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FOOD FOR THOUGHT
Figure 4.3
Microscopes as a Window on the World of Cells
• Microscopy: purpose to magnify images too small
to see
• Magnification
– Is an increase in the specimen’s apparent size.
• Resolving power
– Is the ability of an optical instrument to show two
objects as being separate.
Euglena
– The light microscope is used by many scientists.
• Light passes through the specimen.
• Lenses enlarge, or magnify, the image.
• The electron microscope (EM) uses a beam of
electrons.
– It has a higher resolving power than the light
microscope.
• The electron microscope can magnify up to
100,000X.
– Such power reveals the diverse parts within a cell.
• The transmission electron microscope (TEM) is
useful for exploring the internal structure of a cell.
A beam of electrons transmitted through the sliceproduces a cross section
• The scanning electron microscope (SEM) is used to
study the detailed architecture of the surface of a cell.
Beam of electrons reflected off surface- 3-D image
• Cells were first discovered in 1665 by Robert
Hooke.
• The accumulation of scientific evidence led to the
cell theory.
– All living things are composed of cells.
– All cells are formed from previously existing
cells.
– Cells are smallest unit of life
Isolating Techniques of cool stuff inside a cell
- Cell fractionation
- Split everything apart
- Centrifuge based on mass
The Two Major Categories of Cells
• The countless cells on earth fall into two
categories:
– Prokaryotic cells
– Eukaryotic cells
• Prokaryotic and eukaryotic cells differ in several
respects.
Figure 4.4
• Prokaryotic cells
– Are smaller than eukaryotic cells.
– Lack internal structures surrounded by
membranes.
– Lack a nucleus.
– Examples: Bacteria and Archae
Figure 4.5
• Eukaryotic cells
– Are larger than prokaryotic cells.
– Have internal structures surrounded by
membranes.
– DNA contained within a nucleus.
– Examples: Protists, Fungi, Plant and Animal
A Panoramic View of Eukaryotic Cells
• An idealized animal cell
• An idealized plant cell
Cytoplasmic Streaming
The Microscopic World of Cells
• Organisms are either:
– Single-celled, such as most bacteria and protists
– Multicelled, such as plants, animals, and most
fungi
– For the most part cells are small
• Exception: bird eggs, neurons, some algae and
bacteria
Tour of a Eukaryotic Cell
- Cytoplasm
- Nucleus
- Ribosomes
- Endomembrane System
- Nuclear Envelope
- ER
- Golgi Apparatus
- Lysosomes
- Vacuoles
- Plasma (Cell) Membrane
- Mitochondria
- Chloroplasts
- Cytoskeleton
Cytoplasm
All cells have cytoplasm that includes everything
inside the cell like organelles. AKA cytosol it is
a jelly-like substance.
The Nucleus
• Nucleus Definition:
• The nucleus is the manager of the cell.
– DNA that holds the genes in the nucleus store
information necessary to produce proteins.
– It contains chromatin and chromosomes.
• DNA + Protein ; condensed chromatin
– It contains a nucleolus.
• Synthesizes Ribosomes
Structure and Function of the Nucleus
• The nuclear envelope (a double membrane)
borders the nucleus and contain pores. Nuclear
lamina on the inside layer of the envelope helps
maintain the shape of the nucleus
Ribosomes
• Ribosomes (folded strands of ribosomal RNA) are
responsible for protein synthesis.
– Free ribosomes usually make proteins that will
function/stay in the cytosol.
– Bound ribosomes (attached to the Endoplasmic
Reticulum) usually make proteins that are
exported or included in the cell's membranes.
– Cool fact: free ribosomes and bound ribosomes
are interchangeable and the cell can change their
numbers according to metabolic needs.
DNA controls the cell by
transferring its coded
information into RNA.
The information in the
RNA is used to make
proteins.
Figure 4.9
The Endomembrane System: Manufacturing and
Distributing Cellular Products
• Includes many of the membranous organelles in the
cell belong to the endomembrane system.
The Endoplasmic Reticulum
• The endoplasmic reticulum (ER)
– System of membranes that produce an enormous
variety of molecules.
