Nutrition/metabolism/energy balance-1

Question 1

What is a nutrient? What is the difference between macronutrients and micronutrients? Is water a nutrient?

Answer 1

• Nutrient: substance in food needed for growth, maintenance, & repair
o used for metabolic fuel
o some are for cell structures and molecular synthesis

-Macronutrients: three major nutrients that make up the bulk of 
ingested food
Carbohydrates 
Lipids
Proteins

-Micronutrients: two other nutrients that are required, but only
in small amounts
Vitamins
Minerals

oWater is required, so technically is a nutrient

Question 2

What is the difference between non-essential and essential nutrients? what is energy measured in?

Answer 2

• Nonessential (dispensable) nutrients – may be eliminated from the diet with no adverse health effects because they are synthesized in the body

• Essential (indispensable) nutrients - cannot be synthesized in the body or are synthesized in insufficient amounts so they must be provided by the diet for growth, health and survival throughout life
o 40 - 50 nutrients are considered essential
o Inadequate intake of any essential nutrient leads to a characteristic deficiency disease, that may ultimately lead to death
o eg iron deficiency anemia

Energy value is measured in kilocalories (kcal)
A calorie is the amount of heat needed to raise temperature of 1 kg H2O by 1oC
One dietary “Calorie” equals 1 kcal

Question 3

What are the 5 food groups represented on canada’s food guide? What are some basic nutrition principles?

Answer 3

• Food groups represented
– Fruits
– Vegetables
– Grains
– Protein
– Dairy

• Basic dietary principles: eat only what you need (eat less
overall); eat plenty of fruits, vegetables, and whole grains; avoid junk food

Question 4

What is the major source of carbohydrates in the diet? What is the difference between soluble and insoluble fiber? What are the uses of carbohydrates in the body? How is excess glucose stored?

Answer 4

Dietary sources
• Primarily from plants, such as starch (complex CHO) in grains and vegetables
• Sugars (mono- and disaccharides) in fruits, sugarcane, sugar beets & honey
• Small amount in milk sugar, glycogen in meats

• Insoluble fiber: cellulose in vegetables provides roughage
• Soluble fiber: pectin in apples and citrus fruits reduces blood cholesterol
levels

Uses in body
Glucose: fuel most used by cells to make ATP
Some cells use fat for energy
Neurons and RBCs rely entirely on glucose
Neurons die quickly without glucose

Excess glucose is converted to glycogen or fat, then stored
Fructose and galactose are converted to glucose by liver before entering circulation

Question 5

What are 3 unique features of lipids? What are dietary sources of lipids?

Answer 5

a family of chemical compounds soluble in organic solvents/insoluble in H2O
Contains more stored energy than any other organic compounds.
Almost entirely C and H with almost no O2

Dietary sources:
–Triglycerides (neutral fats): most abundant form
Found in saturated fats in meat, dairy foods, tropical oils, or hydrogenated oils (trans
fats)
Unsaturated fats found in seeds, nuts, olive oil, and most vegetable oils
–Cholesterol found in egg yolk, meats, organ meats, shellfish, and milk products
Liver makes ~85% cholesterol

Question 6

What are the 2 essential fatty acids the liver can’t synthesize? what are the uses of lipids in the body?

Answer 6

Linoleic acid – an omega-6 fatty acid
– Component of lecithin
Linolenic acid – an omega-3 fatty acid
Both can be found in most vegetable oils

Uses in body
– Adipose tissue offers protection, insulation, fuel storage
– Phospholipids essential in myelin sheaths and all cell membranes
– Cholesterol stabilizes membranes; precursor of bile salts, steroid hormones
– Prostaglandins  smooth muscle contraction, BP control, inflammation
– Major fuel of hepatocytes and skeletal muscle
– Help absorb fat-soluble vitamins

Question 7

What are dietary sources of complete and incomplete proteins?

Answer 7

Dietary sources
Animal products (eggs, milk, fish, most meats), as well as soybeans, are considered complete proteins.
Why?
Legumes, nuts, and cereals contain incomplete proteins
Legumes & cereal grains together contain all essential amino acids
-20 AAs, 9 essential must be provided with food
Essential aa are used to make nonessential AAs (if those are not provided with a diet)
oThe requirement for the essential aa much higher
in children than in adults!!!!

