chapter 24 Flashcards
nutrient
major nutrients
other nutrients
Nutrient: a substance in food that promotes normal growth, maintenance, and repair
Major nutrients
Carbohydrates, lipids, and proteins
Other nutrients
Vitamins and minerals (and, technically speaking, water)
Carbohydrates
dietary sources
Dietary sources
Starch (complex carbohydrates) grains and vegetables Sugars fruits, sugarcane, sugar beets, honey and milk Insoluble fiber cellulose in vegetables provides roughage Soluble fiber: pectin in apples and citrus fruits reduces blood cholesterol levels
Carbohydrates uses
Glucose fuel
Neurons and RBCs
Excess glucose is
Uses
Glucose fuel used by cells to make ATP
Neurons and RBCs rely almost entirely on glucose
Excess glucose is converted to glycogen or fat and stored
carbs dietary requirements
Dietary requirements
Minimum 100 g/day to maintain adequate blood glucose levels
Recommended minimum 130 g/day
Recommended intake: 45–65% of total calorie intake; mostly complex carbohydrates
lipids dietary sources
essentail fatty acids
Dietary sources Triglycerides Saturated fats meat, dairy foods, and tropical oils Unsaturated fats seeds, nuts, olive oil, and most vegetable oils Cholesterol egg yolk, meats, organ meats, shellfish, and milk products
Essential fatty acids
Linoleic and linolenic acid,
in most vegetable oils
Must be ingested
Lipids essential uses of lipids in the body Help absorb Major fuel of Phospholipids are essential in functions of fatty deposits Concentrated source of e
Essential uses of lipids in the body
Help absorb fat-soluble vitamins
Major fuel of hepatocytes and skeletal muscle
Phospholipids are essential in myelin sheaths and all cell membranes
Functions of fatty deposits (adipose tissue)
Protective cushions around body organs
Insulating layer beneath the skin
Concentrated source of energy
Lipids regulatory functions
functions of cholesterol
Regulatory functions Smooth muscle contraction Control of blood pressure Inflammation Functions of cholesterol Stabilizes membranes Precursor of bile salts and steroid hormones
Lipids dietary requirements
Fats should represent
Saturated fats
Daily cholesterol intake
Dietary requirements suggested by the American Heart Association
Fats should represent 30% or less of total caloric intake
Saturated fats should be limited to 10% or less of total fat intake
Daily cholesterol intake should be no more than 300 mg
Proteins Dietary sources
and dietary requirements and uses
Dietary sources
Eggs, milk, fish, and most meats
Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids)
Legumes and cereals together contain all essential amino acids
Dietary requirements
Rule of thumb: daily intake of 0.8 g per kg body weight
Uses
Structural materials
keratin, collagen, elastin, muscle proteins
Most functional molecules
enzymes, some hormones
use of amino acids in the body
Use of amino acids in the body
1. All-or-none rule
All amino acids needed must be present for protein synthesis to occur
2.Adequacy of caloric intake
Protein will be used as fuel if there is insufficient carbohydrate or fat available
- Nitrogen balance
State where the rate of protein synthesis equals the rate of breakdown and loss
Positive if synthesis exceeds breakdown (normal in children and tissue repair)
Negative if breakdown exceeds synthesis (e.g., stress, burns, infection, or injury)
4.Hormonal controls Anabolic hormones (GH, sex hormones) accelerate protein synthesis
Vitamins
Crucial in
Most function as
Organic compounds
Crucial in helping the body use nutrients
Most function as coenzymes
Vitamins D, some B, and K are synthesized in the body
Vitamins two types based on ____
Two types, based on solubility Water-soluble vitamins B complex and C are absorbed with water B12 absorption requires intrinsic factor Not stored in the body Fat-soluble vitamins A, D, E, and K are absorbed with lipid digestion products Stored in the body, except for vitamin K Vitamins A, C, and E act as antioxidants
Minerals
Work with
Uptake and excretion must be
Seven required in moderate amounts:
Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium
Others required in trace amounts
Work with nutrients to ensure proper body functioning
Uptake and excretion must be balanced to prevent toxic overload
minerals examples harden bone essential for oxygen binding to hemoglobin necessary for thyroid hormone synthesis major electrolytes in the blood
