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How Cells Are Put Together
Chapter 3
Cell Theory
• Every organism is composed of one
or more cells
• Cell is smallest unit with properties of
life
• Continuity of life arises from growth
and division of single cells
Cell
• Smallest unit of life
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
Structure of Cells
All start out life with:
– Plasma membrane
– Region where DNA
is stored
– Cytoplasm
Two types:
– Prokaryotic
– Eukaryotic
Overview of cells
Common eukaryotic organelles
Most Cells Are Really Small
Fig. 3-4, p.41
Surface-to-Volume Ratio
• Bigger cell, less surface area per unit
volume
• Above a certain size, material cannot
move in or out of cell fast enough
diameter (cm):
surface area (cm2):
volume (cm3):
0.5
0.79
0.06
surface- to-volume ratio: 13.17:1
1.0
3.14
0.52
1.5
7.07
1.77
6.04:1
3.99:1
Fig. 3-5, p.41
Microscopes
• Create detailed images of something
that is too small to see
• Light microscopes
– Simple or compound
• Electron microscopes
– Transmission EM or Scanning EM
Limitations of Light
Microscopy
• Cells must be thin enough for light to
pass through
• Structures are usually stained
• Light microscopes can see details 200
nm in size
Electron Microscopy
• Uses beams of electrons rather than
light
• Electrons are focused by magnets
rather than glass lenses
• Can resolve structures down to 0.5 nm
Microscopes
Fig. 3-2a, p.40
Structure of Cell Membranes
• Fluid mosaic model
• Mixed composition:
– Phospholipid bilayer
– Glycolipids
– Sterols
– Proteins
Phospholipids
one layer of lipids
one layer of lipids
Fig. 3-6b, p.42
Lipid bilayer organization
Membrane Proteins
Adhesion proteins
Communication proteins
Receptor proteins
Recognition proteins
Passive transporters
Active transporters
Cell membranes
Prokaryotic Cells
• Archaebacteria and eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest cells
Typical prokaryotic cell
Eukaryotic Cells
• Have a nucleus and other
organelles
• Eukaryotic organisms
– Plants
– Animals
– Protistans
– Fungi
Eukaryotic Cell Features
• Plasma membrane
• Nucleus
• Endoplasmic
reticulum
• Golgi body
• Vesicles
• Mitochondria
• Ribosomes
• Cytoskeleton
Table. 3-1, p.45
The Nucleus
• Keeps the DNA molecules separated
from metabolic machinery of cytoplasm
• Makes it easier to organize DNA and to
copy it
The Nucleus
Components:
Nuclear envelope
Chromatin
Nucleoplasm
Nucleolus
The Nucleus
RNA
messages
pore
chromatin nucleolus
nuclear envelope
(two lipid bilayers)
cytoplasm
the cell nucleus
DNA in nucleus
rough ER
smooth ER
Golgi body
Fig. 3-9a, p.46
Endomembrane System
• Related organelles where lipids are
assembled and new polypeptide chains
modified
• Sorts and ships products to various
destinations
• Consists of endoplasmic reticulum,
Golgi bodies, vesicles
The endomembrane system
Endoplasmic Reticulum
• Starts at nuclear membrane and
extends throughout cytoplasm
• Rough ER: ribosome covered,
processes proteins
• Smooth ER: no ribosomes, builds lipids
smooth ER channel, cross-section
smooth ER
Endoplasmic Reticulum
Fig. 3-9d, p.46
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
Secretory pathway ends.
Endocytic pathway begins.
budding vesicle
plasma membrane
Golgi body
Golgi Body
Fig. 3-9e-f, p.46
Vesicles
• Membranous sacs that
move through cytoplasm
• Lysosomes
• Peroxisomes
Mitochondria
• ATP-producing powerhouses
• Membranes form two distinct
compartments
• ATP-making machinery embedded
in inner mitochondrial membrane
outer membrane
outer compartment
inner compartment
inner membrane
Fig. 3-10, p.48
Chloroplasts
• Convert sunlight energy to ATP through
photosynthesis
• Found in plants and some protistans
two outer
membranes
thylakoids
(inner membrane
system folded into
flattened disks)
Fig. 3-11, p.48
Organelle Origins
• Nucleus and ER
– Infolding of membranes formed
compartments
• Mitochondria and chloroplasts
– Endosymbiosis
chloroplast
flagellum
mitochondrion
nucleus
Fig. 3-14d, p.50
Infolding Bacterial Membranes
DNA
infolding of plasma membrane
Fig. 3-15a, p.51
Cytoskeleton
• Present in all eukaryotic cells
• Cell shape and internal organization
• Allows organelle movement within cells
and, in some cases, cell motility
tubulin
subunit
Microtubules
• Largest elements
• Composed of tubulin
• Involved in shape, motility,
cell division
Microfilaments
• Thinnest elements
• Composed of actin
• Take part in movement,
formation, and
maintenance of cell
shape
actin
subunit
Intermediate Filaments
• Only in animal cells
of certain tissues
• Most stable
cytoskeletal
elements
• Helpful in
determining tissue
types
one
polypeptide
chain
Cilia, Flagellum, and Psuedopod
Plant Cell Walls
Plant Vs Animal
Table. 3-2, p.57