a tour of the cell ch. 4 engineering 2 ms. haut. introduction to the world of the cell the...

A Tour of the Cell

Ch. 4Engineering 2

Ms. Haut

INTRODUCTION TO THE WORLD OF THE CELL

• The microscope was invented in the 17th century

• Using a microscope, Robert Hooke discovered cells in 1665

• All living things are made of cells (cell theory) http://www.edu365.com/aulanet/comsoc/

persones_tecniques/Robert_Hooke_archivos/Robert_Hooke.jpg

Principles of the Cell Theory

1. All living things are made of one or more cells

2. Cells are the basic unit of structure & function in organisms

3. Cells come only from the reproduction of existing cells

Microscopes provide windows to the world of the cell

• The light microscope enables us to see the overall shape and structure of a cell

Figure 4.1A

Image seen by viewer

Eyepiece

Ocularlens

Objective lensSpecimenCondenser lens

Light source

Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

Red blood cellsteaching.path.cam.ac.uk/partIB_pract/NHP1/

Electron microscopes

• Invented in the 1950s• They use a beam of

electrons instead of light

• The greater resolving power of electron microscopes – allows greater

magnification – reveals cellular details

websemserver.materials.ox.ac.uk/cybersem/getf...

Scanning electron microscope (SEM)

• Used to see detailed structure of cell surface

Figure 4.1B


Red blood cellshttp://commons.wikimedia.org/wiki/Image:SEM_blood_cells.jpg

http://upload.wikimedia.org/wikipedia/commons/8/82/SEM_blood_cells.jpg

Transmission electron microscope (TEM)

• Used to examine the internal structures of a cell

Figure 4.1CCopyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

Red blood cell in capillarycommons.wikimedia.org/wiki/Image:A_red_blood_...

http://upload.wikimedia.org/wikipedia/commons/2/2f/A_red_blood_cell_in_a_capillary%2C_pancreatic_tissue_-_TEM.jpg

• Cell size and shape relate to function

Figure 4.2


• At minimum, a cell must be large enough to house the parts it needs to survive and reproduce

• The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes

Natural laws limit cell size

• A small cell has a greater ratio of surface area to volume than a large cell of the same shape

30 µm 10 µm

Surface areaof one large cube= 5,400 µm2

Total surface areaof 27 small cubes= 16,200 µm2Figure 4.3


Categories of Cells

•Contains membranous organelles

•No membranous organelles

•DNA in a membrane bound nucleus

•DNA in nucleoid region (no nucleus)

•More complex structure•Simpler structure

•Larger size•Smaller size

EukaryoticProkaryotic

• Enclosed by a plasma membrane

• Usually encased in a rigid cell wall – The cell wall may be

covered by a sticky capsule

• Inside the cell are its DNA and other parts

Ribosomes

Figure 4.4

CapsuleCell wall

Plasmamembrane

Prokaryoticflagella

Nucleoid region(DNA)Pili


Prokaryotes

• All other life forms are made up of one or more eukaryotic cells

• These are larger and more complex than prokaryotic cells

• Eukaryotes are distinguished by the presence of a true nucleus

Eukaryotic cells are partitioned into functional compartments

• An animal cell

Plasma membrane

Figure 4.5A

Golgiapparatus

Ribosomes

NucleusSmooth endoplasmicreticulum

Roughendoplasmicreticulum

Mitochondrion

Not in most plant cells

Cytoskeleton

Flagellum

Lysosome

Centriole

Peroxisome

Microtubule

Intermediatefilament

Microfilament


The Plasma Membrane:A Fluid Mosaic of Lipids and Proteins

• The membranes of cells are composed of:

• Phospholipids• Proteins• Cholesterol

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

http://bio.winona.edu/berg/ILLUST/memb-mod.jpg

Plasma Membrane

• Phospholipids form a two-layered membrane, the phospholipid bilayer.

Figure 4.7a

Figure 4.7b

Plasma Membrane

• Most membranes have specific proteins embedded in the phospholipid bilayer.

• Proteins serve a number of functions• Transport channels• Enzymes

Plasma Membrane

• Cholesterol molecules help keep the membrane “fluid” at lower temperatures

http://www.uic.edu/classes/bios/bios100/lectf03am/cholesterol.jpg

http://sps.k12.ar.us/massengale/images/cell20membrane.jpg

Cholesterol

Fluid Mosaic Model

• Fluid part of model:• Membrane phospholipids and proteins can

drift about in the plane of the membrane.• Mosaic part of model:

• A diversity of molecules exists within the membrane

• Phospholipids• Different proteins• Cholesterol

Membranes• The plasma membrane

separates the living cell from its nonliving surroundings.

• The cytoplasm contains organelles

• Most organelles have membranes– These compartmentalize

the interior of the cell– This allows the cell to carry

out a variety of activities simultaneously

Plant Cells

• A plant cell has some structures that an animal cell lacks:– Chloroplasts – A rigid cell wall– Central vacuole– Plasmodesmata

• The largest organelle is usually the nucleus• The nucleus is separated from the cytoplasm

by the nuclear envelope• The nucleus is the cellular control center

– It contains the DNA that directs the cell’s activities

The nucleus is the cell’s genetic control center

Nucleus

Figure 4.6

Chromatin

Nucleolus

Pore

NUCLEUS

Two membranesof nuclearenvelope

ROUGHENDOPLASMICRETICULUM

Ribosomes


Many cell organelles are related through the endomembrane system

• The endomembrane system is a collection of membranous organelles– Organelles

manufacture and distribute cell products

– Divides cell into compartments

Rough endoplasmic reticulum• The rough ER manufactures membranes• Ribosomes on its surface are sites where

proteins are made

1 2

3

4Transport vesiclebuds off

Ribosome

Sugarchain

Glycoprotein

Secretory(glyco-) proteininside transportvesicle

ROUGH ER

PolypeptideFigure 4.8


http://micro.magnet.fsu.edu/cells/endoplasmicreticulum/images/endoplasmicreticulumfigure1.jpg

