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Chapter 3: Cells
The smallest part of you
Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives

Describe what a cell is and the two general types of
cells.

Describe the structure and functions of cell membranes.

Describe several ways in which molecules move across
membranes.

Describe how cells are connected and how they
communicate with each other.

Describe nine important landmark structures (organelles)
in eukaryotic cells.
The cell: the smallest unit
of life that can function
independently and perform
all the necessary functions
of life, including
reproducing itself.
Cell Theory
1. All living organisms are made up of one
or more cells.
– The human body is a cooperative society of
trillions of cells.
– Every thing we do, every action every
thought, is a reflection of cellular
processes!!
2. All cells arise from other pre-existing
cells.
3.2 Prokaryotic cells are structurally simple,
but there are many types of them.
Every cell on earth falls into one of two basic
categories:
1.
2.
A eukaryotic cell
• has a central control structure called a nucleus
which contains the cell’s DNA.
• Eukaryotes
A prokaryotic cell
• does not have a nucleus; its DNA simply
resides in the middle of the cell
• Prokaryotes
Prokaryotes are:
1. Older (evolutionarily) – first cells on earth
2. Simpler (structurally) – contain few
membrane bound organelles, no nucleus.
3. Smaller than eukaryotes
Bacterial diversity
Eukaryotic cells have organelles:
Chloroplasts and Mitochondria.
3.3 Eukaryotic cells have compartments
with specialized functions.
Stem Cells are cells that do not yet have a function. Their
development can be directed to grow new tissues and organs.
Humans, deep down, may
be part bacteria.
How can that be?
Evidence to support this?
Your Body is an Ecosystem.
• 10 X as many prokaryotic cells in and
on your body than the total number of
your own body cells.
• Probiotics (beneficials in the gut) - are
available in foods and dietary
supplements
– yogurt, fermented and unfermented
milk, miso, tempeh, and
some juices and soy
beverages.
• Use of antibiotics?
Drugs that target cells: Antibiotics
The first antibiotic,
Penicillin, came from a
fungus found to kill
disease-causing
bacteria.
Antibiotics cause lysing of bacterial cells.
Cell walls are the first line of defense for Bacteria, Plants,
and Fungi, but cell membranes are the gatekeepers of all
cells. They regulate what goes in and out of the cell.
3-4. All cells are bordered by plasma
membranes.
Some molecules like water and oxygen can
pass through the membrane passively.
Others, like glucose, must be transported
through membrane proteins.
3.5 Molecules embedded within the plasma
membrane help it perform its functions.
4 types or protein, carbohydrate chains,
and cholesterol
Membrane surfaces
have a “fingerprint”
that identifies the cell.
 Cells
with an
improper
fingerprint are
recognized as
foreign and are
attacked by your
body’s defenses.
How do
you
explain
why HIV
does not
spread
through
from
casual
contact,
such as a
hug or a
hand
shake?
Passive transport uses no cellular energy.
Active transport requires cellular energy.
3.8 Passive transport is the
spontaneous diffusion of molecules
across a membrane.
There are two types of passive transport:
1. Diffusion
2. Osmosis
Diffusion and
Concentration
Gradients
• Solutes
• Solvents
Facilitated
Diffusion
requires
carrier
proteins
3.9 Osmosis is
the passive
diffusion of
water across a
membrane. In
this case, the
solute cannot
move.
Osmotic effects in
celery: What happened
in lab?
Use the terms hypotonic
and hypertonic correctly
to describe the action.
The direction of osmosis
is determined by a
difference in total
concentration of all the
molecules dissolved in
the water. Water always
moves from areas of low
solute concentration to
areas of high solute
concentration.
Two distinct types of active transport:
1. Primary – use of ATP directly
focus on primary
2. Secondary – uses energy from
other molecules

Active transport is necessary if the
molecules to be moved are very large or
if they are being moved against their
concentration gradient.
Primary active transport:
uses energy directly from ATP
Transport of
Large
Molecules:
Exocytosis and
Endocytosis:
An LDL particle is
large and contains
many molecules of
cholesterol.
Proteins embedded
in the membrane
(receptor proteins)
are specific for the
proteins built into
liver cells.
Cholesterol is
processed inside
the cells of the liver.
If cholesterol is not removed from the
blood stream by the liver, it will build
up in the blood vessels as plaque.
Communication beyond receptor proteins…
Cells talk to each other by chemical signaling
across membranes.
3.12 Connections between cells hold them in
place and enable them to communicate with
each other.
Plasmodesmata
Tube-like channels
connecting the cells
to each other and
enabling
communication and
transport between
them
 Consider a plant as
one big cell?
 Consider one big
brain?

The (1) nucleus, (2) cytoskeleton, (3) mitochondria, (4)
lysosomes, (5) rough and smooth ER, (6) Golgi apparatus,
(7) cell wall, (8) vacuoles, and (9) chloroplasts…
3.13 Nucleus: the cell’s genetic control
center.
 The
nucleus is the largest and most
prominent organelle in most eukaryotic
cells.
 The
nucleus has two primary functions:
• genetic control center
• storehouse for hereditary information
Chromatin - a mass of long,
thin fibers consisting of DNA
with some proteins attached
Nucleolus - an area near the
center of the nucleus where
subunits of the ribosomes
are assembled
Ribosomes are like factories
that make proteins from your
genetic code.
How DNA becomes
functional:
1. DNA dictates synthesis
of mRNA.
2. mRNA travels to the
cytoplasm and binds to
ribosomes.
3. As the ribosome moves
along the mRNA, the
genetic message is
translated into a protein
of specific amino acid
sequence.
3.14
Cytoplasm
and
cytoskeleton:
the cell’s
internal
environment,
physical
support, and
movement.
Cilia and Flagellum
3.15 Mitochondria:
the cell’s energy converters
Cellular respiration harvests
energy from food and converts it
to ATP.
3.16 Lysosomes: the cell’s garbage
disposals – breakdown body
The Endomembrane System includes
Rough ER, Smooth ER, and the Golgi
apparatus.
3.17 Endoplasmic reticulum: where
cells build proteins and disarm toxins
Rough Endoplasmic Reticulum
Ribosomes manufacture proteins and
the rough ER folds and packages them.
The Smooth Endoplasmic Reticulum
Smooth ER makes lipids and detoxifies cells.
How can long-term use of one
drug increase your resistance to
another, different drug that you
have never encountered?
Chronic exposure to many drugs from
antibiotics to heroin can cause increased
production of smooth ER, which in turn is
able to detoxify greater quantities of
different drugs.
3.18 Golgi apparatus: Where the cell
processes products for delivery
throughout the body
The Golgi apparatus processes raw
materials (proteins and lipids) made by the
ER, tags them, and sends them to their
place in the body. It is also a site for
carbohydrate synthesis.
3.19 The cell wall
provides additional
protection, water
resistance, and
support for plant cells
Bacteria and fungi
also have cell walls.
3.20 Vacuoles:
multipurpose storage
sacs for cells
The Central Vacuole
functions as storage space
and plays a role in
nutrition, waste
management, predator
deterrence, reproduction
(via attractive pigments),
and physical support
(turgor pressure).
Amoeba use endocytosis and food vacuoles to hunt prey.
Paramecium use contractile vacuoles to maintain salt and
water balance.
3.21 Chloroplasts: the plant cell’s
power plant
The stroma (fluid)
and interconnected
little flattened sacs
called thylakoids
(contain chlorophyll)
Endosymbiosis Theory Revisited
 Chloroplasts
bacteria.
 Circular
 Dual
resemble photosynthetic
DNA
outer membrane