Lecture Five - Energy transformation in cells (enzymes) Flashcards
What is the relationship between photosynthesis and cellular respiration?
The process of photosynthesis provides organic matter from inorganic materials and sunlights. Respiration breaks down the organic matter into carbon dioxide, water and energy.
Photosynthesis = exothermic, catabolic reaction.
Which provides energy for
Cellular respiration = endothermic, anabolic reaction.
Define anabolism and catabolism.
The synthesis of complex molecules in cells is known as anabolism.
The breakdown of food by heterotrophic metabilisn takes place in a number of stages known collectively as catabolism.
Anabolism sees energy stored in cellular components, this is then released during catabolism.
Define autotrphic and heterotrophic metabolism.
Autotrophic - in which complex materials are built up from simple, inorganic materials (carbon dioxide, phosphate and ammonium, etc.) using energy from sunlight or reduced inorganic forms of elements e.g. hydrogen molecules or hydrogen sulfide.
Heterotrphic metabolism in which the energy inherent in organic matter is released as organic compounds such as sugars and fats are broken down to inorganic metter (carbon dioxide, water) = respiration.
What is ATP?
Adenosine triphosphate.
The major intracellular currency for the exchange of energy. ATP synthesis from ADP + Pi requires energy.
ATP hydrolysis to ADP + Pi yields energy.
What are the major details about REDOX reactions?
Oxidation:
Adds oxygen
Removes hydrogen
Removes electrons
Liberates energy
Reduction:
Removes ocygen
Adds hydrogen
Donates electrons
Stores energy
Oxidation and reduction reactions are coupled.
Explain the relationship between chemical bonds and the energy that they hold.
Each type of molecule has a certain level of internal energy, which depends on the molecule and the chemical bonds that make up that molecule.
When a chemical reation takes place, bonds are broken and new bonds are formed. Consequenctly reactants have a different internal energy to products.
Explain the changes in free energy and how that effects the types of reactions that occur.
If the products of a reaction have a higher energy content (free energy) than the reactants, then energy has to be put into the system to drive the reaction.
This type of reaction is an endothermic or endergonic reaction.
If the products of a reaction have a lower energy content (free energy) then the reactants, then energy has to be expelled from the system as the reaction takes place.
This type of reaction is an exothermic or an exergonic reaction.
Explain the term ‘change in Gibbs Free Energy.’
Delta G < 0 = exothermic reaction.
A large negitive value signifies that the reaction will see almost all of the reactant converted to product.
Delta G > 0 = endothermic reaction.
A positive value suggests that the reaction will more give a good yield of product unless energy is put into the system.
Define an enzyme.
The biological catalyst used by living cells. Catalysts speed up the rate of reactions but do not change the over all delta G or hence the final yield of products. Lowers the activation energy of a reaction by presenting the reactants with an alternate pathway, allowing the reaction to reach equillibrium more rapidly than the uncatalysed one.
What causes the specificity of enzymes?
The secondary and tertiary structure of enzymes allows them to interact with the substrate by binding the substrate to the surface of the enzyme at the enzymes active site.
The resulting enzyme-substrate complex is held together by ionic interactions, hydrogen bonding or transient covalent bonds.
What are the models of enzyme action?
Lock and key model and the induced fit hypothesis.
How does the enzyme work?
The interaction between enzyme and substrate molecules places stress on particular bonds in the substrate molecules which leads to the formation of products.
What are co-factors?
Many enzymes contain metal ions or other small organic molecules that help them to function - these are termed co-factors. They do not participate in the reactions themselves.
What are competitive and non-competitive inhibitors?
Competitive inhibitor:
A form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa.
Non-competitive inhibitor:
Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate. That is, it does not bind with the active site, it binds else where on the enzyme.
What is an allosteric enzyme?
One which is switched ‘on’ or ‘off’ depending on whether it is required.
These sort of enzymes oscillate between active and inactive.
Activators stabilise the active state. Inhibitors stabilise the inactive state.
Activators and inhibitors usually bind at an allosteric site, not the active site.
