Chapter 25: Metabolism and Nutrition

Question 1

Define metabolism and differentiate between catabolism and anabolism

Answer 1

Metabolism is all the chemical reactions that occur in the body

Catabolism (decomposition) are chemical reactions that break down complex organic molecules into simples ones; they are exergoic in that they produce more energy then they consume

Anabolism (synthesis) combine simple molecules and comonomer to form the body complex structural and functional components; they are endergonic in they consume more energy then they produce

Question 2

How does ATP link anabolism and catabolism?

Answer 2

When the terminal P group is split off ATP = ADP + P

Some of the energy released is used to drive anabolic reactions

In addition, energy from complex molecules is used in catabolic reactions to combine ADP + P + energy = ATP

Question 3

Describe oxidation-reduction reactions

Answer 3

Oxidation - the removal of electrons from an atom or molecule; the result is decrease in the potential enemy of the atom/molecule

Reduction - the addition of elections to a molecule resulting in an increase in the potential energy of a molecule

These reactions are always couples as each time one stubsance is oxidized, another is simultaneously reduced known as oxidation-reductional reactions

Question 4

What is nicotinamide adenine dinuclotide (NAD)

Answer 4

A derivative of the B vitamin niacin that is a common coenzyme used by animal cells to carry H atoms

Question 5

Define phosphorylation and describe the 3 mechanisms of phosphorylation to generate ATP

Answer 5

phosphorylation - addition of a P group to a molecule to increase energy

1. Substrate-level phosphorylation - generates ATP by transferring a high-energy P group from an intermediate metabolic compound (a substrate) directly to ATP; occurs in cytosol
2. Oxidative phosphorylation - removes electrons from organic compounds and passes them through a seers of election acceptors called the electron transport changes, to molecules of O2l occurs in mitochondria
3. Photophosphorylation - occurs only in chlorophyll-containing plant cells

Question 6

Describe the following ways glucose is used in the body:

ATP production
Amino acid synthesis
Glycogen synthesis
Triglyceride synthesis

Answer 6

ATP production - glucose is oxidized to produce immediate ATP

Amino acid synthesis - use glucose to form several anino acids which can then be incorporated into proteins

Glycogen synthesis - glycogenesis where hundreds of glucose monomers are combined to form the polysaccharide glycogen

Triglyceride synthesis - hepatocytes can transform glucose to glycerol and fatty acids that can be used for lipogenesis, the synthesis of triglycerides

Question 7

How does glucose move into cells?

Answer 7

Absorption in the GI tract is accomplished via secondary active transport (Na+ - glucose symporters)

Entry into most other body cells occurs via GluT molecules, a family of transporters that bring glucose into cells via facilitated diffusion

High levels of insulin increases insertion of GluT, increasing levels of facilitated diffusion

Question 8

Define cellular respiratory and its 4 sets of reactions

Answer 8

Cellular respiration - oxidation of glucose to produce ATP

1. Glycolysis - set of reactions in which one glucose molecule is oxidized and two molecules of pyretic acid are produce; results in 2 ATP molecules and 2 energy-containing NADH+H+
2. Formation of acetyl coenzyme - prepares pyretic acid from extract into Krebs cycle; produces energy-containing NADH+H+ and CO2
3. Krebs cycle reaction - oxidize acetyl coenzyme A and produce CO2, ATP, energy-containing NADH+H+ , and FADH2
4. Electron transport chain reactions - oxidize energy-containing NADH+H+ and FADH2 and transfer their electrons through a series of electron carriers

Question 9

Define anaerobic glycolysis

Answer 9

when oxygen is present, all four phases of cellular respiration occur: glycolysis, formation of acetyl coenzyme A, the Krebs cycle, and the electron transport chain.

However, if oxygen is not available or at a low concentration, pyruvic acid is converted to a substance called lactic acid, this is called anaerobic glycolysis

Question 10

Which of the 4 processes of cellular respiration produces the most ATP?

