Genetic Code MCQ Quiz in मल्याळम - Objective Question with Answer for Genetic Code - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is UAA, UAG, and UGA.

Key Points

• Genetic information from the nucleus is carried as mRNA to the cytosol.
• This mRNA consists of the codon and is read by the ribosome.
• The codon consists of a sequence of DNA.
• It is a triplet and consists of three bases.
• These codons are translated and thus form the polypeptide chain.
• Codons are start codons and stop codons.
• The start codon initiates the translation and is AUG.
• It is present at the 5' end of the mRNA sequence.
• Stop codons aid in termination, and thus stop the formation of the polypeptide chain.
• It is present at the 3' end of mRNA.
• Peptide chain termination codons are UAA, UGA, and UAG.

Additional Information

• There are a total of 64 codons.
• These code for 20 different amino acids.
• Out of the 64 codons, 61 codons code for amino acids, and 3 codons do not code for any amino acids.
• UGC codon codes for cysteine (Cys).
• CGA codes for arginine (arg).
• AGC codes for serine (ser).

Here is a list of some of the codons;-

Correct Answer: Option 4

Concept:

• A DNA molecule is made up of several nucleotides. Each nucleotide consists of a nitrogenous base, a phosphate group, and a 5- carbon sugar.
• There are 4 types of nitrogenous bases - Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). Thus it gives us 4 different nucleotides - adenine nucleotide, guanine nucleotide, cytosine nucleotide, and thymine nucleotide.
• The proteins in an animal body are synthesized from 20 amino acids.
• During translation, the genetic information present on the mRNA (transcribed from complementary DNA) is transferred into a polypeptide chain. This chain is made up of a polymer of amino acids.
• This genetic information is stored in the form of a code called a genetic code. The genetic code consists of codons that specify a particular amino acid.
• A genetic code can therefore be defined as a set of rules that specify the correspondence between the codons in a DNA molecule and amino acids in a protein.

Explanation:

• Characteristics of genetic code:
  • Genetic code is a triplet code: Three consecutive bases constitute a single codon. This single codon in turn specifies a single specific amino acid.
  • Genetic code has a polarity: Genetic code is always read in the 5' → 3' direction and never in the 3' → 5' direction.
  • Genetic code is non-overlapping: Codons do not overlap in a sequence. Each base in a sequence can only be a part of a single codon.
  • Genetic code is commaless: There is no space or any punctuation mark between consecutive codons.
  • Genetic code is degenerate: This implies that a single amino acid can be encoded by more than one codon.
  • Genetic code is non-ambiguous: Each codon will only specify a particular amino acid. No two amino acids can be encoded by the same codon.                                                       

                     Thus a single amino acid can be encoded by more than one codon, but no codon can specify more than one amino acid.

• Genetic code is universal: The genetic code is the same for all organisms from bacteria to a human. A specific codon will specify the same specific amino acid in all organisms.
• Genetic code has an initial codon: In all organisms, AUG that encodes amino acid methionine is the start codon. Synthesis of the protein chain begins with the AUG codon.
• Genetic code has a termination codon: UAA, UGA, and UAG are the termination codons. These codons do not encode any amino acids and are therefore c alled nonsense codons. These codons signal the termination of the translation process.

• Taking into consideration the above-mentioned rules, let us now solve the problem at hand:
  • There are 999 bases in an RNA that codes for a protein with 333 amino acids
    • ​We know that genetic code is a triplet code i.e. 3 bases constitute 1 codon
    • Therefore 999 bases constitute 333 codons.
  • The base at position 901 is deleted such that the length of the RNA becomes 998 bases
    • Using the same rule that genetic code is a triplet code 
    • 998 bases will constitute 333 codons.
  • How many codons will be altered in the above scenario?
    • ​901 to 999 bases account for 99 bases. Of these 99 bases one is deleted, therefore the total number of bases will be 98.
    • Using the rule that genetic code is a triplet code and that the genetic code is non-overlapping,
    • The first 900 bases will remain the same without any alterations. However, the remaining 98 codons will get altered.
    • 98 bases constitute 33 codons
    • Therefore, 33 codons will get altered.

So, from the above-given information, the correct answer is option 4.

Key Points

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• However, no such complementarity exists between the RNA and the proteins for translation to take place.
• Evidences show that changes in nucleic acids also caused changes in the amino acids of the proteins.
• This suggested the existence of a Genetic Code that directs the synthesis of amino acids that form the proteins.
• It was George Gamow who suggested that if the 4 nitrogen bases of nucleic acids have to code for the 20 non-essential amino acids produced in the body, the code should constitute a combination of bases.
• The nitrogen bases include Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.
• A permutation combination of 2 bases would give: 4² = 16 amino acids only, which is not sufficient.
• So, it has to be a combination of 3 bases giving: 4³ = 64 codons.
• Thus it was concluded that 64 codons would code for the 20 amino acids with some codons being signal codons too.

