Structure & Function of Proteins Flashcards
Chapter 1.3
How do hormones bind to receptors?
Through their complementary shape.
Describe primary structure of a protein.
The primary structure of a protein, which comprises the sequence of amino acids in the polypeptide chain, is determined by the specific codons on mRNA that encode for a particular sequence of amino acids.
Describe secondary structure of a protein.
The secondary structure is subsequently determined by its primary structure, namely the positioning of hydrogen bonds which produce alpha-helices or beta-sheets. This is often seen as the intermediate stage between the primary structure and before the polypeptide folds into its three-dimensional shape.
What are the common shapes associated with secondary structure?
Alpha-helices (coiling) and beta-pleated sheets (folding).
Describe tertiary structure of a protein.
The tertiary structure, which is the overall three-dimensional shape, is dependent on the primary and secondary structures - specifically whether amino acids are attracted to, or repelled by, each other to create a specific three-dimensional shape.
What types of interactions occur between amino acids that contribute to its tertiary strcutre?
Hydrogen bonds, ionic bonds and strong covalent disulfide bonds.
Describe the quaternary structure of a protein.
When a protein consists of more than one polypeptide chain, it is therefore deemed a quaternary structure with increased structural complexity. They therefore require multiple genes to code for them, and forms through the chemical bonding of polypeptides.
List the four levels of protein structure.
Primary, secondary, tertiary and quaternary structure.
Describe the characteristics of proteins.
They are globular and have a unique shape that is complementary to the particular molecule they need to bind to.
What are enzymes?
They are biological catalysts that speed up (catalyse) reactions by reducing activation energy of the reaction. Their shape dictates their specificity.
How does binding occur between an enzyme and substrate?
Through the complementary shape of the enzyme and its specific substrate.
Do enzymes usually change after a reaction occurs?
No, they are not typically consumed during a reaction, and can be re-used over and over again.
Why do most enzymes function intracellularly?
As this is the site of cell metabolism.
What happens to bonds during a reaction?
They are broken and/or reformed.
What are antibodies?
Part of the immune system that bind to antigens, which are foreign molecules usually found embedded in the surface of viruses or bacteria, in a complementary manner to deactivate/neutralise the antigen.
What is metabolism?
All biochemical reactions carried out by a living organism, and the overall rate of these reactions is called the metabolic rate.
Define the induced-fit model.
The substrate binds to the active site of the enzyme using weak bonds, forming an enzyme-substrate complex. The active site may change shape slightly to form an exact fit.
What is meant by ‘lowering activation energy’ during an enzymic reaction?
What factors affect enzyme activity?
- Changes in temperature
- Changes in pH
- The presence of chemical inhibitors
- Concentration of substrate/reactants
- Concentration of enzyme
Describe the relationship between temperature and enzyme activity.
Low temperatures mean less kinetic energy, therefore lowering the frequency of collision between substrates and enzymes. Thus, enzyme activity is low. Enzyme activity increases as temperature increases due to the increase of kinetic energy and corresponding frequency of collision, reaching a maximum at optimal temperature. When temperatures increase too high beyond optimum, the enzyme denatures and enzyme activity ceases entirely.
Describe the relationship between pH and enzyme activity.
Enzyme activity is at a maximum at optimum pH, with changes comprising increased acidity or alkalinity denaturing the enzyme. The extent to which this occurs is dependent on how much the pH changes away from the optimal pH value for the enzyme.
Describe the relationship between concentration of substrate and enzyme activity.
At lower substrate concentrations, there is a decreased availability of substrates to collide with the active site of enzymes, slowing rate of reaction. The activity increases as the substrate concentration increases due to elevated frequency of collision between the substrate and enzymes. Increases in concentration above the optimum results in a plateau of activity due to all active sites becoming occupied, meaning that no further binding can occur.
Describe the relationship between concentration of enzyme and enzyme activity.
At lower enzyme concentrations, there is a decreased availability of enzymes to collide with substrates, slowing rate of reaction. The activity increases as the enzyme concentration increases due to elevated frequency of collision between the substrate and enzymes. Increases in concentration above the optimum results in a plateau of activity due to all active sites becoming occupied, meaning that no further binding can occur.
Describe the relationship between competitive inhibitors and enzyme activity.
Competitive inhibitors have a similar structure to the substrate, meaning that it competes with the substrate to occupy the active site of the enzyme. This consequently lowers enzyme activity.
Describe the relationship between non-competitive inhibitors and enzyme activity.
These molecules do not compete with the substrate, but rather, they bind elsewhere on the enzyme at a site which is not the active site. This leads to an alteration of the active site’s shape, preventing substrate from binding as it is no longer complementary. This action underpins the control mechanism for metabolic reactions termed ‘end-product inhibition’.
What is end-product inhibition?
When the final product inhibits the activity of the enzyme.
