Unit 1 Study Review

Question 1

What is IP3 (1,4,5 inositol triphosphate) derived from?

Answer 1

Membrane lipid PIP2 (phosphotidyl inositol biphosphate)

Question 2

A hydrogen bond will not form between the hydrogen of a methyl group and the oxygen of a carbonyl group due to what ?

Answer 2

The lack of a partial positive charge on the hydrogen atom

Question 3

Hydrogen bonds form when a hydrogen atom, with a partial positive charge, is shared between two _______ atoms, each of which has a partial negative charge.

Answer 3

Electronegative

Question 4

What best describes the role of activation-transfer coenzymes in the enzyme-catalyzed reactions ?

Answer 4

They provide functional groups for covalent catalysis (make covalent bonds with the portion of the substrate that will be transferred)

Question 5

In the serine protease mechanism, _____ acts as a general base catalyst and pulls a proton from _____, creating the serine nucleophile at the active site.

Answer 5

Histidine

Serine

Question 6

In the cysteine protease mechanism, the _____ orients the histidine appropriately to remove a hydrogen from cysteine, thereby creating a powerful cysteine nucleophile at the active stie.

Answer 6

Asparagine

Question 7

What happens in cysteine proteases or serine proteases if aspartic acid is replaced by asparagine next to histidine ?

Answer 7

Asparagine is not charged and so can not stabilize the positively charged histidine by hydrogen bonds

Question 8

The activation of zymogens to enzymatically-active proteins occurs due to what initial step?

Answer 8

Alteration in the primary structure - proteolysis of the zymogen leading to removal of a series of amino acids that will activate the enzyme

Question 9

A mutation in a plasma membrane receptor changes its Kd for a growth factor from 10-9M to 10-7M , what would be the consequence of this change?

Answer 9

It would increase the concentration of growth factor required to achieve a cellular response
-Kd has increased, so it dissociates more readily (growth factor)

Question 10

Chymotrypsin is a protease that cleaves peptide bonds. It is characterized as which of the following classes of enzymes ?

Answer 10

Hydrolases

Question 11

Which AA has a side chain that has a pKa that can act as a buffer in a physiological pH range (7.4)

Answer 11

Histidine

Question 12

The “T” state of hemoglobin is stabilized by what interaction ?

Answer 12

Aspartate sidechain forming and ionic interaction with a residue in the H-helix

Question 13

What will Iron binding do to the hemoglobin?

Answer 13

Lead to R state and higher oxygen affinity

Question 14

All intestinal hydrolases (proteases, esterases, glycosidases) utilize _____ catalysis to add the elements of water across the bonds, so pH changes will or will not effect the activity of hydrolases?

Answer 14

Acid-Base catalysis

Will Effect if pH changes

Question 15

As the pH falls below 6.5, protons will not readily dissociate from Hisitdine. This means that enzymes that utilize histidine to abstract a proton from the substrate in ____ catalysis are active only when ?

Answer 15

Acid base catalysis

Over a neutral range in pH because Histidine needs to be able to accept and donate protons within its pH range

Question 16

Nerve gas, such as sarin , will lead to muscle contraction due to what ?

Answer 16

Prolonged opening of the ion channel in the acetylcholine receptor - due to irreversible inhibition of acetylcholinesterase so the signal will not degrade

Question 17

A mutation in a plasma membrane receptor changed its Kd for a growth factor from 10 to the -9M to 10 to the -7M. What is a consequence of this change ?

Answer 17

Increase in Kd = more growth factor required to bind receptor to obtain 50% saturation
(more is needed to reach the same cellular response now as affinity of the receptor for its ligand has decreased )

Question 18

Raising the membrane content of what can increase the membrane fluidity ?

Answer 18

Cholesterol - hydrophobic molecule helps disrupt the rigidity

Question 19

An increase in pH from 7 to 13 usually results in protein denaturation due to what ?

Answer 19

Loss of tertiary structure caused by deprotonation of basic groups
(NH3 converted to NH2 and loss of ionic interactions and hydrogen bonds- destabilizes tertiary structure)

Question 20

Substrate binding to the active site most often utilizes what types of interaction?

Answer 20

Hydrogen bonding

in hydrophobic active sites, hydrophobic forces will be primary driving force in substrate binding

Question 21

A single nucleotide mutation has converted an “I” amino acid to a “N” within a protein. Why might the protein lose activity?

Answer 21

Gain of hydrogen bonding capacity

Isoleucine is non-polar and can not form hydrogen bonds

Asparagine has a carbonyl group linked to a amide group on R chain, and can do hydrogen bonding

Question 22

SH2 Domains on proteins are specific for what residues?

Answer 22

phosphotyrosine residues

Question 23

The number of distinct human chromosomes ?

Answer 23

24
(22 are autosomal distinct)
(2 are sex distinct)
Total each human has is 23 pairs (46 chromosomes)