A TOUR OF THE CELL
Cell Theory
All organisms are composed of one or more cells
Cells are the smallest living units of
all living organisms
Cells arise only by division of a previously
existing cell
Cell Size
relatively small because as size increases,
volume increases much more rapidly.
longer diffusion time
How are cells studied
Microscopy
Magnification
Resolution/resolving power
Cell fractionation
Technique that involves separation of
cellular organelles
Visualizing Cells
Resolution - minimum distance between two
points can be apart and be
distinguished as two separate points
Magnification how much larger an object is
made to appear compared to its
real size
General types of Microscopes
Compound light microscope
Electron microscope
Transmission EM
Scanning EM
Visualizing Cells
Cell Characteristics
Genetic material (DNA)
Single, circular in prokaryotes
double helix in eukaryotes
Cytoplasm fills cell interior
sugars, amino acids,
proteins organelles
Plasma membrane encloses the cell phospholipid bilayer
Living organisms as made up of either
Prokaryotic or Eukaryotic cells
Prokaryotic
(pro=before ; karyon=kernel)
Eukaryotic
(Eu=true; karyon=kernel)
Found only in bacteria and cyanobacteria Found in Protista, Fungi, Plantae and
Animalia
No true nucleus;lack nuclear membrane True nucleus; bounded by nuclear membrane
Genetic material in nucleoid region Genetic material within nucleus
No membrane-bound organelles Contains cytoplasm with cytosol and
membrane-bound organelles
Generalized Prokaryotic and Eukaryotic Cells
Generalized Animal and Plant Cells
Nucleus
Bound by nuclear membrane (two phospholipid bilayers)
Nuclear pores protein gatekeepers
Usually proteins going in and RNA going out
Repository for genetic material organized
w/ proteins = chromosomes
Directs activities of the cell
Usually single, some cells several, RBC none
Nucleolus - region of intensive ribosomal RNA synthesis
Chromosomes
DNA of eukaryotes is divided into linear chromosomes.
exist as strands of chromatin, except during cell
division
associated with packaging histones, packaging
proteins
nucleosomes
Endomembrane System
Includes:
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
(not actually an endomem. but related to the system)
Importance:
Compartmentalizes cell, channeling passage of molecules through cells interior.
Rough ER - studded with ribosomes
Smooth ER - few ribosomes
Endoplasmic reticulum
Extensive membranous network of tubules and sacs (cisternae)
Smooth ERSynthesizes lipids, phospholipids and
steroids
Participates in
carbohydrate
metabolism
Stores calcium ions for muscle contractionDetoxifies drugs
Rough ERManufactures secretory proteins
Manufactures
membrane
Golgi apparatus
Modifies, stores, routes, collects, products of ER
Distribute molecules synthesized at one location in the cell and utilized at
another location
Stacked, flattened membranous sacs (cisternae)\ Has distinct polarity, cis face and trans face
Modifies, stores, routes, collects, products of ER
Distribute molecules synthesized at one location in the cell and utilized at another location
SYNTHESIS OF MEMBRANE COMPONENTS AND THEIR
ORIENTATION ON THE RESULTING MEMBRANE
Lysosomes - membrane-bound vesicles containing digestive enzymes
(lipase, protease, carbohydrase,nuclease)
Microbodies - enzyme-bearing, membrane-enclosed vesicles.
Peroxisomes - contain enzymes that catalyze the removal of electrons and
associated hydrogen atoms
- Peroxide-producing oxidases
- catalase
Vesicles
Cytoplasm
Phagocytosis
Foodvesicle
Golgiapparatus
Lysosomes
Plasmamembrane
Digestion ofphagocytizedfood particles
or cells
Endoplasmicreticulum
Transportvesicle
Old or damagedorganelle
Breakdownof old
organelleExtracellularfluid
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Relationship among Endomembranes: A Summary
Nuclear
envelope
Golgi apparatus
Rough ER Smooth ER
Plasma membraneLysosomes
Vesicles
Vesicles
Membrane and secretory proteins produced
in ER are transported in
Fuse with the forming
face of
Pinch off maturing face
Give rise toFuse with and add to plasma membrane
and may release cellular products to outside
Is an extension of Is confluent with
Ribosomes
Ribosomes are RNA-protein complexes composed of
two subunits that join and attach to messenger RNA.
site of protein synthesis
assembled in nucleoli
Organelles With DNA
Mitochondria
bounded by exterior and interior membranes
interior partitioned by cristae
Chloroplasts
have enclosed internal compartments of stacked
grana, containing thylakoids
found in photosynthetic organisms
Mitochondria
"Powerhouse of the cell" - cellular metabolism
With outer and inner membranes, cristae
Have their own DNA
Chloroplasts
Chloroplasts are larger and more complex than mitochondria
Grana closed compartments of stacked membranes
Thylakoids disc shaped structure light capturing pigment
Stroma fluid matrix
Endosymbiosis
Endosymbiotic theory suggests engulfed prokaryotes
provided hosts with advantages associated with
specialized metabolic activities.
Theory of Endosymbiosis
Evidence for the endosymbiont theory is that
mitochondria and chloroplasts:
- Are appropriate size to be descendants of eubacteria.
- Have inner membranes similar to those on prokaryotic plasma membranes.
- Replicate by splitting, as in prokaryotes.
- DNA is circular and different from the DNA of the cell's nucleus.
- Contain their own components for DNA transcription and translation into proteins .
- Have ribosomes similar to prokaryotic ribosomes.
- Molecular systematics lend evidence to support this theory.
- Many extant organisms are involved in endosymbiotic relationships.
Cytoskeleton
Network of protein fibers throughout the cytoplasm
supporting cell shape, anchoring organelles, motility
Constructed from 3 types of fibers:
Microtubules Microfilaments Intermediate filaments
Microtubule
2. Cellular support 3. Make up centrioles
in animal cells
1. Cell motility (cilia and flagella)
4. Separation of
chromosomes during
cell division
Structure of cilia and flagella
Microfilaments(globular actin and long chain F actin)
Participates in
muscle contraction
Provides support
localized
contraction of cells
Intermediate filaments
Framework
of cytoskeletonReinforce
cell shape
Fix organelle position
Plant Cells
Central vacuole
often found in the center of a plant cell, and serves as a storage facility for water and other materials
Cell wall
primary walls laid down while cell is growing
middle lamella glues cells together
secondary walls inside the primary cell walls after growth
Plant Cell
Animal Cells
Animal cells lack cell walls.
form extracellular matrix
provides support, strength, and resilience