Transcript Inquiry into Life, Eleventh Edition

Inquiry into Life
Eleventh Edition
Sylvia S. Mader
Chapter 5
Lecture Outline
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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5.1 Cell increase and decrease
• Increase and decrease of cell numbers
• Mitosis occurs in somatic cells for growth and repair
• Meiosis occurs in the reproductive organs for the
production of gametes.
• Cell division increases number of somatic cells
• Mitosis-division of nucleus of cell
• Cytokinesis-division of cytoplasm
• Occurs throughout life; for growth, development, and repair
• Apoptosis- programmed cell death decreases cell
number
• Occurs throughout life also
• Prevents abnormal cells from proliferating
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Cell increase and decrease, cont’d.
• The cell cycle
– Set of events that occur between the time a cell
divides and the time the resulting daughter cells
divide.
• Stages of interphase –longest phase of the cycle
Most of the cell cycle is spent in interphase.
– Normal cell functions occur as well as preparation for
division
– G1 stage-organelles double in number, accumulates
materials needed for division
– S stage-DNA replication
– G2 stage-synthesis of proteins needed for division
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The cell cycle
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Cell increase and decrease, cont’d.
• Mitotic stage
– Follows interphase
– Includes mitosis and cytokinesis
Control of cell cycle – certain checkpoints can
stop the cell cycle if abnormalities are present
– The protein cyclin must be present for stages to
progress
– G2 checkpoint-stops cycle if DNA is not done
replicating or is damaged
– M checkpoint-stops if chromosomes not aligned
– G1 checkpoint-protein p53 stops cycle if DNA damaged
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Control of the cell cycle
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Cell increase and decrease, cont’d.
• Apoptosis – programmed cell death.
– Progressive series of events resulting in cell
destruction
– Cells rounds up, and loses contact with surrounding
cells
– Nucleus breaks up and cell undergoes fragmentation
– Mediated by 2 sets of enzymes called capsases
known as the initiators and the executioners.
– Initiators are the set that receive the signal to initiate
the events and activates the Executioners.
– The Executioners are the set that activates enzymes
that digest the cell
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Apoptosis
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5.2 Maintaining the chromosome
number
• Maintaining the chromosome numberterminology
– Chromatin-tangled mass of threadlike DNA in
nondividing cell
– Chromosomes-condensed rod-shaped DNA
molecules during division
– Diploid (2N) number-characteristic chromosome
number, chromosomes in pairs
– Haploid (N) number- half the diploid number,
found in gametes
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Maintaining the chromosome
number cont’d.
• Overview of Mitosis
One division that results in 2 diploid daughter
cells identical to the parent cell.
– DNA replicates before Nuclear division occurs. Nuclear
Division then occurs and chromosome number stays
constant. DNA replication produces duplicated
chromosomes which are composed of 2 identical sister
chromatids held together by a centromere
During mitosis, the centromeres divide and the sister
chromatids of each chromosome separate, and become
the nuclei of 2 daughter cells identical to the original cell
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Mitosis overview
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Maintaining the chromosome
number cont’d.
• Mitosis in detail-animal cells
– Prophase-nuclear membrane disappears,
centrosomes migrate, spindle fibers appear
– Metaphase-chromosomes line up at equator,
associated with spindle fibers
– Anaphase-centromeres divide, sister chromatids
migrate to opposite poles, cytokinesis begins
– Telophase-nuclear membranes form, spindle
disappears, cytokinesis occurs
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Late interphase
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Phases of animal cell mitosis
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Maintaining the chromosome
number cont’d.
• Cytokinesis in animal cells
• Cleavage furrow forms between
daughter nuclei and contractile ring
contracts deepening the furrow until
separation is complete
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Animal cell cytokinesis
• Fig 5.8
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Maintaining the chromosome
number cont’d.
• Mitosis in plant cells
– Occurs in meristematic tissues
– Same phases as animal cells except plant cells do
not have centrioles or asters
• Cytokinesis in plant cells
– Flattened, small disk appears between daughter cells
forming cell plate which will become new cell wall
– Golgi apparatus produces vesicles which move to
disk
– Release molecules which build new cell walls
– Vesicle membranes complete plasma membranes
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Phases of plant cell mitosis
• Fig 5.6
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Plant cell cytokinesis
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Maintaining the chromosome
number cont’d.
• Cell division in prokaryotes-binary fission
–
–
–
–
Prokaryotes have a single chromosome
Chromosomal replication occurs before division
Cell begins to elongate to twice its length
Cell membrane grows inward until division is
complete
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5.3 Reducing the chromosome
number
• Overview of Meiosis
– 2 divisions resulting in 4 haploid daughter cells
not identical to parent cells
– Cells are diploid at beginning of meiosis
– DNA replicates before Nuclear division occurs.
– Pairs of chromosomes are called homologues
– Meiosis I
• Homologues line up side by side at equator-synapsis
• When pairs separate, each daughter cell receives one
member of the pair
• Cells are now haploid
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Overview of meiosis
• Fig 5.9
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Reducing the chromosome number
cont’d.
