DEOXYRIBONUCLEIC ACID & CELL REPRODUCTIONCHAPTER 10-1, CHAPTER 8(PG 184-189; PG 144 - 156)

UNIT 6: LECTURE 1Topics:• 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  A = Adenine• C = Cytosine 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

• 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 IS DNA?

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 moleculeA. Phosphate & Sugar backboneB. 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 2Topics:• 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)

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

HOW DOES DNA REPLICATE?

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 Cat• Addition is when one nucleotide is added in the sequence

• Example: Car Care• Deletion is when one or more nucleotides are removed from

the sequence;• Example 1: Car Cr; Example 2: Automobile Auto

END OF LECTURE 2

UNIT 6: LECTURE 3Topics:• 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

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 copied2. Cell grows to two times its original size3. Cell splits in two

• This process happens very quickly• Type of asexual reproduction• Produces two identical organisms, No genetic diversity

HOW DO CELLS DIVIDE?

BINARY FISSION

E. coli going through binary fission

EUKARYOTIC CELL DIVISION• Remember: Eukaryotic cells have a nucleus and membrane-

bound 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

HOW DO CELLS DIVIDE?

CELL CYCLE (PG 149)

INTERPHASE1. G1 PHASE - GAP 1

• First time gap, cell grows to mature size, does normal cellular activities

2. S PHASE – DNA SYNTHESIS • DNA replicates3. 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

HOW DO CELLS DIVIDE?

END OF LECTURE 3

UNIT 6: LECTURE 4Topics:• 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 4DIVISION 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

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

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

chromatidsC. ANAPAHSE• Spindle fibers shorten and break the centromere in half • Sister chromatids separated and each half is pulled to an opposite

end of the cellD. TELOPHASE• Spindle fibers break down• Nuclear membrane (envelope) reforms around both groups of

chromosomes• Cell gets ready to split

STAGES OF DIVISION (M PHASE)

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

STAGES OF DIVISION

• 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

MEIOSIS

FORMATION OF GAMETES

• Males produce four gametes of equal size• Known as SPERMATOGENESIS

• Females produce one large gamete, and three non-functional gametes (Polar Bodies)• Divides cytoplasm unequally• Known as OOGENESIS

END OF LECTURE 4