Answer 10

Electron transport chain

Question 11

Describe the 3 ways glucose takes part in or is formed in anabolic reactions

Answer 11

Glycogenesis - the synthesis of glycogen; glucose is phosphorylated to glucose 6-phosphate which is then covered into glucose 1-phosphate and then to uridine diphosphate and finally glycogen

Glycogenolysis - the splitting of glycogen into glucose; begins by splitting off glucose molecules from the branches glycogen molecule via phoshoprlation to form glucose 1-phosphate; stimulated by glucagon and epinephrine

Gluconeogensisi - glucose is formed from noncarbohydrate sources when low of glycogen; stimulated by cortisol

Question 12

Define lipoproteins and deceive the four major classes

Answer 12

Lipoproteins- combination of lipids and proteins

1. Chylomicrons - form from mucous epithelial cells of the small I, transport dietary lipids to adipose tissues for storage, enter lacteals of intestinal villi and are carried by lymph into venous blood and then into systemic circulation

Very low density lipoproteins (VLDLs) - form in hepatocytes, contain mainly endogenous lipids, transport triglycerides synthesized in hepatocytes to adipocytes for storage

Low density lipoproteins (LDLs) - carry about 75% of total cholesterol in blood and deliver it to cells throughout the body for use in repair of cell membranes and synthesis of steroid hormones and bile salts, enters cells via receptor-mediated endocytosis where it is broken down (bad cholesterol)

High density lipoproteins (HDLs) - remove excess cholesterol from body cells and the blood and transport it to the liver for elimination (good cholesterol)

Question 13

What are the sources of significance of blood cholesterol?

Answer 13

2 sources: some is present in foods but most is synthesized by hepatocytes

1) High intake of dietary fats stimulates reabsorption of cholesterol containing bile back into the blood and 2) when saturated fats are broken down in the body, hepatocytes use some of the breakdown products to make cholesterol

As total cholesterol levels increase, the risk of coronary artery disease begins to rise (above 200 mg/dL heart attack chance doubles every 50 mg/dL increase)

Question 14

Describe the fate of lipids

Answer 14

They can be oxidized to produce immediate ATP or can be stored in adipose tissue throughout the body and the liver

Question 15

How are triglycerides stored?

Answer 15

Chylomicrons and VLDLs remove triglycerides and store them until they are needed for ATP production

Adipose tissues contsitture 98% of the bodies reserve as they are hydrophobic and store easily

Triglycerides in adipose tissues are continually broken down and resyntheisized and continually released, transported in the blood, and redeposited into other adipose tissue cells

Question 16

Describe lipolysis

Answer 16

aka lipid catabolism - triglycerides are split into glycerol and fatty acids, a process that is catabolized by lipases - Epi and NE enhance triglyceride breakdown into fatty acids and glycerol

If ATP supply is high, glyceraldehyde 3-phosphate is converted into glucose

If ATP supply is low, glyceraldehyde 3-phosphate enters the catabolic pathway to pyruvic acid

Fatty acids undergo beta oxidation and enter the Krebs cycle via acetyl
coenzyme A

Question 17

Describe lipogenesis

Answer 17

aka lipid anabolism - liver cells and adipose cells synthesize lipids from glucose or amino acids, a process stimulated by insulin

This occurs when individuals consume more carols than are needed to satisfy their ATP needs

amino acids -> acetyl CoA -> fatty acids -> triglycerides.

The use of glucose to form lipids takes place via two pathways:

(1) glucose -> glyceraldehyde 3-phosphate -> glycerol
(2) glucose -> glyceraldehyde 3-phosphate -> acetyl CoA -> fatty acids.

Question 18

Describe the fate of proteins in the body

Answer 18

Active transport of amino acids into body cells is stimulated by insulin like growth factors (IGFs) and insulin

Almost immediately after digestion, amino acids are reassembled into proteins

Question 19

What are the possible fates of the amino acids from protein catabolism

Answer 19

Hepatocytes convert some animo acids to fatty acids, ketone bodies, or glucose

Cells throughout the body oxidize a small amount of amino acids to generate ATP via the Krebs cycle and the electron transport chain - they must first be covered to molecules that are part of the Krebs cycle or can enter (CoA)

Question 20

How are essential and nonessential amino acids different?

