Flashcards in Chapter 12 Deck (49)
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A distinguishing characteristic of living things from nonliving things
the ability of organisms to reproduce
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the continuity of life is based upon...
the reproduction of cell, or cell division
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Unicellular organisms
reproduce an entire organism by cell division
i.e. amoeba
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Multicellular organisms
depend on cell division for multiple processes including: development from a fertilized cell or egg, growth of cells to develop tissues, and repair and renew cells that die from normal wear and tear or accidents
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3 reasons for Mitosis to occur
1) Reproduction
2) Growth and development
3) Tissue renewal
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Cell division is
part of the cell cycle
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Cell cycle
the life of a cell from its origin in the division of a parent cell until its own division into two new cells
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Cell division requires
the distribution of identical genetic material -- DNA - to 2 daughter cells
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Cells duplicate their genetic material
before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA
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Genome
(a cell's endowment of DNA, its) genetic information
can range from a single DNA molecule (prokaryotes) to several DNA molecules (eukaryotes)
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DNA molecules in a cell are packaged into
chromosomes
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(Eukaryotic) Chromosomes
have a characteristic number in each nucleus depending on the species and consist of chromatin
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Chromatin
a complex of DNA and protein that condenses during cell division
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in animals, somatic cells...
have two sets of chromosomes
-i.e. human somatic cells have 46 chromosomes (2 sets of 23 from each parent)
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in animals, gametes
have one set of chromosomes
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In preparation for cell division, DNA...
is replicated and the chromosomes condense to make a small package
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Each duplicated chromosome has...
2 sister chromatids, which separate during cell division and contain identical DNA
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During Condensation (of cell division)
the chromatids are connected at a narrow area, called the centromere
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Centromere
narrow area at which the chromatids are connected
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Later in cell division,
the chromatids are pulled apart into the new nuclei at opposite ends of the parent cell to form individual chromosomes
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Eukaryotic cell division consists of
mitosis
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mitosis
the division of the nucleus (karyokinesis), cytokinesis, and maintenance of the chromosome number
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Karyokinesis
the division of the nucleus
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Cytokinesis
the division of the cytoplasm
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Meiosis
sex cells (gametes) have a reduction in chromosome number
- yield 4 nonidentical daughter cells
- each with half the chromosomes of the parent
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Cell cycle
consists of the mitotic (M) phase which alternates with the longer interphase
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mitotic phase is made up of
karyokinesis and cytokinesis
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Interphase
the cell grows and prepared for cell division
divided into sub-phases: G1, S, and G2
G = growth phases
S = DNA synthesis (replication)
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5 distinct phases or steps in mitosis
1) Prophase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase (and cytokinesis)
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Prophase
the chromosomes are tightly packed, chromatids are joined, and the mitotic spindle begins to form
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Prometaphase
the nuclear envelope fragments, the microtubules from the spindle interact with the chromosomes, and the chromatids contain a kinetochore
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Metaphase
sister chromatids are arranged at the metaphase plate
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Metaphase plate
an imaginary plane equidistant from the poles of the cell
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Anaphase
the centromeres divide separating the sister chromatids which are pulled toward the poles
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Telophase
daughter nuclei begin to form at the 2 poles and nuclear envelopes begin to arise
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Mitotic Spindle
an apparatus of spindle microtubules and asters that controls chromosome movement during mitosis and arises from the centrosomes
soem spindle microtubules attach to the kinetochores of chromosome and move the chromosomes to the metaphase plate
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In animal calls, Cytokinesis
follows mitosis (karyokinesis) and occurs by a process known as cleavage, which first appears by forming a cleavage furrow in the cell surface near the metaphase plate
Within the cytoplasm, is a contractile ring of actin microfilaments that facilitates and pinches the cell in two
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Prokaryotes (bacteria) reproduce by a types of cell division called...
binary fission
(typically more rapid than in eukaryotes)
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During binary fission,
the bacterial chromosome, which is circular DNA, replicates and the 2 daughter chromosomes actively move apart
1) Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell
2) Replication continues. One copy of the origin is now at each end of the cell
3) Replication finishes. The plasma membrane grows inward, and new cell wall is deposited
4) 2 daughter cells result
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Regulation of Cell Cycle
the timing and rates of cell cycle division is crucial for normal growth and development of an organism
and is carefully regulated by an exquisite molecular control system
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Frequency of cell division
varies among cell types and the molecules and enzymes present in the cytoplasm also regulate progress through the cell cycle
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The sequential events of the cell cycle are directed by a
distinct cell cycle control system
(similar to a clock) with cyclinally operating enzymes to coordinate the cell cycle
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The clock has
specific checkpoints where the cell cycle stops until a go-ahead signal is received
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The signals are transmitted by..
signal transduction pathways with three major checkpoints in the G1, G2, and M phases
i.e. EGF (epidermal growth factor)
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G1 checkpoint
restriction point
the most important
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p53
is a tumor suppressor
- protein
- regulated gene
- cell health indicator: detect mutations
mutated p53 can cause cancer
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Internal and External signals
control the cell cycles checkpoints:
1) Growth factors: stimulate other cells to divide (i.e. EGF)
2) Density-dependent inhibition: over-crowded cells stop dividing
3) most animal cells exhibit Anchorage Dependence in which they must be attached to a substratum to divide (i.e. EGF)
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Cancer cells
do not respond normally to the body's control mechanisms and form tumors
exhibit neither dentist-dependent inhibition nor anchorage dependence
overgrowth leads to tumors and anchorage-independence results in Metastasis (spreading)
can form clump of overlapping cells
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