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Chapter 5a
Cell Structure and Function
Early Discoveries
• 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`
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`
Cell
• 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 Features
Lipid Bilayer
• 1) Main component
of cell membranes
– a) Gives the
membrane its fluid
properties
• 2) Two layers of
phospholipids`
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`
Microscopes
• 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`
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
Functions of Nucleus
• 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`
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`
Cytomembrane System
• 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`
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
Mitochondria
• 1) ATP-producing powerhouses
• 2) Double-membrane system
• 3) Carry out the most efficient
energy-releasing reactions
• 4) These reactions require oxygen`
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
Specialized Plant Organelles
• 1) Plastids
• 2) Central Vacuole`
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`
Cytoskeleton
• 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`
Cytoskeletal Elements
intermediate
filament
microtubule
microfilament
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`
Mechanisms of Movement
• 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`
Motor Proteins
Flagella and Cilia
microtubule
• 1) Structures for
cell motility
• 2) 9 + 2 internal
structure`
dynein
Flagella
Paramecium
Cell Wall
Plasma membrane
• 1) Structural
component that
wraps around the
plasma membrane
• 2) Occurs in plants,
some fungi, some
protistans`
Primary cell wall of a young
plant
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
Prokaryotic Cells
• 1) Archaebacteria and Eubacteria
– a) DNA is NOT enclosed in nucleus
– b) Generally the smallest, simplest cells
– c) No organelles`
Prokaryotic Structure