Metabolism p1 and 2 Flashcards
Energy and metabolism
Thermodynamics: the study of energy flow in physical and biological processes
Living things continually capture, store and use energy for their survival
- Movement, growth, reproduction, digestion, heat, movement across cells etc
Metabolism
-Refers to all chemical reactions that change or transform matter and energy in cells
- main function is to breakdown energy-rich compounds ex glucose, and convert the energy into a useable form ex. ATP
Coupled reactions
- energy from catabolic reactions is used to power anablic reactions
ATP
Adenosine triphosphate
- the primary source of free energy in living cells
-structure: nitrogenous base adenine attached to the 5 carbon sugar ribose, which is attached to a chain of 3 phosphate groups
How is energy obtained from ATP?
- enzyme called ATPase catalyses the hydrolisis of the phosphate on ther terminal end of molecule, making ADP
- One Pi (inorganic phosphate) molecule is released with a ton of energy
- The energy is not always freely released; the Pi can go on to phosphorylate (add a phosphate to) other molecules changing their shape and making them more active (like in active transport)
- Phosphates repel eachother due to negative charge, so it takes a great deal of energy to add on the third phosphate, which is then where energy is stored and later released
Electron carriers
- redox reactions are coupled reactions: compounds that pick up electrons from energy rich compounds and then donate them to low-energy compounds
- the electron carrier is then recycled
Compound that accepts electrons –> reduced
Compound that loses electrons –> oxidized
Electrongs that pass from one atom to another carry energy with them
- reduced form of a molecule has higher energy
- electrons are said to carry reducing power
- NAD+ picks up two e- and one H+ to become NADH
The big picture of cellular respiration
- photoautorophs, like green plants, transform light energy into chemical potential energy (glucose and other carbs)
- Heterotrophs (animals, fungi, bacteria) rely on autotrophs for energy
- glucose is the primary energy source for almost all organisms. The energy that is extracted by enzymes doing redox reactions.
- When the bonds are broken, more stable compounds are formed and so energy is released
- Released energy is ‘trapped’ and stored as ATP (34% of it)
Aerobic cellular respiration
- Aerobic means oxygen is used
- Accomplished by 20 chemical reactions
- Glucose and oxygen don’t just react spontaneously, they have to overcome the activation energy barrier
Endergonic reactions
Chemical reaction that does not proceed spontaneously, requires energy. ex. photosynthesis
Exergonic reactions
Chemical reaction that releases energy, it tends to proceed spontaneously. ex. cellular respiration
Substrate level phosphorylation
- When ATP is formed through the direct transfer of Pi to ADP using an enzyme
- results in the generation of less energy than oxidative phosphorylation (happens during etc)
Structure of mitochondria
Mitochondria are often described as the powerhouses of the cell because of their central role in the synthesis of ATP a vital source of energy for the body.
Composed of:
- Double membrane (inner is folded into finger-like projections called cristae, houses the ETC and the outer membrane)
- Intermembrane space (between inner and outer membrane, location of the H+ gradient)
- Matrix
- mtDNA
Matrix of the mitochondria
- contains mDNA and ribosomes responsable for the synthesis of around %15 of mitochondrial proteins
- the remaining mitochondrial proteins are encoded in the nucleus and are transported into the mitochondria in an unfolded state, where they take on their final folded structure
Where does pyruvate oxidation take place?
- the 2 pyruvate molecules made in glycolysis are transported to the matrix through the mitochondrial membranes using facilitated diffusion (2 pyruvate oxidations per glucose)
Where does glycolysis take place?
- in the cytoplasm, is the only stage of cellular respiration that’s anaerobic
Where does the Kreb’s cycle take place?
- In the mitochondrial matrix (2 per glucose)
- At the end of Kreb’s, the original glucose molecule is entirely consumed and all energy is now stored as ATP and in the electron carriers (aka coenzymes) NADH and FADH2 or released as body heat
- CO2 diffuses out as waste (6 og carbon atoms are now CO2 molecules)
Where is the etc?
- It makes up the inner mitochondrial membrane
- Each mitochondria has many ETCs
- protein complexes are organized by electronegativity (weakest attraction to strongest at the end) to establish the electronegativity gradient
NADH vs FADH2
- NADH will transfer electrons to the first protein complex (NADH dehydrogenase) in the ETC and so pumps 3 hydrogens per molecule
- FADH transfers its electrons to Q (the second protein in the ETC) and so it pumps 2 hydrogens per molecule –> produces less energy bc it skips the first protein complex
Cytosolic vs mitochondrial NADH
- the inner mitochondrial membrane is impermeable to NADH
- So NADH made in glycolysis must be shuttled via a transport protein into the matrix. In doing so, it becomes FADH
ATP tally
- 4 made by substrate level phosphorylation 2 in glycolysis, 2 in krebs)
Oxidative phosphorylation
- 24 ATP from NADH (6 by pyruvate oxidation, 18 from krebs, none from glycolysis bc it turns into FADH2)
- 8 ATP made from FADH2 (4 from the glycolysis NADH, and 4 from krebs)
In total, 36 ATP is made per one glucose molecule.
Extra info etc
- For ATP to be produced, an H+ resevoir must be maintained
- This means electrons must be continually moving through the ETC
- To keep electrons moving, oxygen must be present to accept them at the end of the chain
- if there is no oxygen, electrons become ‘clogged’
- H+ ions wont be pumped, chemiosmosis stops, so ATP synthase stops, and NADH/FADH2 can’t give up their electrons so they can’t be recycled. The organism will die if oxygen is witheld for too long
Chemiosmosis
- The electrochemical gradient generated during electron transport stores free energy (called proton-motive force PMF)
- inner mitochondrial membrane is impermeable to H+ ions
- PMF forces protons through ATP synthase and the energy from thus drives the synthesis of ATP from ADP and Pi in the matrix
- one ATP is generated per proton pumped into the intermembrane space, so 3 ATP per NADH and 2 ATP per FADH2
- After ATP is made, it is transferred through the mitochondrial membrane by facilitated diffusion into the cytoplasm so it can do things like active transport
Metabolic rate
- Amount of energy consumed by an organism in a given time
- Also a measure of the overall rate at which cellular repiration occurs
- Increases when work is done, but is not “zero” at rest due to functions such as: breathing, maintenance of body temp, muscle contraction, and brain function
Basal metabolic rate
- Amount of energy needed to keep an organism alive (accounts for 60-%70 of energy used in one day)
- Is measured by kJ per square meter body surface per hour
- Increases from birth and first year, then gradually decreases, also affected by fitness and health