Amino acids and protein Flashcards
What is proteomics?
is an emerging field that studies the full range of expression of proteins in a cell or organism and changes in protein expression in response to growth, hormones, stress, and aging.
Amino acid structure
Building block of proteins. Has basic amino group, acidic carboxyl group, a hydrogen atom and a side chain.
Protein contains which isomer of AA and why?
All amino acids in proteins are of the l -configuration because proteins are biosynthesized by enzymes that insert only l -amino acids into the peptide chains.
Isomers of AA
Alfa-asymmetric carbon give rise to two optically active isomers called stereoisomers, mirror images of each other but not superimposable. Also, called enantiomers. They are Levo and dextro isomers.
Importance of R side chain
Determines the properties of AA. Structure and function of protein and their charge.
Aliphatic AA
Glycine, Alanine, Valine, Leucine, Isoleucine - Contains aliphatic hydrocarbon chain and are hydrophobic
Neutral AA
Hydrophilic.
Serine, Threonine - contains hydroxyl group and found on active site of enzymes
Asparagine and glutamine - contains amide group
linkage with sugar and forming Glycopeptides.
Aromatic AA
Contains aromatic side chain. Eg: Tyrosine, Tryptophan, Phenylalanine and are hydrophobic
Acidic AA
Aspartic acid and glutamic acid. Ionized at PH 7 and contains negative charge. Hydrophilic
Basic AA
Lysine, Arginine and Histidine they are protonated at PH 7 and contains positive charge. Hydrophilic
Sulfur containing AA
Cysteine and Methionine.
Hydrophobic
Provides structural support to protein by forming disulfide bond
Imino acid
Proline, contains alfa carbon and alfa amino group.
Zwittor ion
At PH 7, dominant form of AA contains electronically neutral charge and called zwittor ion
Use of Henderson-Hasselbalch equation
Describes the titration of AA and used to predict charge and isoelectric point of a protein
Isoelectric point
The PH at which a molecule has no net charge is called isoelectric PH.
N-terminal AA and C-terminal AA
AA residue consisting of free amino group on one end of the peptide is called N-terminal AA and if contains free carboxyl group then C-terminal AA.
Primary, secondary, tertiary and quaternary proteins structure
Primary - Linear arrangement of AA in polypeptide chain
Secondary:
1. alfa helix - rod like structure, tightly coiled, forms helix by H-bonding between carbonyl hydrogen and amide hydrogen
2. beta pleated sheet - Hydrogen bonding is lateral which produces parallel and antiparallel sheets.
Tertiary: three dimensional, folded and biologically active formed by hydrogen bonds, disulfide bonds, hydrophobic interaction and salt bridge.
Quaternary: formed by covalent and non-covalent interaction between subunits.
Name two AA occurs in B- turns of beta pleated sheets in proteins
Glycine and proline
Protein purification depends on
Charge
Size
Solubility ang
Ligand binding
Carbohydrates and lipids are stored as
Glycogen and Triglycerides
Most sugars in the body has L or D configuration?
Dextro [while AA has L configuration]
Which ketohexose sugar is present in diet or body?
Fructose
Homoglycans and Heteroglycan
Polysaccharides consisting of single sugar - homoglycans
Polysaccharides consisting of different sugar composition - heteroglycans
Saponification
Ester bond of triglycerides rapidly hydrolyzed in presence of strong base (NaOH) and produces glycerol and free fatty acid - process called saponification.
Fluid mosaic model
Proteins are embedded in a fluid phospholipid bilayer; some are on one surface (peripheral) and others span the membrane (transmembrane). Carbohydrates, covalently bound to some proteins and lipids, are not found on all subcellular membranes (e.g., mitochondrial membranes). On the plasma membrane, they are located almost exclusively on the outer surface of the cell.
