Chapter 6
A Tour of the Cell
Size of a Nanometer demo
• http://learn.genetics.utah.edu/content/c
ells/scale/
• Glucose = .9 nm
• Ribosome = 30 nm
• Mitochondria = 4000 nm long
• Skin Cell = 30,000 nm long = 30 um
• 1000 nm = 1 um
Light Microscope - LM
• Uses visible light to illuminate the
object.
• Relatively inexpensive type of
microscope.
• Can examine live or dead objects.
Resolution
• Ability to detect two discrete points as
separate from each other.
• As Magnification increases, Resolution
decreases.
• LM working limits are100 - 1000X.
Limitations - LM
• Miss many cell structures that are
beyond the magnification of the light
microscope.
• Need other ways to make the
observations.
Light Microscope Variations
• Fluorescence: uses dyes to make parts
of cells “glow”.
• Phase-contrast: enhances contrasts in
density.
• Confocal: uses lasers and special
optics to focus only narrow slides of
cells.
After
Before
Electron Microscopes
• Use beams of electrons instead of light.
• Invented in 1939, but not used much
until after WWII.
• Electron beam scans surface of the sample, exciting
electrons which have their signals detected by a device that
translates the pattern of electrons into an electronic signal
to a video screen.
TEM – tracheal
cell, long cilia were
cut longitudinally,
others cut to reveal
cross section
SEM rabbit
trachea
covered in cilia
Advantages
• Much higher magnifications.
• Magnifications of 50,000X or higher are
possible.
• Can get down to atomic level in some
cases.
Disadvantages
•
•
•
•
Need a Vacuum.
High cost of equipment.
Specimen preparation.
Specimen must be dead
Other Tools for Cytology (study of
Cells)
• Cell Fractionation – break the cell apart
and separate out the pieces based on
their density.
Cell Fractionation
History of Cells
• Robert Hooke - Observed cells in cork.
• Coined the term "cells” in 1665.
• 1833 - Robert Brown, discovered the
nucleus.
• 1838 - M.J. Schleiden, all plants are
made of cells.
• 1839 - T. Schwann, all animals are
made of cells.
Cell Theory
• All living matter is composed of one or
more cells.
• The cell is the structural and functional
unit of life.
• All cells come from cells.
• http://www.youtube.com/watch?v=mF9
U5x6Nxnw
Types of Cells
• Prokaryotic - lack a nucleus and other
membrane bounded structures.
• Eukaryotic - have a nucleus and other
membrane bounded structures.
Both Have:
• Membrane
• Cytoplasm
• Ribosomes (but the size is different)
Prokaryotic
Eukaryotic
Nucleus
Eukaryotic
Prokaryotic
Basic Cell Organization
•
•
•
•
Membrane
Nucleus
Cytoplasm
Organelles
Animal Cell
Plant Cell
Membrane
• Separates the cell from the
environment.
• Boundary layer for regulating the
movement of materials in/out of a cell.
Cytoplasm or Cytosol
• Cell substance between the cell
membrane and the nucleus.
• The “fluid” part of a cell.
• Composed of water, dissolved salts and
organic molecules (molecules that
contain Carbon, dissolved proteins, and
the cytoskeleton)
Organelle
• Term means "small organ”.
Formed body (or compartment) in a cell
with a specialized function.
• Important in organizational structure of
cells.
Organelles - function
• Way to form compartments in cells to
separate chemical reactions.
• Keeps various enzymes separated in
space.
You must be able to:
• Identify the major organelles
• Give their structure
• Give their function
Nucleus
• Most conspicuous organelle.
• Usually spherical, but can be lobed or
irregular in shape.
Structure
•
•
•
•
Nuclear membrane
Nuclear pores
Nucleolus
Chromatin
Nuclear Membrane
• Double membrane separated by a 2040 nm space.
• Inner membrane supported by a protein
matrix which gives the shape to the
nucleus.
Nuclear Pores
• Regular “holes” through both
membranes.
• 100 nm in diameter.
• Protein complex gives shape.
• Allows materials in/out of nucleus.
Nucleolus
• Dark staining area in the nucleus.
• 0 - 4 per nucleus.
• Ribosomes are made here
Chromatin
• Chrom: colored
• - tin: threads
• DNA and Protein in a “loose” format.
Will form the cell’s chromosomes.
Nucleus - Function
• Control center for the cell.
• Contains the genetic instructions.
Ribosomes
• Structure: 2 subunits made of protein
and rRNA. No membrane.
• Function: protein synthesis.
Subunits
• Large:
• 45 proteins
• 3 rRNA molecules
• Small:
• 23 proteins
• 1 rRNA molecule
Locations
• Free in the cytoplasm - make proteins
for use in cytosol.
• Membrane bound - make proteins that
are exported from the cell.
Endomembrane System
• Membranes that are related through
direct physical continuity or by the
transfer of membrane segments called
vesicles.
Endomembrane System
Endoplasmic Reticulum
• Often referred to as ER.
• Makes up to 1/2 of the total membrane
in cells.
• Often continuous with the nuclear
membrane.
Structure of ER
• Folded sheets or tubes of membranes.
• Very “fluid” in structure with the
membranes constantly changing size
and shape.
Types of ER
• Smooth ER: no ribosomes.
• Used for lipid synthesis,
carbohydrate storage, detoxification
of poisons/drugs. Stores Ca ions
• Rough ER: with ribosomes.
• Makes secretory proteins.
Golgi Apparatus
• Structure: parallel array of flattened
cisternae. (looks like a stack of Pita
bread)
• 3 to 20 per cell.
• Likely an outgrowth of the ER system.
