Transcript Amino_acid_powerpoin..

Amino acids
• To be able to identify the general
molecular formula of amino acids
• All amino acids have the same basic structure
• They have an amine group (NH2) at one end
• And a carboxyl acid group (COOH) at the other
end
• There is an R group which differs from one
amino acid to another.
• For example
– in glycine, the side chain is a single hydrogen
atom so R = H
– In alanine, the side chain is a methyl group so
R = CH3
α-amino acids
General molecular formula of an amino acid: RCH(NH2)COOH
Structural formula
H
O
O
C
The group that
determines what
amino acid is
R
C
H
N
H
carboxylic acid
group
amine group
H
glycine
aspartic acid
asparagine
cysteine
histidine
These are the essential α-amino acids. The carbon atoms and hydrogen atoms
bonded to them are not shown – just the skeleton
O
H
N
O
S
OH
H3C
OH
NH2
N
CH3
NH2
O
O
H3C
OH
OH
NH2
NH2
O
O
H3C
OH
OH
CH3
NH2
NH2
NH
CH3
O
O
H2N
OH
NH2
In each case circle the
amine group,
carboxylic acid group
and the R group
H3C
OH
NH2
What does ‘essential’
mean?
1. As a class make as many physical models of
alanine as possible (R = CH3). Compare the models
you made and try to sort them into two groups.
2. Draw the structural formula for alanine
3. Try to explain what is meant by non-superimposable
mirror images (also called optical isomers).
4. Why is glycine the only amino acid that cannot exist
in two forms which are non-superimposable mirror
images of one another?
H
O
H
H C
H
H
O
C
C
H
N
H
Optical isomers
•Optical isomerism occurs
when substances have the
same molecular and
structural formulae, but one
cannot be superimposed on
the other.
•Put simply, they are mirror
images of each other
•No matter how hard you try,
the molecule on the left will
not turn into the molecule on
the right – unless you break
and make some bonds!
H
O
O
C
H
C
H
N
H
H
Glycine cannot exist in two forms as the R group
is only a hydrogen atom
Homework
• Amino acids
Questions!
1. Which four elements are present in
every amino acid?
•
Hydrogen, carbon, oxygen and nitrogen
2. Which of these elements is not
present in a carbohydrate or lipid?
•
Nitrogen
3. What is the formula of the amine
group?
•
NH2
4. What is the formula of the acid group?
•
COOH