Biochem: Ch 9, 10 Flashcards
GLUT2 is found in ___ for ___
liver for glucose storage
pancreatic beta islet cells as part of the glucose sensor
GLUT2 has a ___ Km
high
GLUT4 is found in ___
adipose tissue and muscle
GLUT4 is stimulated by ___
insulin
GLUT4 has a ___ Km
low
glycolysis occurs in
cytoplasm of all cells
glycolysis does not require
oxygen
glycolysis yields
2 ATP per molecule of glucose
glucokinase
irreverible
converts glucose to glucose 6-phosphate in pancreatic beta-islet. ells as part of glucose sensor
glucokinase is present in
pancreatic beta-islet cells as part of the glucose sensor
glucokinase is repsonsive to
insulin in the liver
hexokinase
irreversible
converts glucose to glucose 6-phosphate in peripheral tissues
posphofructokinase-1 (PFK-1)
irreversible
phosphorylates fructose 6-phosphate to fructose 1,6-biphosphate in the rate-limiting step of glycolysis
PFK-1 is activated by
AMP and fructose 2,6-biphosphate (F2,6-BP)
PFK-1 is inhibited by
ATP and citrate
phosphofructokinase-2 (PFK-2)
produces the F2,6-BP that activates PFK-1
PFK-2 is activated by
insulin
PFK-2 is inhibited by
glucagon
glyceraldehyde-3-phosphate dehydrogenase
produces NADH, which can feed into the electron transfer chain
3-phosphoglycerate kinase
perform substrate level phosphorylation
place inorganic phosphate (Pi) onto ADP to form ATP
pyruvate kinase
irreversible
perform substrate level phosphorylation
place inorganic phosphate (Pi) onto ADP to form ATP
enzymes that catalyze irreversible reactions
glucokinase, hexokinase, PFK-1, pyruvate kinase
(How Glycolysis Pushes Forward the Process: Kinases)
what happens to the NADH produced in glycolysis when oxygen is present
oxidized by the mitochondrial electron transport chain when oxygen
what happens to the NADH produced in glycolysis when oxygen is not present
+ex
if oxygen or mitochondria are absent, NADH is oxidized by cytoplasmic lactate dehydrogenase
ex: red blood cells, skeletal muscle (during short, intense bursts of exercise), any cell deprived of oxygen
glycolysis in liver
part of the process by which excess glucose is converted to fatty acids for storage
hexokinase is inhibited by
its product G 6-P
glycolysis rxn rq
substrate level phosphorylation
ADP is directly phosphorylated to ATP using high energy intermediate
not dependent on oxygen
feed forward activation
product of an earlier rxn of glycolysis stimulates or prepares a later reaction in glycolysis
in the absence of oxygen, ___ will occur
fermentation
lactate dehydrogenase
oxidized NADH to NAD+
important during fermentation
fermentaion
reduces pyruvate to lactate and oxidizes NADH to NAD+
so that all the available NAD+ isn’t used up if glycolysis continues
dihydroxyaceton phosphate (DHAP)
used in hepatic and adipose tissue for triacylglycerol synthesis
1,3-BPG and phosphoenolpyruvate (PEP)
high energy intermediates used to generate ATP by substrate level phosphorylation
the only ATP gained in anaerobic respiration
why must pyruvate undergo fermentation for glycolysis to continue?