Important Points

• We can find the correct amino acids for the given genetic codes from the above table.
  • GCA - Alanine (Ala)
  • CGA - Arginine (Arg)
  • ACG - Threonine (Thr)
  • GAC - Aspartic acid (Asp)
• In the given question, CGA has been wrongly matched with Proline (Pro).
• Thus the correct answer is option (2).

The Correct answer is genotype

Key Points

• The genotype refers to the genetic makeup of an organism. It is the combination of alleles at specific gene locations on the organism's chromosomes.
• It determines the hereditary characteristics of an organism and remains unchanged throughout its life.
• The genotype is represented by specific letters or symbols that indicate the alleles present, such as "AA," "Aa," or "aa."
• It is a crucial concept in Mendelian genetics, where traits are understood based on dominant and recessive alleles.
• The genotype interacts with the environment to produce the observable traits or physical expression, known as the phenotype.
• For example, in pea plants studied by Gregor Mendel, the genotype "TT" or "Tt" results in tall plants, whereas "tt" results in short plants.
• The study of genotypes is essential in understanding genetic disorders, inheritance patterns, and evolutionary biology.
• Modern technologies like genotyping and DNA sequencing help scientists analyze genotypes for medical and research purposes.

 Additional Information

• DNA
  • DNA (Deoxyribonucleic Acid) is the molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms.
  • It is composed of two strands forming a double helix structure, discovered by James Watson and Francis Crick in 1953.
  • DNA contains the genetic information in sequences of nucleotides, which include adenine (A), thymine (T), cytosine (C), and guanine (G).
  • While the genotype is the combination of alleles, DNA is the physical medium that stores and transmits genetic information.
• Double Helix
  • The term double helix refers to the structure of DNA, consisting of two strands twisted around each other.
  • It was first described by Watson and Crick based on the X-ray diffraction data produced by Rosalind Franklin.
  • The strands are held together by hydrogen bonds between complementary bases (A pairs with T, C pairs with G).
  • While the double helix is a structural property of DNA, the genotype is about the specific genetic information encoded within the DNA.
• Phenotype
  • The phenotype refers to the observable physical or biochemical characteristics of an organism, such as height, eye color, or enzyme activity.
  • It is influenced by both the genotype and the environment.
  • For example, two plants with the same genotype for height might vary in actual height due to differences in soil quality, water availability, or sunlight exposure.
  • While the genotype is the genetic blueprint, the phenotype represents the expression of that blueprint.

Key Points

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• However, no such complementarity exists between the RNA and the proteins for translation to take place.
• Evidences show that changes in nucleic acids also caused changes in the amino acids of the proteins.
• This suggested the existence of a Genetic Code that directs the synthesis of amino acids that form the proteins.
• It was George Gamow who suggested that if the 4 nitrogen bases of nucleic acids have to code for the 20 non-essential amino acids produced in the body, the code should constitute a combination of bases.
• The nitrogen bases include Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.
• A permutation combination of 2 bases would give: 4² = 16 amino acids only.
• So, it has to be a combination of 3 bases giving: 4³ = 64 codons.

Therefore, only a triplet codon system would be effective in producing the 20 amino acids in our body.

Additional Information

The salient features of the genetic code are:

• Triplet codon - Each codon is a triplet of any 3 bases. 61 of the codons code for amino acids and 3 codons act as STOP codons.
• Start codon - The codon AUG acts as a START codon or Initiator codon as well as codes for Methionine(Met).
• Unambiguous & Specific - One codon codes for only one amino acid.
• Degenerate - Some amino acids are coded by more than one codon.
• Contiguous - The codon in mRNA is read in a continuous manner without any punctuation.
• Universal - A codon codes for a specific amino acid for all organisms. Exception - Some mitochondrial codons and some protozoans.

The correct answer is option 2.

Solution

Concept:-

• A set of three-letter combinations of bases that code for a particular amino acid is called a codon.
• There are 64 codons out of which 61 code for amino acids and three are stop codons.

Explanation:

Let us look at the salient features of genetic code:

• The three stop codons (UAA, UAG, UGA) do not code for any amino acid. They are also referred to as terminator codons.
• Each codon, out of the 61 codons, codes for only one amino acid. Hence it is unambiguous and non-overlapping.
• The codons are nearly universal that is UUU codes for phenylalanine in humans as well as bacteria.
• One amino acid can be coded by more than one codon. Hence, code is degenerate.
• The codon in mRNA is read in a contiguous manner and there are no punctuations.
• AUG act as an initiator codon and codes for amino acid methionine.

So, the correct answer is option 2.

Concept:

• A codon is a sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis (Translation).
• Each codon corresponds to a single amino acid (or stop signal), and the full set of codons is called the genetic code.
• As the DNA and RNA molecules are written in a language of four nucleotides; whereas, the language of proteins includes 20 amino acids.
• A nonsense codon is a codon for which no normal tRNA molecule exists, The presence of a nonsense codon causes the termination of translation (ending polypeptide chain synthesis) and are called as stop Codon.

