3 metabolism of carbohydrates

7/26/2019 3 Metabolism of Carbohydrates

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An Overview of

Metabolism


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Metabolism is all the chemical reactions thatoccur in an organism

Cellular metabolism Cells break downexcess carbohydrates rst, then

lipids, nally amino acids if energy needs are notmet by carbohydrates and fat

Nutrients not used for energy are used to build upstructure, are stored, or they are excreted

4! of the energy released in catabolism iscaptured in A"#, the rest is released as heat

Metabolism


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#erformance of structuralmaintenance and repairs

$upport of growth

#roduction of secretions

%uilding of nutrient reserves

Anabolism


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%rea&down of nutrients toprovide energy 'in the form ofA"#( for body processes Nutrients directly absorbed

$tored nutrients

Catabolism


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Cells provide small organicmolecules to mitochondria

Mitochondria produce A"#used to perform cellularfunctions

Cells and Mitochondria


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Carbohydrate Metabolism #rimarily glucose

)ructose and galactose enter the pathways at various points

All cells can utili*e glucose for energy production

+lucose upta&e from blood to cells usually mediated byinsulin and transporters

iver is central site for carbohydrate metabolism +lucose upta&e independent of insulin

"he only exporter of glucose


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%lood +lucose

-omeostasis $everal cell types prefer glucose as

energy source 'ex., CN$(

/01 mg2dl is normal range of bloodglucose in non0ruminant animals4303 mg2dl is normal range of bloodglucose in ruminant animals

5ses of glucose67nergy source for cellsMuscle glycogen)at synthesis if in excess of needs


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)ates of +lucose )ed state

$torage as glycogen iver

$&eletal muscle

$torage as lipids Adipose tissue

)asted state Metaboli*ed for energy

New glucose synthesi*ed

$ynthesis andbrea&down occur

at all timesregardless of

state...

"he relative ratesof synthesis and

brea&down


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-igh %lood+lucose

+lucoseabsorbed

Insulin:Glucagon

#ancreas

Muscle

AdiposeCells

+lycogen

+lucoseabsorbed

+lucoseabsorbed

immediately after eating a meal


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+lucose Metabolism )our ma8or metabolic pathways6

7nergy status of body regulates whichpathway gets energy

$ame in ruminants and non0ruminants

9mmediate source of energy

#entophosphate pathway+lycogen synthesis in liver2muscle#recursor for triacylglycerol synthesis


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)ate of Absorbed +lucose 1st#riority6 glycogen storage

$tored in muscle and liver

:nd#riority6 provide energy Oxidi*ed to A"#

;rd#riority6 stored as fat Only excess glucose

$tored as triglycerides in adipose


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+lucose

5tili*ation

Glucose

PyruvateRibose-5-phosphate

Glycogen7nergy$tores

#entose#hosphate#athway

+lycolysis

Adipose


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+lucose

5tili*ation

Glucose



#entose#hosphate#athway

+lycolysis

Adipose


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+lycolysis $eoes not re


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+lycolysis

+lucose ? : A># ? : #i

: actate ? : A"# ? : -:O


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Adenosine "ri0#hosphate 'A"#( in& between energy releasing and

energy re# ? # ? 7nergy A"#


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Mechanisms of A"# )ormation $ubstrate0level phosphorylation

$ubstrate transfers a phosphate group

directly =e# Creatine ? A"#

Oxidative phosphorylation Method by which most A"# formed $ubstrate transfers electrons to

transporter which enters the electrontransport chain


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)irst =eaction of +lycolysis

"raps glucose in cells 'irreversible in muscle cells(

-exo&inase is used by most plants, animals,and microbes to phosphorylate glucose

+luco&inase in hepatic tissue

Cows do not have hexo&inase


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+lycolysis 0 $ummary+lucose

: #yruvate

: A"#

:A>#

4 A>#

4 A"#

:

NA>

: NA>- ? -


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#yruvate Metabolism"hree fates of pyruvate6

Conversion to lactate 'anaerobic(Conversion to alanine 'amino acid(7ntry into the "CA cycle via pyruvatedehydrogenase pathway


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Anaerobic

Metabolism of#yruvate #roblem6 >uring glycolysis, NA>- is formed from

NA>?

Bithout O:, NA>- cannot be oxidi*ed to

NA>?

No more NA>?