– Is composed of smooth and rough ER.
Smooth ER – lacks surface ribosomes
• Synthesizes: produces phospholipids, steroids and
hormones; metabolizes carbs (in the liver)
• Participates: in hydrolysis of glycogen (animal cells)
• Detoxifies: by chemically modifying drugs and
pesticides
• Stores and modifies: proteins made by ribosomes and
RER
• .
Rough ER
• The “roughness” of the rough ER is due to ribosomes
that stud the outside of the ER membrane.
• Formation:
– Synthesize: Proteins (made by ribosomes) enter RER
– Proteins are altered (folded or have other molecules
attached)
• Carbohydrates are attached to change function and
act as a “name tag” so the protein “knows” where to
go (usually to the membrane)
– Transports: vesicles containing proteins
Figure 4.11
The Golgi Apparatus
• The Golgi apparatus
– Works in partnership with the ER (modifies and
transports proteins).
– Refines, stores, and distributes the chemical
products of cells.
Figure 4.12
Parts of the Golgi
• Three distinct parts (top, middle and bottom):
• Bottom: cis region is close to nucleus/RER
• Receiving end
• Middle: cisternae is in between
• transport
• Top: trans region is close to surface of cell
• Exit end
Lysosomes
• A lysosome is a membrane-enclosed sac.
– It contains digestive (hydrolytic) enzymes.
– The enzymes break down macromolecules, digest food, and
break down damaged organelles.
- Examples:
- Autophagy - recycling of cell parts
- Phagocytosis by amoeba and macrophages
- Development
- Digestion of tadpole tail, webbing between fingers
- Tay-Sach's Disease
- lipid digestion enzyme is missing from lysosomes
and lipids accumulate in the brain
• Lysosomes have several types of digestive
functions.
– They fuse with food vacuoles to digest the food.
Lysosome Formation
Vacuoles
• Vacuoles are membranous sacs. There are three
types:
– Food vacuoles- contain food/water for cell
– contractile vacuoles of protists: used for
osmoregulation (pump water out of cell thru pore)
Paramecium Vacuole
• central vacuoles of plants:
– act as a reservoir of nutrients:
~toxic by-products
~waste products (with storage makes plant taste
bad and protects from predators!)
~nutrients/proteins/carbohydrates
– generate turgor
– aids in growth
Figure 4.14
Peroxisomes
• These organelles collect toxic peroxides which
are byproducts of chemical reactions
• Ex: hydrogen peroxide H2O2
• A review of the endo-membrane system
Figure 4.15
HOMEWORK DUE FRIDAY
Create a story about how 10 cellular organelles
worked together to complete a goal! Must
include functions.
Chloroplasts and Mitochondria:
Energy Conversion
• Cells require a constant energy supply to do all the
work of life.
Mitochondria
• Mitochondria are the sites of cellular respiration,
which involves the production of ATP from food
molecules.
– Found in most eukaryotes
Chloroplasts
• Chloroplasts are the sites of photosynthesis, the
conversion of light energy to chemical energy.
• Mitochondria and chloroplasts share another
feature unique among eukaryotic organelles.
– They contain their own DNA.
• The existence of separate “mini-genomes” is
believed to be evidence that
– Mitochondria and chloroplasts evolved from
free-living prokaryotes in the distant past.
Other features of Chloroplasts
• Plastids- an organelle only in plant cells and
some protists. They can differentiate into…
 Amyloplast- aka leukoplast (white/colorless)
plastid that converts glucose to starch. Found in
potatoes!
 Chromoplast- contain red, orange and/or yellow
pigments. Aid in pollination and seed dispersal
 Chloroplast- green pigment chlorophyll (light
energy converted to chemical energy)
The Cytoskeleton:
Cell Shape and Movement
• The cytoskeleton is an infrastructure of the cell
consisting of a network of fibers.
• Functions of the cytoskeleton
– provide mechanical support for the cell and
maintain its shape.
– Aids in cellular movement/change shape
– Positions organelles within the cell
– Act as tracks for other objects to move on
– Anchor the cell
Figure 4.18a
Microtubules
 Make the internal skeleton for cells and aid in
protein movement thru cell
Push/pull chromosomes to daughter cells
Make up cilia and flagella
Cilia and Flagella
• Cilia and flagella are motile appendages.
