Isfa: (1) Review Of Cells & Cell Organelles

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Organelle

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The component parts of a cell. May be surrounded by multiple or single membranes or no membrane at all.

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Plasma (cell) membrane

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Selective barrier that surrounds the cytoplasm and forms the boundary of the cell.

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Nucleus, nuclei

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Contain most of the cell's DNA, surrounded by nuclear envelope (pair of membranes).

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Nucleolus, nucleoli

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Dense aggregates of protein and nucleic acid. Site of the transcription of ribosomal DNA, the processing of rRNAs and the assembly of ribosomal subunits.

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Nucleolar Organizer DNA

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Site of rRNA production.

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Cytoskeleton

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Composed of proteinaceous fibrillar or tubular elements that provide the structural framework for the cell shape or for support. Also allows for the movement of cells and their components. Includes microtubules, intermediate filaments and microfilaments.

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Nucleosome

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The basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a histone protein core.

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Chromosomes

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Structures comprised of very dense folds of chromatin, such as that found during mitosis.

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Eukaryotic Cells

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Defined by their membrane-bound organelle that houses the cell's genome.

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Microfilament

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Smallest (5-7 nm); composed of a helical, double chain of actin. Found within microvilli and muscle tissue. Involved in motility of cytoplasmic components and membrane proteins.

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Polyribosomes, polysomes

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A collection of ribosomes simultaneously translating a single strand of mRNA.

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Rough Endoplasmic Reticulum (rER)

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Typical of cells producing proteins destined for secretion, a large number of ribosomes are associated with the surface.

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Golgi Apparatus

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The major site of carbohydrate synthesis and a sorting station for material within the apparatus. Further modifies proteins by glycosylation and it brings about the sorting and packaging of proteins in membrane-bound vesicles.

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Intermediate Filament

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Middle (8-12nm); composed of one of a number of subunits that varies depending on the cell. Presumed to be structural and to resist stress, providing considerable tensile strength.

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Microtubule

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Largest (24nm); constructed of repeating dimeric subunits of tubulin. Found in cilia and flagella. Movement mediated by kinesins and dyneins; form the mitotic spindle.

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Smooth Endoplasmic Reticulum (sER)

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Portion of ER unstudded by ribosomes; synthesis of steroid hormones, synthesizes lipid components of lipoproteins and phospholipids for assembly into the cell membranes. Also involved in glucose mobilization and storage.

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Mitochondria, mitochondrion

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Present in all cells except mature RBC. Transform chemical energy from metabolites into ATP. Surrounded by two membranes that form the intermembrane space and matrix.

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Chromatin

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The name generally given to the genetic material when it is not condensed to form chromosomes (as during mitosis).

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Lysosomes

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The major digestive organelles of the cell. Contain hydrolases; surrounded by single membrane that prevents hydrolytic enzymes from entering the cytoplasm.

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Pinocytosis

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"Drinking by cells," smallest scale of endocytosis. Brings the extracellular fluid into the cell.

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Phagocytosis

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Cell processes surround large solid materials like bacteria and fuse together to form a large vesicle called a phagosome which then fuses with a lysosome.

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Autophagy

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The process in which intracellular proteins are degraded
by lysosomes.

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Ribosomes

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Macromolecular complexes that carry out protein synthesis. Composed of a small and large subunit and made up of 50/50 rRNA and protein.

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Centriole

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Made up of microtubules and found at the poles of mitotic and meiotic spindles.

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Cell Junctions

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Consist of various types of connective tissue depending on the location and type of junction.

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Proteasomes

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Large multienzyme protease complexes that breakdown single proteins in the cytoplasm that are no longer needed by the cells.

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Peroxisomes

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Involved in the detoxification of substances and beta oxidation of long chain fatty acids. Produce hydrogen peroxide as a byproduct and are thus membrane-bound to sequester organelle contents.