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?
If one amino acid in the primrary sturcture changes, The R group will change which will change the variations of 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.
How to remember ?
Fibrous = Fibres = Collgen fibres = STRENGTH
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.
How to remember ?
Globular = Glob = Very folded = Quatnery/Tertiary structure.
Globular = Glob = HaemaGLOBin = example
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.