Chapter 12 Flashcards
Which of the following events does not occur during interphase of the cell cycle? Production of new mitochondria Separation of the sister chromatids Protein production Production of the endoplasmic reticulum Duplication of the chromosomes Growth of the cell
Separation of the sister chromatids
Checkpoints in the cell cycle control system
Regulate the cell cycle through a variety of stop and go signals
The region of a chromosome holding the two double strands of replicated DNA together is called
A centromere
The spread of cancer cells to other locations in the body is known as
Metastasis
What is the difference between a benign tumor and a malignant tumor?
Cells of benign tumors do not metastasize; those of malignant tumors do
Mitotic (M) phase includes
Mitosis and cytokinesis
Shortest part of the cell cycle
Interphase is divided into 3 subleases:
G1 phase (first gap) S phase (synthesis) G2 phase (second gap)
During all 3 interphase subphases…
A cell grows by producing proteins and cytoplasmic organelles such as mitochondria and endoplasmic reticulum
S phase
Duplication of the chromosomes
Continues to grow as it copies its chromosomes
G1 phase
Cell grows
G2 phase
Grows more as it completes preparations for cell division
Dividing phase
M
During interphase, the genetic material of a typical eukaryotic cell is
Dispersed in the nucleus as long strands of chromatin
Which of the following events does not occur during prophase of mitosis?
Nucleoli disappear
The centrosomes move away from each other
Each duplicated chromosome appears as two identical sister chromatids
The chromosomes condense
The mitotic spindle breaks down
The mitotic spindle forms
The mitotic spindle breaks down
How many chromatids does a human somatic cell contain after interphase and just prior to mitosis?
92
You would know a dividing cell was a plant cell rather than an animal cell if you saw
It had formed a cell plate
What occurs during metaphase of mitosis?
The chromosomes align along the metaphase plate of the cell
What is part of the mitotic spindle?
The aster
Nonkinetochore microtubules
Centrosome
Kinteochore microtubules
What happens during telophase of mitosis?
Two distinct daughter nuclei form in the cell
One event during prophase is
The beginning of the formation of a spindle apparatus
Which of the following phases of mitosis is essentially the opposite of prometaphase in terms of the nuclear envelope?
Telophase
How does the process of mitosis differ between most eukaryotes and other eukaryotes such as diatoms and dinoflagellates?
The nuclear envelope fragments in most eukaryotes that remains intact in diatoms and dinoflagellates
What happens during anaphase of mitosis?
The sister chromatids are pulled apart toward opposite sides of the cell
What is the difference between mitosis and binary fission?
Binary fission involves the replication and division of a single chromosome, whereas mitosis involves the division of multiple, replicated chromosomes
In animal cell mitosis, the cleavage furrow forms during which stage of the cell cycle?
Cytokinesis
During prophase
Chromatin condenses into distinct chromosomes
Nucleolus disappears
Mitotic spindle apparatus begins to form
Centrosomes move away from each other, propelled along the surface of the nucleus by the lengthening bundles of the microtubules between them
During prometaphase
Nuclear envelope fragments
Kinetochores attach to microtubules
During metaphase
Mitotic spindle aligns the chromosomes at the metaphase plate, a region along the equator of the cell
During anaphase
Centrioles are at opposite ends of the cell
The paired centromeres of each chromosome are separated by spindle microtubules
Sister chromatids begin moving towards opposite poles of the cell
During telophase
A new nuclear envelope begins to synthesize
Mitotic spindle breaks down
Chromatic uncoils
Cytokinesis begins
During binary fission in bacterium
The origins of replication move apart
The complex DNA and protein that makes up a eukaryotic chromosome if called
Chromatin
What occurs during anaphase?
Centrioles are at opposite poles
Identical chromatids move to opposite poles
Spindle made of microtubules is present
The centromeres divide
150 units of DNA to 300 units of DNA after G2 phase. How is this possible?
The DNA was replicated during the S phase of interphase, which occurs between the two G phases
Chromatids are
Identical copies of each other if they are part of the same chromosome
Cytokinesis refers to
Division of the cytoplasm
A cell has 40 chromatids at the beginning of mitosis. How many chromosomes will it contain at the completion of cytokinesis?
