Ch04-Organisms are made of cellsocw.nctu.edu.tw/course/biology/modrenbiologyI_lecturenotes/ch04.pdf · Cell Communication —Plants ... Cell Communication — Distant Cells Signaling

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copyright 2004 --Brooks Cole -- ThomsonLearningCopyright 2005—Brooks/Cole—Thomson Learning 1

Tobin and Dusheck: Asking About Life, 3E Chapter 4

Chapter 4

Why Are AllOrganisms Made of

Cells?



Key Questions

What are cells?What are the advantages and

disadvantages of being amulticellular organism?

What organelles and other partsof cells make them work?

How do membranes act asboundaries and regulate thecontents of cells?

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The Cell Theory

Works of Schleiden, Schwannand Virchow

The Cell TheoryAll organisms are composed of 1

or more cellsCells are alive and are the basic

living unitAll cells come from other cells



Common characteristics ofprokaryotes and eukaryotes

Membrane separating interior (living)from exterior (non-living)

A thick semifluid material enclosed bythe membrane called protoplasmfluid + non-fluid contents within

protoplasm

Hereditary material in control center

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Prokaryotic and Eukaryotic CellsEukaryotic cells have a nucleus with a

nuclear membraneProkaryotic cells have no nuclear

membrane; considered more primitive



How bacterial, animal, andplant cells differ

Eukaryotic cells arecompartmentalized by organellarstructures; prokaryotes, however,are less complicated

Eukaryotic cells have cytoskeleton.Eukaryotic cells have slower rates of

growth and division than that ofbacteria.

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Cell Boundary, Cell Bodyand a Set of Genes

Plasma Membrane is the cell’sboundary

Nucleus — contains DNAOrganelles — tiny structures

with specific tasksCytosol — part of cytoplasm not

in organellesCytoskeleton — network of

protein fibers



How are cells alive?

Are organizedAre made of cellsPerform chemical reactionsObtain energyRespond to environmentChange over timeReproduceHave common evolutionary

history

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Cell maintains its internalenvironment

Cells must move substances acrossthe cell membrane, i.e. taking innutrients and getting rid of wastes,fast enough to meet their need forsurvival.



Can a Cell Be Any Size?

Surface-to-volume ratio

How do largecells (i.e.,eukaryotes)increasetheirtransportingefficiency?

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Most cells are microscopically small

Why are most cells small?As cells grow larger, volume

increases faster than surface areaLarge cells have difficulty to obtain

nutrients and get ride of wastes.Nuclei control activities of smaller

cells more easily.



Cellular Organization

Division of labor among specializedcells

Organisms outlive the cells thatcompose them — replacement ofcells

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Eukaryotic cells: An overview

All eukaryotic cells possess:Many internal organelles

(membranous or bacteria-derived)

Internal protein skeletalframework



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Nucleus

Chromosomes— DNA and protein

Nuclear envelope— double membrane

Nuclear pores— channels



Cytosol

Half of the volume of the cellAqueous plus proteinConsistency of Jell-OThousands of enzymesRibosomesGlycogenFat

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Endoplasmic Reticulum (ER)Single convoluted sheet of membraneMakes proteins and lipids

•Rough ER (studded with ribosomes)•Smooth ER (no ribosomes)



Endoplasmic Reticulum (ER)

Endoplasmic (means “within thecytoplasm”) reticulum (means “a little net”).

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Golgi Complex

Packaging center Traffic director Flattened disksSpherical vesiclesManages flow of proteins to

different destinations



Lysosomes

Present ineukaryoticcells

Small vesiclesenclosed by asinglemembrane

Amoeba —phagocytosis

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Lysosomes

Lysosomes contain many differentdigestive enzymes, proteases,glycosidases, lipases, and nucleases,which are only active under theacidic condition (pH 4.5~5.2).

Lysosome helps cell to renew itsaged (or old) parts and to protectcell from the invasion.



