Biochemistry Ch.1 (3-19)
-Major fuels from diet are carbs, proteins, and fats.
-These are oxidized to CO2 and H2O and energy is released by transfer of electrons to O2
-Energy from this oxidation generates heat and ATP
Energy generating pathways: oxidation of carbs, lipids and proteins
Energy utilization pathways: biosynthesis, detox, muscle contraction, active ion transport
-CO2 travels in blood to lungs, where it is expired, and H2O is excereted in urine, sweat
-As processes use ATP, it is converted back to ADP and inorganic phosphate (ATP-ADP cycle)
Respiration: oxidation of fuels to generate ATP.
-before oxidation, carbs converted to glucose, fats to fatty acids, and proteins to amino acids
-all pathways are similar, they first oxidize fuels to acetyl coenzyme A (acetyl CoA), a precursor
to the TCA cycle
TCA Cycle: series of reactions that completes the oxidation of fuels to CO2
-electrons lost during the reactions are transferred to O2 in the electron transport chain
-ADP + Pi  ATP by oxidative phosphorylation
Catabolic – breaking molecules down (oxidative pathways are anabolic)
Anabolic – build molecules up
-energy often expressed in units called Calories (1 kcal is amount of energy required to raise temp of 1L
of H2O by 1 degree celcius
-1 cal soft drink has 1 cal (1 kcal) of energy
-energy can also be expressed in joules
1 kcal = 4.18 kilojoules (kJ)
Carbohydrates – major carbs in diet are starch, sucrose, lactose, fructose and glucose
-starch is the storage form of carbs in plants (polysaccharide)
-sucrose is table sugar and lactose is milk sugar (both disaccharides)
-fructose and glucose are monosaccharides (glucose predominant sugar in human blood)
-every gram of carbohydrate we eat yields 4kcal of energy
Proteins – composed of amino acids joined to form linear chains. Contain carbon, hydrogen, oxygen,
and 16% nitrogen by weight
-breakdown of proteins yields amino acids in blood. Complete oxidation to CO2, H2O and NH4+, yields
4kcal/g energy
Fats – Fats are lipids composed of triacylglycerols (3 fatty acids esterified to one glycerol)
-usually contain less O2 than carbs or proteins, thus they are more reduced and yield more energy when
oxidized
-complete oxidation to CO2 and H2O yields 9kcal/gram
Alcohol – Ethanol (CH3CH2OH) is oxidized to CO2 and H2O in body and yields 7kcal/g energy, more than
carb and protein but less than fat.
Body Fuel Stores – since we can’t eat constantly, our energy supplies are stored in our body
-fat is stored in adipose tissue, more in hips and thighs
-carbohydrates are stored as glycogen in liver and muscles
-glycogen is glucose joined together to form large polysaccharide
-protein is stored in our large muscle masses
Fat Storage – major fuel store is adipose triacylglycerol
-average man has 15kg of stored fat, accounting for 85% of stored calories
-adipose tissue contains 15% water, therefore an average man with 15kg stored triacylglycerol has only
18kg of adipose tissue
Glycogen Storage – glycogen stored in the liver and muscles
-liver glycogen used to maintain blood glucose between meals, which is necessary for proper CNS
function
-glycogen store fluctuates during the day (200g after a meal and only 80g after an overnight fast)
-muscle glycogen supplies energy for muscle contraction during exercise
-at rest, average 70kg man has 150g of muscle glycogen, almost all cells maintain a little
glycogen
Protein Storage – protein is not solely a fuel store, as muscle protein is essential for body movement,
enzymes, or structural components of cells and tissues
-only a limited amount of protein can be degraded, approximately 6kg in an average 70kg man
Daily Energy Expenditure – in order not to gain or lose weight, we must consume food equal to our daily
energy expenditure (DEE)
-DEE includes energy to support basal metabolic rate (BMR) or resting metabolic rate (RMR) and our
physical activity, plus the energy required to process food we eat (diet-induced thermogenesis or DIT)
Thus, DEE = RMR + Energy for Physical activity + DIT
Resting Metabolic Rate – measure of energy required to maintain life, all the intrinsic reactions in the
body
-basal metabolic rate was first described as energy expenditure of person at rest in thermoneutral
environment 12-18 hours after eating
-resting metabolic rate takes into account heat production and oxygen consumption
-RMR and BMR differ very slightly
-BMR is affected by body size, sex, body temperature, environmental temperature, thyroid status, age
-rough estimate of BMR is to assume it is 24 kcal/day/kg and multiply by body weight,
-easy way to remember is 1kcal/kg/hr
Physical Activity – in addition to RMR energy for physical activity is involved in DEE
-rough estimate for physical activity can be made using 30% of RMR for a very sedentary person and
60%-70% of RMR for a person who exercises 2 hours every day.
Diet-induced thermogenesis – component related to intake of food
-after eating, our metabolic rate increases because energy is required to digest our food
-An American diet uses 10% of the kcal ingested to actually digest the food
-roughly equivalent to the error in rounding of caloric content in carb, fat, and protein, so this is often
discounted.
-registered dieticians use a more accurate calculation for energy requirements, based on the fat-free
mass (FFM), which is equal to the total body mass minus mass of adipose tissue
-with FFM, BMR is calculated using equation BMR = 186 + (FFM)(23.6kcal/kg/day)
-eliminates differences between sexes and ages
-indirect calorimetry is a technique used to measure O2 consumption and CO2 production for
hospitalized patients
-indirect calorimeter is used to produce a respiratory quotient (RQ) which is ratio of O2/CO2
-RQ is 1.00 for oxidizing carbs, 0.83 for protein, and 0.71 for fat
Calculations of Daily Energy Expenditure – total DEE is sum of RMR + physical activity
-can use just RMR and approximate % of RMR in physical activity based on how sedentary you are
Healthy Body Weight – strive to maintain weight consistent with good health
-overweight is defined as more than 20% above ideal weight
-Body mass index (BMI) is calculated as kg/m^2
-Adults with BMI <18.5 are underweight, between 18.5 and 24.9 are healthy, 25-29.9 is overweight, >30
is obese, >40 is morbidly obese
Weight gain and Loss – To maintain body weight, we need to stay in caloric balance, if kcal we eat
equals our DEE.
