week 8: glycolysis regulation, pyruvate dehydrogenase, and citric acid cycle

Question 1

what happens to fructose-6-phosphate in the liver at higher glucose concentration? (enzyme, energy changes, final product)

Answer 1

converted to fructose-2,6-bisphosphate by liver PFK2 (dephosphoenzyme) and converts and ATP to an ADp

Question 2

what happens to fructose-2,6-bisphosphate in the liver at lower glucose concentrations? (enzyme, energy changes, final product)

Answer 2

converted by liver FBPase-2 (phosphoenzyme) to fructose-6-phosphate and forms Pi from H2O

Question 3

is fructose-2,6-bisphosphate a part of glycolysis

Answer 3

no

Question 4

what intermediate from glycolysis does fructose-2,6-bisphosphate come from?

Answer 4

fructose-6-phosphate

Question 5

what enzyme is the main control point in glycolysis

Answer 5

phosphofructokinase

Question 6

how does fructose-2,6-bisphosphate regulate phosphofructokinase

Answer 6

activates it – inhibits corresponding enzyme in gluconeogenesis

Question 7

which enzymes are the three irreversible steps in glycolysis catalyzed by?

Answer 7

hexokinase
phosphofructose kinase
pyruvate kinase

Question 8

why would we need to reverse glycolysis

Answer 8

the brain, nervous system, and red blood cells only use glucose for ATP synthesis, so need gluconeogenesis after vigorous exercise or prolonged fasting to quickly regenerate glucose levels

Question 9

characteristics of hexokinase

Answer 9

hexokinase can catalyze a variety of reactions (nonspecific), lower km, inhibited by G6P

Question 10

characteristics of glucokinase

Answer 10

glucokinase is hexokinase of liver and only works on glucose – much higher km (only works at high [glucose]), not inhibited by G6P

Question 11

how are hexokinase and glucokinase related and when is one used over the other

Answer 11

they are isozymes and can catalyze the same reaction

glucokinase is enzyme in the liver and because of high km only works at higher [glucose]

Question 12

why do most tissues use hexokinase (over glucokinase)

Answer 12

metabolize blood glucose for energy, the G6P is trapped in the cell, so there is only product inhibition once you have enough glucose for energy

Question 13

why does the liver use glucokinase over hexokinase?

Answer 13

it must maintain blood glucose, so when there is high blood glucose is uses glucokinase to store it as glycogen, and it is not inhibited by G6P so it can take up excess glucose and store it

Question 14

when would the liver use hexokinase? (in addition to glucokinase)

Answer 14

keeps a little hexokinase around to do glycolysis for energy when glucose levels are normal/low

Question 15

how are glucokinase and hexokinase regulated by substrate availability?

Answer 15

glucokinase is highly regulated by substrate availability due to Km being nearer to normal glucose levels while hexokinaase has a lower km than normal levels so it’s not really affected by substrate availability

Question 16

how does the cell know when it needs ATP? how is glycolysis regulated to respond to this condition?

Answer 16

high ADP/AMP concentrations tell the cell it needs ATP and will activate PFK-1 and pyruvate kinase

Question 17

which of the three regulated enzymes in glycolysis is the main control point

Answer 17

phosphofructokinase

Question 18

what enzyme is considered the secondary control point in glycolysis?

Answer 18

pyruvate kinase

Question 19

how is pyruvate kinase regulated by the need for glycolysis

Answer 19

fructose 1,6 bisphosphate activates (strongest regulator); Acetyl-coA and NADH inhibits

Question 20

how is pyruvate kinase regulated by ATP

Answer 20

ATP inhibits, and ADP/AMP activate

Question 21

what inhibits phosphofructokinase

Answer 21

citrate

Question 22

what inhibits pyruvate kinase

Answer 22

acetyl coA and NADH

Question 23

what activates phosphofructokinase (PFK)

Answer 23

AMP/ADP, fructose-2,6-bisphosphate

Question 24

what inhibits PFK

Answer 24

ATP, citrate

Question 25

anaerobic glycolysis substrate/product summary

Answer 25

glucose + 2ADP + 2pi --> 2 lactacte + 2 ATP + 2H2O

Question 26

process of alcoholic fermentation in yeast

Answer 26

pyruvate --pyruvate carboxylase--> acetaldehyde --alcohol dehydrogenase--> ethanol

Question 27

what are the 2 primary sources of energy for cancer cells?

Answer 27

glucose and glutamate (but can use any of intermediates of glycolysis as well)

Question 28

how do cells get energy

Answer 28

from C atom oxidation

Question 29

where does the TCA cycle occur?

Answer 29

mitochindrion

Question 30

what are semipermeable membranes permeable to and what is mechanism

Answer 30

hydrophobic (nonpolar) molecules (O2, CO2), small, uncharged molecules (H2O) get in by diffusion

Question 31

what are semipermable membranes impermable to and how do those get across?

Answer 31

large, polar, charged molecules get across via mediated transport system

Question 32

what are 2 types of mediated transport

Answer 32

passive: facilitates diffusion active: uses energy to go against concentration gradient

Question 33

what is a uniport

Answer 33

single channel allows single molecule to go one direction

Question 34

what is a symport

Answer 34

single channel which allows 2 substrates to go in same direction

Question 35

what us an antiport

Answer 35

single channel which allows 2 substrates to go in opposite direction

Question 36

what/how/why is the mitochondrial outer membrane permeable to?

Answer 36

has a protein called porin which punches holes in it so permeable to molecules smaller than 5Kd by diffusion

Question 37

feature of mitochondrial inner membrane

Answer 37

larger surface area due to folds (cristae)

Question 38

what do the cristae due

Answer 38

increase surface area, allow for localized buildup of concentration to control contents of matrix, provides scaffold for ETC to occur

Question 39

how is pyruvate imported into the mitochondria

Answer 39

a symport with H+

Question 40

where does the citric acid cycle occur in eukaryotes

Answer 40

the mitochondrial matrix

Question 41

how do cristae relate to respiratory activity of cell

Answer 41

more cristae = more surface area = more e- transport chain complexes which give more respiration

Question 42

what is oxidative carboxylation

Answer 42

synthesis of acetyl coa from pyruvate

Question 43

what is the use of acetyl coa

Answer 43

its a high energy compound, so cleavage can provide energy to drive the TCA cycle

Question 44

what are sources of acetyl coa and how are these used

Answer 44

amino acids (proteins), fatty acids (lipids), glycolysis (carbohydrates) are all used as sources for acetyl coa in the first stage of cellular respiration

Question 45

what components make up pyruvate dehydrogenase; what kind of enzyme is this

Answer 45

E1, E2, and E3 -- a multienzyme complex

Question 46

what is E1 (in pyruvate dehydrogenase)

Answer 46

pyruvate decarboxylase

Question 47

what is E2 in pyruvate dehydrogenase)

Answer 47

dihydrolipoyl transacetylase

Question 48

what is E3 in pyruvate dehydrogenase)

Answer 48

dihydrolipoyl dehydrogenase

Question 49

what are 2 benefits of multienzyme complexes?

Answer 49

1. enhanced reaction rates due to channeling of intermediates and limited side reactions 2. coordinated regulation

Question 50

how does thiamine pyrophosphate (TPP) work in pyruvate dehydrogenase

Answer 50

a cofactor bound to E1 which decarboxylates pyruvate yielding a hydroxyethyl-TPP carbanion -- has an acidic proton