Ch 3: Bioenergetics Flashcards
Cell membrane
Semipermeable barrier also called sarcolemma in skeletal muscle cells separates cell from extracellular environment
Nucleus
Contains genes composed of DNA. DNA regulates protein synthesis, which determines cell structure and function.
Cytoplasm
Fluid portion of cell called sarcoplasm in muscle cells; contains organelles (mitochondria) and enzymes (enzymes for breaking down glucose)
Metabolism
The sum of all chemical reactions that occur in the body
Anabolic and Catabolic reactions
Anabolic Reactions
synthesis of molecules
Catabolic reactions
breakdown of molecules
Bioenergetics
Metabolic pathways that convert energy from foodstuffs (nutrients: fats, proteins, carbohydrates) into a usable form of energy for cell work
All chemical reactions involve a change in
energy
Endergonic Reactions
Energy required (consumed)
-positive change in energy
Endergonic reactions use the energy released by exergonic reactions
Exergonic Reactions
Energy released (produced)
- negative change in energy
Exergonic reactions power Endergonic reactions
Why are oxidation-reduction always coupled reactions?
because a molecule cannot become oxidized unless it donates electrons to another molecule
Oxidation-reduction reactions often involve
the transfer of hydrogen atoms rather than free electrons
- hydrogen atom contains one electron
- a molecule that loses a hydrogen also loses an electron, therefore it is oxidized
Oxidation reaction
Removing electrons (and hydrogen) from a molecule
Reducing agents: donate electrons and become oxidized
(NADH is reducing agent)
Reduction reaction
Adding electrons (and hydrogen) to a molecule
Oxidizing agents: accept electrons and become reduced
(NAD is oxidizing agent)
What is the role of NAD and FAD in the ETC?
they play an important role in transfer of electrons
- carrier molecules during bioenergetic reactions
Enzymes
are protein catalysts that regulate the speed of chemical reactions in the body
- increase the rate of a cellular chemical reaction (and rate of product formation) by lowering the energy of activation
- cannot change the total amount of energy released from a reaction
Kinases
add a phosphate group
dehydrogenases
remove hydrogen atoms
Oxidases
Catalyze oxidation-reduction reactions involving oxygen
Isomerases
rearrangement of the structure of molecules
How does temperature affect enzymes?
- a small rise in body temperature increases enzyme activity
- exercise results in increased body temperature
- large increase in body temperature can denature enzymes and decrease activity
How does pH affect enzymes?
How does exercise affect pH?
Changes in pH (increase or decrease) can decrease enzyme activity
- high intensity exercise decreases muscle pH (makes more acidic)
During exercise, the primary nutrients used for energy are
fats and carbohydrates
Carbohydrates
1 gram —> 4 kcals
composed of carbon, hydrogen and oxygen
exists in 3 forms
- monosaccharides
- disaccharides
- polysaccharides: complex carbohydrates
Glycogen is a polysaccharide stored in
our muscle and liver cells
Glycogenolysis
process by which glycogen is broken down into glucose
Glucose role in the body
(in muscle cells; and in liver cells)
- in muscle cells, glucose serves as source of energy for muscle contraction
- in liver cells, glucose released in blood stream and transported to body tissues
Why is glycogen synthesis an ongoing process?
Because glycogen stores are depleted within a few hours of prolonged exercise.
Fats
1 gram —> 9 kcals
composed of carbon, hydrogen and oxygen. but the ratio of carbon to oxygen in fats is greater than in carbs
- ideal fuel for prolonged exercise
Phospholipids and steroids are not used for energy.
Fatty acids
the primary type of fat used by muscles for energy
Triglycerides
fatty acids are stored as triglycerides in fat and muscle cells
Lipolysis
process of breaking down triglycerides into glycerol and fatty acids
Proteins
1 gram—> 4 kcals
composed of subunits called amino acids
- numerous structural and regulatory functions in the body… however energy is not a primary function.
