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Chapter 3
Cells
Introduction


The cell is the basic
unit of structure and
function in living
things.
Cells vary in their
shape, size, and
arrangements, but all
cells have similar
components with a
particular function
“COMPOSITE” cells
 “COMPOSITE”
or typical animal cell
contains four major cell parts
– CELL MEMBRANE = the outer boundary
of the cell
– CYTOPLASM = holds the cellular
organelles
– CELLULAR ORGANELLES = perform
specific functions of the cell
– NUCLEUS = control center of the cell
The Cell (Plasma) Membrane
 The
cell membrane is a thin,
dynamic membrane that encloses
the cell and controls what enters and
leaves the cell.

Cell Membrane Structure = Fluid Mosaic
Model
– Composed of a double layer (bilayer) of
phospholipid molecules with many protein
molecules dispersed within it.
The Plasma Membrane
The surfaces of the membrane are
“hydrophilic” due to their polar
phosphate heads
 The internal portion of the membrane is
“hydrophobic” due to the non-polar
fatty acid tails

The Plasma Membrane

The membrane proteins:
– Integral proteins – extend across
bilayer; most are glycoproteins; serve
as channels(pores),
transporters(carriers), receptors(rec.
sites), or enzymes.
– Peripheral proteins – loosely on the
inner or outer surface; serve as
enzymes or cytoskeletal anchors
Membrane Proteins
Membrane Proteins
Membrane Proteins
Phospholipid Bilayer
Plasma Membrane
Membrane Junctions
 Tight
junctions = adjacent plasma
membranes bind together like a
zipper. (impermeable junctions)
 Desmosomes = buttonlike
thickenings of adjacent plasma
membranes (anchoring junctions)
 Gap junctions = neighboring cells
are connected by connexons;
function to allow communication.
CYTOPLASM (cytosol)

The jelly-like fluid (70%) that holds the
cellular organelles and occupies the space
between the nucleus and the cell
membrane.
CYTOPLASMIC ORGANELLES

NUCLEUS: the central core, control
center or “brain” of the cell
– The largest organelle of the cell
– Filled with nucleoplasm
– Contains 3 distinct regions
 A. Nuclear membrane (envelope)
 B. Nucleoli
 C. Chromatin
Nucleus: 3 Regions
 A. Nuclear membrane – (or nuclear
envelope) is a double membrane that
separates the contents of the nucleus from
the cytoplasm
– At various points, these two membranes fuse =
nuclear pore
– The nuclear membrane is “selectively
permeable”; pores serve at sites where mRNA
can pass out of the nucleus during protein
synthesis, and how ribosomes exit the nucleus.
Nuclear Membrane
NUCLEUS: 3 Regions
– 3 regions (cont.)
 A. Nucleoli (pl);
Nucleolus (s) = a
spherical body
within the nucleus;
– Composed of
RNA and
proteins
– Function =
synthesis of
ribosomes
Nucleus: 3 Regions
 C. CHROMATIN = loosely coiled fibers of
DNA and histone proteins present in the
nucleus;
–Nucleosome = fundamental unit of
chromatin; spherical clusters of eight
histone proteins wrapped in DNA
connected like beads on DNA string.
–These fibers of chromatin would be
tightly coiled as chromosomes if the
cell were preparing to divide.
Chromatin
CYTOPLASMIC ORGANELLES

RIBOSOMES:
– Small granules
dispersed
throughout the
cytoplasm and on
the membranes of
some endoplasmic
reticulum (ER)
– Composed of RNA
and protein
– Function = protein
synthesis
CYTOPLASMIC ORGANELLES
ENDOPLASMIC RETICULUM (ER):
 Network of interconnected parallel membranes
(maze), that is continuous with the nuclear
membrane
 Two types

– Rough Endoplasmic Reticulum (RER)
 ER studded with ribosomes
 Function = protein synthesis
– Smooth Endoplasmic Reticulum (SER)
 Lacks ribosomes
 Function = lipid and cholesterol synthesis
Endoplasmic Reticulum
SER and Alcohol
SER of liver helps
to detoxify alcohol
 More someone
drinks, the more
SER they produce
– to a point
 Build up tolerance
 Damage to liver –
can be irreversible