Examples
Calcium, phosphorus, and magnesium salts harden bone
Iron is essential for oxygen binding to hemoglobin
Iodine is necessary for thyroid hormone synthesis
Sodium and chloride are major electrolytes in the blood
Metabolism
Metabolism
biochemical reactions inside cells involving nutrients
Two types of reactions
Anabolism
synthesis of large molecules from small ones
Catabolism
hydrolysis of complex structures to simpler ones
Cellular respiration
Enzymes shift
Phosphorylated molecules are
Cellular respiration
catabolism of food fuels and capture of energy to form ATP in cells
Enzymes shift high-energy phosphate groups of ATP to other molecules (phosphorylation)
Phosphorylated molecules are activated to perform cellular functions
Stages of metabolism
Processing of nutrients
1. Digestion, absorption and transport to tissues
2.Cellular processing (in cytoplasm)
Synthesis of lipids, proteins, and glycogen (anablolism)
Catabolism (glycolysis) into intermediates
3.Oxidative (mitochondrial) breakdown of intermediates into CO2, water, and ATP
Oxidation-Reduction (Redox) Reactions
Oxidized substances
Reduced substances
Coenzymes act as
Oxidation
gain of oxygen or loss of hydrogen
Oxidation-reduction (redox) reactions
Oxidized substances lose electrons and energy
Reduced substances gain electrons and energy
Coenzymes act as hydrogen (or electron) acceptors
Nicotinamide adenine dinucleotide (NAD+)
Flavin adenine dinucleotide (FAD)
ATP Synthesis two mechanisms
Two mechanisms
Substrate-level phosphorylation
Oxidative phosphorylation
Substrate-Level Phosphorylation
occurs in
High-energy phosphate groups directly transferred from phosphorylated substrates to ADP
Occurs in glycolysis and the Krebs cycle
Also occurs in certain muscle fibers
Oxidative Phosphorylation
_____ Process
occurs only in the
Chemiosmotic process
Couples the movement of substances across a membrane to chemical reactions
In the mitochondria
Carried out by electron transport proteins
Nutrient energy is used to create H+ gradient across mitochondrial membrane
H+ flows through ATP synthase
Energy is captured and attaches phosphate groups to ADP
We will look more closely at this in a few minutes when we discuss electron transport.
- Electron trasport protein “pump” protons, creating a proton gradient.
- ATP synthase uses the energy of the proton gradient to bind phosphate groups to ADP
- Occurs only in the mitochondrial matrix
Carbohydrate Metabolism
Glucose is catabolized in three pathways
Oxidation of glucose
C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP + heat
Glucose is catabolized in three pathways (3 steps to cellular respiration)
Glycolysis
Krebs cycle
Electron transport chain and oxidative phosphorylation
Glycolysis \_\_ step pathway occurs in \_\_\_ \_\_->\_\_\_ three major phases
10-step pathway Anaerobic Occurs in the cytosol Glucose → 2 pyruvic acid molecules Three major phases Sugar activation Sugar cleavage Sugar oxidation and ATP formation
phase 1 sugar activation
phosphorylation activates glucose. Glucose is converted to fructose-1,6-biphophate. 2 ATP molecules are used
Phase 2 Sugar cleavage:
fructose-1,6-biphophate is split into two 3-carbon fragments
Phase 3 sugar oxidation and ATP formation
the 3-carbond fragments are oxidized (by removing hydrogen) and 4 ATP molecules are formed
final products of glycolysis Converted to lactic acid if Enter aerobic pathways if 2 NADH + H+ (reduced Net gain of
Final products of glycolysis
2 pyruvic acid
Converted to lactic acid if O2 not readily available
Enter aerobic pathways if O2 is readily available
2 NADH + H+ (reduced NAD+)
Net gain of 2 ATP
Krebs Cycle
occurs in the fueled by transitional phase Each pyruvic acid is converted to Decarboxylation: Oxidation, H+ is removed from Acetic acid + coenzyme A =
Occurs in mitochondrial matrix
Fueled by pyruvic acid and fatty acids
Transitional phase
Each pyruvic acid is converted to acetyl CoA
Decarboxylation: removal of 1 C to produce acetic acid and CO2
Oxidation: H+ is removed from acetic acid and picked up by NAD+
Acetic acid + coenzyme A forms acetyl CoA
Coenzyme A shuttles acetic acid to an
Each acetic acid is
Coenzyme A shuttles acetic acid to an enzyme of the Krebs cycle
Each acetic acid is decarboxylated and oxidized, generating:
3 NADH + H+
1 FADH2
2 CO2
1 ATP
Krebs cycle does not what?