20
Observation of cancer cells in culture support the hypothesis that cancer cells
Do not exhibit density-dependent inhibition
The function of the mitotic cell cycle is to produce daughter cells that
Are genetically identical to the parent cell (assuming no mutation has occurred)
DNA replication occurs in
The S phase of interphase in both somatic and reproductive cells
What describes a cell that undergoes mitosis but not cytokinesis?
The cell contains more than one nucleus
G2 of Interphase
Chromosomes cannot be seen yet because they haven’t condensed
Two centrosomes have formed by duplication of the centrosome
Nuclear envelope encloses the nucleus
Nucleus contains one or more nucleoli (nucleolus)
Each centrosome has
Two centrioles
Prophase
Chromatin fibers become tightly coiled; can be seen
Nucleoli disappear
Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres
Mitotic spindle begins to form
Centrosomes move away from each other, propelled by the lengthening microtubules between them
Mitotic spindle is made of
Centrosomes and microtubules that extend from them
The radial arrays of shorter microtubules that extend from the centrosomes are called asters
Prometaphase
Nuclear envelope fragments
Chromosomes have become even more condensed
Each of the two chromatids or each chromosome now has a kinetochore
Some of the microtubules attach to the kinetochores
Nonkinetochore microtubules interact with those from the opposite pole of the spindle
Metaphase
The centrosomes are now at opposite poles of the cell
Chromosomes have all arrived at the metaphase plate, a plane that is equidistant between the spindle’s two poles
The chromosomes’ centromeres lie at the metaphase plate
For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles
Anaphase
Shortest stage of mitosis, lasts few minutes
Begins when the cohesion proteins are cleaved. This allows the two sister chromatids of each pair to part suddenly
Each chromatids becomes a chromosome
The two daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten
The cel elongated as the nonkinetochore microtubules lengthen
By the end, the two ends of the cel have equivalent and complete collections of chromosomes
Telophase
Two daughter nuclei form in the cell Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system Nucleoli reappear Chromosomes become less condensed Mitotic spindle breaks down Mitosis is now complete
Mitosis
Division of one nucleus into two genetically identical nuclei
Cytokinesis
Division of the cytoplasm is usually well under way by late telophase
Two daughter cells appear shortly after end of mitosis
In animal cells, cytokinesis involves the formation of a cleavage furrow — pinches the cell in two
Genome
A cell’s endowment of DNA
Genetic information
Meosis
Eukaryotic cell division
Sperm and eggs
Prokaryotic genome is often
A single DNA molecule
Eukaryotic genomes have
Numbers of DNA molecules
Chromosomes
What DNA molecules are packed into
Chromatin
Entire complex of DNA and proteins that is the building material in chromosomes
Each eukaryotic species has
A different number of chromosomes in each cell’s nucleus
Human somatic cells
Contain 46 chromosomes
Gametes (reproductive cells)
Have one set or half as many chromosomes as somatic cells
23
Each duplicated chromosome has
2 sister chromatids, which are joined copies of the original chromosomes
When a cell isn’t dividing, and even when replicating, each chromosome is in the form of
A long thin chromatin fiber
After replication, they condense
The two chromatids each contain
An identical DNA molecule
Each sister chromatid has a
Centromere
A region of the chromosomal DNA where the chromatid is attached most closely to its sister chromatid
Mitosis is
The division of the genetic material in the nucleus
Meosis
Yields daughter cells with only one set of chromosomes, half as many chromosomes as the parent cell
Interphase accounts for
90% of the cell cycle
Some cells in multicellular organisms divide
Infrequently or not at all
Spend their time in G1
5 stages of Mitosis
Prophase Prometaphase Metaphase Anaphase Telophase
Mitotic spindle
Many events of mitosis depend on
Forms in the cytoplasm during prophase
Assembles
In animal cells, assembly of the spindle microtubules starts at the centrosome
Centrosome
Subcellular region containing material that functions throughout the cell cycle to organize the cell’s microtubules
A pair of centrioles are located at the center of the centrosome
Aster
Radial area of short microtubules, extends from each centrosome
No centrioles in
Plant cells
Spindle includes the
Centrosomes
Spindle microtubules
Asters
Kinetochore
A structure made up of proteins that have assembled on specific sections of DNA at each centromere
Each of the two sister chromatids of a duplicated chromosome has a
Kinetochore
