metabolism chapter 25. an introduction to cellular metabolism figure 25–1
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Metabolism
Chapter 25
An Introduction to Cellular MetabolismFigure 25–1
Essential Nutrients
45 – 50 molecules must be ingested.
This includes representatives from the 4 major organic molecule groups, plus a number of inorganic substances such as including water, vitamins and minerals (Na, Fe, etc.)
The USDA has made major revision in its nutritional recommendations.
http://www.health.gov/dietaryguidelines/dga2005/document/
It was never based on solid science
Nutrient –A substance in food used by the body for growth,
maintenance, energy and repair.
• Carbohydrates: 271g (55%) 130g (45 - 65%)
• Lipid: total 65g (17%) 20 – 25%
saturated 17g (7.8%)
• Protein: 91g (18%) 56g (10 – 35%)
• Water: 1500 ml (average) per day.
USDA IOM for young adult female
Uses of nutrients
• Carbohydrate: Primary energy molecule. Also found on cell membranes and as part of structure of connective tissue matrix molecules
• Lipid: Energy storage, plasma membrane structure, cushioning, steroid hormones.
• Proteins: Enzymes, receptors, hormones, structures of all kinds. Must be “complete” or “complimentary” in order to supply essential amino acids.
Nutrient Use in Cellular Metabolism
Essential amino acids
10 Essential Amino Acids
• 8 not synthesized: – isoleucine, leucine, lysine, threonine,
tryptophan, phenylalanine, valine, and methionine
• 2 insufficiently synthesized:– arginine and histidine
4 Types of Nitrogen Compounds
1. Amino acids:– framework of all proteins, glycoproteins, and
lipoproteins
2. Purines and pyrimidines:– nitrogenous bases of RNA and DNA
4 Types of Nitrogen Compounds
3. Creatine:– energy storage in muscle (creatine
phosphate)
4. Porphyrins:– bind metal ions– essential to hemoglobin, myoglobin, and
cytochromes
Energy Metabolism
• Metabolism = catabolism + anabolism
• Cellular respiration is a series of catabolic reactions that provide energy for the production of
• This energy is used to generate ATP from phosphorylation of ADP.
• It is a series of Redox reactions.
ATP
Energy Metabolism: Generation of ATP
Overview of aerobic respiration
Summary of steps of energy
metabolism
Generation of ATP by “substrate-level phosphorylation”
Oxidative phosphorylation
Overview of cellular respiration
Carbohydrate Metabolism
C6H12O6 + 6 O2 6 CO2 + 6 H2O + 36 ATP + Heat
Oxidation of Glucose
It is the first stage in cellular respiration
Glycolysis
Stepsof
glycolysis
Aerobic vs anaerobic pathways
Overview of TCA (Krebs cycle)
TCA(Krebs) Cycle
Summary: The TCA Cycle
CH3CO — CoA + 3NAD + FAD + GDP + Pi + 2 H2O CoA + 2 CO2
+ 3NADH + FADH2 + 2 H+ + GTP
The ETS creates an chemiosmotic
gradient
The Electron Transport System
The ETS
Summary of ATP synthesis Gains & losses
Visual summary of
cellular respiration
Carbohydrate Breakdown
and Synthesis
Figure 25–7
Glycogenesis/Glycogenolysis
Gluconeogenesis
• Is the synthesis of glucose from noncarbohydrate precursors:– lactic acid– glycerol– amino acids
• Stores glucose as glycogen in liver and skeletal muscle
Summary of metabolic pathways
Lipid metabolism: oxidation
3 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
Lipid Transport
and Utilization
Figure 25–9
5 Classes of Lipoproteins
• Chylomicrons
• Very low-density lipoproteins (VLDLs)
• Intermediate-density lipoproteins (IDLs)
• Low-density lipoproteins (LDLs)
• High-density lipoproteins (HDLs)
Chylomicrons
• Are produced in intestinal tract
• Are too large to diffuse across capillary wall
• Enter lymphatic capillaries
• Travel through thoracic duct:– to venous circulation and systemic arteries
Distribution of Other Lipoproteins: Step 1
• Liver cells synthesize VLDLs:– for discharge into bloodstream
Distribution of Other Lipoproteins: Step 2
• Lipoprotein lipase removes many triglycerides from VLDLs:– leaving IDLs
• Triglycerides are broken down:– into fatty acids and monoglycerides
Distribution of Other Lipoproteins: Step 3
• When IDLs reach liver:– additional triglycerides are removed– protein content of lipoprotein is altered– LDLs are created
• LDLs are transported to peripheral tissues to deliver cholesterol
Distribution of Other Lipoproteins: Step 4
• LDLs leave bloodstream through capillary pores:– or cross endothelium by vesicular transport
Distribution of Other Lipoproteins: Step 5
• In peripheral tissues:– LDLs are absorbed through receptor-
mediated endocytosis
• Amino acids and cholesterol enter the cytoplasm
Distribution of Other Lipoproteins: Step 6 & 7