Breakdown products of
Cycle intermediates may be used as
Does not directly use O2
Breakdown products of fats and proteins can also enter the cycle
Cycle intermediates may be used as building materials for anabolic reactions
Electron Transport Chain and Oxidative Phosphorylation
The part of metabolism that directly
Chain of proteins bound to
Substrates NADH + H+ and FADH2 deliver
The part of metabolism that directly uses oxygen
Chain of proteins bound to metal atoms (cofactors) on inner mitochondrial membrane, cristae)
Substrates NADH + H+ and FADH2 deliver hydrogen atoms
Electron Transport Chain and Oxidative Phosphorylation
Hydrogen atoms are
Electrons are shuttled along the
Released energy is used to
Respiratory enzyme complexes I, III, and IV pump
H+ diffuses back to the
ATP synthase uses released energy to make
Electrons are delivered to
O– attracts
Hydrogen atoms are split into H+ and electrons
Electrons are shuttled along the inner mitochondrial membrane, losing energy at each step
Released energy is used to pump H+ into the intermembrane space
Respiratory enzyme complexes I, III, and IV pump H+ into the intermembrane space
H+ diffuses back to the matrix via ATP synthase
ATP synthase uses released energy to make ATP
Electrons are delivered to O, forming O–
O– attracts H+ to form H2O
Electronic Energy Gradient
This energy is released in a stepwise manner through th
Transfer of energy from NADH + H+ and FADH2 to oxygen releases large amounts of energy
This energy is released in a stepwise manner through the electron transport chain
Glycogenesis and Glycogenolysis
Glycogenesis
Glycogen formation when glucose supplies exceed need for ATP synthesis
Mostly in liver and skeletal muscle
Glycogenolysis
Glycogen beakdown in response to low blood glucose
Gluconeogenesis
Mainly in the
Protects against
Glucose formation from noncarbohydrate (glycerol and amino acid) molecules
Mainly in the liver
Protects against damaging effects of hypoglycemia
Lipid Metabolism Fat catabolism yields Most products of fat digestion are Only triglycerides are routinely The two building blocks are oxidized separately
Fat catabolism yields 9 kcal per gram (vs 4kcal per gram of carbohydrate or protein)
Most products of fat digestion are hydrolyzed by endothelial enzymes into fatty acids and glycerol
Only triglycerides are routinely oxidized for energy
The two building blocks are oxidized separately
Glycerol pathway
Fatty acid pathway
Lipogenesis
occurs when cellular ___ and ___ are ___
Glucose is easily converted into fat because acetyl CoA is
Triglyceride synthesis occurs when cellular ATP and glucose levels are high
Glucose is easily converted into fat because acetyl CoA is
An intermediate in glucose catabolism
A starting point for fatty acid synthesis
Lipolysis
Oxaloacetic acid is necessary for
Without it, acetyl CoA is converted
The reverse of lipogenesis
Oxaloacetic acid is necessary for complete oxidation of fat
Without it, acetyl CoA is converted by ketogenesis in the liver into ketone bodies (ketones)
Synthesis of Structural Materials Phospholipids for Cholesterol for In the liver synthesis of transport of Synthesis of cholesterol from Use of cholesterol to form
Phospholipids for cell membranes and myelin
Cholesterol for cell membranes and steroid hormone synthesis
In the liver
Synthesis of transport lipoproteins for cholesterol and fats
Synthesis of cholesterol from acetyl CoA
Use of cholesterol to form bile salts
Protein Metabolism
When dietary protein is in excess, amino acids are
When dietary protein is in excess, amino acids are
Oxidized for energy
Converted into fat for storage
Protein Synthesis
is ___ controlled
requires a ___ of amino acids
essentail amino acids must be provided in ___
Is hormonally controlled
Requires a complete set of amino acids
Essential amino acids must be provided in the diet
Catabolic-Anabolic Steady State
A dynamic state in which
Organic molecules (except DNA) are continuously broken down and rebuilt