Question 8

What are the 2 uses of protein in the body? What are three factors that determine how it’s used?

Answer 8

Uses in the body:
Structural materials 
• e.g.: keratin (skin), collagen & elastin (connective tissue) & muscle proteins
Functional molecules
• e.g.: enzymes and some hormones

Three factors help determine whether amino acids are used to synthesize
proteins or burned as fuel:
1. All-or-none rule
– All aa needed must be present for protein synthesis to occur; if not all are present,
then amino acids are used for energy
2. Adequacy of caloric intake
– Protein is used as fuel if insufficient carbohydrate or fat is available
3. Hormonal controls
– Anabolic hormones (GH, sex hormones)   protein synthesis & growth
– Adrenal glucocorticoids (released during stress) promote protein breakdown &
conversion of aas  glucose

Question 9

What is nitrogen balance and what does it mean to have positive or negative nitrogen balance?

Answer 9

Nitrogen balance
Homeostatic state where rate of protein synthesis equals rate of breakdown and loss

Negative nitrogen balance:
breakdown exceeds synthesis (eg: stress, burns, infection, injury,
poor dietary proteins, starvation)

Positive nitrogen balance
synthesis exceeds breakdown (normal in children, pregnant women, tissue repair)

Question 10

What is the main function of vitamins? What is a lessor known function of vitamins? Which ones don’t need to be consumed? What are the 2 types of vitamins?

Answer 10

Most function as coenzymes

Vitamins C, E, and A and mineral selenium are antioxidants that neutralize
free radicals

Most must be ingested, except:
oVitamin D (made in skin)
oSome B and K synthesized by intestinal bacteria
oBeta-carotene (e.g., from carrots) converted in body to vitamin A

Two types of vitamins based on solubility
– Water-soluble vitamins
oB complex and C are absorbed with water
oB12 absorption requires intrinsic factor
oNot stored in the body
– Any not used within 1 hour are excreted

– Fat-soluble vitamins
oA, D, E, and K are absorbed with lipid digestion products
oStored in body, except for vitamin K
– Excessive consumption can cause health problems

Question 11

What are the uses of minerals in the body? What are some mineral rich foods?

Answer 11

Uses in body
Ca2+, P & Mg salts harden bone
Fe is essential for oxygen binding to hemoglobin
Iodine is necessary for thyroid hormone synthesis
Na+ and Cl- are major electrolytes in blood

Mineral-rich foods–Vegetables, legumes, milk, some meats

Question 12

What is the difference between anabolism and catabolism?

Answer 12

Anabolism
-synthesis of large molecules from small ones eg: aa to proteins
Catabolism
-hydrolysis of complex structures to simpler ones e.g.: proteins to aa

Question 13

What is cellular respiration? What is phosphorylation?

Answer 13

• catabolic breakdown of food fuels where energy from food is captured to form ATP in cells
– Goal: to trap chemical energy in ATP which directly powers chemical reactions in cells
• Energy can also be stored in glycogen and fats for later use

• Phosphorylation: enzymes shift high-energy phosphate groups of ATP to other molecules
– Phosphorylated molecules become activated to perform cellular functions

Question 14

what are the 3 stages of metabolism for energy-containing nutrients?

Answer 14

1. GI tract
2. Tissue Cells
3. Mitochondria

Question 15

What are oxidation reactions? What is reduction? What are redox reactions? How are redox reactions catalyzed? What two enzymes act as hydrogen acceptors?

Answer 15

-Oxidation reactions: involve the gain of O2 or loss of H2 atoms (and their electrons)
• most biological oxidations involve the loss of hydrogen atoms & are called
dehydrogenation reactions

-Reduction: opposite of oxidation/ the addition of electrons to a molecule

Oxidation-reduction (redox) reactions are always coupled
– Oxidized substances lose electrons and energy (donor)
– Reduced substances gain electrons and energy (acceptor)

Redox reactions are catalyzed by enzymes that usually require a B vitamin coenzyme

• Dehydrogenases catalyze removal of hydrogen atoms
• Oxidases catalyze transfer of oxygen

Two important coenzymes act as hydrogen (or electron) acceptors in oxidative pathway
• Nicotinamide adenine dinucleotide (NAD+)
• Flavin adenine dinucleotide (FAD)

Question 16

What are the 2 mechanisms used to make ATP?

