DNA - What it is and What it does

DNA is made up of four different molecules. It is easiest to think of these molecules as lego blocks. In the diagram below there are two towers of Lego, each making the same shape and of the same height, but using only the same four colours blocks. However, those four blocks are used in different amounts and different orders.

DNA is made up of the four blocks A, T, C and G. These letters are simply taken from the names of these four blocks:

Adenine
Thymine
Cytosine
Guanine

The technical name for these molecules is nitrogenous bases, but that isn’t really that important to your understanding of DNA.

This is a simplified diagram of DNA, it is a ladder, where each of the rungs are made up of two of the four nitrogenous bases (A, T, C, G). The above is one stand of DNA, DNA live in pairs, twisted around each other (this is called a double helix shape).

You may have noticed that in the two above diagrams, I have only represented Adenine paired with Thymine and Cytosine with Guanine, this is not a coincidence.

These nitrogenous bases bond in pairs within DNA and only these pairs. No matter where Adenine is found within DNA, it will always be paired with Thymine. This is simply because of the different atoms within the bases and their position within the molecule of the base. In other words, due to their shape, the molecules must form the A-T and C-G pairs. This can be seen well in the video on this page:

http://www.dnai.org/a/index.html

Click on - Finding the Stucture>Pieces of the Puzzle>Watson’s Base Pairing

After watching that video, I recommend watching the video under

Putting it together>The DNA double helix

The website above contains wonderful videos, interviews and information about the discovery of DNA and DNA replication, which I recommend perusing if you are interested, at least to watch the videos.

The rule of this paired bonding means that if you take one stand of DNA and ‘unzip’ it – slice it down the middle – you know exactly what the other half of the strand looks like.


If the DNA of all life on earth is made up of ATCG, why do we look so different? This is because the order of the nucleic acids within DNA is very important. In the English language, we have 26 letters which combine to make hungered of thousands of words. These words can be used to write the instruction manual for Monopoly or for how to set up an Xbox. The same letters and words are used, but because of their order, the outcomes are very different. The same goes for DNA, the order of the nitrogenous bases in the ladder of DNA is very important.

In order for the cell to operate the instructions within the DNA need to be read. The problem with this is that the DNA needs to be read outside the nucleus, in the cytoplasm. However, the DNA needs to be protected and is therefore, not allowed outside of the nucleus. Imagine that the nucleus is a library and the DNA is a very important, very rare reference book, which everyone needs to use. Therefore, the DNA is not allowed outside of the library. However, you are allowed to photocopy whatever pages in the DNA book you need. This is how DNA works, it is not allowed out of the nucleus, but copies of sections of DNA are allowed.

So how do our cells photocopy DNA? This is where we introduce DNA’s cousin – RNA. RNA is different to DNA in three important ways.

1. RNA comes only in single strands, not double

2. Instead of having the nitrogenous base Thymine, RNA replaces T with U – Uracil

3. RNA is not as important as DNA, it is simply a copy and therefore, can be taken out of the nucleus, used and then disposed of.

In understanding how DNA is copied (or Transcribed, the technical term), I will explain it in the most simplified way that I can.

When the DNA needs to be copied, a piece of blank RNA comes into the nucleus of the cell from the cytoplasm. The DNA is then ‘unzipped’, this means that the DNA is unwound from its helix shape and then each strand is separated from its partner. The RNA then moves in between the two separated pieces. An enzyme (the worker ant of the cell, I’ll talk more about them in a later blog), then reads one strand of the DNA and copies the corresponding base onto the RNA. This is the best example of why it is important for the bases of DNA to only have one partner.

Once the RNA has been ‘written’ on by the enzyme, it leaves the cell whilst the DNA ‘zips’ back up and whines back into the double helix shape. Once the RNA is in the cytoplasm, another enzyme of a different kind attaches to the RNA. This enzyme is designed to read the RNA and follow its instructions, this process is known as translation. Every three bases are read as one ‘word’ (a codon). These words correspond to 20 different types of amino acids. Amino acids are the building blocks of proteins. Proteins can become many different things, messengers (for example, hormones such as testosterone), enzymes and structural formations inside of cells. Proteins can control cell growth, and ultimately how we appear, our hair colour, height etc. There are transporters within the cytoplasm which carry the different types of amino acids, they each match up with the ‘words’ on the RNA until a chain of amino acids is created, this chain becomes a protein.