Organs have different fuel preferences
Absorptive and Postabsorptive States
Absorptive (fed) state During and shortly after eating Absorption of nutrients is occurring Postabsorptive (fasting) state When the GI tract is empty Energy sources are supplied by breakdown of reserves
Sources of Blood Glucose Postabsorpative
Glycogenolysis in the ___ and ___
Lipolysis in ____ and ____
Catabolism of cellular protein during
Amino acids are deaminated and used for gluconeogenesis in the ___ and later in the _____
Glycogenolysis in the liver
Glycogenolysis in skeletal muscle
Lipolysis in adipose tissues and the liver
Glycerol is used for gluconeogenesis in the liver
Catabolism of cellular protein during prolonged fasting
Amino acids are deaminated and used for gluconeogenesis in the liver and (later) in the kidneys
Postabsorptive State: Hormonal Controls
Glucagon release is stimulated by
Glucagon, a hyperglycemic hormone, promotes
Glucagon release is stimulated by
Declining blood glucose
Rising amino acid levels
Glucagon, a hyperglycemic hormone, promotes
Glycogenolysis and gluconeogenesis in the liver
Lipolysis in adipose tissue
Modulation of glucose effects after a high-protein, low-carbohydrate meal
Postabsorptive State: Neural Controls
In response to low plasma glucose, or during fight-or-flight or exercise, the sympathetic nervous system and epinephrine from the adrenal medulla promote
Fat mobilization
Glycogenolysis
Metabolic Role of the Liver
Process nearly every
Play a major role in regulating plasma
Store
Metabolize
Hepatocytes (liver cells)
Process nearly every class of nutrient
Play a major role in regulating plasma cholesterol levels
Store vitamins and minerals
Metabolize alcohol, drugs, hormones, and bilirubin
Cholesterol Structural basis of Major component of Makes up part of the Transported in
Structural basis of bile salts, steroid hormones, and vitamin D
Major component of plasma membranes
Makes up part of the hedgehog signaling molecule that directs embryonic development
Transported in lipoprotein complexes containing triglycerides, phospholipids, cholesterol, and protein
Lipoproteins
Types of lipoproteins HDLs (high-density lipoproteins) The highest protein content LDLs (low-density lipoproteins) Cholesterol-rich VLDLs (very low density lipoproteins) Mostly triglycerides Chylomicrons
High levels of HDL are thought to
High levels of LDL, especially lipoprotein (a) increase the risk of
High levels of HDL are thought to protect against heart attack
High levels of LDL, especially lipoprotein (a) increase the risk of heart attack
Plasma Cholesterol Levels
The liver produces cholesterol
Saturated fatty acids
Unsaturated fatty acids
Trans fats
The liver produces cholesterol
At a basal level regardless of dietary cholesterol intake
In response to saturated fatty acids
Saturated fatty acids
Stimulate liver synthesis of cholesterol
Inhibit cholesterol excretion from the body
Unsaturated fatty acids
Enhance excretion of cholesterol
Trans fats
Increase LDLs and reduce HDLs
Unsaturated omega-3 fatty acids (found in cold-water fish)
Unsaturated omega-3 fatty acids (found in cold-water fish)
Lower the proportions of saturated fats and cholesterol
Have antiarrhythmic effects on the heart
Help prevent spontaneous clotting
Lower blood pressure
Non-Dietary Factors Affecting Cholesterol
stress smoking cigs
aerobic exercise
apple
pear
Stress, cigarette smoking, and coffee lower HDL levels
Aerobic exercise and estrogen increase HDL levels and decrease LDL levels
Body shape
“Apple”: Fat carried on the upper body is correlated with high cholesterol and LDL levels
“Pear”: Fat carried on the hips and thighs is correlated with lower cholesterol and LDL levels
Energy Balance
Bond energy released from food must equal the total energy output
Energy intake = the energy liberated during food oxidation
Energy output
Immediately lost as heat (~60%)
Used to do work (driven by ATP)
