Biology
DNA: Is it all useful?
Even though the structure of DNA was first described in the 1950s, there is
still much to understand about this twisted ladder.
In this lesson you will investigate the following:
• What is DNA?
• How does DNA control the characteristics of an organism?
• Why is RNA important for DNA to do its job?
Are you ready to CrAck the GeneTic code?
This is a print version of an interactive online lesson.
To sign up for the real thing or for curriculum details
about the lesson go to www.cosmosforschools.com
Introduction: DNA (P1)
DNA is the molecule that holds all the information about every living creature. It is this information that acts like the plans of
a house – it’s the code that decides the shape and functions of every living thing as it grows.
While we can work out what a lot of the DNA code is for, whether it is to hold the design of an eye or a leg, there are vast amounts
of DNA inside plants, insects, animals, and us, which we just can’t decipher.
Scientists are still arguing about what this is for. Some say that this DNA is “junk”, with no real purpose and only there to pad out
the genome.
But others say that this “junk” DNA is itself a code, our genome’s equivalent of a high-level operating system like you find in a
computer.
Recently, it seemed like we had an answer when a worldwide project looked at every one of the three billion letters of DNA that
makes up the human genome. The results found that 80% of our DNA code was “functional”. Sometime, somewhere, one cell or
another in the body was reading almost every bit of the genome.
But even then, some scientists said that just because the DNA code was being read, that didn’t mean it was being useful.
The problem for scientists is that they can’t check for sure what this “junk” DNA does by taking it out of people. But recently
scientists have discovered a new plant in a pond that may give us a better idea of which side of the argument over this “junk” DNA is
right.
The plant, the bladderwort, has almost no “junk” DNA; every piece of its DNA has a purpose that we can work out. And the plant
does just fine. Does that mean our “junk” DNA has no purpose, too? Not necessarily.
Some scientists think that having extra DNA helps more complex animals and plants develop more advanced through evolution
because they have more DNA to add into their functioning DNA code.
Read or listen to the full Cosmos magazine article here.
The carnivorous bladderwort, with its alien-like insect-traps (above right), has virtually no "junk" DNA. Credit: Getty
Images and Enrique Ibarra-Laclette, Claudia Anahí Pérez-Torres and Paulina Lozano-Sotomayor
Question 1
Sequence: One useful way to organise information is to group objects by size. This is especially the case in science, in which the
relative size of an object can provide useful information about how the objects relate to each other.
Sequence the following components of a biological organism from smallest to largest by numbering them from 1 (smallest) to 9
(largest).
cell; organism; nucleus; chromosome; DNA molecule; digestive system; liver organ; liver tissue; protein
9
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Gather: DNA (P1)
What is DNA?
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Credit: Stated Clearly / YouTube.
DNA is often called the "blueprint of life". Like the blueprint for building a complex skyscraper, the DNA of an organism contains all
the details about what should be included, the order in which these parts should be assembled and how they should work
together.
But DNA is more than just a set of instructions that is used once then thrown away. The DNA blueprint remains in every living cell
and continues to provide information about how the cell must function. It does this by ensuring that only the proteins that are
required for the particular cell type are produced.
Question 1
Define: What does DNA stand for?
Question 2
Recall: What is meant by DNA being a "blueprint for life"?
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Credit: Marshall Thompson / YouTube.
Question 3
Deduce: The above clip states that the human genome consists of 100,000. However, more recent estimates have revised this
number down to between 20,000 and 25,000 genes. Propose why this number has changed over time.
Hint: The above clip was produced before 2001, the year that the Human Genome Project was completed.
Question 4
Label: The following illustration demonstrates the relationship between a cell, chromosomes in the nucleus, a DNA molecule and
one of the genes it encodes. Draw lines in the sketchpad to match the name of each component to its visual representation.
Question 5
Categorise: Use the information in the media clip to help you decide whether the statements in the table below apply
chromosomes, gene sequences or DNA molecules. Indicate your choices by typing “chromosomes”, “genes” or “DNA” into the
second column.
Statement
Relates to...
