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1.6 cell division

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1.6 Cell Division
The Cell Cycle
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Describes the life of a cell.
Includes 2 stages:
1)
-
Interphase
the growth and replication (of DNA) stage of the cell
when the cell carries out its regular functions as a cell
consists of the GI, S, and G2 phases
2) Cell Division
- When the cell gets too big, it needs to divide into 2 new cells to become more efficient and maximize its
surface area to volume ratio.
- Allows for asexual reproduction, growth of the organism, and the replacement of damaged cells
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Made of 2 stages
a) MITOSIS – the division of nuclear materials (chromosomes)
o Consists of 4 stages: prophase, metaphase, anaphase, telophase
b) CYTOKINESIS – the division of the cytoplasm and organelles to create 2 new daughter cells
DNA
-
The molecule of heredity for most cells, found within the nucleus
It contains genes, which are instructions on how to make proteins that make you who you are
During interphase, DNA is found in the form of chromatin
CHROMATIN – tangled strands of DNA and proteins
Early in mitosis, the chromatin condenses to form chromosomes
Single Stranded
Chromosome / Chromatid
Double Stranded
Chromosome
Mitosis Terms
Sister Chromatids: the identical chromosome strands that comprise a double stranded chromosome
Centromere: the region of the chromosome where 2 sister chromatids join
Centrioles: a pair of cylindrical cell structures made of protein that will organize the mitotic spindle.
Mitotic Spindle (Spindle Apparatus): made of hundreds of microtubules (proteins) that will attach to the
centromere of chromosomes and align them during mitosis.
MITOSIS and CELL DIVISION
PHASE
INTERPHASE
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-
PROPHASE
-
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MITOSIS
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METAPHASE
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WHAT HAPPENS
The cell grows
Prepares for cell division by
duplicating its genetic
material (DNA)
DNA found in the form of
chromatin
The chromatin shortens and
thickens into double
stranded chromosomes
The nuclear membrane
disintegrates
centrioles move to opposite
poles of the cell
Spindle fibers develop and
attach to centromeres of
chromosomes
The spindle fibers line up
the double stranded
chromosomes in single file
along the equator of the cell,
metaphase plate.
DIAGRAM
ANAPHASE
-
-
TELOPHASE
-
-
CYTOKINESIS
-
-
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The spindle fibers pull on
the centromeres of the
chromosomes separating the
sister chromatids of each
double stranded
chromosomes.
Each single strand is pulled
to an opposite pole of the
cell
The chromatids reach the
opposite poles of the cell
The spindle detaches and
new nuclear membranes form
around the chromatids
Cytokinesis begins even
before telophase completes
with the formation of a
cleavage furrow (indentation
of the cell membrane).
The cell membrane pinches in
to divide the original parent
cell in 2 and create 2 new
daughter cells
Each daughter cell will have
the same number of
chromosomes as the original
parent cell.
The chromosomes recondense to form chromatin
and the cell cycle begins
again with interphase.
Cytokinesis in Plant Cells
-
During telophase, membrane-bound vesicles made
from the Golgi Apparatus move to the center of the
cell and fuse to form a cell plate
-
Eventually, the growing cell plate fuses with the
existing plasma membrane producing 2 daughter cells
with their own plasma membrane
-
A new cell wall will form between the 2 membranes of
the cell plate.
Control of the Cell Cycle with Cyclins
Cyclins:
-
Discovered by R. Timothy Hunt in 1982 while studying the cell cycle in sea urchins.
-
a family of proteins that control the progression of cells through the cell cycle
-
they bind to enzymes called cyclin dependent kinases (Cdk) activating them
-
activated Cdk will activate other proteins by phosphorylation (attaching a phosphate group to the
proteins)
-
these phosphorylated proteins can now perform various functions initiating events in the cell cycle.
•
•
•
•
Cyclin D triggers cells to move from G phase to S phase of interphase
Cyclin E prepares the cell for DNA replication in the S phase
Cyclin A activates DNA replication inside the nucleus
Cyclin B promotes the assembly of the mitotic spindle
CANCER
Cancer: Disorder in which some of the body's cells lose the ability to control their growth.
Tumor: A mass of cells produced by repeated, uncontrolled cell division.
Tumors can occur in any organ. Some tumors grow large and spread to other parts of the body (metastasis). The
diseases caused by the growth of tumors is known as cancer.
Tumors can be benign (harmless) or malignant (ones that can spread)
Oncogene: a gene that has the potential to cause cancer. In tumor cells they are mutated or expressed at high
levels.
Carcinogens/Mutagen (a substance that increases the chance of a mutation leading to cancer)
•
•
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Treatments:
•
•
•
Radiation (gamma, UV, x-ray etc.)
Chemicals (textile dyes, paints and inks)
Viruses (hepititis B and C and HPV)
Surgery (the physical removal of a tumor)
Radiation (a radiation beam is directed at mutated cells to destroy them)
Chemotherapy (medications that target rapidly dividing cells)
Cancer & Smoking
•
There is a strong correlation between smoking and cancer
•
Women smokers are 25.7 times more likely than women who never smoked to develop lung cancer. For
men smokers, it’s 25 times the risk of men who never smoked. (Source: US Surgeon General Report
2014)
•
Besides lung cancer, tobacco use also increases the risk for cancers of the mouth, lips, nose and sinuses,
larynx (voice box), pharynx (throat), esophagus (swallowing tube), stomach, pancreas, kidney, bladder,
uterus, cervix, colon/rectum, ovary (mucinous), and acute myeloid leukemia. (Source: Cancer Facts &
Figures 2014)
Mitotic Index
-
A way to measure the rate of proliferation (growth)
Mitotic Index = # of cells in Mitosis
Total # of cells
1.6 Cell Division – Homework Questions
1) Identify the stages of mitosis and cell division seen in the following micrograph.
DATA BASE QUESTION
2. One of the largest ever studies of the effect of smoking on health involved 34, 439 male British doctors.
Information was collected on how much they smoked from 1951 to 2001 and the cause of death was
recorded for each of the doctors who died during this period. The table shows some of the results.
Type of disease
Non-smoker
107
1037
8
1-14 cigarettes
per day
237
1447
11
15-24 cigarettes
per day
310
1671
33
>25 cigarettes
per day
471
1938
34
Respiratory
Circulatory
Stomach and
duodenal ulcers
Cirrhosis of the
liver
Parkinson’s
6
13
22
68
20
22
6
18
a. Deduce whether there is a positive correlation between smoking and the mortality rate due to all types
of disease.
b. Using the data in the table, discuss whether the threat to health from smoking is greater with
respiratory or with circulatory
c. Discuss whether the data suggests that smoking a small number of cigarettes is safe.
d. Discuss whether the data proves that smoking is a cause of cirrhosis of the liver
e. The table does not include deaths due to cancer. The survey showed that seven types of cancer are
linked with smoking. Discuss three cancers you would expect smoking to cause.
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