Answer 20

Essential (10 of 20) - must be present in the diet because they cannot be synthesized in the body in adequate amounts

Nonessential - can be synthesized by body cells, formed by transamination - transfer of an amino group from an amino acid to pyretic acid or to an acid in the Kreb’s cycle

Question 21

Where is protein anabolism carried out?

Answer 21

Carried out on the ribosomes of almost every cell in the body directed by the cells DNA and RNA

IGF, thyroid hormones, insulin, estrogen, and testosterone all stimulate protein synthesis

Question 22

What group is removed from an amino acid before it can enter the Krebs cycle, and what is this process called?

Answer 22

Amino group must be removed - process is called deamination which occurs in hepatocytes and produces ammonia

Question 23

Briefly describe the difference between metabolism during the absorptive state and post absorptive state

Answer 23

absorptive state - ingested nutrients are entering the bloodstream, and glucose is readily available for ATP production; stimulated by insulin

postaborptive state - absorption of nutrients from the GI tract is complete and energy needs must be met by fuels already in the body; stimulated by Epi, NE, cortisol, and glucagon

Question 24

Describe the dominant reactions that occur during the absorptive stage

Answer 24

1. 50% of glucose is oxidized to produce ATP via glycolysis, Krebs cycle, and the electron transport chain
2. Most glucose that enters hepatocytes is converted to glycogen; small amounts may be used for synthesis of fatty acids and glyceraldehyde 3-phosphate
3. Some fatty acids and triglycerides synthesized in the liver remain there but hepatocytes package most into VDLs for storage in adipose tissues
4. Adipocytes take up glucose no picked by liver and covert it into triglycerides for storage
5. Most dietary lipids are stored in adipose tissue; only small portion is used for synthesis reactions
6. Many absorbed amino acids that enter hepatocytes are delaminated to keto acids, which can either enter the Kreb’s cycle for ATP production or be used to synthesize glucose or fatty acids
7. Some amino acids enter hepatocytes and a re used to synthesize proteins
8. Amino acids not taken up by hepatocytes are used in other body cells for synthesis of proteins or regulatory chemicals

Question 25

Describe the dominant reactions that occur during the postabsorptive stage

Answer 25

The major reactions that produce glucose:
1. Breakdown of liver glycogen - continually being formed and broken down as needed

2. Lipolysisi - glycerol, produced by breakdown of triglycerides in adipose tissue, is also used to form glucose
3. Gluconeogensisi using lactic acid - in the liver lactic acid can be used for gluconeogenesis, and the resulting glucose is released into the blood
4. Glucogensisi using amino acids - occurs in the liver

The major reactions that produce ATP without using glucose:
5. Oxidation of fatty acids - they re fed into Krebs cycle as CoA and produce ATP via electron transport chain

6. Oxidation of lactic acid - cardiac muscle can produce ATP from lactic acid
7. Oxidation of amino acids - amino acids are oxide in hepatocytes
8. Oxidation of ketone bodies - hepatocytes covert fatty acid to seton bodies which can be used by tissues for ATP production
9. Breakdown of muscle glycogen - skeletal muscles break down glycogen to glucose 6-phosphate, which undergoes glycolysis and provides ATP for muscle contraction

Question 26

Define metabolic rate and describe how it is measured

Answer 26

Metabolic rate - the overall rate at which metabolic reactions use energy

Because many factors affect metabolic rate, it is measured under standard conditions, with the body in a quiet, resting, and fasting condition, called the basal state ‘

The measurement obtained under these conditions is the basal metabolic rate (BMR) - most commonly measured by the amount of O2 used /kcal of food metabolized

Question 27

Differentiate between core temperature and shell temperature

Answer 27

Core - the temp in body structures deep to the skin and subQ layer

Shell - temp near the body surface, in the skin and subQ layer (usually 1-6 deg lower than core temp)

If the rate of body heat production equals the rate of heat loss, the body maintains a constant core temp near 37 deg C