Codes for different proteins
Double stranded in the shape of a double helix
Holds an assortment of genes
Acts as blueprint for living things
Humans have 23 from each parent
Made up of four nucleotides (A, T, G, C)
DNA (or deoxyribonucleic acid) is the molecule that carries the genetic information in all living things. It belongs to a class of
molecules called the nucleic acids, which are polymers of nucleotide units. Each nucleotide consists of three components:
A phosphate molecule
A five-carbon sugar molecule (deoxyribose in the case of DNA)
A nitrogenous base, one of: cytosine (C), guanine (G), adenine (A) or thymine (T)
The backbone of the polynucleotide is a chain of sugar and phosphate molecules, where each of the sugar groups in this sugarphosphate backbone is linked to one of the four nitrogenous bases.
Each DNA molecule consists of two complementary strands that twist around each other to form a double-stranded helix. The
nitrogenous bases link across the two strands very specifically such that cytosine (C) on one strand only base pairs with guanine (G)
on the other and adenine (A) on one strand only base pairs with thymine (T) on the other.
Genes are the functional units of genetic information in cells. A gene consists of a specific sequence of nucleotides which codes for
a specific protein. A human being has 20,000 to 25,000 protein coding genes located on 46 chromosomes (23 pairs). These genes
along with all the in-between bits of DNA are known, collectively, as the human genome.
Question 6
Select: Draw a circle around one nucleotide in the following representation of a single strand of DNA.
Note: The dark blue "P" circles represent phosphate molecules while navy blue "S" pentagons represent sugar molecules.
Question 7
Analyse: The following sequence of nitrogenous bases was found in a section of DNA:
AAGGCTTGC
Write the sequence of bases that would be found in the complementary strand.
Question 8
Calculate: If a double stranded molecule of DNA has 30% guanine (G) nitrogenous bases in it, determine:
1. The percentage of cytosine (C) nitrogenous bases
2. The percentage of thymine (T) nitrogenous bases
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Process: DNA (P1)
What is RNA?
Like DNA, RNA (or ribonucleic acid) is a type of nucleic acid and
is a polymer of nucleotides.
Its nucleotides, however, are different from those of DNA. RNA
contains the
sugar ribose (instead of deoxyribose) and uracil (instead of
thymine) as one of its nitrogenous bases. It is also shorter and
single-stranded.
One type of RNA, called messenger ribonucleic acid, or mRNA
for short, is a short lived molecule that exists to carry a small
portion of genetic information from the chromosomal DNA to
the part of the cells which manufactures proteins. In contrast,
DNA has a long life span, is much larger and carries the
instructions for making all possible proteins needed by the cell.
Question 1
Compare: Complete the Venn diagram below to summarise the similarities and differences between DNA and RNA. Use each of the
following terms:
adenine; cytosine; deoxyribose; double-stranded; guanine; nucleic acid; nucleotides; phosphate; ribose; singlestranded; thymine; uracil
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Credit: TED-Ed / YouTube.
Question 2
Summarise: To summarise your understanding of how the following key terms are linked, create a concept map on paper or your
computer using the following terms. Don't forget to write short phrases above the arrows to show your links.
organism; cells; chromosomes; genes; DNA molecule; nucleotides; mRNA; proteins; tissue; organ
Upload your concept map below.
Drag and drop file here to begin upload or
Question 3
Extend: In your own words, explain how some cells "know" to be part of muscle tissue and some cells "know" to be part of bone
tissue within the one organism.
Question 4
Relate: Use the information in this cartoon to explain how DNA, mRNA and protein are related.
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Apply: DNA (P2)
Extracting DNA from Strawberries
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Credit: Learning Solutions / YouTube.
Background Information
Strawberries are a very good source of DNA as they contain seven different types of chromosomes, and have eight copies of each of
these. This means that they contain a lot of DNA in each cell.
