Major Minerals• Magnesium (p 291), Infographic 13.5• Phosphorus (p 291)
Trace Minerals • Manganese (p 328)
?? 1. What two sources of energy would we be unable to use well if we were severely deficient in vitamin B6?2. What macronutrients can be used to synthesize fatty acids when they are eaten in excess?3. Can you anticipate what exhaled waste product is produced when pyruvate is metabolized to acetyl-CoA?4. Examine the flow through the pathways and answer this question: why can’t glucose be synthesized from fatty acids?
Photo credits (left to right): t_kimura/Getty Images, Burwell and Burwell Photography/Getty Images, milanfoto/Getty Images
KEY IDEASEnergy is obtained from the metabolism of carbohydrates, fats, and amino acids by several pathways involving numerous enzyme catalyzed reactions; and many of these enzymes require vitamins or minerals for their activity.Vitamins provide the essential components of coenzymes that are required for many enzyme catalyzed reactions in energy metabolism. See Infographic 11.4.Similar to vitamins, minerals often function as critical cofactors that bind to enzymes and are required for enzymes to catalyze chemical reactions.
Some non-essential amino acids can be interconverted using reactions that use one or more of these nutrients.
Because of the variety of amino acids that are present in our body, once their nitrogen has been removed they form a variety of di�erent chemical compounds (such as pyruvate, acetyl-CoA, and others) that enter metabolic pathways at many di�erent stages or steps.
Biotin functions in the synthesis of glucose and fatty acids because it is used as a coenzyme in reactions that add a carbon dioxide to the original molecule, making it one carbon larger.
Fatty acids are broken down by removing two carbons at a time to produce the two-carbon compound acetyl-CoA. “CoA” is short for coenzyme A which is formed from the vitamin pantothenic acid.
When excess carbohydrates or amino acids are eaten, acetyl-CoA that is not needed to meet our energy needs can be used to synthesize fatty acids that will be stored as triglycerides in adipose tissue.
Acetyl-CoA is produced by the breakdown of carbohydrates, fatty acids, and amino acids.
The release of glucose from glycogen requires the coenzyme that is made from vitamin B6.
When amino acids are used to make glucose (or fat), or are used as an energy source, the first step in their metabolism is to remove the nitrogen in reactions that require the same Vitamin B6 containing coenzyme that is required for glycogen breakdown.
VITAMINS AND MINERALS INVOLVED IN ENERGY METABOLISMFood source information is provided in the Infographics listed below.
ATPATP
AEROBIC METABOLISM
AMINO ACIDS
Fatty Acids
Acetyl-CoA2 Carbons
Various Amino Acids
Various Amino Acids
Pyruvate3 Carbons
Glucose6 Carbons
Glycogen CO2, H2O, Heat
The minerals phosphorus and magnesium are involved throughout metabolism. Phosphorus as a component of ATP, which must form a complex with magnesium to be utilized as an energy source.
VITAMINS AND MINERALS DIRECTLY INVOLVED IN ENERGY METABOLISM
Free radical molecules have unpaired electrons, making them unstable and reactive.
The free radical steals an electron from another molecule to stabilize itself.
Antioxidants can donate an electron without becoming unstable and reactive.
In normal molecules all the electrons are paired
The molecule that lost its electron has been oxidized, creating a new free radical.
This creates a chain reaction; the newly formed free radical oxidizes another molecule by stealing an electron from it.
Antioxidants Defend Against Oxidative Damage Caused by Free Radicals Free radicals are molecules containing unpaired electrons, which makes them highly reactive. The free radical either causes oxidative damage by reacting with another molecule and chemically modifying it, or it stabilizes itself by stealing an electron from a nearby molecule, which creates a new free radical and begins a chain reaction. Antioxidants are able to stop the chain reaction by donating an electron.
NUTRIENTS WITH ANTIOXIDANT FUNCTIONFood sources of each nutrient are found in the Infographics listed in parentheses.