fermentation must occur to regenerate NAD+, which is limited in supply in cells
fermentation generates no ATP or energy carriers, it merely regenerates the coenzymes needed in glycolysis
galactose comes from
lactose in milk
galactose metabolism
- trapped in cell by galactose kinase
- converted to glucose 1-phosphate via galactose-1-phosphate uridyltransferase and an epimerase
fructose comes from
honey, fruit, and sucrose (common table sugar)
fructose metabolism
- trapped in cell by fructokinase
- cleaved by aldolase B to form glyceraldehyde and DHAP
in well fed state, galactose can enter…
glycolysis or contribute to glycogen storage
epimerases
enzymes that catalyze the conversion of one sugar epimer to another
primary lactose intolerance is caused by
hereditary deficiency of lactase
pyruvate dehydrogenase complex (PDH)
irreversible
complex of enzymes that oxiidizes pyruvate to acetyl-CoA
requires multiple cofactors and coenzyme (vitamin B1, TPP, Mg2+)
pyruvate dehydrogenase is found in
the liver
high insulin levels signal to the liver that individual is in…
thus…
a well fed state
the liver should burn glucose for energy and shift fatty acid equilibrium toward production and storage rather than oxidation
possible fates of pyruvate
- conversion to acetyl CoA by PDH
- conversion to lactate by lactate dehydrogenase
- conversion to oxaloacetate by pyruvate carboxylase
how does caetyl CoA affect PDH complex? why?
glycogenesis
glycogen synthesis
production of glycogen using two main enzymes: glycogen synthase, branching enzyme
glycogen synthase
rate limiting enzyme of glycogenesis
creates alpha-1,4 glycosidic links between glucose molecules
branching enzyme
glycogenesis
moves a block of oligoglucose from one chain and adds it to the growing glycogen as a new branch using an alpha-1,6 glycosidic link
glycogenolysis
breakdown of glycogen using two main enzymes: glycogen phosphorylase, debranching enzyme
glycogen phosphorylase
glycogenolysis
removes single glucose 1-phosphate molecules by breaking alpha-1,4 glycosidic links
debranching enzyme
glycogenolysis
moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link
also removes the branchpoint, releasing a free glucose molecule
glycogen is stored in
cytoplasm in granules
isoforms
slightly different versions of the same protein
glycogen storage diseases
accumulation or lack of glycogen in one or more tissues due to glycogen enzyme isoforms
what types of glycosidic links exist in a glycogen granule?
gluconeogenesis occurs in
cytoplasm and mitochondria, predominantly in the liver
small contribution from the kidneys
gluconeogenesis
opposite of glycolysis (with same enzymes)
production of glucose
gluconeogenesis steps thru enzymes
three irreversible steps
- pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK)
- fructose-1,6-biphosphatase –> rate limiting step
- glucose-6-phosphatase
pyruvate carboxylase
gluconeogenesis
converts pyruvate into oxaloacetate
phosphoenolpyruvate carboxykinase (PEPCK)
gluconeogenesis
converts oxaloacetate into phosphoenolpyruvate
fructose-1,6-biphosphatase
gluconeogenesis
converts fructose 1,6-biphosphate to fructose-6-phosphate
rate limiting step of gluconeogensis
glucose-6-phosphatase
gluconeogenesis
converts glucose 6-phosphate to free glucose
glucose-6-phosphatase is found in
endoplasmic reticulum of liver only
glucogenic amino acids
all except leucine and lysine
can be converted into intermediates that feed into gluconeogenesis
ketogenic amino acids
can be converted into ketone bodies, which can be used as an alternative fuel, particularly during periods of prolonged starvation
to produce glucose in liver during gluconeogenesis, fatty acids…
must be burned to provide this energy and stop the forward flow of the citric acid cycle
under what physiological conditions should the body carry out gluconeogenesis?
when an individual has been fasting for >12 hours
hepatic and renal cells must have enough energy to drive the process of glucose creation, which requires sufficient fat stores to undergo beta oxidation
pentose phosphate pathway (PPP)
aka hexose monophosphate (HMP) shunt
glucose 6-phosphate enters the pathways and the products are NADPH, sugars for biosynthesis, and glycolysis intermediates
pentose phosphate pathway (PPP) occurs in
cytoplasm of most cells
glucose-6-phosphate dehydrogenase (G6PD)
PPP
rate limiting enzyme
NAD+
high energy electron acceptor (in many biochemical rxns)
potent oxidizing agent - helps produce NADH
NADPH
primarily acts as electron donor
potent reducing agent
used in biosynthesis, in the immune system, and to help prevent oxidative damage
NADH produced from
reduction of NAD+
NADH
feeds in ETC to indirectly produce ATP
glutathione
reducing agent that helps reverse radical formation before damage is done to cell
what are the major metabolic products of the PPP?
