A Tour of the Cell

Chapter 6

The Cell

Learning Objectives

• Describe principles that limit cell size • Describe fundamental differences between prokaryotic and eukaryotic cell types

• Ability to recognize models of eukaryotic cellular compartments and ascribe functions to each

• Describe essential similarities and difference between animal and plant cells

• Outline intracellular and extracellular protein structures and describe their functions.

2Chapter 6

The Cell 3Chapter 6

Cell Theory

A unifying concept in biologyOriginated from the work of biologists Schleiden and Schwann in 1838-9

States that:All organisms are composed of cells

­ German botanist Matthais Schleiden in 1838­ German zoologist Theodor Schwann in 1839

All cells come only from preexisting cells­ German physician Rudolph Virchow in 1850’s

Smallest unit of life

The Cell 4Chapter 6

Organisms and Cells

Pallisade cells Squamous epithelial and striated muscle

400X 400X

The Cell 5Chapter 6

Sizes of Living Things

In your notes:• Plant and animal cells have an average size of 50 um• Bacterial cells are roughly 10 smaller with an average size of 2-5

um• Virus particles are approx. 100 times smaller than bacterial and

have an average size of 20-50 nm

The Cell 6Chapter 6

Cell Size

Size restricted by Surface/Volume (S/V) ratioSurface is membrane, across which cell acquires nutrients and expels wastes

Volume is living cytoplasm, which demands nutrients and produces wastes

As cell grows, volume increases faster than surface

Cells specialized in absorption modified to greatly increase surface area per unit volumeIn your notes:­

• The cell membrane is like the lungs and intestines of a cell. Therefore the total surface area of the cell membrane must remain large with respect to the cell contents / volume.

• This will only happen if the cell remains small.

The Cell 7Chapter 6

Surface to Volume Ratio

TotalSurfaceArea6­cm2­­­­(X­4)­­ 24­cm2­­­­­(x­4) 96­cm2­

TotalVolume1cm3­­­­(­x­8) 8­cm3­­­(­x­8) 64­cm3­

SurfaceArea/Volume6 3­ 1.5

In your notes: • As the volume of a cube or sphere increases it s total exposed surface

area does not increase proportionally. • Therefore, as cells get larger less surface area is available for gas

exchange and nutrient and waste exchange• For this reason cells must remain small. (active cells are generally less

than 50 um in diameter)

Text:­p­99

The Cell 8Chapter 6

Know your metric measures!

1 m = 100 cm10-2 m = 1 cm = 10 mm (millimeters)10-3 m = 1 mm = 1000 um (micrometers)10-6 m = 1 um = 1000 nm (nanometers)10-9 m

The Cell 9Chapter 6

Microscopes:

Summary: “There are many different technologies applied to microscopy”

You will need to differentiate between: • Light microscopes• Two types of electron microscopes• A couple of others, such as Phase contrast, Imunoflourescence, video enhanced.

The Cell 10Chapter 6

Different techniques for viewing cells: 1. Compound Light Microscope

Light passed through specimen

Focused by glass lenses

Image formed on human retina

Max magnification about 1000X

Resolves objects separated by 0.2 mm, 1000X better than human eye

The Cell 11Chapter 6

Figure 4Aa

The Cell 12Chapter 6

Light Microscopy (1)

The Cell 13Chapter 6

Electron MicroscopyA. Transmission Electron Microscope

Abbreviated T.E.M.Electrons passed through specimenFocused by magnetic lensesImage formed on fluorescent screen

Similar to TV screen Image is then photographed

Max magnification 1,000,000s XResolves objects separated by 0.00002 mm,

100,000X better than human eye

The Cell 14Chapter 6

Figure 6.4 a

The Cell 15Chapter 6

TEM

The Cell 16Chapter 6

b. Scanning Electron Microscope

Abbreviated S.E.M.Specimen sprayed with thin coat of metal

Electron beam scanned across surface of specimen

Metal emits secondary electronsEmitted electrons focused by magnetic lensesImage formed on fluorescent screen

Similar to TV screen Image is then photographed

The Cell 17Chapter 6

S.E.M.Figure 6.4 b

The Cell 18Chapter 6

S.E.M.

