Lesson Overview Lesson Overview The Process of Cell Division Chapter 10 Cell Growth and Division.

Lesson OverviewLesson Overview The Process of Cell DivisionThe Process of Cell Division

Chapter 10Cell Growth

and Division


10.1 Cell Growth, Division, and Reproduction


Information “Overload” – Compare a cell

to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access.

– A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.


Exchanging Materials

– Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way.

– The rate at which this exchange takes place depends on the surface area of a cell.

– The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume.

– The ratio of surface area to volume is key to understanding why cells must divide as they grow.


Ratio of Surface Area to Volume

– Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume.

– If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.


Division of the Cell

– Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.

– Before cell division, the cell copies all of its DNA.

– It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA.

– Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.


– In single-celled organisms, cell division is a form of reproduction.

– Asexual reproduction is reproduction that involves a single parent producing an offspring.

– The offspring produced are, in most cases, genetically identical to the single cell that produced them.

– Simple, efficient, and effective way for an organism to produce a large number of offspring.

– Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

• Bacteria reproduce by binary fission.• Kalanchoe plants form plantlets.• Hydras reproduce by budding.

Asexual Reproduction


Sexual Reproduction

– In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents.

– These fuse into a single cell before the offspring can grow.

– The offspring produced inherit some genetic information from both parents.

– Most animals and plants, and many single-celled organisms, reproduce sexually.


Comparing Sexual and Asexual Reproduction


10.2 The Process of Cell Division


– The genetic information that is passed on from one generation of cells to the next is carried by chromosomes.

– Every cell must copy its genetic information before cell division begins.

– Each daughter cell gets its own copy of that genetic information.

– Cells of every organism have a specific number of chromosomes.

Chromosomes


Prokaryotic Chromosomes

– Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm.

– Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.


Eukaryotic Chromosomes– In eukaryotic cells, chromosomes are located in the

nucleus, and are made up of chromatin.– Chromatin is composed of DNA and histone proteins.– DNA coils around histone proteins to form nucleosomes.– The nucleosomes interact with one another to form coils

and supercoils that make up chromosomes.


The Prokaryotic Cell Cycle– The prokaryotic cell cycle is a

regular pattern of growth, DNA replication, and cell division.

– Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size.

– When DNA replication is complete, the cells divide through a process known as binary fission.

– Binary fission is a form of asexual reproduction during which two genetically identical cells are produced.

• For example, bacteria reproduce by binary fission.


The Eukaryotic Cell Cycle

– The eukaryotic cell cycle consists of four phases: G1, S, G2, and M.

– Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.


G1 Phase: Cell GrowthInterphase!!!

– In the G1 phase, cells increase in size and synthesize new proteins and organelles.


S Phase: DNA ReplicationInterphase!!

– In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.


G2 Phase: Preparing for Cell Division

Interphase!!– In the G2 phase,

many of the organelles and molecules required for cell division are produced.


M Phase: Cell DivisionMitosis and Cytokinesis!!

– In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.

– Mitosis is the division of the cell nucleus.

– Cytokinesis is the division of the cytoplasm.


Mitosis

• Occurs in body cells – all cells of body NOT involved in sexual reproduction– Includes ALL body cells – NOT SPERM AND EGG!!

• Similar to a photocopy machine• Start with one cell. The end result is two

identical cells


Mitosis

• Each daughter cell receives an exact copy of the chromosomes present in the parent cell.

• Mitosis is a continuous process in which each phase merges into the next.

• Interphase – Time between the formation of a cell and the beginning of next mitosis.– G1, S, G2


Mitosis

1. Prophase – Chromatin condenses into chromosomes, nuclear membrane disappears

– Chromatid – each DNA strand in the duplicated chromosome

– Centromere – where the DNA strands are attached.

– The centrioles move to opposite sides of nucleus and help organize the spindle.


Mitosis

2. Metaphase – Chromosomes line up in center of cell


Mitosis3. Anaphase – Separation of chromosomes, move

through cytoplasm to opposite ends of cell4. Telophase – Nuclear membrane forms around

each new set of chromosomes, 2 new cells formed


Mitosis

• Cytokinesis – Process during which cytoplasm divides.– Occurs during telophase– Animal cell - Cell membrane pinches

together forming two new cells– Plant cell – Cell plate forms and

gradually develops into cell membranes

• PMAT• http://www.youtube.com/watch?

v=DD3IQknCEdc


ProphaseTelophase

Anaphase

Metaphase


The Stages of the Cell Cycle


Mitosis Flipbook• You should have the following index cards:

1. Interphase – Label “Interphase – Not a true phase”2. Moving from Interphase into Prophase3. Prophase – Label4. Moving from Prophase into Metaphase5. Metaphase – Label6. Moving from Metaphase into Anaphase7. Anaphase – Label8. Moving from Anaphase into Telophase9. Telophase – Label “Telophase” and also label Cytokinesis10. Two daughter cells

• When you are finished with your flipbook, please show it to me for a grade. Staple on left-hand side!!