All converted to NA>- Bithout NA>?, glycolysis stops


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Anaerobic

Metabolism of#yruvate $olution6

"urn NA>- bac& to NA>?by ma&ing lactate

'lactic acid(

COO

C O

CH3

COO

HC OH

CH3

LactatePyruvate

Lactate dehydrogenase

NADH + H+

NAD+

(oxidized) (reduced)

(oxidized)(reduced)


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Anaerobic

Metabolism of#yruvate A"# yield"wo A"#s 'net( are produced

in the anaerobic brea&down of oneglucose"he : NA>-s are used to reduce :

pyruvate

to : lactate =eaction is fast and doesnDt re


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#yruvate Metabolism 0

Anaerobic#yruvate actate

NA>- NA>?

actate >ehydrogenase

actate can be transported by blood to liver andused in gluconeogenesis


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Cori Cycle

actate is

converted topyruvate in the liver


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#yruvate metabolism

Convert to alanine and export to blood

COO

C O

CH3

COO

HC NH3+

CH3Alanine amino transferase

(AAT)

AlaninePyruvate

Glutamate -Ketoglutarate

Eeto acid Amino acid


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#yruvate >ehydrogenase

Complex '#>-( #repares pyruvate to enter the "CA cycle

7lectron"ranspor

t Chain

"CACycle

Aerobic Conditions


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#>- 0 $ummary#yruvate

AcetylCoA

:NA>

: NA>- ? -

CO:


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"CA Cycle 9n aerobic conditions "CA cycle lin&s

pyruvate to oxidative phosphorylation

Occurs in mitochondria +enerates F! of energy released from

feed

$trategy is to oxidi*e acetyl0CoA to CO:and

capture energy as NA>-')A>-:( and A"#

Metaboli*es carbohydrate, protein, and fat


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"CA Cycle 0

$ummaryAcetylCoA

;NA>

; NA>- ?-

1 )A>

1 )A>-:

1A>#

1 A"#


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#hosphorylation


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=e


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Oxidation and 7lectron"ransport Oxidation of nutrients releases

stored energy )eed donates -?

-?Ds transferred to co0substrate

NA>?? :-?? :e0 NA>- ? -?)A> ? :-?? :e0 )A>-:


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$o, Bhat +oes to the

7"$GGG

)rom each molecule of glucose entering

glycolysis61. )rom glycolysis6 : NA>-

:. )rom the "CA preparation step 'pyruvate to acetyl0CoA(6 :NA>-

;. )rom "CA cycle '"CA( 6 NA>- and : )A>-:

"O"A6 1 NA>- ? : )A>-:


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7lectron "ransport Chain NA>- ? -?and )A>-:enter 7"C

"ravel through complexes 9 H 9I

-?Jow through 7"C and eventuallyattach to O:forming water

NA>- ? -? ; A"#

)A>-: : A"#


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7lectron "ransport Chain


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"otal A"# from +lucose Anaerobic glycolysis H : A"# ? :

NA>-

Aerobic metabolism H glycolysis ?"CA

31 ATP from 1 glucose molecule


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Iolatile )atty Acids #roduced by bacteria in the fermentation of

pyruvate #rovides important energy sources for animals,

particularly ruminants or those that rely oncellulose as a &ey carbohydrate in their diet "hree ma8or I)As

Acetate 7nergy source and for fatty acid synthesis

#ropionate 5sed to ma&e glucose through gluconeogenesis

%utyrate 7nergy source and for fatty acid synthesis $ome use and metabolism 'alterations( by rumen wall and

liver before being available to other tissues


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5se of I)A for 7nergy 7nter "CA cycle to be oxidi*ed

Acetic acidKields 1 A"#

#ropionic acidKields 1/ A"#

%utyric acidKields :L A"# ittle butyrate enters blood


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5tili*ation of I)A inMetabolismAcetate 7nergy Carbon source for fatty acids

Adipose

Mammary gland

Not used for net synthesis of glucose#ropionate

7nergy #recursor of glucose

%utyrate 7nergy Carbon source for fatty acids 0 mammary


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7ect of I)A on 7ndocrine$ystemPropionate9ncreases blood glucose$timulates release of insulin

ButyrateNot used for synthesis of glucose$timulates release of insulin$timulates release of glucagon

9ncreases blood glucoseAcetate

Not used for synthesis of glucose>oes not stimulate release of insulin

Glucose

$timulates release of insulin


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Oxidation and 7lectron"ransport Oxidation of nutrients releases

stored energy )eed donates -?

-?Ds transferred to co0substrate

NA>?? :-?? :e0 NA>- ? -?)A> ? :-?? :e0 )A>-:


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#hosphorylation


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A %=97) 9N"7=5>7


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Need More 7nergy 'More

A"#(GG Bor&ing animals

-orses, dogs, dairy cattle, hummingbirds 9ncrease carbon to oxidi*e

9ncreased gut si*e relative to body si*e

9ncreased feed inta&e 9ncreased digestive en*yme production 9ncreased ability to process nutrients

9ncreased liver si*e and blood Jow to liver 9ncreased ability to excrete waste products

9ncreased &idney si*e, glomerular ltration rate 9ncreased ability to deliver oxygen to tissues and get rid of

carbon dioxide ung si*e and eciency increases -eart si*e increases and cardiac output increases 9ncrease capillary density

