Notes : 2.9 + 2.10 - Proteins & Enzymes Flashcards
Draw the basic structure of an amino acid.
How are polypeptides formed?
Amino acids join together in condensation reactions, forming a peptide bond and eliminating a water molecule.
What is meant by primary structures of proteins?
• Primary = A polypeptide (a sequence of amino acids which have joined together to form a long chain through peptide bonds).
How does the primary structure affect the tertiary (3D) structure?
R group variations produce different bonds.
Sulfur atoms form disulfide bridges, oppositely charged groups form ionic bonds. Hydrogen bonds are always present as they occur between hydrogen and nitrogen/oxygen.
Describe how the structure of fibrous proteins relates to their function.
Long parallel polypeptide chains.
Very little tertiary/quaternary structure aside from cross-linkages for strength(cross linkages form microfibres for tensile strength)This makes them insoluble, and useful for providing structure.
Examples of fibrous proteins include collagen, keratin and elastin.
Give an example of a fibrous protein and explain how its properties relate to its use.
Collagen. Hydrogen and covalent bonds make it very strong. Polypeptide chains form a triple helix which creates fibres. This makes it useful in bones, cartilage and other connective tissue.
Describe how the structure of globular proteins relates to their function.
Compact, highly folded with complex tertiary/quaternary structures. Soluble as their hydrophobic amino acids tucked inside and the hydrophilic amino acids exposed on the outside, forms colloids in water. They are useful for hormones, antibodies, carrier proteins, for example haemoglobin.
Globular proteins with prosthetic groups attached (such as haemoglobin) are referred to as conjugated proteins.
Give an example of a globular protein and explain how its properties relate to its use.
Haemoglobin. Water-soluble, with a complex quaternary structure. Contains four haem groups that oxygen can bind to.
It is therefore used to carry oxygen in the blood to respiring tissues.
What are enzymes?
Proteins that act as biological catalysts. They increase the rate of a reaction by lowering the activation energy. By providing an alternative pathway for the reaction to occur.
How do enzymes work?
One area of the enzyme is called the active site, which is specific to a certain substrate.
When the enzyme and substrate bind they form a enzyme substrate complex, which lasts until the reaction is complete.
What is meant by a ‘specific’ active site?
The 3D structure of each enzyme is unique due to the side chains and branches that are present. This also makes the active site unique, and therefore only the substrates that match each active site can bind there.
Differentiate between intracellular and extracellular enzymes.
• Intracellular = catalyse reactions inside cells. e.g. amylase
• Extracellular = catalyse reactions outside of cells. e.g. RNA polymerase
What is meant by the secondary structure of proteins ?
• Secondary = whether the polypeptide chain is folded into a alpha helix or Beta pleated sheet. This is through hydrogen bonding between the nearby amino acids. Proteins which form neither of these two structures will form a random coil.
What is meant by the tertiary structure of proteins ?
• Tertiary = hydrogen bonds, disulfide bonds(between two cys amino aids), ionic bonds and polar interactions form between the different R groups allowing the protein to fold further to give the protein a 3D structure. If proteins are made of a single polypeptide chain, this is their final overall structure.
What is meant by the quaternary structure of proteins ?
Quarternary structure: This is the structure formed from the interaction of multiple polypeptide chains
held together by bonds.
Haemoglobin is an example of a protein with quaternary structure. It consists of four polypeptide chains (two alpha chains and two beta chains) bonded together. Each chain surrounds an iron-containing haem group. The haem group is referred to as a prosthetic group- non-protein components which are required for protein function.
Burt everything you know about the lock and key model.
Lock and Key model
This model suggests that the substrate fits into the enzyme’s active site in the same way in which a key fits into a lock. The shape of the substrate and the active site are perfectly complementary to each other. Catalysis happens in the following stages:
- The substrate binds to the enzyme’s active site, forming an enzyme-substrate complex (ES complex).
- The enzyme converts the substrate into product, forming an enzyme-product complex (EP complex).
- The product is released from the enzyme’s active site.
Burt everything you know about the induced fit model
The induced fit model suggests that the shapes of the enzyme’s active site and its substrate are not exactly complementary, but when the substrate enters the active site, a conformational change (change of shape) occurs which induces catalysis. The induced fit model can be broken down into the following stages:
- The substrate enters the enzyme’s active site, forming an ES complex.
- The enzyme undergoes a conformational change which causes the conversion of substrate into product, forming an EP complex.
- The product is released from the enzymes active site.
Blurt everything you know about substrate concentration.
• Substrate concentration - as concentration of substrate increases there will be more frequent collisions so , rate of reaction increases. More enzyme-substrate complexes are formed. However, beyond a certain point (the saturation’ point) here all of the enzyme’s active sites are occupied with substrate molecules, the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.
Blurt everything you know about tempurature.
• Temperature - As the temperature is increased, enzymes and substrates have higher amounts of kinetic energy, therefore increases the number of collisions, which increase the formation of ES complex’s, increasing the rate of reaction.up to the optimum temperature (which is the temperature enzymes work best at) as If the temperature becomes really high, hydrogen bonds will begin to break within the protein, causing it to unravel they lose the shape of their active sites which means they cannot bind to their substrate, and become denatured . Rate of reaction decreases beyond the optimum temperature because enzymes denature.
Blurt everything you know about tempurature.
• pH - enzymes work within a narrow range of a specific pH value, values above or below this alter the bonds within its structure, hence the shape of its active site.
Deviations from the optimum pH change the charge on the enzyme, which affects ionic bonding within its structure. Deviations in pH also break hydrogen bonds. This causes it to change shape and become denatured, decreasing the rate of reaction as pH deviates from the enzyme’s optimum conditions.
Don’t need to know but what are competitive inhibitors.
Competitive inhibitors are ones which bind to the active site of the enzyme, blocking the substrate from binding - they compete with the substrate for access to the enzyme’s active site. The effect of a competitive inhibitor can be reduced by increasing substrate concentration. If there is way more substrate compared to inhibitor then the substrate is much more likely to collide with the enzyme’s active site.
Don’t need to know but what are non-competitive inhibitors.
Non-competitive inhibitors are ones which bind to a site on the enzyme away from its active site. This region is known as its allosteric site. The effect of a non-competitive inhibitor cannot be reduced by increasing substrate concentration.
