38 Questions
What is the phase called when a cell is not dividing?
Interphase
What is the typical duration of the M-phase of the cell cycle?
1-2 hours
What happens to the G1 and G2 phases during cleavage of zygote and blastomeres in mammalian development?
They are abolished
What is the special G1 state called when cells have completely ceased cycling?
G0-phase
What is the term for the alternation between mitosis and interphase in the life of a cell?
Cell division cycle
What is the longest phase of the cell cycle?
Interphase
What type of cells have a very short or non-existent G1 phase?
Rapidly dividing cells
How long can the G1 phase last in hepatocytes?
One-half to one year
During which stage of mitosis does the nuclear envelope and nucleolus disappear?
Metaphase
What happens to the sister chromatids during early anaphase?
They move towards the opposite poles of the cell
What happens to the microtubules during late anaphase?
They lengthen and pull the sister chromatids apart
During which stage of mitosis do the poles move farther apart?
Anaphase
What appears in the equatorial plane of the cell membrane during late anaphase?
A cleavage furrow
What happens to the chromosomes during meiosis?
They are duplicated during the S phase
When does telophase begin?
After the chromosomal movement stops
What happens to the nucleolus during prophase?
It disappears
What is the result of the fusion of two haploid cells?
A diploid zygote or diploid cell
What is the point of attachment of the spindle microtubules to the chromosome?
Kinetochore
What is the symbol for the number of chromosomes in a diploid cell?
2n
What happens during cytokinesis?
The cleavage furrow deepens and divides the cytoplasm and organelles in half
What is the term for the process of non-sister chromatids exchanging bits during prophase I?
Crossing over
What is the longest part of meiosis?
Prophase I
What is the number of cells that result from meiosis?
4 cells
What is the term for half the diploid number of chromosomes?
Haploid
What are the two broad events that cell division consists of?
Nuclear division or karyokinesis, and cytoplasmic division or cytokinesis
What happens to the DNA during the S-phase of the cell cycle?
It is doubled from 2N to 4N
What is the result of DNA replication during the S-phase?
Each chromosome becomes a pair of sister chromatids
What happens to the nuclear envelope during prophase?
It remains intact
What happens to the centrioles during prophase?
They separate and migrate to opposite poles of the cell
What is the result of the spindle microtubules during prophase?
They appear between the centrioles
What is the characteristic of the chromosomes during Prophase II?
The sister chromatids are still coupled together at the centromere
What happens to the chromosomes during Metaphase II?
The chromosomes move to the equatorial plane
What is the result of Anaphase II?
The centromeres separate and the sister chromatids are pulled apart
What is the final result of Telophase II?
The former sister chromatids have reached the poles and a nuclear envelop is formed around each nucleus
What is the role of Meiosis in sexually reproducing eukaryotes?
It preserves the genome size and provides mechanisms to diversify the genomes of the offspring
What is the orientation of the equatorial plane during Metaphase II with respect to the previous one of meiosis I?
Perpendicular
What happens to the sister kinetochores during Meiosis?
They pull both sister chromatids toward one pole of the cell
What is the stage of Meiosis where the chromosomes condense again?
Prophase II
Study Notes
Mitosis
- Mitosis is a process of cell division characterized by four stages: Prophase, Metaphase, Anaphase, and Telophase.
- In Prophase, the nucleolus disappears, and the nuclear membrane breaks down.
- In Metaphase, the nuclear envelope and nucleolus disappear, and the chromosomes occupy the equatorial plane of the spindle microtubules.
- In Anaphase, sister chromatids migrate towards the opposite poles of the cell, following the direction of the spindle microtubules.
- In Telophase, the reappearance of the nuclei in daughter cells occurs, and the chromosomes revert to their semi-dispersed state.
Cytokinesis
- Cytokinesis is the process of cell division, characterized by the cleavage furrow progressing until it divides the cytoplasm and its organelles in half.
Meiosis
- Meiosis is a process of cell division characterized by two consecutive divisions: Meiosis I and Meiosis II.
- No DNA synthesis (or S phase) occurs between the two divisions.
- Four cells result, each with half the number of chromosomes of the starting cell (2n → n).
- Fusion of two such cells produces a 2n zygote or diploid zygote.
Symbols and Terminologies
- Diploid: a set of 23 pairs of chromosomes (or 46) symbolized as 2n.
- Haploid: half the diploid number of chromosomes (or 23) symbolized as n.
- DNA in a diploid cell before S-phase is 2N.
- After the S-phase (duplication of DNA) in preparation for mitosis, the DNA is 4N.
Meiosis I
- In Prophase I, the chromosomes become visible, already doubled, with each homologue having been duplicated during the preceding S phase.
- Non-sister chromatids exchange bits, a process called crossing over or chiasmata formation.
- It is the longest part of meiosis.
Meiosis II
- In Metaphase II, microtubules of the spindle fibers attach to sister kinetochores of one homologue, pulling both sister chromatids toward one pole of the cell.
- In Anaphase II, the centromeres separate, and the sister chromatids are pulled apart to opposite poles by the spindle.
- In Telophase II, the former sister chromatids reach the poles, and a nuclear envelope is formed around each nucleus, while chromosomes uncoil again.
Genetic Recombination
- Meiosis not only preserves the genome size of sexually reproducing eukaryotes but also provides three mechanisms to diversify the genomes of the offspring.
Cell Division Cycle
- Every living cell that is not dividing exists in a phase called Interphase.
- Interphase lasts for a variable duration from a few hours to a year or more.
- When a cell is dividing, it enters a phase called Mitosis.
- The alternation between mitosis and interphase in the life of a cell is called the cell division cycle.
Quiz on the stages of mitosis, including prophase and metaphase, covering the breakdown of the nuclear membrane and the movement of chromosomes.
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