UIUC MCB 450 Exam 1

Biomolecules can be divided into four different classes. Which of the following is NOT a major class of biomolecule?

Fatty Acids

Which of the following molecules are the major components of the collagen?

proteins

Water is said to be highly cohesive because water molecules interact with one another through:

hydrogen bonds

Which of the following is considered a noncovalent bond?

-electrostatic interactions

-hydrogen bonds

-Van der Waals interactions

-ALL OF THE ABOVE

What is the [A-]/[HA] ratio when the weak acid is in a solution two pH units above its pKa?

100:1

Brownian motion is due to:

The random fluctuation of the energy content of the environment and thermal noise

Consider a biochemical reaction that is taking place in a 0.1 M buffer. The initial pH is 7.4, and the pKa of the buffer is 7.2. If, in a final reaction volume of 1.0 mL, 10 micromol of protons are generated, what would be the final pH of the solution?

7.22

Solution X is at a pH of 3; solution Y is at a pH of 8. Which of the following statements is TRUE?

solution X contains more protons than solution Y

What are the primary chemical components present in a phosphate buffer at pH 7.4?

H₂PO₄⁻ and HPO₄ ⁻²

Which of the following characterize α-helix regions of proteins?

They are formed principally by hydrogen bonds between a carbonyl oxygen atom in one peptide bond and the amide hydrogen from a different peptide bond.

Autopsies of patients with Alzheimer disease show protein aggregates called neurofibrillary tangles and neuritic plaques in various regions of the brain. These plaques exhibit the characteristic staining of amyloid. Which of the following structural features is the most likely characteristic of at least one protein in these plaques?

A high content of beta pleated sheet structure

Which of the following secondary structures is most likely to be found in a membrane-embedded portion of a protein?

an alpha helix composed entirely of hydrophobic residues

Which of the following statements regarding peptide bonds is least accurate?

favored conformation of peptide bonds is with the sequential alpha carbons in the cis position

Which is an appropriate statement of involvement of the hydrophobic effect in protein folding?

Nonpolar portions of the molecule associate with one another in the interior of the protein.

All of the following would disrupt quaternary structure except:

Treat with ascorbic acid (vitamin C).

The process of digestion in the stomach is carried out in two main ways. One way involves the _____environment that exists in the stomach.

low pH

The pancreas releases _________ to buffer the pH of the stomach juices.

NaHCO3

Pepsin requires _________ to achieve activity.

-zymogen activation

-low pH

-Partial denaturation of protein

The result of lipase activity in digestion is:

Monoacylgycerol and two free fatty acids.

_____ are molecules that aid in lipid adsorption. They are synthesized from cholesterol in the liver and secreted from the _____.

bile salts; gall bladder

What do micelles and chylomicrons have in common?

they both contain fatty acids

Many adults are unable to metabolize the milk and experience gastrointestinal disturbances (diarrhea) if they drink milk. This clinical symptom is most probably due to a deficiency in:

lactase

Chylomicrons are:

lipoprotein transport particles

Which of the following is a complex carbohydrate?

both starch and glycogen

What is the concentration of acetic acid in 250 ml of a 100 mM acetate buffer at pH 4.76?

50 mM

Which of the following amino acids has a relatively uncharged side chain under physiological conditions?

a. Arginine

b. Aspartate

c. Glutamate

d. Lysine

e. Histidine

Histidine

Which of the following best describes the arrangement of amino acid side chains in an alpha helix?

a.The side chains point outward away from the helical axis.

b. The side chains point inward toward the center of the helix.

c. The side chains point toward the N-terminal end of the helix.

d. The side chains point toward the C-terminal end of the helix.

e. The side chains point toward the nearest beta sheet.

