#7 Flashcards by Lindsay Lyons

Lactate metabolism: lactate produced by hardworking muscle can only be converted to ____ (____)

pyruvate, (LDH)

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When lactate leaves the muscle fiber where does it diffuse to?
Is this with or against its concentration gradient?

Extracellular fluid and into the bloodstream
down its concentration gradient

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What is lactate efflux facilitated by?
Where does this occur?

monocarboxylate transporters (MCT)
on sarcolemma and t-tubule membrane

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MCTs can also transport what? Such as?

other monocarboxylates (i.e. pyruvate)

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MCT carry one ____ and one ____ in the same direction
What does this lower?
What MCTs are being used for this?

lactate and H+
lowers cytosolic [H+]
MCT1 AND MCT4

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Once it’s in the blood where can lactate enter?
Here, is its concentration lower or higher than in the blood?
Is it going up or down its concentration gradient?

other organs
lower
down its concentration gradient

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What organs can lactate enter once it’s in the blood?

Skeletal muscle (that did not participate in the exercise), heart, liver, brain, and kidney to a lesser extent

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Cell-cell lactate shuttle: Lactate produced in some ____ such as ____ fibers, diffuses or is transported into ____ fibers and converted to ____

skeletal muscle, IIb fibers, I fibers, pyruvate

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Cell-cell lactate shuttle: What two things can happen with lactate/where can it go?

shuttled directly to adjacent fiber or recirculated through the blood

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Lactate in circulation can also be taken up by ____ and converted to ____

the heart, pyruvate

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Lactate may also be taken up by ____ and utilized (____) or converted to another metabolite (i.e. ____-____)

the liver, oxidative metabolism, glucose - gluconeogenesis

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What happens in the Cori cycle?
____ formed in ____ can ____ to the ____ where it can ____ to ____

lactate or pyruvate, muscle, circulate, liver, be synthesized, glucose

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Glucose formed in the Cori cycle can then enter what?

the circulation

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Intracellular lactate shuttle: mitochondria in skeletal muscle, heart, liver, other cells contain ____

lactate dehydrogenase

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Some have reported that mitochondria isolated from liver, heart, and skeletal muscle ____
Possibly at greater rates than ____

oxidize lactate
Pyruvate

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Rather than lactate being a dead end metabolite formed as a result of O2 deficiency, it may be ____

more of a link between anaerobic and aerobic metabolism than pyruvate

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How is lactate transported into the mitochondia?

MCT

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Mitochondrial lactate shuttling may also be used similarly to the ____ shuttle and ____ shuttle

malate-aspartate, glycerol-phosphate

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NADH equivalent potential energy is transported to the mitochondria using a mechanism for which ____
____ for lactate
Recall that ____ and ____ do not easily diffuse across mito membranes

there is already a specific mitochondrial carrier
MCT
NADH, NAD+

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What is gluconeogenesis?

the synthesis of glucose from compounds that are not carbohydrates

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What is used in gluconeogenesis?

pyruvate, lactate, glycerol, most amino acids

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What type of acids are pyruvate and lactate?

carboxylic acids

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What does glucose synthesis from pyruvate (or lactate that has been converted to pyruvate) involve?

the reversal of seven of the 10 steps in glycolysis

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What 3 reactions of glycolysis are not involved in gluconeogenesis?

1: hexokinase, 3: phosphofructokinase, 10: pyruvate kinase

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Where does gluconeogenesis primarily take place?

the cytosol

gluconeogenesis takes place primarily in the cytosol, but the pyruvate must first be converted to ____ in the ____

oxaloacetate in the mitochondria

Pyruvate is transported from ____ to mito ____

cytosol to mito

What is this reaction catalyzed by?

pyruvate carboxylase

Oxaloacetate is reversibly reduced to ____ What is this reaction catalyzed by?

malate, mitochondrial malate dehydrogenase

____ then leaves the mitochondria via ____ shuttle

malate aspartate

Malate is then reoxidized in cytosol to ____. This produces ____ What is this reaction catalyzed by?

oxaloacetate, cytosolic cytosolic malate dehydrogenase

Oxaloacetate is then converted to ____ What is this reaction catalyzed by?

phosphoenolpyruvate PHOSPHOENOLPYRUVATE CARBOXYKINASE

Conversion of fructose 1,6 biphosphate into ____ Promotes irreversible hydrolysis of the ____

fructose 6 phosphate carbon-1 phosphate

Conversion of glucose-6-phosphate into ____ This is the ___ bypass What type of reaction is this? ____ of glucose-6-phosphate

glucose 3rd final reaction dephosphorylation

What are the main animal organs where gluconeogenesis takes place?

liver and kidneys

What does muscle lack? What does this mean about its ability to convert pyruvate and lactate?

glucose-6-phosphate IT cannot convert pyruvate and lactate directly to glucose

Where can pyruvate and lactate be converted to glucose-6-phosphate? What can it then be converted to?

muscle, glycogen

In glycogenesis what is the link between glucose-6-phosphate and glycogen?

glucose-1-phosphate

In glycogenesis what is the link between glucose-6-phosphate and pyruvate?

fructose-6-phosphate

In glycogenesis what is the link between glucose-6-phosphate and ribose-5-phosphate?

