BCEM 393 Lecture Notes - Lecture 11: Glucose Transporter, Hexokinase, Glut4

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rosefrog223

13 Jun 2018

School

University of Calgary

Department

Biochemistry

Course

BCEM 393

Professor

Robert Allan Edwards

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Glycolysis and Fermentation

GLUCOSE UPTAKE — GLUCOSE TRANSPORTERS

- Transmembrane carrier proteins

- Carrier proteins are involved in facilitated diffusion

- Carrier proteins move molecules down their concentration gradients

- GLUT4 (glucose transporter 4)

- Important to have in blood stream after having a meal because insulin levels are high

- Insulin levels signal the release of GLUT4

GLYCOLYSIS — AN OVERVIEW

- Glycolysis is the sequence of reactions that converts one molecule of glucose into two

molecules of pyruvate while generating ATP

- Function is to generate ATP and to provide building blocks for biosynthesis

- Intermediate molecules can function as precursors to other molecules

GLYCOLYSIS

- Common to both prokaryotic and eukaryotic cells

- In eukaryotic cells, glycolysis takes place in the cytoplasm

- Glycolysis can be broken down into 2 main stages:

- Stage 1: Trap and prep

- Traps the glucose in the cell and forms a compound that can be readily cleaved into

phosphorylated 3-carbon units

- Stage 2: Harvest

- ATP is harvested when the #-carbon fragments are oxidized to pyruvate

GLYCOLYSIS OVERVIEW

- 6 carbons enter the pathway as one glucose, 6 carbons exit the pathway as 2 pyruvate

molecules

- Pathway can be divided into prep and payoff phases

- Carbon is split from one 6 carbon unit into 2, 3 carbon units

- At steady state, flux in stage 2 is 2 times greater than flux in stage 1

- 2 ATP are used to prime (start) the pathway, 4 ATP are produced in the end; net is 2

ATP/glucose

- 2 NAD+ are converted to NADH

STAGE 1 PREPARATION

- Point of regulation: Hexokinase inhibited by its product G6P —> irreversible step

- Main point of regulation: Phosphofructokinase works as the pacemaker of glycolysis —>

irreversible step

- The activities of the points of regulation are regulated by the reversible binding of allosteric

effectors, by covalent modification, or by the regulation of transcription

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HEXOKINASE TRAPS GLUCOSE INSIDE THE CELL

- Dont want too much glucose build up because then glucose cant, or it becomes hard for it

to, enter the cell

- It is phosphorylated by ATP to form G6P by hexokinase

- Requires energy

- Requires Mg2+ for activity (forms a complex with ATP)

- Mg2+ is used to stabilize the charge repulsion in the phosphate group of ATP

- The reaction catalyzed by hexokinase is virtually irreversible and is a site of regulation

- Significance of reaction:

- G6P cannot pass through the cell membrane because it is not a substrate for glucose

transporters

- Ensures glucose does not build up inside the cell so that glucose can continue to move

down its concentration gradient (GLUTs)

- Prepares glucose to become a phosphorylated three-carbon compound with high

phosphoryl-transfer potential —> able to destabilize glucose and facilitate the next series of

metabolic steps

PHOSPHOGLUCOSE ISOMERASE CATALYZES THE REVERSIBLE REACTION OF CONVERTING

G6P TO F6P

- Conversion of an aldehyde sugar (aldose) to a ketone sugar (ketose)

- What is the logic behind this reaction?

- Prepares the cell for later glycolytic steps, which metabolize three-carbon molecules sing

G6P is not readily cleaved into two 3-carbon fragments, while F6P is

PHOSPHOFRUCTOKINASE TRAPS THE SUGAR AS THE FRUCTOSE ISOMER

- Fructose 6-phosphate is phosphorylated by ATP to fructose 1,6-bisphosphate (F-1,6-BP)

- Requires energy

- Requires Mg2+ for activity (forms a complex with ATP)

- This reaction is irreversible under cellular conditions

- The major regulatory site for glycolytic flux (ie. pacemaker)

PHOSPHOFRUCTOKINASE IS AN ALLOSTERIC ENZYME

- Recall, that most enzymes follow Michaelis-Menton kinetics

- Not regulated in the cell; activity is governed simply by substrate presence (maximum rate

achieved by the system, at saturating substrate concentration)

- Allosteric enzymes have multiple active sites and distinct regulatory sites that control the flu

of biochemicals through a metabolic pathway

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Document Summary

Carrier proteins are involved in facilitated diffusion. Carrier proteins move molecules down their concentration gradients. Important to have in blood stream after having a meal because insulin levels are high. Insulin levels signal the release of glut4. Glycolysis is the sequence of reactions that converts one molecule of glucose into two molecules of pyruvate while generating atp. Function is to generate atp and to provide building blocks for biosynthesis. Intermediate molecules can function as precursors to other molecules. Common to both prokaryotic and eukaryotic cells. In eukaryotic cells, glycolysis takes place in the cytoplasm. Glycolysis can be broken down into 2 main stages: Traps the glucose in the cell and forms a compound that can be readily cleaved into phosphorylated 3-carbon units. Atp is harvested when the #-carbon fragments are oxidized to pyruvate. 6 carbons enter the pathway as one glucose, 6 carbons exit the pathway as 2 pyruvate molecules. Pathway can be divided into prep and payoff phases.

