Download Ch. 9.2

The Cell Cycle
multiplies cells
Ch. 9.2
• Cells are always dividing in your body.
• If they aren’t dividing, they are going
through other cellular processes
– Breaking down food, forming proteins, etc.
Chromosomes and Cell Division
• Genes are located in the nucleus of
eukaryotic cells
• Genetic material is microscopic
– Long fibers containing CHROMATIN  DNA
and protein molecules
• Chromatin are microscopic and can not be
seen until they condense down
– Once they condense, they form
CHROMOSOMES  contain genetic material
• # of chromosomes varies depending on the
species
– Humans have 46 chromosomes (23 pair)
• Prior to dividing, chromosomes duplicate
themselves
• Form SISTER CHROMATIDS
• Held together by a CENTROMERE
The Cell Cycle
• Each cell divides at different rates
– Muscle cells divide quickly; why?
– Nerve cells divide slowly, why?
• When cells divide, go through the CELL
CYCLE
Parts of the cell cycle
• 90% of the cell cycle is INTERPHASE
– Cell continues metabolic process such as
growing, increasing proteins
• DNA is duplicated (S phase/synthesis
phase)
• G1 and G2 (gap) phases are before and after
S phase
• Stage when the cell divides  MITOTIC
PHASE
– Mitosis and cytokinesis
• Mitosis splits the chromosomes evenly in to 2
daughter cells
• Cytokinesis splits cytoplasm evenly
• Mitosis gives identical copies of genetic
materials
Concept Check
• Describe how the appearance of
chromosomes changes as a cell is about to
divide.
• Interphase used to be described as a ‘resting
phase.’ Why is this description inaccurate?
• Summarize the events that occur during
mitosis and cytokinesis.