Download Part II The Cell Cell Division, Chapter 3

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Part II
The Cell – Cell Division, Chapter 3
Outline of class notes
Cellular Division Overview
• Types of Cell Division
• Chromosomal Number
• The Cell Cycle
– Mitoses
• Cancer Cells
In Vitro Fertilization
• Infertility
– Affects one in ten American couples
• In vitro fertilization (IVF) can help infertile couples.
– A sperm and an
– The embryo is implanted into the mother’s uterus at the 8 cell stage.
– IVF is one of many reproductive technologies
Cell Division
• Cell Division
– Is the process whereby cells reproduce themselves
– Functions:
• Replace diseased or damaged cells
•
•
– Two types of cell division are:
• Somatic cell division
• Reproductive cell division
Somatic Cell Division
• In somatic cell division:
– Cell undergoes a nuclear division called mitosis and
a cytoplasmic division called cytokinesis.
– Results in two daughter cells genetically identical exactly the same number and type of chromosomes as the parent cell.
Reproductive Cell Division
• In reproductive cell division:
– Cells undergo a process of
meiosis that produces gametes
(eggs or sperm).
– The egg and sperm contain half
the number of chromosomes as
the parent cell.
– Occurs in the ovaries and testes.
– Function: The creation of
offspring by
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Background on Chromosomes
• You inherited 46 chromosomes, 23 from each parent.
– Each somatic cell of the human body, except for sex cells, contains 46 chromosomes
(diploid number).
• These chromosomes are arranged in pairs, thus you have 23 pairs to give a total
of 46 chromosomes.
• Of the 23 pairs, one pair are the sex chromosomes which consist of two X
chromosomes if the person is female or an X and a Y chromosome if the
person is male
– The remaining 22 pairs of chromosomes are called autosomes
– Sex cells (sperm and egg) contain 23 individual chromosomes (haploid number), or half
that of somatic cells.
• The union of a sperm and egg during fertilization restores
A human karyotype has 22 pairs of autosomes and 1 pair of sex chromosomes (23 total pairs)
Cell Cycle
• The cell cycle is an sequence of events in the life of a dividing cell, it lasts from the beginning
of one division to the beginning of the next.
– Cell Cycle consists of two distinct phases:
1.
2.
Sister
Chromatids
Interphase
• Interphase is the time in which the cell performs its normal functions, and if appropriate,
prepares for cell division. Consists of four stages:
– Go Phase: (G = gap): The normal functional state of a cell not dividing.
– G1 Phase: Cell prepares for replication. Cell produces all the enzymes required for
DNA replication and duplicates most of its organelles.
– S Phase: (Synthesis) Chromosomes are replicated and become double stranded. The
replicated chromosome are attached together at the centromere and are known as
sister chromatids. Each is an exact copy of the other and is called a chromatid.
– G2 Phase: Devoted to last minute
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Cell Division in Somatic cells
• Cell division includes two overlapping processes – mitoses and cytokinesis.
– Mitoses:
• The chromosomes within the nucleus divide and are evenly distributed, forming
two daughter nuclei
– Cytokinesis:
•
•
Results in two genetically identical daughter cells
Note: Mitoses is a continuum, but we can divide it into 4 stages: prophase, metaphase,
anaphase, and telophase
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Mitoses: 4 stages
1. Prophase
• Chromatin condenses to form visible (with a microscope) chromosomes.
• Centrioles move toward
•
Centrioles produce spindle fibers (microtubules), which extend and attach to the
centromeres of each chromosome.
– Spindle fibers attach to the kinetochore of the centromere.
• Movement of chromosomes depend on the spindle fibers.
• Nucleolus and the
2. Metaphase
• Chromosomes (each consisting of sister chromatids) line up on the metaphase (equatorial)
plate which is at the center of the cell.
3. Anaphase
• Sister chromatids separate at the centromere forming two sets of identical chromosomes.
– Note: At time of separation, each
•
The daughter chromosomes move toward the opposite ends of the cell.
– Spindle fibers from the centrioles assist in this process.
4. Telophase
• A nuclear membrane forms around each set of chromosomes
• Chromosomes uncoil becoming chromatin
• Nucleoli reappear
• Cell prepares to divide
•
Cytokinesis
• Cytokinesis (cleavage) is the
– Typically
•
The cell membrane constricts along the plane of the metaphase (center) plate forming a
cleavage furrow.
• Cytoplasm divides resulting in two daughter cells each with DNA that is identical to the DNA
of the parent cell
Mnemonic to Remember Mitosis
Mnemonic
Phase
I’ve
Probably
Made
All
This
Correct
Anaphase
Telophase
Cytokinesis
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Control of the Cell Cycle
• Normal animal cells have a cell cycle control system.
– Special proteins within the cell send “stop” and “go-ahead” signals at certain key points
during the cell cycle.
– Example: Nerve and muscle cells are
•
Other cells like our skin cells, are constantly receiving signals to divide.
Cancer Cells: Growing Out of Control
• Cancer is a group of diseases characterized by uncontrolled cell proliferation - is a disease of
the cell cycle.
– Kills one out of every 5 people in the U.S.
• Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells.
These abnormalities may be due to the effects infectious agens or from exosure of
carcinogens such as:
–
•
Cancer cells do not respond normally to the
– They divide excessively and can invade other tissues of the body.
Benign vs. Malignant Tumor
• Cancer cells can form tumors (neoplasms), which are abnormal growths (masses) of body
cells. Two types of Tumors:
1. Benign tumors: Tumor cells remain at the
• Removed surgically if interferes with normal function
2. Malignant tumors: Tumor cells spread into neighboring tissue by way of the circulatory
and lymphatic vessels and may form new tumors.
• Metastasis is the spread of cancer cells.
• An individual with a malignant tumor is said to have cancer.
How Cancers are Named
• Cancers are named according to where they originate and are grouped into 4 categories:
1. Carcinomas: Originate in the external or internal coverings of the body (skin, intestine
etc), lungs, breasts, pancreas, glands.
• Most commonly diagnosed cancers
2. Sarcomas: Originate in support tissues/structures, such as in bone, fat, and muscle
3. Leukemias: Originate in
4. Lymphomas: Originate in
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Human Papillomavirus (HPV)
• HPV causes
– Symptoms and virulence depend on the strain of virus
– Virus can interfere with certain suppressor proteins that inhibit cell replication. This can
cause the persons infected cells to proliferate without control.
Cancer Treatment
• Cancer treatment can involve:
– Surgery: Removes the tumor or cancer.
• Is usually the first step
– Radiation therapy: High energy radiation damages
• Cancer cells divide more often than other cells.
• Can cause nausea and hair loss
– Chemotherapy: Uses drugs that disrupt cell division.
• Usual site is to disrupt spindle fiber formation or function
Cancer Prevention and Survival
• Cancer prevention includes changes in lifestyle:
–
–
–
–
–
–
Avoiding exposure to the sun
Eating a high-fiber, low-fat diet
Visiting the doctor regularly
Performing regular self- and doctor mediated examinations
• Breast
• Prostate
• Cervical
• Testicular
• Colon