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Chapter 27Nutrition and Metabolism

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Overview: Nutrition and Metabolism

• Nutrition: food (nutrients) humans eat– Malnutrition— a deficiency of food, vitamins, and minerals

– Categories of nutrients• Macronutrients— nutrients needed in large amounts (bulk nutrients)

– Macromolecules such as carbohydrates, fats (lipids), and proteins

– Water

– Macrominerals

» minerals needed in large quantity

» for example, sodium, chloride, and calcium

• Micronutrients— nutrients needed in very small amounts– Vitamins

– Microminerals (trace elements)

» minerals such as iron, iodine, zinc, that are needed only in very small quantities

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Metabolism

• Metabolism: “use of food”– the use of nutrients– a process made up of many chemical processes

• Catabolism- breaks food down into smaller molecular compounds and releases two forms of energy— heat and chemical energy

• Anabolism— a synthesis process

• Occur constantly• Chemical energy released by catabolism must be transferred

to ATP, which is used in the cells

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Chemical Energy in Food

• How much energy is in food?– When 1 gram of glucose (C6H12O6) is burned in the

presence of oxygen, 3811 calories are released.

– What is a calorie? A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

• On a food label Calories (with a capital “C”) represent kilocalories. 1 kilocalorie = 1000 calories.

– Cells use the energy in glucose by slowly releasing it.

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Carbohydrates• Dietary sources of carbohydrates

– Complex carbohydrates• Polysaccharides— starches

– found in vegetables and grains

– glycogen is found in meat

• Cellulose

– a component of most plant tissue

– passes through the digestive system without being broken down

– Fiber, “roughage”

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Carbohydrates

• Disaccharides— found in refined sugar

– must be broken down before they can be absorbed

• Monosaccharides— found in fruits

– move directly into the internal environment without being processed directly

– Glucose

» carbohydrate most useful to the human cell

» can be converted from other monosaccharides

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Know for test!

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Carbohydrates• Carbohydrate metabolism— human cells catabolize most of the

carbohydrate absorbed and anabolize a small portion of it– Glycolysis— the first process of carbohydrate catabolism

• of a series of chemical reactions (Figure 27-3)• Glycolysis occurs in the cytoplasm of all human cells• An anaerobic process— provides cells with energy under conditions of

inadequate oxygen• It breaks down chemical bonds in glucose molecules and releases about 5%

of the energy stored in them• It prepares glucose for the 2nd step in

catabolism: the citric acid cycle• Produces 2 pyruvic acid, 2 (net) ATP,

and 2 NADH!

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• FYI!

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Carbohydrate metabolism

Citric acid cycle• formerly called Krebs cycle after Sir Hans Krebs, who

discovered this process• By the end of the reactions of the citric acid cycle, two

pyruvic acids have been broken down to 6 carbon dioxide, 6 NADH, 2 FADH2 and 6 water molecules (Figures 27-4 and 27-5)

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FYI!

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Know for test!

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DING! The magical world of electron transport!

What purpose is the NADH and FADH2?

Electron transport chain (or system) in the mitochondria– http://www.science.smith.edu/departmen

ts/Biology/Bio231/etc.html

• These molecules are very HIGH ENERGY!

• In the mitochondria, for every:– NADH 3 ATP

– FADH2 2 ATP

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Carbohydrate metabolism– Electron transport chain (ETC) (Figure 27-6)

• NADH and FADH2 removed during CAC enter a chain of molecules

that are embedded in the inner membrane of the mitochondria

• As electrons move down the chain, they release small bursts of energy to pump protons between the inner and the outer membrane of the mitochondrion

• Protons move down their concentration gradient and across the inner membrane, driving ATP-synthase

– Oxidative phosphorylation— the joining of a phosphate group to ADP (di) to form ATP (tri) by the action of ATP synthase

– http://www.sp.uconn.edu/~terry/images/anim/etsanim.gif

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Must understand the concept but not the names of the proteins (except ATP synthase)

