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Chatper 4 – A Tour of the Cell
I. Intro
A. Cell theory - All living organisms are made of cells and
all cells came from other cells (how do we know?)
B. Cells are invisible to our eyes – need microscope
C. Cells are highly ordered and organized (city building
analogy)
II. Microscopes provide windows to the world of the cell
A. Two important aspects of microscope
1. Magnification
2. Resolution (resolving power)
a) Ability to tell 2 points apart as separate points
b) ex: If a microscope has a resolving power of 2um,
two points must be at least 2um apart to see them as
separate points. Any closer and they will look like one
point.
B. Three different types of microscopes – each with pluses
and minuses compared to others
1. Light Microscope (LM)
a) Pass visible light through specimen; lenses bends
light to magnify image to the human eye
b) 1000 to 2000X magnification limit
c) Great for observing living organisms
d) Micrograph – photo taken with any microscope
2. Scanning Electron Microscope (SEM)
a) Instead of light you bounce electrons off the
surface of the sample that has been coated with a
metal and use a computer to collect the bounced
electrons and generate an image.
b) 10,000 to 20,000X magnification
c) Great for showing the surface of organisms
d) Organism cannot be living (in a vacuum, etc…)
3. Transmission Electron Microscope (TEM)
a) Take a thin slice of specimen and hit with electrons
b) Electrons are bent just like light in LM, but by
using magnetic lenses
c) 100,000 – 200,000X magnification
d) Great for showing internal cell structures
(specimen is dead – vacuum).
III. Cell sizes vary with their function (structure-function
relationship again!)
A. Need to use smaller units when discussing cells –
discuss going from mm to um to nm
B. Nerve cells – signal transduction across great distances
(electrical wires)
C. Bird Eggs (Ostrich especially)- nutrient storage
(ovalbumin)
D. Blood Cells – surface area for gas exchange, fit through
capillaries
IV.
Natural Laws Limit Cell Size
A. Maximum - Large cells have a smaller ratio of surface
area to volume than small cells (small house vs. large
house analogy). Not enough surface area to get nutrients
from outside!!
B. Minimum – need to be able to hold all the things
necessary to live (DNA, proteins, internal structure, etc…)
Nanoarchaeum equitans – 400nm diameter
V. Two very different cell types have evolved –
prokaryotic and eukaryotic
A. Prokaryotic cells – small and structurally simple –
bacteria and archaea
1. Small - .5 to 10um in length (.0005 to .01mm or 1/100th
of mm)
2. No nucleus – DNA is in the cytoplasm in a distinct
“nucleoid” region
3. Ribosomes – found in semifluid– machines that
assemble amino acids into polypeptide chains
4. Plasma membrane – surrounds the contents of the
cells, separating is from outside world (skin) – made of
phospholipids
5. Prokaryotic cell wall – rigid, protective covering, made
of amino acid/monosaccharide polymer called
peptidoglycan
6. Capsule – found around some prokaryotes – sticky
outer protective coat (made of carbohydrates)
7. Some prokaryotes have projections
a) Pili – assist in surface attachment
b) Prokaryotic Flagella – swimming
B. Eukaryotic cells – animals, plants, fungi, protests (a city)
1. Much larger than prokaryotic cells (10 to 100um in
width or .01 to .1mm – 1/100th to 1/10th of a mm)
2. DNA enclosed in a special membrane called the
nucleus
3. More complex than prokaryotes
4. cytosol – fluid region of the cell between nucleus and
plasma membrane
5. Cytoplasm – cytosol plus organelles
6. Organelles – structures within the cell having
specialized function – membranous and nonmembranous
a) Membranous – nucleus, ER, golgi apparatus,
mitochondria, lysosomes, peroxisomes and others
(1) Compartments, each can maintain conditions that
are different than the others for cellular metabolism
(reactions in the cell) – different offices in the same
building doing different jobs simultaneously
(2) Increases membrane surface area
b) Non-membranous – ribosomes, microtubules,
centrioles, flagella, cytoskeleton and others
(disputed!)
