Med Biochem L2 - Amino acids and Peptides Flashcards
Definition of protein:
derived from Greek protos (first, primary), meaning the most basic and important substance of animal and plant nutrition.
Catalyst:
various enzymes, about 1/3 of human genes encode enzymes.
Transporter:
Oxygen transport (hemoglobin),
Fatty acid transport (albumin),
Various nutrients,
Hormones,
Drugs,
Toxic substances, etc.
Regulatory role:
Growth factors,
Transcription factors,
Various hormones such as insulin and
Glucagon, etc.
Contraction:
Myosin and actin in muscle
Immune system:
Immunoglobulins,
Complement proteins
Blood clotting:
Fibrinogen and coagulation factors
Strructural Functions:
Bones,
Ligaments,
Extracellular matrix proteins
Cytoskeleton:
Keratin,
Microtubules,
Microfilaments, etc
A variety of protein functions are possible by unique 3D structures that are …
dictated by unique amino acid sequences.
Some amino acids have an amino group on another carbon, for example, …
on an epsilon carbon in Lys.
Amino acids have 2 stereoisomers:
L and D isomer.
In nature, the L isomer is dominant
L isomer is … configuration.
S
Under acidic pH, amino acids are … charged.
positively
Under basic pH, amino acids are … charged.
negatively
Under neutral pH, amino acids have … form.
Zwitterionic
The … form cannot exist under any pH.
nonionic
(Hydropathy index)
Positive:
hydrophobic
(Hydropathy index)
Negative:
hydrophilic
… can form cystine
Cysteine
… : nonpolar thioethergroup
Methionine
Cystine is …
hydrophobic
-SH - …
Sulfhydryl group
-S-S- - …
Disulfide bond
Absorbance maxima at … nm
280
Lysine pKa of side chains …
10.5
Arginine pKa of side chains …
12.5
Histidine pKa of side chains …
6.0
The only AA that has a pKa near neutral pH
Aspartate pKa of side chains …
3.65
Glutamate pKa of side chains …
4.25
Isoelectric Point (pI): the point where the net charge is …
0
pI = (pK1 + pK2) / 2 (average of two pKa values)
At the neutral pH, Histidine side chain is …
not charged.
The reverse reaction is favored. (K<1)
The amino group is a good nucleophile, but the hydroxyl group is a poor leaving group
The pI of any polypeptide can be …
calculated.
A polypeptide chain has …
only one alpha-amino group and one alpha-carboxyl group
The pKa of the alpha-amino group in a polypeptide \
The pKa of the alpha-carboxyl group in a polypeptide - is …
The pKa of the side chains in a polypeptide /
slightly different from that in AA
The peptide bond is not a single bond. This has some double bond characteristics. Double bonds are …
not rotatable.
So, the 6 atoms are stuck on a plane.
Bond lengths
C-N 1.49 Angstrom
C=N 1.27 Angstrom
C-N in peptide 1.32 Angstrom
