CHAPTER 9 CELLULAR REPRODUCTION P

C^HAPTER 9 C^ELLULAR REPRODUCTION

P. 243-257

S ^ECTION 9-1

C ^{ELLULAR GROWTH}

Page 244

E ^SSENTIAL Q ^UESTION

 

Why is it beneficial for cells to

remain small?

M ^{AIN IDEA}

 Cells grow until they reach their size limit, then they either stop growing or divide.

C ^{ELL SIZE} LIMITATIONS

 Most cells are smaller than a period at the end of a sentence.

 There are two reasons cells divide rather that continue to grow.

  The larger the cell becomes, the more demands the cell places on it DNA.

  The larger the cell becomes, the more trouble the cell has moving nutrients and wastes across the cell membrane.

H^{OW DOES THE AMOUNT OF SURFACE AREA}

CHANGE AS THE CELL’^{S VOLUME INCREASES}?

R ^{ATIO OF SURFACE AREA TO}

VOLUME

 The key factor that limits the size of a cell is the ratio of its surface area to volume.

  The surface area refers to the area covered by the plasma membrane.

  The volume refers to the space taken by the inner contents of the cell, including the organelles in the cytoplasm and the nucleus.

H^{OW DOES THE AMOUNT OF SURFACE AREA}

CHANGE AS THE CELL’^{S VOLUME INCREASES}?

R ^{ATIO OF SURFACE AREA TO}

VOLUME

 As a cell grows in size, its volume increases faster than its surface area.

 This means the cell might have trouble

supplying and transporting nutrients and expelling enough waste products.

 By remaining small, cells can sustain themselves more easily.

C ^{ELL CYCLE}

 Once a cell reaches its size limit, it will either stop growing or divide.

 Most cells divide. Nerve and muscle cells do not divide.

 Cell division also is the way the cell reproduces so that you grow and heal certain injuries.

 Cells reproduce by a cycle of growing and dividing called the cell cycle.

C ^{ELL CYCLE}

  3 main stages……..

  Interphase – cell grows, carries out certain cellular functions, replicates its DNA [3 substages]

  Mitosis – cell’s nucleus and nuclear material, DNA, divide [4 substages]

  Cytokinesis – cytoplasm divides

C ^ELL C ^YCLE

S ^{TAGES OF INTERPHASE}

 G1 stage (normal cell growth) has the longest duration.

 G1 - 1^st stage, a cell is growing, carrying out normal cell functions, and preparing to replicate or copy DNA

 S - 2^nd stage, cell copies its DNA in preparation for cell division

  Chromosomes contain the genetic material that is passed from one generation to the next.

S ^{TAGES OF INTERPHASE}

  Chromatin is the relaxed form of DNA in a cell’s nucleus.

 

Chromatin condenses or tightens to

form chromosomes.

 

G2 - 3

stage, Cell prepares for the

division of its nucleus.

  The cell makes sure everything is ready for mitosis.

 

A cell spends the majority of its

lifetime in interphase.

S

9-2

MITOSIS AND CYTOKINESIS

Page 248

M ^AIN I ^DEA

 Eukaryotic cells reproduce by mitosis, the process of nuclear division, and

cytokinesis, the process of cytoplasmic division.

M ^{ITOSIS AND} CYTOKINESIS

P

M

- P

 1^st phase - longest

 Chromatin tightens into chromosomes that are X-shaped and become visible.

 Centrioles separate and move to opposite poles of the cell.

 Nuclear membrane disintegrates.

 Nucleolus disappears.

 Mitotic spindle begins to form between the poles.

C ^HROMOSOMES

P^ROPHASE

xxxx xxxx xxxx

P ^ROPHASE

 Spindle apparatus is made of spindle fibers, centrioles, and aster fibers.

 The spindle apparatus is important in organizing and moving

chromosomes before cell division.

 Plant cells do not have centrioles.

B

,

FOLLOWING HAS OCCURRED

:

 By the end of prophase, the following has occurred:

  Nuclear envelope seems to disappear.

  Spindle fibers attach to sister chromatids on both sides of the centromere.

M ^ETAPHASE

 2^nd phase - shortest

 Sister chromatids are pulled along the

spindle apparatus to center of cell and line up in the middle.

 Tension of spindle fibers pulls them along.

M ^ETAPHASE

xxx

ANAPHASE

 3^rd phase

 The centromeres that join the sister chromatids split.

 The sister chromosomes become individual chromosomes.

 The two sets of chromosomes move apart to opposite poles.

ANAPHASE

T ^ELOPHASE

 4^th phase - last phase

 Chromosomes gather at opposite

ends of the cell and lose their shape.

 Two new nuclear envelopes form.

 Nucleoli reappear.

 Spindle apparatus comes apart.

TELOPHASE

C ^YTOKINESIS

 Cytokinesis usually happens at the same time as telophase.

 The cell membrane is pulled inward until the cytoplasm is pinched into two nearly equal parts.

 Results are two cells, with identical nuclei.

 In plant cells, a cell plate forms that later becomes cell wall to divide the cells.

CYTOKINESIS

S

9-3

CELL CYCLE REGULATION

Page 253

M ^{AIN IDEA}

 The normal cell cycle is regulated by cyclin proteins.

C ^YCLINS

 In a multicellular organism, cell growth and cell division are carefully controlled.

 When an injury such as a cut in the skin occurs, cells at the edge of the cut divide rapidly.

 When the healing process is nearly

complete, the rate of cell division slows and then returns to normal.

CYCLINS

 When cells come into contact with one

another, molecules on their surface signal them to stop growing.

 Cyclins, a group of proteins, regulate the timing of the cell cycle in eukaryotic cells.

 Cyclins are one group of proteins involved in cell cycle regulation.

 Other proteins, called regulatory proteins, regulate the cell cycle in different ways.

C ^ANCER

 Contols on cell growth can be turned on and off by the body.

 Cancer is a disorder in which some of the body’s cells lose the ability to control

growth.

 Cancer cells do not respond to the signals that control the growth of most cells.

 As a result, cancer cells divide uncontrollably.

C ^ANCER

 Cancer cells reproduce rapidly because they spend less time in interphase.

 Cancer cells do not stop growing when they touch other cells.

 They continue to grow and divide until their supply of nutrients is used up.

C

….

 Changes that occur in the regulation of

cell growth and division of cancer cells are due to mutations or changes in segments of DNA.

 The changes can damage the control of the proteins that regulate the cell cycle.

 The genetic change or damage can often be repaired by various repair systems

 If repair systems fail, cancer can result.

CARCINOGENS

 Various environmental factors can affect the occurrence of cancer cells.

 Substances that are known to cause cancer are called carcinogens.

 Examples: cigarettes, asbestos, X rays, the Sun’s ultraviolet rays

APOPTOSIS

 Apoptosis is programmed cell death.

 Cells going through apoptosis actually shrink and shrivel in a controlled

process.

 Example: When hands and feet begin to develop, there are cells between fingers and toes that look like webbing.

 The webbing is not present in the mature organism.

S ^{TEM CELLS}

 Most cells in a nulticellular organism are designed for a specialized function.

 Stem cells are unspecialized cells that can develop into specialized cells when under the right conditions.

 Two basic types of stem cells:

  Embryonic- After a sperm terilizes an egg, the resulting mass of cells divides until there are about 100-150 cells.

S ^{TEM CELLS}

  Adult- Found in various tissues in the

body and might be used to maintain and repair the same kind of tissue where

they are found.

 

Researchers think certain kinds of

adult stem cells might be able to

develop into different kinds of cells for

treatment of disease and conditions.