Chapter 4

Notes Over Text

 Many organisms start as just one cell.  The number of cells in your body changes as you develop.  Your body is constantly changing; even after growth stops. 

Red blood cells are produced at a rate of 2 to 3 million per second.

Cells go through ____________ as they live.  The time it takes to complete a cell cycle depends on the type of cell.  It may be 20 minutes or 19 hours.

Most of a cell’s life is spent in ____________ which is a state of rapid growth, DNA synthesis, and division prep.  Cells that no longer divide are always in interphase.  The ____________ and muscle cells in one’s body are examples of these.

____________ – is the process in which the nucleus divides to form two identical nuclei with the same number and type of chromosomes as the original.  The steps of mitosis are ____________ , ____________ , ____________ , and ____________ .

____________ – are structures in the nucleus that contain DNA.  You can only see these when the cell is dividing.

____________ – are tightly coiled thickened, identical strands of chromosomes.

____________ – is a region that holds together double stranded chromosomes.  It is the center of the X.

MITOSIS
	1.     ____________ – rapid growth, DNA synthesis, and division prep.
	2.     ____________ – chromosomes are now visible, the nuclear membrane is gone, and centrioles move to opposite ends of cell, and spindles begin to stretch across the cell.
	3.     ____________ – double stranded chromosomes line up across the center of the cell and centromeres become attached to a spindle fiber.
	4.     ____________ – centromeres divides, chromosomes separate and begin moving toward opposite ends of the cell.
	5.     ____________ – centrioles and spindle fibers disappear.  Chromosomes stretch out and are harder to see.  Nuclear membrane forms around mass of chromosomes and a new nucleolus appears in each new nucleus.

After the nucleus divides, the cell’s cytoplasm separates and two cells are formed by pinching in the cell membrane.  Interphase begins again with rapid growth in both new cells.

Within a plant cell the cell wall cannot pinch in.  Thus a new ____________  is formed which becomes the cell wall between the two new cells. 

The result of mitosis is ____________ identical ____________ that are exactly like the mother cell.

____________ is the process by which an organism produces others of its same kind.  There are two types – ____________ and ____________ (remember that a or an on the front of a science word means without)

·        ____________ reproduction – is the production of new offspring from one parent.

o       ____________ – is the division of an organism whose cells do not contain a nucleus copies its genetic material and then divides into two identical organisms.

o       ____________ – occurs when a new organism grows from the body of the parent organism.  When the bud can live on its own, it ‘pops’ off.

o       ____________ – a whole organism may develop from just a piece of the parent organism.  Some organisms replace missing or damaged parts while others can produce an entire organism.

·        ____________ Reproduction – is the making of a new organism from the uniting of two sex cells which are called gametes. 

o       ____________ – sex cell from male.

o       ____________ – sex cell from female.

o       ____________ – is the uniting of egg and sperm. 

o       ____________ – The single cell that forms is called a zygote.

Sex cells have only half of the chromosomes so when 2 are united the total is the same as body cells.  The production of sex cells is called Meiosis.

Cells that have pairs of similar chromosomes are called ____________ .

Cells that have only half of the chromosomes (1 of each) are called ____________ .  Sex cells must be haploid.

____________ is the production of haploid sex cells.  Two divisions of the nucleus occur during meiosis – ____________ and ____________ .

Phases of meiosis:

1.     ____________  – chromosomes are double and spindle fibers appear.  Nucleus membrane is dissolved.  Each duplicated chromosome comes near its similar duplicated mate.

2.     ____________  – the chromosomes line up in the middle and centromeres become attached to spindle fibers.

3.     ____________  – chromosomes separate and are pulled to opposite ends of the cell.

4.     ____________  – cytoplasm divides and two cells form.

5.     ____________  – chromosomes and spindles reappear.

6.     ____________  – chromosomes line up in the middle and attach to spindles.  Each centromere now attaches to two spindle fibers instead of one.

7.     ____________  – centromere divides, chromatids separate and move to ends of cell.

8.     ____________  – spindles disappear, nuclear membrane forms and cytoplasm divides.

The result of meiosis is ____________ cells each with half the number of chromosomes as the parent cell (haploid).

____________  are mistakes or changes in DNA of an organism.  Mistakes during these divisions do occur.  In plants mistakes are common; in animals mistakes are rare.  In zygotes produced from sex cells with mistakes death may occur or the zygote may not grow normally. 

____________  – deoxyribonucleic acid – is the master copy of an organism’s information.  It controls the cells activities with coded information.  Every body cell contains the body’s entire set of codes.

In 1952, ____________   discovered that DNA was a double spiral form by using x-rays. 

In 1953, ____________   and ____________   made a model of the DNA molecule.

This model is still used today.  It shows a ____________   shape (which looks like a ladder that is twisted). 

·        The sides are made of ____________  (deoxyribose) and ____________  molecules.

·        The Stairs are made of ____________ . 

o       ____________  , ____________  , ____________  , and ____________   are the bases.

o       ____________  always pairs with ____________  

o       ____________   always pairs with ____________  

DNA copies itself by unwinding, ‘unzipping’ the molecule using an enzyme, attaching new bases and finally new sugar and phosphate groups.

____________  – are parts of the DNA molecule that directs the making of a specific protein.  The entire organism’s traits are controlled by the production of certain proteins.  Proteins are made of chains of hundreds or thousands of ____________   in a specific order.  Genes are sometimes turned on or off.

Genes are found in the nucleus, but proteins are made on ribosomes.  The codes are carried there by the ____________  – ribonucleic acid.

RNA is different from DNA because it is only single stranded, it contains ____________  instead of thymine, and it contains ribose sugar instead of deoxyribose sugar.

There are three types of RNA

1.    ____________  RNA (mRNA) carries the information to the ribosome. 

2.     ____________  RNA (rRNA) makes up the ribosome.

3.     ____________  RNA (tRNA) is in the cytoplasm and picks up the appropriate amino acid to attach together to form the protein. 

 ____________  do occur during cell reproduction.  This is a permanent change in a gene or chromosome of a cell.  These mutations may be caused by factors such as X rays, sunlight, and chemicals.

If the mutation occurs in a body cell, it may or may not be life threatening.  Some mutations are harmless or even beneficial.  If it occurs in a sex cell, the organism may not survive because all cells of the organism will have the mutation.

Mutations may add variety to a species – which is the basis of evolution.