Amino Acids & Proteins Flashcards
Are fibrous proteins water soluble?
no
Are globular proteins water soluble?
yes
What is the role of fibrous proteins?
structural
What is the role of globular proteins?
dynamic (e.g enzymes and receptors)
What is an example of a part globular, part structural protein?
myosin
What percentage of dry cell weight do proteins represent?
50%
What is the role of proteins?
to perform the functions essential for life
know the structure of an amino acid
Carboxyl group
Amino group
R group
H atom
What causes the folding of proteins?
The hydrophobic effect (driven by the need of internalise hydrophobic polypeptide chains) (polar chains on outside, non-polar on inside)
What is pKA?
PH value at which a weakly ionising group is 50% associated
What is the role of di-sulfide bridges?
Hold polypeptide chains in shape
What is the most hydrophobic amino acid?
phenylalanine
What are the aromatic amino acids?
phenylalanine tyrosine tryptophan
What is the primary structure?
linear sequence of amino acids
What is the secondary structure?
regions of regularly repeating conformations of the peptide stabilised by hydrogen bonding between the peptide groups e.g alpha helices and beta sheets
What is tertiary structure?
the 3D shape of the folded chain. Arrangement of all amino acids including R groups and any prosthetic groups (in a single polypeptide chain)
What is the quaternary structure?
the arrangement of two or more polypeptide subunits in an oligomeric protein (multi chain only)
How is a peptide bond formed
removal of O from one peptide and 2 H from the other O=C-N-H
which amino acids have ionising side chains?
Asp, Glu, His, Arg, Ly, Tyr and Cys
How do we know that ionising side chains have an affect on protein structure and function?
Use electrophoresis to separate proteins and amino acids at different PHs, because they carry different charges at different PHs
How do you write an amino acid
C terminus first. N terminus on right
Describe the structure of a right handed alpha helix
Each C=O is hydrogen bonded with the amide hydrogen of the residue 4 places ahead
What’s an example of an alpha helix
Alpha keratin
What’s an example of a beta pleated sheet?
virus coat proteins
Differences between alpha helix and beta sheet?
Alpha helix more compact
-look at structures
Describe the tertiary structure of Mb
- contains a heme group
- globular
- folded to be very compact (with hydrophobic on inside)
- 75% of amino acids folded into a right handed alpha helix
Why is Hb an allosteric protein?
It has multiple ligand binding sites
What is the structure of Hb made up of?
Two molecules of alpha globin
Two molecules of beta globin
Tetramer organised into a pair of dimers
Largely alpha helical
What is collagen?
A major protein in vertebrae connective tissue (25-35% of total proteins in mammals)
What is collagen made up of?
- Units of the triple stranded tropocollagen molecule. The triple helix is held together by H bonds between chains.
- multiple repeats of -Gly-X-Y (where X is often proline and Y is often hydroxyproline)
- Three left handed helical chains coiled around each other in a right handed supercoil
What is an enzyme?
Usually a protein (can sometimes be RNA) that accelerates biological reactions
Why are enzymes important for life?
- Accelerates metabolic reactions
- enables regulation of metabolic reactions
- integration of metabolism
What are the biomedical applications of enzymes?
- Diagnostic reagents (e.g enzymes being released into blood after tissue damage)
- Lab reagents
- Drug metabolism
- Drugs work by inhibiting enzymes
What are isozymes?
Tissue-specific physically distant form of an enzyme
