Transcript Document 7220250

Chapter 5
Cell Structure
Warning!!
Much
of this chapter is
covered in Biology I so the
pacing will be rapid.
Focus on what is new to you
while you review what is
already familiar.
“Faith is a fine
invention when
gentlemen can see,
but microscopes are
prudent in an
emergency.”
Emily Dickinson
Cell Biology or
Cytology
Cyto
= cell
- ology = study of
Should use observations
from several types of
microscopes to make a total
picture of how a cell is put
together.
Light Microscope - LM
Uses
visible light to
illuminate the object.
Relatively inexpensive type
of microscope.
Can examine live or dead
objects.
Light Microscope
Occular Lens
Objective Lens
Stage with specimen
Light Source
Resolution
Ability
to detect two discrete
points as separate from each
other.
As Magnification increases,
resolution decreases.
LM working limits are
100 - 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.
Electron Microscopes
Use
beams of electrons
instead of light.
Invented in 1939, but not
used much until after WWII.
TEM
SEM
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.
Specimen must stop the
electrons.
High cost of equipment.
Specimen preparation.
Transmission Electron
Microscope - TEM
Sends
electrons through
thinly sliced and stained
specimens.
Gives high magnification of
interior views. Many cells
structures are now visible.
TEM Limitations
Specimen
dead.
Specimen preparation uses
extreme chemicals so
artifacts are always a
concern.
Scanning Electron
Microscope - SEM
Excellent
views of surfaces.
Produces 3-D views.
Live specimens possible.
Other Tools for
Cytology
Cell
Fractionation
Chromatography
Electrophoresis
Cell Fractionation
Disrupt
cells.
Separate parts by
centrifugation at different
speeds.
Result - pure samples of cell
structures for study.
Cell Fractionation
Chromatography
Technique
for separating
mixtures of chemicals.
Separates chemicals by size or
degree of attraction to the
materials in the medium.
Ex - paper, gas, column,
thin-layer
Electrophoresis
Separates
mixtures of
chemicals by their movement
in an electrical field.
Used for proteins and DNA.
History of Cells
Robert
Hooke - Observed
cells in cork.
Coined the term "cells” in
1665.
History of Cells
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.
1840 - J.E. Purkinje, coined
the term “protoplasm”.
Cell Theory
All
living matter is composed
of one or more cells.
The cell is the structural and
functional unit of life.
R. Virchow
“Omnis
cellula e cellula”
All cells are from other cells.
Types of Cells
Prokaryotic
- lack a nucleus
and other membrane
bounded structures.
Eukaryotic - have a nucleus
and other membrane
bounded structures.
Both Have:
Membrane
Cytosol
Ribosomes
different)
(but the size is
Prokaryotic
Eukaryotic
Nucleus
Eukaryotic
Prokaryotic
Why Are Cells So Small?
Cell
volume to surface area
ratios favor small size.
Nucleus to cytoplasm
consideration (control).
Metabolic requirements.
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.
Exists in two forms:
gel
- thick
sol - fluid
Organelle
Term
means "small organ”
Formed body 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 20-40 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.
Storage area for ribosomes.
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.
Rough ER: with ribosomes.
Makes secretory proteins.
Golgi Apparatus
or Dictyosomes
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.
Distribution - packaging of
ER products for transport.
Golgi 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,
Pompe’s Disease
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
Large
single vacuole when
mature making up to 90% of
the cell's volume.
Tonoplast - the name for the
vacuole membrane.
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: use up
hydrogen peroxide.
Glyoxysomes: lipid digestion.
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.
Mitochondria
Have
ribosomes (small size).
Have their own DNA.
Can reproduce themselves.
May have been 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
Contain
ribosomes (small size).
Contain DNA.
Can reproduce themselves.
Often contain starch.
May have been independent
cells at one time.
Plastids
Group
of plant organelles.
Structure - single membrane.
Function - store various
materials.
Examples
Amyloplasts/
Leucoplasts -
store starch.
Chromoplasts - store
hydrophobic plant pigments
such as carotene.
Ergastic Materials
General
term for other
substances produced or
stored by plant cells.
Examples:
Crystals
Tannins
Latex
Resins
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.
Components
Microtubules
Microfilaments
Intermediate
Filaments
Microtubules
Structure
- small hollow
tubes made of repeating units
of a protein dimer.
Size - 25 nm diameter with a
15 nm lumen. Can be 200 nm
to 25 mm in length.
Tubulin
Protein
in microtubules.
Dimer - a and b tubulin.
Microtubules
Regulate
cell shape.
 Coordinate direction of
cellulose fibers in cell wall
formation.
Tracks for motor molecules.
Microtubules
Form
cilia and flagella.
Internal cellular movement.
Make up centioles, basal
bodies and spindle fibers.
Cilia and Flagella
Cilia
- short, but numerous.
Flagella - long, but few.
Function - to move cells or to
sweep materials past a cell.
Cilia and Flagella
Structure
- 9+2 arrangement
of microtubules, covered by
the cell membrane.
Dynein - motor protein that
connects the tubules.
Dynein Protein
A
contractile protein.
Uses ATP.
Creates a twisting motion
between the microtubules
causing the structure to bend
or move.
Centrioles
Usually
one pair per cell,
located close to the nucleus.
Found in animal cells.
9 sets of triplet microtubules.
Help in cell division.
Basal Bodies
Same
structure as a
centriole.
Anchor cilia and flagella.
Basal Body
Microfilaments
5
to 7 nm in diameter.
Structure - two intertwined
strands of actin protein.
Microfilaments
are stained green.
Functions
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:
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
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.
Intercellular Juctions
Plants-Plasmodesmata
Plasmodesmata
Channels
between cells
through adjacent cell walls.
Allows communication
between cells.
Also allows viruses to travel
rapidly between cells.
Intercellular Juctions
Animals:
Tight
junctions
Desmosomes
Gap junctions
Tight Junctions
Very
tight fusion of the
membranes of adjacent cells.
Seals off areas between the
cells.
Prevents movement of
materials around cells.
Desmosomes
Bundles
of filaments which
anchor junctions between
cells.
Does not close off the area
between adjacent cells.
Coordination of movement
between groups of cells.
Gap Junctions
Open
channels between
cells, similar to
plasmodesmata.
Allows “communication”
between cells.
Summary
Answer:
Why is Life cellular
and what are the factors that
affect cell size?
Be able to identify cellular
parts, their structure, and
their functions.