BIOL115 - Lecture 11

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  • Created by: Katherine
  • Created on: 15-05-16 13:15
What are the 3 things that can affect enzyme activity?
Inhibitors, Physical factors, cellular regulation
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What are physical factors that affect enzyme activity?
Temperature, Ph
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How does temperature affect enzymes, and why?
As temperature increases, collisions between substrates and active sites occur more frequently as molecules move faster. Thermal agitation disrupt the weak bonds that stabilize the protein conformation, leading to thermal denaturation.
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How does pH affect enzymes, and why?
pH influences protein conformation and electrostatic interactions between enzyme and substrate (ionisation).
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What is the optimum pH for most enzymes, and what it is for digestive enzymes and those found in the intestine?
between pH 6-8. Digestive enzymes in the stomach are designed to work best at pH 2, while those in the intestine are optimal at ph 8, both matching their work environemnts.
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What are the two factors that determine how much enzyme activity is present in a cell
How much enzyme is present is a balance between rates of synthesis and degradation. The activity of enzyme present is dependent on regulation.
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How are enzymes regulated?
The simplest way if by changing S and P. More S means more product. High P can inhibit enzyme activity (product inhibition). But, S and P only affect overall measured rates of reaction, not the catalytic properties of an individual enzyme.
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What is feedback inhibition?
It
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Biochemical pathways often have a committed step:
The first irreversible reaction, often rate limiting step.
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What often behaves as an inhibitor of the enzyme that catalyses the committed step>
The final product
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W
f
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What is the allosteric effect?
An effect at one site on a molecule caused by binding of a molecule at a second, distinct site.
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What is allosteric regulation usually associated with?
Multi-subunit enzymes.
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There may be positive and negative regulators invovled. What type of binding is it if it is positive?
Co-operative binding
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What does allosteric regulation allow?
Feedback control of metabolic pathways
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Do allosteric enzymes obey Michaelis Menton kinetics?
No
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For allosteric regulation, the Rate vs S plot is,,,
Igmoidal
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What does sigmoidal mean?
It means
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In allosteric regulation, substrate binding t one site increases or decreases the Km at other active sites?
Increases
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What does this result in?
Rapid responses to increases in S
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Allosteric enzymes can exist in two states, what are these?
T tense (low activity), R - relaxed (high activity)
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Sigmoidal plot is a combination of two Michaelis Menton type lots, what are these?
T tense (low activity), R - relaxed (high activity)
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In allosteric regulation of Aspartate transcarboamylase (ACTase), what is the first step?
ACTase is the first committed step in pyrimidine synthesis. End points are nucleotides, including cytidine triphosphate.
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What is ACTase?
It is a multi-subunit enzyme
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What are the subunits of ACTase?
The catalytic subunit and the regulatory subunit
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What does the catalytic subunit of ACTase do?
It binds the substrates, catalyses formation of products, it is not affected by CTP
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What does the regulatory subunit do?
It binds CTP, does not have any catalytic activity
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The complete structure of ACTase has how many regulatory and catalytic subunits?
It has 6 of each
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What is the structure of ACTase?
It has two layers of catalytic trimers surrounded by regulatory dimers.
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In ACTase co-operative binding, substrate binding induces what type of change?
A conformational change
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In ACTase allosteric inhibition, what happens?
The CTP binds the regulatory subunits and stabilises the T state. Enzyme activity i regulated byy the balance between substrate and end point product.
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What are Isozymes?
They are different versions of the same enzyme with different catalytic properties e.g. Km, Vmax, response to regulatory molecules.
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What makes isozymes different from each other?
They are encoded by different genes - gene families.
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What is the point of isozymes?
It allows for the same reaction to have different affects on metabolism in different tissues, or to take place under different conditions. It allows for fine tuning of metabolism.
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What is invovled in both glucose metabolism and glucose biosynthesis?
Lactate dehydrogenase (LDH).
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What is LDH?
Lactate Dehydrogenase
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LDH occurs as two isozymes, what forms are these?
H form (heart) and M form (skeletal muscle)
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What is the LDH isozyme in H form like?
It has a higher affinity for substrates, allosterically inhibited by pyruvate, optimised to convert lactate to pyruvate to provide fuel for aerobic metabolism.
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What is the LDH isozyme in M form like?
It is optimised to convert pyruvate to lactate to allow anaerobic glycolysis.
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What is an isofomr?
It is a combination of the isozymes.
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How many isoforms does LDH have?
It has 5 major isoforms.
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Which LDH isoforms are prevalent when a rate is an adult, and which is most prevalent when a rat is in the womb?
As an adult, LDH1 & LDH2 - In the womb: LDH5.
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What are physical factors that affect enzyme activity?

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Temperature, Ph

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How does temperature affect enzymes, and why?

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Card 4

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How does pH affect enzymes, and why?

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What is the optimum pH for most enzymes, and what it is for digestive enzymes and those found in the intestine?

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