Integration of Metabolism in Integration of Metabolism in Energy, Protein and LipidsEnergy, Protein and Lipids

Metabolism Metabolism

• A term referring to all chemical reactions necessary to maintain life. Substances are constantly being broken down and built up.

– Catabolism: complex structures broken down into simpler ones (digestion)

– Anabolism: larger molecules are built from small ones (like AA’sproteins)

The Nutrient PoolThe Nutrient Pool

• Contains all organic building blocks cell needs:– to provide energy– to create new

cellular components

6 categories of nutrients• Carbohydrates• Lipids• Proteins• Vitamins• Minerals• Water

Lipids release 9.46 C/gCarbohydrates release 4.18 C/gProteins release 4.32 C/g

Carbohydrates Carbohydrates

• Dietary sources–Predominately plants–Sugars – fruits, honey, milk, candy, soda–Starch – grains, legumes, root veggies–Cellulose – veggies

Carbohydrates, cont.Carbohydrates, cont.

• Uses in the body– Glucose is a major fuel to make ATP

• Carbohydrate digestion yields fructose and galactose, liver converts them to glucose before circulation

– *when glucose is in excess, it is converted to glycogen or fat and stored for later use*

Lipids Lipids

• Brown fat had a small molecule, more blood vessels, low ATP produced and make more EN than White fat (Birth animal)

• Wild animal had lean meat (low marbling) and more PUFA ( >30% total FA vs. 12% in domestic animal )

• FUFA in wild ani. made unfavour meat from FUFA-phospholipids

form.

Lipids, cont.Lipids, cont.

Glycogen & Lactic cycle ( Cori cycle)Glycogen & Lactic cycle ( Cori cycle)

Insulin moving glucose to glycogen (storage in liver, mm)

Glucagon activate glycogenolysis for glucose in Liver, and Lactic in MM.

ProteinsProteins

• Dietary sources–Primarily animal products (eggs, milk,

meat)–Legumes, nuts, & cereals are nutritionally

incomplete because they are low in one or more essential AA’s

Proteins, cont.Proteins, cont.

• Uses in the body– Structural materials (collagen, elastin, keratin)– Functional proteins (enzymes, hemoglobin, H’s)

• Hormonal controls– Anabolic hormones accelerate protein synthesis

• i.e. growth hormone, sex hormones, adrenal glucocorticoids, etc.

Proteins, cont.Proteins, cont.

• Adequacy of caloric intake–For protein synthesis you must have

adequate intake of carb’s & fats for ATP production

»If not…dietary & tissue proteins are used for En

Energy Yield of Aerobic MetabolismEnergy Yield of Aerobic Metabolism

• For 1 glucose molecule processed, cell gains 36 molecules of ATP:– 2 from glycolysis– 4 from NADH generated

in glycolysis– 2 from TCA cycle (through

GTP)– 28 from ETS

Carbohydrate Synthesis Carbohydrate Synthesis and Breakdownand Breakdown

Figure 25–7

• Gluconeogenesis - the synthesis of glucose from noncarbohydrate precursors:– lactic acid, glycerol, & AA’s– Stores glucose as glycogen in liver and

skeletal muscle

• Glycogenesis - the formation of glycogen from glucose

• Glycogenolysis - Is the breakdown• of glycogen to

glucose

LipolysisLipolysis

• Breaks lipids down into pieces that can be converted to pyruvic acid & channeled directly into TCA cycle

• Hydrolysis splits triglyceride into component parts:– 1 molecule of glycerol & 3 fatty acid molecules

• Different enzymes convert fatty acids to acetyl-CoA (beta-oxidation)

Fat & Glucose in Non RuminantFat & Glucose in Non Ruminant

Fat & Glucose in RuminantFat & Glucose in Ruminant

3 Energy Benefits of Beta-Oxidation3 Energy Benefits of Beta-Oxidation

1. For each 2-carbon fragment removed from fatty acid, cell gains:

– 12 ATP from acetyl-CoA in TCA cycle– 5 ATP from NADH

2. Cell can gain 144 ATP molecules from breakdown of one 18-carbon fatty acid molecule

3. Fatty acid breakdown yields about 1.5 times the energy of glucose breakdown

Free Fatty Acids (FFAs)Free Fatty Acids (FFAs)

• Are lipids that can diffuse easily across cell membranes

• In blood, are generally bound to albumin (most abundant plasma protein)

