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Deoxyribonucleic Acid - DNA
 Found primarily in the nucleus in chromosomes stores and transmit information to make proteins.
 Structure
Consists of two strands of nucleotide monomers
Parts of a nucleotide
Deoxyribose - 5-carbon sugar
Phosphate group
Nitrogen base
Nitrogen base
 Purine - nitrogen base with a double ring of
carbon and nitrogen atoms.
Adenine
Guanine
 Pyrimidine - nitrogen base having a single ring of
carbon and nitrogen atoms.
Thymine
Cytosine
Two strands of nucleotides twist around a central axis to
form a double helix
First described by Watson and Crick in 1953.
Similar to a twisted ladder
Sides of alternating sugar and phosphate
Rungs consist of pairs of nitrogen bases equal in length.
Purine always pairs with a pyrimidine
-have hydrogen bonds.
Adenine bonds with thymine
Guanine bonds with cytosine
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Base sequence one strand is exact
complement of base sequence in
second strand.
1st Strand Sequence
A-G-C-T-T-A-G-C
2nd Strand Sequence
T-C-G-A-A-T-C-G
Replication
Process of duplicating the DNA molecule
Each strand serves as a template or mold for
new complementary strand to be built.
Process of Replication
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DNA helicase attaches to DNA molecule - "unzips" the 2
strands - breaks hydrogen bonds between bases.
Unpaired bases of strands react with complementary
bases of nucleotides in nucleus - hydrogen bonds form.
DNA polymerase catalyzes formation of sugar to
phosphate bonds - connect one nucleotide to the next.
Result - two new DNA molecules - each consists of 1 "old"
strand and 1 "new" strand.
Process doesn't begin at one end and proceed to the
other - may occur simultaneously at many points.
DNA may be damaged by body heat,
radiation, chemicals, etc.
Cell can "proofread" for mistakes
Can be repaired and corrected
Ribonucleic Acid – RNA

Nucleic acid that uses information stored in DNA to
synthesize proteins.
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Structure
Consists of a single strand of nucleotide monomers.
Parts of nucleotide
Ribose - 5-carbon sugar
Phosphate group
Nitrogen base
Nitrogen bases of RNA
Purines
Adenine
Guanine
 Pyrimidines
Uracil
Cytosine
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RNA differs from DNA in 3 ways
 RNA consists of only one strand of
nucleotides instead of the 2 strands of DNA.
 RNA contains the 5-carbon sugar, ribose,
instead of deoxyribose
 RNA contains the nitrogen base, uracil,
instead of thymine.
Types of RNA
 Messenger RNA (mRNA) - single, uncoiled strand,
transmits information from DNA for protein
synthesis; acts as template for amino acid assembly
during protein synthesis at ribosomes.
 Transfer (tRNA) - single strand of RNA folded back
on itself in hairpin fashion; allows some bases
pairing; exists in 20 or more varieties each for only
1 specific type of amino acid.
 Ribosomal RNA (rRNA) - globular form of RNA;
major constituent of ribosomes.
Transcription
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Process where mRNA is produced from the DNA - transcribed according
to the information coded in the base sequence of DNA.
Base sequence of mRNA complementary to sequence of DNA from
which it was transcribed.
Directed by enzyme, RNA polymerase
Process
Enzyme binds to DNA causing strands to separate.
Hydrogen bonds to form between DNA template and
complementary RNA nucleotide bases.
Enzyme moves to next section of DNA, bonds form between
phosphate groups and ribose.
RNA molecule released when enzyme reaches DNA sequence that
acts as a termination signal.
Protein Synthesis
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Structural and functional characteristics of proteins are determined
by the sequence of amino acids in the protein
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Sequence of amino acids in a protein encoded in DNA
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Genetic Code - System that contains information needed by cells for
proper functioning; built into the arrangement of nitrogen bases in a
particular sequence of DNA.
Codon - series of three bases in mRNA that codes for a
specific amino acid.
Anticodon - series of three bases in tRNA, complementary to a
codon; pairs with the codon during translation
Translation - process where protein molecules are
made from information encoded in mRNA.
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mRNA moves out of nucleus through a nuclear pore
mRNA migrates to a group of ribosomes
Amino acids in the cytoplasm are transported to the ribosomes
by tRNA - each specific for an amino acid.
