CHAPTER 4

BODY WEIGHT AND HEALTH

 

Enzymes and Metabolism

      Enzymes

      Proteins that catalyze (speed up) chemical reactions in a cell

      Metabolism: all chemical reactions occurring in
the body

      Enzymes work by lowering the activation energy needed for a reaction

      Substrate are substances being catalzyed

      Active site is where the substrate binds to the enzyme

      The binding of the substrate and enzyme causes a shape change and called induced fit

      Specificity of the enzyme to the substrate is based on enzyme shape and active site

      A calorie is the amount of energy required to raise the temperature of 1 gram of water by 1C.

      1000 calories  1 kilocalorie or Calorie

      Calorie:

      Unit of energy represented on food labels

      Calories are consumed by cells to do work

      Extra calories can be stored as fat

      Metabolic rate: the rate at which the body uses energy

 

      Basal Metabolic Rate or BMR represents the resting energy of a awake, resting but alert person.

      70 Calories/hour or 1680 Calories/day

      Metabolic rate is influenced by many factors:

      Body weight, sex, exercise, genetic makeup, age, and nutritional status

 

Cellular Respiration

      Cellular respiration is a series of enzymatic reaction that converts energy from food into energy stored in ATP.

      ATP consists of adenine, a sugar, and 3 phosphate groups.

      When a phosphate group is transferred from ATP to another molecule (phosphorylation), energy
is transferred and ADP is produced.

      The energy from ATP can power different kinds of work in the cell.

      As ATP is used in the cell it must be replenished by cellular respiration.

      Aerobic cellular respiration occurs in the mitochondria and requires the presence of oxygen.

      C6H12O6 + 6O2 6CO2 + 6H2O

      Aerobic cellular respiration takes the energy from glucose and uses it to make ATP.

      This process occurs in three complex steps starting in the cytosol of the cell and completing in the mitochondria.

 

Cellular Respiration - Step 1: Glycolysis

      6-carbon glucose molecule is broken down into two 3-carbon pyruvic acid molecules.

      Takes place in the cytosol and doesnt require oxygen and produces 2 ATP.

      NAD+ is used as a chemical taxi cab.

      These pick up the electrons and hydrogen ions released during glycolysis and become NADH.

 

Cellular Respiration - Step 2: Citric Acid Cycle

      Citric acid cycle: series of chemical reactions catalyzed by 8 different enzymes in the mitochondrial matrix

      The result is the generation of 2 ATP, release of carbon dioxide and NADH.

 

Cellular Respiration - Step 3: Electron Transport and ATP Synthesis

      Electron transport chain acts like a conveyor belt, moving electrons through a series of proteins.

      NADH drops off its electrons and hydrogen ions

      The protein carriers move the electrons through the chain and move the hydrogen into the intermembrane space.

      The concentration of H+ ions increases within the intermembrane space.

      H+ ions are charged, and cant simply diffuse back across the membrane.

      They pass through protein channels called ATP synthase, generating 32 or 34 ATP molecules as they do.

      At the end of the chain, the electrons combine with oxygen to produce water.

 

Cellular Respiration - Metabolism of Other Nutrients

      Proteins and fats can also provide energy when carbohydrates are unavailable.

      They are broken down and their subunits feed into aerobic cellular respiration.

 

Cellular Respiration - Metabolism Without Oxygen: Anaerobic Respiration and Fermentation

      Cells can generate energy without oxygen through anaerobic respiration.

      Muscle cells can produce lactic acid to regenerate NAD+ through fermentation.

      Bacteria in yogurt also use fermentation to make lactic acid.

      Yeast cells use fermentation to convert glucose to ethanol.

 

Body Weight and Health

      Difficult to define overweight precisely

      Women need more body fat to maintain fertility than men do

      Average healthy body fat percentages:

      Women: 22% and Men: 14%

      Body Mass Index (BMI): correlates amount of body fat with risk of illness and death, using both height and weight

      Healthy range of BMI = 20-25

      Obesity: BMI of 30 or higher

      Risk of obesity is influenced by both lifestyle (diet, exercise) and genetics

      Obesity increases risks of:

      Diabetes

      Hypertension

      Heart disease

      Stroke

      Joint problems

      Diabetes: disorder of carbohydrate metabolism

      Insulin: hormone that triggers cells to take up glucose; produced by beta cells of the pancreas

      Type 1 Diabetes (not associated with obesity)

      Usually arises in childhood

      Cannot produce insulin (no beta cells)

      Treated with daily insulin injections

      Type 2 Diabetes (associated with obesity)

      Usually arises in adults

      May be controlled by diet and exercise

      Hypertension: high blood pressure (the force exerted on blood vessels by the blood)

      Systolic: blood pressure as the heart contracts

      Diastolic: blood pressure while heart is relaxing

      Normal blood pressure is about 120 systolic and 80 diastolic (120/80)

      Hypertension: persistently over 140/90

      Heart attack: a sudden loss of blood to the heart because of blocked arteries

      Stroke: a sudden loss of blood to the brain because of blocked arteries

      Cholesterol: a lipid that can build up in arteries

      Low-density lipoproteins (LDLs): distribute cholesterol throughout the body and dumps excess in the arteries

      High-density lipoproteins (HDLs): carry excess cholesterol to the liver for excretion as bile

      Anorexia: self-starvation

      Can starve heart muscles, producing altered rhythms

      Amenorrhea: cessation of menstruation; can be permanent and result in sterility

      Increases risk of osteoporosis

      Bulimia: binge-eating followed by purging

      Many of the same health effects as anorexia

      May lead to stomach rupture

      Dental and gum problems from stomach acid

      Dehydration (sometimes fatal)