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Flashcards in Amino Acids And Peptides Deck (21):
1

Protonic Equilibria of Amino Acids

Both the NH2 and the COOH groups in an amino acid undergo ionization in water.
At pH 7.4: a zwitterion forms, both + and - charges, neutral, amphoteric, amino group is protonated and carboxyl group is deprotonated.

2

Isoelectric point

Point at which the compound has no net charge, is average of pKa's

3

How can the protonation state of a functional group be determined?

By comparing the pKa of the functional group to the pH of the solution.

If pHpKa the group will be largely protonated
If pH is near the pKa the group will exist as a mixture of the two forms

4

Hydrophobic and Aliphatic AA's

Gly, Ala, Leu, Ile, Val

5

Hydrophobic and Aromatic AA's

Phe, Tyr, Trp, (His)

6

Hydrophilic and polar AA's

Asn, Gln

7

Hydrophilic and hydroxyl AA's

Ser, Thr, (Tyr)

8

Hydrophilic and charged AA's

Arg, Lys, Asp, Glu, (His)

9

Sulfur-containing

Met, Cys

10

Special

Gly (no R), Pro (imino)

11

All amino acids (except glycine) are optically active.

Dextrorotatory?

Levorotatory?

Dextrorotatory - rotating the plane of polarization of light to the right, D-amino acids are often found in bacteria and used as antibiotics and drugs that inhibit AIDS virus HIV-1 from entering cells

Levorotatory - rotating the plane of polarization of light to the left, all amino acids are found in L

12

Does geometry of proteins affect reactivity?

Yes

13

What connects AA residues?

Peptide bonds

Residue: AA-H20

14

Acid-base properties

Peptide bond is neither acidic nor basic, charge determined by terminal groups and amino acid side chains.

15

What is the fundamental linkage in the structures of peptides and proteins?

Planar amide bond

16

Covalent Bonds

Peptide Bonds
Disulfide Bonds

17

Non-Covalent Bonds

-Ionic bonds or electrostatic interactions
-Hydrogen bonds
-Hydrophobic interactions
-van der Waals forces

18

Hydrophobic interactions

Tendency of non polar compounds to self- associate in an aqueous environment.
Driving force is increase in entropy of water structure which occurs when no polar molecules/groups coalesce.

19

Van der Waals forces

-attraction of 2 atoms due to charge distribution
-induced dipoles
-becomes repulsion at close distances

20

Naming Peptides

Name from the free amine
Use -yl endings for the names of AA's
The last AA with the free carboxyl group uses AA name

21

Physiologically Active Peptides

Hormones - insulin, glucagon, oxytocin
Glutathione
Bradykinin