The Cellular Basis of Reproduction and Inheritancefaculty.collin.edu/cdoumen/1408/1408_Ch8_9/1408_Ch8A1.pdf · Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology:

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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey

The Cellular Basis of Reproduction and Inheritance

Biology 1408 Dr. Chris Doumen

!  In a healthy body, cell division allows for –  growth,

–  the replacement of damaged cells, and

–  development from an embryo into an adult.

–  These cell division occur by means of a process of mitosis

!  In addition, sexually reproducing organisms require eggs and sperm cells –  These are made by a cell division process called

meiosis.

Introduction

© 2012 Pearson Education, Inc.

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!  The human body contains about 50 trillion cells. And they all function perfectly. How do you get 50 trillion from one fertilized cell ?

Introduction


! Also, the body is continuously replacing worn out cells. Every day, million of cells need to be replaced.

!  For example : Every second, about 2 million new red blood cells are destroyed and 2 million new ones are made in a healthy human individuals.

Introduction


!  Bone tissue is remodeled constantly and old bone material is replaced with new. Estimates are that 10 % of your bone mass is remodeled every year.

!  This requires an enormous productive cell division (aka mitosis)

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!  Humans can regenerate certain tissues, but major regrowth of structures (such as a limb) is not programmed into our repair mechanism (yet).

Introduction


!  A seastar can regenerate a lost arm by means of cell division and growth ( also by mitosis)

!  On the other hand, what happens when cells divide out of control ? We call this cancer.

!  Cancer cells

–  start out as normal body cells,

–  undergo genetic mutations,

–  lose the ability to control the tempo of their own division, and

–  run amok, displace other normal tissue causing organ malfunction, death….

Introduction


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!  Understanding cell division, cell repair and cell “behavior” is extremely important since it allows us the understand the processes involved in health, disease and healing.

Introduction


!  For example, two-thirds of breasts tumor cells carry receptors for estrogen.

!  The binding of estrogen stimulates and enhances cell division

!  Some breast cancer therapy thus use estrogen receptor blockers (such as Tamoxifen)

!  The more information known about the normal and abnormal cell division, the better we can find specific therapies for specific individuals

!  Understanding cell division and cell repair is extremely important since it allows us the understand the processes involved in health, disease and healing.

!  Research on the details of cell division and the regulatory aspects of cell division will someday provide us with an upper-hand in the battle against cancer

!  Someday we may be able to regenerate lost limbs like a sea-star !?

Introduction


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CELL DIVISION AND REPRODUCTION


8.1 Cell division plays many important roles in the lives of organisms

!  Organisms (species) reproduce their own kind, a key characteristic of life. It requires that each new cell we make has all the information to remain true to it’s owner.

!  Everyone knows that flies make flies, frogs mate and make more frogs, dogs will reproduce into dogs, you can’t turn a donkey into a horse ,etc…

!  It is the concept of species and the continuation of the species.


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!  The key issue is that all the information for a cell’s function and how the species looks is located in the DNA.

!  The DNA is organized into chromosomes but the number of chromosomes is only one aspect of the puzzle.

!  Example : all these species have 46 chromosomes

!  Homo sapiens

!  Lepus europaeus

!  Aplodontia rufa

!  Hippotragus niger




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!  The chromosomes are made out of DNA and organized into genes. The genes code for specific proteins.


!  It is the number of genes , the quality of the expressed proteins and the overall combination and integration of these proteins that determines cell function, tissue and organ organization.

!  Small variations within the genes result in the different looks within a species.


!  Organisms thus reproduce their own kind, a key characteristic of life. It requires that each new cell we make has all the information to remain true to it’s owner.

!  In typical Cell Division, the result is two cells. Biologist name them the off-spring cells or the daughter cells (it does not mean the cells are females).


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!  One key issue is that all the information for a cell’s function is located in the DNA.

!  Thus, the two new daughter cells need exact copies of the DNA from the mother cell otherwise the new cells may not function correctly

!  A typical cell division hence requires –  the duplication of the DNA (chromosomes), and

–  delivery of the right copies (sorting of the new sets ) of chromosomes into the resulting pair of daughter cells.

–  In addition, each daughter cell receives all the cytoplasmic components required for cellular metabolism ( such as ribosomes, mitochondria,….)


!  A typical cell division is used

–  for reproduction of single-celled organisms,

–  growth of multicellular organisms from a fertilized egg into an adult,

–  repair and replacement of cells

!  A special type of cell division is used for sperm and egg production.



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Cell division plays many important roles in the lives of organisms

!  Living organisms reproduce by two methods.

–  Asexual reproduction

–  involves inheritance of all genes from one (1) parent.