CYTOPLASMIC ORGANELLES

GOLGI APPARATUS
(COMPLEX):
– Flattened membranous
sacs (“cisternae”) arranged
in stacks (“stack of
pancakes”) associated with
many vesicles (membrane
bound sacs containing
proteins);
– Function = modification,
packaging, and
transport of proteins
– Vesicles pinch off as
“secretory vesicles”
CYTOPLASMIC ORGANELLES

LYSOSOMES:
– Spherical membranous sacs containing
digestive enzymes
– “suicide sacs” which destroy anything the cell
no longer wants or needs
– Autolysis is the process by which worn cell
parts are digested by autophagy.
Tay-Sach’s Disease
Enzyme = beta-hexosaminidase A does not
break down fatty gangliosides
 Loss motor skills
 Seizures
 Vision and hearing
loss
 Intellectual
disability
 Paralysis
 Usually lethal
Pompe’s Disease
Enzyme in lysosome
does not break down
glycogen
 Muscle weakness
 Enlarged liver
 Heart problems
 Breathing problems

CYTOPLASMIC ORGANELLES

PEROXISOMES:
– Membranous sacs containing oxidase enzymes
– Function = detoxification of harmful or toxic
substances (i.e. alcohol, formaldehyde,
oxygen free radicals)
– H2O2 (peroxide)  water
CYTOPLASMIC ORGANELLES
MITOCHONDRIA:
 Kidney-shaped organelle
whose inner membrane is
folded into shelf-like
partitions called “cristae”
 Powerhouse of the cell =
site of cellular respiration
where energy is released
from glucose

Mitochondria Myopathy and
Encephalomyopathy
Mitochondria do
not function
properly because
defective protein
 Low energy
 Free radical
production
 Lactic acidosis

Mattie Stepanek
Ambassador 2002-2004
Dies at 14 yrs
CYTOPLASMIC ORGANELLES
CYTOSKELETAL ELEMENTS:
 Protein structures called microfilaments,
microtubules, and intermediate filaments
 Form “muscle and bones” of the cell
 Can be broken down and reassembled

Cytoskeleton
MICROTUBULES
STRUCTUREhollow tubes made of
protein tubulin
Funtion – 1. Support
2. Anchorage for
organelles and tracks
for organelle
movement
3. Play a role in mitosis

MICROFILAMENTS


2.
3.
Structure – solid,
helical rods made of
protein actin
Function – 1.Support
Movement and
shape change of
entire cell
Play important role in
muscle contractions
Cell Membrane Surface
Modifications

Cilia – short, hair-like
cellular extensions
(eyelashes); help
move substances
through
passageways; located
in lining of resp. tract
and fallopian tube
CELL MEMBRANE SURFACE
MODIFICATIONS

Flagella – tail-like
projection; only one
per cell in humans;
aids in cell
locomotion; sperm
cell
Cell Membrane Surface
Modifications

Microvilli – small,
finger-like extensions
of the external
surface of the cell
membrane;
function=increase
surface area; located
in the lining of the
digestive tract.
Centrosome and Centrioles
Pair of microtubules
located near the
nucleus.
 Aid in movement of
chromosomes during
mitosis.

Which organelle provides energy
for the cell?




A.
B.
C.
D.
Chloroplast
Mitochondria
Lysosome
Vacuole
Which organelle makes proteins?




A.
B.
C.
D.
Rough ER
Centrioles
Lysosomes
Ribosomes
Which organelle is found in large
amounts in the liver where it
detoxifies poisons consumed by
body?




A.
B.
C.
D.
Golgi Body
Lysosomes
Rough ER
Smooth ER
Which cell structure controls what
moves into and out of the cell?




A.
B.
C.
D.
Cell wall
Cell membrane
Nucleus
Chromatin
Which organelle is the packaging
and shipping center?



A. Rough ER
B. Smooth ER
C. Golgi Body
Which cell part provides structure
and support to the cell?




A. centriole
B. cytoskeleton
C. cytoplasm
D. peroxisome