-we lose 1lb whenever we expend 3,500 kcal more than we consume
-therefore, if we eat 1000kcal less than we expend per day, we lose 2lb/week
Dietary Requirements – we must have regular supply of nutrients, vitamins and minerals and the
essential fatty acids and essential amino acids which we cannot synthesize on our own
-essential means they are essential in our diet
-Recommended Daily Allowance (RDA) and Adequate Intake (AI) provide quantitative estimates of
nutrient requirements.
-RDA for a nutrient is the average daily dietary intake level necessary to meet the requirement
of nearly all healthy individuals in a particular gender and life stage group (pregnancy, lactation)
-AI is recommended intake value used when not enough data are available for RDA
1.) Carbohydrates – no carbs are essential as dietary requirements.
-can be synthesized from amino acids, and can be interconverted from one to another
-health problems do begin when you eliminate carbs from diet, because low carb diet = high fat
diet to provide energy we need
2.) Essential Fatty Acids – most lipids required for cell structure, fuel storage and hormone synthesis can
be made from carbs or proteins, we need a minimum level of lipids for optimal health
-essential fatty acids include α-linoleic and α-linoleic acid are supplied by dietary plant oils
-eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplied in fish oils
-precursors of the eicosanoids, a set of hormone-like molecules secreted by cells to have effects
on nearby cells
-eicosanoids include prostaglandins, thromboxanes, leukotrienes
3.) Proteins and Essential Amino Acids – RDA for protein is 0.8 high quality protein per kg of body
weight
-high quality means all essential amino acids in adequate amounts, such as from milk, eggs,
meat proteins
Essential Amino Acids – of the 20 amino acids, 9 amino acids are essential in the diet of an adult
human
-lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine,
and histidine
-some amino acids are conditionally essential, only required in diet under certain
conditions, such as children and pregnant women who are constantly growing need
arginine in their diet despite being able to synthesize it.
-histidine is essential in very small amounts because body is able to efficiently recycle it
-tyrosine and cysteine are conditionally essential – tyrosine is synthesized from
phenylalanine and is only essential if dietary phenylalanine is low.
-cysteine is synthesized by using the sulfur from methionine, and may also be required
under low methionine conditions
Nitrogen Balance – proteins undergo constant turnover, and free amino acids have one of three
fates
1.) Make proteins
2.) Precursors to nitrogen containing compounds (DNA, RNA, Heme)
3.) Oxidized to yield energy
-when amino acids are oxidized, their nitrogen is secreted in the urine as urea
-urine also contains nitrogenous compounds such as uric acid, creatinine, and ammonium ion
-Nitrogen Balance is the difference between the amount of nitrogen taken into the body each
day and the amount of nitrogen in compounds lost.
-if more Nitrogen is ingested than excreted = positive nitrogen balance
-occurs in growing individuals constantly synthesizing proteins
-if more nitrogen is excreted than ingested = negative nitrogen balance
-occurs when someone is eating too little protein
-healthy adults are in nitrogen balance (neither positive nor negative)
Vitamins – vitamins are organic molecules required in very small quantities in diet for health,
growth, and survival
-deficiency in vitamins can cause deficiency signs and death
-Often divided into water-soluble and fat-soluble vitamins, related to absorption and transport
of fat-soluble vitamins with lipids
-most vitamins are used for synthesis of coenzymes, complex organic molecules that help
enzymes
-some vitamins also act as hormones
-RDA varies for age and sex
-Example: RDA for riboflavin is 0.9mg/day for males 9-13, 1.3mg/day for males 19-30
-Vitamins cannot be synthesized by the body, unless it is from a very specific dietary precursor
and in very small amounts
-Niacin can be synthesized from tryptophan (an essential amino acid), but not enough
for our needs, therefore niacin is still a vitamin
-Excessive vitamins are detrimental to health
-excess vitamin A, a fat-soluble vitamin, can cause desquamation of skin and birth
defects
-high doses of vitamin C can cause diarrhea and GI disturbance
-Tolerable Upper Intake Level (UL) – highest level of daily nutrient intake that is likely to pose no health
risk to all individuals in a general population
-Multiple vitamin deficiencies are more common than diseases lacking just one vitamin. Single vitamin
deficiencies do exist
-Single vitamin deficiency occurs as a result of conditions that interfere with uptake or utilization
of vitamin or as a result of poor food choices that lack variety in diet
Minerals – divided into classifications of electrolytes (inorganic ions dissolved in fluids), minerals
(relatively large quantities), trace minerals, and ultratrace minerals
-Na+, K+, Cl- are major electrolytes in the body – establish ion gradients, maintain water balance,
neutralize positive and negative charges.
-Ca2+ and P serve as structural components of beons and teeth and required in large amounts
-P is required for ATP formation
-Mg2+ activates many enzymes and forms complexes with ATP
-Zinc and molybdenum are required in very small quantities
-Sulfer is ingested in amino acids of cysteine and methionine, found in connective tissue of cartilage and
skin
Xenobiotics – our diet contains large number of chemicals with no nutritional value, no use in the body,
and can be harmful