Answer the questions below. You should use the Chart of amino acids to
answer some of the questions.
1. Name one chemical element found in all amino acids.
Answer- An alpha carbon
2. Identify one acidic and one basic amino acid and write their corresponding
three letters and one letter symbols in the space below.
Acidic D, Asp
Basic G, Arg
3. Justify the reason why the amino acids you chose to answer question 2, are
acidic and basic, respectively.
Why is aspartic acid acidic?
Answer- Aspartic acid has an acidic side chain, its side chain has a carboxylic
acid group that has the ability to lose protons and become positively charged.
It also has a low PKa value.
Why is arginine basic?
Answer- Arginine contains a basic side group, its side chain contains nitrogen
which is a base, its Pka is high enough to bind to a proton and they gain a
positive charge.
4. Which amino acid doesn’t have stereoisomers?
Answer- Glycine
5. How are the D - and L - stereoisomers of amino acids identified?
Answer- The alpha carbon is a chiral carbon which means it has 4 different
substituents attached to it. This means most amino acids are able to rotate
the plane of polarised light either to the left (L isomer) or the right (D-isomer).
Follow from the CO to R to NH2, if these groups are arranged in a clockwise
manner then its an L isomer whereas if its arranged in an anticlockwise
manner then its a D isomer.
1
answer some of the questions.
1. Name one chemical element found in all amino acids.
Answer- An alpha carbon
2. Identify one acidic and one basic amino acid and write their corresponding
three letters and one letter symbols in the space below.
Acidic D, Asp
Basic G, Arg
3. Justify the reason why the amino acids you chose to answer question 2, are
acidic and basic, respectively.
Why is aspartic acid acidic?
Answer- Aspartic acid has an acidic side chain, its side chain has a carboxylic
acid group that has the ability to lose protons and become positively charged.
It also has a low PKa value.
Why is arginine basic?
Answer- Arginine contains a basic side group, its side chain contains nitrogen
which is a base, its Pka is high enough to bind to a proton and they gain a
positive charge.
4. Which amino acid doesn’t have stereoisomers?
Answer- Glycine
5. How are the D - and L - stereoisomers of amino acids identified?
Answer- The alpha carbon is a chiral carbon which means it has 4 different
substituents attached to it. This means most amino acids are able to rotate
the plane of polarised light either to the left (L isomer) or the right (D-isomer).
Follow from the CO to R to NH2, if these groups are arranged in a clockwise
manner then its an L isomer whereas if its arranged in an anticlockwise
manner then its a D isomer.
1
