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NST103 Final, 5/18/06
Spring 2006 (200 points Total)
Name
SID
I. (4 pts each = 48 pts) Choose a single best answer:
1.Which of the following processes require energy?
a. Transfer of glucose molecules across a cell membrane using the GLUT family of transporters
b. Transfer of glucose across the brush border membrane of enterocytes
c. Transfer of cholesterol across the brush border membrane of enterocytes
d. Transfer of the amino group from an amino acid to a ketoacid via a transaminase
e. Transfer of fatty acids across the mitochondrial membrane
Answer ____B___________
2.Which of the following molecules can be transported from the lumen into enterocyte without further
digestion?
a. Retinyl esters
b. Disaccharides
c. Diacylglycerides
d. Cholesterol esters
e. Dipeptides
Answer ____E___________
3.Dietary fat soluble vitamins are delivered first to which of the following organs/tissues?
a. Adipose tissue
b. Adipose tissue capillaries
c. Chylomicron remnants
d. Liver
e. Muscle
Answer ____D__________
4.Which molecules directly contribute the nitrogen that is incorporated into the urea molecule?
a. Glutamine and alanine
b. Glutamine and aspartate
c. Ammonia and aspartate
d. Ornithine and ammonia
e. Citrulline and glutamate
Answer ____C___________
5.Which hormone influences energy expenditure by increasing resting metabolic rate?
a. Thyroid hormone
b. Glucocorticoids
c. Insulin
d. Catecholamines
e. Epinephrine
Answer _____A__________
6.Vitamin B12 is required for metabolism of some amino acids because?
a. It is a coenzyme for aminotransferase enzymes
b. It facilitates intramolecular transfer of alkyl groups and hydrogen atoms
c. It increases transcription of key enzymes
d. Transcobalamin facilitates transfer of amino groups
e. It serves as a coenzyme for methionine synthase
Answer ____B___________
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7.In the U.S. some foods are fortified with folate because folate deficiency is associated with?
a. Increased risk of cancer
b. Homocysteine accumulation
c. An associated deficiency in Vitamin B12
d. Inadequate DNA methylation
e. Neural tube defects
Answer _____E__________
8.To have Vitamin A activity, a molecule must be able to be metabolized to which product?
a. Retinol.
b. Retinal.
c. Retinoic acid
d. Retinyl ester
e. Retinoid
Answer _____C__________
9.Vitamin K deficiency results in abnormal blood clotting because
a. Platelets do not aggregate due to insufficient glycoprotein
b. Calcification of the soft tissue at the wound site is not adequate
c. Prothrombin is not adequately activated
d. The activity of matrix gla protein is reduced
e. Transcription of the fibrinogen gene is inhibited
Answer _____C__________
10. Which statement regarding hemoglobin degradation is true?
a. Hemoglobin degradation rate is dependent on turnover rate of erythrocytes
b. The globin portion of the molecule is released and can condense with a newly synthesized heme
molecule
c. Heme degradation is regulated via aminolevulinate synthase
d. The released iron molecule is transferred to the ferrochelatase enzyme
e. Pyridoxal phosphate serves as coenzyme for heme oxygenase
Answer _____B__________
11. Which is true about vitamin C?
a. Vitamin C can be synthesized from glucose in all mammals.
b. Vitamin C cannot be synthesized from glucose in humans
c. Vitamin C cannot be synthesized from dehydroascorbate in humans
d. Vitamin C cannot be converted to dehydroascorbic acid in humans
e. Vitamin C cannot be regenerated from the ascorbate free radical in humans
Answer _____B__________
12. Which is true about bone turnover?
a. Osteoblasts secrete acid to degrade bone and provide Ca for the body
b. Osteoclasts synthesize bone matrix proteins
c. Vitamin D stimulates bone growth regardless of plasma calcium level
d. Blood vessels develop as new bone is formed
e. Parathyroid hormone stimulates synthesis of new bone
Answer _____D__________
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II. (1pt each = 35 pts) Fill in the blanks:
1. Vitamin C is required for hydroxylation of the amino acids
Proline
and
___Lysine____________, facilitating coiling of the protein _______(tropo)Collagen________ .
2.
IF Intrinsic factor
is a binding protein required for receptor-mediated transport of
vitamin B12 across the gut epithelium.
TC-II transcobalamin
Is a binding protein
required for transport of vitamin B12 into tissues.
3.
Mobilferrin or DMT1
is a protein that transports iron across the brush border of
epithelial cells.
Transferrin
is a binding protein required for transport of
iron from one tissue to another.
Ferritin
is a binding protein that facilitates
intracellular storage of iron.
4. Retinoic acid and 1,25-dihydroxy Vitamin D both influence
binding to
Receptors
in the
Nucleus
Transcription
of cells.
by
5. During fasting, two hormones that are likely to be elevated are
Glucorcorticoids
and
Glucagon
. A hormone that is likely to be reduced is ____Insulin__________.