Related Questions

1. C6H12O6 + 6O2 Ã 6CO2 + 6H2O Glucose is being _____ to _____ and oxygen is being _____ to _____. a. oxidized; carbon dioxide; reduced; water b. oxidized; water; reduced; carbon dioxide Incorrect c. reduced; water; oxidized; carbon dioxide d. reduced; carbon dioxide; oxidized; water

2. Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? a. the citric acid cycle Incorrect b. glycolysis c. the digestion of starch to glucose d. oxidative phosphorylation

3. Which of the following is a catabolic pathway? a. gluconeogenesis b. production of starch Incorrect c. glycolysis d. production of glycogen

4. Per molecule, the oxidation of a fatty acid results in _____ energy storage than the oxidation of glucose. a. the same b. less Incorrect c. more d. None of the above; fatty acids cannot be oxidized.

5. Of the eight reactions in the citric acid cycle, how many are oxidation-reduction reactions? a. one b. two c. three d. four e. five

6. The process of glycolysis transfers the energy in sugar molecules into the stored energy of activated carriers such as ATP and NADH. Which statement is true about glycolysis? a. Only eukaryotic organisms do glycolysis. b. The ten reactions of glycolysis are identical in all eukaryotic cells, but are different in prokaryotic cells due to their diverse metabolic strategies. Incorrect c. The ten reactions of glycolysis are identical in almost all living organisms on the planet. d. There are many ways to oxidize glucose and transfer energy into activated carriers; the diversity of organisms on the planet is reflected in the diversity of their mechanisms of glycolysis.

7. Referring to the sentence completed in #13 above, the purpose of the latter reaction (in active muscle cells) is to _____. a. accumulate lactic acid in the cell, which provides additional energy for the production of ATP Incorrect b. slow down glycolysis until oxygen becomes available again c. accelerate the Krebs cycle, which will restore the oxygen supply d. regenerate NAD+ so that glycolysis can continue in the absence of oxygen

8. What are the products of the citric acid cycle? a. carbon dioxide, NADH, FADH2 and GTP b. carbon dioxide, NAD+, FAD and GTP c. NADH, FADH2, and acetyl CoA Incorrect d. carbon dioxide and water

9. Which statement is true about enzymes? a. Enzymes catalyze chemical reactions because they make inherently endergonic reactions exergonic. b. Each enzyme in a cell can catalyze many different chemical reactions involving chemically different substrates. Incorrect c. Enzymes can only catalyze reactions in one direction. d. After catalyzing a reaction, an enzyme is permanently altered and can no longer bind substrate. e. None of the above is true. 1

10. âG measures the change in free energy in a system as it converts reactant (Y) into product (X). When [X] = [Y], âG is equal to _____. a. RT b. ÎGÂ° + RT c. ÎGÂ° d. ln [X]/[Y]

11. The âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. What conditions in the cell would lead to a âG for ATP hydrolysis of -11 kcal/mol? a. An increase in the ATP/ADP ratio b. An increase in anabolic activity in the cell c. Transport of ATP out of the compartment where the reaction is occurring Incorrect d. A decrease in the ATP/ADP ratio

12. In the first reaction of glycolysis, a phosphate transferred from ATP to a glucose molecule to produce glucose-6-phosphate and ADP. Under conditions existing in the cell, the free energy change for this reaction is -8.0 kcal/mole. Which of the following statements is true? Recall that the âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. a. Glucose concentrations in the cell are always low, making this reaction more favorable than would be expected. b. This reaction is less favorable than would be expected, given the âGÂ° of ATP hydrolysis. c. Glucose-6-P concentrations in the cell are very low relative to glucose concentrations, making the reaction more favorable than would be expected. d. The âGÂ° for the addition of a phosphate to glucose must be -0.7 kcal/mole.

13. Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S --> ES Keq for ES = 10 E + I> EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? a. When S is present in excess, no I molecules will bind to E. b. E binds I more tightly than S. c. The binding energy of the ES interaction is greater than that of the EI interaction. d. Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative.

