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Genetic Code in Chemistry

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Genetic Code
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Still Working On It

The Human Genome Project started in 1990 with the lofty goal of sequencing the complete set of human DNA. This project was completed in April 2003, ahead of schedule and under the budget set for it (a rare occurrence for a government project). With this knowledge, we can now identify genetic disorders quickly and personalize treatment for many diseases. However, much work still remains to fully understand the connections between specific DNA sequences and specific diseases.

The Genetic Code

Each particular organism contains many protein molecules that are specific to that organism. The particular base sequence of DNA is responsible for the production of all of the different proteins that are present in each and every living thing that has ever inhabited the Earth. How does that work? Cells use the unique sequence of DNA bases to decide which proteins to synthesize. A gene is a segment of DNA that carries a code for making a specific polypeptide chain. The cell essentially decodes the DNA in order to make whatever peptides and proteins are needed by that organism.

The genetic code works as a series of three-letter codes. Each sequence of three letters, called a triplet, corresponds to one of the twenty common amino acids. The triplets are read by the cell, one after the other, in the process of protein synthesis. The Table below shows all of the possible triplets and the amino acids that result from each three-letter code.

DNA Triplet Codes for Amino Acids

AAA

Phe

GAA

Leu

TAA

Ile

CAA

Val

AAG

Phe

GAG

Leu

TAG

Ile

CAG

Val

AAT

Leu

GAT

Leu

TAT

Ile

CAT

Val

AAC

Leu

GAC

Leu

TAC

Met

CAC

Val

AGA

Ser

GGA

Pro

TGA

Thr

CGA

Ala

AGG

Ser

GGG

Pro

TGG

Thr

CGG

Ala

AGT

Ser

GGT

Pro

TGT

Thr

CGT

Ala

AGC

Ser

GGC

Pro

TGC

Thr

CGC

Ala

ATA

Tyr

GTA

His

TTA

Asn

CTA

Asp

ATG

Tyr

GTG

His

TTG

Asn

CTG

Asp

ATT

End

GTT

Gln

TTT

Lys

CTT

Glu

ATC

End

GTC

Gln

TTC

Lys

CTC

Glu

ACA

Cys

GCA

Arg

TCA

Ser

CCA

Gly

ACG

Cys

GCG

Arg

TCG

Ser

CCG

Gly

ACT

End

GCT

Arg

TCT

Arg

CCT

Gly

ACC

Trp

GCC

Arg

TCC

Arg

CCC

Gly

The DNA code word GCA corresponds to the amino acid arginine, while the DNA code word TCG corresponds to the amino acid serine. Most amino acids are represented by more than one possible triplet code, but each triplet code yields only one particular amino acid. Three of the DNA code words (ATT, ATC, and ACT) are end or termination code words. The translation of a DNA base sequence begins immediately after one termination code word and runs until another termination code word is reached. 

Even with only four different bases, the number of possible nucleotide sequences in a DNA chain is virtually limitless. The particular DNA sequence of a particular organism constitutes the genetic blueprint for that organism.  This genetic blueprint is found in the nucleus of each cell of the organism and is passed on from parents to offspring. The incredible diversity of life on Earth stems from the differences in the genetic code of every living thing.

Summary

Practice

Read the material at the link below and answer the following questions:

http://nihrecord.od.nih.gov/newsletters/2010/02_05_2010/story3.htm

  1. What did Marshall Nirenberg do?
  2. When did he first report his results?
  3. What did he win for his discovery?

Review

  1. What is a gene?
  2. What does the genetic code do?
  3. What is the nucleotide code for phenylalanine?

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