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 cells

2) 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 potential

to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce

Cell

Structure of Cells

All 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 layerof lipids

one layerof lipids

Figure 4.3Page 56

Membrane Proteins

Protein pump across

bilayer

Protein channel

across bilayer

Protein pump

Recognition protein

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 be moved 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

Electron Microscopy

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 Cytoskeleton Figure 4.10b

Page 61

Plant Cell Features

Cell wall Central vacuole Chloroplast

Plasma membrane Nucleus Ribosomes Endoplasmic

reticulum Golgi body Vesicles Mitochondria Cytoskeleton Figure 4.10a

Page 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 into daughter cells

Functions of Nucleus

Components of Nucleus

nuclear envelope

nucleoplasm

nucleolus

chromatin

Figure 4.11bPage 62

Nuclear Envelope

Two outer membranes (lipid bilayers) Innermost surface has DNA attachment sites

Nuclear pore bilayer facing cytoplasm Nuclear envelope

bilayer facing nucleoplasm

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 to

final destinations Material arrives and leaves in vesicles

budding vesicle

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 bacteria

that were engulfed but not digested

Plastids

Central Vacuole

Specialized Plant Organelles

Chloroplasts

Convert 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

intermediatefilament

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

onepolypeptidechain

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 4.25Page 73

Plant Cell Walls

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

tightjunctions

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

Cell Structure and FunctionEarly DiscoveriesDeveloping Cell TheoryCell TheoryCellStructure of CellsLipid BilayerMembrane ProteinsWhy Are Cells So Small?MicroscopesLimitations of Light MicroscopyElectron MicroscopyEukaryotic CellsAnimal Cell FeaturesPlant Cell FeaturesFunctions of NucleusComponents of NucleusNuclear EnvelopeCytomembrane SystemComponents of Cytomembrane SystemEndoplasmic ReticulumGolgi BodyVesiclesMitochondriaMitochondrial OriginsSpecialized Plant OrganellesChloroplastsOther PlastidsCytoskeletonCytoskeletal ElementsMicrotubulesMicrofilamentsIntermediate FilamentsMotor ProteinsFlagella and CiliaPlant Cell WallsPlant CuticleMatrixes between Animal CellsCell-to-Cell JunctionsAnimal Cell JunctionsProkaryotic CellsProkaryotic Structure