Up Learn – A Level biology (AQA) – Biological Molecules
The Peptide Bond
A peptide bond forms between two animo acids as a result of a condensation reaction.
More videos on Biological Molecules:
Tertiary Structure of Protein – Part 1
Tertiary Structure of Protein – Part 2
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Biological Molecules
2. Monosaccharides
3. The Condensation Reaction
4. The Hydrolysis Reactions
5. Glycosidic Bonds
6. Polysaccharide Shapes
7. Structure and Function of Cellulose
8. Structure and Function of Glycogen and Starch
9. Benedict’s Test
10. Colours of the Benedict’s Test
11. Iodine Test
2. Lipids and Fatty acids
3. Structure of Triglycerides and Ester Bonds
4. Unsaturated and Saturated Fatty Acids
5. Properties of Triglycerides – Part 1
6. Properties of Fatty Acids
7. Properties of Triglycerides – Part 2
8. Functions of Triglycerides
9. Structure of Phospholipids
10. Properties of Phospholipids
11. Functions of Phospholipids
12. Triglycerides and Phospholipids are Soluble in Alcohol
13. The Emulsion Test
2. Proteins and Amino Acids
3. Amino and Carboxyl Groups
4. The Peptide Bond
5. The Primary Structure
6. The Secondary Structure
7. The Tertiary Structure – Part 1
8. The Tertiary Structure – Part 2
9. The Quaternary Structure of Proteins
10. Prosthetic Groups and Conjugated Proteins
11. Protein Shapes
12. pH and Protein Structure
13. The Biuret Test
We’ve seen that amino acids are the building blocks of proteins.
But, now, how do two amino acids [pulse box two circles on the chain] join together to form a bigger molecule [pulse box whole chain]?
To begin with, this amino acid has a hydroxyl group, here, and this amino acid has an H atom in its amino group, here
Next to chain these two amino acids together, a chemical bond is formed between these two groups
And, as this bond is formed, the two hydrogens… and the oxygen… are eliminated.
Giving us this bigger molecule, and one molecule of…
The two hydrogens and the oxygen join together to form one molecule of water, like this.
And this reaction, which results in a chemical bond and the elimination of a water molecule, is an example of…
This reaction is an example of a condensation reaction.
And, when a condensation reaction forms a bond between two amino acids, we call this a peptide bond.
So now, circle the peptide bond in this molecule.
This is the peptide bond in this molecule, connecting two amino acids together.
And, now, which of these molecules have peptide bonds?
Because these molecules are made up of multiple amino acids, these molecules have peptide bonds.
Next, if a peptide bond is formed between two amino acids, we call the resulting molecule a dipeptide. [Greek ‘di’ = two]
And if peptide bonds are formed between lots of amino acids, we call the resulting molecule a polypeptide. [Greek ‘poly’ = many]
, have this chain run across the whole screen, to suggest this molecule is really long.
And, because polypeptides are long chains of amino acids, like this one here [the one on screen], biologists often call polypeptides: polypeptide chains
So, now, identify these molecules…
These are dipeptides because they’re made up of two amino acids…
… whereas these are polypeptides because they’re made up of lots of amino acids.
Next, if we add water to a dipeptide or a polypeptide, then the peptide bond breaks.
So, just like we’ve seen with other polymers, this reaction is an example of…
This reaction is an example of a hydrolysis reaction.
Finally, polypeptides can combine with other polypeptides to form a protein.
And we’ll start to look at how proteins are structured, next!
But first, to sum up…
A peptide bond is…
A peptide bond is a bond between two amino acids, formed by a condensation reaction.
And if a peptide bond is formed between two amino acids, we call the resulting molecule…
If a peptide bond is formed between two amino acids, we call the resulting molecule a dipeptide.
And, if peptide bonds are formed between lots of amino acids, we call the resulting molecule…
If peptide bonds are formed between lots of amino acids, we call the resulting molecule a polypeptide, or a polypeptide chain.
Finally, polypeptides can combine with other polypeptides to form…
Polypeptides can combine with other polypeptides to form a protein.