Biochemical Energy Production Flashcards
Is glycolysis an aerobic process?
No
glycolysis does not require O2
Overall products of glycolysis
2 pyruvate
2 ATP
2 NADH
Does glycolysis require energy?
yes, during the energy investment phase requires 2 molecules of ATP
What is the first step in glycolysis?
glucose enters the cell and hexokinase converts glucose to glucose 6-phosphate
this prevents glucose from leaving the cell
Which steps of glycolysis require ATP?
steps 1 and 3
What is the second step of glycolysis?
glucose 6-phosphate is converted to fructose 6-phosphate by glucose 6-isomerase
What is the third step of glycolysis?
fructose 6-phosphate gets converted to fructose 1,6-bisphosphate by PFK1
uses ATP
what is the rate limiting step / commitment step of glycolysis?
fructose 6-phosphate to fructose 1,6-bisphosphate
What is the fourth step of glycolysis?
fructose 1,6-bisphosphate is cleaved to G3P and DHAP by aldolase
What is the last step of the energy investment phase of glycolysis?
DHAP is converted to G3P
What is the first step of the energy payment phase of glycolysis?
convert G3P to 1,3-bisphophate glycerate by G3P dehydrogenase
convert NAD+ to NADH
What is the second step of the energy payment phase of glycolysis?
PGK converts 1,3-bisphosphate glycerate to 3PG
one phosphate is pulled off
used to make ATP
In what steps of glycolysis is ATP created?
steps 7 and 10
What is the final step of glycolysis?
PEP converted to pryuvate by pyruvate kinase
form another molecule of ATP
Where do pyruvate and NADH go in aerobic conditions?
pyruvate enters the citric acid cycle
NADH goes to the ETC
Where do pyruvate and NADH go in anaerobic conditions?
into fermentation to reproduce NAD+ for glycolysis
What is the goal of fermentation?
to reproduce NAD+
What do high levels of citrate do to glycolysis?
inhibits PFK1 and downregulates glycolysis
What do high levels of NADH do to glycolysis?
downregulate it
insulin effects on the cell
insulin places more GLUT4 receptors on cell
allows for more glucose uptake and glycolysis
When blood sugar is low what molecule is high?
glucagon
glucagon effects on the cell
glucagon inhibits glycolysis and upregulates gluconeogenesis
how does glucose 6-phosphate regulate glycolysis?
it inhibits hexokinase
glucokinase
a form of hexokinase in the liver and pancreas
glucokinase has a lower affinity for glucose and is not affected by glucose 6-phosphate
Why is it beneficial for glucokinase to not be affected by glucose 6-phophate?
glucokinase can breakdown large amounts of glucose even when G6P is present
PFK1 regulators
downregulated by high levels of ATP and citrate
upregualted by ADP and fructose 2,6-bisphosphate
Fructose 2,6-bisphosphate works on …
PFK1 to activate it
fructose 1,6-bisphosphate to deactivate it
What makes fructose 2,6-bisphosphate?
PFK2
What breaks down fructose 2,6-bisphosphate?
fructose 2,6-bisphosphatase
How does glucagon affect fructose 2,6-bisphosphate?
it inhibits PFK2 and activates fructose 2,6-bisphosphatase
downregulates fructose 2,6-bisphosphate to increase gluconeogenesis and decrease glycolysis
How does insulin affect fructose 2,6-bisphosphate?
it activates PFK2 and inhibits fructose 2,6-bisphosphatase
upregulates fructose 2,6-bisphosphate to increase glycolysis and decrease gluconeogensis
What is the goal of glucagon?
to add more glucose to the blood
What is PK regulated by?
ATP inhibits
What reaction does PK catalyze?
the conversion of PEP to pyruvate
lactate dehydrogenase
reduces pyruvate and forms lactic acid
How many steps are in lactic fermentation?
1
simultaneous reduction of pyruvate and oxidation of NAD+
Ethanol fermentation
2 steps
first have a decarboxylation step
converts sugar to ethanol, while oxidizing NAD+
Where does gluconeogensis take place?
in the liver and to a lesser extent, the kidneys
Where in the cell does gluconeogenesis take place?
in the mitochondria and then moves to the cytosol
What is the starting molecule for gluconeogenesis?
pyruvate
Where does pyruvate for gluconeogenesis come from?
proteins, glycerol from fatty acids, or lactate
How does gluconeogenesis convert pyruvate to PEP?
takes 2 steps
first, pyruvate carboxylase makes oxaloacetate in the mitochondria
then PEP carboxylkinase converts oxaloacetate to PEP in cytosol
How does gluconeogenesis convert F16BP to F6P?
uses fructose 1,6-bisphosphatase
How does gluconeogenesis convert G6P to glucose?