• Draw Mitosis and hand in.


10.3 Regulating the Cell Cycle


– The controls on cell growth and division can be turned on and off.

– For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows when the healing process nears completion.


The Discovery of Cyclins

– Cyclins are a family of proteins that regulate the timing of the cell cycle in eukaryotic cells.

– This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.


Regulatory Proteins

– Internal regulators are proteins that respond to events inside a cell. They allow the cell cycle to proceed only once certain processes have happened inside the cell.

– External regulators are proteins that respond to events outside the cell. They direct cells to speed up or slow down the cell cycle.

– Growth factors are external regulators that stimulate the growth and division of cells. They are important during embryonic development and wound healing.


Apoptosis– Apoptosis is a

process of programmed cell death.

– Apoptosis plays a role in development by shaping the structure of tissues and organs in plants and animals.

• For example, the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development.


– Cancer is a disorder in which body cells lose the ability to control cell growth.

– Cancer cells divide uncontrollably to form a mass of cells called a tumor.


• A benign tumor is noncancerous. It does not spread to surrounding healthy tissue.

• A malignant tumor is cancerous. It invades and destroys surrounding healthy tissue and can spread to other parts of the body.

• The spread of cancer cells is called metastasis. • Cancer cells absorb nutrients

needed by other cells, block nerve connections, and prevent organs from functioning.


What Causes Cancer?

– Cancers are caused by defects in genes that regulate cell growth and division.

– Some sources of gene defects are smoking tobacco, radiation exposure, defective genes, and viral infection.

– A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to growth signals.


Treatments for Cancer

– Some localized tumors can be removed by surgery.

– Many tumors can be treated with targeted radiation.

– Chemotherapy is the use of compounds that kill or slow the growth of cancer cells.


10.4 Cell Differentiation


– All organisms start life as just one cell.

– Most multicellular organisms pass through an early stage of development called an embryo, which gradually develops into an adult organism.

– During development, an organism’s cells become more differentiated and specialized for particular functions.

• For example, a plant has specialized cells in its roots, stems, and leaves.


Defining Differentiation

– The process by which cells become specialized is known as differentiation.

– During development, cells differentiate into many different types and become specialized to perform certain tasks.

– Differentiated cells carry out the jobs that multicellular organisms need to stay alive.


Differentiation in Mammals

– Cell differentiation in mammals is controlled by a number of interacting factors in the embryo.

– Adult cells generally reach a point at which their differentiation is complete and they can no longer become other types of cells.

– One of the most important questions in biology is how all of the specialized, differentiated cell types in the body are formed from just a single cell.

• Biologists say that such a cell is totipotent - literally able to do everything, to form all the tissues of the body.

• Only the fertilized egg and the cells produced by the first few cell divisions of embryonic development are truly totipotent.


Human Development– After about four days of

development, a human embryo forms into a blastocyst - a hollow ball of cells with a cluster of cells inside known as the inner cell mass.

– The cells of the inner cell mass are said to be pluripotent - they are capable of developing into many, but not all, of the body's cell types.


Stem Cells

– Stem cells are unspecialized cells from which differentiated cells develop.

– There are two types of stem cells: embryonic and adult stem cells.


Embryonic Stem Cells

– Embryonic stem cells are found in the inner cells mass of the early embryo.

– Embryonic stem cells are pluripotent. – Researchers have grown stem cells isolated from

human embryos in culture. Their experiments confirmed that embryonic stem cells have the capacity to produce most cell types in the human body.


Adult Stem Cells– Adult organisms contain some types of stem cells.– Adult stem cells are multipotent - They can produce

many types of differentiated cells.– Adult stem cells of a given organ or tissue typically

produce only the types of cells that are unique to that tissue.

• Lung cells produce lung tissue


Frontiers in Stem Cell Research

– What are some possible benefits and issues associated with stem cell research?

– Stem cells offer the potential benefit of using undifferentiated cells to repair or replace badly damaged cells and tissues.

– Human embryonic stem cell research is controversial because the arguments for it and against it both involve ethical issues of life and death.


Potential Benefits

– Stem cell research may lead to new ways to repair the cellular damage that results from heart attack, stroke, and spinal cord injuries.

– One example is the approach to reversing heart attack damage illustrated below.


Ethical Issues

– Most techniques for harvesting, or gathering, embryonic stem cells cause destruction of the embryo.

– Government funding of embryonic stem cell research is an important political issue.

– Groups seeking to protect embryos oppose such research as unethical.

– Other groups support this research as essential to saving human lives and so view it as unethical to restrict the research.

Lesson Overview Lesson Overview The Process of Cell Division Chapter 10 Cell Growth and Division.

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