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Name________________________________________ Date: _________________
BIOLOGY: Ch. 10-1 & Ch. 8 – DNA, Cell Division & Reproduction
Chapter 10-1/ DNA
DNA & Cell Reproduction: Part 1 - DNA
Big Ideas:
•
The primary function of DNA in organisms is to store and transmit
information that tells cells what to do.
•
It is the DNA that allows cells to have different forms and to perform
different functions.
What is DNA?
Deoxyribonucleic acid or DNA is a double stranded nucleic acid made of repeating
nucleotides.
Main Function:
Store and transmit the genetic information that tells cells which proteins to make
and when to make them.
DNA -The Double Helix- Discovery of DNA: The Double Helix
In 1953, Scientists James D. Watson and Francis Crick suggested a model for
the structure of DNA.
Using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins,
Watson & Crick indicated that DNA had a helical structure – shaped like a twisted
ladder. “We’ve found the secret of life!” ~ Francis Crick (1916-2004)
Structure of DNA
Each DNA molecules is made of only 4
smaller, repeating subunits (monomers) called
NUCLEOTIDES.
Each nucleotide is made of 3 parts:
1. Sugar
2. Phosphate
3. 4 different Nitrogen Bases
The sugar and phosphate groups are identical
in each nucleotide
4 different Nitrogen bases:
Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) = Often labeled A, G, T, C
Chargaff’s Data
Originally it was thought that the bases A, T, G, and C occurred in all living things
in the same repeated pattern, such as: ATGC ATGC ATGC ATGC …
The research of biochemist Erwin Chargaff revealed the percentage of each base
(A, T, G, & C) found in the DNA of various organisms.
The following table contains some of his actual data…
Nitrogen Base Make-Up of Different Organismal DNA (by %)
ORGANISM
A
T
G
C
Mycobacterium tuberculosis
15.1
14.6
34.9
35.4
Yeast
31.3
32.9
18.7
17.1
Wheat
27.3
27.1
22.7
22.8
Sea Urchin
32.8
32.1
17.7
17.3
Marine Crab
47.3
47.3
2.7
2.7
Turtle
29.7
27.9
22.0
21.3
Rat
28.6
28.4
21.4
21.5
Human
30.9
29.4
19.9
19.8
Did you observe any patterns in this data?
Complementary Base Pairing:
Chargaff’s Rule states: Each base always pairs with its ‘partner’ base.
A pairs with T, T pairs with A
G pairs with C, C pairs with G
Also known as: Complementary Base Pairing
Adenine always bonds with thymine to form a step
Cytosine always bonds with guanine to form a step
Deoxyribose sugar and phosphate are the backbone or sides of the ladder
DNA Replication
Cells that divide must pass exact copies of their DNA to offspring cells.
REPLICATION - the process of duplicating a DNA molecule.
During replication, the double helix unwinds & separates. Each chain serves as a
template for a new chain, or strand of DNA
The Steps of DNA Replication:
1. The double helix unwinds. As with all metabolic activities, enzymes called
“helicase” are needed for this process.
2. DNA helicase unzips the 2 strands of nucleotides in between the bases – a point
called the replication fork. Now the bases are exposed.
3. Complementary nucleotides floating in the nucleus pair with the exposed bases.
DNA polymerase (another enzyme!) assists in the addition and bonding of the
complimentary nucleotide.
Result: Two new strands of DNA (identical to the original DNA), each consisting of
½ the old DNA strand and ½ the new strand, are created.
Accuracy & Repair of DNA
DNA replication is accurate!!
• usually only 1 error in every 10,000 paired nucleotides
• But any error, called a mutation, can have serious effects
• Radiation, chemicals , heat can damage DNA (mutation)
• Cell has proofreading techniques – like spell check. Even so, errors
can occur
• Over 20 or more repair enzymes fix errors
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Name________________________________________ Date: _________________
BIOLOGY: Ch. 10-1 & Ch. 8 – DNA, Cell Division & Reproduction
Part 2: Modern Biology Chapter 8-1/ Chromosomes
Big Ideas:
•
As a cell prepares to divide, its DNA coils around proteins and twists into
rod-shaped CHROMOSOMES
Chromosomes & Cell Reproduction
Before a cell can divide, the loosely packed replicated DNA (referred to as
chromatin) coils into very compact structures called: CHROMOSOMES
Each chromosomes consists of two identical strands of DNA tightly wrapped
around proteins called histones.
These two identical halves are
referred to as chromatids (or ‘sister
chromatids’)
•
• Centromeres hold the two
chromosomes together.
