Nutrition

Describe how vitamin b-6 is absorbed, transported, stored, & excreted

* Absorbed by passive diffusion * Transported to liver, then transported in blood bound to albumin * Stored in muscle tissue * Excreted in urine

Describe how thiamin is absorbed, transported, stored, & excreted

* Absorbed in small intestine by sodium-dependent active transport * Transported by red blood cells in coenzyme form * Little is stored * Excess is filtered out by kidneys

13.10 Briefly describe why choline is included in this chapter and 3 functions of choline.

* Choline isn't a water-soluble vitamin or even a vitamin, per se, but it is absorbed similarly to water-soluble vitamins. Its functions are also similar to water-soluble vitamins. * Functions: It is a component of the compounds commonly known as lecithin (found in cell membranes) and sphingomyelin, required for the synthesis of myelin. It is a precursor for acetylcholine, an important neurotransmitter. It helps prevent fat from accumulating in the liver because it is needed for VLDL synthesis. * Choline also participates in methyl metabolism in the body.

Describe how folate is absorbed, transported, stored, & excreted

* Folate polyglutamates are broken down to monoglutamates for absorption (active transport) * 100% absorbed as supplement and without food * Transported to liver * Body cells convert folate to polyglutamate form, trapping folate in cell * Excreted in urine, feces, and bile

Describe how riboflavin is absorbed, transported, stored, & excreted

* Hydrochloric acid releases bound riboflavin * 60 to 65% is absorbed via active transport or facilitated diffusion * Transported by protein carriers * Converted to coenzyme form in most tissues * Small amount is stored * Excess excreted in urine, which gives urine a bright yellow color

Describe how niacin is absorbed, transported, stored, & excreted

* Readily absorbed from stomach and small intestine by active transport and passive diffusion * Bioavailability is low in some grains, especially corn • Niacin is bound to a protein and can be released * Transported to liver and stored or delivered to body cells * Excess is excreted in urine

13.3 What are 2 general functions of riboflavin?

* Riboflavin forms a coenzyme required for energy metabolism. * It is necessary for the activation of other B-vitamins including niacin, vitamin B-6, and folate. * It is required for the synthesis of the antioxidant compound glutathione.

Describe how biotin is absorbed, transported, stored, & excreted

Absorption, transport, storage, and excretion: • Biotinidase releases biotin from lysine in small intestine • Absorbed by sodium-dependent carrier • Stored in muscles, liver, and brain • Excreted in urine and bile

Describe how pantothenic acid is absorbed, transported, stored, & excreted

Absorption, transport, storage, and excretion: • Pantothenic acid is released during digestion and absorbed in small intestine • Transported in the body bound to red blood cells and excreted in urine

13.9 Which foods are good sources of vitamin B-12?

Animal foods are the only natural food sources. Fortified plant foods (cereals, milks, meat analogs, etc) provide vitamin B-12. Clams, oysters, and liver have very high amounts of the vitamin. Meat, eggs, dairy products are also sources.

List important food sources for vitamin b-12

Animal foods, fortified ready-to-eat breakfast cereals

List important food sources for vitamin b-6

Animal protein foods, potatoes, bananas, legumes, avocados

13.3 Describe why a riboflavin deficiency may cause fatigue. (Again, think metabolism here!)

Because FAD is required for normal energy metabolism, a deficiency likely will result in an energy deficit and fatigue. FAD is needed for every glycolysis reaction and (another FAD for) every turn of the Krebs cycle.

Identify the water-soluble vitamins

B vitamins: thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin b-6, folic acid, vitamin b-12, Other: choline, vitamin C

List important food sources for vitamin C

Citrus fruits, papayas, strawberries, broccoli, potatoes, greens

13.11 What are 4 good sources of vitamin C?

Citrus fruits, peppers, strawberries, broccoli, kale, cantaloupe, fortified cereals.

13.5 What is the coenzyme formed from pantothenic acid?

Coenzyme A (as part of acetyl coA)

13.11 Impaired synthesis of what compound is responsible for the symptoms of scurvy (ie bleeding gums)?

Collagen synthesis can be impaired. Vitamin C is required for the proper formation of collagen. If enough collagen isn't made, scurvy can develop.

List important food sources for pantothenic acid

Common sources include meat, milk, and vegetables • Unprocessed foods are best source

13.3 What foods are rich in riboflavin?

Dairy products, enriched cereals and grains, meat, egg, leafy green vegetables.

Thiamin deficiency can be found among: A. heavy users of alcohol B. poor people in developing regions reliant on corn as a staple food C. poor people in developing regions reliant on white rice as a staple food D. both a and b E. both a and c

E. both a and c

List important food sources for choline

Eggs, meat, fish, milk, wheat germ, plus self-synthesis

13.1 Describe 2 specific ways that fruits and vegetables are stored and prepared can impact their water-soluble vitamin retention.