Water-Soluble VitaminsVitamin C is an electron donor and functions as a water-soluble antioxidant (Infographic 11.13)Riboflavin is part of an essential coenzyme that is required by an enzyme that has an antioxidant function, and is particularly important in red blood cells (Infographic 11.7)
Fat-Soluble VitaminsVitamin E neutralizes free radicals by donating an electron (Infographic 10.9)
Trace MineralsThe minerals copper (Infographic 14.10), zinc (Infographic 14.9), manganese (Infographic 14.12), and selenium (Infographic 14.11) function as essential components of enzymes that are involved in important antioxidant defense mechanisms that neutralize free radicals
PhytochemicalsBeta-carotene and other phytochemicals may provide health benefits by their ability to function as antioxidants in our body (Infographic 9.6)
Cigarette smoking
DNA
Protein
Lipids
Air pollution UV light Some drugs
Immune responsesMitochondrial
energy metabolism
FORMATION OF FREE RADICALS
DAMAGE FROM FREE RADICALS
FREERADICALS
LDL
Chain reaction of oxidation caused by free radicals
Neutralized free radicals
Damaged phospholipids
Vitamin E
Free radical
Vitamin E neutralizes free radicals and breaks the chain of oxidative damage.
Phospholipidbilayer
Sources of Free Radicals and Their Effects The free radicals we are exposed to can come from environmental sources or are produced by our own bodies. Although free radicals have necessary functions in our body, high levels can cause damage.
The Antioxidant Functions of Vitamin E Vitamin E can break the chain of oxidation by donating an electron to free radicals without becoming unstable. Because it is a fat-soluble vitamin it is particularly good at performing this function in cell membranes, and even in lipoproteins like LDL.
?? 1. Why might those who suntan regularly have increased skin wrinkling as they age?2. What characteristics do antioxidants possess that allow them to break the chain of oxidative damage?3. What might be the consequences of free-radical damage to the DNA of a cell?
?? 1. Why might those who suntan regularly have increased skin wrinkling as they age?2. What characteristics do antioxidants possess that allow them to break the chain of oxidative damage?3. What might be the consequences of free-radical damage to the DNA of a cell?
KEY IDEASSome vitamins and minerals function as antioxidants. Antioxidants can donate an electron and neutralize a free radical without becoming unstable and reactive.
1 Vitamin D is synthesized from cholesterol in skin with exposure to ultraviolet light.
2 Vitamin D is metabolized to its active hormone form in two steps, the first occurring in the 2a) liver and the second in the 2b) kidneys.
3 When blood calcium concentrations drop, parathyroid hormone (PTH) and the active hormone form of vitamin D act together to raise blood calcium concentrations. In response to increases in PTH and active vitamin D levels: the kidneys excrete less calcium; the small intestine increases calcium absorption;and bone releases more calcium into blood.
4 PTH is not required for active vitamin D to increase calcium absorption in the small intestine.
1
2a
2b
3
4
Vitamin D, Parathyroid Hormone, and Blood Calcium Concentrations The active hormone form of vitamin D and parathyroid hormone work together to maintain calcium concentrations in blood.
KEY IDEASBone is an active organ, it is constantly being remodeled as it is undergoes continual cycles of being broken down and rebuilt.All body cells require calcium to function, and its absorption, excretion and release from bone is tightly regulated.The interaction of vitamins and several minerals are needed to build and maintain bone.
Inactive vitamin Denters blood and istransported to the liver.
Parathyroid hormone (PTH) isreleased from the parathyroidglands in response to lowblood calcium levels.
PTH stimulates thekidney to produceactive vitamin D.
Together PTH and active vitamin D stimulate kidneys to excrete less calcium.
More calcium is returned to blood stream.
Together PTH and active vitamin D increase calcium release from bone.
Active vitamin Dincreases calciumabsorption.
Conversion to theactive form of vitamin D begins in the liver.
Dietary sources of vitamin D
UVlight
Skin
Parathyroid glands
KidneySmall Intestine
Bone
Liver
Activevitamin D
PTH
Inactive vitamin D is synthesized in the skin
and consumed inthe diet.
