Carbohydrates Flashcards
Does insulin induce or activate glucokinase? Does insulin induce or activate PFK-2?
induces glucokinase in liver cells
activates PFK-2 by dephosphorylating it
Via which complex do the electrons from NADH enter the ETC? How do the electrons from FADH2 enter the ETC?
complex I
complex II
Name the linkage that iso-maltase cleaves.
alpha-1,6 glycosidic linkage
Where are the bulk of dietary sugars absorbed?
duodenum and upper jejunum
Glycolysis occurs in which part of the cell?
cytoplasm
What are the important enzymes of the HMP shunt (aka pentose phosphate pathway)?
glucose-6-P dehydrogenase and transketolase
Which enzyme complex in the Krebs cycle requires cofactors?
alpha-ketoglutarate dehydrogenase
If galactokinase is impaired, what happens?
galactose builds up in the blood and spills in the urine, but there is no build up of the toxic compound galactose-1-P
How many carbons are in a heptose?
7
What are the three necessary cofactors for all carboxylases?
ATP, biotin, and carbon dioxide
Is the pentose phosphate pathway (aka HMP shunt) reversible?
yes, controlled by metabolic needs of cell
Which enzyme converts glucose to glucose-6-P?
hexokinase or glucokinase in combination with ATP converts glucose to glucose-6-P
What two types of tissue produce lactate most frequently?
muscles (working anaerobically)
RBCs (no mitochondria)
Name two positive and three negative regulators of citrate synthase.
+ acetyl CoA, OA
- NADH, fatty acyl CoA, succinyl CoA
Name the monosaccharide that is a constituent found in glycoproteins and in plants gums.
mannose
Name the four kinases in glycolysis. Which are reversible and which are irreversible?
hexokinase, phosphofructokinase, and pyruvate kinase are controlled enzymes that catalyze irreversible steps in glycolysis
phosphoglycerate kinase catalyzes a reversible step
Where do the RBCs and brain cells get their glucose from between meals?
liver
Which polysaccharide that has glucose molecules bound by beta-1,4 linkages and is not able to be broken down by most animals?
cellulose
Which enzyme in the liver converts glucose-6P to glucose?
glucose-6-P phosphatase
What enzyme is responsible for the buildup of galactose products in the lens?
aldose reductase
What is the significance of the first half of the HMP shunt? Second half?
production of NADPH
production of ribose-5-P
T/F: lactose uses the anomeric carbon of both sugars and has no mutorotation.
F
Where does the body obtain the alanine used to make pyruvate via gluconeogenesis between meals?
it is the result of protein breakdown in muscle tissue
Name the enzyme involved in the conversion of pyruvate to acetyl-CoA.
pyruvate dehydrogenase
Where is 2,3-BPG made?
in the RBC by the conversion of the glycolysis intermediate 1,3-BPG to 2,3-BPG
Name the polysaccharide that is made up of repeating fructose molecules and is a starch found in many roots. It is also excreted in the urine with no resorption in the renal tubules.
inulin
Where do the electrons go from cytochrome C?
complex IV (aka cytochrome oxidase)
Name the three biochemical pathways by which insulin increases glucose use.
oxidation (facilitates glucose entry into glycolytic pathway)
glycogenesis
lipogenesis
Where is glucokinase found?
liver
What is the function of PEPCK?
converts OAA to PEP
How many ATPs are produced in aerobic glucose metabolism, assuming mitochondria are available?
38 via malate shuttle: 36 via G3P shuttle
What is the net gain of ATP per glucose molecule in the TCA cycle?
