much smaller and simpler than eukaryotic cells, typically about 0.5 to 5 µm long, and have no nucleus and no membrane-bound organelles.
• Cell wall: made of peptidoglycan (murein), a polymer of sugars cross-linked by short chains of amino acids. It gives shape and strength and stops the cell bursting by osmosis. It is not made of cellulose.
• Cell surface membrane: controls entry and exit of substances.
• Cytoplasm containing 70S ribosomes, smaller than the 80S ribosomes of eukaryotic cytoplasm.
• Circular DNA in a region called the nucleoid, not surrounded by a membrane and not associated with histones in the same way as eukaryotic DNA.
• Food stores, such as glycogen granules and lipid droplets.Structures found in some bacterial cells
• Plasmids: small extra loops of DNA, often carrying genes such as antibiotic resistance.
• Capsule (slime layer): a layer outside the wall that protects against drying out and against phagocytes.
• Flagella for movement and pili for attachment.Comparison with eukaryotic cells
Bacteria lack a nucleus, mitochondria, chloroplasts, ER, Golgi apparatus and lysosomes. Their DNA is circular rather than linear, their ribosomes are 70S rather than 80S, and their cell wall is peptidoglycan rather than cellulose (plants) or chitin (fungi). Reactions such as respiration happen in the cytoplasm and on the cell surface membrane.
• Cell wall: made of peptidoglycan (murein), a polymer of sugars cross-linked by short chains of amino acids. It gives shape and strength and stops the cell bursting by osmosis. It is not made of cellulose.
• Cell surface membrane: controls entry and exit of substances.
• Cytoplasm containing 70S ribosomes, smaller than the 80S ribosomes of eukaryotic cytoplasm.
• Circular DNA in a region called the nucleoid, not surrounded by a membrane and not associated with histones in the same way as eukaryotic DNA.
• Food stores, such as glycogen granules and lipid droplets.Structures found in some bacterial cells
• Plasmids: small extra loops of DNA, often carrying genes such as antibiotic resistance.
• Capsule (slime layer): a layer outside the wall that protects against drying out and against phagocytes.
• Flagella for movement and pili for attachment.Comparison with eukaryotic cells
Bacteria lack a nucleus, mitochondria, chloroplasts, ER, Golgi apparatus and lysosomes. Their DNA is circular rather than linear, their ribosomes are 70S rather than 80S, and their cell wall is peptidoglycan rather than cellulose (plants) or chitin (fungi). Reactions such as respiration happen in the cytoplasm and on the cell surface membrane.