Cytochromes are critical participants in the electron transport chains used in photosynthesis and cellular respiration. How do cytochromes donate and accept electrons?
The cytochromes donate electrons excited by photons to other cytochromes that accept electrons as replacements for lost electrons.
Each cytochrome has an iron-containing heme group that accepts electrons and then donates the electrons to a more electronegative substance
Every cytochrome’s iron-containing heme group accepts electrons from oxygen and donates the electrons to the next cytochrome in the chain.
Cytochromes donate electrons directly to the energy-carrier molecules NAD and FAD and accept electrons from less electronegative substances.
The correct answer and explanation is :
The correct answer is:
“Each cytochrome has an iron-containing heme group that accepts electrons and then donates the electrons to a more electronegative substance.”
Explanation:
Cytochromes are proteins that play an essential role in the electron transport chains (ETC) of cellular respiration and photosynthesis. They function as electron carriers, facilitating the transfer of electrons through redox (oxidation-reduction) reactions.
Each cytochrome contains a heme group, a prosthetic (non-protein) component with an iron (Fe) atom at its core. The iron atom in the heme group can alternate between two oxidation states:
- Fe²⁺ (reduced state) – when it gains an electron
- Fe³⁺ (oxidized state) – when it loses an electron
This ability allows cytochromes to accept an electron from a preceding electron donor and pass it to a more electronegative acceptor, ensuring the flow of electrons in the ETC.
In cellular respiration, cytochromes are part of the mitochondrial ETC, where they contribute to the sequential transfer of electrons from NADH and FADH₂ to oxygen, the final electron acceptor. This transfer powers the pumping of protons across the inner mitochondrial membrane, generating a proton gradient that drives ATP synthesis.
In photosynthesis, cytochromes, particularly cytochrome b6f, participate in the electron transport chain of the light-dependent reactions, helping transfer electrons from photosystem II to photosystem I, which leads to ATP and NADPH production.
Importantly, cytochromes do not donate electrons directly to NADH or FADH₂, nor do they accept electrons from oxygen. Instead, they pass electrons along a gradient of increasing electronegativity, ensuring a controlled and efficient transfer of energy.