Lab 4 Flashcards
What are the phases of the cell life cycle?
- Interphase - in between divisions; the cell is not dividing (this happens before both mitosis of meiosis)
- Cell division - in the form of mitosis of meiosis
What phase does a cell spend the majority of it life in?
Interphase
Gap 1 interphase (G1)
Occurs immediately after a cell division.
The cell grows and performs all its routine metabolic functions (such as protein synthesis and organelle duplication)
Synthesis interphase (S)
DNA replication is occurring
The DNA will partially uncoil and the strands separate at the H bond point. Each old base pair can now join with a newly made complimentary nucleotide and the H bond reforms. This continues till there are 2 identical molecules of DNA
Cell is now committed to performing some type of cell divi.
Gap 2 interphase (G2)
Accumulation of energy is reserved to prepare for cell division
What are the 3 substages of interphase?
G1 - Gap 1
S - Synthesis
G2 - Gap 2
G0 phase
A variation of the G1 phase;
Cells that are destined to never be able to divide again
Ex. Mature nerve cells
How do human chromosomes work?
Since we are diploid organisms we carry 2 copies of each unique chromosome, so the formula is 2n.
Humans have 46 chromosomes so the formula is 2n = 46 (with n being 23)
You receive 23 from each parent.
The 2 copies of the same chromosomes join together to form homologous pairs, but the gene contained in each chromosome may differ, which is called alleles
Mitosis
The division of the nucleus.
The division of original parent cell nucleus makes sure that the chromosomal content of the 2 new daughter cells made by cytokinesis are identical to that of the parent cells.
Cytokinesis
The division of the actual cell (division of the cytoplasm) to form two distinct new daughter cells.
(Accompanies the telophase part of mitosis)
What are some functions of mitosis?
- human growth/development by forming new cells
- replaces or repairs worn-out, injured or dead cells
Prophase (mitosis)
- chromosomes shorten and coil (become visible as individuals)
- centrosomes position at the poles of the cell and spindle fibres are being produced
- nuclear membrane begins to disintegrate
- kinetochore forms on the centromere
Types of microtubules
Kinetochore - microtubules that grab onto the kinetochore protein found in the centromere
Nonkinetochore - microtubules that extend from pole to pole
Astral rays - help stabilize the spindle fibres, they reach to the edge of the cell
Metaphase (mitosis)
- chromosomes meet in the middle (metaphase plate)
- each chromosomes is attached to the poles by the kinetochore microtubules
- nucleus disappears
Anaphase (mitosis)
- sister chromatids of each chromosome are separated at the centromere.
- kinetochore microtubles pull the chromosomes towards the poles.
- nonkinetochore microtubules begin to elongate the cell (oval shape).
Telophase
- chromosomes decondense
- as the nuclear membrane reappears, it forms 2 diploid nuclei each containing 2n unduplicated chromosomes.
- coincides with cytokinesis to produce to new daughter cells
Meiosis
A nuclear division that creates haploid (n) gametes used for sexual reproduction.
(Haploid = half of the genetic info = 23 chromosomes)
Meiosis I - reduces genetic content from 2n duplicated chromosomes to n duplicated chromosomes
Meiosis II - same as mitosis but go from haploid to haploid
Prophase I
Similar to mitosis:
- chromosomes condense
- spindle fibres start to form
Differences:
- chromosomes find their homologous pair (to form a tetrad) and lay side by side (synapsis) to get ready to exchange genetic info.
- crossing over occurs between nonsister chromatids in order to combine alleles.
Synapsis
The members of each pair of homologous chromosomes move together, and lay side-by-side
Crossing over
A form of genetic variability
Occurs in prophase I
As the homologous chromosomes lay side by side (synapsis), genes of nonsister chromatids are exchanged to create unique combination of alleles.
Metaphase I
Similar to mitosis:
- chromosomes attached to spindle fibres and arranged on metaphase plate
- nuclear membrane disappears
Differences:
- chromosomes on the plate are arranged as tetrads(4 sister chromatids XX)
-independent assortment occurs because the arrangement on the metaphase plate is random
Independent assortment
A form of genetic variation
Occurs in metaphase I
The orientation of each homologous pair along the metaphase plate is random. Genetic variation is made based on how the maternal and paternal chromosomes in each of the 23 pairs align.
Anaphase I
Similar to mitosis:
- chromosomes have moved towards the poles
Differences:
- each half of a tetrad (X) is attached to a spindle fibre, so one X is taken to the left pole, one X taken to the right pole. (separation of XX tetrad).
Telophase I
Similar to mitosis:
- chromosomes decondense
- formation of nuclear membrane
- cytokinesis forms 2 daughter cells
Differences:
- the nuclei of the daughter cells have only half as many (haploid) chromosomes as the parent cell had since it divided into 2 cells
- genetic variation created by crossing over and independent assortment
- you are left with 23 chromosomes and 46 chromatids
