Question

What is the minimum number of base substitutions that must be made to change the codons from a) glutamic acid to lysine? b) leucine to alanine? c) phenylalanine to glycine? d) tryptophan to serine? e) valine to glutamic acid?

Short answer

a) 1 base substitution b) 1 base substitution c) 2 base substitutions d) 2 base substitutions e) 1 base substitution

Step-by-step solution

a) Glutamic acid to lysine

The codons for glutamic acid are \(GAA\) and \(GAG\). The codons for lysine are \(AAA\) and \(AAG\). We just need to change the first base from \(G\) to \(A\) in either of the codons for glutamic acid to turn it into a codon for lysine. Therefore, the minimum number of base substitutions is 1.

b) Leucine to alanine

The codons for leucine are \(UUA\), \(UUG\), \(CUU\), \(CUC\), \(CUA\), and \(CUG\). The codons for alanine are \(GCU\), \(GCC\), \(GCA\), and \(GCG\). By changing the first base in any of the leucine codons starting with \(C\) to \(G\), we can convert it into an alanine codon. Thus, the minimum number of base substitutions is 1.

c) Phenylalanine to glycine

The codons for phenylalanine are \(UUU\) and \(UUC\). The codons for glycine are \(GGU\), \(GGC\), \(GGA\), and \(GGG\). To change a phenylalanine codon to a glycine codon, we need to change the first two bases: \(UU\) to \(GG\). Hence, the minimum number of base substitutions is 2.

d) Tryptophan to serine

The codon for tryptophan is \(UGG\). The codons for serine are \(UCU\), \(UCC\), \(UCA\), \(UCG\), \(AGU\), and \(AGC\). We can convert the tryptophan codon into a serine codon by changing the first two bases from \(UG\) to \(UC\). Thus, the minimum number of base substitutions is 2.

e) Valine to glutamic acid

The codons for valine are \(GUU\), \(GUC\), \(GUA\), and \(GUG\). As mentioned earlier, the codons for glutamic acid are \(GAA\) and \(GAG\). We can change a valine codon into a glutamic acid codon by changing the second base from \(U\) to \(A\). Therefore, the minimum number of base substitutions is 1.

Key concepts

Codon Substitution

Codon substitution is a fundamental concept in molecular genetics, referring to the change of one or more nucleotides in a DNA or RNA sequence, altering the genetic code. This change can lead to different amino acids being coded for, potentially affecting the structure and function of proteins.
For instance, if we want to change the codon for glutamic acid (GAA or GAG) to lysine (AAA or AAG), a single base substitution is enough. By altering the first nucleotide from G to A, we switch from one amino acid to the other. This kind of substitution is crucial in understanding mutations' impacts.

• A single base change could result in a completely different protein function.
• Codon substitution is often a result of point mutations.
• This process is significant because it illustrates how genetic variations can lead to diversity in biological organisms.

Understanding codon substitutions is essential for genetic research and medicine, as it helps explain how genetic disorders or diseases might arise from seemingly minor changes in the DNA sequence.

Amino Acids Conversion

In genetic code terminology, the conversion of amino acids refers to how sequences of nucleotides translate into amino acids. Codons, which are units of three nucleotides, correspond to specific amino acids. This translation from codons to amino acids is not one-to-one, meaning multiple codons can code for the same amino acid — a concept known as degeneracy of the genetic code.
For example, leucine can be coded by UUA, UUG, CUU, CUC, CUA, and CUG. Conversely, changing leucine to alanine involves altering the first nucleotide of these codons to a G, as in GCU, GCC, GCA, or GCG for alanine.

• This conversion is vital for protein synthesis within cells.
• Translating codons accurately ensures proteins are made correctly, maintaining cellular functions.
• Errors in conversion can lead to diseases or dysfunctional proteins.

Understanding how codons translate into amino acids helps scientists manipulate genetic information, providing insights into protein engineering and gene therapy.

Molecular Genetics

Molecular genetics focuses on understanding the molecular structure and function of genes. It examines how genetic information is encoded, replicated, and expressed within an organism.
Key processes in molecular genetics include transcription and translation, where genetic information is transcribed from DNA to RNA and then translated into proteins. Codon substitutions, like changing valine (GUU, GUC, GUA, GUG) to glutamic acid (GAA, GAG), highlight the precision needed in these processes.

• The field provides insights into genetic variation and mutation effects.
• Advancements in molecular genetics have led to breakthroughs in genetic engineering, where genes are altered for research or therapeutic purposes.
• It plays a crucial role in understanding inherited diseases, allowing for the development of potential treatments.

Studying molecular genetics allows researchers to unravel the complex mechanisms behind gene functionality, ultimately contributing to more refined approaches in medicine and biotechnology.