• Are an important energy source:– during periods of starvation when glucose

supplies are limited• Liver cells, cardiac muscle cells, skeletal

muscle fibers, etc. metabolize free fatty acids

ProteinsProteins

• The body synthesizes 100,000 to 140,000 proteins:– each with different form, function, and

structure

• All proteins are built from the 20 amino acids

Protein MetabolismProtein Metabolism

• Cellular proteins are recycled in cytosol:– peptide bonds are broken– free amino acids are used in new proteins

• If other energy sources are inadequate:– mitochondria generate ATP by breaking down

amino acids in TCA cycle

• Not all amino acids enter cycle at same point, so ATP benefits vary

3 Factors Against Protein Catabolism3 Factors Against Protein Catabolism

1. Proteins are more difficult to break apart than complex carbohydrates or lipids

2. A by-product, ammonium ion, is toxic to cells3. Proteins form the most important structural

and functional components of cells

Protein Synthesis Protein Synthesis

• The body synthesizes half of the amino acids needed to build proteins (Nonessential AA’s)– amino acids made by the body on demand

• 10 essential AA’s:– 8 not synthesized: isoleucine, leucine, lysine,

threonine, tryptophan, phenylalanine, valine, and methionine

– 2 insufficiently synthesized: arginine and histidine

Summary: Pathways of Catabolism and Summary: Pathways of Catabolism and AnabolismAnabolism

Figure 25–12

Metabolic InteractionsMetabolic Interactions

Body has 2 patterns of daily metabolic activity:

1. absorptive state 2. postabsorptive state

The Absorptive StateThe Absorptive State

• Is the period following a meal when nutrient absorption • most excess metabolites will be converted to fat for storage if

not used in anabolism• carbs-->liver to covert to glu-->released to blood or makes &

stores glycogen & makes fat to release to blood for storage by adipocytes

• triglycerides-->FA’s + glycerol-->sk mm, liver cells, & adipocytes use FA’s as primary E source-->most FA’s & glycerol re-enter adipose tissue & reconvert to triglycerides for storage

• AA’s-->some to liver for deamination to keto acids-->Kreb’s for ATP formation or conversion to liver fat stores; liver uses some AAs for plasma protein synthesis but most go into general circulation for uptake by other body cells to use for anabolism

The Postabsorptive StateThe Postabsorptive State

• When nutrient absorption is not under way (fasting state)• Primarily catabolic to maintain blood glucose levels w/in

normal range b/t meals– glycogenolysis in liver can maintain blood glu levels for ~ 4 hrs– glycogenolysis in skeletal mm - glucose cannot be released to

blood as w/liver (lacks all necessary enzymes) but…partial oxidation to pyruvic acid (or lactic acid) occurs-->goes to liver for conversion back to glucose & is released to blood

– lipolysis in adipose tissue & liver -->leads to glycerol-->liver converts to glucose & releases to the blood

– catabolism of cellular protein - primary source of blood glucose w/fasting (glycogen stores are depleted)-->AAs are deaminated & coverted to glucose in liver & are released to blood

Glucose for EnergyGlucose for Energy

• enzymes break apart glucose – yielding energy

• inadequate supply of carbohydrates– ketone bodies (fat fragments) are an alternate

energy source during starvation– excess ketones can lead to ketosis: imbalance

of acids in body

Protein MetabolismProtein Metabolism

• protein turnover– constant making and breaking of

proteins• frees amino acids to “amino acid pool”

– can be used to make body proteins– nonessential amino acids can be made from

other amino acids

• amino acid pool– Excreat of nitrogens and made available for

energy• deamination

– make fat• amino acids are deaminated, nitrogen is

excreted, carbon is converted to fat and stored• protein-rich foods can cause weight gain

Feasting and Fasting

Feasting and Fasting

FastingFasting

• several hours after a meal, glucose is used up

• protein is used for energy• shift to ketosis

– suppresses appetite

• hormones slow metabolism• eventually starvation

Regulatory Hormones on MetabolismRegulatory Hormones on Metabolism

Table 25–1

Basal Metabolic Rate (BMR)Basal Metabolic Rate (BMR)

• Is the minimum resting energy expenditure:– Involves monitoring respiratory activity– Energy utilization is proportional to oxygen

consumption

Hormonal EffectsHormonal Effects

• Thyroxine:– controls overall metabolism

• Cholecystokinin (CCK):– suppresses appetite

• Adrenocorticotropic hormone (ACTH):– suppresses appetite

• Leptin:– released by adipose tissues– binds to CNS neurons that suppress appetite

Heat ProductionHeat Production

• BMR estimates rate of energy use• Energy not captured is released as heat:

– serves important homeostatic purpose

ThermoregulationThermoregulation

• The body produces heat as by-product of metabolism

• Increased physical or metabolic activity generates more heat

• Body controls heat gains and losses to maintain homeostasis