Chapter 15 Flashcards
Three Stages of Energy Generation from Food
- Large molecules in food are broken down into smaller molecules
- The many small molecules are processed/converted into key molecules of metabolism, mainly acetyl CoA
- ATP is produced from complete oxidation of acetyl CoA
- Energy in form of ATP is essential for cell growth, cellular functions, and information processing
- ATP is also essential for whole organism growth and development, daily activities and movements, and response to injury and repair
The three main things energy is needed for is _________
Movement: need muscle contraction to take place in cell
Active transport: involving molecules and ions
Biosynthesis: building complex molecules from simple ones (otherwise, growth and repair of damaged cells and tissues couldn’t occur)
Phototrophs
An organism that can meet its energy needs by converting light energy into chemical energy
- Ex. plants
Chemotrophs
An organism that obtains energy by the oxidation of foodstuffs (through oxidation of carbon fuels)
- Ex. humans
Energy Currency
- All life uses ATP as ultimate energy currency
- Carbon fuel oxidation generates ATP
Basic Principles that Govern Energy Manipulation in all Cells
- Molecules are degraded or synthesized stepwise in a series of reactions called metabolic pathways
- ATP is the universal energy currency of life
- ATP can be formed by the oxidation of carbon fuels
- Although many reactions occur inside cell, a limited # of reaction types that involve particular intermediates are common to all metabolic pathways
- Metabolic pathways are highly regulated
- The enzymes involved in metabolism are organized into large complexes
Metabolic pathways: general overview
- Metabolism consists of two main types of reactions: energy yielding and energy requiring
- The two main types of reactions will be linked such that energy liberated in one series of reactions will be channeled into another series of reactions that require energy
- Metabolic pathways = stepwise reactions breaking down or synthesizing molecules
- Overall reactions are actually limited and will often involve common intermediates
- Metabolic reactions are defined as a specific substrate converted into a specific end point
- Example: Glucose into pyruvate; glucose into acetyl-CoA; glucose into CO2, H2O, and ATP
Intermediary metabolism
- There will be a multitude of metabolic pathways in a cell, which can be linear, branched, circular and/or interconnected
- Pathways interact w/ other pathways
- All reactions within a cell are considered “intermediary metabolism”
- “Systems biology” is an emerging field that attempts to study the pathways all at once
- Typically, isolated pathways are studied. Then link different components to different pathways together
Types of metabolic pathways
Catabolic:
- Convert energy from fuel (from carbon sources) to ATP (Ex. glycolysis)
- set of metabolic reactions that transform fuels into cellular energy
- using energy to breaking down complex molecules
- big structures to small (= uses/releases energy)
Anabolic:
- Requires energy for synthesis (Ex. gluconeogenesis, synthesis of DNA, glucose, or fats)
- set of metabolic reactions that require energy to synthesize molecules from simpler precursors
- needs energy to create big complex molecules from small ones
- small structures to big (= needs energy)
Catabolic and anabolic pathways often share reactions (ex. enzymes) and there may be shuttling of molecules between these two types of pathways
There will be key, regulated irreversible reactions and steps for distinct pathways
Thermodynamics of Pathways
- Reaction coupling couple unfavorable endergonic reactions w/ a favorable exergonic reaction and it will be spontaneous and favorable moving forward
- For reaction coupling…
- Each reaction must be SPECIFIC in the pathway
- The overall pathway MUST be thermodynamically favorable
- Exergonic = releases energy, negative G, WILL be spontaneous
- Endergonic = requires energy, positive G, WON’T be spontaneous
- thermodynamically unfavorable reaction CAN be converted into a favorable reaction by coupling it to the hydrolysis of ATP
ATP: High Energy Phosphates
- ATP = universal energy currency, attributed to the high energy phosphates the molecule has
- Hydrolysis of ATP is exergonic b/c triphosphate unit contains 2 unstable phosphoanhydride bonds
- Energy is released upon ATP hydrolysis and used to power cellular functions
- Hydrolysis of ATP to ADP and Pi will liberate -30.5 kJ/mol (-7.3 kcal/mol)
- Hydrolysis of ATP to AMP and pyrophosphate will liberate -45.6 kJ/mol (-10.9 kcal/mol)
Properties of ATP
Factors that contribute to ATP being an ideal energy currency:
1. Electrostatic repulsion
2. Resonance stabilization
3. Increase in entropy
4. Stabilization due to hydration
Electrostatic repulsion:
at pH 7.4, phosphates have negative charges
Triphosphate of ATP carries 4 negative charges
