Teachers' Day

Thanks to all who still drop by my blog even though it hasn't been updated in ages!!! I've been busy with my classes as you can see from above.

To all who are students out there - appreciate your teachers; and to all those who teach - "Happy Teachers' Day!".

Hope to write on something more scientific soon...so...drop by again yah?!

Viruses...arrggh!!!

I've just been infected with one of these...YES...the FLU VIRUS!

Such simple structures yet they are indeed formidable in making one feel so sick!

In general, viruses are composed of 2 main components - a protein envelope and a core composed of genetic material (which can either be DNA or RNA). It cannot survive on its own but is dependent on a host cell to replicate and propagate! Sigh...in my case...that's my cells!

Viruses are host specific. Meaning a plant virus cannot infect a bacterial cell. Neither can a bacterial virus infect a human cell. However, at times, mutation in the viral genome can occur which allows the virus to "cross" their host boundaries. That's when pandemics can arise. An example of this is the recent "Bird Flu virus"!

Well, I suppose I should be thankful that mine is just a case of the common influenza virus. So, back to bed for now and hopefully I'll be back on my feet in a couple of days!

Happy Chinese New Year!

Wishing all my readers a Happy Chinese New Year! May this year bring you a double dose of happiness, a bountiful harvest of success, good health and abundant wealth!

Will be back soon with a new post after the Chinese New Year celebrations...which means after I've stuffed myself with all the sweet snacks ;p

More about the Genetic Code - start codons, stop codons and degeneracy

Still staying on the same topic of the Genetic Code...Now let's learn more about it!

When decoding information on DNA, a messenger RNA (mRNA) transcript is first made by the process of transcription. The first codon on this mRNA transcript is almost always "AUG" which codes for the amino acid "methionine" or "M". This is referred to as the START codon. If you noticed, I had intentionally started my New Year's wish for you with "M" too!

aug
M A N Y

H A P P Y

D A Y S !

As the saying goes - where there is a beginning, there is also an end. In the case of a mRNA transcript, where there is a start codon, there is also a stop codon. In the Genetic Code, there are 3 different STOP codons that can be used. Any 1 of these 3 stop codons may be found at the end of a mRNA transcript.

The start codon "M" is indicated in orange and 3 stop codons are indicated in red, in the Genetic Code table below.

The 3rd noteworthy point about the Genetic Code is - DEGENERACY.

If you had been decoding my New Year's wish for you in my earlier post (5th Jan '08), you may have realized that the 3 "A"s found in the coded message were coded for by 3 different codons. Similarly so, for the 3 "Y"s and 2 "P"s.

gcc uau
M A N Y

gcg ccc cca uac
H A P P Y

gca uau
D A Y S !

This feature of the Genetic Code, where there is more than 1 codon coding for the same amino acid is termed "DEGENERACY".

I hope with this, you now understand start codons, stop codons and degeneracy of the Genetic Code! You can then create your own "DNA" encoded message! How about sending me one to decode! ;p

My New Year's Wish for You!

It is high time I came back with the decoded message of my New Year's wish for you! Here's wishing you...

M A N Y

H A P P Y

D A Y S

Hope all of you managed to decode that correctly! Especially after reading my post about how the genetic code works!

Now as a reward...how about listening to the title song of the classic American sitcom "Happy Days" in the video posted today!

The Genetic Code - DNA decoded

We got for our son a very special birthday card this year (as seen above). In it, he had to crack a code in order to uncover what was wished for him in the card. So it is with DNA in our cells. The genetic information on DNA is written in a code - THE GENETIC CODE!

Recall, in my post before this titled "The DNA double helix - a story of 2 perfectly paired strands", I explained that there are 4 nitrogenous bases used in making a strand of DNA. These are adenine (A), thymine (T), cytosine (C) and guanine (G). These 4 bases (A,T,C and G) are used like letters in an alphabet. The sequence of these bases on DNA code for specific genetic information.

In order to use the encoded genetic information, the sequence of DNA bases is first copied onto RNA (ribonucleic acid) by a process called "transcription" (I will elaborate on this process in another post...for now, all you need to know is that DNA is copied onto RNA).

In RNA, the bases A, U (uracil), C and G bases are used. Notice in RNA there is no "T" , unlike DNA. Instead, a "U" is used in place of "T" in RNA. Recall, from my previous post, the nitrogenous bases in DNA exhibit complementary base pairing, where "A" pairs with "T" and "C" pairs with "G". It is via this complementary base pairing that the sequence of bases in DNA gets copied onto RNA. As in DNA, "C" pairs with "G". However, unlike DNA, "A" pairs with "U" in RNA (due to the absence of "T").

Every 3 bases on RNA code for 1 amino acid - where an amino acid is the building block of proteins. Hence, by reading every 3 bases on RNA, the cell is able to string together a chain of amino acids. We call this a "polypeptide" chain. Subsequently, each polypeptide chain made from RNA will be folded into a functional protein to be used by the body.

Below is the GENETIC CODE, showing which combination of 3 bases on RNA codes for which amino acid. Each of these combination of 3 bases on RNA is called a "codon".


From the above genetic code, we see that the codon "AUG" codes for the amino acid "methionine" and the codon "AAA" codes for the amino acid "lysine".

Each amino acid may also be represented using a single letter code as shown in the table below.


So, the codon "AUG" codes for the amino acid "methionine", which can be represented by the single letter code "M". And the codon "AAA" that codes for the amino acid "lysine", can be represented by the single letter code "K". Note that the single letter representation for the amino acid need NOT correspond to the first letter of that amino acid!

Having understood the genetic code...now try decoding my New Year's wish for you below! You can do so by matching each codon to its amino acid. Then match the amino acid coded for to its single letter code.


Eg. "AUG" - "M" and "AAA" - "K".


AUG GCC AAU UAU


CAC GCG CCC CCA UAC


GAC GCA UAU UCA !


Managed to crack my "New Year's wish" code?! Check back for my next post to see if you got the answer right! Good luck!

The DNA double helix-a story of 2 perfectly paired strands

Today was my niece's wedding day! They had a lovely Catholic church service followed by a delightful lunch reception. Weddings tend to leave a lingering sweet, warm feeling to all who witness the joyful union of 2 becoming 1.

Some couples have very similar characters and interests, yet others attract total opposites from themselves! As for DNA found in our cells...this is a story of the perfect complement. Each of the 2 strands comprising the DNA double helix were "made for each other"! Let me explain...

DNA - deoxyribonucleic acid, is made up of of 2 strands of polynucleotides. Each strand of polynucleotide is a polymer of monomer units called - nucleotides. Each nucleotide comprises 3 components - a phosphate group, a sugar group and a nitrogenous base.

Nucleotides join to make a single strand of polynucleotide via phosphodiester bonds between alternating phosphate and sugar groups. We call this the "sugar-phosphate backbone" of a single strand of polynucleotide.

Now, this is where the love story begins...How do 2 polynucleotide strands come together to become 1 DNA macromolecule? They do so through their complementary base pairing between their nitrogenous bases. There are 4 different nitrogenous bases - Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). These display specific base pairing where "A" will always pair up with "T" and "C" will always pair up with "G". Hence, when there is an "A" on 1 polynucleotide strand, this will pair up with "T" on the opposite polynucleotide strand. Similarly, when there is a "C" on 1 polynucleotide strand, this will pair up with "G" on the opposite polynucleotide strand. It is via this complementary base pairing that 2 polynucleotide strands come together to make 1 DNA macromolecule. What wedded bliss!