Understanding the Genetic Code: Rules for Protein Synthesis, Slides of Biochemistry

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GENETIC CODE

dr. I Gde Haryo Ganesha, S.Ked Dept. of Medical Education

Maria Septiana Parmonang Aroean

Angkatan 2016 (1602511167)

FACULTY OF MEDICINE UDAYANA UNIVERSITY

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TABLE OF CONTENTS

TABLE OF CONTENTS ....................................................................................................... ii CHAPTER I INTRODUCTION ............................................................................................. 1.1 Background ....................................................................................................................... 1.2 Problem Statement ............................................................................................................ 1.3 Purpose.............................................................................................................................. 1.4 Benefit ............................................................................................................................... CHAPTER II CONTENT ....................................................................................................... 2.1 Definition .......................................................................................................................... 2.2 Characteristic of Genetic Code ......................................................................................... 2.3 Gene Expresion ................................................................................................................. 2.4 Function of Genetic Code ................................................................................................. 2.5 Mutation Gen and Disease ................................................................................................ CHAPTER III SUMMARY .................................................................................................. REFERENCES

corresponding anticodon complementary to a codon and ribosome connect amino acids into a polypeptide chain. Ribosome adds each amino acid carried by tRNA to the end of the growing polipeptide chain.

The genetic code codes for proteins. The information of the DNA is ‘translated’ into a chain of amino acids that forms a protein. These proteins form the building blocks for structures within the cells and ultimately the whole body. Proteins also form enzymes and other chemicals that perform various functions in the body. Each gene can code for different proteins and thus the number of proteins known to exist in the cells is more than the number of genes. All genes are not expressed or do not code for any protein. This could be organ specific for example a liver cell expresses different genes than kidney cells. The environment also plays a role in determining the ultimate trait. The phenotype of an organism thus depends on the interaction of genetics with the environment. The environment for example, has a role in effects of the human genetic disease phenylketonuria. The mutation that causes phenylketonuria disrupts the ability of the body to break down the amino acid phenylalanine. This leads to toxic build-up of an intermediate molecule leading to mental retardation and seizures. Persons with phenylketonuria mutation on a strict diet that avoids this amino acid may remain normal and healthy.

1.2 PROBLEM

1. What is the genetic code?
2. What are properties of the genetic code?
3. What is meant by the start codon and stop codon?
4. How the process of protein synthesis?
5. What are the functions of the genetic code?
6. What is relation between mutation and genetic code?

1.3 PURPOSE

1. To know the genetic code
2. To know properties of the genetic code
3. To know meant by the start codon and final codon
4. To know the process of protein synthesis

5. To know the functions of the genetic code in the body
6. To know the relation between mutation and genetic code

1.4 BENEFIT

1. Giving additional information to public about genetic code

• Nonoverlapping code The code is sequentially read in group of three. A nucleotide that forms part of a triplet never forms part of the next triplet. Each triplet is read from 5’ - > 3’ direction so the first base is 5’ base, followed by the middle base then the last base which is 3’ base.

Examples:

5’-AUG-3’ codes for methionine

5’-UCU- 3’ codes for serine

5’-CCA-3’ codes for proline

• The coding dictionary

Picture 1. The Codon Table

• Degenerate code All amino acids except methionine (AUG) and tryptophan (UGG) are coded by several codons: that is; some codons are synonyms. For example, theonine is coded by four codons ACU, ACC, ACA and ACG.

• Universality of code Genetic code is largely universal for all living organisms and viruses. However a few exceptions are found in mitochondria. For example, UGA, one of the termination codons in human, is the code for tryptophan yeast in mitochondria. Few other examples are stated below:
• Non ambiguous code The code is unambiguous under normal conditions, that means that each codon specifies the same amino acid all the time.
• Chain initiation codons The initiation signal for the synthesis polypeptide chain is AUG
• Chain termination codons The termination signal is provided by three codons UAG(Amber), UAA (ochre) and UGA (opal). These chain termination codons do not code for any amino acids and hence termed as non sense codons.
• Polarity The genetic code has polarity, the code is always read in fixed direction, in the 5’^ to 3’ direction. It is apparent that if the code is read in opposite direction, it would specify 2 different protein.

2.3 GENE EXPRESSION

The process of gene expression simply refers to the events that transfer the information content of the gene into the production of a functional product, usually a protein. Although there are genes whose functional product is an RNA, including the genes encoding the ribosomal RNAs as well as the transfer RNAs and certain other small RNAs, the vast majority of genes within the cell are protein-encoding genes. Mechanism of gene expression are as follows:

• Nucleus-Cytoplasmic RNA Transport Unlike bacteria, the eukaryotic cell is compartmentalized. Therefore, the final processed product (mRNA) must be transported through the nuclear envelope to reach the cytoplasm and be engaged with the ribosomes for translation.
• Translation Translation is essentially the reading of the sequence in the mRNA to direct the synthesis of a unique protein. There are two components of translation: Ribosome, a multicomponent RNA-protein structure that serves as the framework upon which protein synthesis takes place and which also provides the enzymatic activity for formation of the peptide bonds; and tRNA, a set of small RNAs, each specific for a given amino acid. The tRNA carries the amino acid to the ribosome for insertion into the growing polypeptide chain. The anticodon in the tRNA is complementary to the codon in the mRNA. The proteins are synthesized from N terminus to C terminus in 3 steps: initiation, elongation, and termination.