Low bloodcalcium levels
Increasedblood calciumconcentration
Calcium
Inactivevitamin D
Inactivevitamin D
VitaminsMinerals
Calcium, Phosphorus, and Magnesium are the Primary Mineral Components of Bone Accounting for 98% of the body’s total mineral content by weight, calcium, phosphorus, and magnesium play key roles in the development and maintenance of bone and other calcified tissues.
VITAMINS AND MINERALS INVOLVED IN BONE HEALTHFood source information is noted in parentheses.
Fat-Soluble VitaminsVitamin D is required for calcium absorption, and proper bone growth and maintenance. (Infographic 10.3)
—Severe vitamin D deficiency in children can cause rickets, which results in soft bones and skeletal malformations. See chapter 10.—In adults vitamin D deficiency can cause osteomalacia, causing bones to become soft and weak as they are depleted of bone mineral. —Because only a few foods are naturally good sources of vitamin D, fortified foods are an important source of vitamin D for many individuals.
Vitamin K is required for reactions that chemically modify some bone proteins — making them able to bind calcium. (Infographic 10.11)
Water-Soluble VitaminsVitamin C is required as a cofactor for enzymes that chemically modify the fibrous protein collagen to increase its strength. (Infographic 11.13)
Major MineralsCalcium is the most abundant mineral in the human body and is the main component of bones and teeth. (Infographic 13.3)
Phosphorus is the second most abundant mineral in the body and a structural component of bone. Phosphorus is found In most protein-rich foods such as meat and dairy and deficiency is rare.
Magnesium is required for absorption and metabolism of calcium. Magnesium contributes to the strength and firmness of bones and makes teeth harder. Fifty to sixty percent of the total magnesium in the body is found in bone. (Infographic 13.5)
Manganese is required for the synthesis of non-collagen bone proteins. (Page 328)
Trace Minerals
Copper is required as a cofactor for enzymes that chemically modify collagen to increase its strength. (Infographic 14.10)
Bonetissue rebuilt
Collagen
Thyroid
Parathyroidglands
Magnesium makes up about 1% of bone mineral. It is found primarily on the surface of calcium/phosphorus crystals.
Calcium/phosphorus crystals
Bone tissueis continually
remodeled as some cells break down bone and others
rebuild it.
Vitamin K and manganese are required for the synthesis of non-collagen bone proteins.Copper and vitamin C
are required for collagen synthesis.
Crystals of bone mineral deposited on a protein matrix
Bonetissuebrokendown
BONE REMODELING
VitaminsMinerals
Crystals of bone mineral are deposited on a matrix of protein that is comprised primarily of collagen.Weight-bearing exercise stimulates bone remodeling to make bones denser, which reduces the risk of osteoporo-sis and bone fractures (see Infographic 13.4).
Nutrients Involved in the Production and Function of RBCs Anemia can be caused by nutrient deficiencies that impair hemoglobin synthesis, the division and maturation of RBC, or RBC survival.
• Copper is required to mobilize iron from sites of storage.
• Zinc and sulfur function as cofactors for enzymes involved in heme synthesis.
• Vitamin B6, niacin, riboflavin, and pantothenic acid are components of coenzymes required by enzymes involved in heme synthesis.
B-Vitamins and trace minerals required for heme synthesis
NUTRIENT ROLES IN THE PRODUCTION AND FUNCTION OF RED BLOOD CELLS
NUTRIENTS REQUIRED FOR HEMOGLOBIN SYNTHESIS The iron containing heme group has a deep red color, and is the oxygen carrying component of hemoglobin in RBCs.
When hemoglobin production is adequate RBCs can be produced.
When a nutrient deficiency causes hemoglobin production to be low, RBCs are smaller (microcytic) and paler in color (hypochromic) because they do not contain as much hemoglobin.
Oxygen binds to iron in
hemoglobin.