Answer 16

1. Substrate-level phosphorylation
   – High-energy phosphate groups are directly transferred
   from phosphorylated substrates to ADP
   – Occurs twice in glycolysis and once in Krebs cycle
   – Necessary enzymes are in cytosol for glycolysis and in mitochondria for
   Krebs cycle
2. Oxidative phosphorylation
   - More complex process, but produces most ATP
   ‒Chemiosmotic process: couples movement of substances across membranes to chemical reactions
   Energy released from oxidation of food is used to pump H+ across
   inner mitochondrial membrane, creating a steep H+ concentration
   gradient
   As H+ flows back through ATP synthase membrane channel protein,
   energy from flow is used to phosphorylate ADP

Question 17

How is glucose oxidized? What are the 3 pathways required for glucose catabolism?

Answer 17

When glucose enters a cell, it is phosphorylated to glucose-6-phosphate
Most cells (except intestinal cells, kidney and hepatocytes) lack enzymes
for reverse reaction, so glucose becomes trapped inside cell

Complete glucose catabolism requires three pathways

1. Glycolysis: occurs in the absence of O2
2. Krebs cycle: occurs in the absence of O2
3. Electron transport chain & oxidative phosphorylation

Question 18

Where does sugar splitting occur? What are the 3 major phases of sugar splitting?

Answer 18

Occurs in the cytosol

– Three major phases
Phase 1: Sugar activation
-Glucose is phosphorylated 2X by ATP
resulting in fructose-1,6-bisphosphate

Phase 2: Sugar cleavage
- Fructose-1,6-bisphosphate is split into two 3-carbon fragments
-Fragments can interconvert into one of two isomers:
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate

Phase 3: Sugar oxidation and ATP formation
-Six steps involved, with two major events
(a) Each 3-C fragment is oxidized by removal of a pair of H, which is picked up by NAD+,
forming reduced NADH + H+
H carries a portion of glucose’s energy

(b) Inorganic phosphate groups (Pi) are then attached to each oxidized fragment
Cleavage of these phosphate groups from both fragments will result in formation of 2 pyruvic acid and 4
ATPs by substrate-level phosphorylation

Question 19

What are the final products of glycolysis? What is the fate of lactic acid in glycolysis?

Answer 19

2 pyruvic acids (C3H4O3)
2 reduced NAD+ (NADH + H+)
Net gain of 2 ATP

Some may leave cell and be picked up by liver, which can convert it back to glucose-6-phosphate
Some may be oxidized back to pyruvic acid when oxygen becomes available
– Can then enter aerobic pathways
– Prolonged anaerobic metabolism can lead to acid-base problems
– Glycolysis results in faster ATP production than aerobic respiration, but
yields far less ATP

Question 20

Where does the Krebs’ cycle occur? What are the 3 stages of the transitional phase?

Answer 20

Occurs in the mitochondrial matrix

1. Decarboxylation: 1 carbon from pyruvic acid is removed, producing CO2 gas, which diffuses into blood to be expelled by lungs
2. Oxidation: remaining 2-C fragment is oxidized to acetic acid by removal of H atoms, which are picked up by NAD+
3. Formation of acetyl CoA: acetic acid combines with coenzyme A to form acetyl CoA

Question 21

Did I make any specific cards on the kreb’s cycle?

Answer 21

No, review slide 34/35/36

Question 22

What are the 2 phases of oxidative phosphorilation?

Answer 22

• Phase 1: Electron transport chain creates a proton (H+) gradient across
mitochondrial membrane using high-energy electrons removed from H from food
fuels
• Phase 2: Chemiosmosis uses the energy of the proton gradient to synthesize ATP

review slide 38-41

Question 23

What is the overall summary of ATP production?

Answer 23

– Flow of energy: Glucose → NADH + H+ → ETC → proton gradient energy →
ATP
– Net energy gain from complete oxidation of 1 glucose molecule
1. Substrate-level phosphorylation: 4 ATPs
– 2 from glycolysis and 2 from citric acid cycle
2. Oxidative phosphorylation: 28 ATPs
– For each NADH + H+ brought in, proton gradient generates 2.5 ATPs
• 10 NADH + H+ are made, so 25 ATPs
– For every FADH2 brought in, only 1.5 ATPs are created
• 2 FADH2 are made, so 3 ATPs created
– Totals between substrate-level phosphorylation and oxidative phosphorylation
equal 32 ATPs
– But….energy is required to move NADH + H+ generated in glycolysis into
mitochondria, which uses up ~2 ATPs, so final total is 30 ATPs produced
There is still uncertainty on final total
Oxidation of Glucose

Question 24

What is the difference between glycogenesis, glycogenolysis and gluconeogenesis?

