Lesson 13 of 13 · 13 min
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Must-know facts
20 facts
- 01Virchow (1855) added 'Omnis cellula-e cellula' to the Schleiden (1838) and Schwann (1839) cell theory.
- 02Leeuwenhoek was the first to see and describe a live cell; the nucleus was discovered by Robert Brown (1831).
- 03Smallest cells: Mycoplasmas. Largest isolated single cell: ostrich egg. Human RBC: about 7.0 μm in diameter; bacteria 3–5 μm.
- 04Mycoplasma is the one prokaryote without a cell wall.
- 05Bacterial envelope: glycocalyx (slime layer if loose, capsule if thick and tough), cell wall, plasma membrane.
- 06Mesosome functions: cell wall formation, DNA replication and distribution, respiration, secretion, more surface area and enzymes.
- 07Prokaryotic ribosomes are 70S (50S + 30S), and mitochondria and chloroplasts also carry 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S (60S + 40S).
- 08Human RBC membrane: about 52% protein, 40% lipid. Fluid mosaic model: Singer and Nicolson, 1972.
- 09Na⁺/K⁺ pump is active transport and uses ATP.
- 10Cell wall layers outward: secondary wall, primary wall, middle lamella (calcium pectate).
- 11Endomembrane system = ER + Golgi + lysosomes + vacuoles; mitochondria, chloroplasts and peroxisomes are excluded.
- 12SER makes lipids and, in animal cells, steroidal hormones; RER is continuous with the outer nuclear membrane.
- 13Golgi: discovered by Camillo Golgi (1898); cisternae 0.5–1.0 μm; cis = forming (convex) face, trans = maturing (concave) face; site of glycoprotein and glycolipid formation.
- 14Lysosomes are packaged by the Golgi and hold hydrolases (lipases, proteases, carbohydrases) that work best at acidic pH.
- 15Vacuole membrane is the tonoplast; the vacuole can fill up to 90% of a plant cell.
- 16Mitochondria: 0.2–1.0 μm wide (average 0.5 μm), 1.0–4.1 μm long; matrix has circular DNA, some RNA and 70S ribosomes; divide by fission.
- 17Leucoplasts: amyloplast = starch, elaioplast = oils and fats, aleuroplast = proteins.
- 18Chloroplasts: 5–10 μm long, 2–4 μm wide; one per cell in Chlamydomonas, 20–40 per mesophyll cell.
- 19Axoneme is 9+2 (doublets); centriole is nine peripheral triplets with a central hub and no central microtubules.
- 20Nucleolus is not membrane-bound and is the site of active rRNA synthesis; perinuclear space is 10–50 nm.
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Key terms
20 terms
- Prokaryotic cell
- A cell whose genetic material lies free in the cytoplasm with no nuclear envelope and which has no membrane-bound organelles.
- Plasmid
- A small circular DNA outside the bacterial chromosome that carries extra traits such as antibiotic resistance.
- Mesosome
- An inward fold of the bacterial plasma membrane that helps with wall formation, DNA handling, respiration and secretion.
- Glycocalyx
- The outermost layer of the bacterial envelope, called a slime layer when loose and a capsule when thick.
- Polysome
- A string of ribosomes translating the same mRNA at the same time.
- Inclusion bodies
- Membrane-free stores of reserve material in prokaryotic cytoplasm, such as glycogen or phosphate granules.
- Fluid mosaic model
- The Singer–Nicolson picture of the membrane as a quasi-fluid lipid bilayer with proteins that can drift sideways.
- Middle lamella
- The calcium pectate layer that cements adjacent plant cells together.
- Plasmodesmata
- Cytoplasmic channels passing through plant cell walls that connect neighbouring cells.
- Endomembrane system
- The functionally linked set of ER, Golgi apparatus, lysosomes and vacuoles.
- Cisternae
- The flat, stacked, disc-like sacs that make up the Golgi apparatus.
- Tonoplast
- The single membrane surrounding the plant vacuole.
- Cristae
- Folds of the inner mitochondrial membrane that increase its surface area.
- Grana
- Stacks of thylakoids inside the chloroplast, linked by stroma lamellae.
- Svedberg unit (S)
- The unit of sedimentation coefficient, an indirect measure of a particle's size and density.
- Axoneme
- The microtubule core of a cilium or flagellum, arranged in a 9+2 pattern.
- Basal body
- A centriole-like structure at the base of a cilium or flagellum from which it grows.
- Kinetochore
- A disc-shaped structure on either side of the centromere.
- Satellite
- A small chromosome segment set apart by a secondary constriction.
- Microbodies
- Small membrane-bound vesicles containing various enzymes, present in plant and animal cells.