Intro to carbs and glycolysis Flashcards Preview

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Flashcards in Intro to carbs and glycolysis Deck (38):

When does de novo synethesis of glucose occur?

This is gluconogenosis and this occurs during fasting when blood glucose levels are falling and glucose is needed for certain organs


What and when does glycogenesis take place?

When glucose levels from diet are more than needed, the excess is stored as glycogen through glycogenesis


When need the glycogen is degraded through glycogenolysis


Go from Glycogen to lactate


What are the two minor pathways of glucose

Hexose monophosphate shunt- produces ribose-phosphate for nucleotide synthesis and NADPH that supplies power for bopsynthetic reactoin (making fatty acids)


Galatose and fructose metabolime-- can sytnehsize sugar and sugar derivitatives.


Where can glucose be obtained from

Storage (glycogen) or diet


In storage glycogen is cnoverted to glucose or glucose 6-phosphate


Glcuose from diet has different sources. What are they? examples of each kind

Monosaccarides- honey and fruit- these can be easily absorbed by enterocytes

Disaccarides- milk sugar (lacatose) and table sugar (sucrose)- hudorlyzed by enzymes in the brush border of intestinal tract


Polysaccarides- starch (from plants) and glycogen(animals from their storage) and they contain alpha 1-4 glycosdies linkages and alpha 1-6 glycosidic linkages


What is lactose, sucrose and trehalose composed of

Lactose- glucose and galactose
Sucrose- glucose and fructose

Trehalose di-glucose


Where does the major daily caloric intake come from? How is each absorbed?


CARBS! mono, di and poly


1. Monosaccharides are absorbed directly;

2. disaccharides are digested by
intestinal surface enzymes
3. polysaccharides need to
be reduced to smaller molecules


Explain the absorption of strach and glycogen

1. The amylose chains (1-4 glycosidic chain/ linear) are degraded by alpha-amylase in the saliva and pancreatic juices
 making glucose, maltose (di) and maltotriose (tri).

2. The 1-6 glycosidic chains (amylopectin/branched) are hydolyzed by isomaltase

3. Further digestion of oligiosaccharides occurs on the surface of the intestinal epithelial cells by alpha-glucosidases (maltases)

4. Oligosacc not hydolyzed by amlyase or intesintal enzymes reach the ileum where bateriametablizes the sugas anerobically to short fatty acids, H2, methane and CO2


What happens in pathology of digestion? Explain oral tolerance test>


Undigested disaccharides go to the LI and they cause osmotic diarheea. Bacterial digestion results in production of large amounts of CO2, methane and hydrogen gas.


Oral tolerance test can measure the amout of hydrogen gas in a breath and can identify enzyme deficieny


What can cause disaccharide intolerance?

1. Loss of brush cells in intestinal tract

2. Intesitnal disease

3. Drugs that damage the mucosa of the SI


Temp disorder can lead to severe diarhea


Explain what happens when someone is lactase intolerant

Latase definicity so lactose passes into the LI where it is digested by bacteria causing GI distress, cramping, bloating due to the CO2 and methane that is being produced.


What is isomaltase sucrose deficienty

Results in intolerance to sucrose. in about 10% of greenland eskimos and 2% of NAmericans are heterozygous


Where do intestinal cells obtain energy?

From glutamine metabolism--- they don't depend on glucose


How and by what are monosacc absorbed?


What is the exception?

By entercytes through facilitated diffusion


Pentoses and L-sugars enter through passive transport (so we can use xylose to test ability of mucosal cells for absorption)


How does glucose and ____ get absorbed?


Difference from mannose



Through the Na-monosaccharide (SGLT-1)  co transporter driven by Na gradient and the hydrolyze of ATP, so the mono sacc can go against it's gradient



** this is different from the Na-dependent transporter used for manose***


What does GLUT-5 transport?



What passes through GLUT-2?

Glut -2 transports all monosacc through the membrane of the lumen into the capillaries. CAn pas glucose, galactose, fructose


steps after monosacc have passed into the capillary through the Glut-2

Monosaccs. go to the liver. Gluocse is distributed into general circulation, while galactose, fructose and mannose are processed by the liver


Why can every cell use glycolysis? Names cells that only use it

Because its anerobic and doesn't require O2


Scelera, retina, RBC, cornea-- so they rely on the 2 ATPs formed by glycolysis


Name some functions of glycolysis

1. Yields 2 atps (cells that have no mitochondria rely solely on these two ATPs)

2. Sets the stage for aerobic oxidation because pyruvate can become Acytl CoA

3. Stores glycogen which is an intermediate for carb storage

4. Supplies intermediates for pentose phosphate pathway (making of NADPH and 4,5,7 Carbon sugars)

5. Supplies intermediates for 2-3 BPG

6. Supplies intermediates for special carbohydrate synthesis

7. can take up glycerol from triacykygylercols


Where does glycolysis, TCA and oxidative phosphorylation take place

Glycolysis – in cytosol
TCA – in mitochondrial matrix
Electron transport and oxidative phosphorylation – in inner membrane and inter-membrane


Glucose--> pyruvate        2 ATP
Pyruvate--> CO2              2 ATP



List organs

1. Dependent on glucose that make pyruvate

2. Dependent on glucose that make lactate

3. Dependent on glycolysis b/c of low mitochondria

1. Dependent on glucose that make pyruvate-- brain

2. Dependent on glucose that make lactate-- No mitochondria so make pyruvate- RBC, retina, sclera, lens

3. Dependent on glycolysis b/c of low mitochondria-- renal medulla, testis, WBC, Whte mucle fibers



*** heart is aerobic but uses mostly fatty acids**


3 stages of glycolysis

Explain the first

1. priming
 2. Spillting

3. oxidareduction phosphorylation 



The priming stage is activating the pathway by converting glucose to fructose 1-6 biphosphate (this requires 2ATPs).


here takes place the 1st regulatory step. Hexokinase (and glucokinase an isoenzyme) both run phosphorylation of glcuose to glucose 6 phosphate where we have a junction point in metabolism


Right after hexokinase is PFK-1 (2nd regulatory step MOST important and rate limiting- invest 1 ATP in PFK-1)--- this decides to run or stop glycolysis


Glucose 6-phosphate is a junction point inmetabloim.. What can form from it?

