Proteins and enzymes Flashcards
Describe the structure of an amino acid
One carboxyl group, an amino group, a hydrogen atom and a variable R group bonded to a central carbon atom.
What is a dipeptide?
Two amino acids joined by a peptide bond
What type of bond joins two amino acids together?
A peptide bond
What type of reaction forms a peptide bond?
A condensation reaction
What happens during a condensation reaction?
A bond is formed and a molecule of water is released.
What is a polypeptide?
A polymer made from multiple amino acid monomers joined by peptide bonds in condensation reactions.
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide, held by peptide bonds
What is the secondary structure of a protein?
Local interactions of the polypeptide chain to form 3D structures like alpha helices and beta pleated sheets. It’s held together by hydrogen bonding.
State two types of secondary structure in a protein
Alpha helices, beta pleated sheets
What is the tertiary structure of a protein?
The further coiling of a protein into its functional 3D shape. Held by hydrogen, ionic and disulphide bonds, and hydrophobic interactions.
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.
What is the quaternary structure of a protein?
-Not always applicable
-Describes the interactions of multiple polypeptide chains
-Held together by hydrogen, ionic and disulphide bonds, and hydrophobic interactions.
Give one example of a protein with a quaternary structure
Haemoglobin
Give 5 uses of proteins in the body
-Membrane proteins for transport
-Receptors
-Hormones
-Antibodies
-Enzymes
What roles do globular proteins have in the body?
Metabolic roles
What roles do fibrous proteins have in the body?
Structural roles
Describe how the structure of fibrous proteins relates to their function.
Long polypeptide chains, folded in parallel. Very little tertiary and quaternary structure aside from cross-linkages for strength. This makes them soluble and useful for providing structure.
Give an example of a fibrous protein and explain how its properties relate to its use.
Collagen - hydrogen and covalent bonds make it strong. Polypeptide fibers form a triple helix which creates fibers. 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, forms colloids in water. They are useful for hormones, antibodies, etc.
Give an example of a globular protein and explain how its properties relate to its use.
Hemoglobin - Water-soluble, with quaternary structure. Contains four haem groups that oxygen can bind to. Used to carry oxygen in the blood to respiring tissues.
What are enzymes?
Biological catalysts that speed up the rate of metabolic reactions without being used up or permanently altered.
Define catalysis
The process where a substance speeds up a chemical reaction by lowering activation energy without being used up itself.
What are enzymes made of?
Protein
What class of proteins are enzymes generally made up of?
Globular proteins
How do enzymes work?
The active site is specific to a certain substrate. When the enzyme and substrate bind they form a complex, which lasts until the reaction is complete.
What is meant by a specific active site?
The 3D structure of each enzyme is unique because of the side chains and branches. This makes the active site unique as well, so only substrates that match the active site can bind there.
Differentiate between intracellular and extracellular enzymes
Intracellular: catalyse restions inside the cells.
Extracellular: catalyse reactions outside of cells.
Describe the lock and key model.
- Substrate and active site come into contact. 2. Substrate binds and the enzyme-substrate complex is formed.
- Reaction takes place, products are formed. 4. Products are released from the active site and the site can bind to another substrate.
Describe the induced fit hypothesis
- Enzyme approaches the substrate.
- Enzyme binds
- The substrate induces a subtle change in the active site so that it fits the substrate precisely.
- The enzyme catalyses reaction and creates an enzyme product complex
- The enzyme releases the products.
Describe the effect of t° on the rate of an enzyme controlled reaction.
As t° increases, so does rate of reaction. Once t° exceeds the optimum, the enzyme denatures and the rate of reaction decreases.
Why does the rate of an enzyme-controlled reaction increase when the t° increases?
As t° increases, the particles have more kinetic energy. This increases chances of collisions between molecules being successful and leading to a reaction.
If t° increases above the optimum, how does this affect enzyme function?
As the atoms in the active site gain more energy, they vibrate more which disrupts the bonds. The active site will be distorted and the bonds are broken. This denatures the enzyme and so it will no longer fit the substrate and can’t catalyse the reaction.
Describe the effect of pH on the rate of an enzyme-controlled reaction.
-The rate of an enzyme catalysed reaction is faster at the optimum pH.
-If pH is too high or low, the enzyme will work less efficiently and the active site may be denatured at extremes of pH
How does substrate concentration affect the rate of an enzyme-controlled reaction?
If enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration. Once all active sites become full, the rate no longer increases. It’s a limiting factor.
How does enzyme concentration affect the rate of an enzyme-controlled reaction?
If substrate concentration is fixed, rate of reaction increases proportionally to the enzyme concentration. When all the substrates occupy active sites, the rate no longer increases. It’s a limiting factor.