The Cell 19Chapter 6

S.E.M.

The Cell 20Chapter 6Two classes of cells. 1. Prokaryotic cells

Lack a membrane-bound nucleusStructurally simpleTwo of lifes Domains are prokaryotes.

A. Bacteria Three Shapes

Bacillus (rod)Coccus (spherical)Spirilla (spiral)

B. Archaea (“Ancient Bacteria) Live in extreme habitats (High temp., High salt, toxic gas)

The Cell 21Chapter 6

Shapes of Bacterial Cells

In your notes: Bacteria have three general shapes1. Cocci = round. 2. Bacilli = rod shaped. 3. Spirochete = spiral shaped.

The Cell 22Chapter 6

Prokaryotic Cells: Visual SummaryParticles,­not­organelles,Very­similar­to­eukaryoticBut­smaller

Fig. 6.5 p97

The Cell 23Chapter 6Prokaryotic Cells:The Envelope

Cell Envelopes (some have a cell envelope!) Glycocalyx

­ Layer of polysaccharides outside cell wall­ May be slimy and easily removed, or­ Well organized and resistant to removal (capsule)

Cell wall – peptidoyglycans (recall = struct. Carb.) Plasma membrane (all have plasma membrane)

­ Like in eukaryotes­ Form internal pouches (mesosomes)

The Cell 24Chapter 6

CytoplasmSemifluid solution within the cell No organelles – only small granules of stored nutrients called inclusion bodies

AppendagesFlagella – Provide motilityFimbriae – small, bristle-like fibers that sprout from the cell surface

Sex pili – rigid tubular structures used to pass DNA from cell to cell

Prokaryotic Cells:Cytoplasm & Appendages

The Cell 25Chapter 6

2. Eukaryotic Cells

Domain EukaryaProtistsFungiPlantsAnimals

Cells are subdivided into specialized compartments

- All other life forms on earth are eukaryotes

The Cell 26Chapter 6Eukaryotic Cells :Organelles

Compartmentalization: Isolates reactions from eachother…..therefore…. Increased efficiency and specialization of reactions Allows eukaryotic cells to be larger than prokaryotic cells Two classes of eukaryotic compartments: 1.Endomembrane system:

Organelles that communicate with one anothervia membrane channelsVia small vesicles: includes Golgi, Endoplasmic reticulum,

Nucleus, lysosomes, transport vessicles2. Energy related organelles

Mitochondria & chloroplastsHave their own DNA and ribosomes

The important advancement of eukaryotes: ** copy to your notes!

The Cell 27Chapter 6

The membrane system of cells consists of a phospholipid bilayer

Fig. 6.6 p98

The Cell 28Chapter 6

Label Diagram!

Integral transmembrane protein

Peripheral (surface) protein

Phospholipid (f)

(e)

(g) (i)

The Cell 29Chapter 6

Origin of Eukaryotic Cells

MesosomesSurround geneticmaterial

In your notes:The endosymbiont hypothesis for the origin of eukaryotes.A prokaryote predecessor is thought to have given rise to eukaryotes via incorporation of other advantageous prokaryotes. Defn:Symbiosis = two or more organisms providing each other with some advantages.

(p. 517 Chap. 25)

The Cell 30Chapter 6

Experimental methods for isolating organelles and determining their functions. • Cell fractionation: the breaking apart of cellular

components• Differential centrifugation: Separation of cell

parts by size and density

Works like spin cycle of washerThe faster the machine spins, the smaller the

parts that settled out

The Cell 31Chapter 6

Animal Cell Anatomy

Notes: Animal cells have• Nuclei• Mitochondria• Golgi bodies• Lysosomes• Endoplasmic reticulum• Centrioles• Microtubules• ribosomes• Others

