Chapter 4
Studying Cells
• Scientists are limited to studying that
which they can see or document
• Observation is Key
‘Cells’ or ‘Compartments’
Compound Light Microscope
Scanning Electron
Microscope (SEM)
• Different types of
microscopes
Unaided eye
Electron Microscopes
– Can be used to
visualize different
sized cellular
structures
Transmission Electron
Microscope (TEM)
1
The Three Domains of Life
3.
1.
Domain
Kingdom
Phyla
Class
2.
DOMAIN ARCHAEA
Order
Family
The metric system
Prokaryotes and Eukaryotes
• Bacteria and Archaea are comprised of
prokaryotes, single-celled organisms with
prokaryotic cells
• Eukarya
Genus
Species
Generalized
Prokaryotic Cell
Generalized
Eukaryotic
Animal Cell
– Eukaryotes: plants, animals, fungi, protists
Prokaryote and
Eukaryote to Scale
Prokaryotic Cell Structure
2
Eukaryotic Cell Structure: A
Generalized Animal Cell
All Cells: Cell Membranes
Structure: phospholipid bilayer
The phoshpolipid bilayer has a
hydrophobic region and a
hydrophiliic region
• Contains lipids as well as
embedded membrane proteins
that have a wide variety of
functions
Eukaryotic Cell Structure: A
Generalized Plant Cell
All Cells: Plasma Membrane
Chemist’s version
Biologist’s version
Sesame Street
version
Extracellular
environment
H20
cytoplasm
Phospholipid bilayer
Membrane Proteins
Function:
• Boundary separating living cell from its nonliving
surroundings
• Regulates traffic of molecules entering and
exiting the cell
– Selectively permeable
• Contains lipids as well as MEMBRANE
PROTEINS that have a wide variety of functions
3
Membrane Proteins have a variety
of functions
Cytoplasm
Fibers of
extracellular
matrix
Fluid Mosaic Model
• Membrane phospholipids and membrane
proteins can drift laterally in the membrane
c Enzymatic activity
b Cell signaling
• Diversity of membrane proteins
a Attachment to
cytoskeleton and
extracellular
matrix
e Intercellular
joining
d Transport
f Cell-cell
recognition
Cytoplasm
Cytoskeleton
Figure 4.8
Examples of membrane proteins:
Outside of cell
DOPAMINE
+
1. Membrane Receptor Protein:
very specifically binds a ligand, which
can be: a hormone, a neurotransmitter,
a drug, anything that functions as a
‘signal
2. Membrane Transport Protein:
very specifically allows an ion,
nutrient, etc, to pass from outside of
the cell to inside of the cell (or vice
versa)
+
Inside of cell
Cell Walls: Plants, fungi,
prokaryotes
• Structure of plant cell walls
– Matrix of strong cellulose fibers embedded in
other polysaccharides and protein
• Function
– Provides rigidity, structure, protection from
environment
•Fungal cell walls and bacterial cell walls
contain some different building blocks
Plant Cell Walls: Cellulose
Glucose
monomer
Starch granules in
potato tuber cells
Plant Cell Walls
• Plant Cell Walls
have channels,
plasmodesmata
(a) Starch
Glycogen
Granules
In muscle
tissue
(b) Glycogen
Cellulose fibril in
a plant cell wall
• Allows for sharing
of the cytosol
between cells:
water, nutrients,
hormones, etc.
Cellulose molecules
(c) Cellulose
4
Cell Wall as Drug Target
• What is the mechanism of action of penicillin?
• How does penicillin kill bacteria, and not
humans?
• What is specific about a bacterial cell wall?
Cell Wall as Drug Target
• Penicillin specifically inhibits the formation of
BACTERIAL cell walls
– Penicillin inhibits the cross-linking of peptidoglycan in
bacterial cell walls FYI
Oh no, penicillin!!!! It
prevents me from
making a cell wall!!!
What is INSIDE of Eukaryotic
Cells?
• Numerous organelles and structures
– Some have their own lipid membrane
– Some do not
– Some have 2 lipid membranes!!
Oh no, penicillin!!!! It
prevents me from
making a cell wall!!!
The Nucleus: Genetic Library of
the Cell
• Stores and transmits genetic
information, DNA
• DNA is organized into
discrete chromosomes
DNA
• The nucleus contains most of
the genes in the
eukaryotic cell
• DNA is the blue-print for RNA
and thus protein
Chromatin= DNA plus small,
associated proteins
DNA is stored like thread on a
spool
Chromosome=one long fiber,
or thread of DNA
The nuclear envelope
– A double membrane that encloses the
nucleus, separating its contents from the
cytoplasm
Nuclear
– Pores
Envelope
Pores
Humans have
46
chromosomes
5
The nucleolus
• Found within the
nucleus
• Site of ribosomal RNA
(rRNA) synthesis, the
major component of
ribosomes
All cells: Ribosomes
Ribosome ‘dots’ are actually a multisubunit
complex of RNA and protein
• Function: The ‘workbench’ upon which
proteins are assembled
• Can be free floating or attached to the ER
• Structure: depicted as
‘dots’ in every text book
Ribosome ‘dots’ are actually a multisubunit
complex of RNA and protein
1. DNA is copied to
RNA in the nucleus
2. RNA exits the
nucleus and
attaches to a
ribosome
3. At the ribosome,
RNA is converted
into protein
X
Bacterial ribosomes are made of slightly different
components than eukaryotic ribosomes.
