Transcript Chapter 9 - SchoolRack

Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz
Biology for a
Changing World
FIRST EDITION
Intro to Biology
Dr. Steve Schwendemann
CHAPTER 9
Cell Division and Mitosis
Copyright © 2012 by W. H. Freeman and Company
Chapter 9
Paramedic Plants
Copyright © 2012 by W. H. Freeman and Company
Conventional drugs vs. herbal supplements
• In conventional drugs, a
specific active ingredient is
purified from a plant or
fungus or synthesized in a
laboratory and
concentrated into pill,
capsule, or injectable form.
Conventional drugs vs. herbal
supplements
• Conventional drugs have been tested in
clinical trials and shown to be safe and
effective.
Conventional drugs vs. herbal
supplements
•
In herbal supplements, plants, algae, fungi, and combinations of these, are used as
a tea, an extract, or ground into power and sold in capsule form.
– They contain complex mixtures of different unpurified plant molecules.
Conventional drugs vs. herbal
supplements
• Unlike drugs, herbal supplements typically contain several compounds,
and they can target diverse biochemical pathways.
Conventional drugs vs. herbal
supplements
• Herbal supplements do not have to be tested in clinical trials.
Conventional drugs vs. herbal
supplements
• There is a lack of consistency in herbal
supplements.
– Many supplements are contaminated with
dangerous heavy metals or bacteria.
– The active ingredient in many supplements
commonly varies from pill to pill and bottle to
bottle.
Conventional drugs vs. herbal
supplements
• The FDA now allows companies to apply to
the agency to market an herbal supplement
almost like a pharmaceutical drug.
– This process requires clinical trial data showing
that a supplement works and proof that the
company can produce the supplement with
consistent quality and quantity from batch to
batch.
– This is not a mandatory process, but financial
incentives are offered.
Cell division
• Cell division is the process by which a cell
reproduces itself.
Why do normal, healthy cells divide?
• Cell division is
important for
normal growth,
development, and
repair of an
organism.
Why do normal, healthy cells divide?
• Cells divide for growth and development.
Why do normal, healthy cells divide?
• Cells divide for cell replacement.
Why do normal, healthy cells divide?
• Cells divide to heal wounds.
How do cells divide?
• A cell doesn’t simply split in half to form two
new cells.
– If it did, each new cell would be smaller than the
original cell, and each cell would lose half of its
contents with each division.
How do cells divide?
• Before a cell
divides, it
makes a copy of
its contents so
that each new
cell has the
same amount
of organelles,
DNA, and
cytoplasm as
the original cell.
How do cells divide?
• Through cell
division, one
parent cell
divides into two
new daughter
cells, each of
which is identical
to the parent
cell.
The cell cycle
• The cell cycle is an
ordered sequence
of stages through
which a cell
progresses in
order to divide
during its life.
• The purpose of
the cell cycle is to
replicate cells.
Stages of the cell cycle
• The cell cycle consists of preparatory phases (collectively know
as interphase) and division phases (mitosis and cytokinesis).
Stages of the cell cycle: Interphase
• Interphase is the
stage of the cell
cycle in which cells
spend most of
their time,
preparing for cell
division.
Stages of the cell cycle: Interphase
• Interphase is
divided into
three stages:
G1, S, and G2.
Stages of the cell cycle: Interphase
• During the G1
Phase of
interphase, the
cell grows and
prepares to
divide both its
DNA and its
organelles.
Stages of the cell cycle: Interphase
• During the S Phase
of interphase, DNA
replication occurs.
Stages of the cell cycle: Interphase
• During the G2
Phase of
interphase,
the cell
prepares for
division.
Stages of the cell cycle: Mitosis
• During mitosis,
the sister
chromatids of
each chromosome
are separated
from one another,
setting up the two
identical nuclei of
the daughter cells.
Cell division:
The chromosome perspective
• Chromosomes are duplicated during the S Phase of
interphase.
Cell division:
The chromosome perspective
• A sister
chromatid is
one of the two
identical DNA
molecules that
make up a
duplicated
chromosome
following DNA
replication.
Cell division:
The chromosome perspective
• The sister
chromatids are
joined together at a
region of the
chromosome
known as the
centromere.
Cell division:
The chromosome perspective
• During mitosis and cytokinesis, the sister
chromatids pull apart and move into separate
daughter cells.
Stages of the cell cycle: Cytokinesis
• During
cytokinesis, the
cytoplasm
divides into two
cells, each
containing a full
complement of
organelles and
DNA.
Up Close: The phases of mitosis
• Mitosis occurs in a series
of phases that are part of
the cell cycle.
Up Close: The phases of mitosis
• In interphase, the chromosomes are loosely
gathered in the nucleus.
Up Close: The phases of mitosis
• In prophase, replicated chromosomes begin to
coil up, the nuclear membrane begins to
disassemble, and the protein fibers of the
mitotic spindle begin to form.
Up Close: The phases of mitosis
• In prometaphase, the chromosomes condense
to shorten them, and spindle fibers attach to
the chromosomes on both sides at the
centromere region.
Up Close: The phases of mitosis
• In metaphase, spindle fibers from opposite
ends of the cell pull on chromosomes, aligning
them along the middle of the cell.
Up Close: The phases of mitosis
• In anaphase, spindle fibers shorten and pull
sister chromatids to opposite ends of the cell.
Up Close: The phases of mitosis
• In telephase, an identical set of chromosomes
reaches each pole, the spindle fibers
dissemble, and a nuclear membrane forms
around each set of chromosomes to form the
daughter cell nuclei.
Up Close: The phases of mitosis
• During cytokinesis, the cell membrane pinches in to
completely surround each new daughter cell.
• The cell cycle starts over with two newly formed identical
daughter cells in interphase. Each daughter cell has the same
number of chromosomes as the parent cell.
Cell division is tightly regulated
• Cell cycle
checkpoints
ensure that each
stage of the cell
cycle is
completed
accurately by
preventing a cell
from progressing
to the next stage
until it accurately
finishes the
current stage.
Cell division is tightly regulated
• When a normal cell
has irreparable
damage, it undergoes
apoptosis, or
programmed cell
death to prevent cells
from producing more
damaged daughter
cells.
What is cancer?
• Cancer is a disease of unregulated cell
division. Cells divide inappropriately and
accumulate, in some instances forming a
tumor.
Comparing cancer cells to normal cells
• Cancer cells have
damaged
checkpoint
mechanisms,
allowing them to
divide when they
should not. The
damaged cells also
bypass apoptosis,
passing the
damaged DNA to
each daughter cell.
Fighting cancer: Surgery
• Surgery to remove the cancerous tumor is
effective for certain solid tumors, but it is not
an effective treatment for blood cancers or
cancers that have undergone metastasis – the
spread of cancer cells from one location in the
body to another.
Fighting cancer: Chemotherapy
• Chemotherapy
uses drugs to
interfere with
cell division to
treat cancer.
Fighting cancer: Radiation therapy
• In radiation therapy, high-energy radiation beams are used to
kill dividing cells, severely damaging molecules and DNA to
trigger apoptosis.
Fighting cancer: Side-effects
• The side-effects of
chemotherapy and
radiation therapy can
be quite severe.
• Herbal supplements
may complement
cancer treatment by
reducing the severity
of traditional sideeffects and enhancing
the effect of
chemotherapy.