L2 Carb Catabolism Flashcards
Energy Transfer
- in presence of O2, cells can break down 1 mole of glucose into CO2, water, 686 kcal
- Large fraction of energy is lost as heat
- Other energy is transferred to ATP
Metabolsim
all the chemical reactions involving in maintaining life
Catabolism
breakdown
occurs when the body needs energy
Anabolism
Synthesis
occurs when the body has enough energy
ATP
known as energy currency
energy is released from ATP in presence of water and ATPase
sole function is to transfer energy from molecules storing energy to energy requiring processes
Hydrolysis
energy being released from ATP
Catabolic process in which energy is released when chemical bonds are broken in presence of water
1 ATP = removal of terminal phosphate, release of 7kcal
Stored ATP
quantity is extremely limited
almost all activities powered by ATP must be generated instantly through catabolism
1 Calorie
= 1,000 calories
= 1 kcal
How are calories measured in food?
Food in placed in bomb calorimeter
heat is produced, which is equivalent to total energy value that food has
How are calories burned by the body measured?
human calorimeter (direct)
cold water at constant rate removes heat, temperature difference represents heat production
can also measure via O2 uptake (indirect)
Enzyme
suffix is ASE
specific protein catalyst that accelerates forward and reverse rates of chemical reactions without being consumed or changed in reaction
enzymes are reused
Substrate
any substance acted upon by an enzyme
Conenzyme
nonprotein substance that facilitates enzyme action by assisting in binding the substrate with its specific enzyme
much less specific than enzymes
Examples: B vitamins
Condensation
anabolic process in which energy is used and a molecule of water is formed
Reduction
involves a gain of electrons
Oxidation
involves loss of electrons
Redox reaction
oxidation or reduction reaction
Common oxidized form/reduced forms
NAD+ (oxidized)
NADH + H (reduced)
O2 (oxidized)
H2O (reduced)
Glycolysis summary
- always anaerobic
- Only catabolizes monosaccharides
- Convert one 6 carbon molecule into 3 carbon molecules (glucose to pyruvate)
- All reactions occur in cytoplasm
Net gain of Glycolysis
2 ATPs are USED
Net gain: 2 ATP , 2 NADH, 2 pyruvates
Pros of GLycolysis
- replenishes ATP more rapidly than oxidative pathway
- Plays major role in fueling sports that require max energy production for 30-120s
- Only means of ATP production in RBCs
Which skeletal muscle fiber type has the highest concentration of glycolytic enzymes?
Type 2
Cons of Glycolysis
inefficient in terms of total ATP made vs how much energy is in 1 glucose
Beginning of glycolysis
ATP molecules are used
1st Step: ATP donates phosphate to glucose to make glucose-6-phosphate
This reaction traps glucose inside most cells b/c phosphorylated molecules can’t cross cell membranes
What cells can allow phosphorylated glucose molecules to pass through their membrane?
LIVER (and kidney)
contain an enzyme which removes phosphate, allowing glucose to leave the cell
Later Steps in Glycolysis
4 Hs are removed from glucose, reduce 2 molecules of NAD
Remember that there are irreversible steps in glycolysis
Phosphofructokinase (PFK)
KEY regulatory enzyme for glycolysis
-Activity of PFK is sensitive to energy status of cell
-When cell has enough energy/ATP/citrate, PFK’s activity is inhibited
-When cell’s energy level is low (high AMP/ADP inside cell), PFK’s activity is increased
Aerobic Conditions after glycolysis
In the presence of O2, pyruvate enters the Krebs cycle where it is broken down into smaller fragments and CO2
Anaerobic Conditions after glycolysis
Pyruvic acid is converted in lactic acid by LDH
2 H are transferred from NADH + H to pyruvic acid, making lactic acid
lactic acid becomes a storage site for H+
When does pyruvic acid get converted to lactic acid?
Whenever a cell’s energy demands eexceeds either its O2 supply or rate of O2 utilization
Examples of when pyruvic acid is converted to lactic acid
skeletal muscle cells when cells are contracting at a fast rate
RBC continually form lactic acid because they do not have mitochondria
Ischemia–downstream cells become hypoxic
Lactic acid dehydrogenase
LDH catalyzes pyruvic acid to/from lactic acid
Which cell types have the greatest concentration of LDH?