NADPH and ribose-5-phosphate
acetyl-CoA
contains high energy thioester bond that can be used to drive other reactions when hydrolysis occurs
acetyl coa can be formed from
- pyruvate via pyruvate dehydrogenase complex (PDH)
- fatty acids that enter the mitochondria using carrier
- carbon skeletons of ketogenic amino acids, ketone bodies, and alcohol
pyruvate dehydrogenase kinase
phosphorylates PDH when ATP or acetyl CoA levels are high, turning it off
pyruvate dehydrogenase phosphatase
dephosphorylates PDH when ADP levels are high, turning it on
acetyl coA formation from fatty acids
- fatty acids couple with CoA in cytosol to form fatty acyl CoA, which moves to intermembrane space
- acyl (fatty acid) group is transferred to carnitine to form acyl-carnitine which crosses the inner membrane
- acycl group is transferred to a mitochondrial CoA to reform fatty acyl CoA, which can undergo beta oxidation to form acteyl CoA
citric acid cycle/krebs cycle/TCA cycle occurs in
mitochondrial matrix
citric acid cycle/krebs cycle/TCA cycle main function
oxidation of acteyl COA to CO2 and H2O
produces high energy electron carrying molecules (NADH and FADH2) and GTP
citric acid cycle steps
- citrate formation
- citrate isomerized to isocitrate
- alpha-ketoglutarate and CO2 formation –> rate limiting enzyme: isocitrate dehydrogenase
- succinyl-CoA and CO2 formation
- succinate formation
- fumarate formation
- malate formation
- oxaloacetate formed anew
citric acid cycle
citrate formation
citric acid cycle
citrate isomerized to isocitrate
citric acid cycle
alpha-ketoglutarate and CO2 formation
citric acid cycle
succinyl-coA and CO2 formation
citric acid cycle
succinate formation
citric acid cycle
fumarate formation
citric acid cycle
malate formation
citric acid cycle
oxaloacetate formed anew
citrate synthase
citric acid cycle: 1 citrate formation
citrate synthase inhibitors
ATP, NADH, succinyl-CoA, citrate
aconitase
citric acid cycle step 2: 2 citrate isomerized to isocitrate
isocitrate dehydrogenase
citric acid cycle: 3 alpha ketoglutarate and CO2 formation
isocitrate dehydrogenase
activators
ADP, NAD+
isocitrate dehydrogenase inhibitors
ATP, NADH
alpha-ketoglutarate dehydrogenase complex
citric acid cycle: 4 succinyl-CoA and CO2 formation
alpha-ketoglutarate dehydrogenase complex activators
ADP, Ca2+
alpha-ketoglutarate dehydrogenase complex inhibitors
ATP, NADH, succinyl-CoA
succinyl-CoA synthetase
citric acid cycle: 5 succinate formation
succinate dehydrogenase
citric acid cycle: 6 fumarate formation
fumarase
citric acid cycle: 7 malate formation
malate dehydrogenase
citric acid cycle: 8 oxaloacetate formed anew
dehydrogenases
subtype of oxidoreductases
transfer hydride ion to electron acceptor (NAD+ or FAD)
synthases
create new covalent bonds without energy input
synthetases
create new covalent bonds with energy input
flavoprotein
covalently bonded to FAD
control points of citric acid cycle
- citrate synthase
- isocitrate dehydrogenase
- alpha-ketoglutarate dehydrogenase complex
what enzyme catalyzes the rate limiting step of the citric acid cycle?
isocitrate dehydrogenase
electron transport chain occurs in
matrix facing surface of inner mitochondrial membrane
electron transport chain
- NADH donates electrons to the chain, which are passed from one complex to another
- as ETC progresses, reduction potentials increase until oxygen receives the electrons
- 4 complexes
complex I
complex II
complex III
complex IV
NADH shuttles (why?)