12 per cycle of the TCA -> 24 per glucose
Name the three proton pumps located in the inner mitochondrial membrane.
complex I, III, IV
In sucrose, carbon 1 of glucose is attached to carbon __ of fructose?
carbon 2
What are the inhibitors of glycogen synthase in liver and muscle?
glucagon and epinephrine in the liver
epinephrine in muscle
Human salivary amylase breaks down which type of linkage?
alpha-1,4 linkage
Glucagon activates (protein kinase/protein phosphatase) which promotes (glycogen synthesis/glycogenolysis).
protein kinase
glycogenolysis
What tissues contain the pentose phosphate pathway (aka HMP shunt)?
liver, mammary tissue, adrenal cortex, RBC
What is the first step in the metabolism of galactose?
galactokinase produces galactose-1-P
What is the main sugar-regulating hormone secreted in the post-absorptive state (between meals)?
glucagon
Which complex in the ETC does cyanide inhibit?
complex IV (aka cytochrome oxidase)
What will happen in aldolase B is impaired?
fructose-1-P will build up in the liver
Which disaccharide has two glucose units?
maltose
Describe the functions of cortisol on sugar, fat and protein metabolism.
stimulates gluconeogenesis in the liver
mobilizes amino acids from extrahepatic tissue
inhibits glucose uptake in muscle and adipose
stimulate lipolysis
What is the common name of glucose (alpha-1, beta-1)-fructose?
sucrose
What are the three substrates for gluconeogenesis?
alanine, lactate, and glycerol-3-P
What is the function of glycogen phosphorylase?
it will break alpha-1,4 bonds to release glucose-1-P until it encounters the first branch point
Name the reactions in glycolysis and the TCA cycle which produce NADH.
Glycolysis: glyceraldehyde-3-P dehydrogenase and pyruvate dehydrogenase
Krebs: isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, malate dehydrogenase
Trace the pathway whereby insulin can activate PFK-1.
insulin activates PFK-2 by causing it to become dephosphorylated.
PFK-2 then converts fructose-6-P to fructose-2,6-bisP
Fructose-2,6-bisP activates PFK-1
Name five important polysaccharides.
amylose, amylopectin, glycogen, inulin, cellulose
Describe the activity of debranching enzyme.
debranching enzyme breaks the alpha-1,4 bond nearest the branch point and transfers the oligoglucose unit to the end of another chain.
It then goes back and hydrolyzes the alpha-1,6 bond, releasing a single glucose
Are galactose and mannose epimers or are they just isomers?
isomers
Where does acetyl-CoA get produced?
mitochondrial matrix
Is a five membered ring with four carbons and one oxygen a pyranose or furanose?
furanose
Which glands secrete the enyzymes in the small intestine that hydrolyze disaccharides on the brush border?
Brunner and Lieberkuhn glands
What is the rate limiting step of glycolysis?
conversion of fructose-6P to fructose-1,6-bisphosphate by PFK-1
Where does the breakdown of sucrose occur? Which enzyme is responsible?
sucrase (aka invertase) will split sucrose into glucose and fructose in the jejunum
In lactose, carbon one of glucose is attached to carbon ___ of glucose.
lactose is formed by a glycosidic bond between C1 of galactose and C4 of glucose
To activate pancreatic enzymes, does the pH need to be raised or lowered?
alkalinization (raising the pH) is needed to activate pancreatic enzymes to work effectively
Glucose-6-P dehydrogenase deficiency: What molecule is decreased if this enzyme is inactive?
NADPH
What are the four unique enzymes of gluconeogenesis (that are not also used in glycolysis)?
pyruvate carboxylase, PEP carboxykinase, fructose-1-6-bisphosphatase, glucose-6-phosphatase
Name the linkages that maltase cleaves.
glycogen alpha 1,4 glycosidic linkages
Which complex of the ETC does NADH give its electrons to?
complex I (aka NADH dehydrogenase)
If the oxygen on the anomeric carbon (carbonyl group) of a sugar is not attached to any other structure, is this a reducing or non-reducing sugar?
reducing sugar
Which cytochrome contains bound copper atoms? What complex is this cytochrome part of?
cytochrome A/A3, located in complex IV (aka cytochrome oxidase)
What are the main cells that fructose is used in?
liver, kidney cells
How does the ATP get out of mitochondria after it is produced?
it is exchanged for ADP through ATP/ADP translocase
Name three common disaccharides.
sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose)
Where does the Krebs cycle take place?
mitochondria
What is the key limiting step in gluconeogenesis?