RBCs, heart, skeletal muscle, liver kidney
due to each unique metabolic requirements
LDH and the heart
in case of a thrombus, all downstream cells by hypoxic and can die
so heart cells begin to upregulate the production of LDH in attempt to continue producing ATP to allow for contraction
LDH leakage is present after MI, peaks 48-72 hours after
What must be present for glycolysis to continue?
NAD
has to accept hydrogen for glycolysis to continue
What happens to lactic acid after it is formed?
- Converted by aerobic respiration to CO2 and water
- Some lactic acid goes through the Cori Cycle
Lactic Acid and Cori Cycle
- Lactate in blood goes to the liver
- In the liver, LDH converts lactate to pyruvate
- Liver converts pyruvate to glucose-6-phosphate
- G6P can be used to make glycogen or broken down to glucose
Purpose of Cori Cycle
removes lactate from the blood
path for gluconeogenesis
Lactic ACID vs lactate
Lactic acid is an acid, meaning it can release a proton.
When it releases H+, it joins with a positive cation to form acid salt (like sodium lactate, which is not charged)
Lactic Acid Key points
- Likely is not what causes the burn felt during intense exercise, because it is very quickly turned into lactate.
- Acidosis is likely not responsible for muscle fatigue
Acidosis during exercise
an increase in H+ causes acidosis during exercise
lactate production is the CONSEQUENCE not the CAUSE of acidosis
Lactate production helps to slow down acidosis; it coincides with acidosis
Muscle fatigue and lactic acid
individuals who are unable to accumulate lactic acid fatigue more rapidly
lactic acid has been shown to have beneficial effects on performance
Pyruvate breakdown (aerobic)
Has to be broken down into acetyl-CoA before entering the krebs cycle
enters the mitochondria and undergoes this: Pyruvate + CoA +NAD+ –> Acetyl CoA + CO2 + NADH + H
(this is for one pyruvate, glucose contains 2, so multiply everything by 2 for 1 glucose molecule)
Acetyl Coenzyme A
Entry point for all metabolic fuels to enter Krebs cycle
Derived from B5 vitamin
Function: transfer 2-carbon acetyl groups from one molecule to another
Where do acetyl groups come from?
pyruvic acid
breakdown of fatty acids, some AA
Krebs Cycle net production
For 1 acetyl CoA:
1 ATP, 3 NADH, 3 H+, 1 FADH2
Krebs Cycle Overview
- Operates only under aerobic conditions, O2 is not used directly
- Occur entirely in the mitochondrial matrix
- Operates only under aerobic conditions
Oxidative Phosphorylation
produces energy when H combines with O2 to form water, ultimately used to make ATP
Where does hydrogen come from that is used in oxidative phosphorylation?
From the reduced coenzymes NADH and FADH2 in the Krebs Cycle
Net production of Oxidative Phosphorylation
O2 + NADH + H+ –> H2O + NAD+ + 53 kcal
Proteins that mediate Oxidative Phosphorylation
Embedded within the inner mitochondrial membrane
Two groups: Cytochromes and ATP Synthase
Cytochromes
mediate transfer of H+ to O2
called the electron transport chain
ATP Synthase
couple the energy that is released as electrons move from cytochrome to cytochrome to form ATP
How is ATP produced in the electron transport chain?
- Electrons are passed down the chain, small amounts of energy is released
- Energy is then used to pump H+ ions from mitochondrial matrix to cytosolic side of inner mitochondrial membrane, forming H+ gradient
- H+ gradient passes through ATP synthase channel, forms energy
ATP Formation in ETC
3 ATP = from each NADH that goes through the ETC
2 ATP. = from each FADH2 that goes through the ETC, enters further along vs NADH
Why do we get either 4 or 6 ATP from the coenzymes generated in glycolysis?
- In glycolysis, H+ bound to conensymes are transferred to a carrier that can cross the mitochondrial wall
- H+ are then transferred to NAD+ or FAD+
- FAD+ produces less ATP vs NAD+, depends on the type of cell
Why don’t we make 98 ATP from the breakdown of 1 glucose?
686 kcal is broken down 1 glucose, but we only produce 38 ATP and not ATP
remaining 61% of energy lost is released as heat
