Q. 16.65 - An Introduction to General, Organic, and Biological Chemistry

Question

What are sonse differences between each of the following pairs? (16.1, 16.2. 16.3)

a. secondary and tertiary protein structures

b. exsential and nonessential amino acids

c. polar and nonpolar amino acids

d. dipeptides and tripeptides

Step-by-Step Solution

Answer

(Part a) This is because hydrogen bonds are present.

(Part b) Non-essential amino acids include alanine, cystine, glutamine, aspartic acid, and proline.

(part c) Alanine is the best example of a nonpolar compound.

(Part d) A tripeptide is a peptide made up of three amino acids linked together by peptide bonds.

Step 1: Introduction (Part a)

• The ability of amino acids to form various secondary structures varies.
• A tertiary structure is globular and consists of a folded polypeptide chain stabilised by R group interactions.

Step 2: Given information (part a)

Secondary and tertiary protein structures 

Step 3: Explanation (Part a)

• The secondary protein structure is similar to that of a helix, -plated sheet or triple helix structure.
• This is because hydrogen bonds are present.
• The ability of amino acids to form various secondary structures varies.
• A tertiary structure is globular and consists of a folded polypeptide chain stabilised by R group interactions.
• Disulfide bonds and salt bridges are examples of such interactions.
• Some tertiary structure proteins have highly specific functions.

Step 4: Given information (Part b)

Essential and nonessential amino acids 

Step 5: Explanation (Part b)

• Humans require the amino acids phenylalanine, valine, threonine, tryptophan, methionine, lysine, leucine, histidine, arginine, and isoleucine.
• Not because they are more important to the body, but because they are not synthesised in the body and must be obtained through diet.
• Protein synthesis requires essential amino acids. Dietary sources of essential amino acids should be used. 
• Our bodies require non-essential amino acids, but they are produced in our bodies. 
• Non-essential amino acids include alanine, cystine, glutamine, aspartic acid, and proline.

Step 6: Given information (Part c)

Polar and nonpolar amino acids 

Step 7: Explanation (Part c)

• Non-polar amino acids have pure hydrocarbon side chains, such as an alkyl group or an aromatic group. 
• Alanine is the best example of a nonpolar compound.
• Polar amino acids have a side chain with different functional groups such as acids, amides, alcohols, and amines. 
• The side chain gives amino acids a more polar character. Serine is the best example of a polar amino acid.

Step 8: Given information ({Part d)

Dipeptides and tripeptides 

Step 9: Explanation (Part d)

• A dipeptide is a molecule made up of two amino acids linked together by a single peptide bond. 
• Valinylserine is the best example of a dipeptide bond.
•  Dipeptides are typically synthesised from polypeptides. 
• A tripeptide is a peptide made up of three amino acids linked together by peptide bonds.