The side chains point outward away from the helical axis

Which of the following secondary structures is most likely to be found in a membrane-embedded portion of a protein?

a.An alpha helix composed entirely of hydrophobic residues

b. An alpha helical coiled coil

c. An single extended beta strand

d. An open antiparallel beta sheet composed of hydrophobic residues

e. An open parallel beta sheet composed of hydrophilic residues

An alpha helix composed entirely of hydrophobic residues

Which of the following is necessarily characterized by a covalent linkage?

a.Base-pairing interaction

b. Disulfide bond

c. Hydrogen bond

d. Induced fit

e. Van der Waals interaction

Disulfide bond

Enzymes that are activated by specific proteolytic cleavage are called?

a.Isozymes

b. Zymogens

c. Allosteric

d. Heterozymes

e. Nuclease

Zymogens

Denature of proteins by gastric acids is due to the disruption of _____ by low pH.

a.Peptide bonds

b. Disulfide bridges

c. Ionic bonds and hydrogen bonds

d. Hydrophobic interactions

e. Ester bonds

ionic bonds and hydrogen bonds

Deficiency of which of the following enzyme leads to the lactose intolerance?

a. Maltase

b. Lactase

c. Sucrase

d. a-amylase

e. a-glucosidase

Lactase

_____ are molecules that aid in lipid adsorption. They are synthesized from cholesterol in the liver and secreted from the _____.

a.Bile salts; pancreas

b.Bile salts; gall bladder

c.Bile salts; intestine

d.Lipases; pancreas

e.Cholesterol esterase, gall bladder

bile salts; gall bladder

What is the function of ApoCII in the chylomicrons?

a.It is recognized by hepatic receptors for recycling.

b.It is the structure protein for the formation of chylomicrons.

c.It is required for the transportation of chylomicrons in the blood.

d.It is necessary for the activation of lipoprotein lipase.

e.It is involved in the re-synthesis of TAG in the small intestine.

It is necessary for the activation of lipoprotein lipase

Which of the following is the ultimate electron acceptor in oxidative phosphorylation?

a) ATP

b) ADP

c) coenzyme Q

d) cytochrome C

e) Oxygen

oxygen

_______________ is the name given to the hypothesis proposed by Peter Mitchell to explain how ATP synthesis is coupled to electron transport.

a. Chemiosmosis

b. Electron transport chain

c. Oxidative phosphorylation

d. Electron transport potential

e. Proton pump

chemiosmosis

The rotation of the _______of ATP synthase, driven by proton gradient, powers ATP synthesis.

a. F1 subunit

b. Alpha-beta subunit

c. c ring

d. Na-ATP pump

e. ADP-ATP translocase

C-Ring

A diet pill that acts to increase oxygen consumption and a high amount of electron transport without ATP production is likely what kind of compound?

a. uncoupler

b. ATP synthase activator

c. site I inhibitor

d. site II activator

e. cyanide

uncoupler

Which one of the following statements concerning a 1-week-old male infant with undetected classic phenylketonuria is correct?

a. Tyrosine is a nonessential amino acid for the infant.

b. High levels of phenylpyruvate appear in his urine.

c. Therapy must begin within the first year of life.

d. A diet devoid of phenylalanine should be initiated immediately.

e. When the infant reaches adulthood, it is recommended that diet therapy be discontinued.

High levels of phenylpyruvate appear in his urine

The major regulated step of the urea cycle is which one of the following?

a. Carbamoyl phosphate synthetase I

b. Ornithine transcarbamoylase

c. Argininosuccinate ynthctase

d. Argininosuccinate lynse

e. Arginase

carbomoyl phosphate synthetase 1

Which of the following compounds serves as an acceptor for the amino groups of

many amino acids during catabolism?

(a)glutamine

(b)α-ketoglutarate

(b) asparagine

(d) oxalate

alpha-ketoglutarate

A patient with maple syrup urine disease should be put on a life-long diet restricted in which of the following?

