Chapter 5 Flashcards
What does cell division allow?
A single-celled fertilized egg to grow into an organism with trillions of cells.
What are somatic cells?
Body cells that continue to undergo cell division even as an adult.
What is apoptosis?
Programmed cell death. It decreases the number of cells when cells age and no longer function well. It also plays an important role in preventing cancer.
What is the cell cycle?
The orderly sequence of stages with cell division.
What is interphase?
What cell does between times of division.
What are the 3 stages of interphase?
G1: stage before DNA synthesis.
S: DNA synthesis
G2: Stage after DNA synthesis.
Describe G1.
Cell doubles its organelles and accumulates material. Mostly, cell is in growth phase and if DNA is damaged, cell will undergo apoptosis.
Describe S stage.
At start, each chromosome consists of one DNA molecule, called chromatid. Each chromatid makes an exact copy of itself, and after DNA replication, each chromosome now consists of two sister chromatids.
Describe G2.
The cell synthesizes proteins for cell division. Cell also checks if there is any damage that happened when sister chromatids were made. If so, apoptosis occurs.
What is the mitotic stage?
When cell undergoes division. Usually a very short period of time.
What is mitosis?
Division of the nucleus.
What is cytokinesis?
Division of the cytoplasm.
When does cytokinesis occur?
Just after mitosis, the two daughter cells become two identical cells.
What are caspases?
The enzymes responsible for apoptosis as they are unleashed by external and internal signals.
Describe internal signals.
Ensure the stages follow one another in the normal sequence and properly completed.
Describe external signals.
Tell the cell whether or not to divide.
Describe the 3 checkpoints that control the cell cycle.
G1: stops if DNA is damaged
G2: stops if DNA did not finish replicating
M: stops if chromosomes are not going to be properly distributed.
The checkpoints are critical for preventing cancer development.
What are chromosomes composed of?
Chromatin.
What is a diploid (2N)?
Cells that have two of each type of chromosome.
What is a haploid (1n)?
Cells have half the diploid number of chromosomes.
Describe the overview of mitosis.
Nuclear division in which chromosome number stays constant, one 2n cell becomes two 2n cells. DNA replication produces duplicated chromosomes. Each duplicated chromosome is composed of two sister chromatids held together by a centromere.
What is mitosis?
Nuclear division that forms two daughter nuclei with the same number of chromosomes and the same kind of chromosomes.
Are daughter cells the same as parental cells?
Yes.
What does a spindle do?
Brings an orderly distribution of chromosomes to the daughter cell nuclei.
Describe prophase.
Nuclear membrane disappears, centrosomes migrate, spindle fibres appear. Chromatin condenses and chromosomes become visible. (Each is composed of 2 sister chromatids) and the chromosomes have no particular orientation.
Describe prometaphase.
Centromeres attach to spindle fibres, centrosomes have migrated to either end.
Describe metaphase.
Spindle fully forms and consists of poles, asters, and fibres. Chromosomes line up at metaphase plate.
Describe anaphase.
Centromeres divide, and sister chromatids are moved to opposite poles by fibres.
Describe telophase.
Nuclear membrane reforms, spindle disappears, cytokinesis occurs. Chromosomes become more diffuse again. Nucleolus appears in each daughter nucleus.
Describe mitosis in plant cells.
Basically the same, permits growth and repair as in animal cells, goes through same phases as animal cells and does not use centrioles or asters.
Describe cytokinesis in animal cells.
Cleavage furrow forms between daughter nuclei, contractile ring contracts, deepening the furrow. Process continues until separation is complete.
Describe cytokinesis in plant cells.
Requires creation of new cell wall between daughter cells. A flattened, small disk appears between daughter cells and a cell plate forms.
Describe meiosis.
Occurs in the life cycle of sexually reproducing organisms. Reduces the chromosome number in half. Provides offspring with a different combination of traits from that of either parent.
Describe the process of meiosis.
Begins with one diploid parental cell. Requires two cell divisions, ends with four haploid daughter cells. Involves pairs of chromosomes called homologues that are inherited from each parent.
Describe meiosis 1.
