Chapter Two: Overview of Cells

The role of cells

Obtain nutrients and other essential substances from the surrounding body fluids, use nutrients to make the molecules it needs to survive, dispose of it s wastes, maintain its shape and integrity, replicate itself

Organelles

Small structures in the cytoplasm that perform specific functions for the cell

Main parts of a human cell

Plasma membrane, cytoplasm, and nucleus

Plasma Membrane Structure

Membrane made of a double layer of lipids embedded with proteins; externally facing proteins and some lipids have attached sugar groups

Plasma Membrane Functions

Serves as an external cell barrier; acts in transport of substances into or out of the cell; externally facing proteins act as receptors and in cell-to-cell recognition

Cytoplasm Structure

Cellular region between the nuclear and plasma membranes; consists of fluid cytosol containing disolved solutes, inclusions, and organelles

Ribosome Structure

Dense particles consisting of two subunits, each composed of ribosomal RNA and protein; free or attached to rough ER

Ribosome Function

The site of protein synthesis

Rough endoplasmic reticulum (Rough ER) Structure

Membrane system of sacs and tubules externally studded with ribosomes

Rough ER Function

Makes proteins that are secreted from the cell; makes the cell’s membranes

Smooth Endoplasmic Reticulum (Smooth ER) Structure

Membranous system of sacs and tubules; free of ribosomes

Smooth ER Function

Site of lipid and steroid hormone synthesis, lipid metabolism, and drug detoxification

Golgi Apparatus Structure

A stack of smooth membrane sacs close to the nucleus

Golgi Apparatus Function

Packages, modifies, and segregates proteins for secretion from the cell, inclusion in lysosomes, and incorporation into the plasma membrane

Lysosomes Structure

Membranous sacs containing acid hydrolases

Lysosomes Function

Sites of intracellular digestion

Mitochondria Structure

Rodlike, double-membrane structures; inner membrane folded into projections called cristae

Mitochondria Function

Site of ATP synthesis; powerhouse of the cell

Peroxisomes Structure

Membranous sacs of oxidase enzymes

Perioxides Function

The enzymes detoxify a number of toxic substances; the most important enzyme, catalse, breaks down hydrogen peroxide

Microfilaments Structure

Fine filaments of the contractile protein actin

Microfilaments Function

Involved in muscle contraction and other types of intracellular movement; help form the cell’s cytoskeleton

Intermediate FIlaments Structure

Protein fibers; composistion varies

Intermediate Filaments Function

The stable cytoskeleton elements; resist tension forces acting on the cell

Microtubules Structure

Cylindrical structures made of tubulin proteins

Microtubules Function

Support the cell and give it shape; involved in intracellular and cellular movements; form centrioles

Centrioles Structure

Paired cylindrical bodies; each composed of nine triplets of microtubules

Centrioles Function

Organize a microtubule network during mitosis to form the spindle and asters; form the bases of cilia and flagella

Nucleus Structure

Surrounded by the nuclear envelope; contains fluid nucleoplasm, nucleoli, and chromatin

Nucleus Function

Control center of the cell; responsible for transmitting genetic information and providing the instructions for protein synthesis

Nuclear Envelope Structure

Double-membrane structures; pierced by the pores; continuous with the cytoplasmic ER

Nuclear Envelope Function

Separates the nucleoplasm from the cytoplasm and regulates passage of substances to and from the nucleus

Nucleoli Structure

Dense spherical (non-membrane-bounded) bodies

Nucleoli Function

Site of ribosome subunit manufacture

Chromatin Structure

Granular, threadlike material composed of DNA and histone proteins

Chromatin Function

DNA constitutes the genes