4.4.5 The Evolution of Glycolysis Flashcards Preview

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Flashcards in 4.4.5 The Evolution of Glycolysis Deck (8)
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1
Q

glycolysis

A
  • evolved before the Krebs cycle. Glycolysis occurs in all cells; it generates the chemical precursor for the
    Krebs cycle; and it takes place in the cytosol and therefore is not dependent on a membrane-bound organelle.
    • The primitive environment of Earth had no free oxygen, a lot of hydrogen sulfide and a lot of iron. A primitive cell could have synthesized ATP to drive glycolysis by hydrolyzing hydrogen sulfide
2
Q

note

A
  • It is presumed that glycolysis evolved before the Krebs cycle. Glycolysis is common to all cells, including very ancient cells. It also sets the stage for the Krebs cycle by producing pyruvate. Glycolysis occurs in the cytosol so it is not dependent on membrane-bound organelles. Remember that the first cells did not have mitochondria.
  • The primitive environment had no free oxygen (O2), a lot of hydrogen sulfide (H2S) and a lot of iron (Fe).
  • Some triphosphorylated nucleotides formed spontaneously, but there was a need for more ATP to phosyphorylate glucose, which was likely available in the environment. It is possible that a hydrogenase produced H+ from H2 gas, which was produced in reactions between iron and sulfur compounds. The hydrogen ions could have driven the synthesis of ATP from ADP.
  • Glycolysis evolved under anaerobic conditions. When oxygen did enter the atmosphere, about 2.0 bya, it created a harsh environment for organisms until the capability for aerobic respiration evolved in, for example, the purple bacteria.
3
Q

The most widely accepted theory concerning the origin of metabolism is that

A
  • chemoautotrophs obtained carbon from carbon dioxide

- chemoautotrophs synthesized their own ATP through chemiosmosis.

4
Q

Which of the following is not one of the conditions of the primitive environment?

A
  • oxidizing atmosphere
5
Q

Which of the following statements concerning the accumulation of oxygen in the early Earth’s atmosphere is NOT correct?

A
  • ALL ANSWERS ARE CORRECT
  • Cyanobacteria first appeared about three billion years ago.
  • The first evidence that oxygen levels began increasing in the atmosphere is the appearance of rust in terrestrial rocks.
  • No oxygen was present approximately 4 billion years ago, when the first prokaryote fossils appeared.
  • Oxygen first began accumulating in the atmosphere about two billion years ago.
6
Q

It is likely that the first organism capable of energy metabolism was a

A
  • chemoautotroph
7
Q

Glycolysis

A
  • breaks down organic molecules and uses the energy to generate ATP
8
Q

The theory that the first organisms were chemoheterotrophs

A
  • relies on an early Earth condition of an abundant supply of abiotically produced organic molecules

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