6. HDL retrieves cholesterol from peripheral tissue via the interaction between the apoprotein,
___Apo A-1_____ and the ABC receptor. In HDL particles, the enzyme LCAT converts the
cholesterol into
Cholesterol ester
, which is transferred into LDL particles using the
enzyme
CETP . The process by which cholesterol is transported from peripheral tissues
to the liver is referred to as reverse cholesterol transport.
7. -oxidation requires mobilization of TAG stores via the enzyme HSL , transport of fatty acids to
tissues, entry into mitochondria via the transporter __CPT1, CAT, CPTII_., and hydrolysis
resulting in production of
AcCoA
(name molecule).
8. During a prolonged fast,
muscle
is the tissue that provides most of the substrate that
is used for gluconeogenesis. Two metabolic pathways required for this to occur include the
urea cycle and the TCA cycle
.
9. During a prolonged fast,
Adipose
is the tissue that provides most of the substrate that
is used to produce the ketone bodies that are synthesized primarily within the
Mitochondria
(name cellular compartment) of cells in the Liver
(name the organ). These ketone
bodies are used by other tissues for Energy
.
10. AcetylCoA Carboxylase requires the coenzyme _Biotin__ and catalyzes the flux generating step
for the synthesis of ____FFA______.
11. Essential fatty acids such as ____Linoleic, Linolenic_____ are required in the diet because
humans do not have the appropriate enzymes generally called _____Desaturases___ to create
certain double bonds.
12. The reducing equivalent, ___NADH___ ,is needed in the cytosol for gluconeogenesis. Glycolysis
requires the reducing equivalent,___NAD+___, in the cytosol.
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III. (4pts each =24pts) State whether the following statements are true or false, provide a justification for
your answer:
1. Dietary fat promotes absorption of vitamin E.
TRUE. Lumenal fat promotes formation of micells, allowing Vit E incorporated into
micelles since they are fat soluble
2. There are health consequences of both low and high concentrations of plasma calcium.
TRUE. Too low, hypocalcemia; too high, hypercalcification of soft tissues
3. Acetyl CoA is a substrate for gluconeogenesis in the fasting state
FALSE. Use of Ac CoA for this purpose leads to depletion of TCA intermediates
4. Orange juice may increase efficiency of iron absorption.
TRUE. C reduces Fe3+ to Fe2+ increasing solubility and absorption
5. Levels of the hormone form of Vitamin D (1,25-dihydroxy D) are to some extent self-regulated.
TRUE - Inhibits formation by inhibiting 1-OHase in kidney. Increases excretion by activating
24-OHase leading to (1,)24,25OH Dexcreted
6. It is advantageous to have glucose transporters in the liver that have a high Km.
TRUE. With a high Km, glucose is not extracted by the liver when glucose concentrations
are low, sparing glucose for use by other tissues. Only at high concentrations, would liver
effectively extract glucose from plasma and metabolize it. Thus, a high Km glut is preferred in the
liver as that helps coordinate needs of various organs.
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IV. (1pt each =13 pts) Indicate the name of the vitamin associated with each of the following statements.
(You can use one vitamin more than once)
Prevents osteomalacia
Cures acute cystic acne
Deficiency causes megaloblastic anemia
Deficiency causes microcytic anemia
Deficiency causes dementia, dermatitis and diarrhea
Required for post-translational modification of osteocalcin
A fat-soluble vitamin that has no known means of storage in liver
Deficiency causes beriberi
May cause birth defects if taken in excess
Reverses xerophthalmia
Is reversibly dephosphorylated for transport across cell membranes
A fat-soluble vitamin that acts as an antioxidant
A water-soluble vitamin that acts as an antioxidant
____1,25 (OH)2 D_________
_____A ________________
_______Folate, B12_______
(accept Fe, Cu, Zn) B6_____
_____Niacin_____________
______Vit K______
_________K______________
_____Thiamin_________
______A___________
_____A_______
______thiamin______
____
Vit E________
________Vit C___________
V. (1pt each = 6 pts) Indicate the name of the mineral associated with each of the following statements.
(You can use one mineral more than once).
Forms a complex with ATP to neutralize its positive (should be negative)charge Mg__________
