lolz Flashcards
What is Maltose’s linkage?
Two glucose units joined thorough C-1 of left hand sugar and at C-4 of the right hand sugar
- -> alpha 1,4-glycosidic linkage
- -> As bond from C-1 (anomeric carbon) is pointing down
- -> It is a reducing sugar
What is Cellobiose linkage?
Two glucose units linked group B linkage (1,4)
What is Surcrose’s linkage?
D-glucose and D-fructose linked
–> Glucose in pyranose form (A)
–> Fructose in furanose form (B)
Non reducing
What is Amylose’s linkage?
Polysaccharide of glucose units
–> Alpha
What is Cellulose’s linkage?
Polymer of glucose with b-1,4 glycosidic bonds
- Digestive enzymes have reactive sites which are the right shape for α-1,4’-glycosidic linkages
β-1,4’-glycosidic links do not fit
What is the reactivity order of acid derivatives?
Amide < carboxylic acid = ester «_space;acid anhydride = acid chloride
Amino acid stereochemistry?
- -> All are chiral exept for glycine
- -> All are S except for cysteine
- -> Fisher is drawn with COOH at the top and R group at the bottom
- -> All natural chiral acids exist to L form (NH2 is on the left)
What is the Isoelectric point?
Isoelectric point (pI) is the pH at which the maximum number of molecules have a nett zero charge --> Corresponds to first eq point
Why do peptides adopt secondary structures?
In an aqueous environment, the chain will adopt a conformation so as to expose
the polar side chains (hydrophilic groups) and bury the non polar side chains
(hydrophobic groups) ie maximise favourable non-covalent interactions
–> Stabilises
What are disulphide bridges?
Disulfide linkages can also strongly influence the conformation and
shape of peptides
What are the steps to peptide synthesis?
- Protect amino groups with BOC (removed later with acid)
- Make Gly-OMe (deprotect later with base)
- DCC reaction catalyst
- Deprotect
Why does peptide hydrolysis proceed with difficulty?
•H2O is a poor nucleophile
•the C=O of an amide is unreactive towards nucleophiles
–> Can be achieved by heating with a strong acid
What are the properties of Chymotrypsin?
- -> Enzyme found in the digestive system
- -> Catalyses the hydrolysis of peptide bonds, specifically the peptide bonds on the carboxy side of a aromatic amino acid
- -> Recognises aromatic side chains (via a hydrophobic binding pocket)
- -> The binding site position the peptide bond for processing which contains a catalytic triad
What are the properties of Carboxypeptidase A?
–> It recognises the carboxylate of the C-terminal amino acid and efficiently hydrolyses the adjacent peptide bond. Thus it effectively clips off the C-terminal residue and exposes the next one for processing
Factors:
- Reactants held close together
- Zn2+ makes C=O more suseptible to nucleophilic attack
- H2O is deprotonated to make a better nucleophile
Why is the OH group of tyrosine able to act as a proton donor?
Usually the proton of an alcohol group is not acidic.
However the OH group of tyrosine is attached to a
benzene ring and this influences its acidity and
reactivity.
What are nucleosides?
Nucleosides are formed by the combination of a sugar unit with a purine or pyrimidine base
–> In each case the bases are attached to the sugar at C-1’ in the β-orientation
(same side of ring as C-5’)
Basic/acidic centres of Nucleosides?
N functions are more nucleophilic than O functions • The NH2 group is amide-like and is not appreciably nucleophilic • N-9 is not appreciably nucleophilic • Attack is likely at N-1, N-3 or N-7
What are Nucleotides?
Nucleotides are phosphate derivatives of nucleosides
Phosphate is usually connected to the 5’ position of the sugar
ATP hydrolysis factors?
The negative charges on the phosphates of ATP repel nucleophiles.
• Hydrolysis is normally very slow but is rapid in enzyme-catalysed reactions
• Mg2+ enzyme mediated hydrolysis of ATP in the active site (decreases negative charge - Nu can readily approach)
What is the Nucleic acid stucture?
Polymers of nucleotides linked by phosphate ester bonds in the 5’ and 3’ positions of the sugar --> triphosphate at C'5 and Oh group at C'3
What are the properties of Nucleic acid hydrolysis?
RNA is faster then DNA
–> 2’ OH group in RNA - internal nucleophile helps to break the linkage
What is the rate unit?
Mol L-1 S-1
What is a second order rate unit?
L mol-1 s-1
What is a first order rate unit?
s-1
What is a third order rate unit?
L2mol-2s-1