PEPCK
How much CO2, NADH, QH2, and GTP are created from each acetyl-CoA that enters the Krebs cycle?
one GTP (or ATP)
3 NADH
1 QH2
2 CO2
Which enzyme has a lower Km for glucose: hexokinase or glucokinase?
hexokinase
What is the chemical formula for glucose?
C6H12O6
Which two steps does galactose have to go through to enter glycolysis?
galactokinase turns galactose into galactose-1-P
galactose-1-P uridyl transferase turns galatose-1-P into glucose-1-P
Where do the proton pumps in the ETC pump protons to?
they pump protons across the inner mitochondrial membrane into the intermembrane space
Carbohydrates with an aldehyde as their most oxidized functional group are called?
aldoses
Which polysaccharide contains alpha-1,4 glycosidic linkages, and has branch points with alpha-1,6 glycosidic linkages?
amylopectin
Name the three products that glucose-6-phosphate can be converted to.
glucose-1-P (glycogen pathway)
fructose-6-P (TCA)
6-phosphogluconolactone (ribose-5-phosphate pathway)
What is the treatment for someone with a galactose metabolism enzyme deficiency?
complete restriction of galactose-containing products (dairy)
Name the sugars that are C2 epimers.
glucose and mannose
Which molecules directly trigger the breakdown of glycogen in the liver and in muscle?
glucagon triggers breakdown in liver
EPI controls breakdown in liver and muscle
AMP controls breakdown in muscle
How is NAD in a RBC replenished?
lactate dehydrogenase
Where do the electrons coming in from FADH2 go?
directly to coenzyme Q (aka ubiquinone), bypassing complex I
Name the 8 steps of the TCA.
acetyl-CoA to citrate to isocitrate to alpha-ketoglutarate to succinyl-CoA to succinate to fumarate to malate to oxaloacetate
In oxidative phosphorylation, on what side of the mitochondrial membrane is ATP produced?
mitochondrial matrix
In which enzymes of galactose metabolism are deficiencies most commonly found?
deficiencies in galactokinase and galactose-1-phosphate uridylyltransferase (aka GALT) are MC
What is the most complicated step of gluconeogenesis?
conversion of pyruvate to PEP
Name the three drugs that inhibit complex IV?
cyanide, carbon monoxide, azide
Which enzyme converts fructose-6-P to fructose-1,6-bis-P?
phosphofructokinase (rate limiting step of glycolysis)
Which storage molecule is similar to amylopectin in structure, but is more highly branched?
glycogen
What is the common name for galactose (beta 1,4) - glucose?
lactose
When is the use of lactate dehydrogenase essential to replenish the NAD?
when the ETC is not working (lack of oxygen) or not present dt lack of mitochondria (RBC)
Name four intermediates of the Krebs cycle that can be used in other pathways.
citrate (FA synthesis)
succinyl CoA (heme synthesis)
fumarate (urea cycle)
malate (gluconeogenesis)
What enzyme is required for alanine to be used in gluconeogenesis?
alanine transaminase
NADH feeds back on which three control points of the Krebs cycle?
isocitrate dehydrogenase, citrate synthase, alpha ketoglutarate dehydrogenase
Name the non-branching polysaccharide comprised of alpha-1,4 glycosidic linkages that forms a helical or coil shape.
amylose
Glucose-6-P dehydrogenase deficiency: What cells are most sensitive to this kind of damage?
RBCs
What is the rate limiting step for glycolysis?
