The Cell Cycle and Mitosis Flashcards
Diploid (2n)
Contain two copies of each chromosome
Haploid (n)
Containing only one copy of each chromosome
Interphase
First 3 stages of cell cycle: contains G1, S, and G2 –> longest part of the cell cycle; actively dividing cells spend about 90% of their time in interphase.
G0 phase
Cell is simply living and carrying out its functions, without any preparation for division
G1 stage
Cells create organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum) while also increasing their size.
Restriction point
Occurs in G1 stage. Certain criteria, such as containing the proper complement of DNA, must be met for the cell to pass the restriction point and enter the synthesis stage.
S stage
Cell replicates its genetic material so that each daughter will have identical copies.
Does cell ploidy change after replication in synthesis stage?
No: chromatids have doubled, so twice as much DNA is present, but ploidy is still the same.
G2 stage
Cell checks to ensure that there are enough organelles and cytoplasm for 2 daughter cells.
p53`
The main protein in control of the restriction checkpoint, and also at the G2/M checkpoint.
Molecules responsible for the cell cycle
Cyclins and Cyclin-dependent kinases (CDK)
How do CDKs work
During the cell cycle, concentration of the various cyclins increase and decrease during specific stages. These cyclins bind to CDKs, creating an activated CDK-cyclin complex, which can then phosphorylate transcription factors –> then promote transcription of genes required for next stage of cell cycle.
List the phases of mitosis and describe briefly
Prophase – chromosomes condense, spindle forms
Metaphase – chromosomes align
Anaphase – sister chromatids separate
Telophase – new nuclear membranes form
Meoisis I
Results in homologous chromosomes being separated, generating haploid daughter cells; this is known as reductional division.
Meiosis Ii
Similar to mitosis: results in separation of sister chromatids without a change in ploidy –> therefore known as equational division
How is Prophase I meiosis different than Prophase in mitosis
In meiosis, in prophase I, homologous chromosomes come together and intertwine in a process called synapsis. Then crossing over occurs during genetic recombination
Tetrad
In prophase I of meiosis, each chromosome consists of 2 sister chromatids –> each synaptic pair contains 4 chromatids
Synaptonemal complex
The group of proteins that hold together homologous chromosomes in prophase I of Meiosis
Chiasma (plural chiasmata)
Point of contact between homologous chromosomes, where they may break and exchange equivalent pieces of DNA –> crossing over.
Mendel’s second law of independent assortment
States that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes, explained by crossing over.
How is Metaphase I in meiosis different than metaphase in mitosis
In mitosis, each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole).
In meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber
How is Anaphase I in meiosis different than anaphase in mitosis
Process is called disjunction, accounts for Mendel’s first law (of segregation). Each chromosome of paternal origin separates from its homologue of maternal origin –> either chromosome can end up in either daughter cell –> this random separation is called segregation
How is Telophase I different than telophase in mitosis
Cells are now haploid in meiosis: e.g in humans, only 23 chromosomes are now found in each daughter cell.
Hemizygous
Describes the characteristic way males inherit genes on the X chromosome, as they only have one copy.
SRY (sex-determining region Y)
One notable gene on the Y chromosome, which codes for a transcription factor that initiates testis differentiation and , thus, the formation of male gonads.
