I'm supposed to pick three that are true, and my personal guesses are 2, 3 and 6. I'd love to know if these are right and if so, why are they right. If not, could someone possibly lead me in the right direction?
1. Leu-Glu-His-Val-Cys-Lys-Ser is a likely repeat in the α helix of keratin.
2. Each polypeptide in the dimer has 3.5 residues per turn, resulting in the slight winding, or twist, around the other polypeptide, that helps form the coiled coil.
3. The residues at positions b and c are less likely to be polar or charged because they are in contact with the solvent.
4. Keratin molecules are very strong due to hydrophilic interactions between charged amino acid side chains.
5. Lys-Val-Ser-Cys-Ser-Glu-Thr is a likely repeat in the α helix of keratin.
6. The α helix of the coiled coil is wound less tightly than predicted for an α helix.
7. α-Keratin is rich in Cys residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the protein.
To determine if your choices are correct, let's analyze each statement one by one:
1. Leu-Glu-His-Val-Cys-Lys-Ser is a likely repeat in the α helix of keratin.
To verify the accuracy of this statement, we need to understand the properties of amino acids in the context of α helices. In an α helix, the pattern of amino acids tends to exhibit specific recurring patterns, with certain amino acids being more likely at specific positions. The commonly observed α helix-forming amino acids are alanine (Ala), leucine (Leu), and glutamic acid (Glu), while histidine (His), valine (Val), cysteine (Cys), and lysine (Lys) can also be present. Serine (Ser), on the other hand, is less commonly found in α helices. Therefore, based on the information given, it is likely that the statement is incorrect.
2. Each polypeptide in the dimer has 3.5 residues per turn, resulting in the slight winding or twist around the other polypeptide that helps form the coiled coil.
This statement pertains to the structural characteristics of a coiled coil, which is a specific type of protein structure formed by two or more α helices. In a coiled coil, the helices wind around each other, and the pitch (number of residues per turn) is crucial for the stability of the structure. The accepted value for the pitch is indeed approximately 3.5 residues per turn. Hence, the statement is likely correct.
3. The residues at positions b and c are less likely to be polar or charged because they are in contact with the solvent.
To evaluate the validity of this statement, we need to understand the spatial arrangement of amino acids in a protein. In protein structures, amino acids are typically classified based on their position within an α helix, referred to as positions a, b, c, and d. Amino acids at positions b and c are usually found on the solvent-exposed surface of the protein, which implies that polar or charged amino acids are less likely to be present. Therefore, the statement is likely correct.
4. Keratin molecules are very strong due to hydrophilic interactions between charged amino acid side chains.
This statement suggests that hydrophilic interactions between charged amino acid side chains contribute to the strength of keratin molecules. However, keratin's strength primarily comes from the presence of covalent disulfide bonds formed between cysteine residues, which provide stability and resilience to the protein structure. Therefore, the statement is likely incorrect.
5. Lys-Val-Ser-Cys-Ser-Glu-Thr is a likely repeat in the α helix of keratin.
Similar to Statement 1, this statement involves analyzing the potential amino acid composition of an α helix in keratin. While lysine (Lys), serine (Ser), and glutamic acid (Glu) can be present in an α helix, valine (Val) and threonine (Thr) are not commonly observed. Therefore, it is likely that this statement is incorrect.
6. The α helix of the coiled coil is wound less tightly than predicted for an α helix.
The pitch of an α helix within a coiled coil can deviate from the standard value of 3.6 residues per turn for a regular α helix. This deviation results in a looser winding or a helix that is wound less tightly compared to a perfect α helix. Hence, the statement is likely correct.
7. α-Keratin is rich in Cys residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the protein.
This statement correctly highlights the significant presence of cysteine (Cys) residues in α-keratin. Through the formation of covalent disulfide bonds (cross-links) between the cysteine residues, α-keratin gains additional strength, enabling it to form durable structures in biological systems. Therefore, this statement is likely correct.
In summary, based on the explanations provided, statements 2, 3, and 7 are likely to be correct, while statements 1, 4, 5, and 6 are likely to be incorrect.