Exercise 3: The Cell – Anatomy and Division

Nucleus
The control center of the cell and is necessary for cell reproduction; site of the “genes,” or genetic material-DNA.

Chromatin
Structures in the nucleus that carry the hereditary factors (genes).

Chromosomes
Barlike bodies of tightly coiled chromatin; visible during cell division.

Nucleoli
Dark-staining spherical bodies found within the nucleus where ribosomal subunits are assembled.

Nuclear Envelope
Double membrane barrier separated by a fluid-filled space.

Nuclear Pores
Permit large molecules like protein and RNA molecules to pass easily.

Plasma Membrane
Separates cell contents from the surrounding environment, has a double-layered lipid structure that the protein molecules (some with attached sugar groups) float in. Determines which substances may enter or leave the cell and in what quantity.

Microvilli
Minute fingerlike projections that greatly increase the surface area of the cell.

Cytosol
Fluid portion of cytoplasm.

Organelles (Literally, “small organs”)
Metabolic machinery of the cell, organized to carry out specific activities for the cell as a whole.

Inclusions
The cell cytoplasm contains various other substances and structures, including stored food (glycogen granules and lipid droplets), pigmet granules, crystals of various types, water vacuoles, and ingested foreign materials. Not part of the active metabolic machinery of the cell.

Ribosomes
Tiny spherical bodies (actually made up of two subunits) consisting of RNA and protein; actual sites of protein synthesis; seen floating free or attached to a membranous structure (the rough ER) in the cytoplasm.

Endoplasmic Reticulum (ER)
Membraneous system of tubules that extends throughout the cytoplasm; two varieties: (1) rough ER-studded with ribosomes (tubules of the rough ER provide an area for proteins made on the ribosomes to be transported to other cell areas; external face synthesizes phospholipids and cholesterol) and (2) smooth ER-a site of steroid and lipid synthesis, lipid metabolism, and drug detoxification (no protein synthesis-related function).

Golgi Apparatus
Stack of flattened sacs with swollen ends and associated small vesicles; found close to the nucleus; plays a role in packaging proteins or other substances that will be exported from the cell or incorporated into the plasma membrane and in packaging lysosomal enzymes.

Lysosomes
Various-sized membranous sacs containing digestive enzymes (acid hydrolyses); digest worn-out call organelles and foreign substances that enter the cell; if ruptured, they have the capacity to totally destroy the cell.

Peroxisomes
Small lysosome-like membranous sacs containing digestive enzymes that detoxify alcohol, hydrogen peroxide, and other harmful chemicals.

Mitochondria
Generally rod-shaped bodies with a double-membrane wall; inner membrane is thrown into folds, or cristae; contain enzymes that oxidize foodstuffs to produce cellular energy (ATP); often referred to as “powerhouses of the cell”.

Centrioles
Paired, cylindrical bodies lie at right angles to each other, close to the nucleus; direct the formation of the mitotic spindle during cell division.

Cytoskeletal Elements: Microtubules, Intermediate Filaments, and Microfilaments
Provide cellular support; function in intracellular transport; microtubules form the internal structure of the centrioles and help determine cell shape; intermediate filaments, which are stable elements made up of a variety of proteins, resist mechanical forces acting on cells; microfilaments (formed largely of actin, a contractile protein) are important in cell mobility ( particularly in muscle cells).

Mitosis
Nuclear division; the products are two daughter nuclei that are genetically identical to the mother nucleus. The function is to increase the number of cells for growth and repair.

Cytokinesis
Division of the cytoplasm, which begins after mitosis is nearly complete.

Interphase
Longer period when the DNA and centrioles duplicate and the cell grows and carries out its usual activities and cell division, when the cell reproduces itself by dividing.

Prophase
As cell division begins, the chromatin threads coil and shorten to form densely staining, short, bar like chromosomes.

Metaphase
The chromosomes align along the equator of the spindle.

Anaphase
The centromeres split, and the chromatids (now called chromosomes again) separate from one another and move slowly toward opposite ends of the cell with their “arms” dangling behind them. Complete when poleward movement ceases.

Telophase
The chromosomes uncoil and resume the chromatin form, the spindle breaks down and disappears, a nuclear envelope forms around each chromatin mass, and nucleoli appear in the daughter nuclei.

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