The Cell 32Chapter 6

Cell division, separation of chromosomes

Cellular protection – digestion of macromolecules from invasive organisms

Lipid synthesis

Processes packages and Secretes cell products

Protein synthesis

Cellular­respirationProduces­ATP

-­enzymes:­alcohol­deydrogenase

The Cell 33Chapter 6

Plant Cell Anatomy

Notes.Plant cells:(in addition to animal cell compartments have)• Large central vacuole• Chloroplasts• Cell walls (cellulose)• Does not have centrioles

Cell Structure and Function

The Cell 34Chapter 6

FunctionsA. Nucleus

The genetic command center of cell, usually near center

Separated from cytoplasm by nuclear envelopeConsists of double layer of membraneNuclear pores permit exchange between nucleoplasm & cytoplasm

Contains:Chromatin = semi fluid form of DNAChromosomes. Before cells divide, DNA must condense in to chromosomes Nucleolus: production center for rRNA

­ Produces subunits of ribosomes.

The Cell 35Chapter 6

Anatomy of the Nucleus

Fig. 6.9p103

The Cell 36Chapter 6

B. Ribosomes

Serve in protein synthesisComposed of rRNA

Consists of a large subunit and a small subunit

Subunits made in nucleolusMay be located:

On the endoplasmic reticulum (thereby making it “rough”), or

Free in the cytoplasm, either singly or in groups called polyribosomes

The Cell 37Chapter 6

Anatomy of a Ribosome

The Cell 38Chapter 6

C. Endomembrane System

(Improves efficiency of eukaryotic cells by isolating mechanisms and reactions to specialized compartments)

Consists of:a. Endoplasmic reticulum (both smooth and rough)

b. Golgi apparatusc. Vesicles

­ Several types­ Transport materials between organelles of system

The Cell 39Chapter 6

a. The Endoplasmic Reticulum

i. Rough ERStudded with ribosomes on cytoplasmic sideProtein anabolism (building proteins)

­ Synthesizes proteins­ Modifies proteins

Adds sugar to proteinResults in glycoproteins

ii. Smooth ERNo ribosomesSynthesis of lipids (triglycerides, steroids, phospholipids)

-modifications occur In golgi apparatus

The Cell 40Chapter 6

Endoplasmic Reticulum

LipidsIn smooth ER

ProteinsIn rough ER

To golgi apparatus

Fig. 6.11 p105

The Cell 41Chapter 6

The Golgi Apparatusb. Golgi Apparatus

Consists of 3-20 flattened, curved sacculesResembles stack of hollow pancakesModifies proteins and lipids

­ Packages them in vesicles­ Receives vesicles from ER on cis face­ Prepares for “shipment” in vesicles from trans faceWithin cellExport from cell (secretion, exocytosis)

Note: Learn to recognize in a cellular cartoon. Remember its function: Packages and modifies proteins and fats for shipment elsewhere inside and outside of the cell.

The Cell 42Chapter 6

Golgi Apparatus

The golgi receives lipids and proteinsFrom the rough and smooth ER; theyAre modified in the Golgi and the shippedEither out of the cell or to other regionsOf the cell

Fig 6.12 p106

The Cell 43Chapter 6The Golgi also constructs Lysosomes

Lysosomes : vessicles containing hydrolytic enzymes that can digestcellular debris (damaged organelles), incoming food particles, phagocytosed foreign cells and viruses.

The Cell 44Chapter 6

c. Lysosomes

Membrane-bound vesicles (not in plants)Produced by the Golgi apparatusLow pHContain lytic enzymes

­ Digestion of large molecules­ Recycling of cellular resources­ Apoptosis (programmed cell death, like tadpole losing tail)

Some genetic diseasesCaused by defect in lysosomal enzymeLysosomal storage diseases (Tay-Sachs)

Notes:

Remember the term “Hydrolysis” ?- lytic- lysis- lysosome……….all these terms have something to

do with enzymatically degrading or taking apart of organic molecules.

Old cells or unspecialized cells have to make way for newer or more specialized cell………getting rid of old cells involves a procecess called APOPTOSIS.

The Cell 45Chapter 6

Endomembrane System: A Visual Summary

Exocytosis: sends materialout (exits) of the cell.

