micrb 265 lec 6
What is metabolism?
Metabolism = catabolism + anabolism. Catabolism breaks larger molecules into smaller ones and releases energy. Anabolism uses energy to build cellular material from smaller molecules.
What do all cells need metabolically?
Cells need water, free energy, reducing power, and precursor metabolites for biosynthesis.
What is free energy used for in cells?
Free energy is used for chemical work, transport work, and mechanical work, and ATP is the main immediate energy currency.
What is reducing power?
Reducing power is stored electrons carried mainly by NADH and FADH2, which can later be used to make ATP or drive other reactions.
What are the three major ways ATP is generated?
Substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.
What is substrate-level phosphorylation?
ATP is made directly from an energy-rich bond on a substrate, without using an electron transport chain.
What is oxidative phosphorylation?
Electrons from carriers like NADH and FADH2 move through the electron transport chain, generating proton motive force, and ATP synthase uses that force to make ATP.
What is photophosphorylation?
Light energy generates proton motive force, and ATP synthase uses that proton motive force to make ATP.
What is oxidation?
Oxidation is loss of electrons.
What is reduction?
Reduction is gain of electrons.
What is the key idea of the redox tower?
Electrons flow from better electron donors at higher energy to better electron acceptors at lower energy, and that energy drop can be captured by cells.
Why is oxygen a strong terminal electron acceptor?
Oxygen has a very high tendency to accept electrons, so transferring electrons to oxygen releases a lot of energy.
What are the two main reduced electron carriers in this lecture?
NADH and FADH2.
What is the oxidized form of NAD?
NAD+.
What is the reduced form of NAD?
NADH.
What is the oxidized form of FAD?
FAD.
What is the reduced form of FAD?
FADH2.
Why are NADH and FADH2 important?
They carry high-energy electrons from catabolic pathways to the electron transport chain.
What is an enzyme?
An enzyme is a biological catalyst that speeds up a reaction without being consumed.
How do enzymes speed up reactions?
They lower activation energy, making it easier for the reaction to occur.
What is activation energy?
It is the energy barrier that must be overcome for a reaction to proceed.
What is the active site?
It is the region of an enzyme where the substrate binds and the reaction occurs.
What is the induced fit model?
The enzyme changes shape slightly when the substrate binds, improving the fit and helping catalysis.
What factors affect enzyme activity?
Temperature, pH, substrate concentration, and sometimes inhibitors or cofactors.
Why does high temperature decrease enzyme activity after a point?
Because the enzyme can denature, which changes its shape and damages the active site.
Why does pH affect enzyme activity?
Changes in pH can alter charges and shape in the enzyme, especially at the active site.
What is a cofactor?
A non-protein helper needed for enzyme activity, often a metal ion.
What is a coenzyme?
An organic helper molecule used by enzymes, often derived from vitamins.
What are the six major classes of enzymes?
Oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
What do oxidoreductases do?
They catalyze oxidation-reduction reactions.
What do transferases do?
They transfer functional groups from one molecule to another.
What do hydrolases do?
They break bonds by adding water.
What do lyases do?
They add or remove groups to form or break double bonds without using water or redox.
What do isomerases do?
They rearrange atoms within a molecule.
What do ligases do?
They join two molecules together, usually using energy such as ATP.
How are organisms classified by carbon source?
Autotrophs use CO2 as their carbon source, while heterotrophs use organic carbon.
How are organisms classified by energy source?
Phototrophs use light, while chemotrophs use chemicals.
How are organisms classified by electron source?
Lithotrophs use reduced inorganic compounds, while organotrophs use organic compounds.
What is a chemoorganoheterotroph?
An organism that gets energy from chemicals, electrons from organic compounds, and carbon from organic compounds.
What is a chemolithoautotroph?
An organism that gets energy from chemicals, electrons from inorganic compounds, and carbon from CO2.
What is glycolysis?
A pathway that breaks glucose into pyruvate and captures energy as ATP and NADH.
Where does glycolysis occur?
In the cytoplasm.
What is the net yield of glycolysis per glucose?
2 ATP, 2 NADH, and 2 pyruvate.
What does glycolysis do before respiration or fermentation?
It partially oxidizes glucose and produces pyruvate, ATP, and NADH.
What happens to pyruvate when oxygen is available and respiration occurs?
Pyruvate is further oxidized, and its electrons can ultimately enter the electron transport chain through reduced carriers.
What is fermentation?
A process that uses an organic molecule as the final electron acceptor and does not use an electron transport chain.
What is the main purpose of fermentation?
To regenerate NAD+ so glycolysis can continue.
How much ATP does fermentation itself add beyond glycolysis?
Usually none. The ATP associated with fermentation comes from glycolysis by substrate-level phosphorylation.
What is respiration?
A process where electrons pass through an electron transport chain to a final electron acceptor.
What is the difference between aerobic and anaerobic respiration?
Aerobic respiration uses oxygen as the final electron acceptor, while anaerobic respiration uses a different inorganic acceptor.
What is the electron transport chain?
A series of membrane-associated carriers that pass electrons stepwise and use the released energy to pump protons.
What does the electron transport chain create?
A proton motive force.
What is proton motive force?
A stored form of energy made by a proton gradient and charge difference across a membrane.
What are the two parts of proton motive force?
A chemical gradient from different proton concentrations and an electrical gradient from charge separation.
What does ATP synthase do?
ATP synthase uses proton motive force to make ATP from ADP and phosphate.
How does ATP synthase work in simple terms?
Protons flow down their gradient through the enzyme, causing rotation and shape changes that drive ATP formation.
Why is ATP synthase called a molecular machine?
Because it physically rotates and converts proton gradient energy into mechanical energy and then chemical bond energy in ATP.
What are the two main parts of ATP synthase?
The membrane portion that lets protons flow through and the catalytic head that makes ATP.
What happens if ATP concentration is high and the proton gradient is low?
ATP synthase can run in reverse, hydrolyzing ATP to pump protons across the membrane.
Why is the proton gradient so important?
It stores the energy released by electron transport and links that energy to ATP production.
What is the big picture link between glycolysis, electron carriers, ETC, and ATP synthase?
Glycolysis and other catabolic pathways remove electrons from food, NADH and FADH2 carry those electrons to the ETC, the ETC builds proton motive force, and ATP synthase uses that force to make ATP.