Exposure to heat, light, air, and alkaline substances can decrease water-soluble vitamin content. In general, store fruits and vegetables in a cool place, limit exposure to oxygen, lightly cook vegetables, and consume frozen and canned fruits and vegetables within 12 months of purchasing.

Is this statement true or false? When compared with whole-grain products, enriched cereals and grains provide the same or higher amounts of all the B-vitamins.

False

13.3 What are the 2 coenzymes formed from riboflavin?

Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). You should know about FAD.

13.8 What are the 2 main ways that folate affects DNA function?

Folate coenzymes are critical for DNA synthesis and DNA methylation. Thymine, a DNA base, requires a folate coenzyme for its synthesis. The degree of DNA methylation may affect risk for cancer.

13.8 How do folate in food and synthetic folic acid differ? Which form is better absorbed?

Folate has one or more glutamate acid molecules added to folic acid. Folic acid has no glutamate molecules. Folic acid (though synthetic) is better absorbed.

13.10 Which foods are the best sources of choline?

Foods of animal origin, e.g., eggs, milk, chicken, beef and pork, are the best sources but grains, nuts, some vegetables and fruits provide smaller amounts.

13.6 Like every B-vitamin described before this one, biotin is a coenzyme for several enzymes. In general, what do these biotin-dependent enzymes do?

Generally coenzymes combine with apoenzymes to form active enzymes. More specifically carboxylase enzymes add carbon dioxide to various compounds. One example is the addition of carbon dioxide to pyruvate, forming a citric acid cycle intermediate.

13.9 What are 2 metabolic pathways that require a niacin coenzyme? (Chapter 9 strikes again!)

Glycolysis, the citric acid cycle, the conversion of pyruvate to acetyl-CoA all require NAD. Fatty acid synthesis requires an NAD derivative.

List important food sources for folate

Green vegetables, liver, enriched cereal products, legumes, oranges

Describe how vitamin b-12 is absorbed, transported, stored, & excreted

In food, vitamin B-12 is bound to a protein • HCl and pepsin release vitamin B-12 in stomach Free vitamin B-12 binds to another protein • Enzymes release vitamin B-12 in small intestine Free vitamin B-12 combines with intrinsic factor • Complex travels to ileum for absorption * Vitamin B-12 is transferred to a blood transport protein * Delivered to liver * Liver can store vitamin B-12 for several years * Secreted into bile, but reabsorbed (ie "recycled") in enterohepatic circulation (Think: entero = intestines + hepatic = liver)

13.4 Why are populations in Latin America NOT afflicted with pellagra, despite relying heavily on a corn-based diet?

Latin Americans don't suffer pellagra because of the way corn is prepared. In South and Central America it is treated with alkali to make the corn flour. This treatment liberates niacin from protein in the corn.

Describe how vitamin C is absorbed, transported, stored, & excreted

Least stable vitamin; easily lost in storage, processing, and cooking Absorption is by active transport and facilitated diffusion in small intestine • Efficiency of absorption decreases with increased intake High concentrations are stored in: • Pituitary and adrenal glands • White blood cells • Eyes • Brain

13.10 Which organs are most affected by a choline-free diet?

Liver and muscle.

13.8 What are 3 foods that are good sources of folate?

Liver, legumes, leafy green vegetables, avocados, orange juice, fortified cereals, and grains.

13.7 What are 3 good food sources of vitamin B-6?

Meat, fish, poultry; beans, bananas, oatmeal, potato

List important food sources for niacin

Meat, poultry, fish, enriched and whole-grain breads and cereals, tryptophan conversion to niacin

13.8 What type of anemia signifies a folate deficiency? Why does the presence of this type of anemia indicate that you don't have enough folate?

Megaloblastic or macrocytic anemia signals deficiency of folate. The red blood cells are larger than normal and still retain their nuclei. Red blood cells do not divide normally and remain large and immature. When you find these large macrocytes in the bloodstream, it means folate deficiency affected DNA synthesis (within the RBC).

List important food sources for riboflavin

Milk and milk products, mushrooms, eggs, liver, enriched grains

13.4 Describe why niacin intakes in the U.S. are generally very good for many individuals.

Niacin can be obtained from the diet as preformed niacin and it also can be synthesized from the amino acid tryptophan (in all protein sources). These different sources each provide about 50% of niacin intake.

Describe how choline is absorbed, transported, stored, & excreted

Not a vitamin per se, but is absorbed and acts like a water-soluble vitamin * Absorbed by transport proteins in small intestine * All tissues store some choline * Can be obtained from the diet and synthesized in cells

List important food sources for biotin

Nuts, seeds, fish, whole grains, many other foods

13.5 What are 3 good food sources of pantothenic acid?

Pantothenic acid is widespread in foods. Many meats, milk, avocados, corn and other vegetables are good sources.

