Proteins (DP IB Biology)
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What are proteins made of, and what determines their function?
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What are proteins made of, and what determines their function?
Proteins are polymers made of amino acids. The sequence, type, and number of amino acids within a protein determine its shape and function.
Name some essential roles of proteins in cells.
Proteins form enzymes, cell membrane proteins (e.g., carriers), hormones, immunoproteins (e.g., immunoglobulins), transport proteins (e.g., haemoglobin), structural proteins (e.g., keratin, collagen), and contractile proteins (e.g., myosin).
What are the monomers of polypeptides?
Amino acids serve as the monomers of polypeptides.
Describe the general structure of an amino acid.
An amino acid consists of a central carbon (alpha carbon) bonded to an amine group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and an R group (which varies among amino acids).
Name the parts labelled A, B, and C on the diagram of the amino acid below.
A = amine group
B = R-group
C = carboxyl group
How many naturally occurring amino acids are there?
There are 20 naturally occurring amino acids common to all living organisms.
What is a peptide bond?
A peptide bond forms between two amino acids when a hydroxyl group (-OH) from one amino acid and a hydrogen atom from another amino acid combine. Water is released in this condensation reaction.
How are polypeptides formed?
Polypeptides result from the condensation of three or more amino acids. Proteins may have one polypeptide chain or multiple interacting chains.
What breaks peptide bonds during hydrolysis reactions?
The addition of water breaks peptide bonds, resulting in the breakdown of polypeptides into individual amino acids.
Why is a well-balanced diet important for protein synthesis?
Nine essential amino acids must be obtained from our diets. While meat contains all nine, vegetarian or vegan diets require variety to ensure regular consumption of essential amino acids.
What determines the number and order of amino acids in a polypeptide?
The genetic code, meaning the DNA base sequence, determines the number and order of amino acids in a polypeptide.
True or False?
Polypeptides can only be a few amino acids long.
False.
Polypeptides can vary in length from a few to thousands of amino acids.
Name three examples of polypeptides.
Examples of polypeptides include:
Rubisco
Insulin
Rhodopsin
Collagen
Spider silk
or any other valid answer.
What is denaturation?
Denaturation is the irreversible change of protein conformation caused by temperature and pH extremes that interfere with the bonds maintaining protein structure.
True or False?
The bonds between different R groups in proteins are stronger than peptide bonds.
False.
The bonds that form between different R groups are relatively weak compared to the peptide bonds that hold the amino acids in sequence.
Define optimum pH for a protein.
The optimum pH for a protein is the pH at which the protein's 3D structure is not denatured.
Why do certain proteins medications need to be delivered by injection rather than orally?
Certain protein drugs need to be delivered by injection because they would be denatured by stomach acid if taken orally.
What is an extremophile?
An extremophile is an organism that has evolved to have proteins that are stable even at extreme pH or temperature.
True or False?
Denaturation is always reversible.
False.
Denaturation is almost always irreversible, meaning the protein cannot be re-formed in its original conformation by reversing the change in conditions.
What is the optimum pH for pepsin, and why?
Pepsin, a protein-digesting enzyme, has an optimum pH of 2 because it works in the stomach where the low pH causes proteins in the diet to become denatured.
How can denaturation of enzymes be useful in experiments?
Denaturation of enzymes can be used in experiments to measure enzyme activity, such as establishing the optimum pH or temperature of an enzyme like pepsin or lipase.
Define conformation in relation to proteins.
Conformation refers to the three-dimensional shape or structure of a protein, which can be altered by the breaking of bonds between different R groups.