the plant cell cycle chapter 3. nucleus dna replication cytoskeleton
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The plant cell
NUCLEUS
MITOCHONDRIUM
CHLOROPLASTCHLOROPLAST
CHLOROPLAST CHLOROPLAST
MITOCHONDRIUM
MITOCHONDRIUM
MITOCHONDRIUM
CYTOSOL
Notes: 1) cytosol is the same as cytoplasm 2) not all of the plant cell structures and organelles are shown
Cell wall
Plasma membrane
Fig. 3-8, p. 37
0.2 µm1 µmnuclear envelope
one pore
lipid bilayer facingthe nucleoplasm
nuclearenvelope
lipid bilayer facingthe cytoplasm pore complex that
spans both bilayers
Nucleus
-Ovoid or irregular shaped
-Surrounded by double membrane (nuclear envelope)
Central dogma of Molecular Biology
+
DNA
REPLICATIONTRANSCRIPTION
TRANSLATION
RNA
mRNA
protein
Ribosome
Early Prophase cell
Chromosome
Nucleolus(rDNA, rRNA, ribosomal proteins, etc…)
nuclearenvelope
Nucleolus: production center for ribosomes
Fig. 3-9a, p. 37
A nucleosomeconsists of part ofa DNA moleculelooped twicearound a coreof histones (chromosomal proteins).
core ofhistonemolecules
Fig. 3-9b, p. 37
Immerse achromosome insaltwater and itloosens up to abeads-on-a-stringorganization. The“string” is oneDNA molecule.Each “bead” isa nucleosome.
Fig. 3-9c, p. 37
At a deeperlevel of structuralorganization, thechromosomalproteins and DNAare organized asa cylindrical fiber (again a helical structure).
Fig. 3-9d, p. 37
At times when a chromosome is mostcondensed (during Mitosis), the chromosomal proteinsinteract, which packages loops of alreadycoiled DNA into a “supercoiled” array (two additional helical organizations).Such a tightly packaged DNA molecule is more easily moved around compared to when it would be a long “loose” thread (important during cell division)
Cytoskeleton
• Structures in cytoskeleton– Microtubules– Motor proteins– Microfilaments
• Specialized proteins connect microtubules and microfilaments to other organelles– Connections thought to coordinate many cell processes
Fig. 3-15, p. 43
some cellsleave the
cycle pre-DNA synthetic phase or gap phase
DNAsynthesis
phaseInterphaseMitosis (M)
cytokinesis
telophase
anaphase
metaphase
prophase
premitosis phasesome cellsleave the
cycle
CELL
CYCLE
G1
G2
S
Note: Interphase includes G1, S and G2 phases
Fig. 3-18, p. 45
microtubulesnucleus
cell wall
cytoplasm
band ofmicrotubules
Formation of the preprophase band of microtubules in meristematic cells:
A) Section at right angles to the plane of the future cell plate shows a cross section of microtubules. B) Section in the plane of the future cell plate shows microtubules encircling the nucleus. C) Three-dimensional drawing of A and B.
A B C
Fig. 3-19, p. 46
Early Prophase Late Prophase Metaphase Late anaphase Telophase
cellplate
spindlefiber
pole
kinetochorechromosome
nucleolus
nuclearenvelope
Mitosis
a b c d e
Fig. 3-17, p. 45
The roles of microtubules in mitosis
Visualization of tubulin (component of microtubules) during mitosis.
Cell division in Plants versus Animals
• Animal cells do not have a cell wall
Because plant cells have cell walls, the direction of cell division is a major determinant of overall plant development (cells are caught in a rigid structure and cannot reorganize after cell division has been completed). The direction/orientation of cell division is controlled by plant hormones.
Cell division in Plants versus Animals
• Animal cells do not form a preprophase band (PPB)
• During Telophase: - in plants: a cell plate is formed at the start of cytokinesis (direction
of cell plate formation depends on hormone action via effects on PPB formation)
- in animals: the cell pinches in the middle to form two cells, no cell plate is formed.
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