3.13 Amino Acids, Proteins And DNA
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What are the two functional groups of amino acids?
NH2 and COOH (amine and carboxylic acid)
How many naturally occurring 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
Alpha amino acids It means that NH2 is always on the carbon next to COOH
Draw a general formula for alpha amino acid
Slide 10
Are alpha amino acids chiral? Why?
Yes, one carbon has 4 different substituents. Except glycine, where R = H
Which enantiomer do alpha amino acids exist as in nature
• enantiomer
How can amino acids be synthesised industrially
RCHO + NH4CN —> RCH(NH2)CN via nucleophilic addition RCH(NH2)CN + HCI + 2H2O —> RCH(NH2)COOH + NH4CI (hydrolysis, HCI 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 likelihood. An equal amount of each enantiomer is formed, so no net effect on plane polarised light
In what form do amino acids exist as solids? What consequence 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
Define zwitterion
Ions which have both a permanent positive and negative charge, but are neutral overall
How do zwitterions occur in amino acids? Draw a general structure of one
COOH is deported —> COO- NH2 is protonated —> NH3+ slide 28
What happens to amino acids in acidic conditions? Draw this
Gains a proton on NH2 group Slide 30
What happens to amino acids in alkaline conditions? Draw this
Loses a proton from COOH group Slide 32
What is the peptide linkage?
-CONH- Slide 34
What is a dipeptide? Draw a general one for amino acids
Two amino acids bonded together
What name is given to chains of amino acids up to 50 amino acids?
Polypeptides
What name is given to chains of amino acid 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 mol dm-3 HCI, reflux for 24 hours
What is the primary structure of a protein? How is if 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