Assembly of polypeptide begins when A - U - G codon attaches
to the ribosome.
Codon pairs with its anticodon adding specific amino acid to the
growing polypeptide chain.
Process continues until a "stop" codon reaches the ribosome.
mRNA is released and polypeptide is complete and released
Gene - region of DNA that directs the
formation of a polypeptide.
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Proteins usually consist of more than one
polypeptide.
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Several genes may direct protein
synthesis
Process by which cells reproduce.
 Cell Theory
Cell is basic unit of life
Living things are made of cells or cell
fragments.
All cells come form existing cells.
 Reasons Cells Divide
Maintenance
Repair
Growth
Reproduction
Nucleus
 Organelle that directs the everyday metabolic activities of the cell.
 Composed of Chromatin
Normally - grainy mass of material
During cell division appear as bodies called chromosomes.
Composed of DNA and protein
Carries the "genetic code"
Individual heredity units are genes - determine cell
characteristics and how cell functions - by proteins
that are synthesized.
 Each time the cell divides the genetic material must be replicated –
makes exact copy
Must then be distributed to the new cell.
Replication occurs during interphase.
Chromosome Number
 The number of chromosomes found in the nucleus.
Varies from one organism to another.
Man - 46
Fruit Fly - 8
Bullfrog - 26
 All cells of an organism will have the same number of
chromosomes.
Exception is the sex cells or Gametes
Egg - female
Sperm - male
 Body cells called Somatic Cells or Somates.
Humans 23 pairs of chromosomes - total of 46 chromosomes.
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Pairs of chromosomes are known as being Homologous.
Individual members of the pair are called Homologs.
Get one homolog of each pair from each parent
Each homolog of pair has same size and shape.
Number of pairs of chromosomes in a somate is expressed as
"n" - total number of chromosomes expressed as "2n"
Humans: n = 23; 2n = 46
Total number of chromosomes is Diploid Number = 2n
Total number of different pairs in cell is its Haploid Number
(Monoploid) = n
Features of the cell's chromosomes including size and
number make up cell's Karyotype - arranged by size and
shape.
Actually talking about division of nuclear
material
 Two types of nuclear division
Mitosis
Meiosis
 Cytokinesis - division of the cytoplasm
Process by which the nucleus divides to produce 2 new nuclei, each with
the same number of chromosomes as the parent nucleus.
From the Greek - Mitos - Thread
Occurs in somatic cells.
Requirements
Precise replication of the genetic material
Distribution of a complete set of chromosomes to each new cell called Daughter Cells
 Five Phases of Cell Cycle - continuous
Interphase
Prophase
Metaphase
Anaphase
Telophase
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Interphase – not really a part of mitosis
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Once called the "resting" stage
Cell performing various metabolic activities
Occupies about 2/3 of cell's life cycle
Genetic material replicates during phase.
Nucleus clearly defined by membrane
Chromosomes not visible - chromatin appears grainy.
Consists of 3 subphases
G1 Phase - first phase of interphase; cell doubles in size;
enzymes and organelles,roughly double in size.
S Phase - DNA in the chromatin replicates
G2 Phase - Cell undergoes rapid growth that prepares it for
mitosis, synthesizing necessary enzymes and structures.
Prophase
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Early prophase - chromatin coils; forms chromosomes.
Chromosomes appear as rod-like structures.
Nucleolus and nuclear membrane breakdown and
disappear.
Centrioles appear next to the disappearing nucleus move to opposite ends or poles of cell (not plants).
Spindle fibers form - asters radiate from centrioles in
animal cells.
Chromosomes appear as double stranded structure
Each strand is a Chromatid
Two chromatids are joined at a Centromere.
Metaphase
 Chromosomes arrange themselves on
equator of spindle
 Chromosomes attach to spindle fibers at
the centromere.
 Centromeres aligned on the equator.
Anaphase
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Centromere divides - one chromatid
moves toward 1 pole of spindle while
other chromatid moves to the opposite
pole.
Telophase
Two identical sets of chromatids are
clustered at opposite ends of the cell.
 Centrioles and spindle fibers disappear.
