Top3-Ch3-P71-77 Flashcards
- Nucleotides are subunits of ?
- amino acids are subunits of ?
- monosaccharides are subunits of ?
- nucleic acids (DNA)
- proteins
- polysaccharides
Amino acids are the monomers for _____ polymers
BUT Also……AA’s have specialised functions. Name three of them and explain a bit.
protein
- Glutamate and glycine neurotransmitters
- Parkinson’s disease due to reduced dopamine. Dopamine synthesised from tyrosine.
- Derivatives of AAs eg. Histamine, derived from histidine implicated diseases such as asthma.
Describe basic structure of amino acid
All amino acids have:
- the same skeleton of a central (or alpha) carbon atom, with attachments of:
- an amino group;
- a carboxy group;
- a hydrogen atom; and
- an R side-chain group.
How many different amino acids are there
20
Explain optical activity in relation to amino acids.
As R varies with all the amino acids, the α carbon will be asymmetric or chiral (nonsuperimposable mirror image) in all cases but one. This exception is glycine, where the R group is H. This means that all amino acids except for glycine are optically active and hence there are two
isomers.
Optical rotation (optical activity) is the turning of the plane of linearly polarized light about the direction of motion as the light travels through certain materials. It occurs in solutions of chiral molecules such as sucrose (sugar), solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or molecules.
any crystal or molecule that can’t be superimposed on its mirror image will be optically active
all amino acids found in natural proteins in most
animals are L or D -isomers? Because of this we write the structures with the amino groups on the left or right side?
L-isomers
left side.
That means the D is on the right side.
Amino acid nomenclature diagram
In the structure of amino acids the α-carbon atom has a ‘____ centre’
chiral
optically active means it can
rotate polarized light
amino acids have L and D forms
BUT:
almost all AA in proteins are __ stereoisomers
cells specifically _____ _ stereoisomers.
The exception is?
L
synthesise L
NOTE: glycine is the exception, does not have a chiral carbon. Is NOT optically active
See diagram of L v D configuration and explanation
- Numbering of C starts at carboxyl carbon
- Based upon similarity of configuration to L- and D-glyceraldehyde
- Cells specifically form L- isomer, as active site of enzymes are asymmetric
Describe Alanine the simplest chiral amino acid
As you can see amino group is on left for L-AAs
Describe Glycine. Is it chiral or not?
No chiral centre and chiral centre means that all the 4 off Carbon must be different and chiral centre is easiest way to identify chiral compound
Amino acids are classified by their R-group. Name the five groups
- non-polar, aliphatic (Non polar and hydrophobic)
- aromatic (relatively nonpolar - hydrophobic - All can participate in hydrophobic interactions.
- polar, uncharged (more soluble in water, more hydrophilic.)
- positively charged (basic) - ( most hydrophilic groups are those either positively or negatively charged)
- negatively charged (acidic) - ( most hydrophilic groups are those either positively or negatively charged)
Nonpolar, aliphatic R groups, name them and give formulaes
Aromatic R groups, name and formula and give some rules.
- Relatively non-polar,
- hydrophobic interactions
- Some H-bonding
Aromatic electron cloud, see picture
Aromatic Amino Acids absorbs
UV light
Polar, uncharged R Group, name, give group descriptions.
- Hydrophilic,
- H bonds
- Polarity-
- serine, threonine
- -OH group
- Cysteine:
- sulfhydryl group
- weak acid. pKa 8.2
- weak H bonding
- Asparagine + glutamine
- amide group
- serine, threonine
Negatively charged (acidic) R Groups, name, describe.
- Often found at hydrophilic
- Enzyme active sites
- Note similarity to Asparagine & Glutamine from the polar, uncharged group
Explain formation of Disulfide bond
- Cysteine thiol group is nucleophilic and easily oxidised to Cystine (reversible)
- Both are hydrophobic residues
- Important role in stabilising protein structures by cross linking polypeptides
Positively charged (Basic) R Groups, name
Learn groups and amino acids and symbols see attached
