PL.4 Flashcards
Amino acids, optical stereoisomerism, and the formation of peptide bonds
What functional groups does amino acids contain?
At least one amino group, -NH2 and one carboxylic group, -COOH.
When is an amino acid an ๐ amino acid?
When the ๐ carbon is attached to a COOH group, NH2 group, a H and a R group respectively.
Amino acids are an example of what type of compound?
Bifunctional compound.
Amino acids show properties of both functional group such as?
Amineโs base properties, such as reacting with acids to form salts, and the carboxylic acidโs acidic properties, such as reacting with bases to form salts.
What type of ion is formed with the proton donating COOH group interact with the proton accepting NH2 group?
A zwitterion.
What is a zwitterion?
An ion that contains both negatively charged group and positively charge group.
In aqueous solutions, in what form are amino acids normally present in?
As zwitterions, this means that amino acids are very soluble in water as they are effectively ionic.
Are amino acids always neutral in the respect that they occur as zwitterions?
Not always, as some amino acids may have extra NH2 groups or COOH groups present in the R group.
What is the general formula of amino acids in neutral solutions?
H3N+CHRCOO-
What is the general formula of amino acids in acidic solutions?
H3N+CHRCOOH
What is the general formula of amino acids in alkaline solutions?
H2NCHRCOO-
A solution like amino acid that can withstand the addition of small amounts of acid or alkali without much change in pH is known as what?
Buffer solutions.
What type of isomerism do amino acids show?
Optical isomerism.
Why do amino acids show optical isomerism?
Because they usually have four different groups around a carbon atom.
Optical isomerism is a type of what isomerism?
Stereoisomerism. Where groups can be arranged differently in space.
What is the carbon atom called that has four different groups attached to it?
It is called a chiral carbon.
What type of mirror image do molecules exert when they have a chiral centre?
Non superimposable mirror images.
What are the different forms of optical isomers known as?
Enantiomers.
Do amino acids in our bodies exist as different enantiomers?
No, they only exist as one enantiomer of each amino acid, also known as L enantiomers.
What is the mixture called when it contains 50:50 of each enantiomer?
Racemic mixture.
When two amino acids join together by a secondary amide link, what is the secondary amide group also known as?
A peptide link.
When two amino acids are joined together, what is it called?
Dipeptide.
When naming a dipeptide, the first part of the name refers to which amino acid?
The one reacting with its COOH group.
When naming a dipeptide, the second part of the name refers to which amino acid?
The one reacting with its NH2 group.
What are proteins?
Naturally occurring condensation polymers made from amino acid monomer joined together by peptide links.
All proteins are built from how many different amino acids arranged in different ways?
20
Why are amino acids referred to as residues in context of proteins?
Residue is when an amino acid has lost the element of water in forming proteins.