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CHAPTER 6: ”CELL REPRODUCTION”

Section 1: The Cell

Cycle

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TARGET GOALS… •  I CAN: •  --explain “why” cell

division is important. -----explain the steps

of the cell cycle.

How do little elephants grow up to be BIG elephants?

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You, elephants, and even oak trees share an important feature…

•  We are all made of cells. ..In fact, trillions of them!!

Why do you grow? •  Multicellular

organisms grow because cell division increases the number of cells in your body.

•  Even after growth, cell division is still important.

•  In fact, everyday, billions of red blood cells in your body wear out and are replaced by new cells.

•  By the time you read this sentence your bone marrow would have made 6 million new blood cells !

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Where do cells come from?

ü All cells are created from pre-existing cells

ü New cells are produced for growth and to replace damaged or old cells

•  (*Many organisms start off as just one cell. •  That cell divides and make two….then that cell divides to

make four..and so on !! All of the “division” takes place during a process called “mitosis”!)

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Mitosis begins after fertilization

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• Reproduction

• Growth

• Repair

Why do cells divide?

How does the cell know how to divide?

The DNA has the instructions for all of the cell’s activities.

add this to your notesguide!!!!

Is cell division the same in “all” living organisms???

ü Cell division differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)

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Cell Division in Prokaryotes ü  Prokaryotes such as

bacteria make new cells by dividing into 2 identical cells using a process called binary fission. This is where a single chromosome makes a copy of itself and a cell wall forms between the chromosomes forming 2 identical cells.

ü  This is a type of “Asexual Reproduction”.

11 2 identical daughter cells

Chromosome replicates

Cell splits

Cell division in Eukaryotic Cells

•  Eukaryotic cells are larger and more complex than prokaryotic cells.

•  This means they have a lot more DNA.

•  So, the cell must go through several steps to divide. These steps form the “cell cycle”.

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Cells are living things…. •  Just as every living

organism has a life cycle,

•  “ALL” living cells have a cell cycle.

•  In eukaryotes, cell division involves the nucleus of the cell..

1.  Interphase - Preparation

2.  Mitosis – Nuclear division

3.  Cytokinesis – Splitting

•  Adult human cell: ~24 hrs

•  18-20 hours in interphase

•  2 hours in mitosis

•  Embryonic cells: 30 min.

3 Parts

How long does it take?

The sequence of development and division of a cell

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3 Phases (stages) of the Cell Cycle

ü  interphase—(preparation) ü  mitosis---( nuclear division)

ü  cytokinesis—(splitting)

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Interphase

•  Involves the process of making copies of DNA “before” the cell can divide!!!!

•  Most of the life of eukaryotic cells is spent in this period of growth and development.

•  This is the longest stage!!!

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Add this illustration in the space provided on your notes guide…

Why is it important to copy genetic material?

The instructions for making cell parts are encoded in the DNA, It’s important to copy genetic material so each new cell must get a complete set of the DNA molecules

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DNA Replication

ü What has to happen “before” the cell can divide?

ü DNA must be copied or replicated

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Original DNA strand

Two new, identical DNA strands

Chromosomes in Dividing Cells

ü DNA is not the only thing that is replicated and copied.

ü Centrioles are also copied.

20 Called Sister Chromatids

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Eukaryotic Chromosomes ü All eukaryotic cells store genetic information in chromosomes

ü Most eukaryotes have between 10 and 50 chromosomes in their “body” cells

ü Human body cells have 46 chromosomes or 23 identical pairs

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How are the chromosomes arranged?

The chromosomes from a human cell are arranged in pairs by size

ü First 22 pairs are called homologous chromosomes (look the same).

ü Last pair are the “sex chromosomes”

ü XX female or XY male 22

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Boy or Girl?

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Y - Chromosome

X - Chromosome

The Y Chromosome Decides

Now the cell is ready to divide!!!

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Before we go any further… (Let’s review)

•  “Why” is it important for cells to divide? to make new cells, replace damaged and worn out cells •  What are the three steps of the cell cycle? •  interphase, mitosis, cytokinesis •  Which step is the “LONGEST” step? Why??? •  Interphase: this is where growth and

maturity takes place!!

