BIOL 3021 Lecture 14
When does gluconeogenesis occur?
during recovery from exercise
What enzyme replaces glycolysis's phosphofructokinase and hexokinase in gluconeogenesis?
phosphatase enzymes, uses GTP instead of ATP
During exercise, _____ is subject to positive feedback by a low energy charge (high AMP). Also, ____ is activated by feedforward stimulation by fructose 1-6-bisphosphate.
phosphofructokinase Pyruvate kinase
Under aerobic conditions, the product of glycolysis is
pyruvate
Name the two enzymes in glyconeogenesis that are used to bypass glycolysis's pyruvate kinase.
pyruvate carboxylase and phosphoenolpyruvate carboxykinase
To become acetyl-CoA, pyruvate goes through the _____ and loses a molecule of ____
pyruvate dehydrogenase, CO2
It takes two enzymes in gluconeogenesis to by pass the glycolysis enzyme ____
pyruvate kinase
In the TCA cycle acetyl CoA is oxidized to ____ molecules of CO2
2
Draw the reaction of pyruvate to lactate using NADH.
COO⁻ COO⁻ C=O + NADH + H⁺ ⇌ NAD⁺ + HO-C-H CH3 CH3
How many extra ATPs can be produced from the NADH in glycolysis and under what conditions?
4 additional ATP, but only under aerobic conditions. anaerobic glycolysis can't use the NADH for ATP so stops at a net of 2 ATP
UPD synthesis uses ____ intermediates with no chirality to keep the reaction going
4-ketone
The _____ describes the physiological process that occurs when glucose is converted to lactate during intense exercise, and when the lactate is converted back to glucose during the recovery period.
Cori Cycle
When an organism is resting, the three essentially irreversible enzymes are subject to negative feedback. name them.
Hexokinase, inhibited by its product glucose 6-phosphate. Phosphofructokinase and pyruvate kinase are inhibited by a high energy charge (high ATP).
Why is the conversion of pyruvate to lactate so important?
It uses the NADH up and regens the NAD+ to allow glycolysis to continue
What does phosphoenolpyruvate carboxykinase do in glyconeogenesis?
Phosphoenolpyruvate carboxykinase uses one GTP to convert oxaloacetate to phosphoenolpyruvate.
What does pyruvate carboxylase do in glyconeogensis?
Pyruvate carboxylase uses one ATP to convert pyruvate to oxaloacetate.
Which type of respiration produces CO2?
aerobic
What conditions are needed for NADH from glycolysis to be used in oxidative phosphorylation?
aerobic (oxygen is important for oxidative anything)
Does aerobic or anaerobic glycolysis produce more ATP and why?
aerobic. it generates 2 NADH, which can yeild an additional 4 ATP via oxidative phosphorylation. anaerobic doesn't make NADH, just 2 ATP from glycolysis
3. The regulation of glycolysis and gluconeogenesis involves _____ in which metabolites bind to target enzymes at regulatory sites and either activate or inhibit enzyme activity.
allosteric control mechanisms
Which single reaction in glycolysis is bypassed by two reactions in gluconeogenesis? Select one: a. hexokinase b. pyruvate kinase c. phosphofructokinase d. aldolase e. phosphoglycerate kinase
b. pyruvate kinase
1. While almost every reaction in glycolysis and gluconeogenesis is subject to some type of control, it appears as if the _____ are subject to the most stringent regulation. These are the essentially irreversible reactions in glycolysis.
bypass sites (involving the interconversion of glucose and glucose 6-phosphate, the interconversion of fructose 6-phosphate and fructose 1-6-bisphosphate, and the interconversion of phosphoenolpyruvate and pyruvate.)
Why is the lactate dehydrogenase reaction an important addition at the end of the glycolysis pathway? a. It makes additional ATP. b. It converts pyruvate to acetylCoA and carbon dioxide. c. It increases the standard free energy of glycolysis. d. It allows glycolysis to proceed under anaerobic conditions. e. It makes additional NADH.
d. It allows glycolysis to proceed under anaerobic conditions.