PFK-1 conversion of fructose-6-P to fructose-1,6-bis-P
Glucagon phosphorylates PFK-2, which turns glycogen synthase __ and turns phosphorylase __.
off
on
Which polysaccharide has beta-1,4 glycosidic linkage?
cellulose
What is the only enzyme deficiency in glycolysis that is clinically relevant?
pyruvate kinase
What are the two enzymes involved in the breakdown of glycogen?
glycogen phosphorylase and debranching enzyme
What happens to glucose-1-P?
converted to glucose-6-P (glycolysis) or it can be added to glycogen (glyconeogenesis)
Insulin activates (protein kinase/protein phosphatase) which promotes (glycogen synthesis/glycogenolysis).
protein phosphatase
glycogen synthesis
Which substrates do not produce NADH or FADH2 as they go through the Krebs cycle?
citrate, succinyl-CoA, fumarate, oxaloacetate
What is the clinical significance of transketolase?
thiamine-requiring enzyme that used to test the thiamine levels in people
Which polysaccharide contains alpha-1,4 glycosidic linkages and branch points that contain alpha-1,6 glycosidic linkages?
amylopectin
Describe the activity of branching enzyme. Where does it break and form bonds?
it break alpha-1,4 bonds about 6-8 glucose molecules from the end
after breaking of the end of the chain it goes back about four glucose molecules on the original chain and then make an alpha-1,6 bond to create a branch
What is fructose-6-P converted to and what is required for this?
fructose-1,6-bisphosphate by PFK-1 and ATP
How does cytoplasmic NADH enter the mitochondria?
it doesn’t
it uses the malate or glycerol-3-P shutle to transfer electrons into the mitochondria
Name the hormone that favors the breakdown of liver and muscle glycogen and decreases the release of insulin via production of cAMP.
EPI
What type of bonds does glycogen synthase make?
alpha-1,4 bonds
What happens if galactose-1-P uridyl transferase is impaired?
galactose builds up into the blood and spills into the urine
there is a build-up of the toxic metabolic galactose-1-P
During oxidative phosphorylation, how do protons get moved into the mitochondrial matrix?
the protons pass through the F0 subunit of the ATP synthase enzyme (complex V)
Where is hexokinase found?
throughout the body (muscle, RBC, brain)
Does hexokinase have a high or low affinity for glucose?
very high
What is the mechanism of oligomycin inhibition of ATP synthase?
oligomycin prevents the influx of protons through ATP synthase, effectively shutting down ETC.
What enzyme converts 1,3-BPG to 2,3-BPG?
bisphosphoglycerate mutase (in RBC)
Name two negative regulators of alpha dehydrogenase.
succinyl-CoA, NADH
Name the disaccharide otherwise known as table sugar.
sucrose
The position of the C-4 hydroxyl group differs in glucose and galactose. These two sugars are therefore called?
C-4 epimers
In the fed state, phosphoglycerate is converted to which molecule? Which enzyme catalyzes this reaction?
phosphoenolpyruvate (PEP)
enolase
Why does anaerobic glycolysis occur in the RBC despite abundant oxygen?
no mitochondria
Name three uncouplers of oxidative phosphorylation.
2,4-DNP, thermogenin (brown adipose), high doses of salicylates (aspirin)
How is alpha amylase deactivated?
by the lower pH in the stomach
What are the two main subunits of ATP synthase and what do they do?
F0 is a channel for protons
F1 is where phosphorylation occurs
What is the rate limiting step of glycogen synthesis?
activation of glycogen synthase by glucose (locally) and insulin (globally)
What is another name for succinate dehydrogenase?
complex II of ETC
Free glucose move across the lumen of the small intestine into the portal system by which transporter?
sodium-dependent hexose transporter
Is fructose a ketose or an aldose?
ketose
What is the enzyme that takes the electrons from NADPH and gives them to glutathione?
glutathione reductase
Name the cells that produce salivary alpha-amylase, pancreatic alpha-amylase, alpha-glucosidase (maltase), alpha dextrinase, sucrase and lactase.
acinar cells
How many monosaccharides are needed to make up a polysaccharide?
12 or more
What does PEPCK require? Which hormone induces PEPCK?
GTP
induced by glucagon
What is the smallest sugar polymer that is present after pancreatic enzyme digestion?
disaccharides
T/F: maltose has an alpha and beta structure.
T
Which ocular pathology may occur in galactokinase deficiency?
cataracts dt lens swelling
In the well-fed insulin state, does acetyl-CoA enter the Krebs cycle?