Question 28

The production of hear is proportional to metabolic rate - describe which factors affect the metabolic rate and thus the rate of heat production

Answer 28

1. Exercise - metabolic rate increases during strenuous exercise
2. Hormones - thyroid hormones regulate BMR; BMR increases as thyroid hormone levels increase (slow change tho)
3. Nervous system - sympathetic NS cause release of NE and Epi which increase metabolic rate
4. Body temp - the higher the body temp, the higher the metabolic rate
5. Ingestion of food - raises metabolic rate 10-20% due to energy of digesting, absorbing, and storing nutrients
6. Age - metabolic rate decreases as you age
7. Other factors: sex (lower in females), climate (lower in tropical regions), sleeping (lower), malnutrition (lower)

Question 29

Describe the 4 ways heat can be transferred from the body to its surroundings

Answer 29

1. Conduction - heat exchange that occurs between molecules of two materials that are in direct contract with each other (ex. jewellery with body)
2. Convection - transfer of hear by the movement of a fluid between areas of different temperature (ex. air conditioning fan would increase convection)
3. Radiation - transfer of heat in the form of infrared rays between a warmer object and a cooler one without physical contact (you lose more heat if the surrounding objects are cooler than you are)
4. Evaporation - conversion of liquid to vapor due to sweat, respiration; can be affected by the humidity of the air

Question 30

Describe how normal body temperature is maintained by negative feedback loops involving the hypothalamic thermostat

Answer 30

Thermoreceptors in the skin and mucous membranes of the hypothalamus and stimulated due to changes in temp and send nerve impsules to the prep-tic area of the hypothalamus

When temp is higher the prepoptic area generates nerve impulses at a higher frequency; and the opposite when temp is lower

These nerve impulses are propagated to two other areas of the hypothalamus: the heat-losing center and the heat-promoting center which when stimulated set in motion a series of responses that lower or raise body temp:

• vasoconstriction decreases heat loss
• skeletal muscles contract repeatedly (shivering)
• adrenal medulla and thyroid gland release hormones that increase cellular metabolism and metabolic rate to increase temp

If the body temp rises above normal, a negative feedback loop opposite from this occurs

Question 31

Define energy homeostasis and the 3 components that contribute to total energy expenditure

Answer 31

The precise matching of energy intake (in food) to energy expenditure over time - this results in a constant body weight

Energy intake depends only on the amount of food consumed (and absorbed), but three components contribute to total energy expenditure:

1. The basal metabolic rate accounts for about 60% of energy expenditure.
2. Physical activity typically adds 30–35% but can be lower in sedentary people.
3. Food-induced thermogenesis, the heat produced while food is being digested, absorbed, and stored, represents 5–10% of total energy expenditure.

Question 32

Describe nutrients and the 6 main types

Answer 32

Nutrients are chemical substances in for that body cells use for growth, maintenance, and repair

1. Water
2. Carbs
3. Lipids
4. Prtoeins
5. Minerals
6. Vitamins

Question 33

Define minerals and identify the major classes

Answer 33

Minerals are inorganic elements that occur naturally in the earth’s crust

Minerals with known functions in the body: calcium, phosphorus, potassium, surfer, sodium, chloride, magnesium, iron, iodide, manganese, copper, cobalt, zinc, fluoride, selenium, and chromium

Question 34

Define vitamines and describe their two main groups + antioxidant vitamins

Answer 34

Vitamines are organic nutrients required in small amounts to maintain growth and normal metabolism

Fat-soluble vitamins (A, D, E, K) are absorbed along with other dietary lipids in the small I and packed into chylomicrons and stored in hepatocytes

Water-soluble vitamins (B, C) are dissolved in body fluids and excess are excreted via urine

Antioxidant vitamins (E, C, and beta-carotene) inactive oxygen free radicals

Question 35

Define provitamins

Answer 35

The body can assemble some vitamins if the raw materials, called provitamins, are provided

Question 36

Describe a fever

Answer 36

Elevation of core temp caused by resetting of the hypothalamic thermostat typically due to infection or toxins