Flashcards in Amino acids Deck (19):
what are the pka's of carboxyl group, aspartate, glutamate, histidine, amino group, lysine, arginine
glutamate and aspartate: 4
Name the 9 nonpolar amino acids and two with special properties.
glycine, alanine, valine, isoleucine, leucine, proline, methionine, tryptophan, phenylalanine.
glycine is achiral and proline is 15% of the time found in cis conformation and is stabilized.
Name the 6 uncharged polar amino acids. and their one letter symbols
cysteine, serine, threonine, glutamine, asparagine, tyrosine.
GLUTAMINE IS LONGER THAN ASPARAGINE (glutton)
c, s, t, Q, N, Y
asparagine is N
Arginine the base is R
Will you see disulfide bonds in the cytoplasm?
No, because the intracellular environment is reducing and disulfide bonds form under oxidation. So for example, it won't be present in the active site. It adds stability to the protein but is not the driving force of the folding. Insulin is stabilized by disulfide bonds. Oxidize = remove electrons,
What are the two amino acids with acidic side chains? Which is longer? Which is more acidic? What are the letter symbols?
glutamate and aspartate. Glutamate is longer and its pka is larger, wonder why bech.
GlutamatE = E
Aspartate = D
what are the three basic amino acids and their one letter symbols. What is histidine special for?
Korean human resources
K = lysine
If histidine is present then it is doing something important. It is great for pH sensing because it has a pKa close to physiological pH. We would say it is neutral and useful in a narrow range.
How to determine buffer region?
+1 or minus 1 the pKa.
phi and psi
There are only two sets of phi, psi angles that can be repeated without steric collisions. If you repeat one set over and over, you would get a coil. If you alternate sets you would get a beta. So these angles determine secondary structures.
Describe the alpha helix stats
Right handed, 3.6 residues per turn,
5.4 angstroms per turn
1.5 angstroms per rise (per residue)
every turn is 360 degrees. Every turn has 3.6 residues. So at every 100 degrees there is a side chain sticking out.
For an antiparallel beta sheet, how many angstroms per residue?
3.5 angstroms per residue, almost double the distance covered by the alpha helix residue
Parallel vs antiparallel beta sheet
Parallel beta sheets are looped by an alpha helix. These sheets are usually buried in the protein interior, therefore, they are hydrophobic.
Antiparallel beta sheets and amphipathic, and exposed on the surface. They usually have a polar and non polar face. And they don't need a linking motif.
All beta sheets make hydrogen bonds with their neighboring beta strands via backbone C=O and N-H
Name the four motifs.
helix-loop helix (alpha chains) - can have packing perpendicular or parallel to itself.
beta -hairpin: beta chains
greek key: beta hair pins that folds back over.
Those two are antiparallel.
beta alpha beta motif - parallel beta sheet, covered by alpha chains.
Which amino acids tend to be phosphorylated? Which amino acid functions as a nitrogen donor?
Serine, threonine, tyrosine. In metabolism, glutamic acid functions as a nitrogen donor in metabolism.
Describe primary, secondary, tertiary and quartenary structures
Primary- the sequence which is defined by covalent bonds. Includes disulfide bonds.
Secondary - local arrangements of the peptide bond, defined by hydrogen bonds
Tertiary - arrangement of secondary structures into domains
Quartenary - multisubunit protein
What is an up-down beta barrel
Transmembrane up down beta barrel
Greek key barrel
alpha beta singly wound barrel
doubly wound alpha beta.
The helix loop helix motif is found in alpha helix bundles (can be perpendicular)
It is an antiparallel beta sheet wrapping to form a barrel, protecting its nonpolar side.
The opposite. This beta barrel wants the polar on the inside because the membrane interior is a hydrophobic environment. (beta hairpin)
The more strands for each barrel, the larger the pore.
Greek key barrel: the greek key motif is unable to form the barrel structure. It forms more a sandwich around the molecule. Like the doubly wound barrel.
Alpha/beta singly wound barrel: small parallel beta sheet barrel, surrounded by amphipathic alpha helices. Helices are only on one side of the beta sheet.
alpha/beta doubly wound: shown like a sandwich. you have barrels on both sides of the beta sheet. The sheet just remains flat instead of curling around.
what are characteristics of cis proline?
The peptide bond is planar, it is in L configuration, not common to secondary structures,
it is common in turns and therefore is often located on surfaces rather than interior of proteins.
Turns - non repetitive secondary structures, 4 residue beta bend is stabilized by a hydrogen bond. Now the functional property of a protein is due to the turns and loops. Cis proline always creates a turn in the backbone and so is found on surfaces of proteins.
How many residues in an alpha helix that spans a lipid bilayer of 33 A?
1.5A per residue so 33/1.5 = 22 residues.
Can be polar residues but never charged.
What would happen from an insertion of one additional amino acid into the strand of an anti-parallel beta sheet?
Insertion of any amino acids will disrupt the polar non polar alternation that creates the hydrophilic and hydrophobic faces.