metabolism summary ch25

8/10/2019 Metabolism Summary Ch25

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METABOLISM

CHAPTER 25 SUMMARY

The food we eat, (carbohydrates, lipids, and proteins), are our onlysource of energy for doing the biological work of cells.

All molecules (nutrient molecules included) have energy stored in the

bonds between their atoms.

Three major metabolic uses for nutrients:. used immediately for energy for active processes!. synthesi"ed into structural or functional molecules#. synthesi"ed as fat or glycogen for later use as energy

$%&'AT&$*+'-T&$ *+A-T&$

$/idation 0 the removal of electrons from a molecule and results in a

decrease in the energy content of the molecule. 1ecause most biologicalreactions involve the loss of hydrogen atoms, they are calleddehydrogenation reactions.

*eduction 0 the opposite of o/idation2 the addition of electrons to amolecule, and results in an increase in the energy content of themolecule.

An important point to remember in $/idation*eduction reactions is thato/idation is usually an energyreleasing reaction.

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'uring digestion, polysaccharides are converted to monosaccharides(primarily glucose), which are absorbed through capillaries in villi andtransported to the liver via the hepatic portal veins.

7lucose is the body8s preferred source for synthesi"ing AT9.&f cells reuire immediate energy, glucose is o/idi"ed by the cells toproduce AT9.

7lucose can also be used to form amino acids, which then can beincorporated into proteins.

+/cess glucose can be stored by the liver (!;


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fatty acids that can be used for synthesis of triglycerides in a processcalled lipogenesis.

7lucose -atabolism:7lucose o/idation is also called aerobic or cellular respiration. &toccurs in every cell of the body (e/cept red blood cells because they

lack mitochondria), and provide the cells main source of energy.

The complete o/idation of glucose to -$!, 3!$ results in large amounts ofenergy (AT9) and occurs in successive stages: glycolysis, formation ofacetyl coen"yme A, the tricarbo/ylic acid cycle and the electrontransport system.

7lycolysis:. *efers to the breakdown of the si/carbon glucose molecule into twothreecarbon molecules of pyruvic acid.

!. 7lycolysis reactions use two AT9 molecules, but produce four,resulting in a net gain of two AT9.

#. 7lycolysis occurs in the cytoplasm of the cell.

>ormation of Acetyl -oen"yme A:. 9yruvic acid is prepard for entrance into the tricarbo/ylic acid cycle(?reb8s cycle)by conversion to a twocarbon compound (acetyl group)followed by the addition of coen"yme A (-oA) to form acetyl coen"yme A(acetyl -oA).

!. -oen"yme A is derived from pantothenic acid, a 1 vitamin.

Tricarbo/ylic Acid -ycle (T-A):. Also called the ?reb8s cycle or -itric Acid -ycle.

!. The T-A is a series of biochemical reactions that occurs in the matri/of mitochondria.

#. A large amount of chemical potential energy stored in intermediatesubstances derived from pyruvic acid is released step by step.

@. The T-A cycle involves decarbo/ylations, o/idations and reductions ofvarious organic acids.

;. >or every two molecules of acetyl -oA that enters the T-A cycle, 3B, A'3 and ! >A'3! are produced by o/idationreduction reactions and twomolecules of AT9 are generated.

+lectron Transport ystem:


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. &nvolves a seuence of electron carrier molecules on the innermitochondrial membrane, capable of a series of o/idationreductionreactions.

a) As electrons are passed through the chain, there is a steplikerelease of energy from the electrons which is used for the generation ofAT9.

b) in aerobic cellular respiration, the last electron receptor of thechain is molecular o/ygen ($!).

!. The process involves a series of o/idationreduction reactions inwhich the energy in A'3 and >A'3! is liberated and transferred to AT9for storage.

a) This mechanism of AT9 generation links chemical reactions (electronspassing along the electron chain) with pumping of hydrogen ion (3B).

b) This process is called chemiosis.

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

ummary of Aerobic -ellular *espiration:

-3!$ B $! DDDDDD -$! B 3!$ 0 # AT9CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

ote: -arbohydrate loading is the practice of eating large amounts ofcarbohydrates prior to an athletic endurance event such as a marathonrun. This is done to fill up the carbohydrate (glycogen) storage areasand provide additional energy for the marathon race. -arbohydrates arethe main source of energy for humans.

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The conversion of glucose to glycogen for storage in the liver andskeletal muscle is called glycogenesis. The process is stimulated byinsulin.

The conversion of glycogen back into glucose is called glycogenolysis.

This process occurs between meals and is stimulated by glucagon andepinephrine.

7luconeogenesis is the conversion of protein or fat molecules intoglucose. 7lycerol from fat can be converted to glyceraldehyde#phosphate and some amino acids may be converted to pyruvic acid. 1oth ofthese compounds can enter the T-A cycle to provide energy.


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6&9&' 5+TA1$6&5

5ost proteins are transported in the blood in combination with proteinsas lipoproteins. There are @ classes of lipoproteins:

. chylomicrons!. E6'68s (very low density lipoproteins)

#. 6'68s (low density lipoproteins)@. 3'68s (high density lipoproteins)

-hylomicrons:>orm in small intestinal mucosal cells and contain dietary lipids. Theyenter villi lacteals, are carried into the systemic circulation intoadipose tissue where their triglyceride fatty acids are released andstored in the adipocytes and used by muscle cells for AT9 production.

