1-1: How does an understanding of DNA help us investigate ......1-1: How does an understanding of...
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1-1: How does an understanding of DNA help us investigate living things?
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Image credits: singularityhub.com
Any uncredited images throughout this powerpoint are from Science Connections 10 textbook or
publisher’s powerpoint.
Big Ideas
• The variation in living things we see
around us is due to DNA.
• DNA is made of many nucleotides linked together in a
specific order.
• DNA exists in chromosomes, which contain thousands of
genes.
• The structure of DNA is important to passing on
information.
• The different genetic make-up of organisms is reflected
in the diversity of living things.
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Key Vocabulary
• DNA (deoxyribonucleic acid)
• Nucleic acid
• Nucleotide
• Nitrogenous base
• Cytosine
• Guanine
• Thymine
• Adenine
• Complementary base
• Protein
• mRNA
• tRNA
• Transcription
• Translation
• Codon
• Anti-codon
• Genome
• Chromatin
• Chromosome
• Sex chromosomes
• Autosomes
• Homologous chromosomes
• Genes
• Alleles
• Karyotype
• DNA replication
• Helicase
• DNA Polymerase
• DNA Ligase
• Biodiversity
• Species diversity
• Genetic diversity
• Ecosystem diversity
• Population
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Concept 1: The variation in living things
we see around us is due to DNA.
• All living things have DNA.
• Variations among all organisms are due to DNA.
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Figure 1.1: Life, variety, and
DNA. Questioning: What is
the role of DNA in the variety
of Earth’s organisms? Do
you think it is the only factor?
DNA
What is DNA?
• Deoxyribonucleic acid
• Double-stranded nucleic acid that stores genetic information in the nucleus
• Inherited: passed on to future generations
Differences in DNA result in variations in characteristics and allow organisms to exist in diverse aquatic and terrestrial ecosystems.
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Concept 1: The variation in living things we see around us is due to DNA.
Image credits: yourgenome.org
Example: Brown vs Blonde Hair6
Concept 1: The variation in living things we see around us is due to DNA.
Image from: https://www.researchgate.net/publication/263431247_The_secret_of_a_natural_blond
Summary:
one base pair
difference causes
blonde hair instead
of brown
Example: Sickle Cell Anemia7
Concept 1: The variation in living things we see around us is due to DNA.
Slide from https://www.slideshare.net/ThetSuWin/mutation-and-dna-repair-53021983
Summary:
one base pair difference
in DNA causes sickle cell
anemia (a blood
disease)
Discussion Questions
1. Why is there variation among organisms on Earth?
2. Choose one group of organisms in Figure 1.1 and
describe some of the similarities and differences
between species in that group. Use examples not
already listed in the text.
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Concept 1: The variation in living things we see around us is due to DNA.
Concept 2: DNA is made of many
nucleotides linked together in a specific
order.
• There are two types of nucleic acids:
1) DNA (deoxyribonucleic acid)
2) RNA (ribonucleic acid)
• All living things use one of the two types of nucleic acids
as genetic information.
• Nucleotides are the basic building blocks of nucleic
acids.
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The Structure of DNA
Nucleotides consists of three components:
1) a phosphate group
2) a sugar
3) a nitrogenous base
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Figure 1.2: Nucleotides
are the basic building
blocks of DNA and RNA.
The Structure of DNA (cont’d)
Nitrogenous bases in DNA include:
1) adenine (A)
2) cytosine (C)
3) guanine (G)
4) thymine (T)
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Figure 1.2: Nucleotides are the
basic building blocks of DNA
and RNA.
Concept 2: DNA is made of many nucleotides linked together in a specific order.
The Structure of DNA (cont’d)
Characteristics of the DNA molecule:
• Two strands of nucleotides
• Twisted ladder (double helix)
structure
• Sides of ladder made up of sugar
and phosphate groups
• Rung of ladder is made of two
nitrogenous bases held together by
hydrogen bonds
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
The Structure of DNA (cont’d)
Nitrogenous bases that pair
together are complementary
bases:
• adenine (A) and thymine (T)
• cytosine (C) and guanine (G)
Remember:
Apples in a Tree; Car in a Garage
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Figure 1.3: DNA is found in the nucleus
of a cell. The bases of the nucleotides
pair only in specific ways.
Concept 2: DNA is made of many nucleotides linked together in a specific order.
The Function of DNA
• DNA stores genetic information.
• Parents pass their DNA on to their offspring.
• DNA codes for specific proteins that are essential
for life functions.
• A complete sequence of DNA is called a genome.
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Protein Synthesis: Summary15
Concept 2: DNA is made of many nucleotides linked together in a specific order.