a. Initiation Initiation of protein synthesis involves recognition of a methionine codon (AUG) in the mRNA by a special methionyl tRNA, different from the methionyl tRNA that is used for elongation. The initiation event is accomplished through the action of several initiation factors that allow interaction of the mRNA with the small ribosomal subunit, GTP, and the initiator met-tRNA. The recognition of the initiating AUG codon in the mRNA is facilitated by the RNA sequences that surround the codon. Once the interaction takes place, the large subunit of the ribosome interacts and protein synthesis begins.

b. Elongation Codons in the mRNA are recognized by tRNAs which carry the appropriate amino acid to the translation machinery. Codon recognition involves base pairing between the codon in the mRNA and the anticodon in the tRNA. There are two functional sites on the ribosome that are occupied by tRNA and that facilitate peptide bond formation. The P site (peptidyl) and the A site (aminoacyl). Following formation of the peptide bond, the tRNA remaining in the P site leaves and the tRNA-peptidyl complex moves to the P site. A new aminoacyl-tRNA, specified

by the mRNA codon, then moves into the A site and peptide chain elongation continues. The catalysis of peptide bond formation is a function of the large ribosomal subunit.Very recent evidence indicates that it is the ribosomal RNA component of the large subunit that carries the enzymatic activity of peptidyl transferase.

c. Termination Three codons (UAG, UAA, and UGA) do not specify an amino acid-tRNA and thus cause termination of translation. These codons signal the release of the peptidyl-tRNA complex when recognized by termination factors. This results in the release of an uncharged tRNA lacking an attached amino acid residue as well as the completed polypeptide chain. The ribosome then disengages from the mRNA and the subunits dissociate, ready to start the cycle over again.

2.4 FUNCTION OF GENETIC CODES

Genetic codes play a role in synthesize of protein. Genetic code becomes a basic to explain how abnormality of proteins can gave some effect such as genetic disorder and we can uphold diagnosis and treatment that should given for genetics disorder. Genetic code that formed by 64 codons, 61 codons bring information of amino acid and three codons induced termination of protein synthesize. We all know that each codon specifies one single acid(Picture1). Previously we have discuss about characteristic of genetic code, especially every characteristic of genetic code have their function, example to helps prevent effects of DNA mutations, most amino acids have more than one codon, and it is unambiguous that means each codon has only one meaning for one acid.

2.5 GENETIC CODES AND MUTATION

As we know genetic code are composed by codon. Codon is a sequence of three base DNA or RNA and we can also called it as triplet base.

than normal because it can't finish adding all the necessary amino acid and these protein usually are not functional then it may caused many genetic disorder. Then what will happen if the stop codon doesn’t occur? These mRNA that lack of stop codon will cause the translation to continue into the poly-A (lysine). Since there is no stop codon is present, the ribosome attached to the mRNA, it will cause the activation of a pathways known as non-stop decay.

The other changes of genetic code is present in the codon that produce amino acid, when the genetic code is changed then it will produce the different amino acid which mean that the protein are differs from the normal one and it may caused the health problem. There are 4 mutation that will changes the genetic code. Transvertion is the changes pirimidin becomes purin for example if we had the DNA with base TAC it becomes GAC the problem is mRNA will transcript different code and it will leads to different protein. Transition is the change in genetic code where the purin becomes purin and pirimidin becomes pirimidin. Deletion is a change of genetic code caused by deleted some base. And insertion is the change of genetic code because of additional base.

CHAPTER III

SUMMARY

Genetic code is the set of rules by which information encoded within genetic material (DNA or mRNA sequences) is translated into protein by living cells. Genetic code composed by codon, codon is a sequence of three DNA or RNA nucleotides that corresponds with specific amino acid or stop signal during protein synthesis.

There are specific characteristics of genetic codes, such as that a codon that are composed of three nucleotides bases, have a total of 64 for 30 amino acids, therefore there are more than one code for the same amino acid with exception of methionine(AUG) and tryptophan (UGG) that only have one code for each. Another example is that genetic code has polarity and have a main function in synthesizing of protein.

The process of gene expression simply refers to the events that transfer the information content of the gene into the production of a functional product, usually a protein. The mechanism of gene expression are transcription, post-transcriptional event, RNA modification, nucleus- cytoplasmic RNA transport, translation. Meanwhile the process of protein synthesizing follow the order of initiation, elongation, and termination.

A mutation is a change in genetic codes which we can find it in DNA, the hereditary material of life, such that the genetic code differs from what is found in most people. Mutation is classified in two ways, heredity mutation and acquired/somatic mutation. In addition, there are several types of mutations that change genetic codes. There are transversion, transition, deletion and insertion.