Transcript Mitosis, Meiosis, DNA Notes

I.
Cell Growth and Division
A. Cell Cycle:
1. Sequence of events that occurs in a
cell from mitosis to mitosis.
2. 5 parts:
a) G1 phase – cell growth occurs (make
new proteins + organelles).
b) S phase – DNA is copied in
preparation for mitosis.
c) G2 phase – Organelles needed for
nuclear division are made.
d) Mitosis – nuclear division.
e) Cytokinesis – cytoplasm divides.
3. Interphase – G1 + S + G2 phases.
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4. Figure 10-4 page 245
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B. Mitosis
1. Chromosome structure:
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2. Done to produce more cells (growth and
replacement).
3. Occurs in somatic cells (body cells)
not sex cells (gametes)
4. 4 steps:
a)Prophase:
1)Nuclear membrane + nucleolus
disappear.
2)Chromosomes condense + become
visible.
3)Centrioles form + move to poles.
4)Spindle fibers first appear.
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b)Metaphase:
1)Spindle fibers attach to
centromere (center of chromosome).
2)Chromosomes line up at the
equator.
c)Anaphase:
1)Sister chromatids spilt.
2)Chromosomes (now w/ only 1
chromatid) move to opposite poles.
d)Telophase:
1)Nuclear membrane + nucleolus
reappear.
2)Chromosomes spread out + become
invisible.
3)Spindle fibers disappear.
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5. Figure 10-5 page 246-47
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C. Cytokinesis – division of the cytoplasm.
1. After mitosis, one cell with two
nuclei.
2. Animals – cytoplasm pinches in
(cleavage furrow)
3. Plants – cell plate forms in the center
and works towards the cell wall.
a)Figure 10-6 page 248
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D. Uncontrolled cell growth
1. Cancer – uncontrolled cell growth
(tumor).
2. Causes:
a)Smoking/chewing tobacco
b)Radiation exposure (X-rays, tanning
beds, etc.)
c)Viruses
d)Other (chemicals, defective genes,
etc.)
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II. Production of Sex Cells
A. Meiosis
1. Nuclear division that reduces the
number of chromosomes by half.
2. Production of gametes (sex cells:
sperm + eggs)
3. Homologous chromosomes – pairs of the
same chromosomes
a) Humans – 46 chromosomes (23 pairs)
b) Diploid – both homologs are present
(2N)
c) Haploid – only 1 chromosome of each
homolog pair is present. (1N)
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4. 2 parts:
a)Meiosis I
b)Meiosis II
B. Meiosis I
1. Prophase I: 2N
a)Chromosomes become visible.
b)Nuclear membrane + nucleolus
disappear.
c)Spindle fibers appear.
d)Synapsis (pairing of homologs)
occurs.
1)Forms a tetrad (4 chromatids = 2
chromosomes).
e)DNA may be exchanged between tetrad
(crossing over) = genetic variety 10
2. Metaphase I: 2N
a)Tetrads move to equator by the
spindle fibers.
3. Anaphase I: 2N -> 1N
a)Tetrad splits, however each
chromosome still has two chromatids.
4. Telophase I: 1N
a)Cytoplasm divides.
b)Nuclear membrane + nucleolus
reappear.
c)Spindle fibers disappear.
d)Now have two cells.
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C. Meiosis II (1N)
1. Prophase II:
a)New spindle fibers form.
b)Nuclear membrane + nucleolus
disappear.
2. Metaphase II:
a)Chromosomes move to equator by
spindle fibers.
3. Anaphase II:
a)Sister chromatids are split with each
chromatid moving to opposite poles.
4. Telophase II:
a)Same as Telophase I.
b)Have 4 cells now.
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 Figure 11-15 page 276 – 77 Meiosis I
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• Meiosis II
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
Summary:15
Mitosis:
Meiosis:
Start
1 cell, 2N
1 cell, 2N
End
2 cells, 2N
4 cells, 1N
D. Human gamete Production
1. Males = 4 (1N) sperm cells from
Meiosis.
a)Starts at puberty
2. Females = 1 egg (1N) + 3 polar bodies
(garbage).
a)Starts in the womb but not completed
until ovulation.
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 Figure 11-7, page 278
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III. Deoxyribonucleic acid, DNA – double helix
molecule that carries hereditary
information for genes.
A. Structure:
1. Composed of 3 parts:
a) Deoxyribose (sugar)
b) Phosphate group
c) Nitrogen base
2. Double helix shape
a) Discovered by James Watson and
Francis Crick.
b) Twisted ladder shape.
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c)Figure 12-7 page 294
3. Four Nitrogen Bases
a)Adenine (A)
Purine
b)Guanine (G)
“
c)Thymine (T)
Pyrimidine
d)Cytosine (C)
“
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4. Bonding patterns:
a) G ≡ C (3 bonds)
b) A = T (2 bonds)
B. Replication – process of copying a DNA
molecule.
1. Needed for mitosis (S phase)
IV. Ribonucleic acid, RNA – single strand
nucleic acid used for protein synthesis.
A. Different from DNA:
1. Single stranded
2. Ribose not Deoxyribose
3. Uracil instead of Thymine (A = U)
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B. Types:
1. Messenger RNA (mRNA) – carries message
from DNA to make proteins.
2. Transfer RNA (tRNA) – brings amino
acids to ribosome to make proteins.
3. Ribosomal RNA (rRNA) – makes up the
ribosomes.
4. Figure 12-12 page 300
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C. Transcription – process of making RNA
from DNA.
1. DNA  all types of RNA
2. Ex:
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V.
Protein synthesis – formation of proteins
using genetic code from DNA and carried
out by RNA.
A. Translation – process of forming
proteins from mRNA.
1. mRNA leaves nucleus (nuclear pores)
and goes to ribosomes.
2. mRNA is grouped into 3 consecutive
bases called codons.
a) Each codon corresponds with a
certain amino acid.
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b)Figure 12-17 page 303
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3. DNA – transcription – mRNA –
translation – proteins
4. tRNA has a compliment (opposite) base
sequence to the codon called anticodon.
a)The amino acid that corresponds with
the codon is attached to the tRNA.
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5. Figure 12-18 page 304
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VI. Mutations – spontaneous changes in a gene
or chromosome.
A. Many types
1. Single Base switch:
a) Ex:
Normal
Mutation
DNA: ATG CGA
GTG CGA
RNA: UAC GCU
CAC GCU
AA : Tyrosine
Histidine - Arginine
- Arginine
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2. Single Base
a)Ex:
Normal
DNA: ATG CGA T
RNA: UAC GCU A
AA : Tyrosine
- Arginine
Deletion:
Mutation
AGC GAT
UCG CUA
Serine - Leucine
3. Environmental factors may cause, but
not always.
4. Not passed to offspring unless occurs
in gametes (sex cells)
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