Ribosomes are a drug target
Specificity: drug is toxic only to invader and not host
Chloramphenicol, Erythromycin, Tetracycline, Streptomycin
all work by specifically inhibiting bacterial ribosome function
6
Eukaryotic Cells: Endoplasmic
Reticulum (ER)
Structure: a connected
network of membranous
sacs and tubes
Endoplasmic Reticulum (ER)
• Rough ER
• Smooth ER
•Double membrane
•Continuous with the
nuclear envelope
(part of the Endomembrane System)
Rough Endoplasmic Reticulum (rER)
• Structure: ‘Rough’ surface is
studded with ribosomes
• Functions
• site of membrane
production
• site of membrane-protein
production
• Site of secreted protein
production
• Protein modification
(part of the Endomembrane System)
Golgi Apparatus
• Structure: a stack of flattened,
membranous sacs
• Function:
– Site of some ‘refinery’ of ER
products
• Importantly, a site of sorting!!
(part of the Endomembrane System)
Smooth Endoplasmic Reticulum
(sER)
• Structure: smooth, membranous sacs
• Function:
– Site of lipids, phospholipids, steroids
synthesis
– Carbohydrate metabolism
– Detoxifies drugs and poisons
(part of the Endomembrane System)
Golgi Apparatus
•The ER, the Golgi & the plasma
membrane are ‘connected’ via
membrane bound vesicles, shuttles
•Vesicles are received on one side
of the stack and exit at the other side
•Proteins leaving the Golgi now
contain ‘sorting information’ like a
zip-code
(part of the Endomembrane System)
From ER
•The Golgi receives vesicles
containing membrane and secreted
proteins
To final destination,
carried in a vesicle
7
Interconnectedness of the
Endomembrane System
CARGO TO THE
PLASMA MEMBRANE
VESICLE
LYSOSOME
Lysosomes
Lysosomes
• Structure: Membrane bound sacs of
digestive enzymes that bud from the Golgi
• Function:
– digest food, or ingested matter
– Recycling of components
• The fusion of a lysosome with other
vesicles usually activates the ‘recycling’
function
1. Invagination of the phospholipid
membrane, endocytosis
1.
2. Pinching off of new vesicle
LYSOSOME
2.
e
ran
mb
me
LYSOSOME
3. Fusion of vesicle w/Lysosome
3.
+
(part of the Endomembrane System)
ACTIVE LYSOSOME
Vacuoles
• Structure: Large vesicle
• The Central Vacuole is a
prominent organelle in plants
and some protists
• Function: storage of water,
nutirents, toxins
(part of the Endomembrane System)
8
How does a cell ‘get’ usable energy
to do work?
• Mitochondria: the power plant,
sites of cellular respiration
carbs/sugars and fats → ATP
Mitochondria
• Structure: enclosed by two membranes
– A smooth outer membrane
– An highly folded inner membrane folded into
cristae
Mitochondrion
Intermembrane space
• Chloroplasts: the solar panels,
sites of photosynthesis (in
plants and algae)
solar energy → sugars
Outer
membrane
-Divide and reproduce by
themselves and have their
own DNA!
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 µm
The Chloroplast
Plastids
– Structure: Chloroplasts are also enclosed by two
membranes, with an intermembrane space
– Found in leaves and other green parts of plants
algae, and photosynthetic protists
– Specialized plasmid containing chlorophyll,
enzymes and other molecules for photosynthesis
• A family of related membrane bound plant
organelles
• Chloroplasts, chromoplasts, and
amyloplasts
Chloroplast
Chloroplast
Origins of Mitochondria and
Chloroplasts
Chromoplast
Amyloplast
Endosymbiosis
• Would you believe that a
mitochondria may have once
been lunch for another cell?
• What would happen if a
mitochondria took up
residence in the host, instead
of being digested apart?
[Greek, endon = within + syn = together + bios= life] The close
association of two organisms, one of which lives inside the other.
9
Cell Structure, Infrastructure
Cytoskeleton: Microtubules
• Structure: dynamic, hollow tubes, comprised of
tubulin subunits
• Found in Eukaryotic cells
Courtesy: Dr Mark Kerrigan, Dr Andrew Hall & Linda Sharp, Membrane Biology Group, School of Biomedical and Clinical Laboratory
Sciences.
Cytoskeleton: Microtubules
Function:
– Provide shape and support to cell
– The ‘roads’ or tracks for motor proteins
– vesicle travel: neurotransmitter,membrane receptors,
secreted proteins
– Chromosome separation during cell division
– Components of cilia and flagella
In class demo
In class demo
• Clear your throat
• Ahemmm.
Functions of MTs
• Clear your throat
• Clear your throat again, and notice what
happens next
• You swallowed!
• Foreign particles sent to stomach for
destruction!
• Cilia in windpipe
10
Intercellular junctions in animal
cells
• Tight junctions =tight seal across layer of
cells
Intercellular junctions in animal
cells
• Tight junctions =tight seal across layer of
cells
URINE-TO-BE, in kidney tubule
CAPILLARY
Intercellular junctions in animal
cells
• Anchoring junctions=
fasteners, create
strong sheets of cells
• Communicating junctions:
– specialized pores, through which ions, sugars,
amino acids may pass
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