lecture 10 - prokaryotes, bioenergetics

what is the net reaction methanogens use to make methane?

they combine 2co2 and 6h2 to produce (ch2o)n, ch4 and 3h2o.

why are methanogens called strict anaerobes?

any oxygen shuts down their key reactions.

where do methanogens live?

they live in very diverse habitats including swamps, oil deposits and animal guts such as cow stomachs.

how do methanogens like archaeoglobus contribute to natural gas release?

they grow in deep oil wells above 80 c and produce methane that adds to natural gas.

how does methane's greenhouse effect compare with co2's today?

methane is currently about 16 times worse than co2 at causing the greenhouse effect.

what role did methane play in early earth history?

it helped keep the earth warm.

why was atmospheric co2 so high on early earth?

high co2 compensated for the faint, young sun.

what is the order of early gas changes as first life, methanogens and oxygen producers appeared?

first life began consuming co2, then methanogens made major methane contributions, then oxygen-producing bacteria got their start.

what happened to methane levels once oxygen began to appear in the atmosphere?

methane dropped as oxygen rose.

how does the gas history link oxygen's rise to global ice ages?

oxygen began appearing about 2.3 billion years ago, around the time of the first global ice age, while methane declined.

when did oxygen concentrations stay low until, and what rock evidence came before the buildup?

oxygen stayed low until about 2 billion years ago, and several periods of iron oxide deposition came before the buildup.

why might iron oxide deposits appear before free atmospheric oxygen accumulated?

oxygen produced by early photosynthesizers was likely used up reacting with iron before it could build up in the atmosphere.

which evidence types support the early timeline of life and cyanobacteria?

isotope, signature molecule and fossil evidence all support it, with cyanobacteria appearing very early.

which domain is more closely related to eukaryotes, archaea or bacteria?

archaea are more closely related to eukaryotes than bacteria are.

what two lineages does the tree of life suggest merged to create eukaryotes?

archaea and aerobic alphaproteobacteria joined to form the eukaryote lineage.

what three things does life require?

life requires an energy source, atp production and a source of fixed carbon.

what are the two ways cells make atp?

they use direct phosphorylation of adp or chemiosmosis, which uses a proton gradient and atp synthase.

what is the difference between autotrophy and heterotrophy?

autotrophs fix their own carbon from inorganic sources while heterotrophs get organic carbon by predation, scavenging or symbiosis.

what are the three energy sources organisms use to make atp?

they use light, inorganic high-energy reduced molecules or organic high-energy reduced molecules.

what are the nutritional terms for organisms using light, inorganic molecules or organic molecules as energy?

they are phototrophic, chemolithotrophic and chemoorganotrophic respectively.

what carbon source defines autotrophic versus heterotrophic organisms?

autotrophs use inorganic carbon while heterotrophs use organic carbon.

how do photoautotrophs and photoheterotrophs differ?

both use light for energy but photoautotrophs use co2 as carbon while photoheterotrophs use organic compounds.

which strategy do most prokaryotes, saprobes, parasites, pathogens and eukarya use?

they are chemoorganoheterotrophs, using organic compounds for both energy and carbon.

how do chemolithoautotrophs get energy and carbon?

they get energy from inorganic compounds like s, n, fe or h2 and carbon from co2 or other small carbon molecules.

what are examples of chemolithoautotrophs?

methanogenic archaea and sulfur-oxidizing, nitrifying and iron-oxidizing bacteria.

what strategy do methanotrophic bacteria use?

they are chemoorganoautotrophs that use organic compounds for energy and ch4 as their carbon source.

what do redox reactions accomplish in organisms?

they transform physical and chemical energy entering organisms into useful biological energy and convert environmental molecules into useful metabolites.

in a redox reaction, which partner loses electrons and what is it called afterward?

the donor loses electrons and becomes oxidized.

in a redox reaction, which partner gains electrons and what is it called afterward?

the acceptor gains electrons and becomes reduced.

what do the mnemonics leo says ger and oil rig mean?

loss of electrons is oxidation and gain of electrons is reduction.

how is glycolysis a redox reaction?

glucose is oxidized to 2 pyruvate while nad+ is reduced to nadh, and 2 atp are also produced.

why does glycolysis have a net gain of only 2 atp?

it uses 2 atp in the investment phase but forms 4 atp in the payoff phase.

what is substrate-level phosphorylation?

it is the transfer of a phosphate from an organic substrate to adp to make atp.

where does glycolysis occur and what does it produce besides pyruvate?

it occurs in the cytosol and produces atp by substrate-level phosphorylation plus electrons carried by nadh.

