Unit 3: Section 8 - Amino Acids, Proteins and DNA
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What are the 2 functional groups of amino acids?
NH2 and COOH (amine and carboxylic acid)
How many naturally occuring amino acids are there in the body?
20
What type of amino acids are found in the body? What does this mean about their structure?
α - amino acids (alpha) it means that NH2 is always on the carbon next to COOH
Are α-amino acids chiral? Why?
Yes, one carbon has 4 different substituents - except glycerine where R = H
Which enantiomer do α-amino acids exist as in nature?
(-) enantiomer
How can amino acids be synthesised naturally?
RCHO + NH4CN -> RCH(NH2)CN via nucleophilic addition RCH(NH2)CN + HCl + 2H2O -> RCH(NH2)COOH + NH4Cl - hydrolysis, HCl is dilute - need to reflux the reaction mixture
Is the product from amino acids being synthesised naturally optically active? Why?
No, a racemic mixture is formed as the CN- ion can attack from above or below the planar C=O bond with equal probablitity An equal amount of each enantiomer is formed, so no net effect on the plane polarised light
In what form do amino acids exist as solids? What consequences does this have?
Zwitterions (ionic lattice) - high melting and boiling points
What colour solids are most zwitterions at room temperature?
White solids
Do zwitterions dissolve in water? Non-polar solvents? Why?
Yes, but not in non-polar solvents - due to ionic nature/polar bonds
What is the definition of a zwitterion?
Ions which have both a permanent positive and negatice charge, but are neutral overall
How do zwitterions occur in amino acids?
COOH is deprotonated -> COO- NH2 is protonated -> NH3+
What happens to amino acids in acidic conditions?
Gains a proton on NH2 group
What happens to amino acids in alkaline conditions?
Loses a proton from COOH group
What is the peptide bond?
-CONH- O H = - -C-N-
What is a dipeptide?
Two amino acids bonded together (a dimer)
What name is given to chains of amino acids up to 50 amino acids?
Polypeptides
What name is given to chains of amino acids with more than 50?
Proteins
What are polypeptides and proteins found in?
Enzymes Wool Hair Muscles
What is the process called by which polypeptides or proteins can be broken down into their constituent amino acids?
Hydrolysis
What conditions are needed for hydrolysis to occur?
6 moldm^-3 HCl, reflux for 24 hours
What is the primary structure of a protein? How is it bonded?
The sequence of amino acids along the protein chain - bonded by covalent bonds
How is the primary structure represented?
Sequence of 3 letter abbreviations of the amino acids
How can the primary structure of a protein be broken up?
Hydrolysis, 6M HCl, 24 hour reflux