Unit 4: Mitosis Flashcards
Cell division (mitosis and meiosis):
•from the moment of fertilization, cells are continuously growing, dying, and being replaced.
•each new cell must contain the same genetic information as the original cell, or parent cell.
•DNA is this genetic information. It is found within the nucleus of each and every cell in the body.
•DNA is tightly packaged into chromosomes.
•”unpackaged” DNA is referred to as chromatin.
-chromatin only condenses into chromosomes when the cell is about to divide. Each nucleus of a human cell contains about 3 meters of DNA.
One chromosome (unduplicated):
-chromatid.
-not a sister chromatid.
One chromosome (duplicated):
-one side is a chromatid.
-both are sister chromatids.
-has a centromere.
Chromosome number varies from species to species:
•more chromosomes DOES NOT equal higher intelligence or complexity.
•humans have 23 pairs of homologous chromosomes (46 in total).
-22 pairs of autosomes.
-1 pair of sex chromosomes.
-homologous chromosomes carry different forms of the same genes (alleles).
-because human cells carry two pairs of each chromosome, we are said to be diploid.
Human autosomes:
•human autosomes are diploid or “2n”.
•human sex chromosomes are haploid or “n”.
- 2n = 46.
- n = 23.
Chromosomes in other organisms:
•some organisms, such as earthworms, contain more than two homologous chromosomes in each cell. These organisms are said to be polyploid (3n, 4n, 5n, etc.)
Allele:
-different forms of the same trait.
Autosome:
-body cell (except sperm/egg).
Diploid:
= 2 sets = 2n = 46.
Haploid:
= 1 set = n = 23.
The cell cycle:
•each cell goes through three phases before it actually divides.
1. G1 phase (cell growth).
2. S phase (DNA replication).
3. G2 phase (preparation for division).
•collectively, these phases are referred to as interphase (90% of cell life).
•interphase is followed by cellular division, or “M phase” (mitosis).
•the last phase accounts for the actual division of genetic information (mitosis) and splitting of the cytoplasm itself (cytokinesis).
Mitosis:
•2n —> 2n: produces somatic/body cells.
•goal: to produce daughter cells that are identical (same DNA) to the parent cell.
•purposes: growth, maintenance, repair.
•after DNA replication (interphase), cells go through four stages of mitosis before cytokinesis can occur:
-prophase.
-metaphase.
-anaphase.
-telophase.
Somatic cells:
-body cells/autosomal cells (every cell but sperm/egg cells).
- Prophase:
•at this stage, each pair of homologous chromosomes has been duplicated, so the cell contains twice as much DNA as normal.
•chromatin condenses to form chromosomes.
•nuclear membrane breaks down (nucleus breaks down).
•centrioles move to opposite poles of the cell and spindle fibres begin to form.
-spindle fibres are required to eventually pull the duplicated chromosomes apart.
- Metaphase:
•spindle fibres attach to the centromere of each chromosome, guiding them to the equator of the cell.
•duplicated chromosomes line up, forming the “metaphase plate”.
-(metaphase plate = equator).
- Anaphase:
•spindle fibres shorten and sister chromatids are pulled apart from one another; centromeres split.
•two opposing poles are formed, each with a complete diploid set of DNA.
- Telophase:
•chromosomes reach opposite poles of the cell.
•spindle fibres break down.
•chromosomes begin to unwind into chromatin.
•nuclear membrane forms around each new set of genetic info.
-(nuclear membrane = nucleus).
Cytokinesis:
•cleavage furrow forms.
•cytoplasm splits to form two identical daughter cells with the same genetic content as the original parent cell.
-daughter cells are now in G1 of interphase.
Cytokinesis (plant cells):
•telophase and cytokinesis in plant cells looks a bit different.
-because plant cells contain a rigid cell wall, cytoplasm will not furrow and pinch off.
-instead, a cell plate forms between the two daughter nuclei, eventually developing into a cell wall.
What would happen if cells were constantly dividing?
•cancer.
-uncontrolled cell growth due to the under-production of chemicals that regulate growth factors or the over-production of growth factors themselves.