A fantastic video of translation is found at: http://www.dnai.org/a/index.html
Under - Reading the Code>Putting it Together>Translation

To sum up the important information which I have relayed to you:

DNA is the instruction manual
> RNA messenger
> Proteins leaders of action
> Enzymes and biological chemicals do the work
= growth and development

I hope that this has been informative, if you have any questions, corrections or comments, please either comment on this blog or email me at:

spottedlabcoat@gmail.com

-Bethany

Natural Selection

Natural selection is one of those terms which is thrown around a lot by people in the scientific and lay community alike, however many people are not aware of exactly what natural selection is or how it works. Not only this, but there are some people who believe that natural selection is something which happens ‘out there’ in nature, and doesn’t really affect us directly. I will show you some of the ways in which natural selection does affect our everyday life and of course, talk to you about natural selection in general.

Natural selection was first accredited to have been ‘discovered’ by Charles Darwin, the man who made the link between humans and primates, telling the world that we evolved from our hairy cousins. Darwin studied finches on the Galapagos Islands and was able to come up with the theory of natural selection. However, I will get to the finches later.

If you have a population of rabbits (a population is a group of the same species of animals, such as a herd of cows or school of salmon), within that population you will find white rabbits, brown rabbits and black rabbits. If we assume that all the rabbits are the same, they are all the same size, they run at the same speed and all have perfect eye sight, then the only thing which is different is pure luck and fur colour. During spring and summer, the surroundings of the rabbits are green, which means that all the rabbits stand out equally, no matter the colour of their fur. It is just as easy to see and eat a white rabbit (you know, if you are a hawk) as it is to see and eat a brown rabbit.

However, during winter, the ground is covered with snow; this means that the white rabbits are much harder to see than the black or brown rabbits. Therefore, the black and brown rabbits are much more likely to get eaten by the hawk, and thus, we have what is called a Selective Pressure. A selective pressure is a change in the environment which causes one organism (or rabbit) to be ‘fitter’ than the other. The phrase ‘survival of the fittest’ is one which many people associate with natural selection. It means that not only those organisms which are strong and fit survive, but those who ‘fit’ their environment survive, those with camouflage, or able to dig in the sand (if they live in the dessert). So during winter, the white rabbits are the ‘fittest’, resulting in more of the black and brown rabbits being eaten.

After winter is over, the population of rabbits looks a little more like this:



During winter, less of the white rabbits got eaten, so more of the white rabbits were able to breed and have babies. While more of the black and brown rabbits got eaten, and a few survived due to pure luck. As you can see, the overall fur colour of the population has changed dramatically. This is natural selection at work.

Natural selection is not stationary, just because a population changed in some way, doesn’t mean that it cannot change again. If there were a fire for example, the black rabbits would camouflage very well in the soot covered environment – thus leading to an increase in black rabbits.

Now to the finches I mentioned earlier.

The Galapagos Islands were once one large land mass, many years ago, the land mass broke up into islands, and those islands began to float away from each other. When the land mass broke up, some animals were trapped on the islands, and as the distance between the islands grew, travel between them became harder and harder for flying and swimming animals. The type of plants found on these islands began to change due to changes in position, which led to changes in climate (a selective pressure!). Because of the change in vegetation, some finches were better suited to eating seeds, while others insects, depending on their beak shape. Just as the white rabbits were more suited to winter. Over time, the shape of the beaks of the finches changed dramatically between the island species. This can be seen well in the picture below.

Picture from here: http://www.cs.helsinki.fi/u/ssmoland/rpg/planeettojen_suunnittelu/latex_sorsa/

Darwin observed these differences, as well as the differences in vegetation, and came up with the theory of natural selection. One of the most interesting parts about this is that one species of finch actually uses sticks to reach the grubs within tree bark – it will even break the stick into small lengths if needed. While we accept that for a primate to use a tool is pretty ordinary – for a bird to use a stick, considering their small brain size - it’s amazing!

This video talks about Darwin's Finches and it also shows the Tool Using Finch at work at time 1:54. Clicking on the YouTube logo will take you back to the original video.

How is natural selection all around us?

