CHAPTER 7 Flashcards
A non-allosteric protein that binds oxygen independently.
Myoglobin
An allosteric protein that binds oxygen cooperatively.
Hemoglobin
An allosteric enzyme that exhibits cooperative binding similar to hemoglobin.
Aspartate transcarbamoylase (ATCase)
Proteins that change their shape in response to a signal, leading to changes in function. Examples include hemoglobin and ATCas
Allosteric proteins
Myoglobin
Hemoglobin
Aspartate transcarbamoylase (ATCase)
Allosteric proteins
Catalyzes the first step in the biosynthesis of cytidine triphosphate (CTP), a nucleotide needed for RNA and DNA synthesis.
ATCase function
An energy-intensive process involving multiple steps.
Pathway producing nucleotides
This is an excellent example of how metabolic pathways are controlled to prevent overproduction of essential compounds.
ATCase regulation
A regulatory mechanism that shuts down an entire metabolic pathway when the final product is in excess.
A regulatory mechanism where the end product of a pathway inhibits the first enzyme in the pathway, preventing overproduction.
Feedback inhibition
An allosteric enzyme that catalyzes the first step in the biosynthesis of cytidine triphosphate (CTP).
ATCase
An inhibitor of ATCase, demonstrating feedback inhibition.
CTP
cytidine triphosphate
An oligomer whose biological activity is affected by other substances binding to it changes the enzymes activity by altering its quaternary structure.
Allosteric enzyme
A substance that modifies the behavior of an allosteric enzyme.
Allosteric effector
A type of allosteric effector that increases the enzyme’s activity.
Allosteric activator
A type of allosteric effector that decreases the enzyme’s activity.
Allosteric inhibitor
Indicates allosteric behavior in enzyme kinetics.
Sigmoidal curve
Both CTP and ATP bind to the same site on ATCase, but CTP is an inhibitor while ATP is an activator
ATCase regulation by CTP and ATP
When CTP is in short supply, ATP binding ______ ATCase activity of the enzyme.
ATP effect on ATCase
Increases
Models for allosteric enzymes
The two main models are the Concerted Model (1965) and the Sequential Model (1966).
A model that assumes all subunits of an allosteric enzyme exist in either a T (tense) or R (relaxed) state, and the transition between these states is concerted.
Concerted Model
A model that allows for individual subunits to change conformation independently, leading to a more gradual transition between the T and R states.
Sequential Model
Comparative simplicity.
Concerted Model
Provides a more realistic picture of protein structure and behavior.
Advantage of the Sequential Model
The enzyme exists in two conformations: R (relaxed) and T (tight or taut). The R state binds substrate tightly, while the T state binds substrate less tightly.
Enzyme conformations in the Concerted Model
A model proposed by Wyman, Monod, and Changeux in 1965 to explain allosteric behavior.
Concerted Model
Conformational changes in the Concerted Model
All subunits of the enzyme change conformation simultaneously when transitioning between the T and R states.
Conformational changes in the Concerted Model
In the absence of substrate, most enzyme molecules are in the __________ form. The binding of substrate shifts the equilibrium towards the _______ form.
Substrate binding in the Concerted Model
T(Inactive)
R (active)
A model that explains allosteric behavior by proposing that the binding of substrate to one subunit induces a conformational change that is passed along to other subunits.
Sequential Model
Substrate binding induces a conformational change from the T to the R form.
The conformational change is induced by the fit of the substrate to the enzyme (induced-fit model).
The model represents cooperativity.
Main features of the Sequential Model
The binding of substrate to one subunit triggers a conformational change that is transmitted to other subunits, leading to a cooperative effect.
Substrate binding in the Sequential Model
An enzyme whose activity is ________ by molecules binding at sites other than the active site.
modulated
Allosteric enzyme
____, the pathway’s end product involving ATCase, inhibits ______ activity through feedback inhibition.
CTP, ATCase
The regulation of an enzyme’s activity by the binding of molecules at sites other than the active site.
Allosteric regulation
A molecule that binds to allosteric sites on ATCase and inhibits its catalytic activity.
CTP
A non-allosteric enzyme that does not exhibit allosteric regulation.
Chymotrypsin
An inactive precursor of an enzyme that requires proteolytic activation to become the active enzyme.
Zymogen
A single-chain of polypeptide composed of ____ amino acid residues cross-linked by __ disulfide bonds.
245, 5
Chymotrypsinogen structure
A zymogen ______ and _____ in the pancreas, destined for secretion into the small intestine.
synthesized, stored
Chymotrypsinogen
Non-protein chemical compounds or metallic ions that help enzymes perform their catalytic functions.
Cofactors
___________ molecules that assist enzymes in their catalytic activities.
Non Protein
Cofactors and Coenzymes
Cleavage of a __-amino acid peptide of trypsin from the N-terminus gives Pi - chymotrypsin that removes ___ dipeptide fragments leading to the formation of fully _________-chymotrypsin.
15, 2
active α
Activation of chymotrypsinogen
Organic molecules that are a _____ of cofactors.
subset
Coenzymes
Cofactors can ______ enzyme structure, _______ in the actual catalytic reaction, or____ in substrate binding
stabilize, participate, assist
Role of cofactors
Examples of cofactors:
Mg2+ for DNA polymerase, Zn2+ for alcohol dehydrogenase. and Fe2+ they are also inorganic ions
Organic cofactors that assist enzymes in catalyzing reactions by acting as carriers for _________ or electrons.
Often derived from vitamins.
chemical groups
Coenzymes
Nature of coenzymes: Organic Molecules
Participate in reactions by _______ accepting or donating atoms, ions, or functional groups.
temporarily
Role of coenzymes
often regenerated after the reaction, allowing for their repeated use.
Coenzymes
Biotin
Back: A coenzyme involved in carboxylation reactions. Vitamin precursor: _____
Coenzyme A
A coenzyme involved in acyl transfer reactions. Vitamin precursor: ________
Flavin coenzymes
Coenzymes involved in oxidation-reduction reactions. Vitamin precursor: _________.
Lipoic acid
A coenzyme involved in acyl transfer reactions. Vitamin precursor: None.
Nicotinamide adenine coenzymes
Coenzymes involved in oxidation-reduction reactions. Vitamin precursor: _______
Pyridoxal phosphate
A coenzyme involved in transamination reactions. Vitamin precursor:_________
Front: Tetrahydrofolic acid
Back: A coenzyme involved in the transfer of one-carbon units. Vitamin precursor: _______
Front: Thiamine pyrophosphate
Back: A coenzyme involved in aldehyde transfer reactions. Vitamin precursor: _______
Biotin
Pantothenic acid.
Riboflavin (B2)
Niacin
Pyridoxine (B6).
Folic acid.
Thiamin (B1).
Cofactors
Non-protein chemical compounds or metallic ions that assist enzymes in their catalytic functions.
Coenzymes
Organic molecules that are a subset of cofactors.
Difference between cofactors and coenzymes
Cofactors can be inorganic (metal ions) or organic, while coenzymes are always organic.
Relationship between cofactors and coenzymes
All coenzymes are cofactors, but not all cofactors are coenzymes.
Role of coenzymes in enzymatic reactions
Coenzymes often participate directly in the enzymatic reaction.
Role of cofactors in enzymes
Some cofactors may play more structural or stabilizing roles.
Good Luck We can do it Fighting !!!!!!!!!
If u reached this may choco ka next week
