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DEOXYRIBONUCLEIC ACID
& CELL REPRODUCTION
CHAPTER 10-1, CHAPTER 8
(PG 184-189; PG 144 - 156)
UNIT 6: LECTURE 1
Topics:
•  DNA Structure
•  Covers information from:
•  Chapter 10-1 (pgs 185 – 187)
WHAT IS DNA?
• 
DNA - Deoxyribonucleic Acid
• 
EVERY living organism has its own unique DNA
• 
DNA stores all genetic (hereditary) information
•  DNA is known as the “blueprint” for an organism, it tells the
body what it will look like
•  Each gene codes for a different trait or appearance
•  Each gene is a code for a protein
•  Each strand of DNA (chromosome) contains hundreds of
genes!
WHAT IS DNA?
Structure
•  DNA structure was discovered in 1953 by
James Watson and Francis Crick
•  Took X-ray pictures of DNA molecule
•  Used photography technique developed by
another scientist, Rosalind Franklin
•  The shape of DNA was described as a
“double helix”
•  Each DNA molecule is made up of two long strands of
molecules known as NUCLEOTIDES
•  There are four types of nucleotides in DNA
•  T = Thymine  
•  C = Cytosine
A = Adenine
G = Guanine
WHAT IS DNA?
•  Each DNA nucleotide is made up of three parts:
•  A sugar molecule (DEOXYRIBOSE)
•  A phosphate group
•  A nitrogen containing base
WHAT IS DNA?
•  The sugar and phosphate are identical in each DNA nucleotide
•  The shape and structure of the nitrogen base is what makes
each nucleotide different
•  Thymine and Cytosine have a single ring structure
•  PYRIMIDINE– single ring nitrogen base
•  Adenine and Guanine have a double ring structure
•  PURINE– double ringed nitrogen base
WHAT IS DNA?
•  To connect the two strands, two nucleotides
attach, or pair, together
•  Adenine always pairs with Thymine
•  A pairs with T
•  Guanine always pairs with Cytosine
•  G pairs with C
•  Purines can only pair with
pyrimidines because of the shape
of the nitrogen base
•  When two DNA nucleotides pair
together, they are called
COMPLEMENTARY BASE PAIRS
•  Held together by hydrogen bonds
WHAT DOES A MOLECULE
OF DNA LOOK LIKE?
•  Each DNA molecule is made up of two long strands of nucleotides
•  The two strands are parallel & are connected by the pairing of the
complementary base pairs
•  The shape of DNA is described as a “double helix” or a twisted
ladder
Parts of a DNA molecule
A.  Phosphate & Sugar backbone
B. Nitrogen base
(center of helix, "rungs” of the ladder)
•  The nitrogen bases from the 2 strands
are attached by Hydrogen bonds
END OF LECTURE 1
UNIT 6: LECTURE 2
Topics:
•  DNA Replication
•  Mutations
•  Covers information from:
•  Chapter 10-1 (pgs 188 – 189)
CELL DIVISION
•  Remember The Cell Theory:
•  All cells come from the division of pre-existing cells.
•  CELL DIVISION - process where a cell splits to produce a new cell
•  Before a cell divides, all the genetic material (DNA) must be copied.
•  This will allow for both cells (2 after cell splits) to have a complete
copy of the genetic material.
HOW DOES DNA
REPLICATE?
•  DNA REPLICATION - when a strand of DNA copies
itself
1.  The two parallel strands are pulled apart. The
bonded complementary base pairs separate.
• 
Two sides of DNA are separated by
enzymes called HELICASES
2.  Helicase enzyme moves along DNA, breaking
hydrogen bonds between base pairs
(separates left & right strands)
HOW DOES DNA
REPLICATE?
3.  DNA POLYMERASE (another enzyme) bonds to
each separated strand and makes a new
complementary strand of DNA for each side.
4.  New hydrogen bonds form between base pairs
5. Two new exact copies of the original DNA
molecule are produced
•  Each new DNA molecule has
•  1 old strand and
•  1 newly copied strand
CAN THE ENZYMES
MAKE MISTAKES?
•  YES! Known as a MUTATION
•  Mutations can be caused if:
•  The order of nucleotides changes, wrong nucleotides paired
together, or certain sections of DNA were deleted or repeated
•  Our cells have a proofreading and repair process to fix mutations.
Most of the mutations are fixed, but some are overlooked.
•  About 1 in every 1 billion nucleotides is a mutation
•  If a mutation changes the order of nucleotides in a gene, which
can change the appearance of that trait.
•  Mutations can happen:
•  When DNA is making a copy of itself.
•  When a gene in DNA is being used to make a protein
•  If you are exposed to harmful chemicals and/or UV rays
CAN THE ENZYMES
MAKE MISTAKES?
•  Mutations can have the following affect on the organism:
•  Negative – some mutations are very bad and can even be fatal
•  Positive – some mutations can actually be helpful
•  Neutral – some mutations don’t affect the organism at all
•  Some of the most common types of mutations are:
•  Substitution is when one nucleotide is changed to another;
•  Example: Car à Cat
•  Addition is when one nucleotide is added in the sequence
•  Example: Car à Care
•  Deletion is when one or more nucleotides are removed from
the sequence;
•  Example 1: Car à Cr; Example 2: Automobile à Auto
END OF LECTURE 2
UNIT 6: LECTURE 3
Topics:
•  Introduction to Cell Division
•  Binary Fission
•  Cell Cycle – Interphase
•  Covers information from:
•  Chapter 8-2 (pgs 148 – 149)
HOW DO
CELLS DIVIDE?
•  Cell division is just one small part of the cell cycle
•  For the majority of the cell’s life, it is doing normal cellular
activities.