A. Aromatic amino acids (phenylalanine, tyrosine, and tryptophan)

B. Branched-chain amino acids (leucine, valine, and isoleucine)

C. Sulfur-containing amino acids (methionine and cysteine)

D. Thiamine

E. Fructose

branch chain amino acids

Which of the following answers completes the sentence correctly? Cytosine is a ____.

a. purine base.

b. purine nucleoside.

c. pyrimidine base.

d. pyrimidine nucleoside.

pyrimidine base

During the synthesis of pyrimidine nucleotides, the pyrimidine ring framework that becomes attached to the ribose is

a. uracil.

b. orotate.

c. cytosine.

d. adenine

orotate

Which one of the following enzymes of nucleotide metabolism is correctly paired with its pharmacological inhibitor?

Dihydrofolate reductase----methotrexate

b. IMP dehydrogenase----hydroxyurea

c. Ribonucleotide reductase----5-fluorouracil

d. Thymidylate synthase----allopurinol

e. Xanthine oxidase----probenecid

dihydrofolate reductase

What is the biochemical deficiency that leads to severe combined immunodeficiency

disease (SCID)?

a nucleoside phosphorylase

b xanthine oxidase

c adenosine deaminase

d all of the above.

adenosine deaminase

Which of the following chemicals can be used for the treatment of gout?

a. methotrexate

b. 5-Fluorouracil

c. Colchicine

d. Sulfonamides

colchicine

Which of the following describes the direction of proton movement relative to electron transfer and phosphorylation?

Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the matrix.

What is the source of electrons at complex II (succinate-Q-reductase)?

FADH2 from the citric acid cycle

The rotation of the gamma subunit of the mitochondrial F1 ATPase requires the presence of:

A proton motive force or ATP.

The path taken by electrons to water from NADH generated during the citric acid cycle will NOT pass though:

FAD

Which of the following vitamins help to prevent cellular damage by free radicals?

E

The uncoupler dinitrophenol (DNP) prevents ATP synthesis while allowing electron transport to proceed because:

DNP is capable of transporting protons across the membrane, dissipating the proton gradient.

Which compound does not cross the inner mitochondrial membrane due to lack of a specific transport protein?

NADH

Oligomycin inhibits ATP synthase. What effect will this have on the electron transport chain?

Electron transport will halt

For the proton motive force to be able to synthesize ATP in a normal mitochondrion, there must be:

More positive charge on the outside of the inner membrane than on the inside.

During the degradation of many amino acids, the first step involves transfer of the amino group to which citric acid cycle intermediate?

alpha - ketoglutarate

Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea such that the urea can be excreted. In the production of urea, only one of the nitrogens in the product comes from ammonium ions.What is the source of the other nitrogen?

Aspartate

The carbon skeletons of which two amino acids directly enter metabolism at the level of pyruvate?

Alanine and serine

Which of the following is incorrect concerning synthesis of carbamoyl phosphate?

-The nitrogen source can be either ammonia or glutamine.

-It plays a role in pyrimidine synthesis.

-It is mediated by different enzymes in the cytosol and mitochondria of the liver.

- It plays a role in the urea cycle.

Cleavage of which of these amino acids creates urea?

Arginine

The activity carbamoyl phosphate synthetase I of the urea cycle is regulated by:

N-acetylglutamate and arginine.

The most serious consequence of failure of the urea cycle is:

increase in blood ammonia levels

In the context of a patient with classical PKU, which of the following normally non-essential amino acids should be added to their diet?

tyrosine

A 19-year-old patient with classic PKU is fed radio-labeled phenylalanine, which contains a radioactive atom in the aromatic ring of phenylalanine, and a urine sample is collected 24-hours later. Which of the following compounds would you expect to contain the greatest amount of label in the urine sample?

phenylketone

Biochemical requirements for vitamin B6 increase when consuming a high:

protein diet

Which compound is involved in reducing levels of homocysteine in the blood?

The conversion of homocysteine into methionine involves which of these co-factors?

methylcobalamin

For humans, 11 amino acids are referred to as being "nonessential." This means that:

We have the capability of synthesizing these amino acids and thus do not need them in the diet.