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ATP Synthase

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Carbohydrate Metabolism– The anaerobic pathway- Lactic

Acid Fermentation• Without O2

• a pathway for the catabolism of glucose

• transfers energy to ATP using only glycolysis

• Converts NADH back to NAD+

• paying the “oxygen debt”- Box 27-4

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Oxygen uptake during and after exercise

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Glucose Use

– Glycogenesis• Glucose join together strand of glucose beads = glycogen• a process that operates when the blood glucose level increases

above the midpoint of its normal range (Figures 27-11)

– Glycolysis—the first process of carbohydrate catabolism• in cytoplasm of all human cells

• An anaerobic process

• It breaks down chemical bonds in glucose molecules and releases about 5% of the energy stored in them

• It prepares glucose for the second step in catabolism—the citric acid cycle

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Control of Glucose Metabolism– Hormonal and neural devices maintain

homeostasis of blood glucose concentration

• Insulin– secreted by beta cells in pancreas

– decreases blood glucose level

• Glucagon– Secreted by alpha cells in pancreas

– Breaks down glycogen only in liver increases blood glucose level

• Epinephrine– hormone secreted in times of stress by adrenal

medulla

– Breaks down glycogen in liver AND muscles increases blood glucose level

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• Adrenocorticotropic hormone (ACTH)

– stimulates adrenal cortex to increase its secretion of glucocorticoids

– Glucocorticoids accelerate gluconeogenesis

» Gluconeogenesis is the formation of new glucose from proteins and fats

» Increases blood glucose levels

• Growth hormone

– Made by pituitary

– increases blood glucose level by shifting from carbohydrate to fat catabolism

Control of Glucose Metabolism

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Carbohydrate Metabolism

– Hormones that cause the blood glucose level to rise are called hyperglycemic

– Insulin is hypoglycemic because it causes the blood glucose level to decrease

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Lipids• Dietary sources of lipids

– Triglycerides• the most common lipids• Composed of a glycerol subunit that is attached to 3 fatty acids

– Phospholipids— an important lipid found in all foods– Cholesterol— an important lipid found only in animal

foods• Used in cell membrane

Dietary fats• Saturated fats contain no double bonds• Unsaturated fats contain some double bonds

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Lipids• Lipoproteins and fatty acids are transported in the

blood – 95% of lipids are in the form of lipoproteins

• Consists of lipids + protein

• Formed in the liver– Blood contains 3 types of lipoproteins

» very low density

» Low Density (LDL)

» High Density (HDL)

– Cholesterol lipoproteins associated with heart disease

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Proposed Functions of Lipoproteins

• Some people have very few LDL receptors on the surface of their cells and cannot store excess cholesterol inside the cell so it accumulates in the blood

• High levels of LDL leads high risk of atherosclerosis (“hardening” of the arteries) high risk for heart attack or stroke

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• High HDL levels low risk of atherosclerosis

• HDL binds to the surface of a cell and stimulates the release of cholesterol which HDL takes to the liver for excretion

• High LDL (>180mg)- lots of cholesterol is being delivered

• High HDL (>60mg)- lots of cholesterol is being removed

Proposed Functions of Lipoproteins

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Omega-3 fatty acids

• An essential fatty acid- our body is unable to produce polyunsaturated fats so we must eat them in order to obtain them

• Fish contain this fat in their cell membranes– This is what causes fish from very cold areas

to be oily and not freeze– “fish oil”– Examples: salmon, herring, trout

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Lipids• Lipid metabolism

– Lipid catabolism

• beta-oxidation acetyl-CoA citric acid cycle

– Lipid anabolism

• lipogenesis

– Control of lipid metabolism is through the following hormones:

Insulin

Growth hormone

ACTH

Glucocorticoids

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Proteins • Sources of proteins

– 20 different amino acids– The body synthesizes amino acids from other

compounds in the body• Only about half of the necessary types of amino acids

can be produced by the body• the rest are supplied through diet—found in both meat

and vegetables

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Proteins• Protein metabolism— anabolism is primary, and catabolism

is secondary– Protein anabolism— process by which proteins are synthesized by ribosomes

