Cell Growth and Division

CHROMOSOME STRUCTURE

• (CHROMATIN) in Nucleus is coiled into CHROMOSOMES.

• Chromosomes made of DNA and Proteins.

• The DNA wraps around Proteins called HISTONES.

• Each half of the Chromosome is called a CHROMATID or SISTER CHROMATIDS.

• The Centromere holds the Two Chromatids together.

• The DNA of most Prokaryotes comprises only ONE Chromosome.

• Circular DNA Molecule and associated Proteins.

CHROMOSOME NUMBERS

• HUMAN CELL CONTAINS 46 CHROMOSOMES, OR TWO SETS.

• TWO COMPLETE SETS OF CHROMOSOMES IS CALLED A DIPLOID CELL. (abbreviated as 2n.)

• EVERY ORGANISM HAS A DIPLOID NUMBER (2n).

• EXAMPLES:  FRUIT FLIES - 8, LETTUCE - 14, GOLDFISH 94, AND HUMANS 46.

• ONLY ONE COMPLETE SET OF CHROMOSOMES IS CALLED A HAPLOID CELL. (abbreviated as 1n.)

• GAMETES, EGGS AND SPERM CONTAIN ONLY ONE COMPLETE SET. 

• HUMAN SPERM OR EGG (GAMETE) CONTAINS 23 CHROMOSOMES, (1n) FOR ALL HUMANS.

• EGG AND A SPERM JOIN TO PRODUCE A NEW INDIVIDUAL, CALLED FERTILIZATION.

• THE SINGLE CELL THAT RESULTS IS A ZYGOTE.

• IT CONTAINS TWO COMPLETE SETS OF CHROMOSOMES, ONE SET FROM EACH GAMETE, FORMING A DIPLOID CELL. 

• SEX CHROMOSOMES Determine the SEX of an Organism.

• In Humans, Sex Chromosomes are either X or Y.  Females XX and Males XY

• All the Other Chromosomes are called AUTOSOMES.

• TWO of the 46 Human Chromosomes are Sex Chromosomes, the remaining 44 are Autosomes.

• MATCH SET OF AUTOSOMES ARE CALLED HOMOLOGOUS PAIRS.  BOTH CONTAIN INFORMATION THAT CODES THE SAME TRAIT (GENES). 

Example Eye Color.

CELL DIVISION

• All cells are derived from preexisting cells.  • Cell division differs in prokaryotes and

eukaryotes.

CELL DIVISION IN PROKARYOTES

BINARY FISSION is the Division of a Prokaryotic cell INTO TWO Offspring Cells.

Binary Fission consist of THREE General Stages:

STAGE 1 - The Chromosome makes a COPY of Itself, Resulting in Two Identical Chromosomes.

STAGE 2 - The Cell continues to grow until it reaches approximately TWICE its Normal Size. Then a CELL WALL Begins forms between the Two Chromosomes.

STAGE 3 - The Cell SPLITS into TWO NEW CELLS.  Each New Cell contains on the Identical Chromosomes.

THE CELL CYCLE

• THE CELL CYCLE CONSISTS OF THREE PHASES:    A. INTERPHASE    B. MITOSIS    C. CYTOKINESIS

• MITOSIS is a Series of PHASES in Cell Division during which the NUCLEUS of a Cell Divides into TWO NUCLEI WITH IDENTICAL GENETIC MATERIAL. 

• MITOSIS OCCURS ONLY IN EUKARYOTES.

INTERPHASE • INTERPHASE IS THE PORTION OF THE

CELL CYCLE BETWEEN DIVISION. • Interphase is the LONGEST Phase in the Cell

Cycle of a typical Cell.  Interphase used to be referred to as the "RESTING PHASE".

• During Interphase, cells carry on all their usual functions, such as respiration and enzyme production.  The Cell also GROWS and DEVELOPS into MATURE FUNCTIONING Cells while in Interphase.  It is the period of normal metabolic activity.

• INTERPHASE CONSIST OF THREE PHASES:

• G1 PHASE - PERIOD OF NORMAL METABOLIC CELLULAR ACTIVITIES: THE NUMBER OF ORGANELLES AND AMOUNT OF CYTOPLASM IN A CELL INCREASE.

• S PHASE - THE GENETIC MATERIAL (DNA) IS DUPLICATED (COPIED).  THE CHROMOSOMES OF THE CELL REPLICATE

• G2 PHASE - Structure directly involved with mitosis are formed.  The Cell makes the Organelles and substances it needs for Cell Division.  A time during which the Cell prepares to divide.

• REPLICATION IS THE PROCESS OF COPYING GENETIC MATERIAL.

• REPLICATION RESULTS IN TWO IDENTICAL COPIES OF A CHROMOSOME CALLED SISTER CHROMATIDS.

CELL DIVISION

• CELL DIVISION IS THE PROCESS BY WHICH ONE CELL PRODUCES TWO NEW IDENTICAL DAUGHTER CELLS.

• MITOSIS - FIRST STEP. A SERIES OF  PHASES IN CELL DIVISION DURING WHICH THE NUCLEUS OF A CELL DIVIDES INTO TWO NUCLEI WITH IDENTICAL GENETIC MATERIAL.

• CYTOKINESIS - SECOND STEP. THE CYTOPLASM OF THE CELL DIVIDES INTO TWO NEW CELLS CALLED DAUGHTER CELLS.