E6'68s:Are transport vehicles that carry triglycerides synthesi"ed in

hapatocytes to adipocytes for storage.

6'68s:-arry about =;< of total blood cholesterol and deliver it to cellsthroughout the body. Fhen present in e/cessive numbers, 6'68s depositcholesterol in and around smooth muscle fibers in arteries.

3'68s:*emove e/cess cholesterol from body cells and transport it to the liverfor elimination.

$T+:There are two sources of cholesterol in the body: food we eat, and liversynthesis.

>or adults, desirable levels of blood cholesterol are under !GG mgHd6 fortotal cholesterol2 6'6 under #G mgHd62 and 3'6 over @G mgHd6. ormally,triglycerides are in the range of GIG mgHd6.

+/ercise, diet and drugs may be used to reduce blood cholesterol levels.

>ate of 6ipids:

ome lipid may be o/idi"ed to produce AT9, where each unit of lipidproduces TF&-+ the amount of AT9 as an euivalent unit of carbohydrate.

ome lipids are stored in adipose tissue.

$ther lipids are used as structural molecules or to synthesi"e essentialmolecules. +/amples include phospholipids of cell membranes,lipoproteins that transport cholesterol, and cholesterol used tosynthesi"e bile salts and steroid hormones.


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Triglyceride torage:Triglycerides are stored in adipose tissue, mostly in the subcutaneouslayer.

Adipose cells contain lipases that hydroly"e fats into glycerol and fattyacids.

6&9&' AA1$6&5: 6ipogenesis

6ipogenesis 0 the conversion of glucose or amino acids into lipids.

6&9&' -ATA1$6&5: 6ipolysis

6ipolysis 0 triglycerides are split into fatty acids and glycerol.As a part of normal fatty acid catabolism, ketone bodies are formed.

An e/cess of ketone bodies (ketosis), may cause acidosis or abnormallylow blood p3.

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'uring digestion, proteins are hydroly"ed into amino acids, which arethen absorbed by the capillaries of villi and enter the liver via thehepatic portal vein.

Amino acids, under the influence of human growth hormone and insulin,enter the body cells by active transport.

&nside cells, amino acids are synthesi"ed into protein that function asen"ymes, transport molecules, antibodies, clotting chemicals, hormones,contractile elements in muscle fibers and structural elements such ashair. They may also be stored as fat or glycogen or used for energy.

9rotein -atabolism:1efore amino acids can be cataboli"ed, they must be converted tosubstances that can enter the T-A cycle. These conversions involvedeamination, decarbo/ylation, and hydrogenation.

Amino acids can be converted into glucose, fatty acids and ketone bodies.

9rotein Anabolism:&nvolves the formation of peptide bonds between amino acids to producenew proteins.

9rotein synthesis is stimulated by human growth hormone, thyro/ine, andinsulin.


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15* is also a measure of how much thyro/ine the thyroid gland isproducing, since thyro/ine regulates the rate of AT9 use and is not acontrollable factor under basal conditions.

3eat is a form of kinetic energy that can be measured as temperature ande/pressed in units called calories. A calorie is the amount of heatenergy reuired to raise the temperature of gram of water from @

degrees - to ; degrees -.

1ody Temperature 3omeostasis:&f the amount of heat production euals the amount of heat loss, a humanmaintains a constant core temperature of IK. degrees >, (#= degrees -).

-ore temperature refers to the body8s temperature in body structuresbelow the skin and subcutaneous tissue.

hell temperature refers to the body8s temperature at the surface (skinand subcutaneous tissue).

Too high a core temperature kills by denaturing proteins.Too low a core temperature causes cardiac arrhythmias that can result indeath.

3eat 9roduction:&s influenced by metabolic rate and responses that occur when bodytemperature starts to fall.

>actors that affect metabolic rate include e/ercise, hormones, thenervous system, body temperature, ingestion of food, age, gender,climate, sleep, and malnutrition.

3eat conservation mechanisms include vasoconstriction, sympatheticstimulation, skeletal muscle contraction (shivering), and thyroid hormoneproduction.

The hypothalamus is involved in thermoregulation and several negativefeedback loops are involve in raising or lowering body temperature whenit is too low or too high.

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Two centers in the hypothalamus related to regulation of food intake arethe feeding (hunger) center and the satiety center. The feeding centeris constantly active but can be inhibited by the satiety center.

timuli that affect the feeding and satiety centers are: glucose, aminoacids, lipids, body temperature, distention of the 7& tract and thehormone cholecystokinin (--?).


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E&TA5&

Eitamins are organic nutrients that maintain growth and normalmetabolism. 5any function in en"yme systems as coen"ymes.

5ost vitamins cannot be synthesi"ed by the body, and no single food

contains all of the reuired vitamins.

Two groups:

. >at soluble 0 are emulsified into micelles and absorbed along withingested dietary fats by the small intestine. They are stored in cells,especially liver cells, and include vitamins A, ', +, and ?.

!. Fater soluble 0 are absorbed along with water in the 7& tract anddissolve in the body fluids. +/cess uantities of these vitamins aree/creted in the urine. The body does not store watersoluble vitamins

well. They include the 1 vitamins and vitamin -.

Eitamins -, + and beta carotene are termed antio/idant vitamins becausethey inactivate o/ygen free radicals in cells. ee pages 929-930.____________________________________

+nd of 5etabolism ummary

metabolism summary ch25

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