glucose 6-phosphatase
How is fructose 1,6-bisphophatase regulated?
inhibited by AMP and fructose 2,6-bisphophate
Where does the citric acid cycle take place?
in the mitochondria
Where does pyruvate dehydrogenase take place?
on the inner-mitochondrial membrane
How does pyruvate enter the mitochondria?
by being converted to acetyl-CoA
How does the pyruvate dehydrogenase complex work?
oxidizes pyruvate to acetyl-CoA by removing CO2
simultaneously reduces NAD+ to NADH
What is the structure of acetal-CoA
a thioester connected to CoA group
What is the main goal of the citric acid cycle?
to reduce electron carriers
make FADH2 and NADH
What are other names for the citric acid cycle?
Krebs Cycle
TCA cycle
What is the first step of the citric acid cycle?
acetyl-CoA combines with oxaloacetate to produce citrate
What is the rate limiting step of the citric acid cycle?
step 3
the conversion of isocitrate to alpha-ketoglutarate
lose a carbon to CO2
1 NADH produced
What is step 4 of the citric acid cycle?
convert alpha-ketoglutarate to succinyl-CoA
lose CO2
1 NADH produced
What is the final step of the citric acid cyle?
convert malate to oxaloacetate
produce NADH
What drives the thermodynamically unstable final step of the citric acid cycle?
Le Chatlier’s principle
oxaloacetate is quickly combined with acetyl-CoA when it is formed, driving the final step of the cycle
What does one pyruvate molecule produce?
1 NADH (PDC) 1 GTP 3 NADH 1 FADH2 2 CO2
How many pyruvates does one glucose produce?
2
What step of the ETC has the highest reduction potential?
the final step
oxygen is reduced to water
What happens to NADH in the ETC?
it is oxidized to NAD+ at complex I
ends up generating 2.5 ATP
What happens to FADH2 in the ETC?
it is oxidized to FAD+ at complex II
ends up generating 1.5 ATP
Which molecule generates more ATP, NADH or FADH2?
NADH
How many net ATP molecules are produced from one glucose?
around 30
What happens to the electrons in the ETC?
they keep moving to higher reduction potentials
What comes first in the ETC, ubiquinone or cytochrome c?
ubiquinone
Where does control of aerobic respiration start?
at the pyruvate dehydrogenase complex
What do high levels of fatty acids do to aerobic respiration?
they downregulate PDC since fatty acids can also become acetyl-CoA
Cyanide and the ETC
cyanide can bind to cytochrome C’s heme group and interrupt the ETC
cytochrome c makeup
cytochrome c is made up of a heme group and can carry one electron on its Fe
Fe3+ to Fe2+
When glucose levels are low how can a cell get energy?
1) use lipids and make ketone bodies for energy
2) glycogen breakdown to release glucose
Why is glycogen stored in a branched structure?
branching creates large number of terminal residues for glycogen phosphorylase to act on
glycogen branching also increases its solubility
What type of glycosidic links can be broken down?
alpha links (in glycogen and starch)
What type of glycosidic links can not be broken down?
beta links (in cellulose)
What type of glycosidic bonds are seen in glycogen?
alpha 1,4 in chains and alpha 1,6 at branching points
Where is glycogen stored?
muscle and liver cells
When does glycogenesis occur in muscle cells?
after exercise when glycogen levels are depleted
What is the starting product for glycogenesis?
glucose 6-phosphate
Steps of glycogenesis
glucose 6-phosphate to glucose 1-phosphate to UDP glucose to glycogen
Glycogen synthase
makes alpha 1,4 linkages on pre-existing branches
glycogen branching enzyme
allows us to make new branches at alpha 1,6 linkages
glycogenin
central protein in glycogen that allows glycogen linkages to start growing
glycogen phosphorylase
breaks down glycogen at alpha 1,4 bonds
general steps of glycolysis
glycogen to glucose 1-phosphate to glucose 6-phosphate
phosphoglucomutase
interconverts glucose 1-phosphate and glucose 6-phosphate
epinephrine and blood glucose levels
epinephrine increases blood glucose levels by activating glycogen phosphorylase in muscle cells
glucagon and glycogen
glucagon raises blood glucose levels by activating glycogen phosphorylase in liver cells
Ca2+ and glycogen
Ca2+ is released when muscles are contracting and using energy
Ca2+ indicates that we need glucose and activates glycogen phosphorylase in skeletal muscles
How does insulin activate glycogen synthase?
it inhibits its inhibitor
What does the Pentose phosphate pathway do?
it converts NADP+ to NADPH and glucose to ribose 5-phosphate
ribose 5-phosphate
building block for nucleotides
produced from the pentose phosphate pathway
What does the non-oxidative phase of the PPP do?