Ironatom
Fe2+
H3C
H3C
H2C
NC
CC
CC
C
C CC
CCH
CH
CH3
CH2
CH3−OOC
−OOC CH2
CH2
CH3
CH
CH3
CHHC
HC
C
CC
C
C
CNN
N
Proteinchain
Proteinchain
Normal RBC
RBC with low hemoglobin
contentHeme group Hemoglobin
02
THREE MAJOR COMPONENTS OF BLOOD HEALTH
OXYGEN TRANSPORT IMMUNE FUNCTION CLOTTING
Production and function of red blood cells (RBC)
Production and function of white blood cells (WBC) Clotting Control
Anemia can result from impaired hemoglobin synthesis,
cell division or cell survival.
Impaired WBC function increases the risk of infection.
Excessive clotting can cause a heart attack or stroke, while inadequate clotting can lead
to excessive blood loss.
VitaminsMinerals
In bone marrow, precursor red blood cells divide and mature normally.
Cells divide normally
Cells are unable to divide adequately
Red blood cell precursor
Normalred blood
cells
Macrocytic(megaloblastic) cellsIn the blood, normal mature red
blood cells no longer contain nuclei.In the blood, these immature red blood cells are larger than normal
and they contain large nuclei.
Folate and vitamin B12 adequate
Folate and vitamin B12 deficient
In bone marrow, impaired DNA synthesis will arrest cell division and block
the full maturation of red blood cells.
Nutrients Required for Cell Division and Development Vitamin B12, folate, zinc, and iron are required for DNA synthesis and cell division. A deficiency that disrupts DNA synthesis will have the most detrimental effects on cells in the body that are dividing most rapidly, such as red blood cells.
Red Blood Cell Survival Deficiencies of nutrients that protect red blood cell membranes from oxidative damage can cause anemia because cells are destroyed and removed from blood before their normal lifespan is over.
Chain reaction of oxidation caused by free radicals
Neutralized free radicals
Damaged phospholipids
Vitamin E
Freeradical
Vitamin E neutralizes free radicals and breaks the chain of oxidative damage.
Phospholipidbilayer
• Because vitamin E is a fat-soluble vitamin it is particularly good atprotecting cell membranes from oxidative damage.
• The B-vitamins Niacin and riboflavin are necessary to form coenzymes which assist enzymes in the task of removing free radicals.
• The trace minerals zinc, copper, and selenium function as cofactors for enzymes that remove free radicals.
VitaminsMinerals
• Deficiencies of folate and vitamin B12 are the most common causes of anemia resulting from impaired cell division.
KEY IDEAS All but two of the vitamins and about half of the major and trace minerals play some role in maintaining blood health.
?? Why does iron deficiency cause RBCs to be paler in color? ?? An individual is found to have a low number of red blood cells, but the cells all appear to be of normal size and color. What is a likely cause of the anemia?
?? Why does a vitamin K deficiency impair clotting?
Fibrin
Mast CellBasophil Natural killer cell
Neutrophil Monocyte B Cell T CellMacrophage Dendritic cellEosinophil
Red blood cells
Platelets
Blood vessel
An injury activates a cascade of reactions that sequentially activate a number of protein clotting factors.
The function of some of these clotting factors requires vitamin K and calcium
The clotting cascade results in the formation of a mesh produced when many linked molecules of the protein fibrin trap RBCs and other cell fragments (platelets), forming a plug that stops bleeding.
Vitamin KCalcium
Micronutrients and Immunity Together, the variety of cells that make up our immune system require nearly every vitamin, and major and trace mineral to function appropriately. The nutrients are required for: 1) adequate cell division and development, 2) regulation of the immune response, 3) functions designed to kill bacteria and virus infected cells, and 4) protect the immune cells from free radicals that are produced to kill bacteria.
• Vitamin K is required for an enzymatic reaction that modifies several protein clotting factors.
• The vitamin K dependent modification of these clotting factors allows them to bind calcium.
• The binding of calcium to clotting factors is necessary for them to function.
• Because infants have low levels of vitamin K when they are born, they are typically given a vitamin K injection just after birth to prevent uncontrolled bleeding.
VitaminsMinerals
Blood Clotting is Dependent on Calcium and Vitamin K
