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 ofa 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 amountsof 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 outthe 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 acomputer.

Recently, it seemed like we had an answer when a worldwide project looked at every one of the three billion letters of DNA thatmakes up the human genome. The results found that 80% of our DNA code was “functional”. Sometime, somewhere, one cell oranother 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 recentlyscientists 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 isright.

The plant, the bladderwort, has almost no “junk” DNA; every piece of its DNA has a purpose that we can work out. And the plantdoes 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 evolutionbecause they have more DNA to add into their functioning DNA code.

Read or listen to the full Cosmos magazine article here.

For best results when printing activities, enable your web browser to print background colours and images.

The carnivorous bladderwort, with its alien-like insect-traps (above right), has virtually no "junk" DNA. Credit: GettyImages 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 therelative 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

99

Gather: DNA (P1)

What is DNA?

Credit: Stated Clearly / YouTube.

Loading...

DNA is often called the "blueprint of life". Like the blueprint for building a complex skyscraper, the DNA of an organism contains allthe details about what should be included, the order in which these parts should be assembled and how they should worktogether.

But DNA is more than just a set of instructions that is used once then thrown away. The DNA blueprint remains in every living celland continues to provide information about how the cell must function. It does this by ensuring that only the proteins that arerequired 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"?

Credit: Marshall Thompson / YouTube.

Loading...

Question 3

Deduce: The above clip states that the human genome consists of 100,000. However, more recent estimates have revised thisnumber 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 andone 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 applychromosomes, gene sequences or DNA molecules. Indicate your choices by typing “chromosomes”, “genes” or “DNA” into thesecond 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 ofmolecules 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 sugar-phosphate 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. Thenitrogenous 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 fora specific protein. A human being has 20,000 to 25,000 protein coding genes located on 46 chromosomes (23 pairs). These genesalong with all the in-between bits of DNA are known, collectively, as the human genome.

For best results when printing activities, enable your web browser to print background colours and images.

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:

A A G G C T T G C

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

Process: DNA (P1)

What is RNA?Like DNA, RNA (or ribonucleic acid) is a type of nucleic acid andis a polymer of nucleotides.

Its nucleotides, however, are different from those of DNA. RNAcontains thesugar ribose (instead of deoxyribose) and uracil (instead ofthymine) as one of its nitrogenous bases. It is also shorter andsingle-stranded.

One type of RNA, called messenger ribonucleic acid, or mRNAfor short, is a short lived molecule that exists to carry a smallportion of genetic information from the chromosomal DNA tothe part of the cells which manufactures proteins. In contrast,DNA has a long life span, is much larger and carries theinstructions 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 thefollowing terms:

adenine; cytosine; deoxyribose; double-stranded; guanine; nucleic acid; nucleotides; phosphate; ribose; single-stranded; thymine; uracil

Credit: TED-Ed / YouTube.

Loading...

For best results when printing activities, enable your web browser to print background colours and images.

Question 2

Summarise: To summarise your understanding of how the following key terms are linked, create a concept map on paper or yourcomputer 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 bonetissue within the one organism.

Question 4

Relate: Use the information in this cartoon to explain how DNA, mRNA and protein are related.

Apply: DNA (P2)

Extracting DNA from Strawberries

Credit: Learning Solutions / YouTube.

Loading...

Strawberries are a very good source of DNA as they contain seven different types of chromosomes, and have eight copies of each ofthese. This means that they contain a lot of DNA in each cell.

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

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.

Background Information

Materials

Method

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 thatcame 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 thisexperiment 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. Youmight 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?

For best results when printing activities, enable your web browser to print background colours and images.

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? Whatmight the similarities and differences be?

Question 6

Conclude: Outline what you have observed and learned about DNA by conducting this experiment.

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 littlewhite threads of DNA is her favourite part of the day.

As a head scientist at the Walter and Eliza Hall Institute, Marniespends a good part of her workday experimenting in her lab andhelping her staff and students with their experiments, too. Shealso gets to play around with dry ice and liquid nitrogen, growstem cells, and of course, extract DNA from cells.

To get to the DNA, Marnie must first burst open the cells, get ridof the proteins inside them, and then separate the DNA fromthe soupy remains. Each burst cell releases about 2 metres ofthe tiny white threads of DNA ready for testing – and eventhough 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 howgenes are switched on and off so that the level of gene activity ischanged without changing the DNA sequence. Marnie hopesthat by studying epigenetics, she’ll be able to understand whatpart it plays in various diseases.

Marnie has always been interested in how our bodies work, andwhat 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. Shequickly learned she couldn’t stand the sight or smell of blood! Asa scientist, though, Marnie can still help sick patients by lookingat the genetic source of the problem.

When she isn’t dishing up DNA soup in the lab, Marnie loves tocook at home and grow vegetables in her backyard.

Credit: L'Oréal Australia

Question 1

Argue: In this lesson, you have learned that genes code for proteins; however, the role of non-coding "junk DNA" is still poorlyunderstood. Recently the Supreme Court in Australia reached a decision to prevent human genes from being patented by privatecompanies.

Construct two arguments, one for and the other against, whether "junk DNA" should be patented.

For best results when printing activities, enable your web browser to print background colours and images.

Cosmos Live Learning team

Education director: Daniel PiklerEducation editor: Bill CondieArt director: Robyn Adderly

Profile author: Megan ToomeyLesson authors: Anne-Lise Haugen, Deborah Taylor and Hayley Bridgwood