PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
Cell Cycle
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cyclical process of growth and mitosis
Consists of interphase and mitosis
Checkpoints before mitosis
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Terminologies/notes
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Heterologue - chromatins are contributed from
2 different parents.
Homologue -chromatins that contain the same
genetic materials.
Gametes - sex cells
Humans contain 23 pairs of chromosomes with
a total of 46 individual chromosomes.
Female chromosome – XX
Male chromosome – XY
Genetic disorders that result from uncontrolled
division – Down syndrome
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Interphase
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Stage between cell division
Occupies about 90% of the total cell cycle.
The process wherein the cells duplicate
themselves.
The chromosomes appear irregular – granular
form and are maintained as chromatin fibers.
Normal activities of the cell during interphase:
o Metabolism
o Cellular respiration
o Protein synthesis
o Lipid synthesis
Divided into subphases.
o G1 phase
 early growth phase
 Cell continues to grow in
volume.
o S phase
 Synthesis phase
 Involved DNA replication.
o G2 period
 Prepares for cell division.
 Replication of mitochondria
 Synthesis of microtubules
 Chromosome condensation
G1 phase – 1st checkpoint
o Checking the materials are complete
and if there are any errors in the cell.
 Apoptosis – programmed cell
death or g0 phase also known
as resting phase.
nd
G2 phase – 2 checkpoint
o Checking for replication error
o Checking if there are enough organelles
before cell division.
o If there are mitotic spindles available
Metaphase – 3rd checkpoint
o Check whether the spindle fibers are
properly attached to the centromeres.
Mitosis
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Only applies to somatic cells.
The goal is to produce 2 identical daughter cells.
o Also called duplication division
o For growth and development and
replacements for old cells.
Refers to the division of the nucleus
(karyokinesis)
Division of the cytoplasm (cytokinesis)
Consists of 4 phases
o Prophase
o Metaphase
o Anaphase
o Telophase
Prophase
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Each chromosome consists of 2 chromatins that
are joined at the centromere.
Centrioles move to the opposite ends of the
cell.
Nucleus and nuclear envelope start to dissolve.
Mitotic apparatus is nearly formed. (Asters and
spindle fibers)
=
Metaphase
PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
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Mitotic spindles are now full formed.
The chromosomes align at the metaphase plate.
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Anaphase
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The phase of migration
Chromatids separate to form two sets of
identical chromosomes.
Cytokinesis begins.
o Plant cells – cell plate
o Animal cell – cleavage furrow
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Telophase
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the phase of reconstruction
chromosome uncoils.
o Chromatins recondenses.
Nucleus develops.
Spindles disappear.
Formation of 2 new daughter cells with 23 pairs
of chromosomes each.
Ploidy level – diploid
o Formula: 2n = 23
Meiosis
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Produces 4 daughter cells with the haploid
number of chromosomes as parent cells.
Also called reduction division
o Reducing ploidy level from 2n -> n
Involves meiosis I and II
Formula = n = 23
Meiosis I
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Results in reducing the number of
chromosomes.
Accompanied by cytokinesis.
o Prophase I
 Crossing-over
–
process
wherein
the
chromatids
exchange segments and transfer
genes.
 Chiasma – site of
crossing over.
 Chiasmata
–
overlapping
region
during crossing over.
Metaphase I
o Separates chromosomes (tetrads) and
places them in the metaphase plate.
o Produces diversity in the 2 gametes.
Anaphase I
o The chromosomes are separate pulling
to either region of the cell
Telophase I
o The chromosomes arrive at the pole of
the cell
o Each pole has a haploid chromosome
cell
Meiosis II
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Prophase II – spindle fibers form
Metaphase II – Line up at the metaphase plate
Anaphase II – Separate the chromosomes.
Telophase II – nuclei form at the poles
Cytokinesis occurs.
23 individual chromosomes from the sperm
23 individual chromosomes from the egg
2 haploids = diploid
PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
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Eukaryotic Chromosomes
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Eukaryotic chromosomes are composed of
chromatin.
Chromatin is the aggregate mass of DNA and
histone proteins.
Karyogram– graph that shows chromosomes.
Organization of a chromosome
1. The supercoiling of chromatin within the
chromosome.
a. Supercoiling is the processing of folding
chromatins to become a chromosome.
2. Folding within the supercoil
3. An individual fiber in the supercoil consists of a
nucleosome: a DNA strand coiled around
histones like beads on a string.
4. Linker proteins anchor DNA to the core and
wind the chain in to a cylinder.
DNA
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Sex chromosomes (XY and XX) differ in males
and females, and function in sex determination.
Autosomes are not involved in sex
determination.
Number of chromosomes
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The number of chromosomes is constant within
species.
but chromosome numbers vary among different
species.
N identifies the number of different kinds of
chromosomes
o Diploid (2N) – 2 sets of chromosomes
o Haploid – 1 set of chromosomes
o Polyploid – more than 2 sets of
chromosomes
 Polyploidy – changes in the
entire sets of chromosome
DNA (deoxyribonucleic acid) as the candidate
Able to code for the sequence of amino acids in
proteins a control protein synthesis.
Able to replicate itself prior to cell division.
Contained in the nuclei of eukaryotic cells.
