Limited Time Offer: Get 2 Months of ABCmouse.com for only $5!

Chapter 3 Notes (cont.) (10/28/08)

III.  Gene Action

1.  Protein Synthesis

           maintains homostasis

           form plasma membrane microfilaments, microtubules, centrioles, flagella, cilia, and mitotic spindle

           hormones, antibodies, and contractile elements

           enzymes

           determine physical and chemical characteristics

           instructions are found in the DNA

           DNA à RNA à Proteins

Two principle steps; transcription and translation

A.     Transcription = DNA is copied by a strand of RNA

a.       Made up of Nitrogen bases: Adenine, Guanine, Cytosine, Thyamine

b.      RNA – uses Uracil instead of Thyamine

c.       Introns = do not code for proteins (Start and Stop codons)

d.      Exons = Code for proteins (all other codons for a.a.)

e.       See drawing from class for DNA and RNA strands

  

B.     Translation – there are 20 different amino acids that are available for the making of proteins, and since there is no set number of a.a. that can make up a certain protein then there is an infinite number of possible combinations available.

 

IV.              Cell Division

·        There are two types of cell division (division of the nucleus) Mitosis and Meiosis.

·        Mitosis – Somatic cell division

·        Meiosis – sex cell division

·        In 24 hours the body loses billions of cells        

·        Somatic Cell division consists of Mitosis where the parent cell divides into two diploid daughter cells (identical)

Reproductive cell division consists of Meiosis where the parent cell divides on two separate occasions in order to produce 4 haploid cells (containing only half as many chromosomes as the parent cell.)

·        Humans have about 100,000 functional genes, only a fraction are functional @ any one given time.

A.  Somatic Cell Division – is made up of a series of stages that make up the process of     mitosis.  They are described in detail as follows:

1.   Interphase – (resting stage)

·        centrosomes replicate

·        organelles replicate

·        DNA replicates (as chromatin)

·        estimated that each cell contains 3 billion nitrogen bases

·        process pretty accurate, but can make mistakes called mutation: some are beneficial and some harmful

2.   Mitosis – is divided into 4 stages

a.   Prophase –

·        chromatin coils up

·        nucleolus starts to disappear

·        nuclear membrane breaks down

·        chromatin coils up until chromosomes and shows visible chromatids

·        centrosomes replicate and start migrating toward opposite poles

·        See diagram from class à

b.      Metaphase –

·        centromeres line up on the equator

·        centrosomes reach poles

·        spindle fibers attach to centromere

·        See diagram from class à

c.       Anaphase –

·        chromatids finish replicating

·        chromatids now called chromosomes

·        chromosomes begine migrating toward opposite poles

·        See diagram from class à

d.      Telophase –

·        identical chromosomes reach poles

·        new nuclear membrane starts to form around each set of chromosomes

·        chromosomes uncoil to chromatin

·        nucleolus reappears

·        spindle fibers break down

·        microtubules wrap around equator, pinches cell into two.

·        See diagram from class à

 

C.     Reproductive Cell Division – is made up of series of stages that requires the cell to go through two different nuclear divisions in order to produce 4 haploid cells.  This keeps the cells from consistently increasing the number of possible chromosomes available in each of the cells.  This type of cell division is called Meiosis.

     New cells produced by the union of 2 different sex cells (gametes) from each parent

     Ovum (egg) produced in female gonads (ovaries)   

     Sperm produced in male gonads (testes)

     This union is called fertilization and the result is called a Zygote.

     Cell division differs in the # of chromosomes;

Somatic cells = have 46 chromosomes (diploid – 2n)

Sex cells = 23 chromosomes (haploid – 1n)

     the formation of sperm cells is called – spermatogenesis

     the formation of egg cells is called – oogenesis

     Meiosis occurs in 2 mitotic divisions: a reduction division (meiosis I) and a equatorial division (meiosis II)

1.  Interphase – is the same as that of mitosis (resting stage)

2.  Meiosis I – the first of two divisions of the nucleus into 2 cells

a.  Prophase I –

     DNA coils up

     nuclear membrane disappears

     nucleolus disappears

     centrosomes migrate to poles

     centrioles start to make spindle fibers

     chromosomes find their homologous pairs (at this point crossing over of the sister chromatids can occur.

     see diagrams from class à ?

 

b.  Metaphase I –

     homologous pair line up on equator

     spindle fibers attach to centromeres

     centrosomes arrive at the poles

     See diagram from class à ?

 

c.  Anaphase I –

     synapse dissolves

     dyads migrate to poles

     See diagram from class à ?

 

d.  Telophase –

     usually non-exsistant

     cytokinesis splits cell

     nuclear membrane does not reappear

     See diagram from class à ?

 

3.  Meiosis II – the second of two divisions of the nucleus into 2 cells (keep in mind that each one of these stages is occurring simultaneously in both cells.)

a.  Prophase II –

     no coiling of DNA is required

     no dissolving of the nuclear membrane is needed

     centrosomes replicate and migrate to the poles of each cell.

     centrioles produce spindle fibers and start extending towards the centromeres

     See diagram from class à ?

 

b.  Metaphase II –

     dyad line up on the equator

     centrioles arrive at the poles

     spindle fibers attach to centromere

     see diagram from class à ?

 

c.  Anaphase II –

     sister chromatids finish replicating

     chromatids are now called chromosomes again

     spindle fibers begin to shorten and pull the chromosomes to opposite poles

     See diagram from class à ?

 

d.  Telophase II –

     chromosomes arrive @ poles

     cytokinesis begins to divid each cell resulting in 4 haploid cells

     nuclear membrane reappears around each set of chromosomes in each of the cells

     nucleolus begins to reappear

     spindle fibers dissolve into cytoplasm

     See diagram from class à ?

Get 2 Months for $5!