• Cholesterol not used by the cell:– diffuses out of cell
• Cholesterol reenters bloodstream:– is absorbed by HDLs and returned to liver
Distribution of Other Lipoproteins: Step 8
• In the liver:– HDLs are absorbed – cholesterol is extracted
• Recovered cholesterol is used:– in synthesis of LDLs– in excreted in bile salts
Distribution of Other Lipoproteins: Step 9
• Free HDLs are released into bloodstream:– travel into peripheral tissues– absorb additional cholesterol
Composition of
Lipoproteins
Proteins
• 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
Amino Acid CatabolismFigure 25–10 (Navigator)
AminationFigure 25–11
Amino acid use in TCA
cycle
Protein metabolism in the Liver
Summary: Pathways of Catabolism and Anabolism Figure 25–12
5 Metabolic TissuesEach tissue has its own requirements
1. Liver
2. Adipose tissue
3. Skeletal muscle
4. Neural tissue
5. Other peripheral tissues
Other Peripheral Tissues
• Do not maintain large metabolic reserves
• Can metabolize glucose, fatty acids, and other substrates
• Preferred energy source varies:– according to instructions from endocrine
system
Metabolic Interactions
• Relationships among 5 components change over 24-hour period
• Body has 2 patterns of daily metabolic activity:
1. absorptive state 2. postabsorptive state
Regulatory Hormones: Effects on Peripheral Metabolism
Table 25–1
Pathways of the
Absorptive state
The effects of insulin on
metabolism
The Postabsorptive state
Influences of
Glucagon on blood glucose levels
Lipid and Amino Acid Catabolism
• Generates acetyl-CoA
• Increased concentration of acetyl-CoA:– causes ketone bodies to form
Ketone Bodies
• Acetoacetate
• Acetone
• Betahydroxybutyrate
Ketone Bodies
• Liver cells do not catabolize ketone bodies:– compounds diffuse into general circulation– peripheral cells absorb ketone bodies
• Cells reconvert ketone bodies to acetyl-CoA for TCA cycle
Ketone Bodies
• Are acids that dissociate in solution
• Fasting produces ketosis:– a high concentration of ketone bodies in body
fluids
Ketonemia
• Is the appearance of ketone bodies in bloodstream
• Lowers plasma pH, which must be controlled by buffers
Ketoacidosis
• Is a dangerous drop in blood pH:– caused by high ketone levels– exceeding buffering capacities
Severe Ketoacidosis
• Circulating concentration of ketone bodies can reach 200 mg dl:– pH may fall below 7.05– may cause coma, cardiac arrhythmias, death
Minerals and Vitamins
• Are essential components of the diet
• The body does not synthesize minerals
• Cells synthesize only small quantities of few vitamins
Minerals and Mineral ReservesTable 25–3
Minerals
• Are inorganic ions released through dissociation of electrolytes
Importance of Minerals
• Ions such as sodium, chloride and potassium determine osmotic concentrations of body fluids
• Ions are essential:– cofactors in many enzymatic reactions– in many important physiological processes
Metals
• Each component of ETS requires an iron atom
• Final cytochrome of ETS requires a copper ion
Mineral Reserves
• The body contains significant mineral reserves:– that help reduce effects of variations in diet
The Fat-Soluble Vitamins
Table 25–4
Fat-Soluble Vitamins
• Vitamins A, D, E, and K:– are absorbed primarily from the digestive tract
along with lipids of micelles– normally diffuse into cell membranes and
lipids in liver and adipose tissue
Vitamin A• A structural component of visual pigment
retinal
Vitamin D• Is converted to calcitriol:
– which increases rate of intestinal calcium and phosphorus absorption
Vitamin E• Stabilizes intracellular membranes
Vitamin K
• Helps synthesize several proteins:– including 3 clotting factors
Vitamin Reserves
• The body contains significant reserves of fat-soluble vitamins
• Normal metabolism can continue several months without dietary sources
The Water-Soluble VitaminsTable 25–5
Metabolic Rate
• If daily energy intake exceeds energy demands:– body stores excess energy as triglycerides in
adipose tissue
• If daily caloric expenditures exceeds dietary supply:– body uses energy reserves, loses weight
Hormonal Effects
• Thyroxine:– controls overall metabolism
– T4 assay measures thyroxine in blood
• Cholecystokinin (CCK):– suppresses appetite
• Adrenocorticotropic hormone (ACTH):– suppresses appetite
• Leptin:– released by adipose tissues during absorptive
state– binds to CNS neurons that suppress appetite
Heat Balance
Regulatory pathways for homeostatic
control of body
temperature
Temperature regulation mechanisms
Maynard or Hans?