Unit 4 (Week 12 Mitosis and Meiosis) Flashcards
[16.1 Start - The Eukaryotic Cell Cycle] What is the process of cell reproduction, in which one cell splits into two cells?
Cell division
What is a series of events that leads to cell division. For eukaryotes, it involves a series of phases in which a cell divides by mitosis or meiosis?
Cell cycle
What is the field of genetics that involves the microscopic examination of chromosomes?
Cytogenetics
When a cell prepares to divide, and the chromosomes become tightly compacted, their length decreases but their diameter increases. What results from this?
A consequence of this compaction is that distinctive shapes and numbers of chromosomes become visible under a light microscope.
Researchers usually treat cells with drugs that stimulate them to divide before beginning the procedure for making a karyotype. Why is this treatment useful?
Chromosomes are readily seen when they are compacted in a dividing cell. By adding such a drug, the researchers increase the percentage of cells that are actively dividing.
What is a an individual’s collection of chromosomes? Also, useful technique in laboratories to photograph and analyze chromosome structure and possible abnormal numbers.
Karyotype.
A photographic representation of the chromosomes from an actively dividing cell. A karyotype reveals the number, size, and form of chromosomes found within an actively dividing cell.
T/F Chromosomes viewed in a karyotype of an actively dividing cell have already been replicated.
True.
What are the two duplicated chromatids that are still joined to each other after DNA replication?
Sister chromatids
How many sets of chromosomes does one set of HUMAN chromosomes have?
23 different types of chromosomes
What does the numbering system of chromosomes not apply to?
The 23rd chromosome, which is the sex chromosomes, which determine the sex of the individual.
What are the letters that determine the sex chromosomes of whether or not a human is male or female?
XX and XY.
Females are XX and males are XY.
What are all of the chromosomes found in the cell nucleus of eukaryotes except for the sex chromosomes?
Autosomes. 22 different types
T/F Many eukaryotic species have cells that contain two sets of chromosomes, with 23 different chromosomes in each set.
True.
Therefore, this human cell contains a total of 46 chromosomes.
Why do most eukaryotic species have two sets of chromosomes?
One inherited by the mother and one inherited by the father.
What do you call a cell containing two sets of chromosomes; designated as 2n?
A diploid.
Since humans are 2n, where n = 23. 23 x 2 = 46
What is the haploid cell that is involved with sexual reproduction, such as a sperm or egg cell?
Gamete
What is a 1n cell, which means they contain one set of chromosomes?
Haploid. These are what gametes are considered as.
What is the member of a pair of chromosomes in a diploid organism?
A homolog.
1 chromosome and the other chromosome, within a pair, are homologous of each other.
Homologous = similar in position, structure, and evolutionary origin but not necessarily in function.
What is a similarity that occurs due to descent from a common ancestor?
Homology
The OCA2 gene found in chromosome 15 determines eye color. Do each homolog confer the same color?
Not always. Since 1 is received from each parent, one may confer blue while the other will confer brown.
What is typically the difference between two chromosomes from different parents, like for example, chromosome 1?
Less than 1% in differences.
What chromosomes does homology, even with slight similarities, not apply and they differ in size and genetic composition?
The sex chromosomes - XX and XY.
Certain genes found on the X chromosome are not found on the Y chromosome, and vice versa. The X and Y chromosomes are not considered homologous chromosomes, although they do have short regions of homology.
What types of changes occur in eukaryotic cell division?
Growth, replication, and division.
What are the phases of cell division?
G1, S, G2, and M.
What is produced at the end of cell division?
Two daughter cells.
During the S phase of cell division, what happens to the count of individual or set chromosomes?
It doubles.
For example, the cell dividing has 3 sets (6 individual chromosomes) and in the S phase, they are replicated to equal 12 individual chromosomes or 6 sets.
This replication creates Chromatids!!!
Which phase, during cell division, is the shortest and which is typically the longest?
