Pages 62-75

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It is important to know the organelles within the cell and to understand the general functions of each

◦ Organelles > cell◦ Organs > system◦ Organ systems > human body

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Nucleus = control center; houses DNA Plasma Membrane = selective; boundary Ribosomes = site of protein synthesis Mitochondria = site of cellular respiration Endoplasmic Reticulum = transportation network

◦ Rough = finalizing protein synthesis - folding◦ Smooth = fat metabolism and detoxing

Golgi Bodies =protein packaging; become vesicles Vesicles = move products via endocytosis/exocytosis Lysosomes = garbage crew Peroxisomes = detoxification/neutralizers Cytoskeleton = structural organelle Centrioles =direct cell division via mitotic spindle

ChromatinNucleolus

Nuclear envelopeNucleus

Plasmamembrane

Roughendoplasmicreticulum

Ribosomes

Golgiapparatus

Secretion beingreleased from cellby exocytosisPeroxisome

Centrioles

Mitochondrion

Lysosome

Smoothendoplasmicreticulum

Plasma Membrane Junctions

◦ Cells are bound together in three ways:

1. Glycoproteins act as an adhesive or cellular glue

2. Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion

3. Special membrane junctions are formed, which vary structurally depending on their roles

1. 3 different junctions

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Glycoprotein Glycolipid

Cholesterol

Channel

Cytoplasm(watery environment)

Filaments ofcytoskeleton

Proteins

Extracellular fluid(watery environment)

Sugargroup

Polar headsof phospholipidmolecules

Bimolecularlipid layercontainingproteins

Nonpolar tailsof phospholipidmolecules

Microvilli

Connexon

Underlyingbasementmembrane

Extracellularspace betweencells

Gap(communicating) junction

Plasmamembranes ofadjacent cells

Desmosome(anchoring junction)

Tight(impermeable) junction

Tight junctions

◦ Impermeable junctions made up of the plasma membrane

◦ Bind cells together into leakproof sheets

◦ Prevent substances from passing through extracellular space between cells

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Desmosomes

◦ Anchoring junctions that prevent cells from being pulled as a result of mechanical stress

◦ Created by “buttonlike” thickenings of adjacent plasma membranes kind of like the rivets in the pockets of your jeans-

they keep the material together

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Gap junctions

◦ allow direct diffusion of ions and small molecules between adjacent cells

◦ Hollow cylinders of proteins (connexons) function like tunnels to send messages Molecules can travel directly from one cell to the

next through these channels

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Microvilli

Connexon

Underlyingbasementmembrane

Extracellularspace betweencells

Gap(communicating) junction

Plasmamembranes ofadjacent cells

Desmosome(anchoring junction)

Tight(impermeable) junction

Active Transport of bulk materials

Endocytosis:◦ Plasma membrane engulfs product from

extracellular space to bring into cell◦ Becomes travelling vesicle inside cell

Exocytosis:◦ Vesicle from inside the cell fuses with plasma

membrane to dump contents outside of cell

Extracellular fluid

2

3

1

PlasmamembraneSNARE(t-SNARE)

VesicleSNARE(v-SNARE)Moleculeto besecreted

Secretoryvesicle

Fusion pore formed

Fused SNAREs

The membrane-bound vesiclemigrates to the plasma membrane.

There, v-SNAREsbind with t-SNAREs,the vesicle andplasma membranefuse, and a poreopens up.

Vesicle contentsare released to thecell exterior.

Cytoplasm

(b) Electron micrograph of asecretory vesicle inexocytosis (190,000×)

(a) The process of exocytosis

PlasmamembraneLysosome

Pit

Ingestedsubstance

Detached vesicle

Vesicle

Extracellularfluid Cytosol

Release ofcontents tocytosol

Vesicle fusingwith lysosomefor digestion

Transport to plasmamembrane and exocytosisof vesicle contents

Membranes and receptors(if present) recycled to plasmamembrane

1

(a)

2

3

Cilia: whiplike extensions◦ Propels substances along passageways

Found in respiratory passageways, uterine tubes, kidneys, inner ear

Flagella: longer whiplike extensions◦ Propels the cell

The sperm is the only flagellated cell in the human

Microvilli: extensions of cell membrane◦ Increases cell surface area (often for absorption)

Found along entire small intestine; large numbers along the proximal convoluted tubule in the nephron

Blood vesselsserving the smallintestine

Musclelayers

Villi

Lumen

Circular folds(plicae circulares)

Absorptivecells

Lacteal

Bloodcapillaries

Lymphoidtissue

Intestinalcrypt

Muscularismucosae

(b)Villi

Venule

Lymphatic vessel

Submucosa

Villus

(c) Absorptivecells

Microvilli(brush border)

(a) Small intestine

Nucleus Flagellum

Sperm

(g) Cell of reproduction

Cells can vary in structure and function

Variations include:◦ Modified shape◦ More of a particular organelle◦ Modified organelles

Cells are classified based on their structure and function

This is known as Histology◦ the study of the structure of cells and their

formation into tissues and organs

An Histologist can identify abnormalities in tissues obtained from cultures/biopsies

Epithelial◦ Secrete and aborb

Connective◦ Hold structures together, store nutrients

Muscular◦ Movement

Nervous◦ communication

NucleusIntermediatefilaments

Epithelialcells

EPITHELIAL

Nuclei

Contractilefilaments

Skeletalmuscle cell

Smoothmuscle cells

MUSCULAR

Rough ER and Golgiapparatus No organelles

Nucleus

Fibroblasts

Erythrocytes

CONNECTIVE

Processes

Rough ER

Nucleus

NERVOUS

Nerve cell