Cell Growth and
Reproduction
(BIO.B.1)
DNA
DEOXYRIBONUCLEIC ACID
DNA STRUCTURE
• The chemical components of
DNA are:
–sugar (deoxyribose)
–phosphate groups
–Four different nitrogen
containing bases
THE FOUR BASES ARE:
1. Adenine
2. Guanine
3. Thymine
4. Cytosine
• Nucleotide - made up of a
sugar, a base, and a
phosphate group.
• DNA is like a twisted
ladder and is called a
double helix.
• The uprights of the ladder
are made of the sugar and
phosphate of the
nucleotides.
• The rungs are two nitrogen
bases held together by
hydrogen bonds.
THE DNA LADDER
Uprights = sugars and phosphates
Each rung = 2 bases connected by H bonds
COMPLIMENTARY BASES
• Adenine binds with Thymine.
• Guanine binds with Cytosine.
Figure 16.5 The double helix
DNA
• Chromosome – a long strand of DNA
– One chromosome (one strand of
DNA) has thousands of genes and
millions of base pairs
– Humans have 46 chromosomes and
have an estimated 23,000 - 25,000
genes
• Gene – a section of DNA that gives
instructions for a protein to be made; the
protein controls a trait
• Genome – a sum of all of an organism’s
genes
• Genetic code - the order of the bases
– Different order = different genes
– Different order = different people and
even different species.
• Allele – the form that a gene takes (ex.
some are dominant or recessive)
DNA Replicates
• DNA can make copies of itself
(replicate).
• Why does DNA need to be able to copy
itself?
– DNA replicates so when cells divide
to make new cells, the new cells have
the same DNA as the original cell
REPLICATION OF DNA
• Replication begins with DNA
Polymerase (an enzyme)
binding to a part of DNA.
• DNA polymerase breaks
Hydrogen bonds between
base pairs (unzips the DNA).
• The enzyme then adds
complementary nucleotides
to each new strand.
• Each new DNA molecule
consists of one original chain
and one new chain.
• Proof-reader enzymes - proofread the new chains and check
for mistakes (these include
DNA polymerase).
CELL DIVISION
Types of Cell Division
• Mitosis – makes new somatic (body)
cells in eukaryotes
• Meiosis – makes new gametes (sex
cells) in eukaryotes
WHY DIVIDE?
• Why do multicellular organisms do mitosis?
– To repair or heal
– To grow and develop
– To replace cells that die
• Why do unicellular organisms do mitosis
(eukaryotes)?
– To reproduce asexually (cloning)
• Why do multicellular organisms for meiosis?
– To reproduce sexually
Important part of Cell Division
• Nucleus - contains genetic information (DNA)
• Chromosomes – strands of DNA
• When a cell divides, the new cells made must
have the correct number and kind of
chromosomes.
• Most of the time, DNA looks like a lump of
spaghetti, and is called chromatin.
Cell Cycle
Cell Cycle
• Interphase
– G0 – cell at rest; is not preparing for
division
– G1 – cell gets ready for division
– S – chromosomes copy themselves
– G2 – cell checks for mistakes and
prepares for division
• Mitosis – the process of nuclear division
• Cytokinesis – the division of the cells
cytoplasm
• Most of the time cells are not
dividing.
• Several proteins are involved in
starting division.
• Some cells can divide in as little
as 20 minutes.
• Cells typically stop dividing
when:
– Nutrient levels drop (no
food)
–They come into contact
with other cells (no room)
–Receive chemical signals
to stop.
INTERPHASE
• Cells spend most of their life in
interphase.
• Normal cell activities occur.
• To prepare for cell division, the
chromosomes make copies of
themselves.
• In other words, the DNA replicates.
• Recall, DNA polymerase… etc.
MITOSIS: NUCLEAR DIVISION
FOR EUKARYOTES
Four Stages
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Cells Alive Animation
John Kyrk Animation
McGraw Animation
PROPHASE
• Chromatin condenses and
becomes visible as
chromosomes.
• The nucleus and its various
parts disappear.
• Spindle fibers are made and
attach to the chromosomes.
• Centrioles separate and
move to opposite ends (poles)
of the cell.
• Each copy of the chromosome
is called a chromatid.
Chromosome
chromatids
centromere
METAPHASE
• The chromosomes line up
at the middle of the cell
(equator).
ANAPHASE
• The joined chromatids separate
and move to opposite ends of the
cell.
TELOPHASE
• The chromatids arrive at the opposite
poles of the cell.
• Spindle fibers disappear.
• New nuclei form in the two new
cells.
• Cytokinesis - pinching in of plasma
membrane (formation of cleavage) in
order to form two new cells
END RESULTS OF MITOSIS
• Two new “daughter” cells are made
with each containing the same
number and kinds of chromosomes
as the original (parent) cell.
• They have the same genetic code.
A Little Info on Cancer
CANCER
• Caused by uncontrollable mitosis.
• Cells either fail to stop dividing or get signals to
continue dividing.
• An increased number of cells makes a tumor.
• Tumors can be benign (non-cancerous) or
malignant (cancerous).
• Cancer cells spread (metastasis) throughout
body, unlike normal cells!
Some Causes of Cancer
•
•
•
•
•
Genetics
Radiation
Carcinogens (mutate DNA)
Old Age
Viruses
– Can mutate DNA causing some cancers
– Example: Human papillomavirus (HPV)
associated with cervical cancer in women
• Poor diets
MEIOSIS:
Making sex cells
CHROMOSOME NUMBER
• The number of chromosomes
varies from one kind of
organism to another.
• Humans have 46 chromosomes
& fruit flies have 8.
• Some plants have hundreds.
• Karyotype – a picture of
chromosomes that shows the
number and the size of
chromosomes that a cell has
• Amniocentesis and Chorionic
Villi Sampling– tests done on
pregnant women in order to
look at the chromosomes of the
developing baby
• Chromosomes of animal cells
are usually paired. WHY?
• Humans have 23 pairs, fruit
flies have 4 pairs.
• Haploid - the # of pairs or n
• Diploid - the total number of
chromosomes or 2n
• For humans: n=23 and 2n=46
SEXUAL REPRODUCTION
• Fertilization - the combination of
chromosomes (genetic information)
from two sex cells (combining
sperm and egg)
• Each sex cell gives half of the total
chromosomes.
• Sex cells are also called
gametes.
–Female sex cell = egg or
ovum
–Male sex cell = sperm
• Gametes are haploid (half
the chromosomes).
Gamete Production
• Gametes are produced in gonads.
• Eggs are made in ovaries.
– Females begin making their eggs
before they are born!
– They stop making eggs during
menopause.
• Sperm are made in testes.
– Males make sperm from
approximately puberty until death.
• After fertilization, the developing
organism is called a zygote and
is diploid.
• After fertilization the zygote
grows bigger by doing
MITOSIS.
• A zygote becomes an embryo
and later a fetus.
MEIOSIS END RESULT
• Meiosis makes 4 haploid, sex cells.
• These 4 cells are sex cells (sperm
and egg).
• Each cell has half the number of
chromosomes as the parent cell
(haploid).
• Meiosis increases genetic diversity
in the offspring.