Stored as fat or glycogen
heat energy
Heat energy
Cannot be used to do work
Warms the tissues and blood
Helps maintain the homeostatic body temperature
Allows metabolic reactions to occur efficiently
Obesity
Body mass index (BMI) =
wt (lb) × 705/ht (inches)2
Considered overweight if BMI is 25 to 30
Considered obese if BMI is greater than 30
Higher incidence of atherosclerosis, diabetes mellitus, hypertension, heart disease, and osteoarthritis
Long-Term Regulation of Food Intake
additional factors
Additional factors Temperature Stress Psychological factors Adenovirus infections Sleep deprivation
Metabolic Rate
Total heat produced by chemical reactions and mechanical work of the body
Measured directly with a calorimeter or indirectly with a respirometer
Basal metabolic rate (BMR)
Reflects the energy the body needs to perform its most essential activities
Factors that Influence BMR
As the ratio of body surface area to volume increases, BMR
_____ with age
______with temperature or stress
As the ratio of body surface area to volume increases, BMR increases
Decreases with age
Increases with temperature or stress
Males have a disproportionately higher BMR
Thyroxine increases oxygen consumption, cellular respiration, and BMR
total Metabolic Rate
Total metabolic rate (TMR)
Rate of kilocalorie consumption to fuel all ongoing activities
Increases with skeletal muscle activity and food ingestion
Regulation of Body Temperature
At rest,
During exercise, heat production from
Body temperature reflects the balance between heat production and heat loss
At rest, the liver, heart, brain, kidneys, and endocrine organs generate most heat
During exercise, heat production from skeletal muscles increases dramatically
Regulation of Body Temperature
normal body temp
optimal enzyme activity occurs
increased temp ___
Normal body temperature = 37°C (98.6°F)
Optimal enzyme activity occurs at this temperature
Increased temperature denatures proteins and depresses neurons
Mechanisms of Heat Exchange
four mechanisms
Four mechanisms
Radiation is the loss of heat in the form of infrared rays
Conduction is the transfer of heat by direct contact
Convection is the transfer of heat to the surrounding air
Evaporation is the heat loss due to the evaporation of water from body surfaces
Core and Shell Temperature
_____ is the major agent of heat exchange between the core and the shell
Core temperature vs. shell temperature
Organs in the core have the highest temperature
Blood is the major agent of heat exchange between the core and the shell
Core temperature is regulated
Core temperature remains relatively constant, while shell temperature fluctuates substantially (20°C–40°C)
Mechanisms of Heat Exchange
Insensible heat loss accompanies insensible
Evaporative heat loss becomes sensible (active) when body temperature
Insensible heat loss accompanies insensible water loss from lungs, oral mucosa, and skin
Evaporative heat loss becomes sensible (active) when body temperature rises and sweating increases water vaporization
Hyperthermia
depresses the
(heat stroke) begins at core temperature of ___
Hyperthermia
Elevated body temperature depresses the hypothalamus
Positive-feedback mechanism (heat stroke) begins at core temperature of 41°C
Can be fatal if not corrected
hyporthermia
Shivering stops at core temperature of
Hypothermia
Low body temperature where vital signs decrease
Shivering stops at core temperature of 30 - 32°C
Can progress to coma a death by cardiac arrest at ~ 21°C
Heat exhaustion
Heat exhaustion
Heat-associated collapse after vigorous exercise
Due to dehydration and low blood pressure
Heat-loss mechanisms are still functional
May progress to heat stroke
hypothermia
Hypothermia
Low body temperature where vital signs decrease
Shivering stops at core temperature of 30 - 32°C
Can progress to coma a death by cardiac arrest at ~ 21°C
fever
Controlled hyperthermia
Due to infection (also cancer, allergies, or CNS injuries)
