Lecture 2: Amino Acids

Question 1

what are amino acids

Answer 1

compounds consisting of the amino and carboxyl group and a side chain R group

Question 2

alpha carbon

Answer 2

the first carbon atom that attaches to a functional group, such as a carbonyl

Question 3

chiral center

Answer 3

bonded to 4 different groups

hence the groups can take 2 unique spatial positions

Question 4

Classification of AA

Aromatic amino acids?

Answer 4

• R groups have benzene ring
• R groups are hydrophopic hence are located on the interior of a protein.
• can absorb UV light of wavelenght 250–290 nm

3

the Aronma of the Fine Pine and Yellow Timber are Worth the Tryp

Question 5

stereoisomers

Answer 5

• same molecular formular but different strucutural formula
• nonsuperposable mirror images of each other

Question 6

optically active

Answer 6

can rotate the plane of plane polarised light

all molecules with a chiral center are optically active

Question 7

L and D configuration of amino acids

Answer 7

• the C chain is lined vertically with the chiral C in the center and r group below the alpha carbon

L AA, amino group to the left and D AA, amino group to the right

Question 8

classification of amino acids is based on

Answer 8

• similarities of the R group
• nutritional class( Essential and nonessential)
• product of metabolism of the C skeleton (glucogenic, ketogenic, both)

Question 9

what are proteins?

Answer 9

polymers of amino acids, with each amino acid residue joined to its neighbor by an amide linkage/peptide bond.

Question 10

Differentiate between essential and nonessential amino acids?

Answer 10

essential aa cannot be synthesized in the human body whilst non-essential aa can be synthesized in the human body.

Essential aa consist of Phenylalinine, threonine, valine, histidine, arginine, leocine, lysine , typtophan, isoleucine amd , methionine

Question 11

explain the general structure of an amino acid?

Answer 11

consists of an α carbon is bonded to four different groups: a carboxyl group, an amino group, an R group, and a hydrogen atom.

excluding Glycine with two identical groups

tetrahedral arrangement of the bonding orbitals occurs around the α-carbon atom, the four different groups can occupy two unique spatial arrangements, and thus amino acids have two possible stereoisomers.

Question 12

in what state do amino acids exist at a neutral or Physiological pH, henceexplain the amphoteric nature of AA.

Answer 12

-At neutral pH, the carboxylic group is negatively charged and the amino group is positively and the net charge is 0. (Zwitterion)
-hence AA can function as weak acids and weak bases

Question 13

Explain the titration curve of Aliphatic AA?

Answer 13

• titration curve has 2 buffering regions which correspond to the 2 pka values.
• at low ph AA is fully protonated with a net charge of +1
• upon addition of base, the first buffering region, pKa value corresponds to the removal of H+ from the amino group and lastly the second Pka value corresponds to the removal of H+ from the carboxyl group.
• isoelectric point- is the pH at which all aa molecules are in zwitterion from.
• at high ph, AA is fully dissociated and has a net charge of -1

Question 14

amphoteric nature of amino acids

Answer 14

aa consist of ionizable carboxyl and amino group hence can donate or accept a proton functioning as weak acids and bases

aa are positively charged at low pH

ionisable groups have characteristic pKa values.

Question 15

zwitterion

Answer 15

• is a dipolar ion consisting of negatively charged carboxyl group and positively charged amino group at neutral pH(physiological pH 7.35-7.45)
• the net charge is 0
• is amphoteric in nature

Question 16

isoelectric point

Answer 16

pH at which all molecules of aa are in zwitterionic form

Question 17

carboxyllic group reactions

Answer 17

esters and amides

Question 18

amino group reactions

Answer 18

peptides

Question 19

peptide bond

Answer 19

occurs in a dehydration reaction linking the alpha carboxyl group of one aa to the alpha amino group of another by eliminating a water molecule

Question 20

C-N bond in peptide is shorter?

Answer 20

• due to partial electron sharing between carbonyl oxygen and amide nitrogen
• O has partial negative and N has partial positive creating a small dipole