Homologues line up side by side at the equator (synapsis). When homologous pairs separate, each daughter cell receives one member of the pair. The cells are now haploid.
Describe meiosis 2 and fertilization.
No replication of DNA occurs between meiosis 1 and meiosis 2. Centromeres divide and sister chromatids migrate to opposite pole to become individual chromosomes. Each of the four daughter cells produced has the haploid chromosome number.
Describe fertilization.
Daughter cells of meiosis mature into gametes, sperm and eggs fuse in fertilization. It restores the diploid number.
What does meiosis require?
2 nuclear divisions.
What does meiosis result in?
4 Daughter nuclei.
What is meiosis 1 divided into?
Prophase 1, anaphase 1, metaphase 1, and telophase 1.
What does meiosis insure?
Genetic variation.
How does genetic variation occur?
Crossing-over, and independent assortment.
Describe prophase 1 in meiosis.
Synapsis occurs, nuclear membrane breaks down. Spindle appears, nuclear envelope fragments, and nucleolus disappears. Homologues line up side by side and crossing over occurs.
Describe crossing-over.
This is when chromatids homologous chromosomes exchange pieces of DNA with each other. Resulting chromosomes have sister chromatids that are no longer identical.
Describe metaphase 1 in meiosis.
Homologous pairs line up at metaphase plate, no way to know which homologous chromosomes will go to what pole. One homologue is from maternal other from fraternal. It is independent assortment.
When does independent assortment occur?
When homologues separate from each other during anaphase 1.
What does independent assortment generate?
Cells with different combinations of maternal and paternal chromosomes.
Describe Telophase 1 in meiosis.
See at the end of meiosis 1, nuclear envelopes re-form, nucleoli reappear, cytokinesis may occur, producing two daughter cells which are haploid.
What is interkinesis?
Period of time between meiosis 1 and meiosis 2, no replication of DNA.
Describe prophase 2 in meiosis 2.
Cells have one chromosome from each homologous pair. A spindle appears and the nuclear envelope disassembles, each duplicated chromatid attaches to the spindle. The nucleolus disappears.
Describe metaphase 2 in meiosis 2.
Sister chromatids line up at the metaphase plate.
Describe anaphase 2 in meiosis 2.
Sister chromatids separate, each separated chromatid then goes to either pole.
Describe telophase 2 in meiosis 2.
The spindle disappears and the nuclear envelope re-forms, cytokinesis occurs.
How does meiosis produce haploid cells?
From diploid cells.
What does genetic variation produce?
Cells that are no longer identical to parental cells.
Does Mitosis start with 2N or N?
2N
Does mitosis end with 2N or N?
2N
Does meiosis start with 2N or N?
2N
Does meiosis end with 2N or N?
N
How many divisions of mitosis and meiosis?
Mitosis: 1
Meiosis:2
How many daughter cells for mitosis and meiosis?
Mitosis: 2
Meiosis: 4
Are mitosis daughter cells clones?
Yes
Are meiosis daughter cells clones?
No
What phase of meiosis does crossing over occur?
1
What happens to chromosomes in anaphase 1 of meiosis?
Homologous separated.
What happens to chromosomes in anaphase 1 of meiosis?
Sister chromatids separated.
What happens to chromosomes in anaphase of mitosis?
Sister chromatids separated.
What happens at fertilization?
A haploid sperm and haploid egg fuse, the resulting zygote has a diploid number of chromosomes.
What is spermatogenesis and what does it do?
Meiosis in the testes of males, produces sperm.
What is oogenesis and what does it do?
Meiosis in the ovaries of females, produces eggs.
Describe spermatogenesis.
Primary spermatocytes divide in meiosis 1 to form two secondary spermatocytes. Secondary spermatocytes divide in meiosis 2 to produce four spermatids. Spermatids then mature to sperm.
Describe Oogenesis.
One primary oocyte continues the process of meiosis during each menstrual cycle. Primary oocyte divides in meiosis 1 to produce one secondary oocyte and one polar body. If the secondary oocyte is fertilized, meiosis 2 will proceed. Another unequal division will occur, with the egg receiving most of the cytoplasm. A second polar body is also formed. If not fertilized, egg disintegrates.
