Topic 8: metabolism Flashcards
What is earth’s energy flow?
Sun > producer > consumer > decomposer
Define metabolism
- Totality of an organism’s chemical reaction
- Energy is stored = anabolic processes
- Energy is released = catabolic processes
Define metabolic pathways
- Begins with specific molecules = ends with products
- Each step catalyzed by specific enzyme
- Controlled according to cellular demands
Define catabolic pathways
- Break down complex molecules = simpler molecules
- Release energy e.g. cellular respiration
Define anabolic pathways
- Simple molecules = synthesized into complex molecules
- Consume energy e.g. photosynthesis + protein synthesis
What are the 3 forms of energy?
1) KE = associated with motion
2) Heat = associated with random movement of atoms
3) PE = energy stored due to location + structure of matter + chemical energy stored in molecular structure
Define free energy
- Living system’s energy that can do work under cellular conditions
- Organisms live by spending free energy
Define free energy change
- Indicates whether reaction occurs spontaneously or not
- ΔG = Gfinal- Ginitial
Describe exergonic reactions
- Spontaneous reactions
- Free energy released
- ΔG = negative
- Therefore Gfinal < Ginitial
Describe endergonic reactions
- Non-spontaneous reactions
- Absorb free energy from surroundings
- ΔG = positive
- Therefore Gfinal > Ginitial
Describe equilibrium in metabolism
- Reaction in closed systems = equilibrium
- Cells in body = open system
- Metabolic pathways many stages = constant flow of materials in + out = NOT equilibrium
Describe ATP + function + structure
- Nucleotide that stores energy in phosphate bonds
- It is energy-rich = unstable = tends to break down
- Function = provides energy for cellular functions
- Structure = phosphate groups + ribose + adenine
Define ATP hydrolysis
ATP > ADP + Pi = enery release
Define ATP synthesis
ADP + Pi > ATP = energy stored in phosphate bonds
Explain energy coupling
- Done by ATP to power cellular work
- Is the use of exergonic process to drive endergonic process
- ATP mediated coupling = endergonic process driven by ATP hydrolysis which is exergonic process = provides energy required
3 types of endergonic cellular work powered by ATP hydrolysis
- By phosphorylation
1) Mechanical = phosphorylates motor proteins
2) Transport = phosphorylates transport proteins
3) Chemical = phosphorylates key reactants
Explain ATP hydrolysis
- Exergonic reaction = energy released = either 2 terminal phosphate bonds of ATP broken
- Can be coupled to endergonic reactions
Explain ATP synthesis
1) Catabolic pathways = energy
2) Energy required to regenerate ATP from ADP + Pi
Give the formula for cellular respiration
C6H12O6 + Ο2 —-> CO2+ H2O+ ΑΤP
Define catalyst
- Chemical agent = speeds up reaction without being consumed
Define enzyme
- Catalytic protein = speeds up metabolic reactions by lowering activation energy
- E.g. sucrase hydrolyzing sucrose
Define activation energy
- Initial amount of energy needed to start a chemical reaction
- Needed to de-stabilize the structure of reactants = react more easily
- Supplied as heat = increase speed of molecules = frequent collisions
Explain how enzymes lower AE
- Reaction is catalyzed by lowering AE = speeds up reaction
- Enzyme doesn’t affect if reaction is spontaneous not only speed up reaction already happening
Define substrate
- Reactant of enzyme to act on
- E.g. sucrose is substrate for sucrase
Describe substrate specificity
- Enzyme binds to substrate = enzyme-substrate complex
- Enzyme will only recognize it’s specific substrate
- Enzyme 3D shape = determine function
Describe the active site + induced fit model
- Region on enzyme where substrate binds
- Induced fit = enzyme changes shape when substrate binds to AS = brings chemical groups of AS to positions = enhance ability to catalyze reaction
Explain the catalytic cycle of enzyme
1) Substrate enter AS = enzyme change shape = induced fit
2) Substrate held in AS = by weak H/ionic bonds
3) AS + R group lower AE by:
- Acting as template for substrate orientation
- Stressing substrate + stabilizing transition state
- Providing favorable environment
- Directly participate in catalytic reaction
4) Sustrate converted to products
5) Products released
6) AS back to original shape + available for new substrates
Give environmental factors that effect enzyme activity
- pH
- Temp
- Cofactors
Define co-factors
- Non-protein enzyme helpers required for enzyme activity
1) Inorganic cofactors = metal ions
2) Coenzymes = organic = vitamins
Define denaturation
- Loss of protein conformation due to unraveling = loss of function
Why does temp + pH affect enzyme activity?
- Each enzyme has optimal temp/pH which it functions
- Optimal temp for human enzymes = 37.5
- Optimal pH for pepsin = 2
- Optimal pH trypsin = 8
Describe irreversible inhibitors
- Bind to enzyme via covalent bonding = inhibition permanent
- Toxins + antibiotics + poisons
- Sarin + DDT + parathion = inhibit NS enzymes
- Penicillin derivatives = inhibit enzyme transpeptidase = synthesize bacterial cell wall
Describe reversible inhibitors
- Bind to enzyme via weak bonds = inhibition not permanent can be removed
1) Competitive
2) Non-competitive
Describe competitive inhibitors
- Bind to AS
- Compete with substrate = mimics substrate = inhibits substrate from binding
- Overcome = adding excess substrate
Describe non-competitive inhibitors
- Bind to other part of enzyme = change shape = inhibit function
- Cannot be overcome by adding excess substrate
2 Methods of enzyme regulation
1) Regulation of enzyme production by regulation of gene production
2) Regulation of enzyme activity by feedback inhibition = allosteric regulation
Explain feedback inhibition
- End product of metabolic pathway = inhibits the pathway
- Role = prevents cell from wasting resources by synthesizing more product than needed
- E.g. Inhibition of catabolic pathways by ATP + inhibition of anabolic pathways by end product
Explain allosteric regulation
- Reversible modulation in enzyme = made of polypeptide subunits
- Can be +ve = activation OR -ve = inhibition
- Proteins function at AS affected by binding of regulatory molecules at allosteric site via non-covalent binding = change shape
- Can be hererotropic = allosteric site OR homotropic = substrate is regulatory molecule = bind to AS
Describe heterotropic allosteric regulation
- Activators = stabilize active form
- Inhibitors = stabilize inactive form
Describe homotropic allosteric regulation
- Binding of substrate to AS of 1 subunit = conformation to active state = locks all other subunits in active state
- Cooperativity = +ve allosteric regulation = binding of substrate to 1 subunit increases binding affinity in other subunits = e.g. O2
Give an example of heterotropic allosteric activator/inhibitor
- Activator = AMP activates PFK = glycolysis enzyme
- Inhibitor = CO2 of haemoglobin = reduces haemoglobins affinity for O2 = O2 released in tissues
Give an example of homotropic allosteric activator/inhibitor
- Activator = O2 of haemoglobin
- Competitive inhibitor = CO binds to haemoglobin in O2 site = increases CO affinity = O2 not released into tissues
What are the locations of enzymes in cells?
- Enzymes participating in same pathway = located close to each other
1) Grouped in complexes
2) Incorporated into membranes
3) Contained inside organelles