9ncreased ability to oxidi*e small carbon chains 9ncreased numbers of mitochondria in cells

ocate mitochondria closer to cell walls 'oxygen is lipid0soluble(


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-ummingbirds ung oxygen diusing ability /.3 times

greater than mammals of similar body

si*e -eart is : times larger than predicted for

body si*e

Cardiac output is 3 times the body mass

per minute Capillary density up to times greater

than expected


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=ate of A"# #roduction

')astest to $lowest( $ubstrate0level phosphorylation

#hosphocreatine ? A># Creatine ? A"#

Anaerobic glycolysis +lucose #yruvate actate

Aerobic carbohydrate metabolism +lucose #yruvate CO:and -:O

Aerobic lipid metabolism )atty Acid Acetate CO:and -:O


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#otential Amount of 7nergy#roduced'Capacity for A"# #roduction( Aerobic lipid metabolism

)atty Acid Acetate CO: and -:O Aerobic carbohydrate metabolism

+lucose #yruvate CO: and -:O Anaerobic glycolysis

+lucose #yruvate actate $ubstrate0level phosphorylation

#hosphocreatine ? A># Creatine ? A"#


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+lucose5tili*ation

Glucose



#entose

#hosphate#athway

+lycolysis

Adipose


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#entose #hosphate #athway $econdary metabolism of glucose

#roduces NA>#- $imilar to NA>- =e


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#entose #hosphate #athway+lucose00phosphat

e

0#hospho0glucono0

lactone

0#hospho0gluconate

>0=ibulose030

phosphate

>0=ibose030

phosphate

=NA or

>NA


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+lucose5tili*ation

Glucose



#entose

#hosphate#athway

+lycolysis

Adipose


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7nergy $torage 7nergy from excess carbohydrates

'glucose( stored as lipids in adipose

tissue Acetyl0CoA 'from "CA cycle( shunted to

fatty acid synthesis in times of energyexcess >etermined by A"#6A># ratios

-igh A"#, acetyl0CoA goes to fatty acid synthesis ow A"#, acetyl CoA enters "CA cycle to generate

MO=7 A"#


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+lucose5tili*ation

Glucose



#entose

#hosphate#athway

+lycolysis

Adipose

+lycogenesis


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iver LH1! of wet weight

5se glycogen to export glucose to thebloodstream when blood sugar is low

+lycogen stores are depleted afterapproximately :4 hrs of fasting 'in

humans( De novosynthesis of glucose for

glycogen

+lycogenesis


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+lycogenesis

$&eletal muscle 1! of wet weight

More muscle than liver, therefore moreglycogen in muscle, overall

5se glycogen 'i.e., glucose( for energyonly 'no export of glucose to blood(

5se already0made glucose forsynthesis of glycogen


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)ates of +lucose

)ed state $torage as glycogen

iver

$&eletal muscle $torage as lipids

Adipose tissue

)asted state Metaboli*ed for energy

New glucose synthesi*ed

$ynthesis andbrea&down occur

at all timesregardless of

state...

"he relative ratesof synthesis and

brea&down


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+luconeogenesis

Necessary process +lucose is an important fuel

Central nervous system =ed blood cells

Not simply a reversal of glycolysis

9nsulin and glucagon are primaryregulators


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+luconeogenesis

Iital for certain animals =uminant species and other pre0gastric

fermenters Convert carbohydrate to I)A in rumen

ittle glucose absorbed from small intestine

I)A can not fuel CN$ and =%C

)eline species >iet consists primarily of fat and protein ittle to no glucose absorbed

+lucose conservation and gluconeogenesisare vital to survival


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)asting $ituation in Non0

=uminants Bhere does re


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ow %lood+lucose

#roteins %ro&en>own

Insulin:Glucago

n

#ancreas

Muscle

AdiposeCells

+lycogen

+lycerol, fatty acidsreleased

+lucose released

In a fasted state, substrates for glucosesynthesis (gluconeogenesis) are released

from storage!


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+luconeogenesis

$ynthesis of glucose from non0carbohydrate precursors during fasting inmonogastrics

Occurs primarily in liver, but can also occurin &idneys and small intestine

+lycerolAmino acidsactate#yruvate#ropionate

"here is no glucose synthesis from fatty acids

$upply carbon s&eleton


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Carbohydrate Comparison #rimary energy substrate

#rimary substrate for fat synthesis

7xtent of glucose absorption from gut

MO$" monogastrics P glucose=uminant2pre0gastric fermenters P I

MO$" monogastrics P glucose

=uminant P acetate

MO$" monogastrics P extensive

=uminant P little to none


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Carbohydrate Comparison Cellular demand for glucose

9mportance of gluconeogenesis

Eetone production

Nonruminant P high=uminant P high

MO$" monogastrics P less important

=uminant P very important

MO$" monogastrics P abnormal

3 metabolism of carbohydrates

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