Lysosome Fig 6.15p109

The Cell 46Chapter 6

Getting proteins into the ERSorting:

Fig 17.21 p.352

The Cell 47Chapter 6Plant Cells:A. Peroxisomes

Similar to lysosomesMembrane-bounded vesiclesEnclose enzymes

HoweverEnzymes synthesized by free ribosomes in cytoplasm (instead of ER)

Active in lipid metabolism (break down fats)

Catalyze reactions that produce hydrogen peroxide H2O2­ Toxic­ Broken down to water & O2 by catalase

The Cell 48Chapter 6

PeroxisomesBreaks down fats, oils and proteinsto hydrogen peroxide.More common in plants but also foundin some animal cells (liver).

• Forms a crytaline core structure ofoxidative enzymes• Is not formed from the endomembrane system (self-replic.)

The Cell 49Chapter 6Plants: B. Vacuoles

Membranous sacs that are larger than vesiclesStore materials that occur in excessOthers very specialized (contractile vacuole)

Plants cells typically have a central vacuoleUp to 90% volume of some cellsFunctions in:

­ Storage of water, nutrients, pigments, and waste products

­ Development of turgor pressure (ie: plants can be turgid or

flacid)

­ Some functions performed by lysosomes in other eukaryotes

The Cell 50Chapter 6

Vacuoles

Fig. 6.14, p. 108

The Cell 51Chapter 6Energy-Related Organelles:1. Chloroplasts

Captures light energy to drive cellular machinery

Photosynthesis

Synthesizes carbohydrates from CO2 & H2O

Makes own food using CO2 as only carbon source Autotrophic

The Cell 52Chapter 6

Chloroplast Structure

Bounded by double membraneInner membrane infolded

Forms disc-like thylakoids, which are stacked to form grana

Suspended in semi-fluid stromaGreen due to chlorophyll

Green photosynthetic pigmentFound ONLY in inner membranes of chloroplast

The Cell 53Chapter 6Energy-Related Organelles:Chloroplast Structure

?

Fig. 6.18 p111

The Cell 54Chapter 6Energy-Related Organelles:2. Mitochondria

Bounded by double membrane

Cristae – Infoldings of inner membrane that encloses matrix

Matrix – Inner semifluid containing respiratory enzymes

Involved in cellular respiration

Produce most of ATP utilized by the cell

The Cell 55Chapter 6Energy-Related Organelles:Mitochondrial Structure

Fig. 6.17p111

The Cell 56Chapter 6

The Cytoskeleton

Maintains cell shapeAssists in movement of cell and

organellesThree types of macromolecular fibers

1. Actin Filaments (small)2. Intermediate Filaments (medium)3. Microtubules (bigger)

Assemble and disassemble as needed

The Cell 57Chapter 6The Cytoskeleton:Actin Filament Operation

Function­in­cellular­movement­throughflow­and­movement­of­the­plasma­membrane.

The Cell 58Chapter 6

Intermediate filamentsBigger – hold shape of organelles – used in cell attachment to other cells.

• ­Myosin• Dynein• Kinesin

The Cell 59Chapter 6The Cytoskeleton:Microtubule Operation

Alpha and Beta tubulin pairs form hollow cylinders

Can form, unform and reform again. In this way they movechromosomes into the correct positions for cell division. Also form major structural component of flagella

The Cell 60Chapter 6

Moving chromosomes: Mitotic Spindle

metaphase

anaphase

telophase

The Cell 61Chapter 6Microtubular arrays:Cilia and Flagella

Microtubules can form into specialized structures called:- Cilia- Flagella- Both have a unique 9 + 2 pattern.

The Cell 62Chapter 6

Structure of a Flagellum9 & 2

The Cell 63Chapter 6

Review

Cell TheoryCell Size What restricts cell size?

Prokaryotic CellsEukaryotic Cells

Organelles Know the structure and functions of the following:

­ Nucleus­ Endomembrane System­ Cytoskeleton­ Centrioles, Cilia, and Flagella

How are these cells different?

A Tour of the Cell

Chapter 6

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