M phase is the shortest while G1 is the longest phase.
Which phases make up interphase?
Interphase consists of the G1, S, and G2 phases of the cell cycle.
The portion of the cell cycle consisting of the G1, S, and G2 phases, during which the chromosomes are decondensed and found in the nucleus.
List the phases of cell division in order and what their abbreviations mean.
G1 which is the first gap
S which is the synthesis of DNA, the genetic material.
G2 which is the second gap
M which is the phase of mitosis and cytokinesis
What were G1 and G2 phases originally described to indicate what?
Gaps in the DNA synthesis and mitosis phases.
What phase does the cell grow and copy its chromosomes in preparation for cell division?
The interphase
What phase happens when a cell exits the cell cycle and remain for long periods of time? This is an alternative to proceeding through G1.
G0 or G zero phase.
A cell in the G0 phase has postponed division or, in the case of terminally differentiated cells (such as muscle cells in an adult animal), will never divide again. G0 is a nondividing phase.
What phase in the cell cycle pertains to cell growth and the commitment of division? Typically triggered by environmental conditions and signaling molecules.
G1 Phase
In what phase does each chromosome replicate to form a pair of sister chromatids? At the conclusion of this cycle, a cell will have twice as many chromatids as the number of chromosomes in the previous phase.
S phase.
For example, a human cell in G1 phase has 46 distinct chromosomes, whereas the same cell in G2 phase will have 46 pairs of sister chromatids, for a total of 92 chromatids.
[Bonus] When do we use the phrase sister chromatid?
Term sister chromatid is only used during the parts of cell division when the structures are in that X shape, or when the two copies are connected by a centromere.
What phase is when a cell synthesizes the proteins necessary for chromosome sorting and cell division? Some cell growth may occur.
G2 phase
In eukaryotes, what is the phase in the process in which nuclear division results in two nuclei, each of which receives the same complement of chromosomes?
Mitosis
What follows mitosis, in which the division of cytoplasm produces two distinct daughter cells?
Cytokinesis
T/F Cell division can vary where embryos divide in a few minutes while slow-growing adult cells divide in several months.
True.
For a cell that divides in 24 hours, what is the time it takes for each phase to finish? Think 3-4-3 gaps
G1 phase: 11 hours
S phase: 8 hours
G2 phase: 4 hours
M phase: 1 hour
Again, what triggers cell division? (3)
External factors such as environmental conditions and signaling molecules.
Growth factors have an effect as well on cell division (see picture)
What internal factors effect cell division? (2)
Cell cycle control molecules and checkpoints.
Why is the advancement through the cell cycle highly regulated?
To ensure that the genome remains intact and that the conditions are appropriate for the cell to divide.
What are responsible for advancing a cell through the phases of the cell cycle?
Cyclins - A protein responsible for advancing a cell through the phases of the cell cycle by binding to a cyclin-dependent kinase.
Cyclin-dependent kinases (cdks) - A protein responsible for advancing a cell through the phases of the cell cycle. Its function is dependent on the binding of a cyclin.
To be active, the cyclin-dependent kinases controlling the cell cycle must bind to (are dependent on) cyclins. The numbers of different types of cyclins and cdks vary from species to species.
Why are cyclins named the way they are?
Cyclins are so named because their amount varies throughout the cell cycle.
Cyclin/cdk complexes are needed to transition a cell through the cell division cycle. What is the significance of these complexes, like G1 cyclin/cdk and mitotic cyclin/cdk?
For G1 complex, it increases the nutrients and growth factors. For mitotic complex, it allows for the phosphorylation of proteins needed in the M phase.
Once these complexes complete their jobs, they are degraded and the products are reused at a later time.
How many critical regulatory points called checkpoints are found in the cell cycle of eukaryotes?
Three
At these checkpoints, a variety of proteins act as sensors to determine if a cell is in the proper condition to divide.
Which checkpoint determines if conditions are favorable for division which commits for division and senses if DNA has incurred damage?