What cofactor or prosthetic group serves as a carrier for activated one-carbon units during the synthesis of amino acids and other biological molecules?

tetrahydrofolate

Methotrexate inhibits purine synthesis by targeting formation of:

Tetrahydrofolate from dihydrofolate.

The process wherein the product of a metabolic pathway inhibits the enzyme catalyzing the first committed step of the pathway is referred to as:

feedback inhibition

Central dogma

Information flows in one direction, from DNA to RNA to proteins

What are the 4 biological molecules?

carbohydrates, lipids, proteins, nucleic acids

The bonds found within proteins and how are they formed

peptide bonds

-single amino acids are attached through a covalent bond by peptidyltransferase

The bonds found within DNA and RNA and how they are formed

phosphodiester bond

-joins the phosphate group at position 5 in the pentose sugar of one nucleotide to the hydroxyl group at postion 3 of the next nucleotide

-DNA or RNA polymerase

Where are ester bonds found and how are they formed

found in lipids

-one glycerol molecule bonded with 3 fatty acid molecules

-acyltransferase

what are the bonds found in carbohydrates

-glycosidic bonds

what are the four types of non-colavent interactions

Van der Waals, hydrogen bonds, electrostatic interactions, hydrophobic bonds

What if browian thermal motion

collisions of water molecules with large particles causes the particles to move about randomly

-allows enzymes to find substrates

What is entrop

a measure of the degree of randomness or disorder in a system

What is the Kw of water

[H+ ] [OH-] = 10^-14

what is the pH equation

pH=-log[H+]

whats the [H+] of a solution where the pH is 3.82

1.5x10^14

what are buffers

substances that minimize changes in pH

what is the buffer capacity

generally best within +1/-1 of the pKa

Describe a peptide bond and its planar interactions

-has a partial double bond between the carbon and Nitrogen

-rigid and planar

-transconfiguration

-uncharged but polar

What are the four levels of protein structure?

-primary: aa sequence

- secondary: alpha helix or beta pleated sheets

- tertiary 3-D folding pattern

-quatenary - subunits assemble * not all proteins have

Why is proline an alpha helix breaker

the side chain is bonded to both the alpha carbon and the Nitrogen atom which limits the rotation and reduces flexibility within the polypeptide regions

What are the driving forces in protein folding

covalent and noncovalent interactions between side chains

What cause protein denaturation?

heat - breaks H bonds

low/high pH - disrupts salt bridges and electrostatic repulsion

urea - blocks H bonding and interferes with hydrophobic interactions

What is a disulfide bond?

a covalent bond between two sulfur atoms of two amino acids (strong)

What is the difference between cysteine and cystine?

Cysteine - high solubility (one molecule)

cystine - low solubility (2 molecules)

Amyloidosis

-general term for diseases in which a protein becomes misfolded and insoluable due to a mutation or error in post-translational processing

-results in the formation of protein aggrgates or tangles called amyloid fibrils or plaques usually adapt a beta pleated sheet structure

sickle cell disease

beta globin gene mutation that subsitutes vlaine (hydrophobic) for glutamate (polar)

How is pepsinogen activated? What is the role of pepsin in protein digestion?

pepsinogen is activated by the low pH caused by HCl in the stomach

pepsin is a protease and cleaves proteins

What is the role of HCl in protein digestion

-low pH disrupts salt bridges and electrostatic repulsion

-activates pepsin

What are zymogens/proenzymes?

inactive form of the active enzyme

-need a part to be cleaved in order for them to become active

List the roles of the enzymes in protein digestion.

-Pepsin breaks up proteins creating oligimers

-CCK is released when the intestinal cells detect the polypeptide products of pepsin

-pancrease secretes the zymogens in response to CCK in the system

-Enteropeptidase - secreted by the epithelial cells in the small intestine activates trypsinogen --> trypsin

-trypsin activates the rest of the zymogens