NADH cannot cross intermembrane –> two shuttle mechanisms to transfer electrons
glycerol 3-phosphate, malate-aspartate
glycerol 3-phosphate shuttle
NADH shuttle
malate-aspartate
NADH shuttle
aerobic components of respiration occur in the
mitochondria
anaerobic components of respiration occur in
cytosol
anaerobic components of respiration include
glycolysis and fermentation
proton-motive force
electrochemical proton gradient generated by the complexes of the ETC
As [H+] increases in intermembrane space: pH drops, voltage difference between intermembrane space and matrix inc due to proton pumping
cytochromes
proteins with heme groups in which iron is reduced to Fe2+ and reoxidized to Fe3+
Q cycle
increases the gradient of proton motive force across inner mitochondrial membrane
ATP Synthase
ATP synthase
F0
ion channel that allows protons to travel along their gradient into the matrix
chemiosmotic coupling
allows the chemical energy of the gradient to be harnessed as a means of phosphorylated ADP, forming ATP
ATP synthase
F1
utilizes the energy released from electrochemical gradient to phosphorylate ADP to ATP
key regulators of oxidative phosphorylation
O2 and ATP
respiratory control
O2 dec
O2 is limited –> rate of oxidative phosphorylation decreases –> conc of NADH and FADH2 inc –> inhibits citric acid cycle
oxidative phosphorylation
ATP synthase generates ATP by harnessing the proton gradient
glycolysis produces
2 NADH + 2 ATP
citric acid cycle produces
3 NADH, 1 FADH2, 1 GTP
(6 NADH, 2 FADH2, 2 GTP / molecule of glucose)
each NADH yields ____ ATP
2.5
each FADH2 yields ____ ATP
1.5
pyruvate dehydrogenase produces
1 NADH/molecule of glucose
carbohydrate metabolism produces ____
30-32 ATP/molecule of glucose
respiratory control
ADP inc
ADP conc inc –> decrease in ATP –> ADP allosterically activates isocitrate dehydrogenase –> inc rate of citric acid cycle –> produces NADH and FADH2 –> inc rate of ETC and ATP synthesis
What is the correct order in which cellular respiration takes place?
I. Krebs Cycle
II. Glycolysis
III. Electron Transport Chain
(A) I, III, and II
(B) II, III, and I
(C) II, I, and III
(D) I, II, and III
(C) II, I, and III
Glycolysis takes place first then goes into the Krebs cycle, then finally into the electron transport chain.
What is the net ATP produced in each step of cellular respiration and where does each step occur in the cell?
(1) Glycolysis
(2) Krebs Cycle
(3) ETC
Glycolysis produces a net of 2 ATP molecules and occurs in the cytoplasm of the cell.
Krebs Cycle produces a net of 2 ATP and occurs in the outer lumen of the mitochondria.
Electron Transport Chain (ETC) produces a net of about 34 ATP and occurs in the inner membrane (lumen) of the mitochondria.
Which of the following processes are conducted during aerobic AND anaerobic respiration?
(A) Glycolysis
(B) The Linking Step
(C) Electron Transport Chain
(D) Kreb’s Cycle
(A) Glycolysis
Glycolysis is conducted during aerobic respiration and anaerobic respiration. The linking step (pyruvate dehydrogenase (PDH) step), Kreb’s cycle and electron transport chain are only conducted during aerobic respiration when O2 is available.
Anaerobic respiration in humans results in the production of _____________ while in anaerobic respiration in yeast (known as fermentation) results in the production of ____________.
(A) lactic acid, ethanol
(B) lactic acid, ethane
(C) ethanol, lactic acid
(D) ethane, lactic acid
(A) lactic acid, ethanol
Anaerobic respiration in humans results in the production of lactic acid while in anaerobic respiration in yeast (known as fermentation) results in the production of ethanol (an alcohol).
Glycolysis requires __ ATP and produces __ ATP; thus, this process yields a net total of __ ATP.
