chapter 7 a tour of the cell. cytology: science/study of cells light microscopy resolving power~...
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CHAPTER 7A 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 (internal anatomy)
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 Theory– Cells are the basic unit of structure and function– All cell arise from other cells– All living things are made of one or more cells
Cell Types: ProkaryoticDomains: Bacteria and Archaea
Nucleoid: DNA
concentration
No membrane bound
organellesRibosomes:protein synthesis
Plasma membrane: (all
cells); semi-permeable
Cytoplasm/cytosol(all cells)
Cell types: EukaryoticDomains: Protist, fungi, Plants, and Animals
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 (as well as the % Diffusion)
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
Nuclear Envelope: double membrane with pores
mRNA~ protein synthesis
Ribosomes
Protein manufacture Types: a) free cytosol;protein function in cell
b) bound: on ER; proteins function in membranes, organelles and export
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 Endomembrane System
The Golgi apparatusER products are modified, stored, and then
shipped to either: lysosomes, central vacuole, plasma membrane
Cisternae: flattened membranous sacsTrans face(shipping) & cis face (receiving)Transport vesicles
Lysosomes
Sac of hydrolytic
enzymes; digestion of
macromoleculesPhagocytosis Autophagy: recycle cell’s
own organic material
Tay-Sachs disease~
lipid digestions disorder
VacuolesMembrane-bound
sacs(larger than vesicles)Food (phagocytosis)Contractile (pump excess
water)Central (storage in plants
as well as lysosomal functions) 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 their internal
ribosomes.
• Mitochondria and chloroplasts grow and reproduce as
semiautonomous organelles.
2. Peroxisomes generate and degrade H2O2 in
performing various metabolic functions• What enzyme breaks down H2O2?
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 (protista)site of photosynthesis.Inside the innermost membrane is a fluid-
filled 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.
• have the same ultrastructure.
cilia and flagella
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.
• In plant cells (and others), actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming.
Microfilaments
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.