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Biochemistry > EXAM 2 Practice Test > Flashcards

EXAM 2 Practice Test Flashcards

1
Q

Which of the following statements about catalyzed enzyme reactions is false?

A

the activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed rxn

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2
Q

the number of substrate molecules converted to product in a given unit ofd time by a single enzyme molecule at saturation is referred to as the

A

-turnover number

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3
Q

in the situation of competitive inhibition, an inhibitor

A

-binds reversibly at the active site

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4
Q

Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by reacting covalently with the catalytic serine residue at the active site; this enzyme inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition?

A

-irreversible

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5
Q

when two carbohydrates are epimers:

A

they differ only in configuration around one carbon atom

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6
Q

the phosphodiester bond that joins adjacent nucleotides in DNA:

A

associates ionically with metal ions, polyamines, and proteins

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7
Q

double-stranded regions formed by RNA:

A

can form between two self-complementary regions of the same single strand of RNA.

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8
Q

which of the following is not true of all naturally occurring DNA?

A

-the ratio A+T/G+C is constant for all natural DNAs

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9
Q

In DNA sequencing by the Sanger (dideoxy) method:

A

the role of the dideoxy CTP is to occasionally terminate enzymatic synthesis of DNA where Gs
occur in the template strands.

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10
Q

Which of the following statements about the composition of biological membranes is false?

A

In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially the same complement of lipids and proteins.

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11
Q

Which of these statements is generally true of integral membrane proteins?

A

the secondary structure in the transmembrane region consists solely of a-helices or B-sheets
OR A hydropathy plot reveals one or more regions with a high hydropathy index.

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12
Q

the fluidity of a lipid bilayer will be increased by:

A
  • increasing the temperature

- an increase in the number of double bonds in fatty acids.

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13
Q

the type of membrane transport that uses ion gradients as the energy source is

A

secondary active transport

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14
Q

which of the following is not one of the general types of signaling mechanisms found in multicellular organisms

A

Receptor cAMP cyclases

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15
Q

which of the following does not bind to heterotrimeric G proteins

A

cGMP

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16
Q

a ligand-gated ion channel (such as nACh) is:

A

a membrane protein that permits an ion to pass through the membrane only when opened by the appropriate ligand

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17
Q

which of the following is not a feature of signal transduction?

A

Covalent binding between the ligand and the receptor

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18
Q

in living cells, nucleotides and their derivatives can serve as:

A

-carriers of metabolic energy
-enzyme cofactors
-intracellular signals
-precursors for nucleic acid synthesis
aka ALL THE ABOVE

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19
Q

which one of the following statements about starch and glycogen is false?

A

Both serve primarily as structural elements in cell walls.

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20
Q

steroid response elements (HREs) are ___ which when bound to ____, alter gene expression at the level of

A

sequences in DNA, receptor-hormone-complex, transcription

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21
Q

glucose and galactose are

A

-stereoisomers, enantiomers, and epimers

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22
Q

which of the following statements concerning signal transduction by the insulin receptor is not correct?

A

The substrates of the receptor protein kinase activity are mainly proteins that regulate transcription.

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23
Q

the difference between a ribonucleotide and a deoxyribonucletide is:

A

the deoxyribonucleotide has an -H instead of an -OH at C2 prime

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24
Q

In the Watson-Crick Model for the DNA double helix, which of the followign statements is false?

A

-there are two equally sized grooves that run up the sides of the helix

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25
Q

Triacylglycerols are composed of

A
  • a glycerol backbone
  • 3 fatty acids
  • an ESTER linkage between the FA and the glycerol
26
Q

Which of the following statements about membrane lipids is true?

A) Glycerophospholipids are found only in the membranes of plant cells.
B) Glycerophospholipids contain fatty acids linked to glycerol through amide bonds.
C) Lecithin (phosphatidylcholine), which is used as an emulsifier in margarine and chocolate, is a sphingolipid.
D) Some sphingolipids include oligosaccharides in their structure.
E) Triacylglycerols are the principal components of erythrocyte membranes.

A

-D) Some sphingolipids include oligosaccharides in their structure.

