Transcript CHAPTER 7 A TOUR OF THE CELL

CHAPTER 7
A TOUR OF THE CELL
Cytology: science/study of cells
Light microscopy resolving power~ measure of
clarity
 Electron microscopy
TEM ~ electron beam to study cell
ultrastructure
SEM ~ electron beam to study cell surfaces
 Cell fractionation ~ cell separation; organelle study
 Ultracentrifuge ~ cell fractionation; 130,000rpm
A cell is a living unit greater
than the sum of its parts
• While the cell has many structures that have
specific functions, they must work together.
Cell Types: Prokaryotic
Nucleoid: DNA
concentration
No organelles with
membranes
Ribosomes:protein synthesis
Plasma membrane: (all
cells); semi-permeable
Cytoplasm/cytosol(all cells)
Cell types: Eukaryotic
Nucleus:membrane enclosed organelle containing
chromosomes
Membrane bound organelles of specialized
form and function
 Generally larger than prokaryotic cells
Cell Size
As cell size increases, the surface area to volume
ratio decreases
Rates of chemical exchange may then be
inadequate for cell size
Cell size, therefore, remains small
Nucleus
Genetic material…
 chromatin
 Chromosomes
 Nucleolus: rRNA;
ribosome synthesis
Double membrane
with pores
mRNA~ protein synthesis
Ribosomes
Protein manufacture
 Types: a) free cytosol;protein function in cell
b) bound: endoplasmic reticulum;
membranes, organelles and export
The Endomembrane System
 Endoplasmic reticulum(ER)
 Continuous with nuclear envelope
 Smooth ER




no ribosomes
Synthesis of lipids
Metabolism of carbohydrates
Detoxification of drugs &poisons
 Rough ER
 With ribosomes
 Synthesis of secretory proteins
(glycoproteins)
 Membrane production
The Golgi apparatus
ER products are modified, stored, and then
shipped
Cisternae: flattened membranous sacs
Trans face(shipping) & cis face (receiving)
Transport vesicles
Lysosomes
Sac of hydrolytic
enzymes; digestion of
macromolecules
Phagocytosis
Autophagy: recycle cell’s
own organic material
Tay-Sachs disease~
lipid digestions disorder
Vacuoles
Membrane-bound
sacs(larger than vesicles)
Food (phagocytosis)
Contractile (pump excess
water)
Central (storage in plants)
 Tonoplast membrane
Other Membranous Organelles
1.
Mitochondria and chloroplasts are the main energy
transformers of cells
Both organelles have small quantities of DNA that direct the
synthesis of the polypeptides produced by these internal ribosomes.
•
Mitochondria and chloroplasts grow and reproduce as
semiautonomous organelles.
2. Peroxisomes generate and degrade H2O2 in performing
various metabolic functions
Mitochondria
 Site of cellular respiration
 have a smooth outer membrane
and a highly folded inner membrane, the cristae
 inner membrane encloses the mitochondrial matrix,
a fluid-filled space with DNA, ribosomes, and enzymes.
chloroplasts
found in plants and eukaryotic algae
site of photosynthesis.
Inside the innermost membrane is a fluidfilled space, the stroma, in which float
membranous sacs, the thylakoids.
Peroxisomes
• generate and degrade H2O2 in performing
various metabolic functions
• bounded by a single membrane.
• They form not from the endomembrane system,
but by incorporation of proteins and lipids from
the cytosol.
The Cytoskeleton
• Providing structural support to the cell,
the cytoskeleton also functions in cell
motility and regulation
There are three main types of fibers in the cytoskeleton:
microtubules, microfilaments, and intermediate filaments.
Microtubules
• the thickest fibers, are hollow rods about 25
microns in diameter.
• They move chromosomes during cell division.
• Another function is
as tracks that guide
motor proteins
carrying organelles
to their destination.
cilia and flagella.
• Microtubules are the central structural
support
• Cilia usually occur in large numbers on the
cell surface.
• There are usually just one or a few flagella
per cell
cilia and flagella.
• A flagellum has an undulatory movement
cilia and flagella.
• Cilia move more like oars with alternating
power and recovery strokes.
cilia and flagella
• have the same ultrastructure.
Microfilaments
• the thinnest class of the
cytoskeletal fibers,
are solid rods of the globular protein
actin.
designed to resist tension
• form a three-dimensional
network just inside
the plasma membrane.
Microfilaments
• In muscle cells, thousands of actin filaments are arranged
parallel to one another.
• Thicker filaments, composed of a motor protein, myosin,
interdigitate with the thinner actin fibers
Microfilaments
• In other cells, these actin-myosin aggregates
are less organized but still cause localized
contraction
•Pseudopodia, cellular extensions, extend and
contract through the reversible assembly and
contraction of actin subunits into microfilaments.
Microfilaments
• In plant cells (and others), actin-myosin
interactions and sol-gel transformations
drive cytoplasmic streaming.
Intermediate filaments,
• more permanent fixtures
of the cytoskeleton than
are the other two classes
• reinforce cell shape
• and fix organelle location.
Cell Surfaces and Junctions
1. Plant cells are encased by cell walls
2. The extracellular matrix (ECM) of animal cells
functions in support, adhesion, movement, and
regulation
3. Intercellular junctions help integrate cells into higher
levels of structure and function
4. The cell is a living unit greater than the sum of its parts
Plant cells are encased by cell
walls
• The cell wall, found in prokaryotes, fungi,
and some protists, has multiple functions.
• In plants, the cell wall protects the cell,
maintains its shape, and prevents excessive
uptake of water.
• It also supports the plant against the force of
gravity.
A mature cell wall consists of a primary cell
wall, a middle lamella with sticky polysaccharides
that holds cell together, and layers of secondary cell
wall.
The extracellular matrix (ECM) of
animal cells functions in support,
adhesion, movement, and regulation
• In many cells, fibronectins in the ECM
connect to integrins, intrinsic membrane
proteins.
. Intracellular junctions help
integrate cells into higher levels of
structure and function
• Plant cells are perforated with
plasmodesmata, channels allowing cysotol
to pass between cells.
Animal have 3 main types of intercellular
links: tight junctions, desmosomes, and gap
junctions
• In tight junctions, membranes of adjacent cells
are fused, forming continuous belts around cells.
– This prevents leakage of extracellular fluid.
Desmosomes (or anchoring junctions)
fasten cells together into strong sheets,
much like rivets.
• Gap junctions (or communicating
junctions) provide cytoplasmic
channels between adjacent cells.
Microtubules
• In many cells, microtubules grow out from a centrosome
near the nucleus.
• In animal cells, the centrosome has a pair of centrioles, each
with nine triplets of microtubules arranged in a ring.
• During cell division the
centrioles replicate.