Yes
Where is lactase normally found?
intestinal brush border
Where in the cell does the HMP pathway (aka pentose phosphate pathway) occur?
cytoplasm
Which polysaccharide has an alpha-1,4 glycosidic linkage and a spiral and helical coil shape?
amylose
The regulation of gluocose is primarily dependent on which two hormones?
insulin and glucagon
Name the substrate and end product of aerobic glycolysis.
glucose and pyruvate
What is NADPH used to make in the liver?
synthesis of fatty acids, cholesterol, nucleotides and glutathione
Maltose, lactose, or sucrose: which are reducing sugars?
maltose and lactose
How many ATP are produced by one NADH molecule in the ETC? How many per FADH2 molecule?
NADH produces 3 ATP
FADH2 produces 2 ATP
RBC glucose is ultimately converted to which molecule?
lactate
Where do the electrons go from complex III?
cytochrome c
Where are the enzymes in the ETC located?
inner mitochondrial membrane
Name four disaccharides that complete the conversion of starch/glycogen into usable forms of glucose.
maltase, sucrase, lactase, oligosaccharides
Name two drugs that inhibit complex I of the ETC.
barbiturates and rotenone
Name three positive and two negative regulators of isocitrate dehydrogenase.
+ isocitrate, ADP, AMP
- ATP, NADH
Fructose is central in which two pathways in the liver?
glycolysis and gluconeogenesis pathway
Which steps of glycolysis are irreversible?
glucokinase/hexokinase, PFK-1, pyruvate kinase
What do uncouplers do? What is the effect on the ETC?
increase permeability of the inner mitochondrial membrane to protons.
the ETC goes faster w/o establishing a proton gradient
heat is produced rather than ATP
Which cells secrete glucagon? what other hormone inhibits the release of glucagon?
alpha cells of pancreas
insulin
Which drug inhibits ATP synthase?
oligomycin
What is the common name for glucose-(alpha 1,4)-glucose?
maltose
Name the four monosaccharides.
glucose, fructose, galactose, mannose
Is ATP produced or consumed by the pentose phosphate pathway (aka HMP shunt)?
neither
How is a fructokinase deficiency differentiated form galactokinase deficiency?
no development of cataracts in fructokinase deficiency b/c fructose can be phosphorylated by other enzymes
What happens to acetyl-CoA in the mitochondria if ATP is required (high ADP)?
if ATP is required, acetyl-CoA enters the Krebs cycle
If ATP is not needed, it will be involved fatty acids biosynthesis
Which polysaccharide contains alpha-1,4 glycosidic linkages and is more highly branched than amylopectin with shorter (12-14) glucose residues?
glycogen
What is the only type of cell that has glucose-6-P phosphatase?
hepatocyte
How does glucagon effect PFK-2?
inhibits PFK-2, inhibiting fructose-2,6-bisP production
inhibits stimulation of PFK-1
What are the two pathways that provide glucose in between meals?
conversion of pyruvate to glucose
breakdown of stored glycogen
What are the five cofactors needed for the action of pyruvate dehydrogenase?
thiamine, lipoic acid, coenzyme A, FAD, NAD
Is a six-membered ring with five carbons and one oxygen a pyranose or furanose?
pyranose
What are the two amino acids that cannot create glucose through gluconeogenesis?
leucine and lysine
List the four GLUT receptors from lowest to highest affinity. Where are they located?
Glut-2 (liver, pancreas)
Glut-4 (skeletal muscle, adipose)
Glut-1 (most tissue, brain, RBC)
Glut-3 (most tissue)
Is insulin required for the uptake of glucose by intestinal cells?
no
Which molecule is the common “crossroad” for getting energy from fats, proteins, and carbohydrates?
acetyl-CoA
Cori cycle: how many ATP does it take to turn pyruvate into glucose in the liver?
