L11 Flashcards
How is ATP generated?
1) aerobic respiration - oxidation of glucose, oxidation of fatty acids
2) anaerobic metabolism of glucose (fermentation)
3) photosynthesis
4) electron transport + proton motive force
What types of respiration do organisms have?
Aerobe organisms (strict or obligate aerobe)
Anaerobe organism (strict or obligate anaerobe)
Facultative aerobic or anaerobe
What do aerobe organism (strict or obligate aerobes) do?
Use oxygen for respiration to produce ATP, they die if no O2 available
What do anaerobe organisms (strict or obligate anaerobes) do?
Use another molecule different to O2 for respiration (NO3-, SO42-). Perform anaerobic respiration to produce ATP. They can ferment to produce ATP. Die in the presence of O2
What do facultative aerobe or facultative anaerobe do?
If O2 is available they use O2, if O2 not available they use fermentation or perform anaerobic respiration to obtain ATP.
What factors impact ability of microbes to withstand oxygen?
Ability to breakdown byproducts of oxygen metabolism, which are H2O2 and O2-. Organisms that can live in the presence of oxygen have protective enzymes against reactive oxygen species.
What are most eukaryotes?
Obligate aerobes.
Substrate level phosphorylation v oxidative phosphorylation
Forms 1 glucose, 6 ATP by substrate level phosphorylation, 30 by oxidative phosphorylation. Latter is via electron transport chain
Recap : ETC (mitochondria)
Series of membrane protein complexes that transfer electrons from electron donors. Exergonic process, NADH converts to lower energy NAD. Electrons transferred from lower to higher redox potential. This drives the transport of protons. Oxygen is the terminal acceptor of electrons in the chain. The PMF drives ATP synthesis.
What happens if oxygen is scarce?
Most eukaryotes can generate some ATP by anaerobic metabolism. A few eukaryotes are facultative anaerobes : they can grow in either the presence or absence of oxygen
How do cells generate ATP in the absence of oxygen?
They ferment or carry out anaerobic respiration
What happens in fermentation?
In absence of oxygen, facultative anaerobes convert glucose to one or more carbon compounds which are generally released into the surrounding medium. Does not use ETC.
Fermentation (anaerobic metabolism of glucose) equation?
Glucose + 2ADP + 2Pi -> 2 ethanol + 2CO2 + 2ATP + 2H2O
Why does fermentation occur?
After prolonged periods of muscle contraction oxygen is limited, fermentation of glucose results in 2 molecules of lactic acid, with 2 ATP produced.
In fermentation what happens to 2NADH?
It is oxidised to 2 NAD+. This regenerates a supply of NAD+.
What is NADH yielded from glycolysis used to do?
Reduce pyruvate into different products
What other products can be yielded by reduction of pyruvate?
Ethanol, acetate, lactate.
How is fermentation different to anaerobic respiration?
Fermentation is an anaerobic metabolic process that consumes sugars in the absence of oxygen. The products are organic acids, alcohols and gases. It uses intracellular electron carriers while anaerobic respiration uses membrane bound electron carriers. It produces less energy, 2ATP. Anaerobic respiration uses the ETC and produces less than aerobic but more than fermentation.
What are the steps of anaerobic respiration?
Transfer of electrons via ETC allows free energy in NADH and FADH2 to generate a PMF. PMF fuels ATP synthase to phosphorylate ADP into ATP. Sometimes the PMF is generated by O2 consuming H+ in the cytoplasm. But not all the alternative electron acceptors harness the same amount of energy.
What terminal acceptors would be used?
When O2 is not available, NO3- or SO42-
What does it mean if the terminal electron acceptor has high redox potential?
More ATP
What does it mean if the terminal electron acceptor has low redox potential?
Less ATP
What is ATP yield dependent on?
Last electron acceptor
What organic compounds can be alternative terminal electron acceptors?
Fumarate, Dimethylsulfoxide, Trimethyl N-oxide
What do heterotrophs do?
Harness energy from the substrate that serves as the carbon source
What do autotrophs do?
Use CO2 as source of carbon
What are chemoautotrophs?
Organisms that obtain energy by oxidising inorganic or organic compounds in the environment to obtain reducing power and use CO2 as a source of carbon?
What are photoautotrophs?
Organisms that obtain energy from light and use CO2 as source of carbon
In energy production in chemo and photoautotrophs where is oxygen produced?
Only in oxygen photosynthesis
What is photosynthesis?
Process where light energy is converted into chemical energy that drives the synthesis of organic molecules.
In photosynthesis - what does solar radiation do?
Drive reduction of CO2 to produce carbohydrates, fats and proteins.
What is the site of photosynthesis in plants and photosynthetic bacteria?
Thylakoid membranes
What are the thylakoids in bacteria?
