Download 1.6 Cell Division/Mitosis

1.6 Cell Division/Mitosis
Question?
• Why would a cell want or need to divide?
– Growth/development of tissues/organs
– Repair of damaged tissue/organ
– Reproduction of cells/organisms
Cell Cycle
• The cell’s life cycle (usually just called the cell cycle)
consists of two main parts:
– Interphase – active period in the life of a cell when
many metabolic reactions occur, including
• protein synthesis
• DNA replication
• an increase in the number of mitochondria and/or
chloroplasts
– Mitosis – cell divides
Cell Cycle
• Interphase can be divided into three
phases:
–G1 – cell grows and metabolizes
–S – DNA is replicated
–G2 – cell prepares for division
Mitosis
• Mitosis can be divided into four stages:
–Prophase
–Metaphase
–Anaphase
–Telophase
Mitosis
• Prophase
– Nuclear envelope disappears
– With the aid of special proteins called
histones, DNA supercoils into distinct
chromosomes that are visible under the
microscope
– Each pair of identical segments of DNA, called
sister chromatids, bind together at the
centromere to form one chromosome
Prophase
– Centrioles moved to
opposite ends of the
cell
– Long, tubular
proteins called
“spindle fibers” grow
from the centrioles
and attach to the
centromeres of the
chromosomes
Metaphase
• Spindle fibers pull chromosomes to the
equator (center line) of the cell
Anaphase
• Spindle fibers
shorten
• Sister chromatids are
pulled apart and are
now called
chromosomes
• Chromosomes are
pulled to opposite
ends of the cell
Telophase
• Reverse of prophase:
– Spindle fibers
dissapear
– DNA uncoils and
becomes
chromatin
– Nuclear envelope
reforms
Cytokinesis
– Splitting of the
cytoplasm
– Occurs when
microtubule proteins
pinch inward at the
equator (cleavage
furrow)
– Results in two
separate but
identical cells
Plant Cell Division
• In plants a cell plate forms instead of a cleavage furrow
Overview
• Mitosis produces two genetically identical nuclei
– During the S phase of interphase DNA is replicated
to produce two identical copies
– During prophase the identical copies of each
chromosome (homologous chromsomes) bind
together
– Homologous chromosomes are pulled apart
during anaphase and become part of two separate
nuclei during telophase
• Mitosis serves many purposes:
– Tissue/organ growth
– Embryonic devleopment, when the zygote
divides to produce many smaller cells
– Tissue damage and repair
– Asexual reproduction (unicellular
organisms)
Control of this process
• Cyclins
– Series of proteins that control cells during cell
cycle.
Not always controlled
• Mutagens –
– Physical or chemical agent that changes the DNA
in an organism.
– This increases the frequency of mutations in that
organism above the natural background level.
– Often these mutagens can cause cancer/tumors
Oncogenes
• Sometimes the gene
controlling cell division
(called an oncogene) will
become mutated
• The result is that cell
division continues
repeatedly
• This is how tumors are
formed
• Tumors can form in any
tissue of the body
Stomach Tumor
Metastasis
• Greek for “Next Placement”
• Cells that are going through uncontrolled
proliferation can sometimes slough off of a
tumor and spread through the body to
another area that previously was unaffected.
• These cells will continue their rapid mitotic
division and cause the disease to spread.
Tumors
• Tumors are a mass of cells that are going
through mitosis uncontrollably due to a
mutation in the DNA
• Two major types:
– Malignant: “Badly Born” can spread to invade
other cells throughout the body.
– Benign: lacks the ability to invade neighboring
cells