9. Which statement is true
1 point
O
a. Peptides are amides formed by
addition of a-aminoacid
o
b. The linkage present in peptides
and proteins is -CO-0-
C. peptides are classified as
O monopeptide,
dipeptide...polypeptide
d. peptides are with N-terminal
amino acid on the left and C-
terminal amino acid on the right
Answers
Explanation:
If the amine and carboxylic acid functional groups in amino acids join together to form amide bonds, a chain of amino acid units, called a peptide, is formed. A simple tetrapeptide structure is shown in the following diagram. By convention, the amino acid component retaining a free amine group is drawn at the left end (the N-terminus) of the peptide chain, and the amino acid retaining a free carboxylic acid is drawn on the right (the C-terminus). As expected, the free amine and carboxylic acid functions on a peptide chain form a zwitterionic structure at their isoelectric pH.
By clicking the "Grow Peptide" button, an animation showing the assembly of this peptide will be displayed. The "Show Structure" button displays some bond angles and lengths that are characteristic of these compounds.

The conformational flexibility of peptide chains is limited chiefly to rotations about the bonds leading to the alpha-carbon atoms. This restriction is due to the rigid nature of the amide (peptide) bond. As shown in the following diagram, nitrogen electron pair delocalization into the carbonyl group results in significant double bond character between the carbonyl carbon and the nitrogen. This keeps the peptide links relatively planar and resistant to conformational change. The color shaded rectangles in the lower structure define these regions, and identify the relatively facile rotations that may take place where the corners meet (i.e. at the alpha-carbon). This aspect of peptide structure is an important factor influencing the conformations adopted by proteins and large peptides.

2. The Primary Structure of Peptides
Because the N-terminus of a peptide chain is distinct from the C-terminus, a small peptide composed of different aminoacids may have a several constitutional isomers. For example, a dipeptide made from two different amino acids may have two different structures. Thus, aspartic acid (Asp) and phenylalanine (Phe) may be combined to make Asp-Phe or Phe-Asp, remember that the amino acid on the left is the N-terminus. The methyl ester of the first dipeptide (structure on the right) is the artificial sweetener aspartame, which is nearly 200 times sweeter than sucrose. Neither of the component amino acids is sweet (Phe is actually bitter), and derivatives of the other dipeptide (Phe-Asp) are not sweet.
A tripeptide composed of three different amino acids can be made in 6 different constitutions, and the tetrapeptide shown above (composed of four different amino acids) would have 24 constitutional isomers. When all twenty of the natural amino acids are possible components of a peptide, the possible combinations are enormous. Simple statistical probability indicates that the decapeptides made up from all possible combinations of these amino acids would total 2010
Some Common Natural
The different amino acids that make up a peptide or protein, and the order in which they are joined together by peptide bonds is referred to as the primary structure. From the examples shown above, it should be evident that it is not a trivial task to determine the primary structure of such compounds, even modestly sized ones.

Partial hydrolysis will produce a mixture of shorter peptides and some amino acids. If the primary structures of these fragments are known, it is sometimes possible to deduce part or all of the original structure by taking advantage of overlapping pieces. For example, if a heptapeptide was composed of three glycines, two alanines, a leucine and a valine, many possible primary structures could be written. On the other hand, if partial hydrolysis gave two known tripeptide and two known dipeptide fragments, as shown on the right, simple analysis of the overlapping units identifies the original primary structure.
3. N-Terminal Group Analysis
Over the years that chemists have been studying these important natural products, many techniques have been used to investigate their primary structure or amino acid sequence. Indeed, commercial instruments that automatically sequence peptides and proteins are now available. A few of the most important and commonly used techniques will be described here.
Identification of the N-terminal and C-terminal aminoacid units of a peptide chain provides helpful information. N-terminal analysis is accomplished by the Edman Degradation, which is outlined in the following diagram. A free amine function, usually in equilibrium with zwitterion species, is necessary for the initial bonding to the phenyl isothiocyanate reagent.
I hope its help you dear friend
Answer:
To write an expression, we often have to interpret a written phrase. For example, the phrase “ 6 added to some number” can be written as the expression x + 6, where the variable x represents the unknown number. How Do You Write Mathematical Expressions from Word Problems?