27
Q

which of the following is not a consequence of partial hydrogenation of vegetable oils?
A. Longer Shelf life
B. lower melting point
C. reduction of some cis double bonds to single bonds
D. conversion of some cis double bonds to trans double bonds
E. increased risk of cardiovascular disease upon consumption by humans

A

-Lower melting temperatures

28
Q

what is the practical definition of Km, the Michaelis constant ?

A

-the concentration of substrate at which the enzyme is operating at half its maximal velocity

29
Q

Which of the following answers is not true?

Phospholipase A1 hydrolyzes the fatty acid from the 1-position on the glycerol backbone.

Phospholipase B1 hydrolyzes the fatty acid from the 2-position on the glycerol backbone.

Phospholipase C hydrolyzes the complete phospho-head group from the glycerol backbone.

Phospholipase D hydrolyzes just the head group from the phospho-glycerol backbone.

A

Phospholipase B1 hydrolyzes the fatty acid from the 2-position on the glycerol backbone.

30
Q

where does phosholipase A1 hydrolyze the fatty acid?

A

from the 1 position of the glycerol backbone

31
Q

Lysophospholipases (like phospholipase B) remove the

A

second FA from lysophospholipids

32
Q

phospholipase D hydrolyzes

A

-just the head group from the phospho-glycerol backbone

33
Q

Phospholipase C hydrolyzes

A

the complete phospho-head group from the glycerol backbone.

34
Q

membrane proteins

A
  • are sometimes covalently attached to lipid moieties
  • are sometimes covalently attached to carbohydrate moieties
  • are composed of the same 20 amino acids found in soluble proteins
  • diffuse laterally in the membrane unless they are anchored
35
Q

Which of the following is true of sphingolipids?

A) Cerebrosides and gangliosides are sphingolipids.
B) Phosphatidylcholine is a typical sphingolipid.
C) They always contain glycerol and fatty acids.
D) They contain two esterified fatty acids.
E) They may be charged, but are never amphipathic.

A

A

36
Q

Sphingolipids

A
  • polar head group
  • 2 nonpolar tails
  • no glycerol molecule base
  • long chain fatty amino alcohol
  • found in CNS (think myelin sheath)
37
Q

a hydropathy plot is used to:

A

-predict whether a given protein sequence contains membrane spanning segments (look for + spots at least 20 AA long)

38
Q

cholesterol described in one word

A

-Amphipathic

39
Q

which of the following would NOT alter the equilibrium of a reaction?

A

-adding an enzyme to the reaction

40
Q

Which of these is a general feature of the lipid bilayer in all biological membranes?

A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer.
B) Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the other monolayer.
C) Polar, but uncharged, compounds readily diffuse across the bilayer.
D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules.
E) The polar head groups face inward toward the inside of the bilayer.

A

A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer.

41
Q

noncompetitive inhibitor

A
  • mixed inhibitor
  • binds E or ES
  • increases apparent Km and lowers Vmax
  • higher [S] cannot restore full activity
  • shifts x-intercepts to right and makes higher mark on y intercepts
42
Q

uncompetitive inhibitor

A
  • binds ES
  • decrease in Vmax and cannot be reversed by higher [S]
  • DECREASE in apparent Km
  • x-intercepts shifts left, y intercepts shifts up
  • **graphs are parallel
  • MNEUMONIC PU
43
Q

competitive inhibition

A
  • binds E active site
  • no effect on vmax as it can be “outcompeted” for active site
  • increase apparent Km
  • x-axis shifts to the right and y intercept stays same
44
Q

GLUT 1

A
  • example of passive transport
  • seen in glucose transport from blood plasma to RBC
  • 50,000 times faster than simple diffusion
  • carrier, saturable and substrate specific
45
Q

GLUT 2

A
  • seen in Liver, gut, and pancreas
  • high capacity, low affinity transporter
  • facilitates downhill efflux
  • uniporter, and fasciliated diffusion
46
Q

Na+-Glucose Transporter

A
  • symport and secondary active transport

- seen in intestinal lumen to get glucose in epithelial cell so it can enter blood via facilitated diffusion