Proteins:
Energy production in the liver
Alanine can be converted to glucose (gluconeogenesis) and stored as glycogen
- liver glycogen can be broken down into glucose and used by working muscles
Gluconeogenesis
Forming new glucose from protein (alanine)
Proteins:
Energy production in muscle
Many amino acids (alanine, isoleucine, leucine, and valine) can be converted into “metabolic intermediates” which can be used as fuel in muscle bioenergetic pathways
ATP
energy currency of life
muscle cells don’t store large amounts of ATP
3 Metabolic Pathways of ATP Production:
- Phosphocreatine (PC) Breakdown
- Glycolysis
- Oxidative Phosphorylation
Phosphocreatine Breakdown
ADP + PC —> ATP + C
PC donates phosphate and bond energy to ADP to form ATP aka substrate level phosphorylation
anaerobic (oxygen independent)
occurs in sarcoplasm
Glycolysis
Glucose —> 2 ATP + 2 Pyruvate or 2 lactate
Transfers bond energy from glucose to rejoin phosphate to ADP to make ATP. Breaks down glucose to form 2 pyruvate or lactate
anaerobic (oxygen independent)
occurs in sarcoplasm of muscle cells
- can produce ATP rapidly
- every molecule of glucose requires 2 ATP
Produces 2 ATP
Oxidative phosphorylation
ATP formation in electron transport chain
- the vast majority of ATP formed in cells comes from oxidative phosphorylation, which occurs in mitochondria
Aerobic (oxygen dependent)
occurs in mitochondria
Substrate-level phosphorylation
PC Breakdown
Phosphate and energy are transferred to ADP to form ATP
- most rapid method of ATP Production
- provides energy for muscular contraction at onset of exercise and during short term, high intensity exercise
- very small PC stores in the muscle cell… so limited capacity for ATP production via this system
Glycogen is only minimally stored in the sarcoplasm, so most glucose comes from
liver glycogenolysis
- regardless of the source of glucose for glycolysis, glucose has to be phosphorylated to form glucose 6-phosphate
Glucose obtained from glycogen
Does not require ATP to form glucose-6-phosphate, but instead uses inorganic phosphate (Pi) located in the cell
When glucose is obtained from glycogen as opposed to glucose— 3 ATP is formed bc only 1 ATP is invested and 4 are produced still
In glycolysis, NAD+
accepts a H+ atom
- the NAD+ must be restored, or glycolysis will stop
Two ways to regenerate NAD+
- If sufficient O2, the hydrogens from NADH can be shuttled into the mitochondria, where they can contribute to the aerobic production of ATP (aerobic)
- If insufficient O2, pyruvate can accept H+ ions to form lactate (anaerobic)
Pyruvate —> Lactate (Lactic Acid)
If pyruvate and NADH are being produced faster than aerobic metabolism cab use them, then lactate is formed
aka
if there is no oxygen, then pyruvate turns into lactate
but if oxygen is present, we continue to the Kreb’s cycle
lactate dehydrogenase: converts pyruvate to lactate
Lactate Accumulation
Increases tissue acidity, stressing the buffering systems
associated with fatigue, during intense exercise
Lactate Removal
Used as fuel for aerobic metabolism
Used as a substrate for gluconeogenesis in liver
Gluconeogenesis
forming glucose from lactate and store in the liver
Lactic acid in the body
At normal pH, lactic acid rapidly disassociates into lactate and a H+ ion so lactic acid rarely exists in the body
lactate— conjugate base
Aerobic ATP Production
- when oxygen is present, pyruvate molecules from glycolysis can be used for aerobic production of ATP
occurs in mitochondria
Involves the interaction of 2 cooperating metabolic pathways:
- Krebs cycle (citric acid cycle/ TCA (tricarboxylic acid))
- Electron Transport Chain
Oxygen does not participate in the Krebs cycle, but it is the final hydrogen acceptor at the end of the ETC (H2 + O—> H2O)
3 stage process of aerobic ATP Production
- Formation of acetyl-coA
- Oxidation of acetyl-coA in Krebs cycle (remove electron and H+)
- Oxidative phosphorylation (ATP formation) in the electron transport chain
Products of catabolism must first be shuttled from the cytoplasm into the mitochondrial matrix in order to be converted into Acetyl-coA
Krebs cycle
Removes hydrogen, electrons and associated energy from nutrients
- Pyruvate forms acetyl-coA and CO2
- Oxaloacetate mixes with acetyl-coA to form citrate (enzyme: citrate synthase)
- the goal is to keep forming oxaloacetate
3 NADH and 1 FADH is formed
2 molecules of CO2 are produced
1 glucose—> 2 pyruvate –> 2 acetyl-CoA –> 2 turns of the Krebs cycle
Krebs cycle total after 2 turns
6 NADH + H+
2 FADH2
2 GTP (2ATP)
4 CO2
In summary, the Krebs cycle completes the oxidation of foodstuffs, produces CO2 and provides the electrons necessary for aerobic formation of ATP
Triglycerides are catabolized into
glycerol and fatty acids (transported into the mitochondria)
Glycerol as a fuel source
Glycerol is not an important muscle fuel source
- we don’t rely on it for energy
Beta oxidation
Converting fatty acids into acetyl-CoA
- “chops” fatty acids into 2 carbon molecules, forming acetyl-CoA (divide by 2)
Acetyl-CoA enter Krebs cycle and leads to aerobic ATP formation by the electron transport chain.