A few more… (Let’s review)

•  “Name two things that have to be copied during interphase.

DNA & Centrioles must be copied!! •  The new chromosome that is duplicated is

called a sister _________________. Chromatid

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Target Goal…. “I CAN”….. _____ identify and

describe the four stages of

Mitosis.

Mitosis

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Mitosis ü Is the Division of the nucleus

ü Only occurs in eukaryotes

ü Has four stages ü Doesn’t occur in some cells such as brain cells

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Four Mitotic Stages…..(PMAT)

ü Prophase ü Metaphase ü Anaphase ü Telophase

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The Story of “Love”…

•  Prophase--- (dating)

•  Metaphase---(marriage)

•  Anaphase---(the “break-up”)

•  Telophase---(two rooms)

Prophase ü The Nuclear membrane breaks apart ü  and disappears. ü Chromosomes condense into rod-like

structures.

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Prophase

•  The two pair of centrioles move to opposites sides of the cell.

•  Fibers form between the two pair of centrioles and attach to the centromere.

•  Quick check: What is the centromere? And where is it located?

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Metaphase

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Homologous pairs of chromosomes align along the equator of the cell

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Anaphase ü Occurs rapidly ü Sister chromatids are pulled apart to opposite poles of the cell by the fibers attached to the centrioles.

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Telophase

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Nuclear membrane reappears and forms around each set of sister chromatids. Spindles disappears. .

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Final Phase : Cytokinesis (twins!!) ü Means division of the

cytoplasm ü The cell divides into

two, identical halves called daughter cells

ü  In plant cells, a cell plate forms at the equator to divide cell

ü  In animal cells, cleavage furrow forms to split cell

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Think about it….

•  Create a Nuemonic device to describe the four stages of “Mitosis”.

•  (ex: “Phillip Made A Truffle”)

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TARGET GOALS… •  I CAN: •  --explain the

difference between asexual and sexual reproduction.

Section two: “Reproduction”

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Why do Organisms Reproduce?... to Pass on their

Genetic Traits

Two types of Reproduction…

•  Sexual Reproduction

•  Asexual Reproduction

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From the largest to the smallest…

•  Larger animals such as Vertebrates (--animals with backbones) almost exclusively reproduce sexually.

•  Larger animals have more complex organ systems so they can adapt

•  and survive much better and more easier than smaller animals.

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Smaller or simpler animals… •  Reproduce

asexually. •  These include

animals such as •  Starfish and some

worms.

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Sexual Reproduction •  Sexual Reproduction •  Involves 2 parents •  Egg cell is

fertilized by sperm cell to make a fertilized egg known as a ZYGOTE

•  The offspring are DIFFERENT from parents.

•  (Ex: Meiosis)

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Asexual Reproduction •  Asexual

Reproduction •  Involves a single

organism or cell •  Cell divides •  Offspring are

exactly IDENTICAL to parent (ex: mitosis and binary fission)

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Looks the same to me…. •  In asexual

reproduction, you are making a genetic clone of yourself.

•  Asexual reproduction can occur by:

•  A) Fission (binary) •  B) Budding •  C) Fragmentation

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Fission….. •  Occurs when an

organism splits into two equal halves to make a genetic copy of itself.

•  Most bacteria undergo this process. It is also sometimes called “binary” fission.

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Other examples include… •  Amoeba and

Euglena.

•  Euglena is an odd one-celled member of the Kingdom Protista. . It uses it’s long tail to move through the water. 49

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Animation of Binary Fission

copyright cmassengale

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Budding…. •  Happens when a new

organism grows from the body of the parent organism.

•  Once the new organism is large enough, it simply breaks off.

•  Examples include yeast and hydra.

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Fragmentation…. •  Fragmentation (or

regeneration) is a form of asexual reproduction where a new organism grows from a fragment of the parent.

•  This occurs in some worms, sponges, and also in starfish.

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