Biological Molecules - Proteins Flashcards
Describe the formation of a protein.
Monomers of proteins are amino acids.
A dipeptide is formed when two amino acids join together.
A polypeptide is formed when more than two amino acids join together.
Proteins are made up of more polypeptides.
What is the structure of an amino acid?
A carboxyl group (-COOH), an amino group (-NH2) and an R group (side chain)
How many amino acids are shared between all living things?
What is the difference between them?
20
The difference between them is what makes up their R group.
Amino acids undergo _________ reactions to form __________.
What is released?
What bond is formed?
When does the reverse reaction happen?
Amino acids undergo condensation reactions to form polypeptides.
A molecule of water is released during the reaction.
The bonds formed between amino acids are called peptide bonds.
The reverse reaction (hydrolysis) happens during digestion.
How many structural levels are there of proteins?
4
What is the first structural level of a protein?
Primary structure:
This is the sequence of amino acids in the polypeptide chain.
What is the second structural level of a protein?
Secondary structure:
The polypeptide chain doesn’t remain flat or straight.
Hydrogen bonds form between the amino acids in the chain.
This makes it automatically coil into an alpha helix or fold into a beta pleated sheet.
What is the third structural level of a protein?
Tertiary structure:
The coiled or folded chain of amino acids is often coiled and folded further.
More bonds form between different parts of the polypeptide chain:
- hydrogen bonds
- ionic bonds (attractions between negative and positive charges on different parts of the molecule).
Disulfide bridges also form whenever two molecules of the amino acid cysteine come close together –
– the sulfur atom in one cysteine bond to the sulfur atom in the other.
For proteins made from a single polypeptide chain,
the tertiary structure forms their final 3D structure.
What is the forth structural level of a protein?
Quaternary structure:
Some proteins are made of several different polypeptide chains held together by bonds.
The quaternary structure is the way these polypeptide chains are assembled together.
For proteins made from more than one polypeptide chain
(e.g. haemoglobin, insulin, collagen),
the quaternary structure is the protein’s final 3D structure.
PROTEINS HAVE A VARIETY OF FUNCTIONS
Name the four.
Enzymes
Antibodies
Transport proteins
Structural proteins
What is the role of proteins as enzymes?
ENZYMES:
Usually roughly spherical in shape
due to the tight folding of the polypeptide chains.
Soluble and often have roles in metabolism
e.g. some enzymes break down large food molecules (digestive enzymes)
and other enzymes help to synthesise (make) large molecules.
What is the role of proteins as antibodies?
ANTIBODIES:
Involved in the immune response.
Made up of two light (short) polypeptide chains and two heavy (long) polypeptide chains bonded together.
Antibodies have variable regions – the amino acid sequences in these regions vary greatly.
What is the role of proteins as transport proteins?
TRANSPORT PROTEINS:
e.g. CHANNEL PROTEINS
- Are in cell membranes.
- Contain hydrophobic and hydrophilic amino acids,
which cause the protein to fold up and form a channel.
- These proteins transport molecules and ions across membranes.
(Think hot dog bun)
What is the role of proteins as structural proteins?
STRUCTURAL PROTEINS:
- Are physically strong.
- Consist of long polypeptide chains lying parallel to each other with cross-links between them.
- Structural proteins include keratin (found in hair + nails) and collagen (found in connective tissue).
What is the test for proteins?
BIURET TEST FOR PROTEINS:
1) The test solution needs to be ALKALINE, so first add
a few drops of SODIUM HYDROXIDE SOLUTION.
2) Then add some COPPER (II) SULFATE SOLUTION.
Results:
PRESENT if PURPLE
NOT present if it STAYS BLUE.