1. Transcription:
• DNA is transcribed into
mRNA
2. Translation:
• Ribosome reads mRNA
• mRNA is translated into an
amino acid sequence
through tRNA
3. End result: protein!
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
https://www.youtube.com/watch?v=oefAI2x2CQM
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Post-video Questions
https://www.youtube.com/watch?v=oefAI2x2CQM
1) Why can’t proteins be made directly from the DNA?
Why is mRNA necessary?
2) Where do transcription and translation occur?
3) What is the role of tRNA?
Protein Synthesis: Transcription18
Concept 2: DNA is made of many nucleotides linked together in a specific order.
1. Transcription:
• Part of DNA is copied into
messenger RNA (mRNA)
transcript
• RNA base pairs:
• adenine – uracil (not thymine)
• guanine – cytosine
• Occurs in nucleus
• Codon: 3-base-pair sequence
in mRNA
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
Protein Synthesis: Transcription19
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Practice:
For the DNA sequences below, write the
corresponding mRNA sequence.
a) TAC CAT TAA CAG TAC GGG (DNA)
AUG GUA AUU GUC AUG CCC (mRNA)
b) TAC ATG GCA ATA CGC GAA (DNA)
AUG UAC CGU UAU GCG CUU (mRNA)
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
Protein Synthesis: Translation20
Concept 2: DNA is made of many nucleotides linked together in a specific order.
2. Translation:
• mRNA leaves nucleus, is
‘read’ by ribosome
• Transfer RNA (tRNA) has
matching anticodon and
amino acid
• Result: amino acid chain
= protein (basically!)
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
Protein Synthesis: Translation21
Concept 2: DNA is made of many nucleotides linked together in a specific order.
ib.bioninja.com.au
Protein Synthesis: Translation22
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Ibiologia.com; Georgia virtual school
Charts can help us determine the corresponding amino acids for mRNA codons.
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https://me.me/i/what-most-people-see-when-they-see-ugg-what-i-9e36c5de02174c5fb431e414cab6398a
Protein Synthesis: Translation
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Charts can help us determine the corresponding amino acids for mRNA codons.
Protein Synthesis: Translation24
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Charts can help us determine the corresponding amino acids for mRNA codons.
https://www.youtube.com/watch?v=LsEYgwuP6ko
Protein Synthesis: Translation25
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Practice:
For the mRNA sequences below, write the corresponding amino acid sequence.
a) AUG GUA AUU GUC ACA CCC (mRNA)
b) AUG UAC CGU UAU GCG CUU (mRNA)
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
Question: Why might both these mRNA sequences start with AUG?
Protein Synthesis: Translation26
Concept 2: DNA is made of many nucleotides linked together in a specific order.
Practice:
For the mRNA sequences below, write the corresponding amino acid sequence.
a) AUG GUA AUU GUC ACA CCC (mRNA)methionine – valine – isoleucine – valine –threonine – proline (met-val-ile-val-thr-pro)
b) AUG UAC CGU UAU GCG CUU (mRNA)methionine – tyrosine – arginine – tyrosine –alanine – leucine (met-tyr-arg-tyr-ala-leu)
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/overview-of-transcription
Question: Why might both these mRNA sequences start with AUG?
Protein Synthesis Summary (copy down)
Step Code Extra Notes
DNA TAC GAT Complementary DNA
strand (the one not used
to make mRNA here)
would be ATG CTA
mRNA AUG CUA U instead of T; codon
tRNA UAC GAU Complementary to
mRNA; anti-codon
Amino
acid
Met – Leu
(Methionine –
Leucine)
Based off mRNA codon
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
The Many Functions of Proteins
(do not memorize)
Proteins do everything that a cell (and thus, a living
thing) needs to function, grow, and reproduce.
This includes:
• Structure
• Growth and repair
• Signalling to other cells or organisms
• Facilitating or catalyzing chemical reactions
• Shuttle substances across cell membrane
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
https://www.youtube.com/watch?v=L5-tKciXEG8&ab_channel=Reactions
The Many Functions of Proteins
(do not memorize)
Cool Proteins:
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Protein type or name Function
Sonic Hedgehog (SHH) Controls stem cell growth in limbs
Keratin Structural: makes up hair, feathers
Actin + tubulin
Clock proteins Detects light; establish circadian cycle
Antibodies Bind to harmful pathogens; help neutralize or
tag for destruction
Hemoglobin In red blood cells, stores oxygen or carbon
dioxide
ATP synthase A ‘turbine’ that harnesses proton gradient to
make ATP
The Many Functions of Proteins
(do not memorize)
Cool Proteins:
• Insulin
• Collagen
• Thrombin
• Neuroreceptors (e.g. for GABAa, dopamine)
• Potassium channel
• Oxytocin
• Histone
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Discussion Questions
1. If the bases on one strand of DNA are ATGGGCTA, what
is the sequence of complementary bases on the other
strand of DNA?