(A) 4, 6; 2
(B) 2, 6; 4
(C) 2, 4; 2
(D) 0, 4; 4
(C) 2, 4; 2
Glycolysis requires 2 ATP and produces 4 ATP; thus, this process yields a net total of 2 ATP.
During the fasted state, which of the following mechanisms does the body utilize to maintain its blood glucose level?
I. Glycogenolysis
II. Glycolysis
III. Gluconeogenesis
(A) II only
(B) I and II only
(C) I and III only
(D) I, II and III
(C) I and III only
In a fasted state, blood glucose levels are maintained through glycogenolysis (the breakdown of glycogen) and gluconeogenesis (the formation of glucose).
Before you can breakdown glycogen in Glycogenolysis, you have to create Glycogen. Which of the following statements about Glycogenesis is FALSE?
(A) Glucose-1-Phosphate is used to synthesize glycogen.
(B) Glucose needs to be activated by coupling to UTP.
(C) Glycogen Synthase is the rate-limiting enzyme and forms α-1,4-glycosidic bonds.
(D) A separate branching enzyme must be used to form the α-1,6-glycosidic bonds at branch points.
(B) Glucose needs to be activated by coupling to UTP.
UDP is used for coupling, not UTP.
According to Le Chatlier’s principle, if the concentration of glucose increased within a cell, what would happen to the rate of glycolysis and gluconeogenesis?
If the concentration of glucose increased within a cell, the rate of glycolysis would increase and the rate of gluconeogenesis would decrease.
According to Le Chatlier’s principle, if the concentration of oxaloacetate increased within a cell, what would happen to the rate of glycolysis and gluconeogenesis?
If the concentration of oxaloacetate increased within a cell, the rate of glycolysis would decrease and the rate of gluconeogenesis would increase.
If the concentration of ATP increased within a cell, what would happen to the rate of glycolysis and gluconeogenesis? Why?
If the concentration of ATP increased within a cell, the rate of glycolysis would decrease and the rate of gluconeogenesis would increase. This is because ATP is an allosteric inhibitor of some of the enzymes involved in glycolysis and an allosteric activator of some of the enzymes involved in gluconeogenesis.
CRB Write out a table of the amino acids that are Glucogenic (can be used as intermediates in gluconeogenesis), Ketogenic (can be converted into ketone bodies), or both.
I like to remember that the two “L” amino acids are the Ketogenic-only ones!
When someone has hyperglycemia, their body will produce insulin or glucagon? Why?
When someone has hypoglycemia, their body will produce insulin or glucagon? Why?
When someone has hyperglycemia, their body will produce insulin since insulin promotes the storage of glucose via pathways such as glycogenesis.
When someone has hypoglycemia, their body will produce glucagon since glucagon activates pathways such as gluconeogenesis and glycogenolysis that will increase one’s blood glucose levels.
Why is the production of Ribose-5-phosphate important?
Ribose-5-phosphate is a key component of DNA and RNA.
During each stage of cellular respiration, state how many net ATP/GTP, NADH, and FADH2 molecules are produced per molecule of glucose?
(1) Glycolysis
(2) The Linking Step (Pyruvate Dehydrogenase)
(3) Kreb’s Cycle
(1) Glycolysis - 2 ATP, and 2 NADH
(2) The Linking Step (Pyruvate Dehydrogenase) - 2 NADH
(3) Kreb’s Cycle - 2 GTP [similar to ATP], 6 NADH, and 2 FADH2
In total: 4 ATP/GTP, 10 NADH, 2 FADH2
Where is the majority of the Kreb’s cycle carried out in the mitochondria of eukaroytic cells?
(A) Outer Membrane
(B) Inner Membrane
(C) Intermembrane Space
(D) Mitochondrial Matrix
(D) Mitochondrial Matrix
The majority of the Kreb’s cycle is carried out in the mitochondrial matrix of eukaroytic cells.
During the linking step (pyruvate dehydrogenase), pyruvate is _______________ and becomes ______________.