13.9 How is the condition pernicious anemia related to vitamin B-12 deficiency?

Pernicious anemia results from inadequate intrinsic factor production. Since intrinsic factor is needed to liberate B-12 from a protein it's bound to, low IF means low vitamin B-12 absorption. The disease can result in death if not treated with vitamin B-12 injection/high oral doses of the vitamin.

List important food sources for thiamin

Pork and pork products, enriched and whole-grain cereals, eggs, nuts, legumes

13.2 What are 3 foods that are rich sources of thiamin?

Pork, sunflower seeds, fortified cereals and grains, tuna, navy beans.

13.7 What does PLP stand for and how is the PLP coenzyme used in amino acid metabolism?

Pyridoxal phosphate is called PLP. or vitamin B-6! PLP is a coenzyme that transfers amino groups to allow the synthesis of nonessential amino acids. (For example, with the help of PLP, glutamic acid can donate its amino group to pyruvic acid forming the nonessential amino acid alanine.)

Describe the toxicity symptoms from excess consumption of certain water-soluble vitamins

See slides 100 and 101 of Ch13 slides

List the major functions of & deficiency symptoms for each water-soluble vitamin

See slides 100 and 101 of Ch13 slides

13.2 What does TPP stand for and how is the coenzyme TPP involved in energy metabolism? What is 1 critical reaction that requires TPP?

TPP = thiamin pyrophosphate, which is a thiamine derivative made by an enzyme. TPP is required for the metabolism of carbohydrates and (branched-chain) amino acids. It is required for decarboxylation reactions; you should know that an example of this is the conversion of pyruvate to acetyl-CoA.

13.5 How is pantothenic acid related to the formation of ATP? (Think Krebs cycle!)

The coenzyme A molecule is required for the synthesis of acetyl CoA. Acetyl CoA molecules most often enter the citric acid/Krebs cycle, which leads to the major payoff of ATP production.

13.1 A common role of B-vitamins is to form coenzymes. What is the role of coenzymes in the cell, generally?

The coenzymes combine with apoenzymes ("pre-enzymes") to form active enzymes.

13.2 Why are alcoholics at risk of thiamin deficiency?

They have decreased absorption of thiamin, they excrete extra thiamin in the urine, and they may consume a poor-quality diet lacking thiamin.

13.2 Why do individuals with beriberi feel tired? (Think ATP and Chapter 9.)

They're tired because of impaired carbohydrate metabolism. Since thiamine is needed to convert pyruvate to acetyl-CoA after glycolysis and before the Krebs cycle, deficiency of thiamine impairs carbohydrate catabolism. Additionally, thiamin seems to protect nervous function in other ways.

13.1 Which B-vitamins are added to enriched bread and cereal products? (You're looking for at least 4 here.)

Thiamin, riboflavin, niacin, and folic acid.

13.6 How can a biotin deficiency occur?

This occurs most often as a result of a genetic defect that results in very low amounts of the enzyme biotinidase. This prevents the breakdown of biocytin in foods. Biocytin is biotin bound to the amino acid lysine in food proteins.

13.9 What roles do hydrochloric acid (HCl), pepsinogen, intrinsic factor, and the ileum play in vitamin B-12 absorption?

Vitamin B-12 absorption is complex. HCl activates pepsinogen, forming pepsin. Both HCl and pepsin are required to release vitamin B-12 from the food proteins that it is bound to. Intrinsic factor binds to free vitamin B-12. This complex travels to the ileum, the site of vitamin B-12 absorption.

13.9 How are vitamin B-12 and folate metabolism related?

Vitamin B-12 donates a methyl group to homocysteine, resulting in the formation of methionine. The source of the vitamin B-12 methyl group is the folate coenzyme 5-methyltetrahydrofolate (5-MeTHFA). Because of this folate and vitamin B-12 deficiencies result in some similar symptoms.

13.11 How does vitamin C aid in the function of metalloenzymes in cells?

Vitamin C acts to keep the metals, such as iron, copper, zinc, in metalloenzymes in their reduced form. This increases their activity.

13.7 Which individuals are at risk of having poor vitamin B-6 status?

Women, older adults, smokers, users of oral contraceptive agents, alcoholics, and those with poor diets may have poor vitamin B-6 status.

Deficiencies of ______________ and _____________ are extremely rare.

biotin; pantothenic acid

Vitamin C is required for the formation of a precursor that is needed to synthesize THIS protein found in skin, bones, and connective tissue:

collagen

Niacin can be synthesized in cells from: a. riboflavin b. fatty acids c. glucose d. tryptophan

d. tryptophan

Good sources of folate include:

lentils; spinach; fortified foods

Macrocytic anemia, impaired cognitive function, and peripheral neuropathy are signs of _______________ deficiency.

vitamin B-12