Post on 27-Dec-2015
Limits to Cell Growth
– The larger a cell becomes, the more demands the cell places on its DNA.
– In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.
Ratio of Surface Area to Volume
• As the size of a cell increases, its volume increases faster than the surface area.The decrease in the cell’s ratio of
surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.
Cell Cycle
The cell cycle is the series of events that cells go through as they grow and divide.
Interphase is the period of growth that occurs between cell divisions.
90% of the cell’s time is spent here.
The Phases of the Cell Cycle
The cell cycle consists of four phases:
– G1 (First Gap Phase)
– S Phase (Synthesis Phase)
– G2 (Second Gap Phase)
– M Phase (cell division)Mitosis (Prophase, Metaphase,
Anaphase, Telophase) Cytokinesis (division on cytoplasm)
G1, S, G2= INTERPHASE
Events of the Cell Cycle
During G1 (First Gap phase) the cellincreases in sizesynthesizes new proteins and organelles
During the S (Synthesis phase),chromosomes are replicated or copiedDNA synthesis takes place
– Once a cell enters the S phase, it usually completes the rest of the cell cycle.
During G2 Phase (Second Gap Phase) Copying of certain organelles and molecules required for cell division occursOnce G2 is complete, the cell is ready to start the M phase—Mitosis
Interphase
“Intermission” Normal metabolic
activities Major state cell
spends 90% of time here
DNA= chromatin NOT a stage of
mitosis
Late Interphase (S and G2)
Prepares for mitosis
DNA doubles=Sister chromatidsCentrioles
double in animals
Cell Division
In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called
mitosis. The second stage, division of the cell cytoplasm, is
called cytokinesis. FYI Some books will put cytokinesis as the last step of
mitosis
Why do cells divide by Mitosis?
Growth &Repair
Reproduction of single celled organisms under conditions Amobea
Reproducing
Cells dividing by Mitosis…….
Identical to original cell
Same chromosome #
Identical chromosome makeup
Skin
A Duplicated Chromosome
one chromatid
its sisterchromatid
One chromosome in the duplicated state
centromere
Diploid vs. Haploid
Diploid= 2 sets of chromosomes– One set from mom and one set from dad– Chromosomes come in pairs– Humans have 23 pairs of chromosomes– Somatic Cells all cells except sperm and
egg
Diploid vs. Haploid
Haploid = 1 set of chromosomes– Sperm or egg (sex cells) have
23 single chromosomes
Stages of Mitotic Cell Division
ProphaseMetaphaseAnaphaseTelophase
“1st” or “before”“middle”
“apart”“far” or separate
Prophase
Nuclear membrane disappears
Doubled DNA = condensed
“chromosomes” form
Spindle fibers start to form
Metaphase
Mitotic spindle now formed
– By centrioles in animals– Spindle apparatus in
plants
Chromosomes line up mid- cell or center of cell
Telophase Cell divides Cell plate (plants) or
membranes (animals) form
Nucleus reappears (now 2 of them)
Chromosomes gather at opposite ends of the cell and lose their distinct shape.
Nuclear envelope reappears (now 2 of them)
Plant versus Animal Mitosis
Plant:Cell wall form from cell plate
Spindle apparatus
Animal:No cell wallmembrane
cytokinesis = cleavage furrow
Centrioles
Cytokinesis in Plants
In plants, a structure known as the cell plate forms midway between the divided nuclei. This will become the spot where the cell walls will form
Cell wall
Cell plate
Cancerous cells……...
1.Divide too many times
2.Divide into more than two cells!
Masses of cells =– “tumors”
benign malignant