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Chapter 03
Lecture and
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3.1 Cellular Organization
A.Introduction
• Three main parts of a cell
a.Plasma membrane – surrounds the cell, keeps it
intact, and regulates passage into and out of the
cell
b.Nucleus – control center
c. Cytoplasm – gelatinous, semi-fluid of water and
suspended and dissolved substances
Introduction, cont
2.Organelles (little organs) are scattered
throughout the cytoplasm and have various
functions
3.The cytoskeleton maintains cell shape and
allows the cell and its content to move
A typical animal cell
B.Plasma Membrane
• Separates the inside of the cell (cytoplasm) from the outside
• Fluid-mosaic model
a. Phospholipid bilayer – hydrophilic heads point outward and
hydrophobic tails point inward
b. Attached peripheral and integral proteins serve as receptors,
channels, and carriers
c. Cholesterol molecules stabilize the membrane
d. Glycoproteins and glycolipids attached to outer surface of
some protein and lipid molecules, mark cells as belonging to a
particular individual
Fluid-mosaic model of the plasma membrane
C.The Nucleus
• Stores genetic information
• Chromatin
a.Contains DNA, protein, and some RNA
b.Coils into rod-like structures called chromosomes
before the cell divides
c. Immersed in nucleoplasm
• Nucleoli
a.Dark-staining bodies containing rRNA and protein
b.Site where ribosomes are formed
The Nucleus, cont
4.Nuclear envelope separates nucleus from
cytoplasm
a.Lipid bilayer with many nuclear pores
b.Outer layer is continuous with the endoplasmic
reticulum
The Nucleus
D.Ribosomes
• Composed of two subunits containing protein
and rRNA
• Can be found free within the cytoplasm, singly
or in groups called polyribosomes; produce
proteins that are used inside the cell
• Also found attached to the endoplasmic
reticulum; produce proteins that may be
secreted by the cell
E.Endomembrane System
• Nuclear envelope
• Endoplasmic reticulum (ER)
a.Continuous with the outer membrane of the nuclear
envelope, it is a system of membranous channels and
saccules
b.Rough ER
1)Has attached ribosomes
2)Processes proteins produced by attached ribosomes
Endomembrane system, cont
c. Smooth ER
1)Has no attached ribosomes
2)Synthesizes phospholipids, detoxifies drugs, and
has other functions depending on the type of cell
Endoplasmic Reticulum
Endomembrane System, cont
3.Golgi apparatus
a.Stacks of curved saccules
b.Processes, packages, and secretes various substances
c. Receives protein and/or lipid-filled vesicles from ER
d.Contains enzymes that modify proteins and lipids
e.Vesicles leave the Golgi apparatus and move to other
parts of the cell or to the plasma membrane for
secretion
f. Produces lysosomes
Endomembrane System Function
Endomembrane system, cont
4.Lysosomes
a.Contain hydrolytic digestive enzymes; nick-names
“suicide sacs”
b.Autodigestion responsible for cell rejuvenation
and development and removal of worn-out
organelles
c. Can fuse with vesicles of material brought into the
cell for destruction
d.Tay-Sach’s disease – metabolic disorder involving
missing or inactive lysosomal enzymes in nerve
cells
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F.Peroxisomes and Vacuoles
• Peroxisomes
a.Enzyme-containing vesicles, similar to lysosomes
b.Detoxify drugs, alcohol, and other toxins
c. Large numbers found in liver and kidney
d.Break down fatty acids from fats
• Vacuoles isolate substances captured inside
the cell
G.Mitochondria
• Rod-shaped organelle bound by a double
membrane
• Inner membrane folds into cristae to increase
surface area
• Site of ATP production through cellular
respiration – cell powerhouse
Mitochondrion Structure
H.The cytoskeleton
• Microtubules - help maintain the cell’s shape
and anchors or assists the movement of
organelles
• Intermediate filaments – involved in cell to cell
junctions
• Actin filaments – involved in cell movement
• Assembly regulated by the centrosome
I.Centrioles
• Composed of microtubules with a 9 + 0 pattern
• A pair of perpendicular centrioles are found near
the nucleus of every cell
• In a area called the centrosome
• Involved in cell division by forming the mitotic
spindle
• Form the basal body (anchor point) for each
cilium or flagellum
Structure of basal bodies and flagella
J.Cilia and flagellum
– Cilia are hair-like projections from the free surface
of a cell; beat in unison to move material along
the cell surface
– Flagellum – a single whip-like extension for cell
movement; sperm is the only human cell with a
flagellum
Cilia and flagella
Structures in Human Cells