Valenick Carb Metabolism III Flashcards by Danielle Hayes

How does lactose get to glucose metabolism?

broken down into galactose and glucose

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How does sucrose get to glucose metabolism?

broken down into fructose and glucose

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How does trehalose get to glucose metabolism?

broken down into 2 glucose molecules

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Which can enter glycolysis; disaccharides or monosaccharides?

monosaccharides

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Which monosaccharides can enter glycolysis and at which step?

fructose-> DHAP or G3P
galactose-> G6P
mannose -> F6P

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(blank) comes mostly in the form of dissachride sucrose and tastes sweeter than glucose. It is less rapidly absorbed in the intestine but more rapidly metabolized. Most is phosphorylated in the liver (50%) kidneys, intestines andmuscle

fructose

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Is fructose 1 phosphate a glycolytic intermediate? why is this a problem?
HOw can we solve this?

no
Often times fructose will become phosphorylated turning into F1P, since this cannot by glycolyzed, it will build up; especially because this conversion is super quick and the conversion to fix this into a usable intermediate is very slow
Via Fructose 1-phosphate aldose-> F1P into Glyceraldhyde and dihydroxyacetone phosphate

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What does fructokinase do?

converts fructose to F1P

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Why does the liver metabolize fructose faster than glucose?

Fructose bypasses the rate limiting steps of glucokinase and PFK reactions. In addition fructose is converted to F1P which stimulated pyruvate kinase and glucokinase.

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Natural foods contain fructose together with glucose, why is this good.

Because fructose stimlates glycogensynthase and helps glucose become glycogen

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What does F1P in the liver inhibit?

phosphohexose isomerase
aldolase
glycogen phosphorylase

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What does F1P in the liver stimulate?

glucokinase and pyruvate kinase

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What results in nausea, vomiting, hypoglycemia after meals containg fructose or sucrose, liver damage?

intolerance from aldolase B mutation

intolerance ffrom F1,6 bisphosphatase mutation (but have fasting hypoglycemia i.e cant do gluconeogenesis)

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excess (blank) is toxic

fructose

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Explain how fructose is metabolized in the liver

fructose -> F1P accumulates-> eventually conversation to DHAP and G3P
This happens due to low Km of hexokinase

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Explain how fructose is metabolized in the muscle

Fructose is converted to F6P via hexokinase and enters glycolysis and enters at the regulated step PFK1 so it doesnt bypass this step like it does in the liver, i.e. it is better regulated in the muscle : )
Muscle has high Km for hexokinase

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Why is eating a lot of fructose bad?

F1P accumulates in liver
Phosphate is tied up at slow aldolase reaction
lack of phosphate impairs oxidative phosphorylation
lactate accumulates
increase H+ can cause liver damage
build up of G6P increases uric acid conc.

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Why was fructose once considered better than glucose?

because it bypassed the insulin depndent PFK reaction, however they soon realized fructose caused liver damage :(

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How is galactose metabolized?

it is converted to galactose 1 phosphate via ATP

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What does UDP galactose make?

glycolipids
glycoproteins
proteoglycans

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What is this:
galactose 1-phosphate accumulates, liver damage, vomiting after eating, ties up Pi.
Mental deficiency develops.

Classic Galactosemia Type 1

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(blank) is a relatively benign condition leading to elevated blood galactose levels after consumption of milk and milk products. Cataracts (clouding of the lens) occasionally develop in those who consume milk despite their enzyme deficiency.

galactokinase deficiency

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Most dietary galactose is metabolized in (blank) and (blank)

liver and intestinal mucosa

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The galactose pathway amounts to the ATP-dependent conversion of (UDP galactose) galactose-1-phosphate to (UDP glucose) glucose-1-phosphate. Because of its reversibility, the epimerase reaction is also a source of (blank) for the synthesis of glycolipids, glycoproteins, and proteoglycans.

UDP-galactose

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Explain how galactose is broken down

Galactokinase phosphorylates galactose to galactose-1-phosphate, which then reacts with UDP-glucose to form UDP-galactose. UDP-galactose is epimerized to UDP-glucose.