When you become sick, sometimes that sickness is caused by bacteria(germs). To kill those bacteria, you take a course of antibiotics. If you do not finish that course of antibiotics, even if you feel better, you haven’t killed all the bacteria; you have left behind the lucky and more ‘fit’ bacteria. This is why it is important to finish a full course of antibiotics, because you need to make sure that you kill all of the bacteria, otherwise they may just come back stronger. I will address exactly how bacteria can come back stronger in my next post, but now, on to fish.

When you go fishing, you must throw back fish which are not of a certain length. This means that more large fish of one species are taken out of their population, leaving behind the smaller fish. Over time this means that the maximum size of fish has become smaller. Why is this problem? Because fish need to breed, and when they do, they need space inside themselves to store eggs. If fish in general are smaller than they used to be, then they cannot store as many eggs as normal. The result of this is that fish populations cannot become as large as they used to be, because they cannot breed in the numbers which they did before.

For example:

I go out and I hunt only the big fish in a population of 100. This leaves 50 smaller fish, some fish as babies and some are just small adults. If I stop hunting, then the population will eventually return to 100 fish. If I then hunt the big fish, the population once again goes down to 50. However, this time, there were more small fish breeding then there were big fish breeding. This means that more of the 50 remaining fish are small fish (whether baby or adult). Thus, when I stop hunting, the population only goes up to 75, because the fish physically cannot have as many baby fish. If I were to hunt again, then the population would decrease even more.

This is a sad example of how a law to protect a species, has actually worked against it. So if you are just fishing for fun, please, throw back all your fish.

Well there you have it, natural selection at work.

Happy readings!

- Bethany

Greetings and Many Happy Readings

Science is one of those entities which is all around us, this computer I am typing on, the pen you used to write down a message with, the tap you just turned on to wash your hands – these are all examples of what science has been able to give us. However, despite the degree to which the products of science are integrated into our lives, in general, scientists themselves are not very good at communicating with the wider community.

It is this travesty, which I am aiming to try and lessen through this blog.

My name is Bethany van Hameren and I am currently studying science at the University of Queensland. To be more specific I am studying the Bachelor of Biotechnology. During my studies I have come across much scientific information which I believe isn’t very widely known to those not currently studying science, but which should be because it is important or highly interesting information. None of the opinions or ideas which I may express in this blog are associated with the University of Queensland or any of its staff, it is simply the university where I study.

I hope to use visual aids as much as possible throughout this blog (just not in this first entry obviously) to make it clearer and more interesting. Most of the images which I will use will either be created or photographed by myself, or I will use only with the express permission of those whose image it is and with credit to them. If I ever fail to do this, I encourage you as readers to let me know so that may correct it. My other aim is to write this blog in an order which will hopefully make sense. So that I have given enough related background information on a topic before I talk about it, thus eliminating confusion.

Although I will take the utmost care to make sure that the information which I post on this blog is correct, I also welcome any information to the contrary. I will also try to present information in an unbiased way, however because of my own personal opinions, I won’t be able to do this as successfully as I would like. Thus, I will do my utmost to present both sides of topics when they arise, no matter what the issue, it will probably be obvious however, on which side of the issue I stand.

I also hope to throw in some humor as well because I certainly like to laugh and I think that the more laughter in the world, the better. However, I have been told quite a significant number of times that I am not funny, so I hope that I don’t embarrass myself too much in my attempts to be humorous.

Now to explain a little bit more about why I feel the need to write this blog:

Unfortunately, scientists are not very good at explaining to the public what it is they do, or the reasons for which they do things. We tend to forget that not everyone has the same background knowledge we do, and thus race forward in our details of our new idea/theory/research without stopping to explain important background information about our idea/theory/research. It is this tendency which has led to the building of a wall between lay people and scientists. In the worse cases, this can lead to scientists feeling as though they are underappreciated and that “everyone else” is uneducated, while “everyone else” feels as though scientists are nerdy people with test tubes in uncomfortable places. This can cause very large problems, particularly when it is very important for the scientific community to work hand in hand with the rest of the world to solve a global problem such as, of course, climate change.

So, I hope to use this blog to try and knock down some of the wall which has formed between the lay person and the scientist, to try and improve the world! …at least in some small measure.

Hopefully the first “real” entry into this blog will not take very long to put up.

Wish me luck, I wish you, very many happy readings in the future.

- Bethany