B1.2 Proteins - Pre-IB Biology Work
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What are the five main parts of a general amino acid structure?
Central (alpha) carbon atom Amine group (–NH₂) Carboxyl group (–COOH) Hydrogen atom Variable R-group (side chain)
What determines the identity and properties of an amino acid?
The variable R-group (side chain).
How many amino acids exist in all living organisms?
20 amino acids, shared universally.
What are essential amino acids?
Cannot be made by the body → must come from the diet
What are non-essential amino acids?
Can be synthesized by the body from other amino acids
What are conditional amino acids?
Can be made, but not fast enough during stress (e.g., infancy, illness, pregnancy)
What are the consequences of lacking essential amino acids in the diet?
Protein deficiency malnutrition, which varies depending on the missing amino acids. (Note: Vegans must plan diets carefully to get all essential AAs.)
How are dipeptides and polypeptides formed?
Through condensation reactions, which join amino acids via a peptide bond and release water (H₂O).
What is a peptide bond?
A covalent bond between the amine group (–NH₂) of one amino acid and the carboxyl group (–COOH) of another.
What is a polypeptide?
A long chain of amino acids joined by peptide bonds. Proteins may consist of one or more polypeptide chains.
How can polypeptides be broken down?
By hydrolysis, which adds water to reverse the peptide bond.
Why is there an infinite variety of possible proteins?
20 amino acids with different R-groups Each R-group has unique properties (polar, non-polar, charged) Different sequences → different folding → different shapes and functions
How many amino acids are typically found in natural polypeptides?
Between 50 and 2000 amino acids per polypeptide.
Why is protein folding important?
Folding determines the 3D shape, which is essential for biological function.
What maintains a protein’s three-dimensional shape?
Hydrogen bonds, ionic interactions, and other intermolecular forces.
What are the main functions of proteins and examples of each?
• Structure: Collagen, spider silk • Hormones: Insulin, glucagon • Immunity: Antibodies • Transport: Protein channels • Sensation: Rhodopsin • Movement: Actin, myosin • Enzymes: Rubisco, amylase
What is denaturation in proteins?
A structural change that causes a loss of biological function, usually irreversible.
How does pH affect protein structure?
pH changes alter amino acid charges → affect solubility and folding Optimal pH varies by protein and its environment - Stomach enzymes: acidic - Blood proteins: neutral (~pH 7.4)
How does temperature affect protein structure?
High heat: Breaks hydrogen bonds → unfolding → loss of function Optimal temp: Human proteins function best around 37°C