Cells
Levels of Organization
•
•
•
•
•
•
Chemical (Least complex)
Cellular
Tissue
Organ
Organ System
Organism (Most complex)
History
• 1600’s Anton Van Leeuwenhoek - first to view
nature w/microscope
• 1665 Robert Hooke - Coined term ‘cells’
• 1838 Matthias Schleiden - ‘All plants are made of
cells’
• 1839 Theodor Schwann - ‘All animals are made
of cells’
• 1855 Rudolf Virchow - ‘All cells come from preexisting cells’
Cell Theory
• Schleiden and Schwann 1840.
• All living things are made of cells.
• New cells are produced from existing
cells.
• Cells are the basic units of structure and
function of all living things.
Two types of cells.
• Prokaryotic cells make up prokaryotes.
• Eukaryotic cells make up eukaryotes.
• Prokaryotes: No nucleus, genetic material in
cytoplasm, only organelle = ribosomes, smaller,
simpler, unicellular evolutionarily more ancient
• Eukaryotes: Have nucleus, larger, more complex,
more organelles, evolutionarily more modern.
Basic Cell Structures
• Most prokaryotes (bacteria) difficult to see
with light microscope
• All cells have cell membrane, cytoplasm,
genetic material and ribosomes
• Presence of other cells structures
(organelles) varies
Describing Cell Structures
• Include:
– Structure: describes the shape and smaller
component parts of the organelle
– Location: Nucleus, cytoplasm or cell
membrane, sometimes more specific
– Function: what does it do and how does it do
it
Cell Membrane
• Is a phospholipid bilayer with some
proteins & carbohydrates associated
with it.
• Integral proteins form channels &
pumps to pass substances across the
membrane.
• Represented by the “Fluid Mosaic
Model”.
Cell Membrane Picture
Cell Membrane Functions
• Controls what goes in and out of the
cell.
• Proteins are unique within species and
individuals and therefore serves as a
form of cellular identification.
• Encloses cell contents and separates
from the extracellular space.
• Support & Protection?
Cytoplasm
• A watery gel in which all the organelles
reside
• The site of multiple enzyme controlled
chemical reactions.
• Polar compounds go into solution while
non-polar compound remain suspended
Enzymatic Regulation of Cells
•
•
•
•
Enzymes are biological catalysts.
Enzymes are proteins
Speed up the rate of chemical reactions
Enzyme Action Effected By:
– pH
– Temperature
– concentration
Cell Wall
• When present is exterior to the cell
membrane.
• Made primarily of cellulose and provides
significant support and protection to the
cell.
• Not present in animal cells.
Cell Wall Picture
Nucleus
• Spherical shape which can be seen with
an ordinary light microscope.
• Contains nucleolus & chromatin
• Controls all cell functions by controlling
protein synthesis and hereditary blueprint.
• Surrounded by a nuclear envelope - a
double membrane layer with pores.
Nucleus
• Nucleolus - a dense area where
ribosome production begins.
• Contains DNA bound to histone
proteins. The complex is called both
chromatin and chromosomes depending
on the stage of the cell cycle and the
function it is performing.
Nucleus Picture
Organelles
•
•
•
•
•
•
•
•
•
•
“Little organs” including:
Ribosomes
Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Vacuoles
Chloroplasts
Mitochondria
Centrioles
Cytoskeleton
– (Microfilaments & Microtubules)
Ribosome Picture
Ribosomes
• Structure: “B” shape, smallest
organelle, made of RNA & protein
• Location: Cytoplasm (Free) or surface
of rough endoplasmic reticulum (Fixed)
• Function: AA joined on surface = site of
protein synthesis
Ribosome S.L.F.
•
•
•
•
•
Consisting of a large and small subunit.
Made of rRNA and protein
The smallest organelle.
Can be attached to R.E.R or free.
Site of protein assembly, AA chemically
bonded together here (10 Structure)
Endoplasmic Reticulum
(R.E.R. & S.E.R.) Pictures
Rough Endoplasmic
Reticulum
• A flat & folded internal membrane maze
• In the cytoplasm usually close to the
nucleus.
• Modifies & transports proteins.
• Assembles & transports cell membrane
parts.
Smooth Endoplasmic
Reticulum
• Does not have ribosomes attached.
Golgi Apparatus Picture
Golgi Apparatus S.L.F.
• Stacks of individual enclosed
membranes wider than E.R.
• Located in the cytoplasm
• Assembles & packages lipoproteins
• Binds carbohydrates to proteins
Lysosomes Picture
Lysosomes S.L.F.
•
•
•
•
Found in the cytoplasm
Contains digestive enzymes
Digests food particles
Catabolism of waste & worn out cell
parts
Vacuoles S.L.F.
• Various sac-like shapes in cytoplasm
• Large in plant cells
• Stores water, proteins, carbos, salts
• The term ‘vesicle’ is used for a vacuole
with a transport function.
Vacuoles Picture
Chloroplast Picture
Chloroplast S.L.F.
• Contains maternal DNA, remnants of
photosynthetic prokaryotic ancestors
• Found in plants of course but also in
some protists.
• Captures the energy from sunlight to
transform carbon dioxide and water into
sugars and oxygen.
Mitochondrion Picture
Mitochondria
• Structure: Contains maternal DNA, Kidney
shape, double folded inner membrane
• Location: Cytoplasm
• Function: Aerobic Cellular Respiration =
Converts food energy into a form of energy
(ATP) the cell can use.
• Special: Are remnants of aerobic prokaryotes
as explained by the endosymbiotic theory
Centrisome Picture
Centrisome S.L.F.