negative charges repel each other, creating electrostatic repulsion. Repulsion is reduced when ATP is hydrolyzed
ester bond in AMP displays less repulsion (= less energy) then anhydride bonds between phosphate groups
ADP will contain one anhydride bond
ATP will contain two anhydride bonds (cleavage of bonds = more energy)
High Phosphoryl-transfer potential
- The high phosphoryl-transfer potential of ATP provides further explanation of the utility of ATP as the universal energy currency
- The greater energy yield from ATP hydrolysis provides evidence for the unique molecular structure of ATP and its utility as energy currency
AKA, presence of phosphate group and associated bond cleavage is not enough to generate high levels of free energy
High Phosphoryl-transfer potential and important molecules
- Phosphoryl transfer potential = important form of cellular energy transformation
- Phosphoryl transfer potential refers to transfer of phosphate groups
- Molecules (including ATP) w/ phosphate groups are carries of phosphoryl groups
- Biologically important molecules w/ high phosphoryl transfer potential include:
1, 3-BPG (1,3-biphosphoglycerate)
PEP (phosphoenolpyruvate)
Creatine phosphate
- Phosphoryl transfer potential of ATP is LESS than the three molecules above but GREATER than glucose-6-phosphate or glycerl-3-phosphate
Thus, ATP has intermediate phosphoryl transfer potential amongst biologically important molecules
Resonance Stabilization
Resonance stabilization - where ability to share electrons across molecule will lead to lower energy state, especially where there’s more sharing of electrons
- Orthophosphate has 4 possible resonance states due to electron sharing
- In ATP, w/ two anhydride bonds, electron sharing and possible resonance states are limited to only 3 possible states - limitation contributes to higher energy contained within ATP
Phosphoanhydride bonds
- bonds between phosphate molecules
- high energy bonds linking phosphate groups
- phosphate-phosphate bonds formed when compounds like ATP or ADP are created
Phosphates in Biochemical Processes
Phosphates and their esters are prominent in biology b/c…..
- Phosphate esters are thermodynamically unstable, yet kinetically stable
- Phosphate esters are stable b/c the inherent negative charges resist hydrolysis
- Since phosphate ester are kinetically stable, they are ideal regulatory molecules: can be added to molecules by kinases and removed by phosphatases = covalent modification
ATP: Other Roles & Signal Transduction
- ATP has other roles and may be involved in signal transduction
- Intracellularly, cells maintain very high concentration of ATP
- ATP may function as a biological hydrotope w/ hydrophilic and hydrophobic characteristics
Hydrotrope
Amphipathic molecule w/ hydrophobic and hydrophilic component, but unlike fatty acids, hydrophobic part is too small to self-aggregate
Hydrophobic component would be attributed to adenine and less prominent
Hydrophobic nature is thought to contribute to its ability to prevent formation of protein aggregates within cytoplasm, thus maintaining protein solubility
ATP (adenosine triphosphate)
ATP = immediate donor of free energy for biological activities and systems
- Amount of ATP in the body is 100g
- Amount of ATP in a system is limited
- ATP must be constantly recycled to provide energy to power cells and organisms
Oxidation-Reduction Reactions
- key to understanding metabolic reactions and pathways
- Oxidation reactions = loss of electrons. Must be paired w/ reduction to gain electrons
- Paired reactions are called oxidation-reduction reactions (redox reactions)
- Carbon atoms in fuels are oxidized to yield CO2, and electrons are accepted by O2 to form H2O
- The more reduced a carbon atom is, the greater the amount of more free energy that will be released upon oxidation
- Fats = more efficient food sources than glucose b/c fats are more reduced
Reduced vs. oxidized
- Reduced compounds can oxidize to release electrons
These released electrons power ETC to make energy (ATP) - Oxidized compounds have already lost electrons
Have limited ability to power ETC
More reduced compounds will liberate more energy than more oxidized compounds
Oxidation-reduction reactions & high phosphoryl transfer potential
Compounds w/ high phosphoryl potential can be coupled to carbon oxidation for ATP synthesis
Essence of catabolism is capturing the energy of carbon oxidation as ATP
Oxidation of carbon atom may form a compound w/ high phosphoryl transfer potential that can then be used to synthesize ATP
Glyceraldehye-3-phophsate oxidation into 3-phosphoglyceric acid:
- Carbon oxidation of glyceride-3-phosphate generates an acyl phosphate, which is coupled to the capture of electrons in the reduction of NAD+ to NADH
This generates 1,3-BPG
- The high phosphoryl-transfer potential of 1,3-BPG is utilized to generate ATP w transfer of phosphoryl group to ADP
** This reaction demonstrates carbon oxidation couple to ATP-synthesis AND pairing of oxidation-reduction reaction**