Function of Golgi Bodies
• Processing - modification of ER
products (proteins for secretion).
• Distribution - packaging of ER products
(proteins for secretion) for transport.
Vesicles
• Small sacs of membranes that bud off
the Golgi Body.
• Transportation vehicle for the modified
ER products.
Lysosome
• Single membrane.
• Made from the Golgi apparatus.
Function
• Breakdown and degradation of cellular
materials.
• Contains enzymes for fats, proteins,
polysaccharides, and nucleic acids.
• Over 40 types known.
Lysosomes
• Important in cell death.
• Missing enzymes may cause various
genetic enzyme diseases.
• Examples: Tay-Sachs,
Vacuoles
• Structure - single membrane, usually
larger than the Golgi vesicles.
• Function - depends on the organism.
Protists
• Contractile vacuoles - pump out excess
water.
• Food vacuoles - store newly ingested
food until the lysosomes can digest it.
Plants
• Can have a large single vacuole when
mature making up to 90% of the cell's
volume.
• Function
• Water regulation.
• Storage of ions.
• Storage of hydrophilic pigments. (e.g. red and blues in flower petals).
Function: Plant vacuole
• Used to enlarge cells and create turgor
pressure.
• Enzymes (various types).
• Store toxins.
• Coloration.
Microbodies
• Structure: single membrane.
• Often have a granular or crystalline
core of enzymes.
Function
• Specialized enzymes for specific
reactions.
• Peroxisomes: break down fatty acids,
detoxify, adds H2 to toxis (it has
enzymes in it that convert H2O2 to
H20)
• Glyoxysomes: convert lipids into sugars
(useful for plant seeds)
Enzymes in a
crystal
Mitochondria
• Structure: 2 membranes. The inner
membrane has more surface area than
the outer membrane.
• Matrix: inner space.
• Intermembrane space: area between
the membranes.
Inner Membrane
• Folded into cristae.
• Amount of folding depends on the level
of cell activity.
• Contains many enzymes.
• ATP generated here.
Function
• Cell Respiration - the release of energy
from food.
• Major location of ATP generation.
• “Powerhouse” of the cell.
Comment – be careful NOT to overuse
this phrase.
Mitochondria
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•
•
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Have ribosomes (small size).
Have their own DNA.
Can reproduce themselves.
Likely were independent cells at one
time.
Chloroplasts
• Structure - two outer membranes.
• Complex internal membrane.
• Fluid-like stroma is around the internal
membranes.
Inner or Thylakoid Membranes
• Arranged into flattened sacs called
thylakoids.
• Some regions stacked into layers called
grana.
• Contain the green pigment chlorophyll.
Function
• Photosynthesis - the use of light energy
to make food.
Chloroplasts
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Contain ribosomes (small size).
Contain DNA.
Can reproduce themselves.
Often contain starch.
Likely were independent cells at one
time (cyano-bacteria).
Cytoskeleton
• Network of rods and filaments in the
cytoplasm.
Functions
• Cell structure and shape.
• Cell movement.
• Cell division - helps build cell walls and
move the chromosomes apart.
Cytoskeleton Components
• Microtubules
• Microfilaments
• Intermediate Filaments
Microtubules
• Structure - small hollow tubes made of
repeating units of a protein dimer.
• Size - 25 nm diameter. Can be 200 nm
to 25 mm in length.
Microtubules
• Regulate cell shape.
• Coordinate direction of cellulose fibers
in cell wall formation.
• Tracks for motor molecules.
Microtubules
• Form cilia and flagella.
• Movement of organelles and
chromosomes within the cell
Dynein Protein (Type of
microtubule)
• A contractile protein.
• Uses ATP.
• Creates a twisting motion between the
microtubules causing the structure to
bend or move.
Microfilaments
• 5 to 7 nm in diameter.
• Structure - two intertwined strands of
actin protein.
Microfilaments
are stained green.
Functions
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•
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•
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Muscle contraction.
Cytoplasmic streaming.
Pseudopodia.
Cleavage furrow formation.
Maintenance and changes in cell
shape.
Intermediate Filaments
• Fibrous proteins that are super coiled
into thicker cables and filaments
8 - 12 nm in diameter.
• Made from several different types of
protein.
Functions
• Maintenance of cell shape.
• Hold organelles in place.
Cytoskeleton
• Very dynamic; changing in composition
and shape frequently.
• Cell is not just a "bag" of cytoplasm
within a cell membrane.
Cell Wall
• Nonliving jacket that surrounds some
cells.
• Found in:
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•
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Plants
Prokaryotes
Fungi
Some Protists
Plant Cell Walls
• All plant cells have a Primary Cell Wall.
• Some cells will develop a Secondary
Cell Wall.
Primary Wall
• Thin and flexible.
• Cellulose fibers placed at right angles to
expansion.
• Placement of fibers guided by
microtubules.
Secondary Wall
• Thick and rigid.
• Added between the cell membrane and
the primary cell wall in laminated layers.
• May cover only part of the cell; giving
spirals.
• Makes up "wood”.
Middle Lamella
• Thin layer rich in pectin found between
adjacent plant cells.
• Glues cells together.
Cell Walls
• May be made of other types of
polysaccharides and/or silica.
• Function as the cell's exoskeleton for
support and protection.
Extracellular Matrix - ECM
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Fuzzy coat on animal cells.
Helps glue cells together.
Made of glycoproteins and collagen.
Evidence suggests ECM is involved
with cell behavior and cell
communication.
Why Are Cells So Small?
• Cell volume to surface area ratios favor
small size.
• Nucleus to cytoplasm consideration
(control).
• Metabolic requirements.
• Speed of diffusion.