Amino Acids Flashcards
How are the 20 amino acids classified?
by their R group properties
Which amino acids are hydrophobic??
Gly Ala Val Leu Ile Pro Met Phe Trp
Why can prolines affect structural flexibility of polypeptides?
b/c it has. distinctive amino group NH2 group which forms a cyclic structure making it rigid
Is cysteine hydrophilic or hydrophobic?
hydrophobic even though it is classified as a polar amino acid
Which amino acids has a secondary amino group or imino group?
proline since its imino group forms a cyclic structure
When transferring an amino acid from a non-polar solvent to water and we get delta G < 0, what does this telll us about the reaction?
that the transfer is favorable and the reaction is hydrophilic
When transferring an amino acid from a non-polar solvent to water and we get delta G > 0, what does this telll us about the reaction?
the transfer is unfavorable and the amino acid is hydrophobic
The hydropathy index is directly proportional to what?
Gibbs free energe (delta G of the transfer).
If we have a large positive hydropathy index number, what would this tell us about our amino acid?
this would reflect higher hydrophobicity
Base on hydropathy index, which amino acid is more hydrophobic?
Isoleucine: 4.5 or alanine with 1.8 hydropathy index
They’re both hydrophobic since the number is positive, but isoleucine is higher thus more hydrophobic
What are the two ionizable groups in amino acids and what is their pka?
COOH to COO- + H+ has pka of 2.2
NH2 + H+ = NH3+ has a pka 9.4
You have a carboxyl group and it is placed in a pH of 4 is will it be protonated or deprotonated
deprotonated b/c anything above 3.5 is negative charge
What does it mean when an amino acid is amphoteric at physiological pH?
that the amino acid posses both acid and base properties
what does it mean when an amino acid is zwitterionic?
both positive and negative charges in the same molecule (their charge cancels out)
the isoelectric point is what?
the pH at which the amino acid has neutroa charge or net zero charge (zwitterionic)
What are enantiomers?
they are stereoisomers that are mirror images of each other. they are non-superimposable and each stereoisomer has a unique configuration
Do all amin acids have a chiral center?
no, glycine does not b/c it has 2 hydogen bonds aka it is not optically active
What does it mean to be optically active?
amino acids w/chiral centers can rotate polarized light
What is stereochemistry?
the spatial arrangement of the atoms in the molecule - aka the arrangements of the different groups around the alpha carbon
Trying to superimpose stereisomers that are mirror images of each other is impossible without doing what?
breaking a bond or bonds and rearranging them
Different molecules are in different…
configurations
If enantiomers rotate polarized light clockwise they are called?
positive dextrorotatory or D configuration amino acids
If enantiomers rotate polarized light anti-clockwise they are called?
negative Levorotatory or L configuration
The R and S configuration systems is used to characterize what?
molecules with multiple chiral centers
Are amino acids in the L or D form?
they are almost all in the L form. The D form is rarely found but do occur in bacteria and the human brain
What is stereospecificity?
the ability to distinguish between stereoisomers
-example our sensory receptors can distinguish between aspartame (sweet and its D configuration which is bitter
What is the difference between conformation and configuration
conformation to another conformation requires rotation and configuration to another configuration requires breaking one or more bonds.
