BIOLOGY

1ST CELL THEORY

all organism are composed of cell

2nd CELL THEORY

 the cells serves as the fundamental unit of life

Cell

the basic unit of life ,  Robert hooke was the first one to discover cells

- Average human being is composed of around 100 trillion individual cells

- 50 cells to cover the area of dot on the letter I

3^rd CELL THEORY

all cells originate from previously existing cells

DNA (DEOXYRIBONUCLEIC ACID)

the genetic material found in cells

Robert Hooke (1665)

he studied cork using a microscope in 1665

Cell (cellula) “small rooms”- latin word

Antoon Van leeuwanhoook (1670)

 father of miscroscopy

Matthias Schleiden (1838)

he studied plant cells, friends with german scientist theodor schwann

Theodor Schwann (1839)

he was able to determine that all animals are made of cells

- Published the 1^st statement of the cell theory

Rudolf Virchow ( 1885)

he stated that all cells come from pre existing cells

THE CELL CYCLE

The cell cycle is the series of events that a cell goes through as it grows, copies its DNA, and divides into new cells.

Importance

· Growth and development 

· Repair of damaged tissues 

· Replacement of worn-out cells 

· Reproduction in some organisms 

1. Interphase (Longest Stage)

About 90% of the cell cycle occurs here.

S Phase (Synthesis)

· DNA is replicated. 

· Chromosomes are duplicated. 

G₂ Phase (Gap 2)

· Cell prepares for mitosis. 

· More proteins are produced. 

DNA is checked for errors

. Mitotic Phase (M Phase)

Consists of:

· Mitosis 

· Cytokinesis 

MITOSIS

Mitosis is the process in which one body cell divides to produce two genetically identical diploid daughter cells.

Importance

· Growth 

· Tissue repair 

· Cell replacement 

Prophase

· Chromosomes condense. 

· Nuclear membrane disappears. 

· Spindle fibers form. 

Metaphase

· Chromosomes line up at the center. 

· Spindle fibers attach to centromeres. 

Anaphase

· Sister chromatids separate. 

· Move to opposite poles. 

telophase

· Nuclear membranes reform. 

· Chromosomes uncoil. 

cytokinesis

· Cytoplasm divides. 

Two identical daughter cells form

PMAT

 – Prepare (chromosomes condense)

M – Middle (chromosomes line up)

A – Apart (chromatids separate)

T – Two nuclei form

 MEIOSIS

Meiosis is a special type of cell division that produces four genetically different haploid sex cells (gametes).

Importance

· Produces sperm and egg cells 

· Maintains chromosome number 

· Increases genetic variation 

· Essential for sexual reproduction 

Prophase I

· Chromosomes condense. 

· Homologous chromosomes pair. 

· Crossing over occurs. 

· Nuclear membrane disappears. 

Special Event:

Crossing Over

· Exchange of genetic material. 

· Creates genetic variation. 

Metaphase I

· Homologous chromosome pairs line up. 

· Random assortment occurs. 

Metaphase I

· Homologous chromosome pairs line up. 

· Random assortment occurs. 

Special Event:

Random Assortment

· Chromosomes line up randomly. 

· Produces different chromosome combinations. 

Anaphase I

· Homologous chromosomes separate. 

· Sister chromatids stay together. 

Result:
Chromosome number is reduced from diploid (2n) to haploid (n).

Telophase I

· Nuclear membranes reform. 

· Cytokinesis occurs. 

· Two haploid cells are formed. 

Meiosis II (Equational Division)

No DNA replication occurs before Meiosis II.

Meiosis II (Equational Division)

No DNA replication occurs before Meiosis II.

Prophase II

· Chromosomes condense. 

· Nuclear membranes disappear. 

· Spindle fibers form. 

Metaphase II

· Chromosomes line up single file. 

· Spindle fibers attach. 

Anaphase II

· Sister chromatids separate. 

· Move to opposite poles. 

Telophase II

· Nuclear membranes reform. 

· Cytokinesis occurs. 

· Four genetically different haploid cells are produced. 

 

IV. MITOSIS vs. MEIOSIS

Feature	Mitosis	Meiosis
Purpose	Growth and repair	Produce gametes
Number of Divisions	1	2
Daughter Cells	2	4
Chromosome Number	Diploid (2n)	Haploid (n)
Genetically Identical?	Yes	No
Crossing Over	No	Yes (Prophase I)
Occurs In	Body cells	Reproductive cells
Genetic Variation	No	Yes

V. Important Terms

Term	Meaning
Chromosome	DNA carrying genetic information
Chromatid	One-half of a duplicated chromosome
Centromere	Holds sister chromatids together
Homologous Chromosomes	Chromosome pairs with the same genes
Diploid (2n)	Two sets of chromosomes (46 in humans)
Haploid (n)	One set of chromosomes (23 in humans)
Gametes	Sex cells (sperm and egg)
Crossing Over	Exchange of DNA during Prophase I
Random Assortment	Random alignment of chromosome pairs during Metaphase I
Cytokinesis	Division of the cytoplasm

 

Meiosis I

Pairs Separate."

Homologous chromosomes separate

Meiosis II

"Sisters Separate."
· Sister chromatids separate.