Why can galactosemia cause cataracts?

galactose gets reduced to galacitol in the lens | instead of glucose becoming fructose

What is this: galactose 1-phosphate accumulates causing vomiting after eating, liver damage and within weeks mental deficiency and cataracts develops.

galactosemia

``` Many tissues (seminal vesicles, lens, retina, blood vessels and peripheral nerves) can synthesize fructose via the (blank) using fructose as a primary energy source. (Protective, as bacteria prefer glucose.) ```

polyol pathway

What is the polyol pathway?

glucose->sorbitol->fructose

WHere do you see galactosemia Type 2? Type 1 GALT (classic galactosemia)? GALE deficiency Type 3?

galactokinase issues galactose-1-phosphate uridyl transferase issues UDP galactose 4 epimerase issues

What enzyme is messed up with fructose intolerance?

fructose 1 phosphate aldose

The (blank) accounts for a significant portion of the total glucose oxidation in tissues with active fatty acid or cholesterol synthesis, including liver, adipose tissue, adrenal cortex, and the lactating mammary gland.

pentose phosphate pathway

The (blank) is also important in cells that are exposed to a high oxygen partial pressure. In the cornea of the eye, for example, it accounts for 60% of the total glucose consumption.

pentose phosphate pathway

What do nucelated cells use the pentose phosphate pathway for?

To generate NADPH and precursors of nucleotide biosynthesis

(blank) is used as the reducing agent for biosynthetic reactions and does not feed into the electron transport chain.

NADPH

(blank) is used by glycolytic enzymes

NADH

(blank) is used for reductive biosynthesis of fatty acids and cholesterol and for defense against oxidative damage.

NADPH

Where do you have a lot of NADPH?

in the cytoplasm

The cytoplasmic pentose phosphate pathway, also known as the hexose monophosphate shunt, makes two important products which are.....

ribose-5-phosphate and NADPH.

Explain the pentose phosphate pathway

G6P-> 6 phosphogluconate-> ribulose 5 phosphate-> Ribose 5 phosphate-> nucelotides, coenzymes, DNA, RNA

Specifically, NADPH and/or Ribose 5 Phosphate are used in what four things?

fatty acid biosynthesis cholesterol biosynthesis neurotransmitter biosynthesis nucleotide biosynthesis

(blank) is a precursor for nucleotides, coenzymes, and nucleic acids

ribose 5-phosphate

PPP is minimally active in (blank) or (blank). However, PPP accounts for a significant portion of glucose oxidation in tissues with fatty acid or cholesterol synthesis (liver, adipose, adrenal cortex and lactating mammary gland).

muscle or the brain

what is a nucleoside?

pentose sugar + base

What is a nucleotide?

pentose sugar + base + phosphates

What are the 2 branches to the PPP?

oxidative and non oxidative

What generates NADPH and generates biosynthetic precursors?

oxidative branch of PPP

What recycles the pentoses back into glycolysis or gluconeogenesis and provides biosynthetic precursors?

non-oxidative branch of PPP

(blank) catalyzes the committed and rate-limiting step of the oxidative branch of the PPP. The reaction sequence is irreversible, and this enables the cell to maintain a high [NADPH]/[NADP+] ratio.

Glucose-6-phosphate dehydrogenase

Cells generally contain far more (blank) than (blank) this is in contrast to (blank) whose concentration is generally far lower than the (blank) concentration. For this reason, the cells use NADPH rather than NADH whenever a strong reducing agent is required.

NADPH than NADP+; | NADH NAD+

If NADPH is forming faster than it is being used, [NADP+] decreases and the committed step does not proceed. As a result, more (blank) is available for glycolysis.

glucose 6-phosphate

What regulates the G6PDH (the enzyme that makes the committed step of the oxidative branch of PPP)

the availability of NADP+

What are the products from the non-oxidative branch of PPP

2 x F6P and G3P to feed into glycolysis.

The non oxidative PPP reactions convert pentose phosphates to (blank) phosphates, allowing the oxidative reactions to continue.

hexose

The nonoxidative branch of the pentose phosphate pathway links (blank), the product of the oxidative branch, to glycolysis and gluconeogenesis. The most important enzymes in this reversible reaction sequence are (blank X 2)

ribulose-5-phosphate | transketolase and transaldolase

The nonoxidative phase recycles (blank) pentoses back to (blank) hexoses that shuttle back into glycolysis. This allows continued production of NADPH and the conversion of glucose 6-phosphate (in six cycles) to CO2).