• During division, sister chromatids
from each chromosome separate and
each new cell will get one.
- Every Species has a different number of chromosomes
- For example: Humans have 46 chromosomes (23 pairs)
•
Human and animal chromosomes are either:
•
•
Autosomes – (humans have 44 autosomes (do not determine the sex)
sex chromosomes (humans have 2 sex chromosomes (determine the
sex)
• Females have 2 X chromosomes
• Males have an X and a Y chromosome
Every cell of an organism produced by sexual reproduction has two copies of each
autosome and two sex chromosomes.
•
Referred to as: Homologous chromosomes (sometimes called homologues)
• Each pair is the same size and shape; carry genes for the same traits.
• One comes from mom and one from dad.
KARYOTYPE:
What is a karyotype? *An arranged photomicrograph of chromosomes.
•
•
Shows the number of chromosomes, and what they look like under a
microscope.
Helps determine problems in chromosomes.
• Attention is paid to:
• chromosome number & length
• position of the centromeres
• banding pattern
• sex chromosomes
Trisomy 21 – Down Syndrome
•
3 copies of chromosome 21 instead of 2
Cells having two sets of chromosomes are said to be diploid (2n) - Usually one from
mom and one from dad.
All human cells (somatic), except reproductive cells (sperm & egg) are diploid cells –
having 46 chromosomes - 22 pairs of homologous chromosomes & 2 sex
chromosomes.
Cells with only one of the two chromosomes is considered haploid (1n)
Sperm and egg cells are haploid cells.
Haploid cells have half the number of chromosomes that are present in diploid
cells.
When two haploid cells combine, each new cell will be diploid.
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Name________________________________________ Date: _________________
BIOLOGY: Ch. 10-1 & Ch. 8 – DNA, Cell Division & Reproduction
Part 3: Modern Biology Chapter 8-2 / Cell Division
Big Ideas:
•
All cells are derived from the division (binary fission or Mitosis) of preexisting cells
•
Cell division is the process by which cells produce offspring cells.
•
Cell division differs in prokaryotes and eukaryotes.
•
Cell division differs between somatic cells (body) and germ (sex) cells.
Every prokaryotic and Eukaryotic Cell has a life of its own!
Every prokaryotic and eukaryotic Cell comes from the division of pre-existing cells!
Cell Reproduction or Cell division is the process by which cells produce offspring
cells.
•
allows for growth and repair
•
passing genetic information to future generations (reproduction).
•
Cells reproduce by copying their genetic material (DNA) and then dividing —
a parent cell giving rise to daughter cells.
Cell division is very different for prokaryotes and eukaryotes
Cell Division in Prokaryotes:
Binary fission – division of a prokaryotic cell into two offspring
Single chromosome copies itself
Cell grows to 2X its size
Cell wall forms between the 2 chromosomes
Two new cells
• Each new cell is an identical clone
Cell division in eukaryotes:
•
•
•
•
Mitosis & Meiosis–
MITOSIS: Division of a cell’s nucleus that produces a genetically identical cell
•
It does not change the amount of DNA in a cell
•
occurs in the reproduction of eukaryotic unicellular organisms
•
And in growth (the addition of cells to a tissue or organ) and repair of
eukaryotic multicellular organisms.
MEIOSIS: Division of a cell’s nucleus that reduces the number of chromosomes in
each new cell.
•
Produces gametes (sex cells – sperm & egg)
Cell Division: The Cell Cycle
Every prokaryotic and Eukaryotic cell has a life cycle – the stages it goes through
to grow and divide…called THE CELL CYCLE
•
A beginning (growth)
•
A middle (genetic material replicates and cell prepares for cell division)
•
And an end (division) = TWO NEW CELLS!!
The Cell Cycle starts when a cell is formed and ends when a cell divides to make a
new cell.
The Cycle consists of:
•
•
•
Interphase – time between cell division
Mitosis – nucleus of cell divides
Cytokinesis – division of cytoplasm = 2 new cells!
Interphase
Takes up 80-90% of a cells lifespan
Three distinct parts:
•
G1 (Growth Phase) – cell doubles in size, organelles double in number
•
S (Synthesis Phase) – chromatin (DNA) replicates
•
G2 (Growth Phase) - rapid growth phase & prepare for next division
M Phase or Mitosis
•
Chromosomes separate
•
Nucleus divides
There are four important stages of Mitosis:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
MITOSIS: ***Try this mnemonic***
“(P)LEASE” - Prophase
“(M)AKE” - Metaphase
“(A)NOTHER” - Anaphase
“(T)WIN” – Telophase
There are four important stages of Mitosis (cont.)
