Amino Acids And Peptide Bonds Flashcards
At pH 7 what do amino acids exist as
Exist as zwitterions
What are the different parts of an amino acid and draw the general structure of amino acids
Amino acids can form enantiomers since they have a chiral centre
How are amino acid enantiomers named
Left and right handedness defined using L and D
L= Levo
D= dextro
Amino acids are named relative to glyceraldehyde= relative stereochemistry
What is racimisation
The enantiomers of amino acids can interconvert between them (but this would take 10 years to happen)
So L enantiomers can convert to D enantiomers and vice versa
What is absolute stereochemistry *
Based on opposite orientation
what form of enantiomer are amino acids always found in proteins
All amino acids in proteins are L enantiomers
They’ll have the same stereochemistry
How is a peptide formed from amino acids
Dehydration/condensation reaction to form an amide bond between the carbonyl group of one amino acid and amine group of another (and water)
(OH group comes off carboxylic acid)
What is the ‘backbone’ of a peptide
What is the definition of a peptide
2 or more amino acids linked by peptide bonds
What is the definition of a polypeptide
Lots of amino acids joined together by peptide bonds
What is the C-terminus and N-terminus
What is an amino acid residue
What is the primary structure of a protein and how is it represented
What kind of hybridisation does the carbon, oxygen and nitrogen atom undergo and what shape is the c=o bond
Sp2 hybridisation
Trigonal planar
How do amino acids behave 60% of the time.
There is a c=o bond the p orbital of oxygen and carbon overlap so they share a pair of electrons (which is how the double bond forms)
(Ignore red)
How do amino acids behave 40% of the time
Nitrogen donates one of its electrons from its p orbital to oxygen so that oxygen has a negative charge and nitrogen has a positive charge
This allows for the p orbitals of carbon and nitrogen to overlap forming a double bond between them (instead of between the carbon and oxygen
Because of this, a peptide bond has partial double bond character
How are the electrons arranged in each of the orbitals of the atoms in an amino acid in a peptide bond
Why is a peptide bond polar
After nitrogen donates its electrons to oxygen it pulls the electrons in the N-H bond towards itself due to its higher electronegativity, inducing a sight positive charge on the hydrogen
Meanwhile oxygen has a slight negative charge as it accepts an electron from nitrogen
What is meant by the peptide bond having partial double bond character
Double bond can form between C and N or between C and O
So if there’s a double bond between N and C there wont be one between C and O
What is meant by a peptide bond being planar
All of the atoms attached to the bond are in the same plane
Illustrate the plane of the peptide
What would the trans configuration of a peptide be
Alpha carbons are opposite eachother