Download - The cell cycle
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ULTRASTRUCTURE OF CELLS
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OBJECTIVES
• Identify the cell organelles and their respective
functions
• Recognize the differences of bacterial, plant, and
animal cells
• Appreciate importance of cells to an organism
• Prepare fresh mounts of kinds of cells
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PLANT CELL
• cell wall
• cell membrane
• nucleus
• cytoplasm
• vacuole
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ANIMAL CELL
• cell nucleus
• cytoplasm
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BACTERIAL CELL
• movement – jerky
• rod shaped
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FUNGAL CELLS
• sporangium
• sporangiophore (hyphae)
• rhizoid
• stolon
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COMPARISON
• Size
• Shape
• Protective covering
• Organelles
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THE CELL CYCLE
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CHROMOSOME NUMBER
• all organisms contain chromosome where genes
are found
• thread-like structures in a cell’s nucleus visible under
microscope only during cell division
• somatic cells (non-reproductive body cell) has a
partner chromosome occurring in pairs
• homologous chromosomes - two members of a pair
chromosome
• diploid – chromosomes occurring in pairs (2n)
• haploid – single set of unpaired chromosome (n)
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AUTOSOMES VS SEX CHROMOSOMES
• sex determination is
based on sex
chromosomes
• a pair containing 2 X
chromosomes would
entail female sex and 1 X
and O would entail male
sex
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THE CELL CYCLE
• period from beginning of one division to the
beginning of the next division
• generation time – the period between two
successive divisions/complete revolution of the
cycle
• 8 to 20 hours
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CELL CYCLE
S Phase
• DNA synthesis
• 10-12 hours
• each replicated DNA
molecules intertwine
held tightly together by
a protein
M Phase
• chromosome
segregation and cell
division
• lesser time
• major events: nuclear
division and
cytoplasmic division
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G1 PHASE AND G2 PHASE
• G1 phase is between M-phase and S-phase
• G2 phase is between S-phase and Mitosis
• time delays to allow cell growth
• monitor internal and external environment
• G1 – if external conditions are unfavorable, it
extends to form the G0 phase
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CELL CYCLE CONTROL SYSTEM
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G1 PHASE AND G2 PHASE
G1 Phase
• event between the
previous cell division
and DNA replication
• cell grows
• longest phase
• synthesis of certain
enzymes used in DNA
replication
G2 Phase
• increased protein
synthesis for
preparation in cell
division
• short phase
• beginning of mitosis
marks the end of G2
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INTERPHASE
• period of active growth and maintenance after
mitosis
• synthesizes needed materials
• grows
• chromosomes undergo duplication
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LOCATION OF MITOSIS
• meristems (meristo “divided”)
• shoot and root tips (apical meristems)
• thin cylindrical regions that run the entire lengths
of the stems and roots (lateral meristems)
• temporary meristems are produced when a plant
is wounded or encounters a disease
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LOCATION OF MITOSIS
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MITOSIS
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PROPHASE
• chromatin (long, thin, thread (like material of which
chromosomes are composed) condense and coil
into visible chromosome
• chromosomes become shorter and thicker
• centromere – constricted region
• kinetochore – attached to the centromere where
microtubules bind
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PROPHASE
• nuclear envelope disappears and breaks apart
• the nucleolus shrinks
• microtubules organize between poles to form the mitotic spindle (aids in movement of chromosome)
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METAPHASE
• short period of chromosomes lining up in the
midplane of the cell
• mitotic spindle (visible and made up of
microtubules extending from pole to pole)
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ANAPHASE
• once chromatids are no longer attached to their
duplicates they are considered independent
chromosomes
• chromatids move to opposite poles
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TELOPHASE
• final stage of mitosis
• chromosomes arrive to the poles and return to their
interphase condition
• new nuclear envelope forms
• nucleoli reorganizes
• spindle fiber disappears
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CYTOKINESIS
• division of the
cytoplasm
• begins during telophase
• cell plate → plasma
membrane and cell
walls
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MEIOSIS
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SEXUAL REPRODUCTION
• reproductive cells (eggs and sperm cells) are called
gametes
• half the diploid number of chromosome
• form a complete new organism by uniting
• ♀ gamete (egg) unites with the ♂ gamete (sperm) =
zygote (fertilized egg)
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MEIOSIS
• type of cell division that reduces the number
chromosomes in reproductive cells by half
• “to make smaller”
• haploid cells always contain each homologous pair
• when two numbers of haploid cells unite during
fertilization, the normal diploid number of the cell is
restored
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PROPHASE I
• elongated and thin homologous chromosomes lie
side by side (synapsis)
• crossing over – pieces of maternal and paternal chromatids
break off and rejoined to the opposite chromatid; produces
new combination of genes
• genetic recombination – enhances variety among
sexually produced offspring
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PROPHASE I
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METAPHASE I
• homologous chromosomes line up in pairs along the
midplane
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ANAPHASE I
• homologous chromosome
separate with one moving
toward one pole and the
other toward the other pole
• chromosomes remain united
at centromere
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TELOPHASE I
• duplicated chromosome
(one of each homologous
pair) at each pole
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MEIOSIS II
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PLANT LIFE CYCLE
• diploid plant (sporophyte) produces haploid spores
by meiosis
• Spores divide by mitosis to give rise to a multicellular
plant known as gametophyte whose cells all
contain haploid number of the chromosomes
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SPERMATOGENESIS & OOGENESIS
• spermatogenesis
• produces mature sperm cells
• all four products can acquire a flagellum for locomotion
and a cap-like structure that aid in the penetration of the
cell
• oogenesis
• production of mature ovum or egg cell
• only one of four meiotic products develops into functional gamete
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BRING THE FOLLOWING
• Onion root tips
• prepare by placing in a vial containing 70% ETHYL alcohol
• glass slide, cover slips
• gillette blade or scalpel
• check flies next meeting