Smooth endoplasmic reticulum has a variety of functions

• Smooth ER synthesizes lipids

• In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

SMOOTH ER

ROUGHER

Nuclearenvelope

Ribosomes

SMOOTH ER ROUGH ER

Figure 4.9


Golgi apparatus

• The Golgi apparatus consists of stacks of membranous sacs – These receive and modify ER products, then send

them on to other organelles or to the cell membrane

Figure 4.12

• A membrane-enclosed sac budded off the Golgi– It contains digestive

enzymes.– The enzymes break

down macromolecules

Lysosomes digest the cell’s food and wastes

LYSOSOME

Nucleus

Figure 4.11A

Lysosomal enzymes

• digest food• destroy bacteria• recycle damaged

organelles• function in embryonic

development in animals

http://sun.menloschool.org/~cweaver/cells/e/lysosomes/lysozome.jpg

Peroxisomes

• Specialized lysosome containing catalase

• Produces hydrogen peroxide (H2O2) as waste product

• Catalase breaks down toxic H2O2

H2O2 ---catalase---> H2O + O2

http://faculty.une.edu/com/abell/histo/peroxisome.jpg

• Plant cells contain a large central vacuole– The vacuole

has lysosomal and storage functions

Vacuoles function in the general maintenance of the cell

Centralvacuole

Nucleus

Figure 4.13A


Contractile Vacuole

• Protists may have contractile vacuoles– These pump out

excess water

Figure 4.13B

Nucleus

Contractilevacuoles

Copyright © 2003 Pearson Education, Inc. publishing Benjamin CummingsCollapsing contractile vacuole of Protozoawww.microscopy-uk.org.uk/.../vidjuna.html

• The various organelles of the endomembrane system are interconnected structurally and functionally

A review of the endomembrane system

Transport vesiclefrom ER

Rough ER

Transport vesiclefrom Golgi

Plasmamembrane

Vacuole

LysosomeGolgiapparatusNuclear

envelopeSmooth ER

Nucleus

Figure 4.14Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

ENERGY-CONVERTING ORGANELLES

• Chloroplasts• Mitochondria

Chloroplasts

• Chloroplasts are found in plants and some protists

• Chloroplasts convert solar energy to chemical energy in sugars

Figure 4.16

Mitochondria

• Mitochondria carry out cellular respiration– This process uses the chemical energy

in food to make ATP for cellular work

Figure 4.17

Endosymbiosis– Mitochondria and chloroplasts each contain their own

DNA separate from the nucleus.– Evidence for Endosymbiosis theory

• Mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.

http://faculty.ircc.edu/faculty/tfischer/images/endosymbiosis.jpg

• A network of protein fibers makes up the cytoskeleton

The cell’s internal skeleton helps organize its structure and activities

THE CYTOSKELETON AND RELATED STRUCTURES

Figure 4.17A


• Microfilaments of actin enable cells to change shape and move

• Intermediate filaments reinforce the cell and anchor certain organelles

• Microtubules – give the cell rigidity– provide anchors for organelles– act as tracks for organelle movement

3 Types of fibers make up the cytoskeleton

Figure 4.17B

MICROFILAMENT INTERMEDIATEFILAMENT

MICROTUBULE

Actin subunit Fibrous subunitsTubulinsubunit

7 nm 10 nm25 nm


Cilia and flagella move when microtubules bend

• Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells

• A cilia or flagellum is composed of a core of microtubules wrapped in an extension of the plasma membrane

www.cco.caltech.edu/~brokawc/Demo1/BeadExpt.html

http://fig.cox.miami.edu/~cmallery/150/cells/centriole.jpg

http://www.microscopy-uk.org.uk/mag/imgjan99/janvid2.gif

• Cells interact with their environments and each other through their surfaces

• Plant cells are supported by rigid cell walls made largely of cellulose– They connect by plasmodesmata, channels that

allow them to share water, food, and chemical messages

Cell surfaces protect, support, and join cells

EUKARYOTIC CELL SURFACES AND JUNCTIONS

Figure 4.19A

Vacuole

Layers of one plant cell wall

Walls of two adjacent plant cells

PLASMODESMATA

Cytoplasm

Plasma membrane


Animal cells are embedded in an extracellular matrix

• It is a sticky layer of glycoproteins

• It binds cells together in tissues

• It can also have protective and supportive functions

http://kentsimmons.uwinnipeg.ca/cm1504/Image122.gif

• Tight junctions can bind cells together into leakproof sheets

• Anchoring junctions link animal cells

• Communicating junctions allow substances to flow from cell to cell

TIGHTJUNCTION

ANCHORING JUNCTION

COMMUNICATINGJUNCTION

Plasma membranes ofadjacent cells

ExtracellularmatrixFigure 4.19B


Acknowledgements• Essential Biology with Physiology, 2nd ed., by Campbell, Reece, and

Simon, ©2007. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

• BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.

• Background image found at http://www.paxcam.com/imgs/library/2/thumbnails/slide_19.jpg

http://www.paxcam.com/imgs/library/2/thumbnails/slide_19.jpg

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