 Chromatids unwind and elongate into
chromatin - chromosomes disappear
 Nuclear membrane and nucleolus
reappear.
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Process completed with cytokinesis - get two
distinct cells
Animals – Cleavage Furrow forms from
outside toward the center – pinches cell in
two.
Plants – Cell Plate forms from center and
grows to the outside.
 No reduction in chromosome number
Parent Cell = 2n ----> Each Daughter Cell = 2n
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Process by which the cell nucleus divides resulting in a reduction
of chromosome number from the diploid number (2n) to the
haploid number (n)
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Involves 2 divisions
Chromosome number reduced in first division Meiosis I
Second division - mitotic - Meiosis II
Cell division that results in formation of gametes or sex cells.
Occurs in the Gonads (sex organs)
Ovary - female
Testes - male
Process in males - called Spermatogenesis
Process in females - called Oogenesis
Phases
Interphase
Prophase I
Metaphase I
 Anaphase I
 Telophase I
 Prophase II
 Metaphase II
 Anaphase II
 Telophase II
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Interphase - same as in mitosis
 Chromosomes replicate
Prophase I
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DNA strands coil, shorten, and thicken- Chromosomes
become visible.
Nuclear membrane disappears, spindle fibers appear.
Homologous pairs of chromosomes move together Homologs pair
Pairing movement is called Synapsis
Two double stranded chromosomes are so close
they appear to be joined at their centromeres.
Looks like 4 chromatids connected – group
called a Tetrad.
Crossing Over of chromatids may occur during
synapsis
Metaphase I
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Tetrads align on the equator of the cell
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Have 2 chromosomes with 4 chromatids
attached to single spindle fiber.
Anaphase I
 Homologous pairs of chromosomes separate -
one chromosome of the pair goes to each
pole - centromeres do not divide.
 Each chromosome still consists of 2
chromatids joined by a centromere.
Telophase I
Cytoplasm divides to form 2 daughter cells.
 Nuclear membrane begins to reappear, double
stranded chromosomes disappear; spindle may
disappear.
 Each daughter cell contains one half the original
number of chromosomes that parent cell had.
 Cells may enter resting state – Interkinesis
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Prophase II
 No further replication of DNA occurs
 Spindle reappears; chromosomes
reappear
Metaphase II
 Chromosomes move to cell's equator.
 Centromere attaches to spindle fiber.
 Each chromosome composed of sister
chromatids joined at centromere.
Anaphase II
 Centromere joining chromatids divides.
 Each chromatid moves toward the
opposite pole.
Telophase II
 Spindle disappears
 Nuclear membrane forms around
chromosomes of each daughter cell.
 Each of the 4 cells formed from the original
parent cell has 1/2 the number of
chromosomes of the parent.
Summary
 First Meiotic Division - produces 2 haploid
cells; double stranded chromosomes.
 Second Meiotic Division - 2 haploid cells
divide to produce 4 haploid cells.
 4 haploid cells can develop into gametes.
 Spermatogenesis - Production of sperm
 Oogenesis - Production of egg
Cells at the end of Prophase I
 Male - Primary Spermatocyte – at puberty
 Female - Primary Oocyte - formed as early as
3rd month of development - meiosis stops
until sexual maturity
Two cells at the end of Telophase I
 Male - secondary spermatocyte
 Female - cells unequal - 1 secondary oocyte, 1
polar body
Cells at end of Telophase II
 Male - 4 haploid cells – Spermatids
 Female - 1 Ootid and 3 Polar Bodies (die)
- ootid has most of the cytoplasm.
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Spermatids - mature to form sperm
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Ootid - matures to form egg.
Importance
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Ensures that chromosome number remains constant
in sexual reproduction
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Egg (n) + Sperm (n) -- Fertilization --> Zygote (2n)
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Chromosome number of zygote is thus the same as
the two parents.
Asexual - production of offspring from one
parent
 No fusion of gametes
 Offspring is identical to parent.
 Occurs due to mitosis.
 No genetic variation between parent
and offspring
Sexual - production of offspring through meiosis
and subsequent fusion of gametes from two
parents
 Offspring is different from either parent
 Half of genetic material has come from one
parent; other half has come from the other
parent.
 Introduces variation between the parents and
offspring.