6 | 5

What does transketolase do in its first reacion?

depends on TPP, if it has it, it will transfer 2 carbons to make 2 pentoses into a triose and a heptose

What does transaldolase do?

it takes the heptose and triose made by transketolase and transfers 3 carbons to make a 4 carbon sugar and a 6 carbon sugar

What does transketolase do in its second reaction?

Transfers 2 carbons. generates 2 products of the glyolytic pathway G3P and F6P

In addition to the glycolytic intermediates, (blank) molecules of NADPH are formed for each carbon released as CO2.

two

THere are a bunch of ways to use the PPP. When the cell needs more NADPH than ribose-5-phosphate, the oxidative and nonoxidative branches work in series to form (blank) and (blank) . These products are recycled to glucose-6-phosphate in the gluconeogenic reactions. In this mode, the whole glucose molecule can be oxidized to CO2 and NADPH.

fructose-6-phosphate and glyceraldehyde-3-phosphate

There are a bunch of ways to use PPP, if you just want to make NADPH, you can. Can oxidize G6P to CO2 without consuming or producing ATP if (blank) is funneled into gluconeogenesis.

F6P

There are a bunch of ways to use PPP, if you just want to use ribose only, you can. When the cell needs more R5P than NADPH, how can it be formed.

When the cell needs more ribose-5-phosphate than NADPH, ribose-5-phosphate is formed not only through the oxidative branch but also by reversal of the reactions in the nonoxidative branch.

YOu can use NADPH and C2 unis to make (blank)

FAs

What are all the ways to use the ppp?

NADPH and Ribose-5-P NADPH only Ribose only NADPH and C2 units for FAs

What is the uronic acid pathway?

Uses nucleotide-activated sugars derived from glucose in the biosynthesis of glycolipids, glycoproteins and proteoglycans glucose->udp glucose-> udp-glucuronic acid->proteoglycans and conjugation ****makes NADH***

The carbohydrate in glycolipids, glycoproteins, and proteoglycans is derived from (blank). These “activated” sugar derivatives are made from glucose. (blank) is required for the synthesis of proteoglycans and for conjugation reactions in the liver, is made by NAD+-dependent oxidation of carbon 6 in UDP-glucose. The free glucuronic acid produced during degradation of proteoglycans is metabolized to an intermediate of the (blank).

nucleotide-activated precursors UDP-glucuronic acid pentose phosphate pathway.

Why run the PPP in RBC’s a nonbiosynthetic cell?

To provide the reducing power necessary to protect the RBC’s from oxidative damage.

In RBCs and liver NADPH is used to keep (blank) reduced.

Glutathione Reduced

(blank) protects cells against highly reactive oxygen derivatives (oxidative damage).

Glutathione

(blank) acts as an intracellular sulfhydryl buffer maintaining –SH groups.

GSH (reduced glutathione)

(blank) protects the cell by destroying hydrogen peroxide and hydroxyl free radicals. Regeneration of GSH from its oxidized form (GSSG) requires the (blank) produced in the glucose 6-phosphate dehydrogenase reaction. Only the reduced form of glutathione is an antioxidant. Therefore the dimeric, oxidized form has to be reduced back by the enzyme (blank)

Reduced glutathione (GSH) NADPH glutathione reductase

Why are RBCs affected most by G6PDH deficiency?

cant replace defective proteins by new synthesis

What is this: Hemolytic Anemia after exposure to drugs that generate oxidizing products. Sulfonamides But, the mutation protects you against malaria

G6PD deficiency

What is this" hemolytic anemia may be caused by some offending drugs including the antimalarial primaquine, the sulfonamides sulfanilamide and sulfamethoxazole, the antimicrobial drug nalidixic acid, and the urinary antiseptic nitrofurantoin. Hemolytic attacks can also occur during infections. Even broad beans (Vicia faba) are dangerous, causing severe attacks of hemolysis within 1 to 2 days of eating the beans (“favism”). Although the enzyme deficiency is present in all tissues, only the erythrocytes are seriously affected because they have no alternative routes for NADPH synthesis, and they cannot compensate for low enzyme activity by synthesizing more enzyme. Without sufficient NADPH and reduced glutathione, membrane proteins become covalently cross-linked, aggregates of oxidized proteins become visible in the cells as Heinz bodies, and a hemolytic crisis develops within 2 to 3 days after the initial exposure to the drug.

Glucose-6-phosphate dehydrogenase deficiency