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3.1 Cellular Organization

A.Introduction Three main parts of a cell a.Plasma membrane – surrounds the cell, keeps it intact, and regulates passage into and out of the cell b.Nucleus – control center c.Cytoplasm – gelatinous, semi-fluid of water and suspended and dissolved substances

Introduction, cont 2.Organelles (little organs) are scattered throughout the cytoplasm and have various functions 3.The cytoskeleton maintains cell shape and allows the cell and its content to move

A typical animal cell

B.Plasma Membrane Separates the inside of the cell (cytoplasm) from the outside Fluid-mosaic model a.Phospholipid bilayer – hydrophilic heads point outward and hydrophobic tails point inward b.Attached peripheral and integral proteins serve as receptors, channels, and carriers c.Cholesterol molecules stabilize the membrane d.Glycoproteins and glycolipids attached to outer surface of some protein and lipid molecules, mark cells as belonging to a particular individual

Fluid-mosaic model of the plasma membrane

C.The Nucleus Stores genetic information Chromatin a.Contains DNA, protein, and some RNA b.Coils into rod-like structures called chromosomes before the cell divides c.Immersed in nucleoplasm Nucleoli a.Dark-staining bodies containing rRNA and protein b.Site where ribosomes are formed

The Nucleus, cont 4.Nuclear envelope separates nucleus from cytoplasm a.Lipid bilayer with many nuclear pores b.Outer layer is continuous with the endoplasmic reticulum

The Nucleus

D.Ribosomes Composed of two subunits containing protein and rRNA Can be found free within the cytoplasm, singly or in groups called polyribosomes; produce proteins that are used inside the cell Also found attached to the endoplasmic reticulum; produce proteins that may be secreted by the cell

E.Endomembrane System Nuclear envelope Endoplasmic reticulum (ER) a.Continuous with the outer membrane of the nuclear envelope, it is a system of membranous channels and saccules b.Rough ER 1)Has attached ribosomes 2)Processes proteins produced by attached ribosomes

Endomembrane system, cont c.Smooth ER 1)Has no attached ribosomes 2)Synthesizes phospholipids, detoxifies drugs, and has other functions depending on the type of cell

Endoplasmic Reticulum

Endomembrane System, cont 3.Golgi apparatus a.Stacks of curved saccules b.Processes, packages, and secretes various substances c.Receives protein and/or lipid-filled vesicles from ER d.Contains enzymes that modify proteins and lipids e.Vesicles leave the Golgi apparatus and move to other parts of the cell or to the plasma membrane for secretion f.Produces lysosomes

Endomembrane System Function

Endomembrane system, cont 4.Lysosomes a.Contain hydrolytic digestive enzymes; nick-names “suicide sacs” b.Autodigestion responsible for cell rejuvenation and development and removal of worn-out organelles c.Can fuse with vesicles of material brought into the cell for destruction d.Tay-Sach’s disease – metabolic disorder involving missing or inactive lysosomal enzymes in nerve cells

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F.Peroxisomes and Vacuoles Peroxisomes a.Enzyme-containing vesicles, similar to lysosomes b.Detoxify drugs, alcohol, and other toxins c.Large numbers found in liver and kidney d.Break down fatty acids from fats Vacuoles isolate substances captured inside the cell

G.Mitochondria Rod-shaped organelle bound by a double membrane Inner membrane folds into cristae to increase surface area Site of ATP production through cellular respiration – cell powerhouse

Mitochondrion Structure

H.The cytoskeleton Microtubules - help maintain the cell’s shape and anchors or assists the movement of organelles Intermediate filaments – involved in cell to cell junctions Actin filaments – involved in cell movement Assembly regulated by the centrosome

I.Centrioles Composed of microtubules with a pattern A pair of perpendicular centrioles are found near the nucleus of every cell In a area called the centrosome Involved in cell division by forming the mitotic spindle Form the basal body (anchor point) for each cilium or flagellum

Structure of basal bodies and flagella

J.Cilia and flagellum – Cilia are hair-like projections from the free surface of a cell; beat in unison to move material along the cell surface – Flagellum – a single whip-like extension for cell movement; sperm is the only human cell with a flagellum

Cilia and flagella

Structures in Human Cells