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are molecules with the same chemical formula but different chemical structures. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms in space. There are two main forms of isomerism: structural isomerism and stereoisomerism.
is a form of isomerism in which molecules with the same molecular formula have bonded together in different orders
are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but that differ only in the three-dimensional orientations of their atoms in space.
in organic molecules refers to the first carbon atom that attaches to a functional group. (Alpha-carbon (α-carbon) is also a term that applies to proteins and amino acids. It is the backbone carbon before the carbonyl carbon)
What is unique about glycine
it is not chiral
-A molecule is considered chiral /ˈkaɪərəl/ if there exists another molecule that is of identical composition, but which is arranged in a non-superposable mirror image.
-Two mirror images of a chiral molecule are calledenantiomers
Amino Acids: Absolute configurations at the alpha carbon
- - L and D is different from R and S.
- - L is not always S, and D is not always R.If the priority of NH2 > COOH > R, then L=S and D=R. For example, L-Alanine = S-Alanine.
- - If the priority of NH2 > R > COOH, then L=R, and D=S. For example, L-Cysteine = R-Cysteine.
- - L-amino acids are the more common in nature, and are the type found in proteins. D-amino acids are less common in nature, and are never found in proteins.
Amino Acids as dipolar ions
- At low pH, amino acids exist in the cationic form.
- At high pH, amino acids exist in the anionic form.
- At pH = pI, amino acids exist in the zwitterion form, which is overall neutral.
- is the pH at which a particular molecule carries no net electrical charge
Acidic amino acids: Classification
If the R group contains carboxylic acid, then it's an acidic amino acid. There are two acidic amino acids: aspartic acid and glutamic acid
Basic Amino Acids: Classification
If the R group contains an amine group, then it's a basic amino acid. There are three basic amino acids: lysine, arginine, and histidine.
non charged. Water "fearing"
- charged. water loving
- if amino acid has a base, acid, amine or alcohol attached to it, it's hydrophilic
- =amide bond
- The peptide bond is formed by the amine group attacking the carbonyl carbon.
- The peptide bond is very difficult to hydrolyze. It requires a strong base, or a biological enzyme
- the cleavage of chemical bonds by the addition of water
Any of the 20 or so amino acids that has the amino and carboxyl groups attached to the same carbon atom,usually has an l-configuration, and is the chemical constituent of a protein.