Download EUKARYOTIC CELLS

EUKARYOTIC CELLS
Chapter 4
EUKARYOTES
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True, membrane-bound nucleus
DNA organized into chromosomes
DNA associated with basic proteins
Membrane-bound organelles
Larger and more complex than prokaryotes
SIZE: 10-100 um in diameter
Microorganisms: Algae, Fungi, Protozoa
Other: Higher Plants and Animals
FLAGELLA
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FUNCTION = Locomotion
Some protozoa and algae
Surrounded by cytoplasmic membrane
Contains 9 pairs of microtubles in a ring PLUS 2 single
microtubules in the center
• Moves in a wave like manner
• Few per cell and relatively long
CILIA
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FUNCTION = move foreign material
Same structure as flagella, but shorter
Hundreds per cell
Some protozoa and animal cells
CELL WALL
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Eukaryotic cell walls = rigid polysaccharide
Cellulose - all plants and some fungi
Chitin (NAG polymer) - most fungi
Glucan & mannan - yeasts
Pellicle - protective covering of protozoa
NO PEPTIDOGLYCAN therefore NOT susceptible to penicillin,
etc.
GLYCOCALYX
• FUNCTIONS
– Strengthen membrane
– Attach cells together (ADHESINS)
– Cell-cell recognition
• Animal cells
• CHO, glycolipids, glycoproteins
PLASMA (CYTOPLASMIC) MEMBRANE
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FUNCTION = External covering of the cell
Phospholipid bilayer
Integral and peripheral proteins
CHOs, glycoproteins = cell surface receptors
Contains sterols (cholesterol)
ENDOCYTOSIS - mechanism to internalize extracellular
particles into the cell
– Phagocytosis - engulfment of particles
– Pinocytosis - engulfment of fluid
CYTOPLASM
• Inside the plasma membrane, outside the nucleus
• More complex than prokaryotes
• Cytoskeleton: cell shape and strength; transport within cell; cell
movement
– Microfilaments
– Intermediate filaments
– Microtubules
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A.
B.
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F.
G.
ORGANELLES
NUCLEUS
ENDOPLASMIC RETICULUM
GOLGI APPARATUS
RIBOSOMES
MITOCHONDRIA
CHLOROPLASTS
LYSOSOMES
• H. VACUOLES
• I. CENTRIOLES
A. NUCLEUS
• Largest internal structure; oval or spherical
• Contains ALMOST all the genetic material (DNA)
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– CHROMATIN = DNA + histones
Double membrane = Nuclear envelope
Nuclear pores - communication with cytoplasm
NUCLEOLUS/NUCLEOLI = site of rRNA synthesis
Cell divides by MITOSIS and MEIOSIS
B. ENDOPLASMIC RETICULUM
• ER = Cytoplasmic membranous network structure
• FUNCTION = synthesis of lipids and proteins; transport for
newly synthesized molecules to other sites in cell via
SECRETORY VESICLES
• Continuous from nuclear membrane
• ROUGH ER: Attached ribosomes; protein synthesis
• SMOOTH ER: No ribosomes; lipid synthesis
C. RIBOSOMES
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Sites of protein synthesis
Larger and denser than prokaryotic ribosomes
Cytoplasmic: 80S = 60S + 40S subunits
Mitochondrian: 70S = 50S + 30S subunits
Each subunit = many different proteins + rRNA
D. GOLGI APPARATUS/COMPLEX
• Found near nucleus in cytoplasm
• Stacks of flattened “disks”
• Receives and transports newly synthesized lipids and proteins
from the ER via SECRETORY VESICLES
E. MITOCHONDRIA: Powerhouse of the Cell
• FUNCTION = CELLULAR RESPIRATION = ENERGY PRODUCTION (ATP)
• Spherical or rod shaped with 2 double membranes
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– OUTER MEMBRANE: smooth, contains sterols
– INNER MEMBRANE: highly folded; no sterols
• CRISTAE: increased surface area
ENZYMES for ATP production on the cristae (I.M.)
DNA: DS, circular - most genes: respiration enzyme
RIBOSOME: 70S = 50S + 30S subunits
Autonomous replication
F. CHLOROPLASTS
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FUNCTION = SITE of PHOTOSYNTHESIS
Cytoplasmic membrane-bound organelle of plants and algae
THYLAKOIDS: flattened sacs containing CHLOROPHYLL
DNA: DS DNA
RIBOSOME: 70S
Replicates autonomously
G. LYSOSOMES
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FUNCTION = Contain HYDROLYTIC ENZYMES
Membrane-bound spheres, free in cytoplasm
Derived from Golgi apparatus
Enzymes capable of breaking down engulfed bacteria
Important in phagocytosis
Found in large numbers in WBCs
H. VACUOLES
• FUNCTION = membrane-bound cavity or space for storage
– Proteins, sugars, CHO, organic compounds
– Metabolic wastes
– Water (plants 5-90% cell volume)
• Derived from Golgi complex
I. CENTRIOLES
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FUNCTION = Role in cell division
Found near nucleus
Pair of cylindrical structures at right angles
Each one = ring of evenly spaced bundles
– Each bundle = 3 microtubules
• Form eukaryotic cilia and flagella
PROKARYOTES vs EUKARYOTES
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Larger
Nucleus
Multiple chromosomes
Histones
80S ribosome
Membrane-bound organelles
Membrane sterols
Cell wall = simple
Flagella = 2+ (9x2)
Replicates by mitosis
Smaller
No true nucleus
Single, circular DS DNA
No histones
70S ribosome
No membrane-bound organelles
No membrane sterols
Cell wall = Peptidoglycan
Flagella = Flagellin helix
Replicates by binary fission
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SIZE: 1 - 8 um
Peptidoglycan wall
No membrane sterols
No nucleus
DNA: 1 Chromosome
No histones
Ribosome: 70S
PROKARYOTES vs MITOCHONDRIA
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Replicates autonomously
Binary fission
SIZE: 1 um
No wall
No sterols in I.M.
No nucleus
DNA: 1 Chromosome
No histones
Ribosome: 70S
Replicates autonomously
Increase in size then divide in two
EVOLUTION OF EUKARYOTES
• AUTOGENOUS HYPOTHESIS
– Organelles derived from prokaryotic internal plasma membranes
– Single membrane-bound organelles: Nuclear envelope, ER, Golgi
– More complex eukaryotes then evolved
• ENDOSYMBIONT HYPOTHESIS
– Smaller prokaryotes developed first
– Associated and lived within larger prokaryotes
– Mitochondria and chloroplasts ~ same size as prokaryotes; divide
independently of eukaryotic cell cycle; have double layer membrane
– Eukaryotes evolved from this symbiotic relationship