At metaphase, the centromeres
Of all the duplicated chromosomes are on a plane midway between the spindle’s two poles
This plane is called the metaphase plate
Metaphase plate
Imaginary plate
At the end of anaphase
Duplicate groups of chromosomes are at opposite ends of the elongated parent cell
Nonkinetochore microtubules are responsible for
Elongating the whole cell during anaphase
Nuclei re-form during
Telophase
Spindle dissembles by
Depolymerization of microtubules
Cleavage
Cytokinesis occurs by this process
First sign of cleavage is
The appearance of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate
No cleavage furrow in
Plant cells
Instead, during telophase, vesicles move along microtubules to the middle of the cell, where they produce a cell plate
The cell plate enlarges until
It’s surrounding membrane fuses with the plasma membrane along the perimeter of the cell
Two daughter cells result, each with its own plasma membrane
A cell wall arising from the contents of the cell plate has formed between the daughter cells
Binary fission
Asexual reproduction of single-cells eukaryotes
No mitosis for prokaryotes
Mitosis for single-celled eukaryotes
Origin of replication
Where the DNA of the bacterial chromosome begins to replicate at a specific place on the chromosome
Producing 2 origins
As the chromosome continues to replicate in binary fission,
One origin moves rapidly toward the opposite end of the cell
Mitosis evolved from
Simpler prokaryotic mechanisms of cell reproduction
Cell cycle is controlled by
Specific signaling molecules
Cell cycle control system
Cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
Direct the events
Checkpoint
Control point in the cell cycle where stop and go ahead signals can regulate the cycle
3 most important checkpoints found in
G1
G2
M (mitotic) phase
For a kinase to be active
It must be attached to a cyclin
Because of this requirement, these kinases are called cyclin-dependent kinases (Cdks)
Cyclin
Protein that gets its name from its cyclically fluctuating concentration in the cell
Activity of CDKs rise and fall with changes
In the concentration of its cyclin partner
MPF — Maturation Promoting Factor
M-phase promoting factor
Triggers the cell’s passage into the M phase, past the G2 checkpoint
Acts directly as kinase and indirectly by activating other kinases
G1 checkpoint - “restriction point”
If cell receives go ahead signal at G1, it will usually complete G1, S,G2, and M phases and divide
It it doesn’t, it any exit the cycle, switching into a non dividing state called the G0 phase
Most cells in human body are in G0 phase
Anaphase doesn’t being until
All chromosomes are properly attached to the spindle at the metaphase plate
Growth factor
Protein released by certain cells that stimulates other cells to divide
Density dependent inhibition
A phenomenon in which crowded cells stop dividing
Anchorage dependence
To divide, they must be attached to a substratum
Cancer cells do not
Heed the normal signals that regulate the cell cycle
Cells in culture that acquire the ability to divide are aid to have undergone
Transformation, the process that causes them to behave like cancer cells
Benign
Do not harm and do not metastize
Malignant
Harm
Metastasize
Mestastasis
Spread of cancer cells to locations distant from their original site
Gametes are produced by
A variation of cell division — meiosis
Mitotic spindle made of microtubules controls
Chromosome movement during mitosis
Kinetochores are
Protein complexes associated with centromeres
Since prokaryotes evolved before eukaryotes…
Mitosis probably evolved from binary fission
Cancer cells have neither
Density dependent inhibition
Anchorage dependence
Cancer cells…
Don’t respond normally to body’s control mechanisms
May not need growth factors to grow and divide
Make their own growth factor
Have an abnormal cell cycle control system
May convey a growth factor’s signal without the presence of the growth factor
Normal cell is converted to a cancerous cell by transformation
If abnormal cells only remain at the original site, the lump is
Benign tumor
Malignant tumors…
Invade surrounding tissues and metastasize, reporting cancer cells to other parts of the body
Every chromosome has
A centromere
When a cell in S phase is fused with a cell in G1
DNA synthesis beings immediately in the original G1 nucleus
Tissue culture experiments with PDGF demonstrate that without this substance
Fibroblasts fail to divide
What is a CDK? What does it do?
Cyclin dependent kinase
A kinase that has to be attached to a cyclin to be activated, it is dependent on cyclins
CDKs signal the cell that it is ready to pass into the next stage of the cell cycle
Example of CDK
MPF
Maturation promotion factor
Triggers the cell’s passage into the M phase, past the G2 checkpoint