A catabolic pathway would predictably result in the
A) reduction of a sugar.
B) synthesis of a macromolecule.
C) breakdown of a macromolecule.
D) breakdown of an atom.
2.
The drug Ritonavir is used to treat people with HIV/AIDS. It worksby binding to the active site of HIV-1 protease, an enzyme used bythe AIDS virus to create new proteins for production of newviruses.Once bound, the HIV-1 protease cannot produce proteins.Ritonavir can be classified as a(n)
A) competitive inhibitor.
B) allosteric inhibitor.
C) activator.
D) non-competitive inhibitor.
3.
During cellular respiration, __________ is the final electronacceptor that allows the regeneration of the cellâs supply of NAD+.In fermentation, ____________ is the final electron acceptor forNAD+ regeneration.
A) pyruvate / lactic acid
B) pyruvate / oxygen
C) ethanol / CO2
D) oxygen / pyruvate
4.
Which of the following clues would tell you if a cell isprokaryotic or eukaryotic?
A) whether or not the cell carries out cellular metabolism
B) the presence or absence of ribosomes
C) whether or not the cell is partitioned by internalmembranes
D) whether or not the cell contains DNA
5.
Phosphofructokinase (PFK) is an allosteric enzyme that regulatesglycolysis. When cellular concentrations of ATP and citrate become__________, this enzymeâs activity decreases. When cellularconcentrations of AMP become ________, the enzyme isactivated.
A) high / high
B) high / low
C) low / high
D) low / low
6.
______________ is an enzyme that can utilize the free energy in thehydrogen gradient (voltage) produced between the inner and outermembrane of the mitochondrion. The enzyme uses this energy toproduce ________.
A) ATP synthase/ ATP
B) PFK/ ATP
C) PFK/ glucose
D) ATP synthase/ ADP
7.
ATP is able to do cellular work because it
A) has a high energy phosphate bond that can be hydrolyzed torelease energy.
B) converts light energy into chemical bond energy.
C) contains the sugar ribose, which can provide additional energyfor a cell.
D) its hydrolysis is endergonic.
8.
A solution of starch at room temperature does not readily decomposeto form a solution of simple sugars because
A) the starch solution has less free energy than the sugarsolution.
B) the activation energy barrier for this reaction cannot besurmounted.
C) the hydrolysis of starch to sugar is endergonic.
D) starch hydrolysis is nonspontaneous.
9.
A person exposed to toxins would have more activity in their___________compared to an unexposed person.
A) lysosomes
B) Golgi bodies
C) rough endoplasmic reticulum
D) smooth endoplasmic reticulum
10.
Which of the following statements about fermentation is true?
A) The function of fermentation is to regenerate the fermentingcells' supply of NAD+.
B) Fermentation allows a fermenting cell to gain more energy perglucose molecule than a non-fermenting cell.
C) Fermentation produces either lactic acid or ethanol that thefermenting cell can use as an energy source.
D) Fermentation is a universal process that occurs in all cells andall organisms.
11.
A glucose molecule is completely broken down to carbon dioxide andwater in glycolysis and the citric acid (Krebs) cycle, but togetherthese two processes yield only a few molecules of ATP. Whathappened to most of the energy that the cell obtains from theoxidation of glucose?
A) It was lost as heat.
B) It is stored in the carbon dioxide and water molecules releasedby these processes.
C) It is stored in the ATP that was formed by glycolysis and thecitric acid cycle.
D) It is stored in NADH and FADH2
12.
The First Law of Thermodynamics states that
A) entropy tends to increase in a system.
B) entropy tends to decrease in a system.
C) energy cannot be created nor destroyed.
D) the quality of energy in the universe is decreasing.
13.
The endosymbiotic theory states that _______________ evolved as aresult of a symbiotic relationship between different types ofbacteria. _____________ is thought to be the selective factor thatmade this symbiosis advantageous.
A) mitochondria / A change in the Earthâs atmosphere from anaerobicto aerobic
B) endoplasmic reticulum / A decrease in the amount of foodavailable in the environment
C) chloroplasts / A change in the Earthâs atmosphere from aerobicto anaerobic
D) lysosomes / A decrease in the amount of food available in theenvironment
14.
A mutation in a fruit fly affects one of the proteins that pumphydrogen ions across the inner mitochondrial membrane; thismutation makes that particular protein function less efficiently.When comparing aerobic cellular respiration in this fly with awild-type fly, you would predict that the mutant fly would
A) produce less ATP than a wild-type fly.
B) show no difference in ATP production when compared to awild-type fly.
C) produce more ATP than a wild-type fly.
D) not be able to produce any ATP via aerobic cellularrespiration.
15.
Proteins that are destined to be exported from the cell have unique_________________ that are recognized by signal recognitionparticles and thus moved to the _________________ duringtranslation.
A) phosphofructokinases / nucleus
B) codons / rough endoplasmic reticulum
C) signal recognition sequences / rough endoplasmic reticulum
D) signal recognition sequences / free ribosomes
16.
During the Krebs cycle
A) NADH is oxidized.
B) ATP is produced.
C) pyruvate is produced.
D) Acetly CoA gains a carbon to form pyruvate.
17.
Why does the oxidation of organic compounds by molecular oxygen toproduce CO2 and water release free energy?
A) Electrons are being moved from atoms that have a lower affinityfor electrons (such as C) to atoms with a higher affinity forelectrons (such as O).
B) The electrons have a higher potential energy when associatedwith water and CO2 than they do in organic compounds.
C) The covalent bond in O2 is unstable and easily broken byelectrons from organic molecules.
D) The covalent bonds in organic molecules and molecular oxygenhave more kinetic energy than the covalent bonds in water andcarbon dioxide.
18.
In a chemical reaction, if ?G is negative, it means that thereaction is
A) exergonic, and work needs to be done for the reaction toproceed.
B) exergonic, and work can be done with energy released from thereaction.
C) endergonic, and work needs to be done in order for the reactionto proceed.
D) endergonic, and work can be done with energy released from thereaction.
19.
The energy for an endergonic reaction comes from a(n) ___________reaction.
A) ADP + P --> ATP
B) endergonic.
C) exergonic.
D) anabolic
20.
Glycolysis
A) involves catabolic reactions and ATP is produced.
B) involves anabolic reactions and ATP is produced.
C) involves catabolic reactions and creates energy.
D) involves anabolic reactions and creates energy.

