Cell Reproduction
Cell Division
• Increases the number
of cells and causes
many-celled organisms
to grow
• Cell cycle- series of
events that take place
from one cell division to
the next
Interphase
• Most of the life of a eukaryotic cell, or cell
with a nucleus, is spent in this period of
growth and development
– During interphase, a cell duplicates its
chromosomes and prepares for cell division
– After interphase, the nucleus divides, and then
the cytoplasm separates to form two new cells
• Muscle and nerve cells no longer divide so
they are always in interphase
Chromosomes
• Chromosome- structure in the nucleus that
contains hereditary material
Mitosis
• Process in which the nucleus divides to form
two identical nuclei
Prophase
• Nucleolus and nuclear membrane disintegrate
• Centrioles move to the opposite ends of the
cell
• Spindle fibers begin to stretch across the cell
Metaphase
• Pairs of chromatids line up across center of
cell
Anaphase
• Each centromere divides
• Each pair of chromatids separates and moves
to opposite ends of the cell
Telophase
• Spindle fibers disappear and a new nucleus
forms
Cytokinesis
• For most cells, the cytoplasm separates after
the nucleus divides
– In animal cells, the cell membrane pinches in the
middle and the cell membrane divides
– In plant cells, a cell plate forms
Results
• Each cell in your body,
except for sex cells, has
a nucleus with 46
chromosomes
– People with conditions
such as Down Syndrome,
have extra or less
chromosomes.
• Allows growth and
replaces worn out or
damaged cells
Asexual Reproduction
• A new organism is
produced from one
parent organism
– An organism with no
nucleus divides into two
identical organisms by
fission
– Budding a small exact
copy of the adult grows
from the body of the
parent
– Regeneration a whole
new organism grows from
a piece of the parent
Sexual Reproduction
• Two sex cells, called the
sperm and egg, come
together
– Sperm formed in male
reproductive organs
– Egg formed in female
reproductive organs
• Fertilization the joining
of the sperm and egg
– The new cell that forms
after fertilization is called
the zygote.
Cells
• Your body forms 2 types of cells
– Diploid cells that have 23 pairs of
chromosomes. Includes brain, skin, bone cells.
– Haploid only 23 individual chromosomes, NOT
PAIRS. These are the sperm and egg cells.
Meiosis
• Process that produces haploid cells.
• Insures that offspring will have same total
amount of chromosomes as parent because
after two haploid cells combine, a diploid
zygote is produced
• During meiosis, two nucleus divisions occur
– Meiosis I
– Meiosis II
Interphase
• Before meiosis starts, each chromosome is
duplicated (just like in mitosis)
Prophase I
• Nucleolus and nuclear
membrane disintegrate
• Centrioles move to the
opposite ends of the
cell
• Spindle fibers begin to
stretch across the cell
• Each duplicated
chromosome comes
near its duplicate
Metaphase I
• Pairs of duplicated
chromosomes line up in
center of cell
• The centromere of each
chromatid pair attaches
to a spindle fiber
Anaphase I
• Two pairs of chromatids
of each similar pair
move away from each
other to opposite ends
of the cell.
• Each duplicated
chromosome still has
two chromatids.
Telophase I
• Cytoplasm divides and two new cells form
• Each new cell has one duplicated chromosome
from each similar pair
Prophase II
• The duplicated chromosomes and spindle
fibers reappear in each cell
Metaphase II
• Duplicated
chromosomes move to
the center of the cell
• Each centromere
attached to two spindle
fibers instead of one
Anaphase II
• Centromere divides
• Chromatids separate and move to opposite
sides of the cell
• Each chromatid is individual chromosome
Telophase II
• Spindle fibers disappear.
• New nuclear membrane forms around each
set of chromosomes at each end of the cell
Meiosis
• At the end of meiosis II, the cytoplasm divides.
• SUMMARY
– Two cells form during meiosis I
– Those two cells form two new cells in meiosis II
– Results in FOUR SEX CELLS, each with one half the
number of chromosomes in its nucleus as in the
original nucleus
Let’s Review Meiosis!
DNA
• Deoxyribonucleic acid (a
chemical)
• Contains information for
organism’s growth and
function
• When a cell divides, DNA
code is copied and passed
to new cell
• Watson and Crick made
accurate model of DNA in
1953
DNA Structure
• Similar to twisted ladder
• Sides of ladder are made up of
sugar-phosphate molecules
• The rungs of ladder made of
nitrogen bases
– Adenine and Thymine are base
pairs
– Guanine and Cytosine are base
pairs
• Before cell divides, DNA
duplicates itself by unwinding
and separating its sides, then
each side becomes a pattern
on which new side forms
Genes and RNA
• Genes sections of DNA on a chromosome
• RNA carries the codes for making proteins
from the nucleus to the ribosomes in the
cytoplasm
– Messenger RNA carries the code that directs the
order in which amino acids bond
– Ribosomal RNA makes up ribosomes, where
proteins are built
– Transfer RNA brings amino acids to the ribosomes
to build proteins
Codons
• Every 3 base pairs (such
as UGA) on the
messenger RNA are a
CODON
• Each codon represents
a specific amino acid
• The ribosome reads the
messenger RNA by each
codon, then adds the
correct amino acid to
the protein chain
RNA
RNA
• DNA vs. RNA
• DNA to RNA to Proteins
Mutations
• Any permanent change
in the DNA sequence of
a cell’s genes or
chromosome
– Can be caused by
outside factors like X
rays, sunlight, and
chemicals
– A change in the gene or
chromosome can change
traits of the organism