2. Think of an analogy to describe base pairs. Share it with
a classmate.
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Concept 2: DNA is made of many nucleotides linked together in a specific order.
Warm-up (Concept 2 review)
1) What is the name of the 3-letter codes on mRNA? tRNA?
2) If one strand of DNA reads TACTATACT…
a) What is the complementary strand of DNA?
b) What would the code be on its mRNA transcript?
c) What anti-codons would be found on the matching
tRNAs?
d) What is the amino acid sequence of the final protein?
3) Where do transcription and translation take place?
4a) Why do most mRNA transcripts start with AUG?
b) What are the codes that tell a ribosome to stop
translating?
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Concept 3: DNA exists in chromosomes,
which contain thousands of genes.
• During interphase,
DNA exists as
condensed fibers
called chromatin.
• During mitosis, DNA is
found in a very
condensed form
called chromosomes.
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Figure 1.4: DNA is part of chromatin
fibre, which condenses to form
chromosomes.
Examining Chromosomes: The
Karyotype
Karyotype: a photograph of pairs of homologous chromosomes in a cell
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Figure 1.6: This is a human
karyotype. The chromosome pairs
are arranged and numbered in
order of their length, from longest
to shortest. The sex chromosomes
are placed last.
Chromosomes Are Paired
• 46 chromosomes in human
somatic (body) cells
• Half from father, half from mother
• 23 pairs of chromosomes in total:
o One pair: sex chromosomes (X
and Y chromosomes)
o Other 22 pairs: autosomes
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Homologous Chromosomes Contain
Alleles
Homologous chromosome: a chromosome that contains the same sequence of genes as another chromosome
• Inherit one set from each parent
• Homologous chromosomes are not identical…they may have different alleles
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Figure 1.5: Homologous
chromosomes have several
characteristics in common,
but they are not identical.
Homologous Chromosomes Contain Alleles
(cont’d)
• Gene: a part of a chromosome that governs the expression of a trait and is passed on to offspring
• Allele: one of multiple different forms of the same gene; usually represented by capital/lowercase letters
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Gene Examples (simplified for illustrative purposes)
Allele Examples
Blondeness gene Brown hair, blonde hair
Eye colour gene Blue eyes, brown eyes
Lactase geneLactose tolerant, lactose
intolerant
Homologous Chromosomes Contain Alleles
(cont’d)
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Image: https://slideplayer.com/slide/15085231/, https://www.mansfieldct.org/Schools/MMS/staff/hand/genchromoandgene.htm
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
https://www.youtube.com/watch?v=pv3Kj0UjiLE (stop at 4:35)
Review: mitosis
In mitosis, each cell ends up with
chromosomes that are identical to the
parent cell (one copy of each
homologous chromosome)
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Source: https://slideplayer.com/slide/4787428/
Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Review: meiosis + sexual reproduction
• Chromosome
number halved
• Independent
assortment at
metaphase I plate:
only one of each
homologous
chromosome ends
up in gamete
• Thus: random
inheritance of traits
from parents
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Image: https://www.mrgscience.com/topic-33-meiosis.html
Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Preview: meiosis + sexual reproduction
Biological mother
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Images: https://www.thoughtco.com/allele-a-genetics-definition-373460; https://www.cbsnews.com/pictures/human-eggs-9-fascinating-facts/
Biological father 100% chance of
allele “a”
100% chance of
allele “A”
MeiosisFertilization
(one chromosome from each parent)
Parental DNA Gametes Offspring
DNA
Concept 3: DNA exists in chromosomes, which contain thousands of genes.
100%
Preview: meiosis + sexual reproduction
Biological mother
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Images: https://www.thoughtco.com/allele-a-genetics-definition-373460; https://www.cbsnews.com/pictures/human-eggs-9-fascinating-facts/
Biological father 50% chance of
allele “A”; 50% of
allele “a”
100% chance of
allele “A”
MeiosisFertilization
(one chromosome from each parent)
Parental DNA Gametes Offspring
DNA
50%
50%
Concept 3: DNA exists in chromosomes, which contain thousands of genes.
Preview: meiosis + sexual reproduction
Biological mother
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Images: https://www.thoughtco.com/allele-a-genetics-definition-373460; https://www.cbsnews.com/pictures/human-eggs-9-fascinating-facts/
Biological father 50% chance of
allele “A”; 50% of
allele “a”
50% chance of
allele “A”; 50% of
allele “a”
MeiosisFertilization
(one chromosome from each parent)
Parental DNA Gametes Offspring
DNA
25%
Concept 3: DNA exists in chromosomes, which contain thousands of genes.