Which enzyme in glycolysis converts a six carbon intermediate into two three carbon intermediates? Select one: a. hexokinase b. pyruvate kinase c. phosphofructokinase d. aldolase e. phosphoglycerate kinase
d. aldolase
In fermentation, yeast convert pyruvate to ____ in anaerobic conditions.
ethanol
How does fructose enter glycolysis?
fructokinase uses an ATP to make fructose-1-phosphate, then fructose-1-phosphate aldolase cleaves the molecule into DHAP(enters glycolysis) and glyceraldehyde (uses ATP to make it into G3P, then enters glycolysis)
7. There is a very interesting regulatory circuit involving ____, a side product of glycolysis. The fructose it stimulates phosphofructokinase and inhibits fructose 1-6-bisphosphate phosphatase.
fructose 2-6-bisphosphate
_______ pathway converts lactate or pyruvate to glucose
gluconeogenesis
the liver enzyme glucokinase has a very high Km, so it only works when
glucose is high in the cell. this allows glucose to diffuse out of the liver cells into the blood
what are the two core metabolic pathways?
glycolysis and glyconeogenesis
What is the main energy difference between glycolysis and glyconeogenesis?
glycolysis produces a net of 2 ATP glyconeogeneis consumes a net of 6 ATP
When high energy charge prevails (ATP levels are high) _____ is inhibited and ____ is stimulated.
glycolysis, gluconeogenesis
Does hexokinase have a high or low Km and why
has a low Km, so it's very efficient at low substrate levels, making glycolysis possible 24/7
5. Gluconeogenesis uses ATP so it is activated when the ratio of ATP/ADP and AMP is ____, and inactivated when that ratio is _____.
high low
6. High levels of acetylCoA and citrate tend to ____ glycolysis and ____ gluconeogenesis.
inhibit, stimulate (The buildup of these intermediates is a signal that the TCA cycle is overloaded and does not need more acetylCoA to be fed in from glycolysis.)
glucokinase is induced by ____ , so ___ resistant diabetics have difficulty processing high glucose loads
insulin
Which enzyme converts sucrose into something usable that can enter glycolysis, and what molecules make up sucrose?
invertase, yeilds a glucose and a fructose
What happens to the lactic acid build up in muscles?
it goes to the liver where its converted into glucose
How does lactate become glucose again?
it travels via blood to liver, converted to pyruvate, then to glucose
How does lactose enter glycolysis?
lactase cleaves it to glucose and galactose. galactose is converted to glucose6 phosphate.
Under anaerobic conditions, pyruvate is converted to
lactate
In a sprint or vigorous exercise, pyruvate is diverted into a side reaction usinge the enzyme ______ to convert it to ____.
lactate dehydrogenase, lactate
Name the two anaerobic pathways for regenerating NAD+
lactate fermentation, ethanol fermentation
4. Glycolysis generates ATP so it is activated when the ratio of ATP/ADP and AMP is ____ and inactivated when that ratio is _____.
low high
The overall free energy change for conversion of glucose to CO2 is highly ______
negative. the loss of free energy drives toward product formation
UDP-glucose is an example of _____ sugars, which play an important role in sugar and lipid metabolism.
nucleotide
Biosynthesis of disaccharides and polysaccharides is an uphill reaction that uses ___ to achieve a favorable equilibrium
nucleotide sugars
Because there are distinct enzymes functioning in each direction, it allows for regulation in _____ without exerting the same type of regulation on the other direction.
one direction (you can stimulate or inhibit gluconeogenesis without effecting glycolysis. In contrast, if the reversible steps were targeted for regulation, inhibition of glycolysis would also result in inhibition of gluconeogenesis.)
In a sprint, the rate of acetylCoA oxidation is limited by the availability of _____
oxygen
What is the difference between substrate level phosphorylation and oxidative phosphorylation?
substrate level breaks apart the substrate, steals its phosphate group and gives it to ADP to make ATP (substrate is a loser, ATP wins) where oxidative uses energy in the electron transport to take ADP and inorganic phosphate groups that are available to make ATP (more of a scavenger approach)
Why is glucose 6 phosphate commited to the glycolysis pathway in the first step?
the added phosphate group makes it unable to diffuse back out of the cell membrane isn't recognized by any of the transport proteins. it's stuck and must continue through the pathway it isn't glucose anymore, so more glucose will still want to enter the cell
