4.cell structure

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Cell Structure and Function

Chapter 4



� Mid 1600s - Robert Hooke observed

and described cells in cork

� Late 1600s - Antony van Leeuwenhoek

observed sperm, microorganisms

� 1820s - Robert Brown observed and

named nucleus in plant cells

Early Discoveries



Developing Cell Theory

� Matthias Schleiden

� Theodor Schwann

� Rudolf Virchow



Cell Theory

1) Every organism is composed of one or

more cells2) Cell is smallest unit having properties

of life

3) Continuity of life arises from growth

and division of single cells



� Smallest unit of life

� Can survive on its own or has potentialto do so

� Is highly organized for metabolism

� Senses and responds to environment

� Has potential to reproduce

Cell



Structure of CellsAll start out life with:

± Plasma membrane

± Region where DNA

is stored

± Cytoplasm

Two types:

± Prokaryotic

± Eukaryotic



� Main component of cell membranes

� Gives the membrane its fluid properties

� Two layers of phospholipids

Lipid Bilayer

one layer

of lipids

one layer

of lipids

Figure 4.3Page 56



Membrane Proteins

Proteinpump across

bilayer

Proteinchannel

across bilayer

Protein pump

Recognitionprotein

Receptor protein

extracellular environment

cytoplasm

lipid bilayer

Figure 4.4Page 57



Why Are Cells So Small?

� Surface-to-volume ratio

� The bigger a cell is, the less surface

area there is per unit volume

�Above a certain size, material cannot bemoved in or out of cell fast enough



� Create detailed images of something

that is otherwise too small to see� Light microscopes

± Simple or compound

� Electron microscopes

± Transmission EM or Scanning EM

Microscopes



Limitations of Light

Microscopy� Wavelengths of light are 400-750 nm

� If a structure is less than one-half of a

wavelength long, it will not be visible

� Light microscopes can resolve objects

down to about 200 nm in size



ElectronM

icroscopy� Uses streams of accelerated electrons

rather than light

� Electrons are focused by magnets

rather than glass lenses

� Can resolve structures down to 0.5 nm



Eukaryotic Cells� Have a nucleus and other

organelles

� Eukaryotic organisms

± Plants

± Animals

± Protistans

± Fungi



Animal Cell Features� Plasma membrane

� Nucleus

� Ribosomes

� Endoplasmic

reticulum

� Golgi body� Vesicles

� Mitochondria

� CytoskeletonFigure 4.10bPage 61



Plant Cell Features� Cell wall

� Central vacuole

� Chloroplast

� Plasma membrane

� Nucleus

� Ribosomes

� Endoplasmic

reticulum

� Golgi body� Vesicles

� Mitochondria

� CytoskeletonFigure 4.10aPage 61



� Keeps the DNA molecules of eukaryotic

cells separated from metabolic

machinery of cytoplasm

� Makes it easier to organize DNA and to

copy it before parent cells divide intodaughter cells

Functions of Nucleus



Components of Nucleus

nuclear envelope

nucleoplasm

nucleolus

chromatin

Figure 4.11b

Page 62



Nuclear Envelope� Two outer membranes (lipid bilayers)

� Innermost surface has DNA attachment sites

Nuclear pore bilayer facing cytoplasm Nuclear envelope

bilayer facingnucleoplasm

Figure 4.12bPage 63



� Group of related organelles in which

lipids are assembled and new

polypeptide chains are modified

� Products are sorted and shipped to

various destinations

Cytomembrane System



Components of

Cytomembrane System

Endoplasmic reticulum

Golgi bodies

Vesicles



Endoplasmic Reticulum� In animal cells, continuous with nuclear

membrane� Extends throughout cytoplasm

� Two regions - rough and smooth



Golgi Body

� Puts finishing touches on proteins and

lipids that arrive from ER

� Packages finished material for shipment tofinal destinations

� Material arrives and leaves in vesicles

buddingvesicle

Figure 4.15Page 65



Vesicles� Membranous sacs that

move through cytoplasm

� Lysosomes

� Peroxisomes



� ATP-producing powerhouses

� Membranes form two distinct

compartments

� ATP-making machinery embedded

in inner mitochondrial membrane

Mitochondria



Mitochondrial Origins

� Mitochondria resemble bacteria

± Have own DNA, ribosomes

± Divide on their own

� May have evolved from ancient bacteriathat were engulfed but not digested



� Plastids

� Central Vacuole

Specialized Plant Organelles



ChloroplastsConvert sunlight energy to ATP through

photosynthesis



Other Plastids� Chromoplasts

± No chlorophyll

± Abundance of carotenoids

± Color fruits and flowers red to yellow

� Amyloplasts

± No pigments

± Store starch



� Present in all eukaryotic cells

� Basis for cell shape and internal

organization

� Allows organelle movement within cells

and, in some cases, cell motility

Cytoskeleton



Cytoskeletal Elements

microtubule

microfilament

intermediate

filament



Microtubules

� Largest elements

� Composed of tubulin

� Arise from microtubule

organizing centers (MTOCs)

� Involved in shape, motility,

cell division

Figure 4.21Page 71

tubulinsubunit



Microfilaments

� Thinnest elements

� Composed of actin

� Take part in movement,

formation, and

maintenance of cell

shape

actinsubunit

Figure 4.21Page 71



Intermediate Filaments

� Only in animal

cells of certain

tissues

� Most stable

cytoskeletal

elements

� Six known groups

onepolypeptide

chain

Figure 4.21Page 71



Motor Proteins

� Kinesins and dyneins move along

microtubules

� Myosins move along microfilaments

kinesin

microtubule

Figure 4.24b, Page 72



Flagella and Cilia� Structures for

cell motility� 9 + 2 internal

structure

dynein

microtubule

Figure 4.25

Page 73



Plant CellW

alls

Primary cell wall

Secondary cell wall

(3 layers)



Plant Cuticle� Cell secretions and waxes accumulate

at plant cell surface

� Semitransparent

� Restricts water loss



Matrixes between Animal Cells

� Animal cells have no cell walls

� Some are surrounded by a matrix of cell secretions and other material



Cell-to-Cell Junctions

� Plants

± Plasmodesmata� Animals

± Tight junctions

± Adhering junctions

± Gap junctions

plasmodesma



Animal Cell Junctions

tight

junctions

adhering

junction

gapjunction



� Archaebacteria and Eubacteria

� DNA is not enclosed in nucleus

� Generally the smallest, simplest cells

� No organelles

Prokaryotic Cells



Prokaryotic Structure

DNA

pilus

flagellum

cytoplasm

with ribosomes

capsulecell

wall

plasma

membrane

4.cell structure

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