–  produces an offspring that is identical to the original cell or organism; they become genetic copies of each other


–  This is for example a yeast cell, producing a genetically identical daughter cell by asexual reproduction

!  Prokaryotes (bacteria and archaea) reproduce by asexual reproduction called binary fission (“dividing in half”).

!  The chromosome of a prokaryote is

–  a singular circular DNA molecule associated with proteins and

–  much smaller than those of eukaryotes.

Prokaryotes reproduce by binary fission


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!  Binary fission of a prokaryote occurs in three stages:

1.  duplication of the circular DNA chromosome and separation of the copies to opposite sides of the cell

2.  continued elongation of the cell and movement of the copies, and

3.  division into two daughter cells by constriction; it separates the plasma membrane so each new cell has exactly the same genetic material.



Plasma membrane

Cell wall

Duplication of the chromosome and separation of the copies

Continued elongation of the cell and movement of the copies

Prokaryotic chromosome

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3 Division into two daughter cells

Salmonella bacterium undergoing binary

fission

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!  When conditions are favorable such as the right temperature and nutrients are available, some bacteria like Escherichia coli can divide every 20 minutes.

!  This means that in just 7 hours one (1) bacterium can generate 2,097,152 bacteria.

!  After one more hour the number of bacteria will have risen to a colossal 16,777,216. That’s why we can quickly become ill when pathogenic microbes invade our bodies.



!  Some eukaryotic cells, such as yeast, reproduce by budding

!  The buds grow into fully matured individuals which eventually break away from the parent organism.

Other asexual reproduction


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!  A few multi-cellular organism, such as sponges, Hydra ( a freshwater, sessile, jelly fish relative) and corals also create ‘off-spring” by a budding principle.

Other asexual reproduction


Hydra with bud

Brain coral with buds

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Cell division plays many important roles in the lives of organisms

!  The other mode of reproduction is called Sexual reproduction –  In this process the genes from two

(2) individuals are mixed.

–  produces offspring that are similar to the parents, but show variations in traits

–  involves inheritance of unique sets of combination of genes from two parents.

–  creates offspring with new set of “genetic cards” and new variations on a similar theme.


THE EUKARYOTIC CELL CYCLE AND MITOSIS


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!  Eukaryotic cells

–  are more complex and larger than prokaryotic cells,

–  have more genes, and

–  Whereas prokaryotes have one circular DNA, eukaryotes store most of their genes on multiple chromosomes within the membrane enclosed nucleus.

8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division


!  Eukaryotic chromosomes are composed of chromatin consisting of

–  one long DNA molecule and

–  proteins that help maintain the chromosome structure and control the activity of its genes.

–  When a cell is not dividing, the chromatin of every chromosome is very relaxed and almost invisible with a microscope.



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8.3 Chromosomes are composed of chromatin


In this uncoiled chromatin, the black arrows point at DNA wrapped around proteins (histones). The white arrow indicates segments of DNA without proteins



A schematic representation of the previous slide

DNA wrapped around histone proteins

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In this uncoiled chromatine, most of the proteins have been stripped away

!  To prepare for division, the chromatin of each chromosome becomes

–  highly compact, condensed and becomes visible with a microscope.



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!  Before a eukaryotic cell begins to divide, each chromosome is duplicated exactly, resulting in

–  two copies called sister chromatids

–  The sister chromatids are joined together by a narrowed “waist” called the centromere.

–  Since chromosomes are only “nice and visible” when they are condensed, they have already duplicated. The pictures of chromosomes thus are actually of sets of sister chromatids (duplicated chromosomes)





sister chromatids

Chromosomes duplicated right before division

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Highly visible chromatin (chromosomes) in a plant cell (African

blood lily) just before cell division (mitosis).

Visible chromatin of a bluebell plant cell (Endymion sp.) undergoing cell

division (mitosis).

Sister chromatids

Centromere

!  Thus if a cell has “n” chromosomes, they will become duplicated and the cell will have 2n sister chromatids.

!  Example : a cell has 10 chromosomes. When cell division starts, each become duplicated , resulting in 20 sister chromatids


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Sister chromatids

Centromere

!  When a cell divides, the sister chromatids !  separate from each other, now

called chromosomes, and are sorted into separate daughter cells.

!  This results in two daughter cells, each containing a complete and identical set of chromosomes

!  In the previous example, the sister chromatids become separated and sorted into 2 daughter cells we obtain 2 cells with new sets of 10 chromosomes


Figure 8.3B

Sister chromatids

Chromosomes

Centromere

Chromosome duplication

Sister chromatids

Chromosome distribution

to the daughter

cells

DNA molecules

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The Cellular Basis of Reproduction and Inheritancefaculty.collin.edu/cdoumen/1408/1408_Ch8_9/1408_Ch8A1.pdf · Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: