Medical Cell Biology and Genetics - Amino Acids and Proteins Flashcards
What is the chiral centre of an amino acid?
The central alpha carbon of an amino acid
How are amino acids classified?
According to:
- polarity (how they reach with water at pH 7)
- aromatic (contain benzene ring) or alipathic (no ring)
- whether they are positively or negatively charged
What is a zwitterion?
A neutral molecule with both positive and negative charges
In the case of amino acids the amine group deprotonates the carboxylic group
NH3—-C—-COOH —> NH4+—-C—-COO-
What are the 3 key properties of the peptide bond?
- all atoms are in the same plane
- although it is a single bond it has double bond characteristics therefore does not rotate
- the carbonyl oxygen and amide hydrogen are in the trans orientation
What is the isoelectric point of a protein?
The pH at which the protein has no overall charge
eg Acidic proteins may have negatively charged amino acids therefore have a low pI
eg Alkaline proteins contain many charged amino acids and have a high pI
Define the 4 levels of protein structure:
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
Primary structure - the amino acid sequence
Secondary structure - folding of the peptide chain into alpha helices or beta pleated sheets
Tertiary structure - further folding to form the 3D structure of the protein
Quaternary structure - assembly of a large complex of MULTIPLE peptide chains eg Hb
List the bonds associated with each level of protein structure
Primary structure - peptide bonds
Secondary structure - hydrogen bonds
Tertiary structure - H bonds, van der waals forces, ionic interactions, disulfide bridges, hydrophobic interactions
Quaternary structure - same as above
In general what is the role of globular and fibrous proteins?
Globular proteins are mainly functional - such as enzymes and regulatory proteins eg Hb
Fibrous proteins tend to provide structure and support eg Collagen
What is the role of molecular chaperones?
Ensure that protein folding is correct, therefore preventing disease states due to inefficeint damaged proteins
What are the key features of the alpha helix ?
structure, and helix breakers and makers
Right handed helix
3.6 amino acids per turn
Pro acts as a helix breaker because the rotation around the N-C bond is impossible.
Gly acts as a helix breaker because the tiny H R group supports other conformations.
Small HPHOBIC amino acids are strong helix formers
Describe the structure and bonds of a beta sheet
Can be parallel - run in same direction
Can be antiparallel - run in opposite directions
There are lots of inter-strand hydrogen bonds
What is pK and how is it calculated?
NEED TO FINISH
pK = - Log [H+]