Explanation:

• There are three nonsense codons are called amber (UAG) ochre (UAA) and opal (UGA). They encode no amino acid. The ribosome pauses and falls off the mRNA.
• UGG code for tryptophan
• UGC code for cysteine
• UAC code for tyrosine

Additional Information

• The start codon is AUG.  Methionine is the only amino acid specified by just one codon.

• The genetic code includes 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides.  
• Out of 64 codons, 61 represent amino acids, and three are stop signals.
• The genetic code is described as degenerate, or redundant, because a single amino acid may be coded for by more than one codon.
• The conversion of codon information into proteins is conducted by transfer RNA.  Each transfer RNA (tRNA) has an anticodon that can base pair with a codon.

The correct answer is G U G.

Concept:

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• However, no such complementarity exists between the RNA and the proteins for translation to take place.
• Evidences show that changes in nucleic acids also caused changes in the amino acids of the proteins.
• This suggested the existence of a Genetic Code that directs the synthesis of amino acids that form the proteins.
• The relationship between the sequence of nucleotides on mRNA and sequence of amino acids in the polypeptide is called genetic code.
• It was George Gamow who suggested that if the 4 nitrogen bases of nucleic acids have to code for the 20 non-essential amino acids produced in the body, the code should constitute a combination of bases.
• The nitrogen bases include Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.
• A permutation combination of 2 bases would give: 4² = 16 amino acids only. Thus, it has to be a combination of 3 bases giving: 4³ = 64 codons.
• Thus it was concluded that 64 codons would code for the 20 amino acids with some codons being signal codons too.

Explanation:

• From the above table we can see that GUG is a codon that codes for valine (amino acid).
• Formylated-methionine is encoded by the codon AUG, which is also known as the start codon. 
• As a result, during protein synthesis within the ribosome, formylated-methionine is known to be the first amino acid to dock.
• AUG is a dual function codon: it codes for methionine and it also acts as a initiator codon.
• Usually the codons are non-ambiguous, meaning they code for only one specific amino acid in all organisms.
• GUG is an exception to this rule.
• When AUG codon is absent, GUG operates as a start codon and codes for formylated-methionine as initiator codon for protein synthesis.
• For example, the lacI region of E. coli lac operon has GUG as initiator codon.

Thus, G U G codon usually codes for valine but can also code for formylated-methionine as initiator codon.

Additional Information

• The salient features of the genetic code are:
  • Triplet codon - Each codon is a triplet of any 3 bases. 61 of the codons code for amino acids and 3 codons act as STOP codons.
  • Start codon - The codon AUG acts as a START codon or initiator codon as well as codes for Methionine(Met).
  • Unambiguous & Specific - One codon codes for only one amino acid.
  • Degenerate - Some amino acids are coded by more than one codon.
  • Contiguous - The codon in mRNA is read in a continuous manner without any punctuation.
  • Universal - A codon codes for a specific amino acid for all organisms. Exception - Some mitochondrial codons and some protozoans.

Concept:

• Codon is a sequence of three nucleotides that forms a unit of genomic information encoding a particular amino acid.
• There are 64 different codons-
  • 61 specify for amino acids
  • 3 are used as stop signal during protein synthesis.

Important Points

• AUG codon codes for the amino acid Methionine.
• AUG codon acts as a initiator codon for the process of protein synthesis.
• Initiator codon directs the initiation of the protein translation by stimulating the binding of the initiator tRNA  to the mRNA transcript.
• The initiator codons is  the initial set of codons present on the mRNA transcript.
• 3 codons, namely UAG, UAA, UGA  are known as stop codons as they form the signal for the termination of the translation process.

Additional Information

• Tryptophan is coded by codons CAU and CAC.
• Valine is coded by codons GTA and GTG.
• Arginine is coded by AGA and AGG.

Concept:

• The Genetic Code is a system that directs the synthesis of amino acids to form the proteins.
• The code constitutes a combination of the nitrogen bases: Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.

Salient features of genetic code:

• Triplet codon - Each codon is a triplet of any 3 bases. 61 of the codons code for amino acids and 3 codons act as STOP codons.
• Start codon - The codon AUG acts as a START codon or Initiator codon as well as codes for Methionine(Met).
• Unambiguous & Specific - One codon codes for only one amino acid.
• Degenerate - Some amino acids are coded by more than one codon.
• Contiguous - The codon in mRNA is read in a continuous manner without any punctuation.
• Universal - A codon codes for a specific amino acid for all organisms. Exception - Some mitochondrial codons and some protozoans.

Important Points

• AUG codes for Phenylalanine - NOT TRUE
  • AUG acts as a start codon and codes for Methionine.
  • Phenylalanine is coded by UUU or UUC.
• UAA, UGA and AUG are termination codon - NOT TRUE
  • The termination or stop codons are UAA, UAG and UGA.
  • AUG is the start codon.
• UAA, UGA are start codon - NOT TRUE
  • UAA and UGA are both stop codons.
• AUG is start codon and UAA is termination codon - TRUE
  • AUG is the start codon and UAA is one of the three stop codons.