CELL GROWTH AND DIVISION

  

SECTION 1, CHROMOSOMES

DNA is a long thin molecule that stores Genetic Information.  The DNA in a human cell is estimated to consist of six billion pairs of nucleotides.

LIMITS TO CELL GROWTH

1.     surface to volume ratio

2.     nutrients in and waste out

3.     DNA control of the cell

CHROMOSOME STRUCTURE

Chromosomes are Rod Shaped structures made of DNA and Proteins. They are coiled up chromatin. They are only visible when the cell is undergoing cell division.

Chromatin is the DNA/protein substance in the nucleus that looks like spaghetti (when it is not compact)

 

 

 

PROKARYOTE – no nucleus or nuclear bound organelles. 1 circular chromosome attached to the cell membrane. 1/1000 the size of  a eukaryotic cell.

EUKARYOTE – nucleus and membrane bound organelles. Species specific chromosome number. In the nucleus. 

The DNA in Eukaryotic cells wraps tightly around Proteins called HISTONES.

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

The constricted area of each Chromatid is called a CENTROMERE .

CHROMOSOME NUMBERS       

HUMAN     BODY CELL                                   SEX CELLS                                        SOMATIC CELLS                          GAMETES                                              46 CHROMOSOMES,                     23 CHROMOSOMES                           (2n) DIPLOID  =TWO SETS.          (n) HAPLOID = ½ set                                ALL CELLS BUT SEX CELLS       SPERM & EGG

FEMALE             MALE                                                                                                        23 egg       +    23 = sperm  ΰ FERTILIZATION of ZYGOTE                                                                                                                            


The Chromosomes in the Zygote exist in PAIRS.  For every Chromosome that was in the egg, there is a matching Chromosome from the sperm.

Chromosomes are categorized

1. SEX CHROMOSOMES – determine sex – XX female; XY male  2 chromosomes or 1 pair

2. AUTOSOMES –  all other chromosomes that aren’t sex chromosomes – 44 chromosomes or 22 pairs

  MATCH SET OF AUTOSOMES IN A DIPLOID CELL = HOMOLOGOUS PAIRS.  CONTAIN INFORMATION THAT CODE THE SAME TRAIT (GENES).  Example Eye Color.
 
   
 
 
 

SECTION 2, CELL DIVISION

All cells are derived from preexisting cells.  Cell division is the process by which cells produce offspring cells. 

CELL DIVISION IN PROKARYOTES

 

 

 

 

 

 

 

 

 

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

 The Chromosome makes a COPY of Itself

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

 The Cell SPLITS into TWO NEW CELLS.  Each New Cell contains on the Identical Chromosomes.
 
 
  CELL DIVISION IN EUKARYOTES

 

 

 

 

 

 

 

A Cell typically goes through PHASES  of GROWTH AND DEVELOPMENT before it divides into new cells.

THE PHASES OF LIFE OF A CELL ARE CALLED 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 IS THE PORTION OF THE CELL CYCLE BETWEEN DIVISION. Longest phase. During Interphase, the cell GROWS and DEVELOPS

REPLICATION RESULTS IN TWO IDENTICAL COPIES OF A CHROMOSOME CALLED SISTER CHROMATIDS.  EACH NEW CELL MUST HAVE AN EXACT COPY OF THE ORIGINAL SET OF CHROMOSOMES.

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

A.   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.  

FOUR PHASES OF MITOSIS

PHASE 1- PROPHASE  Chromatin condenses into Chromosomes. THE NUCLEOLUS AND NUCLEAR MEMBRANE DISAPPEAR.  CENTROSOMES appear.  In Animal Cells, each Centrosome contains CENTRIOLES. Plant Cells lack Centrioles.  SPINDLE FIBERS made of microtubules radiate from the Centrosomes in preparation for Mitosis.

PHASE 2 - METAPHASE  - The Chromosomes are moved to the MIDDLE of the CELL. The Two Sister Chromatids of each Chromosome are attached to fibers radiating from OPPOSITE ENDS OF THE CELL.

PHASE 3 - ANAPHASE - The Centromeres of Each Chromosome are pulled by the spindle fibers toward the ends of the cell. THE SISTER CHROMATIDS ARE SEPARATED FROM EACH OTHER.  They are now Considered to be Individual Chromosomes.

PHASE 4 - TELOPHASE - After the Chromosomes reach opposite ends of the Cell, the Spindle Fibers Disassemble.  The Chromosomes return to less tightly coiled Chromatin State.  New Nuclear Envelope begins to form around the Chromosomes at each end of the cell.   THE PROCESS OF MITOSIS IS NOW COMPLETE.  THE CELL MEMBRANE BEGINS TO PINCH THE CELL IN TWO AS CYTOKINESIS BEGINS.

    B. CYTOKINESIS - SECOND STEP. THE CYTOPLASM OF THE CELL DIVIDES INTO TWO NEW CELLS CALLED DAUGHTER CELLS WHICH ARE IDENTICAL TO THE PARENT CELLS.

 CYTOKINESIS = division of the cytoplams

CYTOKINESIS OF

 

 

 

 

 

 

ANIMAL CELLS: CLEAVAGE FURROW forms through the Middle of the Parent Cell (inward pinching).  The Cleavage Furrow Deepens until the parent cell pinches into TWO New Identical Cells.  

CYTOKINESIS OF PLANT CELLS: In a Plant Cell, the material for NEW CELL WALL CALLED THE CELL PLATE  AND MEMBRANES GATHER AND FUSE ALONG THE EQUATOR, OR MIDDLE OF THE CELL, BETWEEN TWO NUCLEI. Forming TWO New Identical Cells.

REGULATING THE CELL CYCLE

Cells in a Petri dish will usually stop growing when they come in contact with other cells. Cancer cells continue to grow even after they come in contact with other cells.

Cyclins regulate the timing of the cell cycle in eukaryotic cells. It tells it when to divide, duplicate chromosomes or enter phases of the cell cycle. 

INTERNAL REGULATORS – proteins that respond to events inside the cell. Allows the cell to proceed only when certain things happen in the cell.

EXTERNAL REGULATORS – proteins that respond to events outside the cell. Growth factors stimulate growth and division of cells. Molecules on the surface of the cell cause this process to stop or speed up.

Cancer cells do not respond to the signals that regulate the growth of most cells. UNCONTROLLED CELL GROWTH.  p53 gene causes the cell to lose the information needed to respond to signals to control the growth.