Chapter 5a

Cell Structure and Function

• 1) Mid 1600s - Robert Hooke observed and

described cells in cork

• 2) Late 1600s - Antony van Leeuwenhoek

observed sperm, microorganisms

• 3) 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`

• 1) Smallest unit of life

– a) Can survive on its own or has potential

to do so

• 2) Is highly organized for metabolism

• 3) Senses and responds to environment

• 4) Has potential to reproduce`

Cell

Cell Features

• 1) Main component of cell membranes– a) Gives the

membrane its fluid properties

• 2) Two layers of phospholipids`

Lipid Bilayer

Lipid Bilayer

Fluid Mosaic Model

• 1) Membrane is a mosaic of– a) Phospholipids– b) Glycolipids– c) Sterols– d) Proteins

• 2) Most phospholipids and some

proteins can drift through membrane`

Membrane Proteins

• 1) Transport proteins

• 2) Receptor proteins

• 3) Recognition proteins

• 4) Adhesion proteins`

Why Are Cells So Small?

• 1) Surface-to-volume ratio

– a) The bigger a cell is, the less surface

area there is per unit volume

– b) Above a certain size, material cannot be

moved in or out of cell fast enough`

• 1) Create detailed images of something

that is otherwise too small to see

– a) Light microscopes

• 1. Simple or compound

– b) Electron microscopes

• 1. Transmission EM or Scanning EM`

Microscopes

Light Microscope

Limitations of Light Microscopy

• 1) Wavelengths of light are 400-750 nm

– a) If a structure is less than one-half of a wavelength long, it will not be visible

– b) Light microscopes can resolve objects down to about 200 nm in size`

Electron Microscopy

• 1) Uses streams of accelerated electrons rather than light

– a) Electrons are focused by magnets rather than glass lenses

– b) Can resolve structures down to 0.5 nm `

Electron Microscope

Eukaryotic Cells

• 1) Have a nucleus and other organelles

• 2) Eukaryotic organisms– a) Plants– b) Animals– c) Protistans– d) Fungi`

Animal Cell

Plant Cell

• 1) Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm

• 2) Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells`

Functions of Nucleus

Nuclear Envelope• 1) Two outer membranes (lipid bilayers)

– a) Innermost surface has DNA attachment sites

– b) Pores span bilayer `

Nuclear Envelope

Nucleolus

• 1) Dense mass of material in nucleus

• 2) May be one or more

• 3) Cluster of DNA and proteins– a) Materials from which ribosomal subunits

are built

• 4) Subunits must pass through nuclear pores to reach cytoplasm`

Chromatin

• 1) Cell’s collection of DNA and associated proteins– a) Chromosome is one DNA molecule and

its associated proteins

• 2) Appearance changes as cell divides`

• 1) Group of related organelles in which lipids are assembled and new polypeptide chains are modified

• 2) Products are sorted and shipped to various destinations`

Cytomembrane System

Components of Cytomembrane System

Endoplasmic reticulum

Golgi bodies

Vesicles`

Endoplasmic Reticulum

• 1) In animal cells, continuous with

nuclear membrane

• 2) Extends throughout cytoplasm

• 3) Two regions - rough and smooth`

Rough ER

• 1) Arranged into flattened sacs

• 2) Ribosomes on surface give it a rough appearance

• 3) Some polypeptide chains enter rough ER and are modified

• 4) Cells that specialize in secreting proteins have lots of rough ER`

Rough ER

Smooth ER

• 1) A series of interconnected tubules

• 2) No ribosomes on surface

• 3) Lipids assembled inside tubules

• 4) Smooth ER of liver inactivates wastes, drugs

• 5) Sarcoplasmic reticulum of muscle is a specialized form`

Smooth ER

Golgi Bodies

• 1) Put finishing touches on proteins and lipids that arrive from ER

• 2) Package finished material for shipment to final destinations– a) Material arrives and leaves in vesicles`

