Chapter 4: Cell Reproduction
Aim: Why is cell division
important?
The Cell Cycle
Series of events that takes place from one
cell division to the next
 Length of time to complete a cell cycle is
different in all cells
 Most of the life of any eukaryotic cell is
spent in interphase-period of growth and
development
 Nerve and muscles cells are always in
interphase (no longer divide)

During interphase, hereditary material is
copied and the cell prepares for cell division
 Cell division begins after interphase
 Cells need to copy hereditary material
before dividing so the new cells have a
complete set of hereditary material to carry
out life functions

Aim: What is the process of
mitosis?
Mitosis
Process in which the nucleus divides to
form two identical nuclei
 New nuclei are identical to original nucleus
 Interphase:
◦ nucleus divides and chromosomes
duplicate forming chromatids-two
identical DNA strands

4 stages of mitosis:
Prophase:
◦ Chromatids fully visible
◦ Nucleolus and nuclear membrane
disintegrate
◦ Centrioles move to opposite ends of cell
(not in plants)
◦ Spindle fibers begin to form
2. Metaphase:
◦ Chromatids line up across the center of
the cell
◦ Centromere of each chromatids attaches
to spindle fibers from each side
1.
3. Anaphase:
◦
◦
Each centromere divides
Chromatids separate and move to opposite
ends of cell and become chromosomes
4. Telophase:
◦
◦
◦
◦
Spindle fibers disappear
Nucleus forms
Cytoplasm being divided
2 new cells form:
 Animal Cell-cell membrane pinches in middle
 Plant Cell- cell plate appears forming a new
cell wall
Results of Mitosis
Each new nucleus has the same number and
types of chromosomes as the original
 Humans:

◦ Every cell has 46 chromosomes-23 pairs, except
sex cells
◦ All the trillion of cells have the same hereditary
material
◦ Use DNA to become different types of cells
◦ Cell division allows growth and replaces
damaged or worn out cells
Aim: What is asexual
reproduction?
Asexual Reproduction



New organism is produced from one organism
New organism’s hereditary material is identical
to the parent’s hereditary material
3 forms of Asexual Reproduction
1. Cellular:
 Used by organisms with eukaryotic cells
 Ex: sweet potato growing in jar of water
(mitosis)
 Bacteria reproduce asexually by fission
 Can’t use mitosis because they don’t
have a nucleus
2. Budding
◦ Bud grows from the body of the parent
organism
◦ Made possible by mitosis
3. Regeneration
◦ Uses cell division (mitosis) to regrow
body parts
◦ Examples: sponges, sea stars
Aim: What is sexual
reproduction?
Sexual Reproduction
Two sex cells come together
 Formed from cells in reproductive organs
 Sperm-male
 Eggs-female
 Fertilization-joining of egg and sperm

◦ Forms a zygote

Following fertilization, cell division begins
Diploid Cells:
◦ Cells have pairs of similar chromosomes
◦ Human body cells-23 pairs, 46
chromosomes
◦ Skin, bones, tissues and organs form from
diploid cells
 Haploid Cells:
◦ Do not have pairs of chromosomes
◦ Sex cells
◦ Have only 23 chromosomes-one from
each of the 23 pairs

Aim: Why is meiosis needed for
sexual reproduction?
Meiosis
Produces hapliod sex cells
 After 2 haploid sex cells combine-a diploid
zygote forms
 Two divisions of the nucleus occur
◦ Meiosis 1
◦ Meiosis 2
 Results in four sex cells

Meiosis 1
 Chromosome is duplicated
 Prophase 1
 Each duplicated chromosome comes
near its similar duplicated
chromosome
 Metaphase 1
◦ Pairs of duplicated chromosomes line
up in center of cell
 Anaphase
1
◦ Each chromatid pair attaches to one
spindle fiber
◦ 2 pairs of chromatids move away to
opposite ends of cell
 Telophase
1
◦ Cytoplasm divides
◦ 2 new cells form
◦ Each new cell has one duplicated
chromosome from each similar pair
Meiosis 2
 Chromatids
of each cell will be
duplicated
 Prophase 2
◦ Duplicated chromosomes and spindle
fibers reappear
 Metaphase
2
◦ Duplicated chromosomes move to middle
of the cell
◦ Each centromere attaches to 2 spindle
fibers instead of 1
 Anaphase
2
◦ Chromatids separate and move to
opposite ends of the cell
◦ Chromatids now chromosomes
 Telophase
2
◦ Spindle fibers disappear
◦ Nuclear membrane forms around the
chromosomes
 After
meiosis 2 cytokenisis occurs-the
division of the cytoplasm
Aim: What are the parts of a
DNA molecule?
DNA
Deoxyribonucleic Acid
 Contains information for an organism’s
growth and function
 DNA code is copied when the cell divides
 1952- Rosalind Franklin discovered it is 2
chains of molecules in a spiral form
 1953 DNA model created by James Watson
& Francis Crick

Similar to a twisted ladder
 Each side of ladder is made up of sugarphosphate molecules
 Rungs of ladder-made of nitrogen bases
 4 kinds of nitrogen bases:

1.
2.
3.
4.
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Cytosine=Guanine
 Adenine=Thymine
 These bases occur as pairs

Aim: What is the function and
structure of RNA?
Genes
Most of your characteristics depend on the
kinds of proteins your cells make
 The instructions for making a specific
protein are found in your genes
 Are a section of DNA on a chromosome
 Determine the order of amino acids in a
protein
 Changing the order makes a different
protein
 Found in the nucleus

Proteins are made on ribosomes
 Codes for making proteins are carried from
the nucleus to the ribosomes by RNA
 RNA:
◦ Made in the nucleus on a DNA pattern
◦ 4 bases: adenine, guanine, cytosine and
uracil (U)
◦ Molecules contain the sugar ribose
◦ 3 types of RNA

mRNA:
1.
◦
◦
◦
Messenger RNA
Protein production begins when it moves into
the cytoplasm
Carries codes to make the amino acids bond
rRNA:
2.
◦
◦
Ribsosomal RNA
Ribosomes made of it
tRNA:
3.
◦
◦
◦
Transfer RNA
Bring amino acids to the ribosomes
Attach with the mRNA to make a protein
Aim: How do mutations occur?
Mutations
Happens when DNA is not copied
correctly
 Are any permanent change in the DNA
sequence of a gene or chromosome of a
cell
 X-rays, sunlight, and some chemicals may
cause mutations
 Examples:
◦ Having an extra chromosome
◦ Missing a chromosome

Without correctly coded proteins an
organism can not grow, repair or maintain
itself
 Can cause death
 Mutations in body cells may or may not be
life threatening
 Mutations in sex cells cause all the cells that
are formed to have the mutation
 Some mutations have no effect
 Some can be beneficial