recycles ribose 5-phosphate to get G6P again
Where is the non-oxidative phase of the PP used?
in cells that need more NADPH than ribose 5-phosphate
cells like liver cells and adipocytes that do not need lots of nucleotides
What cells is insulin produced by?
insulin is produced by pancreatic B-cells
How is insulin released?
when blood glucose levels are high, glucose enters pancreatic cells and goes through glycolysis
the ratio of intracellular ATP increases, which triggers K+ concentration to increase and then Ca2+ concentration to increase
Ca2+ triggers the release of insulin
Acetylcholine and insulin
acetylcholine is produced by the sympathetic nervous system, so it triggers the release of insulin after digestion
Norepinephrine and insulin
norepinephrine is secreted by the parasympathetic nervous system and increases blood sugar levels
so, norepinephrine inhibits insulin release
How does insulin trigger the uptake of glucose?
when insulin binds to its receptors it triggers the release of GLUT4 receptors
How does glucose move into the cell?
through facilitated diffusion
How does insulin affect lipids and proteins?
promotes lipid and protein anabolism
Type I diabetes
can’t produce insulin
Type II diabetes
cells do not respond to insulin
What cells produce glucagon?
pancreatic alpha cells
What does glucagon promote?
glycogenolysis, gluconeogenesis, and lipolysis
Where does glycolysis take place?
in the cytoplasm
What happens after glycolysis if no O2 is present?
fermentation
pyruvate is reduced to lactate and NADH is oxidized to NAD+
What are the possible starting products for gluconeogenesis?
pyruvate, lactate, alpha-ketoglutarmate, oxaloacetate
What is the main enzyme in glycogenlysis?
glycogen phosphorylase
When is beta oxidation used?
can make acetyl-CoA for the citric acid cycle when glycolysis is not working
How does beta oxidation work?
oxidize the beta carbon of a fatty acid
What are possible uses for acetyl-CoA?
Can enter the citric acid cycle or be converted into ketone bodies for transport
What are possible uses for oxaloacetate?
can be used in the citric acid cycle or as a starting product for gluconeogenesis
What are possible uses for glucose 6-phosphate?
glycolysis, PPP, and glycogenesis
What is the first half of the citric acid cycle?
1) acetyl-CoA and oxaloacetate are combined to form citrate
2) citrate becomes alpha ketoglutarate
*produces 1 CO2 and 1 NADH
Is the first step of the citric acid cycle energetically favorable?
yes, it is highly favorable and irreversible
What is the rate limiting step of the citric acid cycle?
step 3
What is the second half of the citric acid cycle?
1) alpha ketoglutarate to succinyl coA
2) malate to oxaloacetate
*2 NADH, 1 FADH2, 1 CO2
How to remember the intermediates of the citric acid cycle?
Our City Is Kept Safe and Sound From Mobsters
Oxaloactetate, citrate, isocitrate, alpha-Ketoglutarate, succinyl-CoA, succinate, fumarate, malate
PFK2
phosphorylates fructose 2,6-bisphophate which activates glycolysis/PFK1
glyceraldehyde 3-phosphate dehydrogenase
catalyzes the reaction of glyceraldehyde 3-phosphate to 1,3-bisphosphoglyerate
produces NADH
part of glycolysis
Lactate dehydrogenase
oxidizes NADH to reproduce NAD+
also performs reverse reaction
How does NADH allow its electrons to enter the inner mitochondrial membrane?
through the glycerol 3-phosphate shuttle or the malate-aspartate shuttle
What three steps must be overcome in gluconeogenesis?
1) pyruvate kinase
2) PFK1
3) hexokinase
How do you bypass pyruvate kinase in gluconeogenesis?
Pyruvate carboxylase and PEP carboxykinase
How do you bypass PFK1?
fructose-1,6-bisphophatase
How do you bypass hexokinase?
glucose-6-phosphatase
What is the rate limiting enzyme of the PPP?
glucose-6-phosphate dehydrogenase
What regulates glucose-6-phosphate dehydrogenase?
NADP+ activates and NADPH deactivates
What is the key enzyme in cholesterol synthesis?
HMG-CoA reductase
What fatty acid can humans synthesize?
palmitic acid
What happens before B-oxidation of fatty acids?
carnitine shuttle
What does B-oxidation of fatty acids produce?
ketone bodies that can be used for acetyl-CoA
How does protein excretion occur?
amino groups are excreted as urea
How many times does the citric acid cycle turn for one molecule of glucose?
two turns
What are the products of the citric acid cycle?
per 1 turn (2 turns per glucose)
3 NADH, 1 FADH2, 1 GTP
How many ATP molecules per NADH?
2.5
How many ATP molecules per FADH2?
1.5