Able to change over time to account for
evolutionary change.
Enzymes involved in DNA synthesis
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Sex Chromosome and autosome
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Aneuploid – occurs due to
nondisjunction
 Trysomy – adds 1 chromosome
 Monosomy – decreases 1
chromosome
 Chromosome 21 mostly
affected sa trysomy
Helicase – protein unwind DNA strands from
double-helix.
Single-strand binding protein – stabilizes DNA
strand after being unwound by the helicase
DNA polymerase – creates a copy
Structure of DNA
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Double helix
With major and minor grooves
Complete spiral every 10 base pairs
Antiparallel: 3-5 and 5-3
The structure of DNA
1. Nucleotide = nitrogenous base with a backbone
of deoxyribose sugar and phosphate groups.
2. Base-pairing
o Adenine – thymine
o Cytosine – guanine
 These nucleotides are coiled
along histones, then are
supercoiled
to
produce
chromosomes.
3. Bases
o Purine (2 rings): A, G
o Pyrimidine (1 ring): C,T
PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
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Hydrogen Bonding of bases
2.
3.
4.
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Dipole-dipole
DNA replication process
1. Helicases unwind the parental double helix.
2. Single-strand binding proteins stabilize the
unwound parental DNA.
3. DNA polymerase synthesizes The leading strand
continuously in the 5 -> 3 directions.
4. The
lagging
strand
is
synthesized
discontinuously.
a. Primase synthesizes a short RNA primer,
which DNA polymerase extends to form
an Okazaki fragment.
5. After the RNA primer is replaced by DNA, DNA
ligase joins the Okazaki fragment to the growing
strand.
Gene to Protein
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Gene – a DNA sequence that codes for one
polypeptide or a trait
Genetic Information is transmitted from the
nucleus to the cytoplasm where the protein
synthesis occurs.
5.
6.
Translation: mRNA – protein
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Transcription: DNA - mRNA
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The process by which DNA is transcribed to
mRNA.
 Generally, the same process as DNA synthesis
but with a transcription synthesizes ribose
nucleic acid (RNA)
o Uracil instead of thymine
1. Involves an enzyme called RNA polymerase
with the help of the protein transcription
factors RNA polymerase separates DNA at a
sequence called the promoter.
DNA strands separate temporarily into
 Template strand (antisense
strand) – will be used to
generate mRNA.
 Non-template strand (sense
strand)
RNA polymerase adds RNA nucleotides to the
DNA template.
Elongation - the process in which RNA
polymerase travels along the template strand.
 During this process, the rna
polymerase base zips back up,
keeping only 10-20 base pairs
open.
Termination – process is done, DNA zips back
up.
After the process, it will produce mRNA and it
will travel to the cytoplasm, particularly in a
ribosome where translation will begin.
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The process by which messenger RNA (mRNA) is
translated into proteins.
Codons – set of 3 bases in the mRNA, codes for
the anticodon that is carried by transfer RNA (
tRNA)
The mRNA carries a code of the specific gene,
tRNA converts codon information into amino
acid sequence.
o catalyzed by rRNA.
mRNAs are single-stranded RNA molecules.
They are copied from the TEMPLATE strand of
the gene, to give the SENSE strand in RNA
o Each tRNA is attached to a specific
amino acid
Reading Frame – the arrangement of
nucleotides into the codons
o 4 possible bases
o 3 letters per codon
o Which gives 64 possible codons
SPECIAL CODONS:
o AUG methionine – start codon.
o UAA, UAG, UGA – stop codons
PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
 Translation process:
1. Start in the small ribosomal subunit that will
bind to an mRNA and initiator tRNA
2. Large ribosomal unit joins to complete the
translation initiation complex
3. tRNA that corresponds to the codon with enter
the ribosome and carries an amino acid. It
becomes covalently bound to the methionine.
4. 1st tRNA leaves and shifts over and the process
continues until it reaches a stop codon.
5. The completed polypeptide swims away for
folding.
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Genotype – genetic composition
Phenotype – visual expression of the genotype
Dominant Allele – Hides the expression of
another allele.
Recessive allele – expression is masked another
allele.
Heterozygous – two different alleles of the gene
occupy the loci of homologous chromosome.
Homozygous – two identical alleles of the gene
occupy the loci homologous chromosome.
Principle of Segregation
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The Genetic Code
Pairs of genes are distributed between
gametes during gamete formation when
homologous chromosomes are distributed
to different gametes during meiosis.
Inheritance Patters In Animals
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A gene or a DNA sequence coding for a trait is
located at a specific locus or site in the
chromosome.
Different alleles of the gene occupy the same
locus.
Terminologies
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Trait – a characteristic brought by the
expression of a gene
Alleles – alternative forms of a gene
o Multiple Alleles – when more than a
pair of alleles control a trait
Codominant – different alleles are both
expressed in a heterozygote.
Incomplete dominance – when one allele is not
completely dominant over another.
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Law of segregation:
Principle of Independent Assortment
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During Meiosis, pairs of genes segregate
independently of one another.
PCZO100-LT112324-DGPAHAYO
MODULE 3 – Cell Division and Genetics
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The distribution of genes for one trait is not
influenced by the genes for another trait.
Punnett Square
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