Cell Cycle and Enzyme Kinetics Flashcards Preview

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Flashcards in Cell Cycle and Enzyme Kinetics Deck (31):

What is the main goal of the somatic cell cycle?

To ensure exact duplication of the genome in the S phase, and exact division of the genome in the M phase to create two identical daughter cells.


How do cells regulate their size by coordinating growth with division at the restriction point R" in G1?"

At the R point, the cell determines whether or not it is big enough to move on to S phase. 


How do cells prevent re-replication of their genome?

By keeping the assembly and activation complexes in separate cell cycle phases. 


What can result from chromosome re-replication in S phase, or mis-segregation -  forms of genomic instability?

Diseases like cancer and birth defects (trisomy 21). 


What does it mean that differentiated post-mitotic cells (like neurons) are stuck at the R" point?"

They will continue to grow without cycling.


What do cell cycle checkpoints do?Where are some of the checkpoints?

They are surveillance units that ensure genomic stability. G1 phase: R site makes sure the cell is large enough to enter the cell cycleS phase: if DNA is damaged, it will not proceed to mitosisM phase: if mitotic spindles are damaged, cell will exit mitosis 


What is the mechanism of cell cycle checkpoints?

A sensor (Rad 17) will sense DNA damage.  The sensor will signal a transducer (ATM) to phosphorylate (activate) an effector protein (p53, CHK2).  The effector will stop the cell cycle either on its own or, in the case of p53, by inhibiting CDK. 


What are some cell cycle regulators that are altered in cancer cells that are being used in patient diagnosis and prognosis?

CDK's: help with cell proliferation, are elevated in some cancersBRCA 1,2: Mutations indicate a DNA checkpoint defect leading to higher risk of genomic instability and breast cancer


What are the main differences between mitosis and meiosis?

Meiosis produces haploid gametes.  The cells undergo two divisions after DNA replication. 


What is an enzyme?

A biological catalyst.  A compound that increases the rate of a chemical reaction without being changed in the process. Enzymes form a specific three dimensional structure with the active site. 


What is activation energy?How does it relate to enzymes?

The energy it takes to start a reaction.Enzymes decrease the activation energy of a reaction by positioning the reactants in a favorable way, thus speeding the reaction. 


What is the free energy of a chemical equation?How is this related to enzymes?

The energy in a chemical system that can be converted to do work. Enzymes can help reactions that are energetically favorable (negative delta G) but slow (high activation energy) occur at a rate that is physiologically favorable by stabilizing the transition state (reducing activation energy). 


What is a cofactor?

A substance (often a metal) that needs to be present in addition to an enzyme to catalyze a reaction. The cofactor does not donate a chemical group to the reaction. 


What is a coenzyme?

A small molecule that works with the enzyme that donates a chemical group that will be used in the reaction. 


How do enzymes lower the energy of the transition state when binding the substrate?

Multiple, weak, non-covalent interactions bind the substrate in such a way that it would be oriented in the high energy transition state, which provides both specificity and catalysis. 


How do enzymes alter the transition state through binding using the induced fit model?

The enzyme has to favor the transition state because this is how the reaction would be sped up.  When the substrate binds, the two form a complex that lowers the activation energy of the reaction.  Binding of the substrate at its transition state is stabilized by the weak non-covalent bonds. 


How do enzymes work by using covalent chemistry?

A transient covalent bond can form between the enzyme and the substrate. 


How do enzymes work by using metallic ion chemistry?

Bound metal ions can help position the substrate or can be a driving force in redox reactions. This is used by about 1/3 of enzymes. 


How do enzymes work using acid base chemistry?

Amino acid side chains can donate or accept protons to stabilize transition states. 


What is Km?

The substrate concentration at which the enzyme velocity will be at 1/2 Vmax.


What is Kcat?

Kcat is called the turnover number. It is equivalent to the number of substrate molecules converted to product in a given unit of time on a single enzyme molecule when the enzyme is saturated with substrate. 


How do competitive inhibitors work?What is the effect on Km? Vmax?

A competitive inhibitor binds only the enzyme so that the normal substrate cannot bind, and thus competes with it.Km increases, Vmax is unchanged


How do uncompetitive inhibitors work?What is the effect on Km? Vmax?

Inhibitor binds to substrate-enzyme complex and blocks the catalytic step.Apparent Km increases, Lowers Vmax


How do mixed inhibitors work?

The inhibitor binds outside of the active site and can bind either to E or ES. Both Km and Vmax are effected. 


What are the reversible inhibitors?



How do irreversible inhibitors work?

They combine with or destroy a functional group on an enzyme that is essential for the enzyme's activity. They make the enzyme non-functional, irreversibly.


What is a noncompetitive inhibitor?

A type of mixed inhibitor that can bind E and ES but do not affect substrate binding, although they still do reduce activity.


How does allosteric regulation of enzymes work?

Often, binding of another molecule (a regulator) will bind to the enzyme and change the conformation and thus function of the enzyme. This occurs often in feedback loops, when a downstream product of a pathway regulates an enzyme early in the pathway.


How does covalent modification of an enzyme help regulate it?

Phosphorylation or another post-translational modification can either activate or deactivate an enzyme.  This occurs often in response to intra or extracellular signals and conditions.


How can the binding of a regulatory protein regulate enzymes?

Much like allosteric regulation, small peptides can bind to enzymes to turn them on or off.


How does proteolytic cleavage regulate enzymes.

Some enzymes are inactive when first made, but are cleaved (generally by another protein) into smaller fragments to become active.  E.g. Chymotrypsinogen, cleaved by trypsin, to chymotrypsin.