Prokaryotic cells

What are the key features of prokaryotic cells?

• Always unicellular.

• Smaller than eukaryotic cells (typically 0.1–5 µm).

• Do not contain membrane-bound organelles.

• DNA is not contained in a nucleus (found in the cytoplasm as a nucleoid).

What is the function of the plasma membrane in prokaryotic cells?

Controls the entry and exit of substances, regulating the internal environment (partially permeable).

What is the structure and role of the cell wall in prokaryotes?

• Made of peptidoglycan or murein

• Provides structural support and prevents osmotic lysis.

What is the nucleoid in prokaryotes?

Region of the cytoplasm containing the single, circular molecule of DNA (not surrounded by a membrane).

What are plasmids?

Small, circular loops of DNA separate from the main chromosome, often carrying genes for antibiotic resistance. Can be exchanged between cells via conjugation.

What is the role of ribosomes in prokaryotic cells?

• Site of protein synthesis (translation).

• Prokaryotes contain 70S ribosomes (smaller than the 80S ribosomes in eukaryotes).

What is the role of the flagellum in some prokaryotic cells?

• Provides motility by rotating.

• Not all prokaryotes have one.

What is the capsule (slime layer) in prokaryotes and its function?

• Protective outer layer made of polysaccharides.

• Helps prevent desiccation/drying out, protects against phagocytosis, and aids in adhering to surfaces.

Do prokaryotes have membrane-bound organelles?

no

How do prokaryotic cells divide?

By binary fission — DNA replication followed by cell elongation and splitting into two genetically identical cells.

What are the key differences between prokaryotic and eukaryotic cells?

• Size: Prokaryotic = small (0.1–5 µm), Eukaryotic = larger (10–100 µm).

• DNA: Prokaryotic = circular, free in cytoplasm; Eukaryotic = linear, inside nucleus.

• Ribosomes: Prokaryotic = 70S; Eukaryotic = 80S.

• Organelles: Prokaryotic = no membrane-bound organelles; Eukaryotic = many.

• Cell wall: Prokaryotic = peptidoglycan; Eukaryotic = cellulose (plants) or chitin (fungi).

• prokaryotic cells have one chromosome whereas eukaryotic have 46

• prokaryotic don’t have mitochondria

• prokaryotic have a slime capsule for protection whereas eukaryotic don’t

what are infoldings/ mesosomes?

Infoldings of the cell-surface membrane (sometimes called mesosomes in older sources) increase the membrane surface area — allowing more enzymes and respiratory proteins to be embedded, which enhances processes such as respiration.

What are pili in prokaryotes and what do they do?

• Structure: Small, thin, hair-like proteins found on the surface of bacteria (shorter and more numerous than flagella).

• Functions:

  • Attachment pili (fimbriae): Help bacteria stick to host cells, surfaces, or each other (important in infection and biofilms).

  • Sex pili: Longer pili that join two bacteria together so plasmids (small DNA loops) can be passed between them – this spreads traits like antibiotic resistance.

  • Motility pili (in some bacteria): Can pull the cell along a surface (“twitching movement”).