Question 401 pts

Kinetic energy is the stored energy that can be used for motion.

True

False

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Question 411 pts

When an electron is transferred from one atom to another, and the two atoms are then electrically attracted to one another, a(n) ________________ bond is formed.

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Question 421 pts

Changing the number of ____________ of an atom would change the chemical properties of the atom.

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Question 431 pts

Forming molecules and breaking down molecules in biological organisms usually requires the use of _________ to help the reaction proceed faster.

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Question 441 pts

Organic molecules have a core composed of .

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Question 451 pts

The building blocks of carbohydrates are

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Question 461 pts

Water molecules crossing a membrane from high to low concentration is .

active transport

cell fate

facilitated diffusion

osmosis

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Question 471 pts

Choose the membrane molecule responsible for the passage of polar molecules and ions into and out of the cell.

phospholipids

transmembrane channel proteins

cell surface proteins

carbohydrate chains

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Question 481 pts

The simplest cells are .

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Question 491 pts

Which of the following membrane bound organelles are found inside bacterial cells:

nucleus

organelles are not found in prokaryotic cells

mitochondria

chloroplasts

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Question 501 pts

Which of the following is a specialized components of the cell, is associated with the rough endoplasmic reticulum, and is responsible for making proteins.

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Question 511 pts

Proteins are sorted, modified, and packaged by the _____________ and later transported to the outside of the cell.

ribosomes

golgi bodies (golgi apparatus)

nucleus

mitochondria

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Question 521 pts

Dehydration synthesis is a process of linking two smaller subunits together to form a polymer. Which of the following statements below is true of dehydration synthesis?

Oxygen is consumed.

A water molecule is removed from the molecules.

A water molecule is added to the molecules

Carbon dioxide is given off.

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Question 531 pts

Proteins are made up of _________ held together by peptide bonds.

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Question 541 pts

Which of the following gives an amino acid its properties?

NH2

R Group or functional group

COOH

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Question 551 pts

The final three-dimensional shape of a protein that includes the bonding of two or more polypeptide chains is call its _____ structure.

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Question 561 pts

How do DNA and RNA differ?

all statements are differences between DNA and RNA.

DNA is double stranded while RNA is single stranded.

They have different sugars.

Thymine is present in DNA but not in RNA.

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Question 571 pts

Which of the following is a component of a DNA nucleotide?

phosphate

a nitrogen containing base

All are components of a nucleotide.

5-carbon sugar

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Question 581 pts

Cell membranes are made up of several different types of molecules. Select the membrane molecule below that is made up of a polar region and two non-polar fatty acid tails.

transmembrane proteins

carbohydrate chains

phospholipids

cell surface proteins

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Question 591 pts

Two organelles which are believed to have once been free-living bacterial cells are ____________ and ______________.

chloroplasts and mitochondria

golgi apparatus and endoplasmic reticulum

ribosomes and nucleolus

peroxisomes and lysosomes

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