Transcript Ch # 10 – Cell Growth & Division

Ch # 10 – Cell Growth &
Division
(Mitosis, Meiosis, and the Cell Cycle)
I. Cell Growth
*Most living things grow by producing more cells.
Eukaryotic cells are all about the same size.
A. Limits to cell growth
Cells divide for 2 major reasons :
1. To avoid DNA “overload” – larger cells place more
demand on DNA (where info is control center).
2. To exchange materials more easily – food, oxygen,
water, & wastes enter/exit cell via cell membrane.
Cell Size Matters
-The rate of exchange depends on a cell’s surface area
(total area of the cell membrane).
-Rate of food/O2 use & waste production depends on a
cell’s volume.
BIG = slow rate of exchange for food, O2, & waste
disposal. Need more food, make more waste.
*To avoid getting too large, cells divide.
Cell division – process by which a cell divides into two
new daughter cells.
Cell Division
Two Types of Cell Division : Mitosis & Meiosis
II. Cell Division
A. Chromosomes
*In eukaryotic cells, genetic info is passed from generation to
generation by the chromosomes, which are made up of DNA.
-Every organism’s cells have a specific # of chromosomes –
46 in humans.
-Before cell division, each chromosome is replicated (copied)
& consists of 2 identical “sister” chromatids. As a cell divides,
sister chromatids separate & 1 goes in each daughter cell.
Chromosome Structure
-Pairs of chromatids are attached by a centromere that appears
in the middle of the chromatids.
B. The Cell Cycle
Cell cycle – the series of events that cells go through as they
grow & divide.
During the cell cycle the cell :
1. Grows to its mature size.
2. Prepares for cell division.
3. Divides to form 2 daughter cells.
The cell cycle consists of 4 phases :
1. G1 phase – period of activity in which cells do most of
their growing.
-During G1 (gap 1), cells increase size & synthesize new
proteins & organelles.
4 Phases of the cell cycle con’t.
2. S phase – phase in which chromosomes are
replicated & the synthesis of DNA molecules takes
place. *Once cells enter this phase, they will
complete the cell cycle.
3. G2 phase – phase in which many of the organelles &
molecules required for cell division are produced. Is
the shortest phase of Interphase.
4. M phase – phase in which mitosis and cytokinesis
occur.
Interphase, Mitosis & Cytokinesis
*Phases G1, S, and G2 of the cell cycle make up
Interphase of the cell cycle.
Interphase - stage of intense growth & preparation
before cell division occurs. Is the longest part of the cell
cycle; cell division is very fast.
Mitosis – stage in eukaryotic cell division during which
the cell nucleus divides (karyokinesis) to form 2
daughter cells. It is somatic cell division – division that
occurs in non-sex cells.
Cytokinesis – stage during which division of the
cytoplasm occurs.