what determines whether pyruvate goes to aerobic respiration or fermentation?

oxygen leads to pyruvate oxidation, the citric acid cycle and the etc, while no oxygen leads to fermentation.

which atp-making steps follow glycolysis in aerobic respiration?

substrate-level phosphorylation occurs in the citric acid cycle and oxidative phosphorylation occurs in the etc and chemiosmosis.

what are the two fermentation types and their products?

alcohol fermentation makes bread, wine and beer while lactic acid fermentation makes yogurt, cheese and pickles.

how much atp can aerobic respiration make per glucose, and where does it come from?

it makes about 30 or 32 atp, with 2 from glycolysis, 2 from the citric acid cycle and about 26 or 28 from oxidative phosphorylation.

which electron carriers feed oxidative phosphorylation from glycolysis, pyruvate oxidation and the citric acid cycle?

nadh and fadh2 from all three stages deliver electrons to the etc.

why is energy metabolism done in small steps instead of one reaction?

h2 reacting directly with o2 releases 229 kj/mol explosively as heat and light, while an etc releases the energy in controlled steps to synthesize atp.

what is an electron carrier and an electron transport chain?

a carrier is any molecule capable of a redox reaction and an etc is a sequence of carriers performing coupled redox reactions.

in which direction do electrons move along an etc in terms of reduction potential?

they move from carriers with higher reduction potential and energy to carriers with lower reduction potential and energy.

how does electron flow in an etc lead to atp production?

electron flow pumps h+ to create an electrochemical gradient that atp synthase uses to make atp from adp and pi.

what is an electrochemical gradient?

it is a difference in both charge and concentration of an ion like h+ or na+ across a membrane.

what are the charge and h+ concentration on each side of the membrane in oxidative phosphorylation?

the intermembrane space is positive with high h+ and the matrix is negative with low h+.

what is the structure of a simple bacterial etc?

it has a dehydrogenase complex, a q shuttle and a cytochrome complex.

how is the more complex prokaryotic etc organized?

it has nadh dehydrogenase complex, a q shuttle, a cytochrome complex, a cytochrome c shuttle and a cytochrome oxidase complex.

what is conserved and what varies in etcs across evolution?

certain electron carriers and overall organization are conserved while other carriers and donor/acceptor pairs vary.

how does a simple etc oxidizing formic acid create a gradient?

it has 2 complexes and a quinone shuttle, generating h+ outside the cell and consuming h+ inside, which creates the h+ electrochemical gradient.

how does atp synthase use the gradient in simple bacterial etcs?

h+ flows back into the cell as an energy source, driving atp synthase to make atp from adp and pi.

what structures bear the etc in aerobic respiration?

the etc is found in the internal membranes of alpha-proteobacteria and the inner membrane cristae of mitochondria.

what are the inputs and outputs of oxidative phosphorylation?

inputs are electrons from nadh and fadh2 plus oxygen, and outputs are an h+ gradient, water and oxidized nad+.

what two shuttles carry electrons between complexes in mitochondrial oxidative phosphorylation?

the quinone shuttle (ubiquinone) and the cytochrome c shuttle.

how does atp synthase turn the h+ gradient into atp?

h+ flowing through the fo channel rotates a subunit, which changes the f1 knob's shape to expose the active site for atp synthesis.

how fast can atp synthase spin?

it spins at up to 50 times per second.

how do aerobic and anaerobic respiration differ in their etc?

aerobic respiration ends with 2h+ + 1/2 o2 forming h2o while anaerobic respiration uses a different final acceptor x that gains an electron to become y-.

how do aerobic and anaerobic etcs end up with the same result despite different acceptors?

both harness energy to produce an h+ gradient for atp synthesis.

what is the terminal reaction in sulfate-reducing etcs?

so4 2- gains electrons to become h2s, reducing sulfur from s6+ to s2-.

how can sulfate reducers use h2 in their etc?

h2 acts as an initial electron donor and is oxidized to h2o.

how do chemoorganoheterotrophy and chemolithoautotrophy differ in energy source?

chemoorganoheterotrophs metabolize glucose through glycolysis and the krebs cycle to make nadh as the etc donor while chemolithoautotrophs use reduced inorganic compounds as etc donors.

how do chemoorganoheterotrophy and chemolithoautotrophy differ in carbon source?

chemoorganoheterotrophs use reduced organic compounds from food while chemolithoautotrophs use nadph from reversed electron transport to fix co2 in the calvin cycle.

which etc type does each chemical-based strategy typically use?

chemoorganoheterotrophs typically use an aerobic respiration etc while chemolithoautotrophs typically use an anaerobic respiration etc.