• Flagella propel the cell in a whiplike motion for
movement of whole cell.
• Cilia move in a coordinated back-and-forth motion
to
– move whole cell (unicellular)
– move materials past cell (multicellular).
Paramecium Cilia
Cilia and Flagella
• Some cilia or flagella extend from nonmoving
cells.
– The human windpipe is lined with cilia.
Microfiliments
• Help cell or parts to move
• Determine and stabilize cell shape
• Formed from actin (protein)
• EXAMPLES 
• Actin and myosin move your muscles
• Pinching to divide cells in mitosis
• Cytoplasmic streaming
Intermediate filiments
• 50 kinds!!
• Built of “ropes” of fibrous proteins
• Functions: Stabilize cell structure
• Make hair and fingernails
• Support microvilli of intestines
• These structures are build to resist tension
Centrioles
Produce mitotic spindle
Found in animal cells (plants lack these)
Composed of specialized microtubules
Membrane Structure
• The plasma membrane separates the living cell
from its nonliving surroundings.
• The membranes of cells are composed mostly of:
– Lipids
– Proteins
• The lipids belong to a special category called
phospholipids.
• Phospholipids form a two-layered membrane, the
phospholipid bilayer.
• Most membranes have specific proteins embedded
in the phospholipid bilayer.
Desmosomes
Gap Junctions
Tight Junctions
• Membrane phospholipids and proteins can drift
about in the plane of the membrane.
• This behavior leads to the description of a
membrane as a fluid mosaic:
– Molecules can move freely within the membrane.
– A diversity of proteins exists within the
membrane.
Evolution Connection:
The Origin of Membranes
• Phospholipids were probably among the organic
molecules on the early Earth.
• When mixed with water, phospholipids
spontaneously form membranes.
Cell Surfaces
• Most cells secrete materials for coats of one kind or
another
– That are external to the plasma membrane.
• These extracellular coats help protect and support
cells
– And facilitate interactions between cellular
neighbors in tissues.
• Plant cells have cell walls,
– Which help protect the cells, maintain their shape,
and keep the cells from absorbing too much
water.
• Animal cells have an extracellular matrix,
– Which helps hold cells together in tissues and
protects and supports them.
Cell Animation Video
CELL WALLS
 Extracellular structure that
 Provides support and limits water absorption
 Acts as a barrier to infection
 Maintains cell shape
 Found in plants, fungi, some protists and bacteria
Cellulose
Polysaccharides that form the fibers of the cell
wall
Plasmodesmata
Membrane lined channels
that run thru cell walls
connecting cells that are
side by side. Allow
movement of water, ions,
RNA etc
Primary cell walls Vs Secondary Cell wall
Primary Cell Wall
Secondary Cell Wall
First wall to develop in
growing/dividing cells
Develops after cell stops
growing/dividing
Acts as normal cell wall
with a few differences:
Acts as normal cell wall
AND
*flexible
*is thicker and stronger
*controls rate / direction /
shape of growth
*contains conducting
systems for nutrients and
water …evolutionary
advantage
Ex: wood
Primary cell walls Vs Secondary Cell wall
Extracellular Matrix
- Extracellular Matrix (animal cells)
- Types of Structures
- Collagen
- 1/4 to 1/2 of the protein inthe human
body) that provides strength
- Proteoglycans
- form the extracellular matrix (ECM)
- Integrins
- Integral proteins that transfer
signals in and out of the cell
- Fibronectins
- proteins that connect integrins to the
ECM
Junctions- like function junction!
All four junctions join cells together
Tight junctions Prevent passage of
material in space
btwn cells. Water
tight seal
 Block passage of
material btwn
lumen (apical side)
and interior of
tissue (basal side)
Junctions
Desmosomes- localized adhesions (proteins) to
resist shearing forces; keep animal cells
attached to each other.
Junctions
Gap junctions Allow passage of some small molecules in the
gaps between cells
Junctions
PlasmodesmataNarrow tunnels that connect two plant cells