(A) oxidized, oxaloacetate
(B) oxidized, acetyl-CoA
(C) reduced, oxaloacetate
(D) reduced, acetyl-CoA
(B) oxidized, acetyl-CoA
During the linking step (pyruvate dehydrogenase), pyruvate is oxidized and becomes acetyl-CoA.
If ATP levels are high, why would it be in the cell’s best interest to inhibit pyruvate dehydrogenase?
If ATP levels are high, that indicates that the cell already has enough energy; thus, it should slow down the production of that energy by inhibiting pyruvate dehydrogenase, which will in turn slow down the citric acid cycle since acetyl-CoA is required for it to run.
Which of the following molecules would Pyruvate be directly converted to in order to enter Gluconeogenesis?
(A) Glycerol
(B) Citrate
(C) Acetyl CoA
(D) Oxaloacetate
(D) Oxaloacetate
Pyruvate is converted to Oxaloacetate to enter Gluconeogenesis.
If calcium levels are high, why would it be in the cell’s best interest to activate pyruvate dehydrogenase?
High levels of calcium result from muscle contraction, which is a process that requires energy. To get more energy, the cell will want to ramp up the linking step and the Kreb’s cycle by activating pyruvate dehydrogenase.
Why is it that glycolysis can be completely turned off while Kreb’s cycle is usually turned on to one degree or another?
Glycolysis is only needed when you are using glucose for energy. The Kreb’s cycle on the other hand is needed for the utilization of sugars, fats, or amino acids for energy. Because cells need energy basically all the time, they will at least want the Kreb’s cycle turned on to some degree or another.
What will happen to the activity of the citric acid cycle when citrate is shuttled out of the mitochondrial matrix in an effort to carry acetyl-CoA to the site for fatty acid synthesis?
The citric acid cycle will slow down since the substrates of acetyl-CoA and citrate are not as available anymore.
Which of the following statements about forming Citrate are true?
I. The Thioester bond in Acetyl-CoA is hydrolyzed, providing the energy to drive Citrate Synthesis.
II. The two carbons from the Acetyl-CoA are incorporated into Citrate’s 5 Carbons.
III. The two carbons Citrate acquired from Acetyl-CoA will leave the TCA cycle as Carbon Dioxide.
(A) I only
(B) I and III only
(C) II and III only
(D) I, II and III
(B) I and III only
Each of the following statements about Citrate are true:
I. The Thioester bond in Acetyl-CoA is hydrolyzed, providing the energy to drive Citrate Synthesis.
II. The two carbons from the Acetyl-CoA are incorporated into Citrate’s 6 Carbons.
III. The two carbons Citrate acquired from Acetyl-CoA will leave the TCA cycle as Carbon Dioxide.
During the electron transport chain, NADH is oxidized to NAD+, resulting in the formation of electrons. Those electrons are then used to convert O2 into:
(A) CO2
(B) ROS
(C) H2O
(D) CO
(C) H2O
O2 is reduced into H2O via the following reaction during the electron transport chain:
2e- + 2H+ + 1/2O2 –> H2O
Fill in the blanks: The electrons from Complexes I and II are transferred to _______________, which are later transfered to _______________.
(A) Ubiquinone, Coenzyme Q
(B) Coenzyme Q, Cytochrome C
(C) Cytochrome C, Coenzyme Q
(D) None of the above.
(B) Coenzyme Q, Cytochrome C
The electrons from Complexes I and II are transferred to Coenzyme Q, which are later transfered to Cytochrome C.
Note that Coenzyme Q is synonymous with Ubiquinone.
Compare oxidative phosphorylation versus substrate-level phosphorylation.
Oxidative phosphorylation is a very specific name for what occurs during the electron transport chain. It entails the oxidation of electron carrier molecules and the phosphorylation of ADP to form ATP (via ATP synthase).
Substrate phosphorylation is when ATP is generated via a generic enzyme (i.e. pyruvate kinase).