Is involved in electron transport via cytochromes
________Fe_____________
Is a component of Vitamin B12
________Co______________
Is a second messenger
________Ca______________
Required for post-translational modification of some proteins
________P______________
Required for uptake of Vitamin B12 into enterocytes
________Ca____________
V. (1pt each = 14 pts) Fill in the blanks with the appropriate term.
Type of reaction used to convert glutamate to ammonia and -ketoglutarate____Deamination_____
Type of reaction used to convert glutamine to ammonia plus glutamate _______Deamidation____
Absorption process that requires a protein transporter by not energy ____Facilitated Diffusion_
Absorption process that allows simultaneous absorption of numerous molecules
_______Endocytosis_______
A characteristic of food that regulates emptying of the stomach
____Energy Content_____
An enzyme required for digestion of dietary lipid
Gastric Lipase (& others
A key absorption process used to transport amino acids across enterocyte membranes
Facilitated, 2ndary active
The term used to describe reabsorption of bile acids from the intestine Enterohepatic recirculation
A characteristic of food that regulates emptying of the stomach
_____BLANK____
A structure that forces nutrients to be transported across (rather than between) enterocytes
Tight junctions (terminal
web)
The type of compound formed when an amino group interacts with a reducing sugar and produces a
double bond between the nitrogen and carbon atoms
_____Schiff base________
An enzyme required for digestion of dietary lipid
_______BLANK _______
The type of cell in the pancreas that produces digestive enzymes
_______Acinar_______
The type of cell in the stomach in which histamine is formed
_______ECL cells______
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VI. Answer the questions briefly: (6 pts ea = 60 pts)
1. Describe how the health of the eye progressively deteriorates with increasingly more severe
Vitamin A deficiency. Explain what accounts for this progression.
Vit A deficiency leads to night blindness (1) due to lack of retinal for production of rhodopsin
(2) .
More severe deficiency leads to disruption of protective epithelial layers (1) due to lack of RA
as transcription factor for synthesis of key proteins (2). This has more serious effects that are
eventually not reversible.
2. Describe the importance of “by pass” steps in glycolysis and gluconeogenesis.
By pass steps allow differential regulation of glycolysis and GNG. Since different enzymes
serve to catalyze the forward and reverse directions at these steps,
3. Describe the relevance of the pentose phosphate pathway to the synthesis of triacylglycerides in
the liver.
Produces NADPH needed to synthesize FA, NADPH required for reduction steps of DNL. FFA
used to synthesize TAG.
4. Explain why HMG-CoA reductase inhibitors, commercially known as statins, are expected to be
very effective plasma cholesterol-lowering drugs.
Cholesterol is contributed to plasma from two sources – diet and newly synthesized in body (de
novo cholesterolgenesis)
HMG-CoA reductase is rate limiting step in de novo chol synth. Limiting new synthesis may
reduce cholesterol levels in plasma.
5. Explain the theoretical rationale for recommending that persons at high risk of type 2 diabetes
consume foods and meals that have a low glycemic index response.
When low glycemic index foods are consumed, there should be more moderate postprandial
increases in plasma levels of glucose and insulin. This suggests that plasma glucose levels
can be maintained will need for less insulin, which reduces requirement for pancreas to
produce insulin. This reduces stress to pancreas. Also, lower insulin levels guard against
development of insulin resistance in tissues.
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6. Explain how the process of de novo lipogenesis suppresses β-oxidation.
MalonylCoA, an important intermediate in the DNL pathway, inhibits CPT1 in
mitochondria. This transporter is needed to move activated fatty acids from the cytosol into
the mitochondria where they would be b-oxidized to produce acetyl CoA. Thus, the
production of malonyl CoA that accompanies DNL inhibits the transport protein needed to
deliver substrate to the mitochondria for b-oxidation.
7.
Explain what is meant by secondary active transport. Provide an example of a nutrient that can
be transported by this process.
Energy required for one process, the result of which allows a second process to occur
without direct input of energy. Eg. E used to transport Na at basolateral membrane out of
cell against conc gradient, maintaining low intracellular [Na]. The concentration gradient
between the high luminal [Na] and low intracellular [Na] drives intake of Glucose since Na
& Glucose are co-transported.
8. Briefly describe the process by which lipid, newly synthesized by the liver, would be delivered to
peripheral tissues. Be sure to mention the key particle(s), apoprotein(s) and receptor(s) that
would be involved.
Lipid incorporated into VLDL with Apo C-II, E, B-100, to capillaries of muscle and AT.
VLDL are recognized by LPL via C-II. LPL in tissue facilitates lipolysis of TAG in VLDL,
and released FFA can be absorbed by muscle and AT. IDL particles remain and can return
to the circulation.
Like VLDL, IDL can be recognized by LPL, and further lipolysis produces LDL particles,
which also can be released into the plasma.
Since Apo E & B-100 are ligands for the LDL-Receptor in liver and other tissues, these
particles can be endocytosed into liver and degraded.
9. Describe two advantages to the body of having components of the urea cycle in several
tissues/organs. Use at least one specific example to illustrate each advantage.
The metabolic processes occurring in one organ can complement the other, serving the
whole body. Eg. Intestine can process much of the glutamine delivered from muscle;
Intermediates can be exported and used for other processes without compromising the
overall cycle. Eg. Production of ornithine and citrulline by intestine and exportation to
liver & kidney. Production of arginine by kidney with exportation to muscle & other tissues
for protein synthesis.
Toxicity is guarded against. Eg. Large amount of ammonia produced by intestine is
delivered directly to liver for incorporation into urea.
10. Describe three main strategies used to maintain plasma calcium levels within the normal range.
State what effect parathyroid hormone has on each.
Increase gut absorption PTH stimulates Vit D
Increase kidney resorption of Ca (decrease excretion), PTH increases this
Increase bone release of Ca PTH stimulates
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