1. Prophase
•
•
•
Chromatin coils and forms chromosomes, which are visible under a
microscope
nucleolus and nuclear membrane disappear
Centrosomes and spindle fibers appear.
2. Metaphase
• Spindle fibers assist in aligning all chromosomes at the center of the cell.
3. Anaphase
•
•
Spindle fibers pull chromosomes apart.
One set of chromosomes is pull toward one pole of the new cell and the
other set toward the other.
4. Telophase
•
•
•
•
Centrioles and spindle fibers disappear.
Middle of an animal cell pinches together.
A nuclear membrane forms around each new set of chromosomes.
In plant cells, a new cell wall and a new cell membrane form down the middle
of the cell.
5. Cytokinesis
Cytoplasm and organelles split and form two daughter cells – exactly like the
parent cell
• Each cell receives an identical copy of the original cell’s chromosomes and
half of the cytoplasm and organelles.
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Name________________________________________ Date: _________________
BIOLOGY: Ch. 10-1 & Ch. 8 – DNA, Cell Division & Reproduction
Part 4: Modern Biology Chapter 8-3 / Cell Division: MEIOSIS
Big Ideas:
*Body cells (somatic cells) are reproduced through mitosis. The number of
chromosomes remains the same in each daughter cell produced.
*However, there is another type of cell division called Meiosis. The number of
chromosomes is cut in half in all daughter cells produced (reproductive cells).
Meiosis – Called the “Reduction Division”
•
Cells divide twice = 4 new cells
•
Reduces the # of chromosomes:
•
From 1 diploid - 2n cell to 4 haploid - 1n cells
Sex Cells, also called gametes fuse during sexual reproduction and form a zygote
with a normal # of chromosomes
Meiosis involves two separate cell divisions, and they occur one right after the
other.
Meiosis I
Meiosis II
Meiosis I: Similar to Mitosis I
1. Prophase I: DNA has already duplicated. Chromosomes are visible. The nuclear
membrane disappears. Spindle fibers appear.
THEN…
Every chromosome lines up with its homologue and forms a tetrad.
Synapsis – pairing of homologous chromosomes – does not occur in mitosis
When the homologous chromosomes form a tetrad, chromatids can exchange
pieces, called crossing – over - Genetic recombination results
2. Metaphase I:
•
Tetrads line up randomly along the midline of the cell
3. Anaphase I:
•
Each homologous chromosome moves to an opposite pole of the dividing cell
•
Independent assortment – the random separation of homologous
chromosomes
•
Genetic recombination occurs again due to random separation of maternal
(mom’s) and paternal (dad’s) chromosomes
4. Telophase I:
•
Chromosomes reach the opposite ends of the cell - Cytokinesis begins
•
New cells are now haploid (1n)
•
they contain only one homologue from each homologous pair
•
But they have two copies of each chromosome because the DNA copied
itself right before beginning Meiosis I
Meiosis II
1. Prophase II: chromosomes DO NOT duplicate.
2. Metaphase II: chromosomes line up in the center of the cell
3. Anaphase II: chromosomes split and separate.
4. Telophase II: cells pinch together. Nuclear membranes form. Four daughter
cells are formed. Each cell has only half the number of chromosomes as the
parent cell.
Gamete Formation
•
Meiosis produces haploid reproductive cells called gametes
•
Meiosis only occurs in cells of the reproductive organs
•
Humans:
•
•
Oogenesis - female ovaries produce 1 egg and 3 polar bodies
(disintegrate)
Spermatogenesis - male testes produce 4 sperm
REPRODUCTION:
Asexual Reproduction
Production of offspring from one parent:
•
•
•
no union of gametes
no genetic diversity
offspring genetically identical (clone)
•
Unicellular organisms –binary fission (prokaryotes i.e. bacteria) or mitosis
(eukaryotes - algae, some yeasts & Plants, and protozoans, such as
paramecium) budding, too
•
Multicellular organisms – budding (i.e. hydra)
•
Except in identical twins, offspring are unique combinations of their parents’
genes
Sexual reproduction The production of offspring through meiosis and the union of
gametes:
•
each parent contributing half their genetic material (DNA) to their
offspring
(1n + 1n = 2n)
•
Except in identical twins, offspring are unique combinations of their parents’
genes
Sexual reproduction gives an evolutionary advantage in is that it enables species to
adapt rapidly to new conditions.