Amino Acids and Proteins Flashcards
Smallest functional protein
tripeptide called thyrotropin-releasing hormone
Protein Basics
can consist of a single polypeptide chain e.g prolactin, or several interacting chains e.g pyruvate dehydrogenase (48 chains)
Unbranched
Unbranched polypeptide chain is polymer of amino acids linked by a peptide bond
Amino Acid Structure
H2N (potentially basic), COOH (potentially acidic), Alpha carbon, R side chain
Amino Acid Functions
Proton donors COOH to COO- + H+
Proton Acceptors NH2 + H+ to NH3+
Isomers
Because amino acid a carbon has 4 different groups attached (except for glycine R double H_ it is asymmetric. D and L
D and L
Proteins contain only L amino acids. D-isomers occur in bacterial cell walls.
L-amino acid NH2 on left and on right in D-amino acid
Ionisation character of amino acid groups
Neutral (R does not ionise), basic and acidic (r does ionise)
Examples of types
Neutral - Gly, Ser, Pro
Basic - Lys (strong), Arg (strong), His (weak)
Acidic - Glu (strong) and Cys (weak)
Electronegativity
Power of an atom to attract electrons towards itself
Protein Structure
Primary structure - amino acid sequence
Secondary structure - arrangement in space of amino acids close to one another in a polypeptide chain e.g a-helix and b-sheet
Protein Structure (contd.)
Tertiary structure:
3D structure of all the atoms in a single polypeptide chain
Interactions between R groups fold protein into a compact 3D shape
Quaternary structure: 3D interaction of protein subunits in proteins with more than one polypeptide chain
Post-synthetic modifications of amino acid side chains 1
Hydroxyproline - OH group stabilises collagen fibre (insufficient hydroxylation leads to scury)
2
Y-carboxyglutamate - carboxylation of Glu in prothrombin (lack of carboxylation leads to haemorrhage)
3
O-phosphoserine - phosphorylation of serine is most common form of regulation of protein activity
Polar R group
Hydrophilic due to presence at pH 7 of full +ve or -ve charge in R group (polar, charged) or partial charges in permanent-dipole bonds in non-ionisable R groups (polar, uncharged)
Nonpolar R group
Hydrophobic, many non polar C-C and C-H groups
Ionisation of amino acids
pH 1 cationic (+1) fully protonated NH3+ at top and COOH on right
ph 7.4 dipolar (0) zwitterion NH3+ at top and COO- right
pH 11 anionic (-) all protons lost
NH2 at top and COO- right
Transport
O2 on haemoglobin, Na+/K+ pump cellular uptake of glucose
Storage
Fe2+ in complex with ferritin in liver
Motion
Muscles, intestinal flagellae
Skeleton support
Collagen in bone and skin
Extra
Control of metabolism, growth and differentiation eg insulin, gene repressors, EGF
