McMurry (Kap. 19,0-19,1) Flashcards
Proteins are very abndant in living organisms.
Give examples of common proteins?
Keratin of skin and fingernails.
enzymes that catalyze the biological reactions in our body.
Regardless of their different functions (proteins), are their structures similiar or different?
Their structure are similair.
They are made up of amino acids linked together.
Amino acids - how many functional groups do they contain?
Difunctional (2)
- acidic Carboxylic acid group.
- basic Amino group.
How do amino acids get joined together?
By forming amid bonds.
-NH2 of one amino acid forms a bond with the -CO2H of another amino acid.
They split off water in the process.
What is the difference between a peptide and a protein?
Peptide = amino acid chains with fewer then 50 amino acids
Proteins = larger chains of amino acids.
A carboxylic acid is deprotonated in the physiological pH (7,3)
The amino group is protonated.
Right?
Yes.
What is the form called of the aminoacid in the body? (carboxylic group deprotonated and amino group protonated?)
zwitterion form.
An amino acid zwitterion is an internal salt and therefore have many similiar properties.
What similiar properties do amino acids have to salts?
- large dipole moment
- Soluble in water
- insoluble in hydrocarbons (organic compounds).
- Crystalline with high melting point.
- They are amphiprotic (reacts as both acid or base, depending on the circumstances).
When is an amino acid a base or acis?
In (aq) basic solution = amino acid reacts as an acid, therefore losing a proton from its NH3+.
In (aq) acidic solution = amino acid accepts a proton to its (CO2-) group to yield a carboxylic acid.
On page 680-681 you can see the 20 different amino acids abundant in proteins.
(their pKa values, their structures, their names, their pI values.
See page 680-681
All the 20 abundant amino acids in proteins are a-amino acids.
What does that mean?
The amino group in each amino acids are substituents on the a-carbon (the one next to the carbonyl group).
Nineteen of the 20 amino acids are primary amines (RNH2)
only one is secondary (PROLINE) - whose nitrogen atom and a-carbon is part of a five-membered pyrrolidine ring.
The different amino acids only differ in the nature of the side chain (R).
correct.
In addition to the 20 amino acids found in proteins, there are more then 700 non protein amino acids - see page 682 for examples.
page 682
Each amino acid has a chiral center (except for GLYCINE).
Hoe many enantiomer for each amino acid, and which one is dominant in the protein?
There are only 2 enantiomers for each amino acid, because only 1 chiral center is present.
the L amino acid is the naturally ocuring amino acid in making proteins, the other form is called the D amino acid. (nature uses the L-configuration).
The 20 amino acids can be further classified as neutral, acidic og basic, depending on the structure of the side chain.
which are wicht?
15 = neutral side chains
2 (aspartic acid + glutamic acid) = one extra carboxylic acid therefore acidic.
3 (lysine, arginine, histidine) = have basic amino groups in their sidechains.
(cysteine and tyrosine) although classified as neutral - they have mildly weakly acidic properties.