– Protein catabolism— deamination takes place in liver cells and forms an ammonia molecule, which is converted to urea and excreted in urine, and a keto acid molecule, which is oxidized or converted to glucose or fat

– Protein balance— rate of protein anabolism balances rate of protein catabolism

– Nitrogen balance— amount of N taken in = N out thru protein catabolic waste

– Two kinds of protein or nitrogen imbalance:• Negative nitrogen balance

– protein catabolism exceeds protein anabolism

– more tissue proteins are catabolized than are replaced by protein synthesis

• Positive nitrogen balance– protein anabolism exceeds protein catabolism

– Control of protein metabolism— achieved by hormones

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• This may have certain things you do NOT need to know for the test!

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Vitamins• Vitamins

– organic molecules necessary for normal metabolism– many attach to enzymes and help them work or have

other important biochemical roles– The body does not make most of the necessary vitamins– they must be obtained through diet

• Body stores fat-soluble vitamins (D,A,K, and E)– Taken up in the small intestine– These molecules are predominantly non-polar

• Body does NOT store water-soluble vitamins– These molecules are predominantly polar

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Vitamins- do NOT memorize locations

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Minerals

• Minerals– inorganic elements or salts found in the earth

– Attach to enzymes and help them work and function in chemical reactions

– Essential to the fluid/ion balance of internal fluid environment

– Are involved in many processes in the body such as muscle contraction, nerve function, hardening of bone, etc.

– Too large or too small an amount of some minerals may be harmful

– Recommended mineral intakes may vary over the lifespan

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Metabolic Rates

• Metabolic rate means the amount of energy released by catabolism

• Metabolic rates are expressed in two ways:– Number of kilocalories (C) of heat energy expended per hour

or per day

– As normal or as a percentage above or below normal

• Basal metabolic rate— rate of energy expended under basal (base) conditions– Factors:

• Size Body composition• Sex Age• Thyroid hormone Body temperature• Drugs other factors

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Metabolic Rates• Total metabolic rate- the amount of energy used over time

– Main determinates:• Basal metabolic rate

• Energy used to do skeletal muscle work

• Thermic effect of foods

• Energy balance and weight— the body maintains a state of energy balance – Body maintains weight when the total calories in the food ingested equals

the total metabolic rate

– Body weight increases when energy input exceeds energy output

– Body weight decreases when energy output exceeds energy input

– In starvation, carbohydrates are used up first, then fats, then proteins (Figure 27-32)

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Mechanisms for Regulating Food Intake

• Hypothalamus plays a part in food intake• Feeding centers in hypothalamus exert primary

control over appetite– Appetite center

• Cluster of neurons in hypothalamus when stimulated, increases appetite

• Orexigenic effects— factors that trigger appetite

– Satiety center• Group of neurons in the hypothalamus that, if stimulated,

brings about decreased appetite• Anorexigenic effects— factors that suppress appetite

(anorexia is loss of appetite)

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Anorexia Nervosa

• Self-induced weight loss, negative perception of body image, and changes in their body due to nutritional depletion

• Predominantly in young, single females, and may be inherited.

• Abnormal menstruation, amenorrhea, and a lowered BMR

• Associated disorders are:– Osteoporosis– Depression– Brain abnormalities

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The Big Picture: Nutrition, Metabolism, and the Whole

Body• Every cell in the body needs the

maintenance of the metabolic pathways to stay alive

• Anabolic pathways build the various structural and functional components of the cells

• Catabolic pathways convert energy to a usable form and degrade large molecules into subunits used in anabolic pathways

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The Big Picture: Nutrition, Metabolism, and the Whole

Body• Cells require appropriate amounts of

vitamins and minerals to produce structural and functional components necessary for cellular metabolism

• Other body mechanisms operate to ensure that nutrients reach the cells