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Chapter 03
Lecture and
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3.1 Cellular Organization
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A. Introduction
1.
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
3
Introduction, cont
2.
3.
Organelles (little organs) are scattered
throughout the cytoplasm and have
various functions
The cytoskeleton maintains cell shape and
allows the cell and its content to move
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A typical animal cell
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B. Plasma Membrane
1.
Separates the inside of the cell (cytoplasm) from
the outside
2.
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
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Fluid-mosaic model of the plasma membrane
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C. The Nucleus
1.
2.
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
3. Nucleoli
a. Dark-staining bodies containing rRNA
and protein
b. Site where ribosomes are formed
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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
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The Nucleus
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D. Ribosomes
1.
2.
3.
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
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E. Endomembrane System
1.
2.
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
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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
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Endoplasmic Reticulum
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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
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Endomembrane System Function
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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
1.
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
2. Vacuoles isolate substances captured
inside the cell
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G. Mitochondria
1.
2.
3.
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
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Mitochondrion Structure
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H. The cytoskeleton
1.
2.
3.
4.
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
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I. Centrioles
1.
2.
3.
4.
5.
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
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Structure of basal bodies and flagella
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J. Cilia and flagellum
1.
2.
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
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Cilia and flagella
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Structures in Human Cells
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3.2 Crossing the Plasma Membrane
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A. Introduction
1.
2.
3.
The plasma membrane is selectively
(semi) permeable – only certain ions and
molecules can cross through
Passive processes – does NOT require
cellular energy (ATP)
Active processes – DOES require cellular
energy
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B. Simple Diffusion
1.
2.
3.
4.
Movement of atoms or molecules from
an area of higher concentration to an
area of lower concentration (down a
concentration gradient)
Movement of atoms or molecules occur
until they are equally distributed
No cellular energy is required (passive)
Small lipid-soluble molecules will diffuse
through the lipid portion of the
membrane; includes blood gases
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Diffusion
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C. Osmosis
1.
2.
3.
Diffusion of water across a plasma
membrane
Occurs when there is an unequal
distribution of water on either side of a
selectively permeable membrane; water
passes freely but solutes do not
Osmotic pressure – force exerted on a
selectively permeable membrane
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Osmosis, cont
4.
Tonicity – concentration of solute versus the
concentration of water
a. Isotonic – equal concentration of solutes
(dissolved substances) and solvent (water)
inside and outside cell; cell shape is maintained
b. Hypotonic – higher concentration of water
(lower concentration of solutes) outside cell;
water moves into cell causing it to swell and
eventually lyse
c. Hypertonic – lower concentration of water
(higher concentration of solutes) outside cell;
water moves out of cell causing it to shrink or
crenate
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Tonicity
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D. Filtration
1.
2.
Filtration is the movement of liquid
from high pressure to low pressure
Blood pressure creates the hydrostatic
pressure in capillaries where filtration
occurs
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E. Transport by carriers
1.
Facilitated diffusion
a. Solutes are transported by means of a
protein carrier
b. Movement from area of higher
concentration to area of lower
concentration
c. No energy required - passive
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Transport by carriers, cont
2.
Active transport
a. Solutes move up their concentration
gradient (low concentration area to
high concentration area)
b. Requires a protein carrier (often called
pumps)
c. Requires the use of cellular energy
d. The sodium/potassium pump (Na+/K+
pump) is an important pump that all
cells have
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Active Transport
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F. Endocytosis and Exocytosis
1.
In endocytosis (bring into the cell) the
plasma membrane envelopes a
substance and forms an intracellular
vesicle
a. Phagocytosis (“cell eating”) – cell
ingests solid particles
b. Pinocytosis (“cell drinking”) – cell
consumes solutions
2. In exocytosis (takes out of the cell) a
vesicle fuses with the plasma
membrane as secretion occurs
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Crossing the Plasma Membrane
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3.3 The Cell Cycle
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A. Introduction
1.
2.
3.
4.
Set of stages that take place between the
time a cell divides and the time the
daughter cell divides
Controlled by external and internal signals
Apoptosis (cell death) occurs at a
restriction checkpoint if the cell did not
complete mitosis and is abnormal
Some specialized cells no longer go
through the cell cycle - muscle cells and
nerve cells
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B. Cell Cycle Stages - Interphase
1.
Cell is not dividing, but is preparing to
divide
2. The cell carries on regular activities
3. Three phases
a. G1 phase – cell doubles number of
organelles and accumulates materials
used for DNA synthesis
b. S phase – “synthesis” phase; DNA
replication occurs
c. G2 phase – cell synthesizes proteins that
will assist cell division and completes
replication of centrioles
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The Cell Cycle
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C. Major events during interphase
1.
a.
b.
c.
d.
e.
Replication of DNA
Before replication, the two strands of DNA are
hydrogen bonded together
Parental DNA strands unwind (hydrogen bonds
are broken)
New complimentary nucleotides pair with
nucleotides in the parental DNA strands and
DNA polymerase joins the new nucleotides
When replication is complete, two identical
double helix molecules have been formed
Each strand of this double helix is equivalent to
a chromatid; held together by the centromere
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Overview of DNA Replication
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Ladder configuration & DNA replication
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2. Protein synthesis
a. DNA also serves as a template for RNA
formation and protein construction
b. Two steps involved in protein synthesis
are:
1) Transcription – formation of mRNA
2) Translation – involves mRNA, tRNA,
and rRNA; specifies the order of amino
acids in a polypeptide
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Protein Synthesis Process
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D. The Cell Cycle – Mitotic Stage
1.
M-stage – nuclear division stage divided into 4
phases
a. Prophase
1) The centrioles near nucleus begin moving
towards opposite ends of nucleus
2) Spindle fibers appear between the centrioles
3) Nuclear envelope begins to fragment
4) Nucleolus begins to disappear
5) Chromosomes appear randomly and attached
to spindle fibers by their centromere
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M-stage, cont
b.
Metaphase
1) Spindle is fully formed
2) Chromosomes are aligned at the equator
c. Anaphase
1) Centromere splits
2) Sister chromatids separate (now called
chromosomes)
3) Chromosomes move toward opposite
poles of the spindle (toward centrioles)
4) Some spindle fibers push the
chromosomes apart while others pull
them toward the poles
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M-stage, cont
d. Telophase
1) Chromosomes become chromatin
2) Spindle disappears and nucleoli appear
3) Nuclear envelope reassembles and two
daughter cell nuclei can be observed
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2. The Cell Cycle - Cytokinesis
a.
b.
c.
Cytokinesis – division of the cytoplasm
and organelles
Begins in anaphase and completes in
telophase
Actin filaments form a ring around the
equator that contracts, pinching the cell
in half
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Mitotic Stage of the Cell Cycle
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Mitosis in a whitefish embryo
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3. Importance of mitosis
a. Maintains chromosome number
b. Each cell in our body is genetically
identical
c. Each cell type has certain genes
turned on and others turned off to give
the different types of body cells
d. Important to the growth and repair of
multicellular organisms
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E. Meiosis
1. Known as reduction division because the
chromosome number is cut in half
2. The four phase of mitosis are repeated twice
with some changes in the steps that occur
3. The gametes (ova and sperm) have half the
chromosomes of normal body cells so that
when they join to form the zygote, the
chromosome number is correct for that
organism.
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