Download (click) this one, giving us the amino acid

Our body is close to 20% protein and many of the foods we eat also contain protein.
Amino Acids
Amino acids are the building blocks of proteins.
Amino Acids
Link
Together
Polypeptide
Chains
Amino acids link together to form polypeptide chains.
Amino Acids
Link
Together
Polypeptide
Chains
Proteins are made
up of one or more
Polypeptide Chains
And proteins are typically very large molecules made up of one or more polypeptide
chains.
Amino Acids
Link
Together
Polypeptide
Chains
Here, we’ll look at how amino acids link together to form polypeptide chains,
Amino Acids
Break
Apart
Polypeptide
Chains
And how polypeptide chains break apart into their building blocks, amino acids.
H
H
N C C
H R
O
OH
The General
Formula for
an Amino
Acid
The general formula for an amino acid can be depicted as a molecule like this.
H
H
N C C
H R
O
OH
Amino
Group
All amino acids have an Amino group, which is the NH2.
The General
Formula for
an Amino
Acid
H
H
N C C
H R
Amino
Group
O
OH
The General
Formula for
an Amino
Acid
Carboxyl
Group
And a carboxyl group, which is COOH. This can also be called a carboxylic acid group. It is the
amino group and the carboxylic acid group that gives these compounds the name amino acids.
H
H
N C C
H R
O
OH
The General
Formula for
an Amino
Acid
Side
Chain
The R group in this general formula represents various side chains that can be attached to the central carbon atom.
There are 21 amino acids used in our body, which means there are 21 different side chains that can be represented
by R.
H
H
N C C
H H
R
O
OH
Glycine
If we replace the symbol R by (click) a single hydrogen atom, we get the simplest amino
acid, which is called (click) glycine
H
H
N C C
O
OH
H CH
R 3
Alanine
If we replace the symbol R by (click) a methyl group, CH3, we get the amino acid, which
is called (click) alanine
H
H
N C C
O
OH
H CH
R
H3C
CH3
Valine
Replacing R with this group (click), gives us the amino acid called (click) valine.
H
H
N C C
O
OH
H CH
R 2
CH2
Methionine
S
CH3
Some contain the element sulphur like (click) this one, giving us the amino acid (click)
methionine
H
H
N C C
O
OH
H CH
R 2
Phenylalanine
Some contain a benzene ring, or phenyl group like (click) this one, giving us the amino acid (click) phenylalanine.
Using a biology text book or searching on the internet, you can find tables that show you the structures for all 21
Here we have two amino acids beside each other. We have used the letter “R” to represent any of the 21 possible
side chains.
One of the H atoms on the amino group of one amino acid,
And the OH from the carboxyl group on a neighbouring amino acid, can be removed in
a dehyration synthesis…
Dehydration Synthesis
water
This releases a water molecule and the two amino acids bond together.
A Dipeptide
water
To form a larger molecule made up of two amino acids. This is called a (click) dipeptide
A Dipeptide
A Peptide bond
water
The new bond that forms between the carbon with the oxygen on one amino acid and
the nitrogen atom on the other amino acid, is called (click) a peptide bond.
Dehydration Synthesis
In a new dehydration synthesis, another amino acid bonds to the dipeptide to form a
larger peptide chain…
Dehydration Synthesis
Dehydration synthesis can continue and the peptide chain continues to grow, while
water molecules are released..
A Polypeptide Chain
A large number of amino acids bonded together, form a polypeptide chain. Polypeptide
chains can get very large, and can contain hundreds or even thousands of amino acids.
A Polypeptide Chain
Proteins are made up of one of more Polypeptide Chains
Proteins are made up of one of more Polypeptide Chains
Ribosomes
Free
Ribosomes
Proteins are synthesized in the ribosomes found in our cells and in the cells of other
animals and also plants.
12 of the 21 amino acids humans require can normally be made by our cells (with
some exceptions).
These are called non-essential amino acids because we don’t need to get them
from the foods we eat.
9 of the amino acids required cannot be synthesized in our body.
They are called the essential amino acids because we must get these from the
foods we eat.
To get essential amino acids into our bloodstream, we first need to digest proteins in
foods that we eat. In our digestive system, when appropriate enzymes are present,
Amino Acids
Break
Apart
Polypeptide
Chains
polypeptide chains in these proteins (click) break apart into smaller peptide molecules, and
eventually into (click) amino acids.
Hydrolysis
Here is a small polypeptide chain. If we add a (click) water molecule to this in the
presence of the correct enzyme, a (click) hydrolysis reaction will take place (click).
Hydrolysis
Amino
Acid
And an amino acid will be removed from the chain like this.
Hydrolysis
Amino
Acid
Another water molecule can be added in the process of hydrolysis, releasing another
free amino acid.
Hydrolysis
As more water molecules are added to this peptide chain, hydrolysis eventually breaks
it down into single amino acids.
Amino Acids
Link
Together
Polypeptide
Chains
To review, we’ve seen how amino acids link together to form polypeptide chains using
the process of dehydration synthesis.
Amino Acids
Link
Together
Polypeptide
Chains
Proteins are made
up of one or more
Polypeptide Chains
And that proteins are very large molecules made up of one or more polypeptide chains.
Polypeptide
Chains
Proteins are made
up of one or more
Polypeptide Chains
Proteins in the foods we consume are made up of polypeptide chains.
Amino Acids
Break
Apart
Polypeptide
Chains
Hydrolysis
polypeptide chains in these proteins (click) break apart into smaller peptide molecules, and
eventually into (click) amino acids using the process of (click) hydrolysis