Cell growth and Division

Somatic cells

cells not involved in Sexual Reproduction

-also called body cells

  Ex: skin cells, muscle cells, 

nerve cells, bone cells

Homologous

airs of matching chromosomes—one inherited from each parent—found in diploid cells, containing the same genes in the same order, though they may have different alleles.

Why somatic cells divide:

-Too big to supply needs of cell

-Growth of organism

-Develop (like an embryo)

-Replace damaged/worn out cells

-Heal wounds

• chromatin

•  When not dividing, the DNA in Eukaryote cells is a tangled mass of thin threads called chromatin.

• chromosomes

• During cell division, the chromatin condenses to form compacted structures called chromosomes.

Just prior to mitosis, each chromosome duplicates to form

sister chromosomes

• A duplicated chromosome is composed of; 

two sister chromatids held together in a region called the centromere. (kinetechore)

Sister chromatids are genetically

identical

At the end of mitosis, each chromosome consists of a single

chromatid

diploid

• number of chromosomes found in the somatic (non-sex) cells.

The haploid

• number of chromosomes contains one chromosome of each kind. 

• In the life cycle of many animals, only sperm and eggs have the haploid number of chromosomes.

Cell Cycle:

• Consist of G1, S, G2 and M phases

o Cells grow

o Then sometimes Reproduce

Interphase

-First stage of cell cycle (G₁, S, & G₂)

-Longest part of the cell cycle

-Nucleus and nucleolus clearly visible

-Chromosomes not visible.

-Not part of “Mitosis”

M Phase:

Cell Division 

- 2 stage process resulting in two new

“daughter”cells from one “parent” cell

1. Mitosis: nucleus divides : each daughter cell

has identical number and types of

chromosomes as parent cell

2. Cytokinesis: Cytoplasm divides 

he Four “phases” of Mitosis

(PMAT)

Prophase:

o nuclear membrane disappears

o nucleolus disappears

o chromatin condenses (chromosomes

            are now visible)

o in animal cells, centrioles start to move

            to opposite ends (poles) of cell

o spindle forms (threadlike structures that 

  spread across the cell, looks like football)

Metaphase

the 2nd phase of mitosis

     o chromosomes attach to spindle and move

  to the center (equatorial plate) of the cell

o the shortest phase of mitosis

Anaphase:

• the third phase of mitosis

o the chromosomes (which doubled earlier

           during interphase) divide in half

o each chromsome moves towards the  

      opposite pole

• cell elongates

Telophase:

(final phase of mitosis)

o two new identical nuclei form

o spindle disintegrates

Cytokinesis animal cells

cytoplasm is divided in half

      o animal cells: cell membrane pinches 

          (cleavage furrow) in 2

plant cells: Cytokinesis

cell plate forms between

  2 new nuclei, grows from center out,

  forms new cell wall

After telophase,

the two new daughter cells

immediately enter interphase and the cycle

starts over again.

Apoptosis

• Programmed cell death; decreases the number of cells.

Apoptosis occurs

• because of two sets of enzymes called capsases.

• The first set, the “initiators” receive a signal to activate the second set, the “executioners”.

• The executioners activate enzymes that tear apart the cell and its DNA.

• Cell division and Apoptosis occur during normal development and growth.

Asexual Reproduction (

 regeneration (new organism grows from 

part of parent, regrowth of lost body 

parts) - MITOSIS

chromosome vs chromatin vs chromatid vvs centromere

Chromatin is loose DNA, chromosomes are condensed DNA, chromatids are the identical halves of a duplicated chromosome, and centromeres hold chromatids together, acting as the anchor point for chromosome counting.

Reddit +2

gamete

mature haploid sex cells (sperm in males, ova/eggs in females) essential for sexual reproduction,

histone

Histones are highly alkaline, positively charged proteins in eukaryotic cell nuclei that act as spools, packaging negatively charged DNA into structural units called nucleosomes.