6-phosphogluconate

What is glycogenesis?

glycogen synthesis

Glucose entering ____ (__) or ____ can be involved in glycogenesis

liver (hepatocytes) or muscle fibers

Where does glycogen serve as a reservoir of glucose? Readily converted to ____ for distribution to other tissues

liver blood glucose

Where is glycogen broken down via glycolysis to provide ATP for muscle contraction?

muscle

What is the protein in the glycogen core?

glycogenin protein

Glycogenin acts as the primer to which ____

the first glucose residue is attached

Glycogenin is the catalyst for synthesis of developing ____

glycogen molecule

Successive addition of ____ units to a growing chain What is the catalyst for this Requires energy input (____) One ____ and one ____ (____) per glucose added

glucosyl glycogen synthase biosynthetic process ATP, UTP, uridine triphosphate

What is the starting point for glycogenesis?

glucose-6-phosphate

What happens to much of the glucose ingested during a meal?

It takes a roundabout path to glycogen

First taken up by ____ in bloodstream and converted to ____

erythrocytes, lactate

Lactate is then taken up by the liver and converted to ____ by gluconeogenesis

glucose-6-phosphate

To initiate glycogen synthesis, glucose-6-phosphate is reversible converted to ____ What is this reaction catalyzed by?

glucose-1-phosphate Phosphoglucomutase

What is then formed? What is this catalyzed by? What type of reaction is this?

UDP-glucose UDP-GLUCOSE PYROPHOS-PHORYLASE key reaction in glycogenesis

This reaction proceeds in the direction of UDP-glucose formation because ____ is rapidly hydrolyzed by ____

pyrophosphate inorganic pyrophosphate

UDP-Glucose is the immediate donor of ___ residues in the formation of ___ by the action of ___

glucose, glycogen, glycogen synthase

Promotes the transfer of the ____ residue from UDP-glucose to the ____ of the branched ____ molecule

glucosyl, non reducing end, glycogen

What kind of chains does glycogen synthesis create?

linear chains

What is needed to form branches of glucosyl chains?

branching enzyme

What does this branching enzyme do when in detaches segments of the existing chain?

transfers it to the interior

What is glycogenolysis?

degradation of glycogen

What is glycogenolysis catalyzed by?

glycogen phosphorylase or phosphorylase

What's different about phosphorylase? It cannot completely ____

catalyze the breaking of bonds in glycogen

What is phosphorylase unable to remove?

glucosyl units lying four or fewer places away from a branch point

When the chain becomes less than 4 units what happens?

another enzyme is involved

Debranching enzyme catalyzes 2 reactions: Transport of what and removal of what?

Transport of three out of the four glucosyl units of a branch to the end of another Removal of the remaining unit by hydrolysis of it particular glycosidic linkage (α1→6)

After the previous reaction the branch is eliminated which then allows ____ to catalyze the reaction

glycogen phosphorylase

Glycogen phosphorylase allows for the release of molecules of ____. What are these produced?

glucose-1-phosphate, produced until the enzyme is four glucosyl units away from the next branch

What will debranching enzyme do next?

Eliminate the branch (and so on and so on)

Glucose-1-phosphate is converted into ____ by ____

glucose-6-phosphate by phosphoglucomutase

Where is pathway activity low and high?

low in skeletal muscle and high in adipose tissue

____ needed in adipose tissue to synthesize ____ from Acetyl-CoA

NADPH, FA

What controls pathway at the first step?

NADPH

High NADPH/NADP ratio inhibits ____

glucose-6-phosphate dehydrogenase

What does high NADPH/NADP and NAD/NADH ratios at same time mean?

biosynthesis and glycolysis can occur at same time at high rates

Because no ATP is required what can happen?

it can continue anaerobically

Ribulose 5-phosphate can be converted to ____ and/or down the pathway

Ribose 5-phosphate

Generation of ____ for biosynthesis of ____, Cholesterol (steroids)

NADPH, FA

What is the formation of ribose-5-phosphate used for?

The synthesis of nucleosides (ATP, CoA, NAD, FAD,NADP, RNA, DNA)

Yield ____ and ____ for glycolysis or for more G 6-P to enter Pentose

2 Fructose 6-P and 1 glyceraldehyde 3-P

Phosphate pathway for ____ (____)

NADPH (reversible reaction or gluconeogenesis)

In the pentose phosphate pathway what does the flow of glucose-6-phospate depend on?

the need for NADPH, ribose-5-phosphate, and ATP

#7 Flashcards

(82 cards)