Electron Transport Chain
Pumping H+ ions out of the matrix across the inner mitochondrial membrane in order to generate potential energy
- Electrons are carried to the ETC by reduced coenzymes (NADH + H+ and FADH2)
- NADH+H+ and FADH2 release their electrons to protein complexes in the inner mitochondrial membrane called cytochromes, which act as electron acceptors
- H+ ions are separated from their electrons because the cytochromes pass the electrons down the line via a chain of oxidation-reduction reactions
- the energy released in these ox-red reactions allows cytochromes to pump the H+ ions across the inner membrane, creating a concentration and electrical gradient
(energy pumps hydrogen out of the matrix… the hydrogens can’t come back in without transport channels
The accumulation of H+ is a source of potential energy
Chemiosmotic Coupling
capturing the potential energy from the ETC to drive the phosphorylation of ADP —-> ATP
Oxygen is the
final electron acceptor
-strong oxidizing agent
If oxygen is not available then oxidative phosphorylation is not possible and we must rely on anaerobic pathways for ATP formation
How many ATP are produced in the ETC?
First Pump: 4 H+
Second pump: 4 H+
Third Pump: 2 H+
4 H+ are required to produce and transport 1 ATP
NADH (10 H+) = 2.5 ATP
FADH2 (6 H+) = 1.5 ATP
How much ATP is produced from Aerobic Metabolism?
32 ATP
Energy from beta oxidation
-2 carbons from the fatty acid can be converted into 1 Acetyl-CoA
- each acetyl-CoA that enters the Krebs cycle produces 10 ATP
- the production of each acetyl-CoA from the fatty acid ( except for the last) also produces 4 ATP
How efficient is oxidative phosphorylation at converting foodstuffs into usable energy?
Overall efficiency of aerobic respiration is 34%
66% of energy released as heat
Rate-limiting enzyme
Typically, one rate-limiting enzyme found early in a pathway that regulates the rate of a metabolic pathway
- prevents accumulation of products
Rate Limiting Enzyme, Stimulators, Inhibitors:
ATP-PC system
Rate Limiting Enzyme: Creatine kinase
Stimulators: ADP
Inhibitors: ATP
Rate Limiting Enzyme, Stimulators, Inhibitors:
Glycolysis
Rate Limiting Enzyme: Phosphofructokinase
Stimulators: ADP, AMP, Phosphate ion, High pH
Inhibitors: ATP, CP, citrate, Low pH
Rate Limiting Enzyme, Stimulators, Inhibitors:
Krebs cycle
Rate Limiting Enzyme: Isocitrate dehydrogenase
Stimulators: ADP, Ca ++, NAD
Inhibitors: ATP, NADH
Rate Limiting Enzyme, Stimulators, Inhibitors:
Electron Transport Chain
Rate Limiting Enzyme: Cytochrome oxidase
Stimulators: ADP, Phosphate ion
Inhibitors: ATP
Having a lot of ATP will ______ all the metabolic pathways
slow down
Short term, high intensity activities require
high contribution of anaerobic energy production
Long term, low to moderate intensity activities require
majority of ATP produced from aerobic sources