Answer 24

Glycogenesis
Glycogen formation (catalyzed by glycogen synthase) when glucose supplies exceed need for ATP synthesis
Mostly in liver and skeletal muscle

Glycogenolysis
Glycogen breakdown via glycogen phosphorylase in response to low blood glucose

Gluconeogenesis
Process of glucose forming new (neo) glucose from non-carbohydrate (e.g.
glycerol and amino acid) molecules

Question 25

How are products of fat digestion transported? How are they hydrolyzed?

Answer 25

Most products of fat digestion are transported in lymph as chylomicrons

Hydrolyzed by endothelial enzymes into fatty acids and glycerol

Question 26

What are the 2 building blocks of triglycerides? What is the difference in how they are broken down?

Answer 26

Glycerol and fatty acids

1. Glycerol breakdownGlycerol is broken down into glyceraldehyde 3-phosphate (same as in glycolysis), which then enters citric acid cycle– Yields 15 ATP/glycerol
2. Fatty acid breakdown
   Fatty acids undergo beta oxidation in mitochondria:
   FAs: broken into 2C acetic acid fragments/coenzymes (FAD and NAD+ are reduced)
   Acetic acid fragment fuses with CoA to form acetyl CoA, which enters citric acid cycle
   – Reduced coenzymes enter electron transport chain

Question 27

What is lipogenesis?

Answer 27

TG synthesis occurs when cellular ATP and glucose levels are high

Dietary glycerol and fatty acids not needed for energy are stored as triglycerides
o50% is stored in adipose tissue; other 50% is deposited in other areas

Glucose is easily converted into fat because acetyl-CoA is:
– an intermediate in glucose catabolism
– a starting point for fatty acid synthesis

Amino acids can also be converted to acetyl-CoA and used to synthesize
fatty acids

Question 28

What is lipolysis?

Answer 28

breakdown of stored lipids into glycerol & FAs; reverse of lipogenesis
– FAs are actually preferred by liver, cardiac muscle, resting skeletal muscle for fuel
– Lipolysis is accelerated when carbohydrate intake is inadequate

Beta oxidation of the released fatty acids results in production of large amounts of
acetyl CoA

Without oxaloacetic acid fat oxidation is incomplete, and Acetyl CoA accumulates
The liver converts acetyl-CoA to ketone bodies (ketogenesis)
Ketone bodies include acetoacetic acid, β-hydroxybutyric acid, and acetone
Oxaloacetic acid can be converted to glucose if CHO are deficient

Question 29

What is unique about protein storage in the body? What are the 3 events of amino acid degradation?

Answer 29

Proteins are not stored in body
–When dietary proteins are in excess, amino acids are:
•Oxidized for energy or
•Converted to fat for storage

Goal is to produce molecules that can be used for energy in citric acid cycle
or converted to glucose

Three events of amino acid degradation
1. Transamination:
amino acids can transfer their amine group to α-ketoglutaric acid, transforming it into glutamic acid
original aa becomes a keto acid
Glutamic acid is an intermediate keto acid of the citric acid cycle
Reaction is reversible

2.Oxidative deamination
In liver, amine group of glutamic acid is removed as ammonia (NH3)
α-ketoglutaric acid is regenerated
NH3 then combines with CO2 to form urea & water
Urea is released to blood and excreted in urine

3. Keto acid modification
   Keto acids formed from transamination are altered to produce metabolites that can enter citric acid cycleMajor metabolites produced: pyruvic acid, acetyl CoA, ketoglutaric acid, oxaloacetic acid
   Glycolysis reactions are reversible, so pyruvic acid metabolites formed can be
   reconverted to glucose

Question 30

What are 4 key facts of protein synthesis?