The restriction checkpoint in the G1 phase. This checkpoint can prevent complexes from being formed.
Where is the second checkpoint located that also checks for DNA damage and ensures all DNA has been replicated? This checkpoint’s proteins also monitor the levels of proteins that are needed to advance through the M phase,
In the G2 phase known as the G2 checkpoint
What is the metaphase checkpoint accomplish? (2)
- Proteins that monitor the integrity of the spindle apparatus (involved in chromosome sorting)
- Checks to see if all chromosomes are attached to the spindle during mitosis
Main purpose of checkpoint proteins in cell division?
A primary aim of checkpoint proteins is to prevent the division of a cell that has incurred DNA damage or harbors abnormalities in chromosome number.
[Bonus] What today is the maturation-promoting factor or MPF that was discovered in leopard frogs when Masui and Markert speculated about the protein triggers in cell division?
Cyclin and cyclin-dependent kinases (cdks)!
[Start 16.2 Mitotic Cell Division] What is a process whereby a eukaryotic cell divides to produce two new cells that are genetically identical to the original cell?
Mitotic Cell Division
What two specific processes does mitotic cell division involve?
Mitosis and cytokinesis
What is a reproductive strategy that occurs when offspring are produced from a single parent, without the fusion of gametes from two parents? The offspring are therefore clones of the parent.
Asexual reproduction
What are two examples of organisms that asexually reproduce?
Baker’s yeast (Saccharomyces cerevisiae) and the amoeba
Other than understanding asexual reproduction, why else is mitotic cell division important?
A second important reason for mitotic cell division is the production and maintenance of multicellularity. Organisms such as plants, animals, and most fungi are derived from a single cell that subsequently undergoes repeated cell divisions to become a multicellular organism.
What is a laymen way of understanding a pair of sister chromatids?
When DNA is replicated, two identical copies of the original double helix are produced.
These copies, along with associated proteins, lie side-by-side are termed sister chromatids.
Essentially, its two strands of replicated DNA attached by a centromere.
Why are sister chromatids easy to see under a light microscope when prepping for cell division?
The heavy compaction increases their width!
What is the region where the two sister chromatids are tightly associated; this is an attachment site for kinetochore proteins?
Bonus Q: What is the protein that holds the sister chromatids together?
Centromere; Cohesin.
Additionally, what does the centromere also act as and for what?
An attachment site for a group of proteins that form the kinetochore.
This is necessary for sorting chromosomes.
What is the structure responsible for organizing and sorting the chromosomes during mitosis?
Mitotic spindle. Also called the mitotic spindle apparatus.
What is the mitotic spindle composed of?
Microtubules.
Where does the microtubules in the mitotic spindle apparatus start to grow?
The microtubule growth and organization starts at two centrosomes, also referred as microtubule-organizing centers (MTOCs)
[Focus Mitotic Spindle Growth]
- In what phase does a single centrosome duplicate?
- What is defined by the centrosomes when entering mitosis?
- What do animal cells have that plant cells do not which consists of a pair with the centrosome and each one has nine sets of triplet microtubules?
- What organizes the construction of microtubules using what proteins?
- What are the three types of spindle microtubules formed in animal cells during cell division cycle?
- Lastly, where are these microtubules located during cell division?
- The interphase
- Two poles; one within each daughter cell.
- Centrioles. These are not required in plants for spindle formation.
- Centrosomes by rapidly polymerizing tubulin proteins.
- Astral, polar, and kinetochore microtubules.
- Astral microtubules emanate away from the region between the poles. Polar microtubules project into the region between the poles. The kinetochore microtubules are attached to the sister chromatids.
What is the sorting process for dividing one cell nucleus into two nuclei?
Mitosis
What are the functions of the three types of microtubules?
