7. Peptides and Proteins Flashcards

1
Q

Proteins

A

• Proteins are polymers of amino acids
• Each amino acids in a protein contains an amino group, NH2
, a carboxyl group, COOH, and an R group, all bonded to the central carbon atom.
•The R (rest) group may be a hydrocarbon or they may
contain a functional group. This R gives the AA’s their distinctiveness.

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2
Q

Common amino acids

A
  • Nature uses 20 amino acidsto build all amino acids in living organisms
  • Each amino acid has a three letter shorthand code.
  • Examples: Ala (alanine), Gly (glycine)

4 groups:

  • non-polar side chains
  • polar, neutral side chain
  • acidic side chain
  • basic side chain
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3
Q

Non-polar side chains

A

-

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4
Q

Polar, neutral side chains

A

-

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5
Q

Acidic and basic side chains

A

-

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6
Q

Peptides

A

• All amino acids present in a proteins are a-amino acids
in which the amino group is bonded to the carbon next to
the carboxyl group
• Two or more amino acids can join together by forming
amide bond, which is known as a peptide bond when they occur in proteins

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7
Q

Peptide formation

A

• A dipeptide
results when 2 amino acids combine together by
forming a peptide bond using amino group of one amino acid and carboxyl group of another amino acid

• A tripeptide
results when 3 amino acids combine together by
forming two peptide bonds, and so on. Any number of amino acids can link together and form a linear chain like
polymer – polypeptid

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8
Q

Acid - base properties of amino acids

A

• contain both an acidic group, COOH, and a basic group, NH

A proton is transferred from the COOH group to the NH
2 group producing a dipolar or zwitterion, with simultaneous positive and negative charge.

The pH at which the net positive and negative charges are
balanced is the amino acids isoelectric point-
the overall charge is zero.

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9
Q

Dissociation of peptides

A

•Acidic media (low pH): zwitterion accepts a proton on the
COO
- group to leave the positively charged NH3+ group
•Basic media (high pH), zwitterion loses a proton from NH3+ group to leave the negatively charged COO
- group

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