Answer 30

Amino acids are most important anabolic nutrients
–Form all proteins as well as bulk of functional molecules
Protein synthesis that occurs on ribosomes is hormonally controlled (example: growth hormone, thyroid hormone, sex hormones)
Synthesis requires complete set of amino acids
–Essential amino acids must be acquired in diet
During our lifetime, depending on body size, we can synthesize 225–450 kg (500–1000 lbs) of protein

Question 31

What is catabolic-anabolic steady state? What is the amino acid pool?

Answer 31

Dynamic state in which organic molecules (except DNA) are continuously broken down and rebuilt
Body uses nutrient pools: amino acids, carbohydrates, fats
Pools are interconvertible because pathways are linked by common intermediates
Amount and direction of conversion are directed by liver, adipose tissue, and skeletal
muscle
Organs have different fuel preferences

Amino Acid pool: body’s total supply of free amino acids
Proteins are lost in urine, hair, and skin cells; replace in diet
Pool is the source for
– Resynthesizing body proteins
– Forming amino acid derivatives
– Gluconeogenesis

Question 32

What are carbohydrate and fat pools?

Answer 32

Easily interconverted through key intermediates
Differ from the amino acid pool in that:
– Fats & CHOs are oxidized directly to produce energy
– Excess carbohydrate and fat can be stored as such (aa not stored as proteins)

Question 33

What is the absorptive state? how does the absorptive state affect the 3 major macronutrients?

Answer 33

Also called fed state (~4 hrs after eating); absorption of nutrients is occurring
Anabolism exceeds catabolism; excess nutrients are stored as fats

Carbohydrates
– Glucose is major cellular energy fuel
– Can be converted in liver to glycogen or fat
Bloodborne glucose enters cells; excess stored as glycogen in muscles or fat in adipose cells

Triglycerides
– Chylomicrons from lymph are hydrolyzed to fatty acids and glycerol before passing through capillary wall
Lipoprotein lipase hydrolyzes TGs of chylomicrons  glycerol & (FFAs)
TGs used by adipose tissue, liver & skeletal and cardiac muscle as primary energy source
Excess FFAs & glycerol converted back to TGs for storage

Amino acids
Some absorbed AAs  in citric acid cycle
Excess amino acids can be stored as fat in liver
Most amino acids are taken up by cells and used for protein synthesis

Question 34

What is the hormonal control of the absorptive state?

Answer 34

– Absorptive state is controlled primarily by insulin
– Insulin secretion by beta cells of pancreas is stimulated by:
Elevated blood levels of glucose & AAs
Intestinal GIP (glucose-dependent insulinotropic peptide) and parasympathetic stimulation
– When insulin binds to membrane receptors, it facilitates diffusion of glucose into muscle and adipose cells
Brain and liver take up glucose without insulin
– Insulin is a hypoglycemic hormone that enhances:
Glucose oxidation for energy
Glycogen and triglyceride formation
Active transport of amino acids into tissue cells
Protein synthesis
– It also inhibits glucose release from liver and gluconeogenesis

Question 35

What is the post-absorptive state? what are the 4 major sources of blood glucose?

Answer 35

also called fasting state, when GI tract is empty and energy sources are supplied by
breakdown of body’s reserves
Catabolism of fat, glycogen, and proteins exceeds anabolism
Goal is to maintain blood glucose between meals by:
–Making glucose available to blood
–Promote use of fats for energy
Glucose sparing saves glucose for organs that need it most, such as brain

Sources of blood glucose
1. Glycogenolysis in liver: first reserve used
2. Glycogenolysis in skeletal muscle: before glucose from liver is exhausted, glycogen stores in skeletal muscles start to break down
3. Lipolysis in adipose tissues and liver
Glycerol used for gluconeogenesis in liver
4. Catabolism of cellular protein: major source during prolonged fasting; limited amount of protein can be broken down before damage
Amount of fat in body determines how long a person can survive without food

Question 36

What are the hormonal and neural controls of the post-absorptive state? What stimulates the release of glucagon?

Answer 36

SNS interacts with several hormones to control events of postabsorptive state• More complex than absorptive state, which utilizes one hormone, insulin
Postabsorptive state is triggered by reduced insulin release as blood glucose
levels drop

Declining blood glucose levels / rising amino acid levels
Glucagon promotes:
– Glycogenolysis and gluconeogenesis in the liver
– Lipolysis in adipose tissue, causing FAs and glycerol to be released