Lecture 4: Enzymes Flashcards
What are exergonic reaction
Reactants have a higher energy level than products, so it is usually catabolic, releasing energy
What are endergonic reaction
Reactants have a lower energy than the products so large activation energy is required so usually anabolic
Where is change in Gibbs free energy represented in the energy profile.
The difference between the energy of reactants and products (not including Ea)
When will energy be released during an exergonic reaction
New bonds form to make the product
What is the difference in energy between exergonic reaction with enzyme and without
Enzyme lowers the Ea without affecting the delta G.
What are enzymes made of
Almost all are proteins with complex 3D structures. Some enzymes are made of RNA called ribozime
What is the catalytic cycle of an enzyme
- Substrates bind to the active site with weak bonds (H/ionic). forming the enzyme substrate complex
- Enzyme destabilises the bonds in the substrate/ makes favourable microenvironment and allow them to reach transition state.
- Bonds broken and new bonds are formed which are released from the active site leaving it available again
What does the overall shape of the enzyme help with - small active site
The enzyme can clasp down on the substrate, forming additional H/ionic bonds. It makes sure the amino acids in the active site are correctly orientated for binding
What are the main points about enzyme names
- ends with ase. They can describe the reaction they catalyse- can include substrate and type of reaction
What do Ribonuclease and Deoxyribonuclease do vs RNA/DNA polymerase
hydrolyse RNA and DNA vs synthesising DNA / RNA
What are cofactors
Non protein helpers for catalytic activity. Some enzymes need several cofactors.
What are the two types of cofactors
Prosthetic groups: organic or inorganic molecules that tightly bond to the enzyme.
Coenzymes : small organic molecules that non covalently (weak) bond to enzyme.
How does concentration influence reaction rate and the graph relationship
The concentration of enzymes is directly proportional to reaction rate (provided substrate increases at same rate), however only increasing substrate conc has a max rate of reaction as enzymes become saturated
How does temperature and pH affect the reaction rate of enzymes and the differences in the graph
Reaction rate increases proportional to temperature up to an optimal temperature/pH which afterwards the enzyme denatures and reaction rate. drops off. For pH the graph is a bell shaped curve whereas temp is more assymetric, with quick drop off.
How is enzyme activity regulated before they are made
The genes that code for particular enzymes can be turned on and off.
Why do enzymes need to be regulated
Enzymes are part of metabolic pathways and so need to be able to turn off and on at specific times
How is enzyme activity regulated after they are made
The inactive precursor of the active is made and activated when needed
The enzymes can be confined to specific organelles (eg lysosome)
The enzymes can oscillate between active and inactive forms - called allosteric regulation. depending on whether the cell produces an activator or inhibitor which binds away from the active site to fix it in the inactive or active state.
How do allosteric regulatory molecules bond and how
They bind somewhere else from the active site. This binding is weak non covalent interaction which result in either stimulation or inhibition of enzyme activity
What is an Allosteric feedback inhibition
This is when the final product of the metabolic pathway builds up and goes to bind to the early enzyme in the pathway to inhibit the enzymes pathway producing it. As the product decreases in conc, it is released from the first enzymes and then continues the cycle
