Cell Structure and Function
Chapter
4
Early Discoveries
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
Microscopes
Create detailed images of something that is otherwise
too small to see
Light microscopes
w
Simple or compound
Electron microscopes
w
Transmission EM or Scanning EM
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
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
Shared Features of Cells
w
Enclosed by plasma membrane
w
Use DNA as hereditary blueprint
w
Contain cytoplasm and ribosomes
w
Obtain energy and nutrients from the environment
w Function
limits size
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
Cell Vocabulary
Prokaryotic (lack
nucleus and other membrane-bound organelles)
Eukaryotic (have
nucleus and other membrane-bound organelles
Unicellular:
single cells
Multicellular:
many cells
Prokaryotic
Eukaryotic
Prokaryotic Cells
Archaea and
Bacteria
DNA is NOT
enclosed in nucleus, but concentrated in nucleoid region
Generally the
smallest, simplest cells
No organelles
A generalized prokaryotic cell
Eukaryotic Cells
Have a nucleus and other organelles
Eukaryotic organisms
w
Plants
w
Animals
w
Protistans
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Fungi
Animal Cell Features
Plant Cell Features
Cell wall
Central vacuole
Chloroplast
Functions of Nucleus
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
Components of Nucleus
Nuclear Envelope
Two outer
membranes (lipid bilayers)
Innermost surface
has DNA attachment sites
Pores span
bilayer
Nucleolus
Dense mass of material in nucleus
May be one or more
Cluster of DNA and proteins
Materials from which ribosomal subunits are built
Subunits must pass through nuclear pores to reach
cytoplasm
The Nucleus Contains Chromosomes
Chromatin
Cells collection of DNA and associated proteins
Chromosome is one DNA molecule and its associated proteins
Appearance changes as cell divides
What Roles Do Membranes Play in Eukaryotic Cells?
The Plasma Membrane Isolates the Cell and Helps It Interact
with Its Environment
Cytomembrane System
Group of related
organelles in which lipids are assembled and new polypeptide chains are
modified
Products are
sorted and shipped to various destinations
Components of Cytomembrane System
Plasma
membrane
Endoplasmic
reticulum
Nuclear
envelope
Golgi
complex
Vesicles
Endoplasmic Reticulum
In animal cells, continuous with nuclear membrane
Extends throughout cytoplasm
Two regions - rough and smooth
Rough ER
Arranged into flattened sacs
Ribosomes on surface give it a rough appearance
Some polypeptide chains enter rough ER and are modified
Cells that specialize in secreting proteins have lots
of rough ER
Smooth ER
A series of interconnected tubules
No ribosomes on surface
Lipids assembled inside tubules
Smooth ER of liver also inactivates wastes, drugs
Golgi Complex
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
Vesicles
Membranous sacs that move through the cytoplasm
Example: Lysosomes
Which Other Structures Play Key Roles in Eukaryotic Cells?
Vacuoles Regulate Water and Store Substances
Chloroplasts Capture Solar Energy
Mitochondria
Mitochondria Extract Energy from Food Molecules,
producing ATP
Mitochondrial Structure
Outer membrane
faces cytoplasm
Inner membrane
folds back on itself
Membranes form
two distinct compartments
ATP-making
machinery is embedded in the inner mitochondrial membrane
Mitochondrial Origins
Specialized Plant Organelles
Central Vacuole:
w Regulates Water and Stores Substances
Chloroplast
w Capture solar energy
Chloroplasts
Convert sunlight energy to ATP
through photosynthesis. Double membrane structure, green color.
Central Vacuole
Fluid-filled organelle
Stores amino acids, sugars, wastes
As cell grows, expansion of vacuole as a result of
fluid pressure forces cell wall to expand
In mature plant cell, central vacuole takes up 50-90
percent of cell interior
Cytoskeleton
Present in all eukaryotic cells
Basis for cell shape and internal organization
Needed for cell division
Allows organelle movement within cells and, in some
cases, cell motility
Cytoskeletal Elements
Microtubules
Largest elements
Composed of the protein tubulin
Arise from microtubule organizing centers (MTOCs)
Polar and dynamic
Involved in shape, motility, cell division
Flagella and Cilia
Cilia and Flagella Move the Cell or Move Fluid Past the
Cell
9 + 2 internal structure of microtubules
Cell Wall
Structural component that wraps around the plasma
membrane
Occurs in plants, some fungi, some protistans
Plant Cell Walls
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