47
Q

chymotrypsin’s pocket and binding hole

A
  • hydrophobic pocket

- oxyanion hole

48
Q

Step 1 of chymotrypsin mechanism

A

1a. His 57 interacts with Ser 195–> His 57 accepts proton and makes Ser 195 into a cool alkoxide ion which attacks peptide bonds
1b. Ser 195 alkoxide attacks carbonyl C, making a tetrahedral acyl-enzyme: negative charge on carbonyl is stabilized by H-bond in oxyanion hole
1c. negative charge developed on carbonyl oxygen atom (the oxyanion)

49
Q

step 2 of chymotrypsin mechanism

A

2a. negative charge on carbonyl oxygen is unstable, so that electron pair moves to make C-O bond, thus double bond re-forms on carbonyl carbon
2b. the C-N bond breaks–> so that carbon wont have 5 bonds. Because the bond broke the amino acid group gets a H from the His57
2c. electron pair from HN bond pauses on His N atom and now product 1 is formed and can leave the enzyme

50
Q

Step 3 of chymotrypsin

A

product 1 leaves S fragment with its new amino terminus

51
Q

step 4 of chemotrypsin

A

4a. incoming water reactant deprotonated by His57
- strongly nucleophilic hydroxide ion
- hydroxide attacks ester to make a tetrahedral intermediate
4b. developing negative charge stabilized in oxyanion hole

52
Q

chymotrypsin step 5

A

5a. tetrahedral intermediate collapses
- reformation of the carbonyl double bond
5b. this breaks the acyl-enzyme bond
- forms carboxylate anion on product 2, moves ser 195 out of the way

53
Q

chymotrypsin step 6

A

-His 57 donates H+ to Ser 195 alkoxide anion, electrons pause on His 57, restoring enzyme to its starting condition with product 2 still bound

54
Q

chymotrypsin step 7

A

-release of product 2 restores enzyme to empty state, ready to go again

55
Q

what feature gives chymotrypsin its substrate specificity?

A
  • The hydrophobic and shape complementarity between the peptide substrate P1 sidechain and the enzyme S1 binding cavity accounts for the substrate specificity of this enzyme
  • the hydrophobic pocket and oxyanion hole
56
Q

peripheral membrane proteins

A
  • generally not covalently bound to bilayer

- practical isolation by disrupting ionic interactions with salt, chelating agents, Na2carbonate and high pH

57
Q

An integral membrane protein can be extracted with:

A) a buffer of alkaline or acid pH. 
B) a chelating agent that removes divalent cations. 
C) a solution containing detergent. 
D) a solution of high ionic strength. 
E) hot water.
A

-a solution containing detergent

58
Q

Integrins are:

A) membrane proteins that are involved in ion transport.
B) membrane proteins that are involved in sugar transport.
C) membrane proteins that mediate cell adhesion.
D) proteins of the extracellular matrix that bind to cell surface proteins.
E) proteins that are found at the membrane-cytoplasm interface.

A

C) membrane proteins that mediate cell adhesion.

59
Q

According to the current model for HIV infection, which of the following is not involved in the process of membrane fusion?

A) A cell surface co-receptor protein 
B) A cell surface receptor protein 
C) A viral glycoprotein complex 
D) The viral chromosome 
E) The viral envelope
A

D) The viral chromosome

60
Q

Which of these statements about facilitated diffusion across a membrane is true?

A) A specific membrane protein lowers the activation energy for movement of the solute through the membrane.
B) It can increase the size of a transmembrane concentration gradient of the diffusing solute.
C) It is impeded by the solubility of the transported solute in the nonpolar interior of the lipid bilayer.
D) It is responsible for the transport of gases such as O2, N2, and CH4 across biological membranes.
E) The rate is not saturable by the transported substrate

A

A) A specific membrane protein lowers the activation energy for movement of the solute through the membrane.

61
Q

Glucose transport into erythrocytes is an example of:

A) active transport. 
B) antiport. 
C) electrogenic uniport
D) facilitated diffusion. 
E) symport.
A

D) facilitated diffusion.

62
Q

The type of membrane transport that uses ion gradients as the energy source is:

A) facilitated diffusion
B) passive transport. 
C) primary active transport. 
D) secondary active transport. 
E) simple diffusion.
A

D) secondary active transport.

Biochemistry (7 decks)

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