Vesicles

• 1) Membranous sacs that

move through the

cytoplasm

– a) Lysosomes

– b) Peroxisomes`

Secretion

• 1) ATP-producing powerhouses

• 2) Double-membrane system

• 3) Carry out the most efficient

energy-releasing reactions

• 4) These reactions require oxygen`

Mitochondria

Mitochondrial Structure

• 1) Outer membrane faces cytoplasm

• 2) Inner membrane folds back on itself

• 3) Membranes form two distinct compartments

• 4) ATP-making machinery is embedded in the inner mitochondrial membrane`

Mitochondrial Origins

• 1) Mitochondria resemble bacteria

– a) Have own DNA, ribosomes

– b) Divide on their own• 2) May have evolved from ancient bacteria

that were engulfed but not digested`

Mitochondrion

• 1) Plastids

• 2) Central Vacuole`

Specialized Plant Organelles

Chloroplasts

1) Convert sunlight energy to ATP through photosynthesis`

Chloroplast

Photosynthesis

• 1) First stage– a) Occurs at thylakoid membrane– b) Light energy is trapped by pigments and

stored as ATP

• 2) Second stage– a) Inside stroma, ATP energy is used to

make sugars, then other carbohydrates`

Central Vacuole

• 1) Fluid-filled organelle– a) Stores amino acids, sugars, wastes

• 2) As cell grows, expansion of vacuole as a result of fluid pressure forces cell wall to expand– a) In mature cell, central vacuole takes up

50-90 percent of cell interior`

• 1) Present in all eukaryotic cells

• 2) Basis for cell shape and internal organization

– a) Allows organelle movement within cells and, in some cases, cell motility`

Cytoskeleton

Cytoskeletal Elements

microtubule

microfilament

intermediatefilament

Microtubules

• 1) Largest elements

– a) Composed of the protein tubulin

• 2) Arise from microtubule organizing

centers (MTOCs)

• 3) Polar and dynamic

– a) Involved in shape, motility, cell division`

Microfilaments

• 1) Thinnest cytoskeletal elements

– a) Composed of the protein actin

• 2) Polar and dynamic

– a) Take part in movement, formation and

maintenance of cell shape`

Cytoskeleton

Accessory Proteins

• 1) Attach to tubulin and

actin

• 2) Motor proteins

• 3) Crosslinking proteins`

Intermediate Filaments

• 1) Present only in animal cells of certain tissues

• 2) Most stable cytoskeletal elements

• 3) Six known groups– a) Desmins, vimentins, lamins, etc.

• 4) Different cell types usually have 1-2 different kinds`

• 1) Length of microtubules or microfilaments can change

• 2) Parallel rows of microtubules or microfilaments actively slide in a specific direction

• 3) Microtubules or microfilaments can shunt organelles to different parts of cell`

Mechanisms of Movement

Motor Proteins

Flagella and Cilia

• 1) Structures for

cell motility

• 2) 9 + 2 internal

structure`

dynein

microtubule

Flagella

Paramecium

• 1) Structural component that wraps around the plasma membrane

• 2) Occurs in plants, some fungi, some protistans`

Cell Wall

Primary cell wall of a young plant

Plasma membrane

Cell Walls

Plant Cuticle

• 1) Cell secretions and waxes accumulate at plant cell surface

• 2) Semi-transparent

• 3) Restricts water loss`

Matrixes Between Animal Cells

• 1) Animal cells have no cell walls

• 2) Some are surrounded by a matrix of

cell secretions and other material`

Cell-to-Cell Junctions

• 1) Plants

– a) Plasmodesmata

• 2) Animals

– a) Tight junctions

– b) Adhering junctions

– c) Gap junctions`

plasmodesma

Animal Cell Junctions

• 1) Archaebacteria and Eubacteria

– a) DNA is NOT enclosed in nucleus

– b) Generally the smallest, simplest cells

– c) No organelles`

Prokaryotic Cells

Prokaryotic Structure