Biochem - Infection and Immunity Flashcards
Acidic functional groups of AA
Carboxyl
Basic functional groups of AA
Amine
Imidazole
Guanidino
Neutral functional groups of AA
Glycine
Amides
Hydroxyl
Sulfhydryl -SH
Aliphatic functional groups of AA
Hydrocarbon
Aromatic functional groups of AA
Carbon rings
Start codon
Met is coded for by AUG - signifies start of chain
When is rotation of adjacent peptides allowed
At N-C (central)
C (central) -C
Structure of proteins
Linear, unbranched
heteropolymers
Size of proteins
50 to >2,000 AA
Primary structure of proteins
Order of AA = sequence
Always written from amino end to carboxyl e.g NH2 - His- Leu-Thr- Pro -COOH
Alpha helix
Rod like structure: polypeptide chain tightly coiled, amino acid side chains extending outwards from the helix axis
Stabilised by H-bonds: backbone amine (NH) and carbonyl (CO) group, 4 residues away along the chain
Beta pleated sheet
Zigzag structure: C-C bonds are tetrahedral –> cannot exist in planar configuration
Stabilised by H bonds: backbone amide (NH) and carboxyl (CO) groups, between diff parts of the chain or between diff chains
Types of proteins
Globular
Fibrous
Soluble
Membrane
Globular proteins
Compact spheres (haemoglobin, albumin)
Fibrous proteins
Filamentous molecules (collagen, keratin)
Soluble proteins
Dissolve in water (Hb, immunoglobulins)
Membrane proteins
Associated w/ membranes (glucose transporter)
Integral protein with a single transmembrane helix
Integral protein w/ multiple transmembrane helix
Peripheral proteins w/ lipid anchors
Peripheral proteins attached to the membrane
Biological function of enzymes
Part of metabolic pathways (glycolysis) Signal transduction and cell regulation (kinases, phosphatases) Digestion (amylases, proteases) Movement (myosin) Energy production (ATP synthase) Drug metabolism (monooxygenases)
Principles of enzyme catalysis
Enzymes are catalysts
Enzymes cannot alter the equilibrium of a reaction
Enzymes accelerate chemical reactions
Km
Measure for the stability of the esc
Large Km (~ 10^-3M)
Low substrate enzyme eaffibty
Small Km (~10^-5M)
High substrate-enzyme affinity
Coenzymes
Helper molecules that play a big part in enzyme-catalysed reactions
Coenzyme as co-substrate
Reversibly bound to enzyme
Coenzyme as prostatic group
Covalently inked w/ enzyme
Examples of energy transferring coenzymes and their entities
ATP - phosphate group
UDP - monosaccharides
CDP - Phosphatidic acids
GTP - phosphate group
e- and oxygen transferring coenzyme
NADH/N ADPH - e-
FMNH2/ FADH2 - e-
Porphyrins - e-, oxygen
Group transferring coenzymes
CoA - acyl groups
Biotin - carboxyl group
Lipoid acid - acyl group
Types of enzyme inhibition
Irreversible
Reversible
Types of reversible inhibition
Comp - enzyme can bind substrate or competitive inhibitor, but not both at same time
Non - comp - enzyme or esc can bind non-competitive inhibitor, and also create enzyme-substrate-inhibitor complex
Ki
Inhibitor contant - indicator for how potent an inhibitor is, conc required to produce half maximum inhibition
Michaelis-Menten eqn
v = Vmax x [S]/([S] + Km)
[S] «_space;Km
v = Vmax x [S]/Km
[S]»_space; Km
v = Vmax
[S] = Km
v = Vmax/2
[S]
Substrate conc
V max
Maximum velocity
Class of enzymes
Oxidorectases Transferases Hydrolases Lysases Isomerases Ligases
Oxidoreductases
Oxidation-reduction reactions
Examples of oxidoreductases
Dehydrogenases
Oxidase
Transferases
Transfer of amino, carboxyl, acyl, methyl, phosphate and other groups between molecules
Examples of transferases
Transaminase
Transcarboxylase
Hydrolases
Cleavage of bonds coupled w/ inserting water
Examples of hydrolases
Esterase
Peptidase
Amylase
Lysases
Cleavage of C-C, C-S and C-N (but not peptide) bonds
Examples of lysases
Decarboxylase
Isomerases
Rearrangement of bonds
Examples of isomerase
Epimerase
Ligases
Formation of bonds between C, O S, N
Examples of ligases
Synethetase
Carboxylase
ALP
Alanine phosphate
Marker of bone disease
Creatine Kinase
CK
Marker of muscle damage
Regulation of enzyme activity
Feedback loops Feedforward activation Allosteric regulation Phosphorylation - dephosphorylation Proteolysis Changes in gene expression
Feedback loops as a regulator of enzyme activity
Feedback inhibition (product)
Feedforward activation as a regulator of enzyme activity
Product activates a downstream enzyme, increasing substrate flow through a pathway
Allosteric regulation as a regulator of enzyme activity
Allosteric regulator binds to a site other than the enzyme’s active site, Changes tertiary or quaternary structure
Phosphorylation - dephospohorylation as a regulator of enzyme activity
Acts as an on/off switch
Phosphorylation requires kinase and dephosphorylation is performed by phosphatases
Proteolysis as a regulator of enzyme activity
Irreversibly activated or inactivated by proteolytic enzymes
Changes in gene expression as a regulator of enzyme activity
Increasing or decreasing transcription using transcription factors
Stop codons
UAA
UAG
UGA
Alpha helix configuration
Right-handed (clockwise) coiled, 3.6 AA’s per turn
Beta-pleated sheets configuration
Polypeptide chain runs in the same direction —> parallel beta-sheet, polypeptide chain runs in opp direction –> antiparallel beta-sheet
Serum protein electrophoresis
Lab test analysing proteins in blood
Serum proteins separated by their size and charge
Albumin is lightest and Ig’s are heaviest