A Tour of the Cell

Every living organism is composed of one or more cells

A cell is the smallest unit having the properties of life

The continuity of life directly arises from the growth and division of single cells

Metabolic activity related to cell volume and surface area

Volume increases faster than surface area

The speed and amount of “stuff” (waste & nutrients) across a cell membrane is determined by the surface area

Larger cell volume needs more nutrients and produces more waste

Eventually the cell becomes big enough that the membrane can’t transport “stuff” fast enough

Prokaryotes“Before the nucleus”—

no nucleus or membrane-covered structures (organelles)

BacteriaVery smallSimplest cells

EukaryotesNucleus and other

complex organellesOrganelle—internal

membrane-bound compartment that serves specialized functions. “Little organs”

Nucleoid region DNA (single loop) Cell membrane Cell wall (in some) Capsule (in some) Cytoplasm Ribosomes Pili Flagellum

Most kinds of living organismsProtozoansAlgaeFungiPlantsAnimals

Organelles allow compartmentalizingDifferent areas of the cell can carry on

reactions without affecting the rest of the cell

Complex systems

NucleusControl centerNucleolus

Constructs ribosomesChromatin

All DNA in cell Organized into

chromosomes 6 Feet of DNA in one

nucleus!!!

Nucleus (cont.)Nuclear envelope/membrane

Regulates transport of molecules Receptors for signaling

Nuclear pores Allow communication with cytoplasm

Endoplasmic Reticulum (ER)Rough

Ribosomes attach Protein synthesis

Smooth No ribosomes Lipid synthesis Carbohydrate synthesis

RibosomesSynthesize proteinsOn rough ER

Golgi Body/ApparatusPackage and process proteins & lipids“Warehouse & finishing factory”Receives vesicles from ERProduces vesicles for finished products

Endomembrane system Interconnecting membrane systemNuclear membrane Rough ER Smooth ER

Golgi apparatus lysosomes/vacuoles plasma membrane

Vesicles—sacs containing enzymesLysosomes

Intracellular digestion Destroy bacteria in white blood cells Breaks down damaged organelles

Peroxisomes Break down fatty acids & proteins Detoxify alcohol & other toxic substances

Vacuoles—large vesicles for storing food & waterOnly some eukaryotes

MitochondriaForms ATP (energy) from

carbohydratesRequires oxygenSite of cellular respirationSimilar to bacteria: have

their own DNA & ribosomes May be artifact of ancient

symbiotic relationship between prokaryotes & eukaryotes

PlastidsChlorloplasts

Photosynthesis (energy from light)

Only in plant cellsAmyloplasts

Store starches Specialized chloroplast

Like mitochondria, may be artifact of ancient symbiotic relationship between prokaryotes & eukaryotes

Central VacuoleStorage (amino

acids, sugars, ions, wastes)

Centrioles—produce microfilaments during cell division.

Protein filaments between nucleus & plasma membrane

Internal shape & organization Can be permanent or temporary

Motor proteins move things within cells Flagella—long outer structures for

movementUsually only a few

Cilia—short outer structures for movementUsually many

Pseudopod“False foot”

Structures outside of the plasma membrane

Holds cells together in tissues Protects & supports plasma membrane Collagen

Glycoproteins Strong fibers

Plasma (cell) membraneRegulates movement of “stuff” in and out of

cellPhospholipid bilayer

Animal Cell JunctionsTight junctions

Tight seal, prevents leakage of fluids

Anchoring junctions Rivets Fasten cells together

Gap junctions Channels, pores Allow small molecules

to travel between neighboring cells

Cell-to-cell communication

Nutrient & waste transfer

Cell wallStrong, gives

permanent shape to cell

Bacteria, protists, fungi, plants

Not found in animals

Plasmodesmata Junctions

between plant cell walls

Circulation and communication between cells