Unit 4 (2.0): The Cell Cycle, Mitosis, Meiosis Flashcards
(21 cards)
What are somatic cells?
Somatic cells are all cells that me up the body
- cells that make up the: liver, heart, skin, muscle, nervous system, etc.
- EXCLUDES sex cells = sperm and egg
How many chromosome pairs are in each human somatic cell?
Humans have 23 chromosome pairs in all somatic cells:
- 1 chromo. from each pair comes from the mother and other chromo from the pair comes from father
- 23 x 2 chrom.es = 46 individual chrom.es
- 22 of 23 pairs are homologous = both members of the pair have recipes for the same protein at exact same spot on chromo.
- ex. = hair color, eye color, etc.
- they can differ in the “flavour” of the recipe
- blue eyes from one parent and brown from
other - these different flavours (versions) of the same
gene are called alleles
- blue eyes from one parent and brown from
Chrom.es numbered 1-23
- 1-22 = autosomal chrom.es
- Chrome 23 = sec chrom.es (homologous in females and non-homologous in males)
- XX: female, XY: male
More info on chrom.es
n is the number of DIFFERENT chrom.es that a given species will have
- referred to as the haploid number
- in humans this number = 23
2n is the TOTAL number of chrom.es that an ind. will have
- formed from a mother and father
- each gives n number of chromosomes to offspring
- referred to as the diploid number
- in humans this number is 46
What is the cell cycle and what are the two stages?
The cell cycle involves the division of one somatic cell into two identical daughter cells. Consists of two stages:
1. interphase
- duplicates cell content to make enough for
two cells
2. mitotic phase (M phase) consists of:
- Mitosis: nuclear division (division of DNA to 2
cells)
- Cytokinesis: cytoplasmic division (division of
organelles to 2 cells)
What are the 3 stages of interphase/what happens during interphase?
Stages = G1, S, and G2
- during interphase, chrom.es are present as chromatin
- normal cell activities are taking place (genes are actively being transcribed into mRNA to form protein)
What happens during the G1 phase?
- period of intense growth and metabolism
- at the end of G1, centrosomes replicate
- any cell that will not divide again will remain in G1 phase (ex.s = neurons and muscle cells), and will be referred to as remaining in the G0 phase
- cells that are destined to divide will enter into S phase
What happens during the S phase?
- DNA is replicated - making identical copies of each chromo.
- replicates are called sister chromatids and are attached to one another by the centromere
- ensures that each daughter cell will receive a complete set of chrom.es
- Kinetochore protein attaches to each centromere, and forms the kinetochore:
- a protein/DNA complex that is attached to the
centromere of one chromo. - occurs before mitosis and meiosis
- a protein/DNA complex that is attached to the
What happens during G2 phase? (the final phase of interphase before cells begin mitosis)
- period of growth and metabolism
- enzymes and other proteins needed for cell division are produced
- each chromo. now has 2 sister chromatids attached to one another at the centromere
What is mitosis?
= the mitotic phase is the cell division stage - everything is already made, it just needs to be separated into two, so consists of:
1. Mitosis: the division of nuclear contents (4 phases = prophase, metaphase, anaphase, and telophase)
2. Cytokinesis: the division of cytoplasmic contents (occurs at the same time as telophase)
- mitosis functions in growth and tissue repair
- outcome = production of 2 genetically identical, somatic daughter cells
- Mitosis is NOT used to produce sex cells (sperm/egg)
What happens during prophase?
- chromatin condenses and becomes visible
- the nuclear membrane disappears
- the nucleoli disappear
- the centrosomes moves to opposite poles of the cell
- the spindle apparatus begins to form at the centromere
- kinetochore proteins attach to spindle
microtubules (called kinetochore microtubules) - the spindle apparatus moves the chrom.es to
the equator of the cell
- kinetochore proteins attach to spindle
What happens during metaphase?
- each chromo. consisting of 2 sister chromatids lines up at the cell equator - called the metaphase plate
- 46 chrom.es in a straight line down the center of the cell
What happens during anaphase?
Kinetochores separate from one another:
- pulls sister chromatids apart from one another
- 46 sister chromatids then migrate to each pole
- cytokinesis begins
What happens during telophase?
- spindle apparatus disassembles
- chrom.es uncoil forming chromatin once again
- nucleoli and nuclear membrane reappear
- cytokinesis is completed
- mitosis ends and cell enters G1 of interphase
- there are now two identical daughter cells
What happens during meiosis?
Only takes place in sex cells, which = precursors to sperm and egg.
Reduction division from a 2n diploid cell to an n haploid cell.
- diploid cells in humans have 2n = 46 chrom.es
- all body cells have the diploid number of
chrom.es EXCEPT the gametes (sperm and egg)
Haploid cells in humans have n = 23 chrome
- gametes must have the haploid number of chome.s b/c fertilization functions to restore the diploid number
What are the two divisions of meiosis?
- Meiosis I separates homologous pairs
- reduces cell from diploid (2n) to haploid (n)
- 1 x 46 duplicated chrom.es = 2 x 23 duplicated
chrom.es - consists of: PMAT I and cytokinesis
- interphase precedes meiosis I
- Meiosis II separates sister chromatids from one another
- end result of meiosis = production of 4 haploid
gametes (ex. sperm) - 2 cells w/ 23 chrom.es each divide, giving 4 cells
w/ 23 chrom.es each - consists of: PMAT II and cytokinesis
- occurs immediately following meiosis I
- interphase does NOT necessarily occur btw.
meiosis I and II
- end result of meiosis = production of 4 haploid
What happens during Prophase I? (most complex phase in all of meiosis)
- homologous pairs match up side by side - called synapsis
- allows them to separate into 2 diff. daughter
cells
- allows them to separate into 2 diff. daughter
- 4 chrom.es arranged in a line
- 2 sister chromatids from one member of the
homologous pair and 2 sister chromatids from
the other - called a tetrad - a sister chromatid from 1 member of the homologous pair exchanges genetic material with a sister chromatid from the other member of the homologous pair =CROSSING OVER
- 2 sister chromatids from one member of the
What happens during metaphase I?
- tetrads align on the metaphase plate
- sister chromatids remain attached at the centromere
- microtubules are attached to the kinetochore
What happens during anaphase I?
- homologous pairs separate from one another
- each pair moves to opposite poles of the cell
- sister chromatids remain attached at the
centromere
- sister chromatids remain attached at the
What happens during telophase I?
- chrom.es arrive at the poles of the cell
- each pole of cell now has haploid chromo. set
- sister chromatids still remain attached at the
centromere
- sister chromatids still remain attached at the
What happens during cytokinesis I?
- overlaps with telophase I
- forms 2 haploid daughter cells w/ 2 sister chromatids per chromosome
- NOTE: interphase may or may not occur btw. meiosis I and II but chrom.es will NEVER duplicate if it does
What happens during Meiosis II?
Stages = identical to mitosis
- diff. = mitosis occurs in a diploid cell and meiosis II occurs in a haploid cell
Meiosis II results in the separation of sister chromatids from one another
- each of these haploid cells (4 in total when each of the daughter cells from meiosis I complete meiosis II) are gametes (either sperm or egg)
