L11 + 12: metabolic diversity

how are different metabolic types defined

energy source, carbon source, + electron source

what is a chemotroph

uses performed molecules as an energy source

what is a phototroph

uses sunlight as an energy source

what is an heterotroph

uses organic compounds as a carbon source

what is an autotroph

uses inorganic compounds as a carbon source

what is an organotroph

oxidise organic molecules for a source of electrons

what is a lithotroph

oxidises inorganic molecules for a source of electrons

what is catabolism

breaking down molecules

what is anabolism

synthesis of molecules

describe the rules that underpin electron transfer

movement from molecules with low reduction potential to high through membrane bound cytochrome complexes

from electron donor → electron acceptor

what drives ATP synthesis

energy generated during electron transfer to generate a proton gradient

what can be used as electron donors

organic molecules (chemoorganotrophs)

inorganic molecules (chemolithotrophs)

light energy to reduce compounds which are used as electron donors (phototrophs)

what processes act as electron acceptors

respiration ((in)organic molecules)

fermentation (organic molecules)

what 2 sources of energy underpin metabolism

reducing power (NADH, NADPH, FADH2)

ATP

what compounds do chemoorganotrophs utilise for electron sources

carbohydrates, lipids, peptides, aromatic compounds

what 2 key metabolites are produced by chemoorganotrophs

Acetyl-CoA + pyruvate

what are the 3 major metabolic types used by chemoorganotrophs

aerobic respiration, anaerobic respiration, fermentation

when do chemoorganotrophs use fermentation

no oxygen available + no alternative electron acceptor available

how does anaerobic respiration occur in chemoorganotrophs

electron transfer via cytochromes, quinones, + iron-sulfur proteins

why is anaerobic respiration important

exploits a wide range of ecological niches

what are 2 types of anaerobic respiration

denitrification + methanogenesis

how does anaerobic respiration differ from fermentation

uses inorganic molecules (not O₂) or organic molecules as terminal electron acceptors via membrane bound respiratory chain

ATP produced by oxidative phosphorylation via PMF

how does fermentation differ from anaerobic respiration

uses organic molecules as electron acceptors without use of a respiratory chain

ATP produced by substrate level phosphorylation in cytoplasm

what do chemolithotrophs use as a carbon sorce

most use CO₂ via the calvin cycle

can also use more complex molecules (acetate)

how do chemolithotrophs fix carbon

require NADH (requires consumption of H⁺ for a reverse electron flow process)

what do chemolithotrophs use as major electron sources

H₂

Fe²⁺

ammonia + nitrites

sulfur derivitives

what do hydrogenotrophs use as an electron donor

H₂ with a wide range of electron acceptors

what is methogenesis

using CO₂ as an electron acceptor

what is dehalorespiration

using chlorinated compounds as electron acceptors

name 4 compounds hydrogenotrophs can use as an electron acceptor

O₂, SO₄²⁺, CO₂, chlorinated compounds

how does iron oxidation occur

reduced iron Fe²⁺ oxidised to Fe³⁺ at low pH

Fe³⁺ (ferric irons) forms insoluble ferric hydroxide as pH gets lower

how does nitrogen oxidation occur

ammonia + nitrites used as electron donors to produce nitrates

aerobic conditions: nitrification

anaerobic conditions: anammox

what do sulfur derivatives produce when used as electron donors

sulfuric acid

how are acid-producing microbes used in biomining

oxidise sulfide of iron + copper. oxidation of Cu+ and acid production dissolves metal from rocks

what are the 2 types of photosynthesis

aerobic + anaerobic

what organisms use aerobic photosynthesis + what photosystems do they use

cyanobacteria + plants: PSI + PLSII

what organisms use anaerobic photosynthesis + what photosystems do they use

bacteriorhodopsin: BR

green sulfur bacteria: PSI

purple bacteria: PSII

what is bacteriorhodopsin

very abundant light-driven proton pump in archaeal membranes

describe the process of photosynthesis in bacteriorhodopsin

contains a pigment (retinal) that undergoes conformational changes once excited by light from trans → cis

conformational change triggers transfer of proton to Asp85

deprotonated retinal pushes against helix F, opening a channel on cytoplasmic side: indiced deprotonation of retinal from Asp96

Asp96 undergoes reprotonation

Asp85 tranfers a proton outside through hydrogen bonding via water molecules + other residues

do cyanobacteria contain chloroplasts

no- they are primitive chloroplasts

how is light captured by cyanobacteria photosystems

by light harvesting complexes which channel energy to a reaction centre

light harvesting complexes contain several pigments which can use light energy at various wavelengths (chlorophylls, carotenoids, bilins, etc)

what is the oxygenic ‘z pathway’ in cyanobacteria

2 distinct photosystems with distinct absorption wavelengths are excited by light

light provides energy to strip electrons from H₂O yielding H+

electron flow is used to pump protons outside the cell to reduce NADP+

H+ gradient is used to generate ATP

NADPH + ATP used to fix CO2 to make glucose

how does anaerobic photosynthesis occur in green sulfur bacteria

light captured by antenna complexes in organelles called chlorosomes

photon energy transferred to PSI reaction centre

PSI donates an electron to ETC

ET pumps protons outside cell + reduces NADP+ via ferredoxin

H+ gradient used to generate ATP

PSI receives electrons from inorganic sulfur derivatives (H₂, H₂S^₎

how does anaerobic respiration occur in purple bacteria

light captured by antenna complexes in organelles called chromatophores

photon energy transferred to the PSII reaction centre

PSII donates an electron to cyclic ETC

electron transport pumps protons outside the cell + H+ gradient used to generate ATP (cyclic photophosphorylation)

NADH is produced by reverse electron flow: electrons are transferred from reduced ETC components with a more positive reducing potential. this is not thermodynamically favourable + consumes energy (H+ pumping)

electrons transfered to NAD+ by ETC components are replenished by inorganic or organic compounds (H₂S, succinate)