The astral microtubules, which extend away from the chromosomes, are important for positioning the spindle apparatus within the cell. The polar microtubules project into the region between the two poles. Polar microtubules that overlap with each other play a role in the separation of the two poles. Kinetochore microtubules are attached to kinetochores at the centromeres and are involved in sorting the chromosomes.
Aside from interphase (which you have already learned), what phases consists of the continuum of phases for mitosis? There are 5 sub phases.
Prophase, prometaphase, metaphase, anaphase, and telophase
What happens in the prophase?
Sister chromatids condense into highly compacted structures which are visible in light microscopy. As this phase proceeds, the nuclear envelope begins to dissociate into small vesicles and the nucleolus is no longer visible.
What phase has the nuclear envelope entirely dissociated into vesicles, and the mitotic spindle is fully formed?
The centrosomes also moves apart and demarcate the two poles. At this point, the spindle fibers can interact with the sister chromatids.
The prometaphase.
The sister chromatids can actually be seen under a microscope undergoing jerking motions as they are tugged, back and forth, between the two poles by the kinetochore microtubules.
In what phase are the pairs of sister chromatids aligned in a single row along the metaphase plate, a plane halfway between the two poles of the spindle apparatus?
The metaphase. When this alignment is complete, the cell is in metaphase of mitosis. The chromatids can then be equally distributed into two daughter cells.
What happens during the anaphase? (3)
- Connections between the pairs of sister chromatids are broken which become individual chromosomes.
- The individual chromosomes are linked to one or two poles by one or more kinetochore microtubules.
- The kinetochore microtubules shorten, pulling chromosomes toward respective poles while the two poles move farther away from each other.
During which phase has the chromosomes reached their respective poles and decondense?
The nuclear envelope now re-forms to produce two separate nuclei.
The telophase
T/F Mitosis is very different between animals and plants while cytokinesis is very similar.
False. Mitosis is very similar in plants and animals. Cytokinesis is quite different, though.
What are the similarities and differences between animal and plant cells with regard to cytokinesis?
Cytokinesis in both animal and plant cells follows mitosis and separates a mother cell into two daughter cells. In animal cells, cytokinesis involves the formation of a cleavage furrow, which constricts like a drawstring to separate the cells. In plants, the two daughter cells are separated by a cell plate, which forms a cell wall between them.
[Start 16.3 Meiosis]
What is the process by which haploid cells are produced from a cell that was originally diploid?
Meiosis
For example, a diploid human cell contains 46 chromosomes, but a human gamete—sperm or egg cell—is a haploid cell that contains only 23 chromosomes.
What are the two rounds of division needed for diploid cells to become gametes?
Meiosis I and Meiosis II
What phases must happen before meiosis begins?
G1, S, and G2 phase.
What are the two events that occur in the beginning of meiosis that do not occur in mitosis?
- Homologous pairs of sister chromatids associate with each other, lying side by side to form a bivalent AKA a tetrad.
- A process called crossing over which is the exchange of genetic material between homologous chromosomes during meiosis; allows for increased variation in the genetic information that each parent may pass to the offspring.
What does crossing over in meiosis accomplish?
Crossing over increases the genetic variation of sexually reproducing species.
What is the process called in which the forming of the bivalent AKA tetrad occurs?
Synapsis
In most eukaryotic species, a protein structure called the synaptonemal complex connects homologous chromosomes during a portion of meiosis. However, the synaptonemal complex is not required for the pairing of homologous chromosomes because some species of fungi completely lack such a complex, yet their chromosomes associate with each other correctly.
During crossing over, what is the connection made at the cross over site between the two pairs of chromatids?
The chiasma (plural = Chiasmata)
This formation resembles an x as the Greek letter chi
After chromosomes are replicated in the S phase, what sequential divisions follow?
Meiosis I and Meiosis II
T/F Meiosis I and Meiosis II also go through a continuum of phases called the prophase, prometaphase, metaphase, anaphase, and telophase.
True
What does the sorting in meiosis I do to the homologous chromosomes?
Separates them
