Download Document

Cell Reproduction 2.55
 In
most cases, a living thing grows because it
produces more cells.
 Cell growth is controlled
 More cells = a larger organism
I. SURFACE-TO-VOLUME RATIO
 Is
greater in small cells than in larger cells
 A greater surface area allows materials to enter and
leave the cell at a faster rate
II. DNA’s ability to produce enough messenger RNA
decreases with an increase in cell growth
 The
cell must either divide or die
Rates
differ from cell type to cell type
Are affected by external conditions
 The
conditions have to be right
Certain
cells, such as in the heart and
the nervous system rarely divide, if at
all.
Cells
of the skin & digestive tract grow
& divide rapidly due to daily wear &
tear.
Cells grow until they come into
contact with other cells.
Cell growth & cell division are turned
on and off to repair injuries.
CANCER: a disorder in which some cells have lost
the ability to control their own rate of
growth (often the result of alterations of
the DNA sequence AKA mutations)
 Cancer
cells do not stop growing when they come in
contact with other cells
Chromatin: Long strands of DNA wrapped
around proteins called histones
 Present
during interphase of the cell cycle
 During the early stages of mitosis, the
chromatin condenses & the chromosomes are
visible
Chromosomes: Condensed genetic information
(DNA) that is passed on from one
generation of cells to the next.
 Are
not visible in cells except during mitosis.
Sister chromatids: 2 identical DNA parts resulting
from DNA replication
Centromere: Holds the 2 sister chromatids together
 In
mitosis, spindle fibers attach here to separate the
sister chromatids.
Cell cycle 1.50
Interphase
 Interphase
is not part of mitosis!!
 Longest part of the cell cycle
 Consists of G1, S, and G2, phases

prepares cell for mitosis by growing & reproducing genetic material
(DNA)
4.28
Cell cycle



G1: Repair & growth of cell
S: DNA replication occurs
G2: Organelles duplicate

If things didn’t happen
perfectly apoptosis (cell
death) occurs

M: Cell divides

G0: Cell “rests”
G1: 1st Growth
G0: Rest
G2: 2nd Growth
S: Synthesis (genetic)
M: Mitosis
1.51
Parent cell
Mitosis:
Daughter cells
The process by which a cell produces an
identical copy of itself for repair & growth.
Prophase
 1st
and longest phase of mitosis
 Chromatin (DNA) condenses to form chromosomes
 Centrioles & spindle fibers appear
 Nucleolus & nuclear envelope vanish
Metaphase
 2nd
and shortest phase of mitosis
 Chromosomes align at the equator
 Spindle fibers attach at centromeres & centrioles
Anaphase
 3rd
phase of mitosis
 Centromeres that join the sister chromatids split causing
the sister chromatids to separate and become individual
chromosomes
 Each chromosome is pulled toward the centrioles by the
spindle fibers
Telophase
 Last
phase of mitosis
 Chromosomes unravel into chromatin
 Nuclear envelopes form around the chromatin sets
 Spindle fibers to break apart, and a nucleolus
becomes visible in each daughter cells nucleus
Cytokinesis: Division of the cytoplasm into 2 cells
 Last step of telophase
Animals: a cleavage furrow is formed and the parent cell
pinches into 2 identical daughter cells
Plants: a cell plate is formed halving the cell. A cell wall
replaces the cell plate creating 2 identical daughter
cells.
Cleavage furrow


Unicellular organisms: it is their method of reproduction
Multicellular organisms: it is used to repair damaged tissue or
replace cells and for growth in body
cells (not for gametes – sex cells)
1 organism
2 organisms
Parent cell
Daughter cells