1-1: how does an understanding of dna help us investigate ......1-1: how does an understanding of...

1-1: How does an understanding of DNA help us investigate living things?

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.

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

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.

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?

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.

Concept 1: The variation in living things we see around us is due to DNA.

Image credits: yourgenome.org

Example: Brown vs Blonde Hair6

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

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.

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.

The Structure of DNA

Nucleotides consists of three components:

1) a phosphate group

2) a sugar

3) a nitrogenous base

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)

Figure 1.2: Nucleotides are the

basic building blocks of DNA

and RNA.

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

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

Figure 1.3: DNA is found in the nucleus

of a cell. The bases of the nucleotides

pair only in specific ways.

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.

Protein Synthesis: Summary15

1. Transcription:

• DNA is transcribed into

2. Translation:

• Ribosome reads mRNA

• mRNA is translated into an

amino acid sequence

through tRNA

3. End result: protein!

https://www.youtube.com/watch?v=oefAI2x2CQM

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

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

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)

Protein Synthesis: Translation20

2. Translation:

• mRNA leaves nucleus, is

‘read’ by ribosome

• Transfer RNA (tRNA) has

matching anticodon and

amino acid

• Result: amino acid chain

= protein (basically!)

ib.bioninja.com.au

Ibiologia.com; Georgia virtual school

Charts can help us determine the corresponding amino acids for mRNA codons.

https://me.me/i/what-most-people-see-when-they-see-ugg-what-i-9e36c5de02174c5fb431e414cab6398a

Protein Synthesis: Translation

https://www.youtube.com/watch?v=LsEYgwuP6ko

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)

Question: Why might both these mRNA sequences start with AUG?

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)

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

Met – Leu

(Methionine –

Leucine)

Based off mRNA codon

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

https://www.youtube.com/watch?v=L5-tKciXEG8&ab_channel=Reactions

(do not memorize)

Cool Proteins:

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

(do not memorize)

Cool Proteins:

• Insulin

• Collagen

• Thrombin

• Neuroreceptors (e.g. for GABAa, dopamine)

• Potassium channel

• Oxytocin

• Histone

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.

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?

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.

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

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

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

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

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)

Image: https://slideplayer.com/slide/15085231/, https://www.mansfieldct.org/Schools/MMS/staff/hand/genchromoandgene.htm

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)

Source: https://slideplayer.com/slide/4787428/

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

Image: https://www.mrgscience.com/topic-33-meiosis.html

Preview: meiosis + sexual reproduction

Biological mother

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

Biological mother

allele “A”; 50% of

allele “a”

100% chance of

allele “A”

Biological mother

allele “a”

50% chance of

allele “a”

1. Describe the relationships among chromatin,

a chromosome, DNA, and a gene.

2. Make an analogy that helps explain homologous

chromosomes.

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

https://www2.le.ac.uk/projects/vgec/highereducation/topics/cellcycle-mitosis-meiosis

• Growth

• Performs regular cell functions

S: DNA replication

• DNA replicated: one → two

sister chromatids per

chromosome

• Double-checking

Mitosis/cytokinesis: cell divides

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.

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.

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

DNA Replication (cont’d)53

1. Explain how the structure of DNA is related to how

genetic material is passed from one generation to the

2. How are genes involved in the production of proteins?

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!

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

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

Ecosystem Diversity

Ecosystem diversity: variety of ecosystems in the

biosphere

• Ecosystems are made up of biotic (living) factors

and abiotic (non-living) factors.

1. Describe the differences among the three types of

biodiversity.

2. Explain how variation in genes is related to all three types

of biodiversity.

“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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