25%
25%
25%
Discussion Questions
1. Describe the relationships among chromatin,
a chromosome, DNA, and a gene.
2. Make an analogy that helps explain homologous
chromosomes.
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
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Concept 3: DNA exists in chromosomes, which contain thousands of genes.
https://www.youtube.com/watch?v=8m6hHRlKwxY
Concept 4: The structure of DNA is important
to passing on genetic information.
• A cell replicates its DNA
once in the cell cycle.
• DNA is passed on to
daughter cells, and to
offspring, influencing all
heritable characteristics
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https://www2.le.ac.uk/projects/vgec/highereducation/topics/cellcycle-mitosis-meiosis
G1 :
• Growth
• Performs regular cell functions
S: DNA replication
• DNA replicated: one → two
sister chromatids per
chromosome
G2 :
• Double-checking
Mitosis/cytokinesis: cell divides
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https://www2.le.ac.uk/projects/vgec/highereducation/topics/cellcycle-mitosis-meiosis
Cell Cycle Review
Concept 4: The structure of DNA is important to passing on genetic information.
DNA Replication
• Replication: a process that
makes identical copies of a DNA
molecule
• Cytosine pairs with Guanine
• Adenine pairs with Thymine
• Each new DNA molecule consists
of an original strand and a new
strand.
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Concept 4: The structure of DNA is important to passing on genetic information.
Figure 1.7: During DNA replication, two
molecules of DNA are made from one. The
resulting new molecules are identical to the
original. Each new molecule contains one
original strand of DNA (shown here in blue) and
one new strand (shown in red).
DNA Replication (cont’d)
Review (transcription/translation):
• DNA is used to produce RNA.
• RNA is then translated to produce a protein.
• The sequence of bases in the DNA molecule determines
the specific sequence of amino acids in the protein
molecule.
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Concept 4: The structure of DNA is important to passing on genetic information.
Figure 1.8: Genetic information
passes from the genes (DNA) to an
RNA copy of the gene, and the RNA
copy directs the sequential assembly
of a chain of amino acids to produce
a protein.
DNA Replication (cont’d)
DNA replication is complex, involving many enzymes
(proteins!), such as:
• Helicase: unwinds, unzips DNA strand
• DNA Polymerases: complementary base pairing, double-
checking
• DNA Ligases: rezips DNA strand
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Concept 4: The structure of DNA is important to passing on genetic information.
DNA Replication (cont’d)53
Concept 4: The structure of DNA is important to passing on genetic information.
Discussion Questions
1. Explain how the structure of DNA is related to how
genetic material is passed from one generation to the
next.
2. How are genes involved in the production of proteins?
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Concept 4: The structure of DNA is important to passing on genetic information.
Concept 5: The different genetic make-up of
organisms is reflected in the diversity of life.
• Biodiversity exists at three different levels:
1) species diversity
2) genetic diversity
3) ecosystem diversity
NOTE: Concept 5 is FYI only: not testable!
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Species Diversity
Species diversity: variety and abundance of
species in a given area
• Species: group of organisms that can interbreed
in nature and produce fertile offspring
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Concept 5: The different genetic make-up of organisms is reflected in the diversity of life.
Genetic Diversity
Genetic diversity: variety of inherited traits within a
species; is due to mutations in genes.
• Gene pool: genetic diversity within a population
• Population: members of the same species living in
the same geographical area at the same time
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Concept 5: The different genetic make-up of organisms is reflected in the diversity of life.
Ecosystem Diversity
Ecosystem diversity: variety of ecosystems in the
biosphere
• Ecosystems are made up of biotic (living) factors
and abiotic (non-living) factors.
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Concept 5: The different genetic make-up of organisms is reflected in the diversity of life.
Discussion Questions
1. Describe the differences among the three types of
biodiversity.
2. Explain how variation in genes is related to all three types
of biodiversity.
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Concept 5: The different genetic make-up of organisms is reflected in the diversity of life.
“Test Outline”
Concept 1:
• Why is DNA related to diversity?
Concept 2:
• Nucleotides
• DNA structure
• Base pair rules: DNA/RNA
• DNA → mRNA (→ tRNA) → amino acid sequence/protein
• Transcription and translation: purpose, location, and basics of how they work
• Overall purpose of proteins
Concept 3:
• How DNA is packaged differently depending on stage of cell cycle
• Karyotype
• Homologous chromosomes
• Sex chromosomes vs autosomes
• Alleles, genes
Concept 4:
• (Cell cycle: should be review)
• DNA replication:
• Complementary base pairing
• Enzymes (helicase, DNA polymerase, DNA ligase)
• General steps
Concept 5: not testable
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