7. Plant cells have similar organelles as animal cells
except:
a) Plant cells DON’T have lysosomes or centrioles
and usually don’t have flagella
b) Animal cells don’t have rigid cell walls like plant
cells or chloroplasts
VI.
Organization of the Eukaryotic Cell
A. The nucleus is the cell’s genetic control center
1. DNA – a parts list, instructions on how to combine
amino acids to make every protein in the cell.
2. Chromatin – nuclear DNA does not hang alone, its
attached to different proteins, forming long fibers
3. Chromosome – each fiber
4. Nuclear Envelope – double-membrane with nuclear
pores (holes/gates) that control what comes in and out
(you need a pass to enter and exit).
5. Nucleolus – Dense region of chromtin, proteins and
RNA where ribosome components are made (factory for
ribosome parts).
B. Overview: Many cell organelles are related through the
endomembrane system
1. Endomembrane system – composed of the different
membranes that are suspended in the cytoplasm within a
eukaryotic cell.
a) the nuclear envelope, the endoplasmic reticulum,
the golgi apparatus, vacuoles, vesicles, and the cell
membrane.
2. compartmentalize the cell into various membranous
organelles
3. protein trafficking, digestion, etc…
a) Endoplasmic reticulum (ER) – two flavors: rough
and smooth – continuous with nuclear envelope
(1) Rough ER – interconnected, flattened sacs
studded with ribosomes
(a) New membrane for other organelles
(b) Ribosomes make polypeptides that snake into the
ER. ER is the way out of the cell. Many of these
proteins are destined to be secreted from the cell
(antibody, digestive proteins, etc…) (mail system)
(c) Glycoprotein
(d) Transport vesicle
(e) functions
(i) lysosomal enzymes, secreted proteins,
membrane proteins
(2) Smooth ER – variety of functions, continuous
with rough ER, but no ribosomes.
(a) Site of lipid synthesis – fats, steroids,
phospholipids (remind – enzymes within at work
here, not membrane part)
(b) In liver – helps to regulate amount of sugar
released into blood, break down drugs/toxins
(i) Exposure to drugs tells liver cells to
increase amount of smooth ER and its
detoxifying enzymes within – drug
resistance (barbiturate – antibiotic problem)
(c) Calcium storage – needed for muscle contraction
b) Golgi Apparatus – modifies, sorts, and ships
proteins/membrane to appropiate places in the cell.
(1) Series of flattened sacs separate from ER
(2) Molecular warehouse and shipping factory
(outgoing mail room)
(3) Receives transport vesicles from ER on the
“receiving side”, chemically modifies glycoproteins,
then ships to proper destination from the “shipping
side”.
c) Lysosomes – “break down body” – contains
hydrolytic digestive enzymes –pH 4.8 compared to 7.2
of cytosol
(1) digest the cells food/recycle old
organelles/apoptosis (programmed cell death)
(2) Produced by rough ER and golgi
(3) Fuse with food vacuoles, help destroy bacteria
(don’t engulf bacteria – too large – find video of
this!), recycling of damaged organelles – break to
monomers and release, apoptosis
d) Abnormal lysosomes can cause fatal disease
(1) Lysosomal storage diseases – hereditary –
impedes enzyme function of lysosome – missing an
enzyme, lysosomes fill up with stuff they can’t digest
(2) Most fatal in childhood
(3) Pompe’s disease – accumulation of glycogen –
lack glycogen-digesting enzyme.
(4) Tay-Sachs – destroys nervous system – lack lipiddigesting enzyme, nerve cells damaged by excess
lipids – show video
e) Vacuoles function in the general maintenance of
cells.
(1) Different shapes and sizes, variety of functions
(a) Store excess water, waste, other chemicals, food
(b) Generally larger than vesicles
(2) Central Vacuole in plants –
(a) can act as a large lysosome (plants don’t have
typical lysosomes)
(b) or absorb water to increase cell volume, store
chemicals or waste products
(3) Contractile Vacuole – collects excess water from
cell and expels it to outside
(a) Found in paramecium and other freshwater
protests (freshwater fish don’t drink)
f) A review of the endomembrane system
VII. Energy-Converting Organelles
A. Chloroplasts (plants and eukaryotic algae) – converts
solar energy to chemical energy
1. Double-membrane
2. Site of photosynthesis
3. Structure-function – light captured on grana and
chemical reactions that form food-storage molecules
occur in stroma.
