A bacterial culture grown in a medium containing radioactive sulphur would incorporate the radiolabel in
the tetra-peptide:
(1) serine-cysteine-tyrosine-methionine.
(2) threonine-lysine-aspartic acid-glutamic acid.
(3) alanine-proline-histidine-glycine.
(4) tryptophan-phenylalanine-valine-isoleucine

How Radioactive Sulfur Incorporation Affects Tetra-Peptides in Bacterial Cultures

In microbiolotive labeling is a powerful technique used to track specific molecules as they are incorporated into cellular structures. One fascinating example involves the incorporation of radioactive sulfur into peptides in bacterial cultures. But which amino acids in a tetra-peptide would incorporate this sulfur?

The question is:
A bacterial culture grown in a medium containing radioactive sulfur would incorporate the radiolabel in the tetra-peptide:

1. serine-cysteine-tyrosine-methionine

2. threonine-lysine-aspartic acid-glutamic acid

3. alanine-proline-histidine-glycine

4. tryptophan-phenylalanine-valine-isoleucine

The correct answer is (1) serine-cysteine-tyrosine-methionine.

Why Sulfur Incorporates into Certain Amino Acids

Sulfur is a key element in the structure of certain amino acids. Specifically, sulfur is found in the side chains of two amino acids:

1. Cysteine – Contains a thiol group (-SH) in its side chain.

2. Methionine – Contains a sulfur atom in its thioether side chain.

Thus, when a bacterial culture is grown in a medium containing radioactive sulfur (S-35), it is primarily incorporated into amino acids that contain sulfur atoms in their structure. This is the reason why cysteine and methionine are key candidates for sulfur incorporation in peptides.

Analyzing the Tetra-Peptides

Let’s break down the given tetra-peptides and see where radioactive sulfur could be incorporated:

1. Serine-cysteine-tyrosine-methionine

   • Cysteine and methionine both contain sulfur atoms, so radioactive sulfur will incorporate into this tetra-peptide.

   • Serine and tyrosine do not contain sulfur in their side chains, so they won’t incorporate the radioactive sulfur.

2. Threonine-lysine-aspartic acid-glutamic acid

   • None of these amino acids contain sulfur in their side chains. Therefore, radioactive sulfur would not be incorporated into this tetra-peptide.

3. Alanine-proline-histidine-glycine

   • Again, none of these amino acids have sulfur in their side chains. No radioactive sulfur would be incorporated here either.

4. Tryptophan-phenylalanine-valine-isoleucine

   • Like the previous one, these amino acids do not contain sulfur in their side chains. Hence, no radioactive sulfur incorporation.

How Radioactive Sulfur Is Tracked

Radioactive sulfur (S-35) emits radioactive particles that can be detected with specialized equipment, like a scintillation counter. This allows scientists to observe how the sulfur is incorporated into various molecules in the cell, such as proteins, nucleic acids, and other macromolecules.

In this case, by analyzing the proteins and peptides in the bacterial culture, scientists can track which peptides are labeled with the radioactive sulfur. This helps in studying protein synthesis, amino acid metabolism, and other biochemical pathways.

Summary Table

Final Thoughts

In conclusion, when growing bacteria in a medium with radioactive sulfur, cysteine and methionine are the amino acids most likely to incorporate the radioactive label due to the sulfur content in their side chains. Understanding this concept is crucial in experiments related to protein synthesis and molecular biology research.

By carefully analyzing the amino acids that contain sulfur and their role in peptide formation, we can track the movement and incorporation of sulfur in bacterial cultures—an invaluable tool in biological and biochemical studies.