Proteins Flashcards
How many different types of amino acids are there and how do they differ?
20
Differ only by side ‘R’ group.
Draw the general structure of amino acids.
Central carbon
Hydrogen bonded to carbon
Amine group (NH₂)
Carboxyl group (-COOH)
R group (different for every amino acid)
Name the elements present in a protein.
Carbon
Hydrogen
Oxygen
Nitrogen
How do you test for proteins in a food sample?
Biuret test confirms presence of peptide bonds,
1~ Add equal volume of NaOH to sample at room temp.
2~ Add drops of dilute copper (II) sulfate solution.
Swirl to mix.
Positive result: colour change - blue to purple.
Negative result: solution remains blue.
Steps 1 & 2 make Biuret reagent.
What is a dipeptide?
When 2 amino acids form a peptide bond during a condensation reaction & eliminates water molecules.
What is a polypeptide?
When 3 or more amino acids form peptide bonds during a condensation reaction.
What is a peptide bond?
A bond formed when amino acids join together.
What is the functional group of a peptide bond?
(-CONH-)
What are the 4 levels of protein structures?
Primary
Secondary
Tertiary
Quaternary
Where do amino acids bond together?
In ribosomes.
What enzyme breaks peptide bonds during a hydrolysis reaction?
Protease.
What’s the difference between a polypeptide and a protein?
A polypeptide has to fold into a complex, 3D shape in order to be a protein and carry out its function.
What is the primary structure of a protein?
The sequence of amino acids linked together to form a polypeptide chain.
Why is the primary structure of a protein important?
Helps determine the final 3D shape of a protein.
Why is the shape of a protein important?
It’s important for its function.
Changing a single amino acid in the primary structure can prevent the protein carrying out its function effectively.
E.G. if the active site of an enzyme changes, it cannot break down molecules effectively as the substrate no longer fits in the enzyme.
What is the secondary structure of a protein?
The REAL answer:
The H bonds cause the polypeptide to fold into ALPHA-HELIX or BETA-PLEATED SHEETS.
HOW is it formed?
When hydrogen bonds form since the partially negative oxygen ion (Oδ-) is attracted to the partially positive hydrogen ion (δ+).
The NH in 1 amino acid bonds to the C=O in another amino acid.
Where is the Oδ- and the Hδ+ found in the polypeptide chain?
The partially negative oxygen is attached to…
C=O
The partially positive hydrogen is attached to…
NH
What are the 2 types of secondary protein structures?
Alpha helix (α-helix)
Beta-pleated sheet (β-pleated sheet)
Describe the alpha helix secondary protein structure.
Spiral shape
Weak H-bonds hold the structure in place
All N-H bonds on same side of protein chain.
Describe the beta-pleated sheet secondary protein structure.
Sheet-like structure.
Weak H-bonds between amino acids hold shape in place.
N-H & C=O groups alternate from one side to the other.
How is the type of secondary structure determined?
By the primary structure in that region.
What is the tertiary structure of a protein?
The 3D structure formed by further folding of polypeptide.
Name the bonds present in the tertiary structure.
Disulfide bridges
Ionic bonds
Hydrogen bonds
Why is the tertiary structure critical for how a protein functions?
Active site of an enzyme depends on the protein forming a very specific tertiary structure.
If change tertiary structure of enzyme by heating it, shape of active site changes and becomes DENATURED.