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Cell Division - Biochemistry

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Lecture notes study book Harper's Illustrated Biochemistry Thirty-First Edition of Victor Rodwell, David Bender - ISBN: 9781259837944, Edition: 31, Year of publication: - (medicine notes)

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  • August 27, 2022
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  • 2021/2022
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CELL DIVISION

I. Mitosis
- somatic cells
- diploid = 46 chromosomes
Homologous pair = diploid cell having 2 chromosomes of each kind
- result in 2 daughter cells

Requisites before the onset of division:
 DNA replication
 twice the normal diploid complement (92)
 Storage of energy

Interphase = period between successive episodes
 Only nucleus & condensed chromatin are seen
 Chromosomes are in extended state

1. Prophase
 Chromosomes become visible
 Chromosomes continue to condense, become shorter & thicker
Chromosomes consist of 2 parallel strands / chromatids
Chromatids joined to one another at the Centromere
Centromere = constricted segment common to both strands
Kinetochore = trilaminar disc at the centromere
 Centrioles replicate & migrate to opposite poles of the cell
 Breakdown of nuclear envelope
2. Metaphase
 Alignment of chromosomes in the same plane in the middle of the cell forming the equatorial plate
Equatorial plate - associated with the development of mitotic spindle
Mitotic spindle = fusiform array of microtubules which extend from centrioles to chromosomes or extend from pole to pole
3. Anaphase
 Separation of single kinetochore of each pair of chromatids into 2 so each chromatid has its own
 Chromatids move to opposite poles as separate chromosomes
 Kinetochore of each chromosome attaches to 1 or more spindle microtubules
 Microtubules are shorten by depolymerization at one end
DYNEIN
4. Telophase
 Chromosomes are clustered at the spindle poles
 Segments of nuclear envelope are formed around
 Chromosomes uncoil except those destined to remain condensed
 Karyokinesis is complete
▪ Nucleoli are reformed
▪ Nuclear envelope coalesce
 Cleavage furrow deepens until it encounters the spindle microtubules
= constriction of the cytoplasm midway between the nuclei
 For a short time, daughter cells remain connected by a slender cytoplasm bridge occupied by residual spindle microtubules
bound together at their midpoint by dense amorphous material (midbody)
 Depolymerization of microtubules completes cytokinesis
In female cells, 1 of the x-chromosomes remains condensed during interphase.

II. Meiosis
- germ cells in ovary & testis
- haploid = 23 chromosomes, results in 4 daughter cells


A. 1st Divison / Reduction
- members of each homologous pair separates & go to opposite poles thus reducing the # of chromosomes in daughter cells by ½
1. Prophase
a. Leptotene
- chromosomes become visible in nucleus
b. Zygotene
- homologous chromosomes begin to come together in close lateral opposition
Synapsis = pairing
- tetrad formation
c. Pachytene
- chromosomes coil becoming shorter & thicker
- homologous chromosomes may give erroneous impression they are single chromosome due to very close apposition

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