Flashcards in Chapter 4 Energy & Cellular Metabolism Deck (28):
For a chemical reaction to take place what must occur? What is needed to usually start a reaction?
Most biological reactions require enzymes to make the rxn occur due to most chemical reactions are energetically unfavorable.
What is the term for the type of energy needed to start the reaction and for it to proceed>
Activation Energy- the hump that needs to be over come for the rxn to take place
What is the role of enzymes in biological rxns?
Enzymes reduce the activation energy
They serve as protein catalysts
Increase the likelihood that the rxn will occur and will also increase the rate of rxn
What happens after the enzyme binds with a substrate and the reaction proceeds
Enzymes are not consumed and left unchanged when the reaction is complete
Do enzymes work for every substrate? And what are the conditions that an enzyme favorably operates at
Enzymes are substrate specific
Most but not all enzymes work best at physiological neutral conditions (pH = 7.4) and a temp of 37 degrees C.
E.g. Of an enzyme that operates at a pH different than 7.4 is enzymes that are located with in the stomach (Pepsin) pH = 2.0
Enzymes sometimes require additional help to either make a rxn proceed or facilitate the binding to a specific substrate? What is the additional help and what is the function of this help?
Some enzymes require co-factors which can be metal ions such as Mg2+, Ca2+, Mn2+, Cu2+, Zn2+ and selenium.
Co-enzymes are derived from vitamins
Co-factors allow the enzyme to work more efficiently and they can change the conformation of the binding site to allow for tighter binding affinity
Co-enzymes can change the conformation of the binding site, but what else can it do in regards to the binging site?
They may serve as carriers for the reactants' functional group. They do not alter the binding site.
Enzymatic activity is very well regulated. What are some of the mechanisms?
I.e. Storage, modification, or modulation etc..
Many enzymes (but not all) are produced and stored as an inactive form
-precursor or zymogen, which are activated proteolytically (small part removed) when needed
-They can be covalently modified by phosphorylation or dephosphorylation
(In many but not all instances adding a -P activates it)
-enzymes activity may be modulated by second messengers.
Ca2+, IP3, cAMP
What is Turnover in regards to enzymes?
Refers to the rate of enzyme destruction or inactivation
Some enzymes are created in several related forms and these are referred to as?
What are their properties and functions?
The related forms means they exhibit slight differences in structure
However, they tend to catalyze the same reactions
Often found in different tissues
Even though isozymes have different structures they don't all share the same properties. What are some of the differences?
They don't share the same properties, reaction rates, conditions of reactions
Ex. Different pH
What is the definition of Reaction rate?
We can monitor the appearance of the product or the disappearance of the reactants for a given reaction.
How fast an enzyme works is the reaction rate
What does it mean when it says the reaction has reached saturation?
I means at saturation, all enzymes are bound by substrate
Once the reactant concentration is saturated, any further increase reactant level does not affect the reaction rate.
In non reversible rxn's the rate goes in what direction?
In reversible rxn's the rate goes in what direction
Non-reversible rxn's goes in the direction the rxn defines most of the time forward!
In reversible rxn's the reaction tens to go toward a state of equilibrium, whether towards the left or the right.
Describe the law of mass action in regards to the direction of the rxn and its rate!
Disturbing the reaction by adding components to either the left or right side of the reaction will drive the reaction to the right or left (respectively) until equilibrium is achieved
What refers to most chemical reaction in biological systems?
What are the subclasses?
Catabolism - breaking down reactants
Anabolism- building up or synthesis
What is the progression of a reaction? Start to finish
Can there be a different outcome of a rxn, meaning direction?
All reactions begin with substrate and progress through intermediates to end with a final product
Some rxns, branch points lead to two or more end products
What is the definition of feedback inhibition?
What in the rxn slows the rxn from continuing?
This occurs when rising concentrations of a product slows the reaction rate
The end product of a given pathway inhibits enzymes of upstream reactions from continuing the rxn. This will slow or stop the products from being formed.
What is the outcome of defects in a Metabolic Pathway?
What does it cause?
What takes place?
Defects in Metabolic Pathway may lead to disease
Sometimes a critical enzyme at the head of a branch point fails to work due to gene defects
The direction always favors the non-defective path there for accumulation of the deceptive products could lead to disease
Give an example of a metabolic pathway that is blocked that yields to disease.
PKU pathway gets blocked, therefore there's is a deficiency of liver enzyme phenylalanine hydroxylase which leads to no tyrosine production.
Elevated levels of phenylalanine levels are toxic to a young developing brain
What governs all chemical reactions in living systems?
What is the First Law of Thermodynamics?
Energy can be transformed but neither created nor destroyed
What is the second law of thermodynamics?
Energy transformations spontaneously occur to increase entropy (this = degree of disorganization of a system)
Everything wants to go from a highly organized state which takes a lot of energy to keep is so organized, to a disorganized state. (Entropy)
Living systems constantly require input of free energy in order to remain highly organized. How is this done?
Coupling of Exergonic reactions (which release energy) with Endergonic reactions (which require the input of energy
Explain Endergonic reactions.
They require the input of energy to proceed.
-the products contain more free energy than reactants
Explain Exergonic reactions.
The energy that is not trapped in high energy rxns becomes what form?
Release energy as they proceed
-reactants contain more free energy than products.
Energy that is not trapped is given off as heat
What is the major for of energy in the body that drives other reactions?
What type of reaction is this?
The hydrolysis of ATP to ADP + Pi
This is an Exergonic reaction