Extensive invaginations of the plasma membrane which form a set of internal membranes.
What are chloroplast bounded by?
Two membranes which do not contain chlorophyll and do not participate in photosynthesis.
What do chloroplast third membrane contain?
Thylakoids
What do thylakoids arrange into?
Stacks called grana
What does the thylakoid contain?
Integral membrane proteins bound to which are light absorbing pigments.
Where does carbohydrate synthesis occur?
Stroma, between the thylakoid membranes and the inner membrane
What is the first stage of photosynthesis?
Absorption of light
What happens in the first stage of photosynthesis?
Photosystems carry out absorption and conversion of light into chemical energy.
What do photosystems consist of?
A reaction centre, where primary events of photosynthesis occur. The light harvesting complexes consisting of numerous protein complexes. They capture the light energy and transmit it to the reaction centre.
What is light absorption mediated by in the photosystems?
Chlorophylls, several green related pigments, attached to proteins in the thylakoid. Consist of a porphyrin ring attached to a long hydrocarbon side chain
What is energy of the absorbed light used for?
Remove electrons from water forming O2. The transfer of electrons to a primary electron acceptor.de
What are the pigments involved in photosynthesis?
Chlorophyll a and b, caretenoids.
What is the second stage of photosynthesis?
Electron transport leading to formation of O2 from H2O reduction of NADP+ into NADPH and generation of proton motive force.
What is an overview of the second stage of photosynthesis?
Electrons move from the primary electron acceptor through a series of electron carriers until they reach NADP+, reducing it to NADPH. The transport of electrons in the thylakoid membrane is coupled to the movement of protons across the thylakoid membrane forming a H+ gradient across the membrane and generating the PMF.
What is the third stage of photosynthesis?
Synthesis of ATP
What happens in the third stage of photosynthesis?
ATP synthesis, the PMF drives ATP synthase to phosphorylate ADP into ATP. The transport of electrons can be either cyclic or non-cyclic.
What happens in non-cyclic transport of electrons?
Used in oxygenic photosynthesis in plants and Cyanobacteria. Requires two photosystems PS1 AND PS2 containing one reaction centre each (RC1 and RC2). RC2 extracts electrons from H2O and transfers electrons to RC1, enabling RC1 to keep producing reducing power (NADPH)
Comparison of non-cyclic transport of electrons - what happens in the ETC (mitochondria)?
Series of membrane protein complexes transfer electrons from electron donors, exergonic process, NADH converts to lower NAD. Electrons transferred from lower to higher redox potential. This drives the transport of protons. Oxygen is the terminal acceptor of electrons in the chain. The PMF drives ATP synthesis.
When is non-cyclic photophosphorylation used?
When there is a need for both ATP and NADPH. If there is a greater need for ATP cyclic photophosphorylation is used.
ATP synthesis in plants?
Photosynthetic electron transport chain, PGR5/PGRL1-dependent cyclic electron transport. If more ATP is required cyclic electron transport occurs.
What happens in the cyclic transport of electrons?
Used in anoxygenic photosynthesis, primarily in purple and green bacteria. Requires on photosystem PS1. Light excites chlorophyll and 2e- are passed through the electron transport chain. Quinone (electron acceptor) in the ETC accepts and releases 2H+ in the periplasmic space, this moves H+ from the cytosol to the outside of the cell. This generates a PMF across the plasma membrane. Electrons are transported back to the reaction centre via a soluble cytochrome, which diffuses in the periplasmic space.
What are purple bacteria?
Gram negative proteobacteria. Pigmented with bacteriochlorophyll a or b with various carotenoids. Use sulphur compounds or hydrogen as electron source. Purple sulfur bacteria (photoautotrophs) purple non-sulfur bacteria (photoheterotrophs). Purple bacteria are anoxygenic phototrophs widespread in nature, especially harsh anoxic aquatic environments.
What are green bacteria?
Gram negative, belong to chlorobiota, photoautotrophic, bacteriochlorophyll c or d. Strictly anaerobic. Prefer mild aquatic conditions, use reduced sulphur compounds as electron source.
What is the purple earth hypothesis?
Earliest photosynthetic life forms were thought to be based on bacteriorhodopsin rather than complex porphyrin based bacteriochlorophyll. Caused earth to look purple from above, halophilic archaeobacteria.
What is the fourth stage of photosynthesis?
Conversion of CO2 in carbohydrates
What happens in the fourth stage of photosynthesis?
Calvin cycle, CO2 fixed into organic molecules in series of reactions that occur in the chloroplast stroma. Initial reaction, catalysed by RuBisCO. Forms a three carbon intermediate. The final product of the Calvin cycle is glyceraldehyde 3-phosphate. Some of the glyceraldehyde 3-phosphate generated in the cycle is transported to the cytosol and converted to sucrose
