18.1 - Glycolysis

Question 1

What is the first stage of cellular respiration and where does it occur?

Answer 1

The first stage is glycolysis.

• Occurs is the cytoplasm, it does not require oxygen and is an anaerobic process

Question 2

What are the stages of glycolysis?

Answer 2

1. Phosphorylation – glucose reacts with 2 molecules of ATP. 2 ADP molecules are formed as 1 phosphate from each ATP binds to the glucose to make hexose bisphosphate.
2. Lysis – the hexose bisphosphate is unstable so it splits to form two triose phosphate molecules
3. Phosphorylation – two free Pi molecules in the cytoplasm react with the triose phosphate molecules to form triose bisphosphate molecules (2 of them).
4. Dehydrogenation & ATP formation –
   
   1. The 2 triose phosphate molecules undergo dehydrogenation (oxidised by removal of hydrogen molecules) forming 2 pyruvate molecules. NAD coenzymes accept the hydrogens and are reduced.
   2. Simultaneously, 4 ATP molecules are produced, from the phosphates from the triose bisphosphate molecules.

Question 3

What is gained in glycolysis?

Answer 3

The ATP production is an example of substrate level phosphorylation – formation of ATP without an ETC.

ATP is formed from the transfer of a phosphate group from a phosphorylated intermediate (in glycolysis that is triose bisphosphate) to ADP

There is a net ATP yield from glycolysis (of 2 ATP)