Download What is amino acid? - TangHua2012-2013

Cissy Gao / Irene Meng / Zero Yao
Today’s Object
• Identify amino acids and understand
their structure
•Identify the peptide bonds in
dipeptides and polypeptides
•Explain why amino acids are soluble in
water
What is amino acid?
• An amino acid is a carboxylic acid with an amine
group at the 2-position.
– A carboxylic acid contains a –COOH group.
– An amine group contains a NH₂ group.
• AAmino
acids
are the
building blocks of proteins.
general
2-amino
acid
CH₃—CH—COOH
NH₂
2-aminopropanoic acid [alanine]
Structure
Hydrogen atom
Amino group
Carboxyl group
Central carbon
Radical group
Structure Summary:
• An amino acid has a central carbon atom bonded to a
hydrogen atom and three groups:
– An amino group(-NH₂)
– An carboxyl/acidic group(-COOH)
– An R group [radical group]
“R" can be quite a complicated group containing
other active groups like -OH, -SH, other amine or
carboxylic acid groups, and so on.
• There are only 20 different amino acids.
– Amino acids differ from one another by their R group
Reaction:
• Amino acids can react with both acids and bases.
Reaction with acids
CH₃—CH—COOH + H⁺
NH₂ [alanine]
CH₃—CH—COOH
+NH₃
Reaction with bases
CH₃—CH—COOH + OH⁻
NH₂
CH₃—CH—COO⁻ + H₂O
NH₂
After reacting with either an acid or base the amino acid is ionic
and remains soluble in water.
Two important properties:
1. Amino acids are highly soluble in water.
Amino acids have both acid and base groups arranged such
that the acid and base groups can “neutralize” each other.
Acidic
Ionic
Basic
zwitterion
H atom is lost from COOH and gained by NH₂
Two important properties:
2. Amino acids link with each other to form “dipeptides” and
“polypeptides”.
• An amino acid can be referred to as a peptide.
• When two amino acids bond together, they produce a
dipeptide.
Question #1:
When three amino acids bond together, what is it called?
Answer: Tripeptide
Question #2:
When more than three amino acids bond together, what is it
called?
Answer: Polypeptide
Two important properties:
2. Amino acids link with each other to form “dipeptides” and
“polypeptides”.
O
O
H—N—CH₂—C—OH + H—N—CH₂—C—OH
H
H
Dehydration synthesis
-water is removed
O
O
H—N—CH₂—C—N—CH₂—C—OH + H₂O
H
H
Dipeptide
Peptide bond
[Amide linkage]
Two important properties:
2. Amino acids link with each other to form “dipeptides” and
“polypeptides”.
• A series of amino acid molecules can be joined by a
series of amide linkages to form a polypeptide.
• A polypeptide is a single chain of amino acids.
• The order or combination of these amino acids
determines which protein is produced.
Practice:
1. Identify which of the following is an amino acid.
2. What is this reaction called ?
Dehydration synthesis
Bonus:
Besides peptide
bond, what other
bond is presented?
Hydrogen bond
Video