•  Cell division makes up about 10% - 20% of the cell cycle
•  Prokaryotic Cell Division – Binary Fission
•  Eukaryotic Cell Division – Mitosis or Meiosis
•  Mitosis
•  How unicellular organisms replicate (asexual reproduction)
•  How multicellular organisms add more cells to their body
•  Meiosis
•  Produces reproductive cells
HOW DO
CELLS DIVIDE?
Binary Fission
•  Prokaryotic cell division
•  Remember: Prokaryotic cells do not have a nucleus or
membrane bound organelles ex: bacteria
•  3 Step Process:
1.  DNA is copied
2.  Cell grows to two times its original size
3.  Cell splits in two
•  This process happens very quickly
•  Type of asexual reproduction
•  Produces two identical organisms, No genetic diversity
BINARY FISSION
E. coli going through binary fission
HOW DO
CELLS DIVIDE?
EUKARYOTIC CELL DIVISION
•  Remember: Eukaryotic cells have a nucleus and membranebound organelles; ex: animal, plant, fungus, protist
•  Eukaryotic cell division is more complicated and a more involved
process than prokaryotic cell division
Eukaryotic Cell Cycle - 2 PARTS
 1.  INTERPHASE
•  Makes up 80% - 90% of a cell’s life, Time between cell division
•  Cell is doing normal cellular activities and preparing to divide
•  Stages in Interphase: G1 , S PHASE, G2
 2.  DIVISION:  M PHASE (Mitosis or Meiosis), CYTOKINESIS
* After cytokinesis, the cells begin G1 again
CELL CYCLE
(PG 149)
HOW DO
CELLS DIVIDE?
INTERPHASE
1.  G1 PHASE - GAP 1
•  First time gap, cell grows to mature size, does normal cellular
activities
2.  S PHASE – DNA SYNTHESIS
•  DNA replicates
3.  G2 PHASE - GAP 2
•  Second time gap, cell grows and gets ready to divide
•  If the cell is not ready to continue, it wont pass these steps
•  It will take a break and go into a phase of the cycle known as G0
•  A cell can stay in G0 for days, months, even years!
HOW DO
CELLS DIVIDE?
DIVISION
 1. “M PHASE” (MITOSIS or MEIOSIS)
•  Has 4 steps: Prophase, Metaphase, Anaphase, Telophase
 2. CYTOKINESIS
END OF LECTURE 3
UNIT 6: LECTURE 4
Topics:
•  Cell Division
•  Mitosis
•  Meiosis
•  Covers information from:
•  Chapter 8-1 (pgs 145 – 146)
•  Chapter 8-2 (pgs 150 – 151)
•  Chapter 8-3 (pgs 153 – 156)
UNIT 6: LECTURE 4
DIVISION
 1. “M PHASE” (MITOSIS or MEIOSIS)
•  Mitosis – Division of the nucleus
•  Has 4 steps: Prophase, Metaphase, Anaphase, Telophase
 2. CYTOKINESIS
•  Cytokinesis – Division of the cytoplasm
STAGES OF
DIVISION
STAGES OF
DIVISION (M PHASE)
A. PROPHASE
•  DNA wraps around Histones to become more condensed and
organized, now known as a Chromosome
•  HISTONE– structural protein
•  CHROMOSOME– condensed, organized strand of DNA
• 
Remember: DNA just replicated, so there are 2 copies of every strand of DNA
•  The identical copies are held together by a CENTROMERE
•  Each half is called a CHROMATID
•  Both halves together are called SISTER CHROMATIDS and
looks like an “X”
•  Nucleolus and nuclear membrane (envelope) break down  
•  Two CENTROSOMES appear and move to opposite ends of the cell
•  Centrosomes separate and begin to make specialized microtubules
known as SPINDLE FIBERS
DNA strand wraped around histone
DNA strand wraped around histone
DNA strand wraped around histone
Chromatids held together by centromere
Chromatids held together by centromere
Chromatids
held together
centromere
DNA
strand wraped
around by
histone
Chromatids held together by centromere
STAGES OF
DIVISION (M PHASE)
B. METAPHASE
•  Chromosomes (Sister Chromatids) line up in the middle of the cell
•  Spindle fibers attach to each side of the centromere on the sister
chromatids
C. ANAPAHSE
•  Spindle fibers shorten and break the centromere in half  
•  Sister chromatids separated and each half is pulled to an opposite
end of the cell
D. TELOPHASE
•  Spindle fibers break down
•  Nuclear membrane (envelope) reforms around both groups of
chromosomes
•  Cell gets ready to split
STAGES OF
DIVISION
2. CYTOKINESIS
•  CYTOKINESIS - dividing of the cytoplasm
•  Steps:
•  Cell membrane pinches inward
•  Cytoplasm divides
•  Cell pinches into 2 cells
•  Two identical cells are formed
•  In humans, produce body cells (SOMATIC CELLS)
•  Each somatic cell has 46 chromosomes
*PLANTS - cell wall can't pinch in, so plants form a CELL PLATE
•  New cell wall forms in the middle of the cell
Cytokinesis in
an animal cell
Cytokinesis in
a plant cell
MEIOSIS
•  Produces GAMETES
•  Gamete – Reproductive cell, aka Haploid
•  Cell divides twice
•  Results in 4 new cells
•  In humans, each gamete has 23 chromosomes
•  Meiosis I - 1st division
•  Meiosis II - 2nd division
•  Separates sister chromatids
FORMATION OF
GAMETES
•  Males produce four gametes of equal size
•  Known as SPERMATOGENESIS
•  Females produce one large gamete, and three nonfunctional gametes (Polar Bodies)
•  Divides cytoplasm unequally
•  Known as OOGENESIS
END OF LECTURE 4