6
Where do the electrons go from coenzyme Q?
complex III
Carbohydrates with a keto-group as the most oxidized functional group are called?
ketoses
In aerobic glycolysis, pyruvate is converted to __ by the enzyme __.
acetyl-CoA
pyruvate dehydrogenase
Name the four kinases in glycolysis. Which consume ATP and which produce ATP?
hexokinase, phosphofructokinase (consume 1 ATP per glucose)
phosphoglycerate kinase and pyruvate kinase (produce 2 ATP per glucose)
Pyruvate can be metabolized into five compounds. Name them.
lactate, acetyl-CoA, oxaloacetate, phosphoenolpyruvate, alanine
What are two enzymes involved in glycogen synthesis?
glycogen synthase and branching enzyme
How does insulin effect PFK-2? How does glucagon effect PFK-2?
glucagon phosphorylates PFK-2 to inactivate it whereas insulin dephosphorylates PFK-2 to activate it
Which two important products does the PPP produce?
ribose-5-P for nucleotide synthesis
NADPH for RBC metabolism and FA production
In the ETC, where do the electrons go after cytochrome oxidase?
they are picked up by oxygen to produce H2O
In what tissues are GLUT-1 and GLUT-3 found? What are their functions?
most tissues, esp. brain and RBCs
basal uptake of glucose
Name three steps that convert glycogen to glucose.
glycogen -> glucose-1-P -> glucose-6-P -> glucose via glucose-6 phosphatase
Can the acetyl CoA created between meals change to pyruvate and then to glucose?
acetyl CoA cannot be converted to pyruvate
Phosphoenolpyruvate is converted to __ via __.
pyruvate via pyruvate kinase
Insulin does not directly affect glucose uptake __, __, or __.
brain, RBCs, hepatocytes
How does acetyl-CoA exit the mitochondria?
conversion to citrate (part of Krebs cycle) which goes through the citrate shuttle
Name the two major sources of pyruvate (beginning of gluconeogenesis) between meals.
lactate, alanine
Insulin dephosphorylates PFK-2 which turns glycogen synthase __ and turns phosphorylase __.
on
off
With PFK-1 being the rate limiting step of glycolysis, what activates the PFK-1 and thus glycolysis?
indirectly activated by insulin through PFK-2
Aldolase converts fructose 1,6 bisphosphate to __ and __.
glyceraldehyde-3-P and dihydoxyacetone-P (DHAP)
Oxidation of the hydroxyl group at carbon six in glucose produces what molecule?
glucuronic acid
Digestion of carbohydrates begins in the mouth. Salivary alpha amylase hydrolyzes what type of linkage?
alpha-1,4 glycosidic linkage
Which two monosaccharides are epimers of glucose?
galactose and mannose
What is the first step in the metabolism of fructose?
fructose -> fructose-1-P by fructokinase
What are the three irreversible steps of glycolysis?
glucose -> glucose-6-P via glucokinase
fructose-6-P -> fructose 1,6-bis-P via PFK-1
PEP to pyruvate via pyruvate kinase
How many ATP equivalents are generated between glucose and pyruvate?
6
Does gluconeogenesis occur in the cytoplasm or in the mitochondria?
both
What happens after branching enzyme makes its branches?
glycogen synthase extends both branches
What is the Cori cycle? Which two cell types participate?
cycle of glucose to pyruvate to lactose and then back to pyruvate and then back to glucose
liver, and RBCs
Insulin induces glucokinase. Specifically, how does induction affect rate (Vmax)?
increases Vmax
What vitamin does FAD come from?
B2 (riboflavin)
The HMP shunt and the malate dehydrogenase reaction both produce ___
NADPH
Name the disaccharid ethat has one anomeric form.
sucrose
In the ETC, where do the electrons go from NADH dehydrogenase?
coenzyme Q (aka ubiquinone)
Why do RBCs only get their energy from the conversion of glycolysis, the conversion of glucose to pyruvate?
They lack PDH b/c they lack mitochondria
PDH, Krebs cycle and the ETC all occur in the mitochondria.
TF, RBCs lack all these stages.
Which shuttle yields more ATP, the malate or G3P shuttle?
malate (3 ATP)
G3P (2 ATP)
What enzyme converts fructose-1,6-bis-P to fructose-6-P?
fructose-1,6-bisphosphatase
What effect does aspirin have on the ETC?
uncoupler
