Metabolism Flashcards
What is bioenergetics
Quantitative study of energy transduction occurring in living cells. Study of the nature and function of the chemical processes that are responsible for these energy transduction
What is the first law of thermodynamics
energy cannot be created or destroyed, but it can be converted from one form to another
What is gibbs free energy
the amount of energy in a system available to do work.
What does free energy change derive from
- Changes in heat content (DH) = enthalpy change
- Changes in the state of order (DS) = entropy change
What doe sit mean if delta G is negative
energy is liberated and the reaction is said to be exergonic and can occur spontaneously
What does it mean if delta G is positive
reaction is endergenic and requires energy input
What biological processes do we require energy for
- Mechanical work e.g., muscle contraction
- Active transport
- Synthesis of complex biomolecules from simple precursors
- Also signal transduction (environmental responses), generation of light (fire flies) and electricity (eels)
How is energy obtained
- Phototrophs – obtain energy by trapping light e.g., photosynthesis
- Chemotrophs – obtain energy by oxidation of food stuffs e.g., catabolism
Where do chemoorganotrophs ge4t their energy from
organic compounds by oxidation (e.g., respiration)
Calories in food groups
- Fats – 9kcal/g
- Carbohydrates – 4kcal/g
- Proteins – 4kcal/g
- Alcohol – 7kcal/g
Why do we control the extraction of energy from food
so we don’t release all the energy at once and increase body temperature excessively
Extraction of energy from food
- Large molecules broken down into smaller units. No useful energy captured
- Small molecules degraded into a few simple units that play a role in central metabolism. Some ATP generated
- ATP produced from the complete oxidation of simple units by the final common pathways for oxidation of fuel
Reduction reactions as an organic compound is degraded
electrons flow through intermediates to oxygen (the final electron acceptor) or are used to reduce other cellular components
Biological redox reaction
1) 1. Direct electron transfer e.g. Fe2+ + Cu2+ ——> Fe3+ + Cu+
- Direct transfer of hydrogen ions e.g.AH2 + B ——-> A + BH2
- Direct combination with oxygen as with mono-oxygenase reactions e.g.R-CH3 + ½O2 ——–> R-CH2OH
What do dehydrogenases do
oxidise organic compounds by abstracting 2H+ and 2 e- and passing them to a mobile carrier in biodegradation and energy abstraction (I.e., respiration)
How can dehydrogenases reduce
can reduce organic compounds by adding 2H+ and 2 e- from a mobile electron carrier typically in biosynthetic pathways
Synthesis and use of NADH
produced in catabolic reactions and by TCA cycle. Used in the generation of ATP by OxPhos. Usually found inside the mitochondria
Use and synthesis of NADPH
produced by PPP. Used primarily for reductive biosynthesis (e.g., FA synthesis). Usually found in the cytoplasm
Use and synthesis of FADH2
produced in catabolic reactions and by TCA cycle. Used in the generation of ATP by OxPhos (generates less energy than NADH)
What bonds does ATP contain
2 phosphoanhydride bonds on its triphosphate unit
ATP equations
ATP + H2O ——> ADP + Pi + energy. ATP + H2O ——–> AMP + PPi + energy
Stability of free energy
free energy is negative and therefore thermodynamically unstable but is kinetically stable.
Use of ATP
principal immediate donor of free energy in biological systems rather than long-term storage form. Consumed within minutes of formation, very high turnover. Around 50kg of ATP consumed in 24h period
How is ATP produced - substrate level phosphorylation
Transfer of phosphoryl group from metabolites with high – phosphoryl transfer potential to ADP producing ATP
How is ATP produced - oxidative phosphorylation
Process of ATP formation as a result of transfer of electrons from fuels via electron carriers (NADH or FADH2) to the final electron acceptor oxygen
4 functions of metabolism
- Obtain energy e.g., ATP
- Convert nutrients into own characteristic molecules
- Polymerize monomeric precursors e.g., polysaccharides
4.Synthesise and degrade molecules required for special cellular functions e.g., intracellular messengers
what are catabolic reactions
transform fuels into usable cellular energy
What are anabolic reactions
utilize the useful energy formed by catabolism to generate complex structures from simple ones
Catabolic v anabolic - ATP
catabolic - produces ATP, anabolic requires ATP
Catabolic v anabolic -free energy
catabolic - negative free energy change. Anabolic - positive free energy change
Catabolic v anabolic - reducing potential
catabolic - produces reducing potential, anabolic - requires reducing potential
Catabolic v anabolic - generating NAD
catabolic - generates NADH and FADH2. Anabolic - uses NADPH
Why is metabolic regulation required
because we need energy to function but we do not have a constant supply of energy but the expenditure is continuous so we need to store and release when it is required
What does metabolic regulation cover
distribution and storage of nutrients after meals, release, delivery and utilisation. Works on a molecular level by modulation of enzyme activities
How is metabolism regulated
- Levels and accessibility of substrates (thermodynamics and compartmentation)
- Amounts of metabolic enzymes (rate of transcription and degradation)
- Modulation of catalytic activities of enzymes (allosteric regulation, covalent modification, association with regulatory proteins)
What is the amount of enzyme present determined by
- Alteration (production) of transcription factor by external signals
- Stability of mRNA species
- Rate of translation (dependent on various factors)
- Rate of protein degradation
Allosteric regulation
An allosteric enzyme has a site distinct from the substrate-binding site. Ligands which bind to the allosteric site are termed allosteric effectors or modulators. Binding causes conformational changes so affinity for substrate or other ligands change. Can be positive (activator) or negative (inhibitor)
What is binding of the end-product dependent on
concentration, and binding affinity induces conformational change affecting active site