Responsible for the cell’s abilityto obtain energy

Make ATPDouble MembraneHave their own DNA

Mitochondria

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PlastidsOrganelles surrounded by double

membrane present in plant cellsChloroplastChromoplastsAmyloplasts



Cytoskeleton

Complex network of proteinfilamentsTypes of filaments:•Microtubules: hollow cylinders 9+2useful in cell division•Actin filaments: finer tubes,involved in shape changes•Intermediate filaments — fibrous,add strength

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Functions of Cytoskeleton

Microfilaments and intermediatefilaments help to support and shape thecell.

Microtubule extends from the center ofthe cell the plasma membrane and actsmainly as the intracellular traffickingnetwork.



A Plasma Membrane

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Principle components ofmembrane

Principle components of membrane:phospholipids, cholesterol, andproteins

Phospholipids have both ahydrophilic head and hydrophobictail that interacts laterally withother phospholipids.



Plasma membrane is a double-layeredstructure containing phospholipids as major

components.

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Structure of Membrane

Fluid Mosaic Model Lipid bilayer with 2 sheets of

phospholipids arranged tail to tail Proteins are dispersed through the

membraneBoth protein and lipid molecules

move freely within membrane (fluidaspect)

Serves as a hydrophobic barrierSome proteins help transport

molecules



Membrane Permeability

Lipid bilayerallows only afew smalluncharged polarmolecules, suchas water (H2O)and ammonia(NH3), and somelipid solublesubstances,vitamines A, D,and E, to passthrough.

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Function of Membranes

Serve as boundaries that separatethe inside from the outside

Regulate contents of the enclosedspaces

Serve as a “workbench”forbiochemical reactions

Participate in energy conversions



Regulation

Membrane is selectively permeableGeneral rules:

Diffusion — movement of moleculesfrom an area of high concentration tolow concentration (concentrationgradient)

Osmosis — movement of wateracross any selectively permeablemembrane in response to aconcentration gradient

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Predicting Movements

Hypotonic — more water movesinto cell than out

Isotonic — water movements inand out are balanced

Hypertonic — more water movesout of the cell than in



Vacuoles

The word “vacuole”means “empty”.Vacuoles are most often found in plant

cells. It makes plant tissues very rigidand holds up the whole structure.

In fresh water protists, the vacuoles maytake up extra water that tends to flow intothe organism. Periodically, thesevacuoles expel their contents by fusingwith the plasma membrane.

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Turgor PressureOccurs in plant cellsCell wall encloses all plant cellsWhen cells take on water,pressure is applied against cellwall — turgor pressure



Passive and Active Transport

Passive transport occursspontaneously, resulting in equalconcentrations of a molecule on the 2sides of the membrane

Active transport moves moleculesagainst a concentration gradient andrequires energy

Facilitated Diffusion uses a protein toincrease rate of diffusion

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Membrane Interactions

Extracellular MatrixNetwork of carbohydrates and

proteinsOccurs in both plant and animals



Import and Export of Particles

Phagocytosis — cells engulf largeparticles, membrane extendsoutward

Endocytosis — cells take in tinyamounts by inward folding

Types: pinocytosis, receptormediated endocytosis

Exocytosis — reverse ofpinocytosis

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Cell Communication — Plants

Immediateneighbors

Plasmodesmata— narrowchannelsbetween plantcells; thinstrands ofcytoplasmstream through



Cell Communication — Animals

Gap Junctions —membranes ofanimal cells areclose together,rivet-like

AdheringJunctions —connect internalcell skeletons

Tight Junctions —membranes arefused

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Cell Communication —Distant Cells

Signaling moleculesReceptors — specialized proteins

that lie either on the surface of acell or within cells

Examples: hormones such asestrogen and testosterone



Key Concepts

Cells have a boundary, a bodyand a set of genes

Eukaryotic cells have a nucleusand other organelles enclosed bymembranes

Cytoskeleton serves as aninternal communication system

Cell membranes establish theboundaries of the cell

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Ch04-Organisms are made of cellsocw.nctu.edu.tw/course/biology/modrenbiologyI_lecturenotes/ch04.pdf · Cell Communication —Plants ... Cell Communication — Distant Cells Signaling