• Term centrisome refers to a set of two
centrioles in a cell.
• 2 centrioles arranged at 900 angles to each
other, made of microtubules in a cylindrical
shape grouped in 9 bunches of 3.
• Aids in cell division as part of the mitotic
spindle.
• Only present in animal cells.
Cytoskeleton
Microtubules
Microfilaments
• Long hollow structures
found at the base of
cilia & flagella and acts
as a rigid lever like
bone aiding cilia &
flagella movement.
Serves to maintain cell
shape as well as be a
track for transport of
organelles.
• Found in the
cytoplasm and
made of actin &
myosin
proteins.Contractile
ability. Part of
cleavage furrow.
When attached to
microtubules causes
movement of cilia &
flagella.
Cytoskeleton
Microtubules & Microfilaments
Pictures
Microtubules
• Structure: long, slender, made of tubulin
proteins with 2 in the middle surrounded
by 9.
• Location: throughout cytoplasm, also at
base of cilia and flagella
• Function: part of mitotic spindle,involved
in movement of cilia & flagella, transport
track
Microfilaments
• Structure: long, slender, made of actin
and myosin proteins
• Location: cytoplasm & base of cilia &
flagella
• Function: contracts like muscle so aids in
the movement of cilia, flagella and cell
division by forming a cleavage furrow,
structure and support of the cell
Other
• Flagella - in humans only found in sperm
• Barr body - the second X chromosome in
females only which is inactivated
Cilia
Cilia Picture
Flagella Picture
Flagella
Cilia & Flagella Structure
Eukaryotic Cilia S.L.F.
• Structure - 2 to 20um long, 9 double
microtubules around 2, usually many in
one cell, .25um diameter
• Location – protruding from cell, but
covered by plasma membrane
• Function – locomotion or movement of
liquids or particles in fixed cells, signal
antenna
Eukaryotic Flagella S.L.F.
• Structure – same as cilia except only 1
or 2 per cell if present, but longer (10 to
200um)
• Location – protruding from cell, but
covered by plasma membrane
• Function – locomotion
The Cell as a Factory
• Cell Membrane - gate security
• Nucleus - C.E.O. office
– Chromosomes = secret recipe
• Cytoskeleton - building supports
• Vacuoles (Vesicles) - raw material storage
and distribution
• Ribosomes - assembly line machinery
• Lysosomes - waste removal system &
cleanup
• Mitochondrion - main power source
• Chloroplasts - power source in ‘green’ plants
• ER - product modification and transport
• Golgi - product packaging
Part 2
Movement Across the Cell Membrane
• The cell membrane is a selectively permeable (semi-permeable) membrane.
• Many large molecules cannot cross.
• Many charged molecules cannot cross.
• Some non-lipid soluble molecules cannot
cross.
Movement Across the Cell Membrane
• Active Transport Mechanisms
– Require energy (A.T.P.)
– Move against a concentration gradient
• Passive Transport Mechanisms
– Do not require energy
– Moving with a concentration gradient
Movement Across the Cell Membrane
• Active Transport Mechanisms
– Endocytosis
• Phagocytosis - cell eating or engulfing solids
• Pinocytosis - cell drinking or engulfing liquid
– Exocytosis
– Protein Pumps
• Passive Transport Mechanisms
– Diffusion
– Osmosis
– Facilitated Diffusion
Movement Across the Cell Membrane
• Diffusion - driven by the movement of
particles in a gas or liquid state from an area
of higher concentration to an area of lower
concentration
• Osmosis - diffusion of water across a semipermeable membrane
• Facilitated Diffusion - movement of particles
down the concentration gradient with the help
of integral proteins in the cell membrane
Tonicity
• Isotonic - an equal concentration of
solutes both in and outside a cell
• Hypertonic - a solution with a greater
concentration of solutes in relation to
another
• Hypotonic - a solution with a lower
concentration of solutes in relation to
another
Tonicity in Cells
• Hypertonic - term used when the extracellular
solute concentration is greater than the cell
resulting in movement of water out of the cell
causing cell shrinkage or crenation
• Hypotonic - term used when the extracellular
solute concentration is less than the cell
resulting in movement of water into the cell
causing cell swelling
Fluid Balance - Homeostasis
• All living things function best in a narrow
range of conditions.
• Living things have mechanisms to
maintain a stable internal environment
• Examples: temperature, pH, water
content
• All living things need water
Water Balance
• In plants, water balance is often
controlled by: stoma, waxy cuticle,
shape, size
• In complex organisms like humans
water balance is primarily influenced by
water intake versus water loss but,
there are several regulating
mechanisms that control this balance.
Water Regulation
• Sweating, respiration, excretion = loss
• Hypothalamus detects [H2O] in the blood.
• Antidiuretic hormone (ADH) released and
kidneys decrease water removal from the
blood & loss in urine.
• Thirst mechanism
• Increased [H2O] in blood decreases [ADH]
and water removal from blood by kidneys
increases again. (Negative Feedback Loop)
Specialized Cell Types
• Differentiated cells contribute to the function
of the organism as a whole.
• Unicellular organisms must perform all the
activities associated with life
• Multicellular organisms are more complex &
interdependent because individual cells
perform only specific functions for the good of
the whole organism.
Examples of Specialized Cells
• Nerve Cells (Neurons) - carry messages
in the form of an electrochemical signal
• Pancreas Cells - some secrete insulin
and some secrete peptidase, amylase
or lipase
• RBC - have hemoglobin to carry oxygen