• Overview of meiosis, cont’d.
– Meiosis II
• No replication of DNA occurs in this division
• Centromeres divide and sister chromatids
migrate to opposite poles to become
individual chromosomes
• Each of the four daughter cells produced
has the haploid chromosome number and
each chromosome is composed of one
chromatid
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Reducing the chromosome number
cont’d.
• Meiosis in detail
– Meiosis I- genetic recombination occurs in 2 ways
• Crossing over-exchange of segments of
DNA between homologues
• Independent assortment of chromosome
pairs
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Independent alignment
• Fig 5.11
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Synapsis and crossing over
• Fig 5.10
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Reducing the chromosome number cont’d.
• Phases of meiosis I
– Prophase I
• Synapsis occurs, nuclear membrane breaks down
• Homologues line up side by side and crossing over
occurs
– Metaphase I
• Homologous pairs line up at equator such that maternal
or paternal member may be oriented toward either pole
– Anaphase I
• Homologous chromosomes (each still consisting of 2
chromatids) undergo independent assortment into
daughter cells
– Telophase I
• Cytokinesis produces 2 daughter cells which are
haploid
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Meiosis I
in animal
cells
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Meiosis I
in animal
cells
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Reducing the chromosome number
cont’d.
• Interkinesis-period between meiosis I and meiosis II
• Phases of meiosis II
– Prophase II• Cells have 1 member of each homologous pair
– Metaphase II
• Chromosomes line up at the equator
– Anaphase II
• Centromeres divide and daughter chromosomes
migrate
– Telophase II
• Nuclei form, cytokinesis
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Meiosis II in animal cells
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Meiosis II in animal cells
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Reducing the chromosome number cont’d.
• Nondisjunction-causes various syndromes which result from
abnormal chromosome numbers
– Failure of homologous chromosomes to separate during anaphase
– Failure of sister chromatids to separate during anaphase II
– Ex: Down syndrome results from nondisjunction of chromosome 21
• Genetic recombination
–
–
–
–
Promotes genetic variability
Independent alignment of paired chromosomes during metaphase I
Crossing over in prophase I
Both assure that gametes will contain different combinations of
chromosomes
– When fertilization occurs, the resulting offspring will be genetically
unique
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5.4 Comparison of meiosis and
mitosis
• In comparison of meiosis to mitosis note that:
– DNA replication occurs only once prior to both
– Meiosis requires 2 divisions, mitosis only 1
– Meiosis produces 4 daughter cells, mitosis produces
2
– Daughter cells from meiosis are haploid, those from
mitosis are diploid
– Daughter cells from meiosis are genetically variable,
while those from mitosis are genetically identical
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Comparison of meiosis and mitosis
cont’d.
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Comparison of mitosis and meiosis con’td.
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Comparison of mitosis and meiosis con’td.
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5.5 The human life cycle
• The human life cycle
– Requires both mitosis and meiosis
– In females meiosis is part of the process of
oogenesis
– In males meiosis is part of spermatogenesis
– At fertilization, the resulting zygote divides by
mitosis for the processes of growth and
development
– Mitosis is used for repair throughout life
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Life cycle of humans
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The human life cycle, cont’d.
• Spermatogenesis
– Begins at puberty and continues throughout life
– Occurs in seminiferous tubules of testes
– Primary spermatocytes (2n) divide in meiosis I to form
2 secondary spermatocytes (1n)
– Secondary spermatocytes divide in meiosis II to
produce 4 sperm
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The human life cycle, cont’d.
• Oogenesis
– Occurs in the ovaries
– Primary oocyte (2n) divides in meiosis I to produce 1
secondary oocyte (1n) and 1 polar body
• Division is unequal as secondary oocyte receives
most of the cell contents and half the
chromosomes
• Polar body functions only to receive half of the
chromosomes
– Secondary oocyte begins meiosis II but stops at
metaphase II; polar body may also divide
– At puberty, after ovulation secondary oocyte is
activated if fertilized to complete division
– Meiosis II produces 1 ovum and 1 polar body
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The human life cycle, cont’d.
• Oogenesis, cont’d.
– Products of oogenesis are 1 large ovum and
up to 3 small polar bodies
– Ovum receives nearly all cytoplasm and
organelles and half the chromosomes
– Polar body gets the remaining half of the
chromosomes
– Allows ovum to have all the cellular
“machinery” it needs for embryonic
development
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Spermatogenesis and oogenesis
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The human life cycle, cont’d.
• Summary
– Spermatogenesis and oogenesis both utilize meiosis
– Spermatogenesis begins at puberty and continues
throughout life
– Spermatogenesis produces 4 sperm per primary
spermatocyte
• Results in production of many sperm
– Oogenesis results in 1 oocyte and up to 3 polar bodies per
primary oocyte
• Divisions are unequal, ovum receives most cell
contents
– Oogenesis begins prior to birth, stops until
puberty, then resumes in a cyclic pattern with
cyclic release of oocytes until menopause when
the process stops
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