B. Mitochondria harvest chemical energy from food –
found in ALL eukaryotic cells with rare exception
(including plants!!!)
1. Double membrane
2. Site of Cellular Respiration – conversion of unusable
chemical energy (sugar) into usable chemical energy
(ATP). (crude oil to gasoline – sort of)
VIII. The Cytoskeleton and Related Structures
A. The cell’s internal skeleton helps organize its structure
and activities
1. Supportive structure of protein fibers (steel framework
of building, “bones of the cell”)
2. Involved in cell movement
3. Vesicle trafficking
4. 3-flavors of protein fibers
a) Microfilaments – thinnest – solid rods – double
chain of actin proteins
flexible, strong, movement
b) Microtubules – thickest – hollow tubes of globular
proteins – tubulins
(1) Anchor organelles
(2) Conveyor belts for vesicles and organelles
(3) Basis of ciliary and flagellar movement
c) Intermediate filaments – ropelike strands of
fibrous proteins
B. Cilia and Flagella move when microtubules bend
1. Cilia – short, numerous, hair-like projections involved
in propulsion
2. Flagella – longer, fewer in number, less complexly
organized
3. Both are small extension of the plasma membrane
surround a complex microtubule arrangement.
a) Function to move whole cells or to move materials
across the surface of or into cells (show examples)
4. Basal Body – anchors the microtubule or cilia at the
base/ foundation for growth – similar construction to
centrioles
5. Dynein arms - protein knobs attached to each
microtubule doublet – held in place, grab, push up
a) Using ATP, exert a force which causes tubules to
bend
IX.
Eukaryotic cell surfaces and junctions
A. Cell surfaces protect, support, and join cells
1. Singled celled organisms – plasma membrane too
weak to interact directly with environment, capsule and
cell wall covering of prokaryotes
2. Plants – cell wall – 10 to 100X thicker than plasma
membrane, also protect and support cells (how plants can
stand upright without skeletons), and involved in joining
neighboring cells – sticky polysaccharide glue
a) Cell wall is a mixture of polysaccharides
(predominantly cellulose) and proteins – multilayered
b) Plasmodesmata – channels through PM and cell
wall connecting cytoplasm of one cell to the adjacent
cell in plants – circulatory and communication system
3. In animals, cells are usually covered with sticky layers
of polysaccharides and proteins, not too supportive
though (Extracellular matrix ECM)
4. Cell junctions in animal tissues – structures
connecting one cell to another – 3 flavors
a) Tight Junctions – leak proof barriers (rain coat)
b) Anchoring Junctions – attach cells to each other,
but allow passage of materials between cells (cotton
shirt) or attach cells to an extracellular matrix (sticky
layer of glycoproteins which cells are embedded in)
c) Communicating Junctions – channels between cells
for the movement of small molecules
X. Functional categories of organelles
A. Eukaryotic organelles comprise four functional
categories
1. GENERAL FUNCTION : MANUFACTURE and
TRANSPORT
a) Nucleus
b) Ribosomes
c) Rough ER
d) Smooth ER
e) Golgi Apparatus
2. GENERAL FUNCTION : ENERGY PROCESSING
a) Chloroplasts
b) Mitochondria
3. GENERAL FUNCTION : BREAKDOWN
a) Lysosomes
b) Peroxisomes
c) Vacuoles
4. GENERAL FUNCTION: SUPPORT, MOVEMENT, AND
COMMUNICATION BETWEEN CELLS
a) Cytoskeleton
b) Cell Walls
c) Extracellular Matrix
d) Cell Junctions
XI. Extraterrestrial life forms may share features with
life on Earth
A. All life-forms on Earth share fundamental features – cell
theory
1. Consist of highly structured units called cells,
membrane bound and separate from environment
2. Have DNA as genetic material
3. Carry out metabolic processes
B. These features are likely to be characteristic of other life
in our universe, the materials might be different