Materials
Small zip lock bag
1 strawberry
2 teaspoons DNA Extraction Buffer (see below)
Square of gauze
Funnel
Ice cold ethanol or isopropyl rubbing alcohol
Test tube with lid
Long cocktail stick
Black cardboard
DNA Extraction Buffer: Makes 500 mL (enough for 20 extractions, to be made by your teacher)
50 mL Shampoo (or 25 mL liquid dish washing detergent)
7.5 g kitchen salt (about 1 teaspoon)
450 mL water
Method
1. Wash the strawberry and remove the green leaves (called sepals).
2. Place the strawberry in a zip lock bag, seal it and crush it with your hand.
3. Add 2 teaspoons of the DNA Extraction Buffer to the bag, seal it and squeeze to mix for about 1 minute.
4. Place a funnel in the test tube. Place the strip of gauze in the funnel.
5. Pour the strawberry buffer mixture into the funnel so it is filtered into the test tube.
6. Carefully pour ice cold ethanol into the tube until it is about half full. The ethanol will form a layer on top of the liquid that
came through the gauze. DO NOT SHAKE.
7. Keep the tube still and hold it at eye level. Watch what happens and record your observations in the project space below.
8. Scoop out the DNA carefully using the cocktail stick.
9. Spread the DNA out on a piece of black card to view it and record your observations in the project space below.
Note:
1. Crushing the strawberries breaks open the tissue to allow the extraction buffer to access more cells. The soap in the extraction buffer
breaks down the cell membranes and the salt makes the DNA molecules stick together and separate from the proteins that are also
released from the cells.
2. The gauze will catch cell debris and unmashed pieces of fruit. The DNA will pass through the gauze into the test tube.
3. DNA is not soluble in alcohol. The rest of the mixture that passed through the gauze will gradually dissolve into the alcohol, leaving
the DNA separate. It precipitates and will appear as a long, rope-like DNA molecule in the alcohol.
Question 1
Apply: From what you have learned so far in this lesson, write some additional information for the Background section of this
experiment to describe the role of DNA in a cell.
Question 2
Collect: Use the project space below to illustrate your results and observations during and after conducting this experiment. You
might like to include photos, sketches and/or a table of observations.
Question 3
Relate: What possible benefits are there in being able to isolate DNA from an organism?
Question 4
Explain: What roles do the DNA extraction buffer and alcohol play in this experiment?
Question 5
Hypothesise: Do you think DNA extracted from a human would look the same as the DNA extracted from a strawberry? What
might the similarities and differences be?
Question 6
Conclude: Outline what you have observed and learned about DNA by conducting this experiment.
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Career: DNA (P2)
Not many people get to experiment with DNA soup as part of their job. For Dr Marnie Blewitt, playing around with those little
white threads of DNA is her favourite part of the day.
As a head scientist at the Walter and Eliza Hall Institute, Marnie
spends a good part of her workday experimenting in her lab and
helping her staff and students with their experiments, too. She
also gets to play around with dry ice and liquid nitrogen, grow
stem cells, and of course, extract DNA from cells.
To get to the DNA, Marnie must first burst open the cells, get rid
of the proteins inside them, and then separate the DNA from
the soupy remains. Each burst cell releases about 2 metres of
the tiny white threads of DNA ready for testing – and even
though it’s a procedure she’s carried out thousands of times,
she still gets excited about doing it.
Marnie works in epigenetics. Epigenetics is the study of how
genes are switched on and off so that the level of gene activity is
changed without changing the DNA sequence. Marnie hopes
that by studying epigenetics, she’ll be able to understand what
part it plays in various diseases.
Marnie has always been interested in how our bodies work, and
what happens when something goes wrong and we fall ill.
Growing up, she thought she wanted to be a doctor or a vet –
until she did her work experience at the end of Year 10. She
quickly learned she couldn’t stand the sight or smell of blood! As
a scientist, though, Marnie can still help sick patients by looking
at the genetic source of the problem.
Credit: L'Oréal Australia
When she isn’t dishing up DNA soup in the lab, Marnie loves to
cook at home and grow vegetables in her backyard.
Question 1
Argue: ​In this lesson, you have learned that genes code for proteins; however, the role of non-coding "junk DNA" is still poorly
understood. Recently the Supreme Court in Australia reached a decision to prevent human genes from being patented by private
companies.
Construct two arguments, one for and the other against, whether "junk DNA" should be patented.
Cosmos Live Learning team
Education director: Daniel Pikler
​Education editor: Bill Condie
Art director: Robyn Adderly
Profile author: Megan Toomey
​ esson authors: Anne-Lise Haugen, Deborah Taylor and Hayley Bridgwood
L
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