1. can go into gylcolysis,

2. can go into glycogen for energy storage,

3. can go tinto glucuronate for carb synthesis,

4. can go into pentose phosphate pathway to synthesis NADPH and 4,5,7Chain Carbon Sugars)


What is the 2nd step of glycosis. Explain it

Spiltting- sptil our 6 carbon sugar into two 3-carbon sugars byt the enzyme aldolase one is glyceraldhyde 3-phosphate (the one that goes into glycolysis) and Dihydroxyacteon phophate. this step is reversible


For fructose the enzyme is Aldolase-B


What is the 3rd and final step of glycolysis. Explain it.

Oxidoreduction - phosphorylation stage prodcues 4 ATPs (2 net). 1. We start with the glyceraldyhyde 3 phosphate (from the spilting stage); here the enzyme GAPDH oxidzes(aerobic conditions) the aldyhyde group to carboxylic acid with reductio of NAD+ to NADH (making about 3 ATPs)

2. Next phospoglycerate kinase produces 2 ATPs per glucose  from 1-3 BPG by substrate level phosphorylation because it occurs with substrate w/o invovlement of oxidative phosphorylation

3. THeo 3_ phosphoglycerate is converted to 2-phosphoglycerate by phosphoglycerate mutase

4. The 2-phosphglyercate to phosphenolpyruvate by enolse

5. Last step before aerobic is phosophenolpyruvate to pyruvate by pyruvatekinase. this is the 2nd substrate level phosphorylation, 3rd regulatory step and makes 2ATP/glcuose


GAPDH- is liek a housekeeping gene because it's in every cell andit is not regulated.


Explain the RBC shunt

1-3 BPG isn't forming 3-phosphglycerate and 2 ATPS through phosphglycerate kinase but instead we are making 2-3 BPG with mutase, So no net ATP and that RBC are taking up much more glycose that you would think is needed because they are shunting up to 25% of glucose for no energy profuction but 2-3 BPG production


End product under anerobic conditions


Can be utlized by liver, skeltal, and muscle cells and turning it back into pyruvate. Liver can use lactate for glucose production (gluconeogenisis)


Why do we need a balance of NAD+ and NADH

Just like anything we need a balacne. GAPDH uses NAD+ to make NADH so we need to have NAD+ avliable for the next cycle for GAPDH


Lactase dehydronease makes NADH reoxidize to NAD+ by produsing lactate

Aeorboic- NADH through the mitochondria becomes NAD


two routes of reoxidizing NADH back to NAD+

1. Lactase dehydronease makes NADH reoxidize to NAD+ by produsing lactate

2. Aeorboic- NADH through the mitochondria becomes NAD+ through the shuttling of H+


What are two shuttle systems? Why arethey important

1. Malate-asprate shuttle (mostly liver)... oxolacetate reduces to malate making NAD+ (in the cytosol) and then NADH is reproduced in the mitochondrial matrix

2. Glycerol phosphate shuttle(mostly muscle)-- NADH is oxidized back to NAD+ in the cytosol close to the mitochondria membrane where DHAP--> Glycerol 3-phosphate  which makes FADH2 in the inner mitochondrial matrix

***Less favored to use glycerol phosphate because you start with NADH (3 ATP potential) and end with FADH2(2 ATP potential), so when we use malate-asparate we make 38ATP (10 NADH, 2FADH, 2 ATP, 2 GTP) when we use the glyverol phosphate 36ATP (8NADH, 4FADH, 2 GTP, 2ATP)




POisions that inhibit glycolysis

Mercury and arsenate inhibit GAPDH (the enzyme used in the oxioreductin-phosphorylation stage of glycolysis to change Glyceraldehyde to 1-3 BPG by oxidizing carboylic acid and reduces NAD+ to NADH)

Fluoride inhibts enolase


PAthway of alchohol metabolism; why is this bad for you

Ethanol-----Alchol DH---> acetaldehyde----- Aldehyde DH--> acetate + NADH


More NADH uses the same shuttle as glycolysis so when too much alchol you're in overload of the shuttle and you lose your balancce of NADH and NAD+ and glycolysis stops 


Why shouldn't we mix drugs and alchols

Drugs are removed from the body through liver through two systems Glucononic acid and and cytochrome P-450 system. Alcohol inhibits the cytochrome P-450 system so drugs are circulating . Gluconoric acid system produces NADH as well (like ethanol/alcohol) so the shuttle stops and the glycolysis stops and removal stops. 


3 regulatory enzymes in glycoslysis

D glucose--- Hexokinase--> Glucose 6-P

Fructose 6-P----PFK-1-> Fructose 1-6 Biphosphate

phosphenlpyruvate--- pyruvate kinase ---> pyruvate