#2 practice

Compared to a typical animal cell, the cell membranes on the paw of a polar bear would most likely have an increased concentration of which macromolecule?

• Triacylglycerol

• Saturated phospholipids

• Unsaturated phospholipids

• Glycoproteins

Catalytic reactions proceed quicker than uncatalyzed reactions because:

• Enzymes lower the delta G of the reaction

• Enzymes lower the activation energy barrier

• Enzymes change the direction of equilibrium so formation of products are favored over formation of reactants.

• Enzymes reduce the amount of binding energy released during the transition state.

The enzyme hexokinase catalyzes the first reaction in glycolysis. What is its sister enzyme that catalyzes the reverse reaction in gluconeogenesis?

• An enzyme that removes phosphate groups

• An enzyme that removes carbon

• An enzyme that produces isomers

• An enzyme that removes hydrogen

During competitive inhibition, Vmax doesn't change but Km increases. Why?

• (I) reversibly binds to the active site so the (E)'s affinity for (S) increases; therefore Km increases but because Vmax will eventually be reached and doesn't change.

• (I) binds elsewhere on (E), which changes the shape of the active site. This lowers affinity for (S) which increases Km. Vmax is eventually reached: when (I) falls off, the active site is free to bind (S).

• (I) reversibly binds to the active site, so (E's affinity for (S) decreases, increasing Km. Vmax is eventually reached by increasing (S) and therefore doesn't change.

• The statement is false. Vmax also decreases because when (E) binds to (I), enzyme concentration goes down (i.e. the amount of enzyme available for binding (S) permanently decreases.

At certain points in glycolysis, two different enzymes are catalyzing the forward and reverse reactions. Here, the two enzymes must be regulated so that an increase of metabolic flux in one direction automatically results in a decrease of flux in the opposite direction. This type of regulation is:

• negative feedback

• covalent control

• genetic control

•  substrate cycle control

A cofactor is:

• A molecule that speeds up the reaction, but is not required for catalytic function.

• Sometimes a metal ion embedded near the enzyme's active site.

• A cosubstrate like NAD+.

• Two of the above

The active site of an enzyme is a perfect geometric and electronegative complement for only a single substrate, so substrate binds tightly to the enzyme as described by the lock and key model.

• True

• False

In what way does cholesterol affect the properties of a lipid bilayer?

• Cholesterol increases fluidity at low temperatures by preventing phospholipids from packing too tightly. 

• At higher temperatures, cholesterol decreases fluidity by pulling phospholipids closer together.

• Cholesterol broadens the phase transition between gel and liquid phases, which helps maintain the fluid mosaic of the membrane when body temperature fluctuates,

• Two of the above

• All of the above.

Which of the following examples describes a group transfer reaction in metabolism?

• Transcription of hexokinase increases in response to steroid hormones in the bloodstream.

• ATP generated by oxidative phosphorylation

• Hydrogen protons are removed from substrates and attached to NAD cofactors.

• 1. 
     

  2. Kinase catalyzes a reaction where phosphate is removed from ATP and attached to a metabolic enzyme or substrate.

Which of the following is not a monosaccharide?

• Glucose

• Fructose

• Sucrose

• Galactose