12-5 Glycolysis (Cambridge AS A Level Biology, 9700)

Summary

This script delves into the intricacies of aerobic respiration, focusing on the process of glycolysis. It explains how glucose, a stable energy molecule, is made reactive through phosphorylation using ATP, transforming into fructose 1,6-bisphosphate. This molecule then splits into triose phosphates, undergoing substrate-linked reactions and oxidation, ultimately yielding two ATP, two NADH, and pyruvate molecules. The explanation simplifies complex biochemical steps, highlighting the net gain in energy and the preparation for further stages of cellular respiration.

Takeaways

• 🧬 Aerobic respiration is the breakdown of organic molecules, such as glucose (C6H12O6), in the presence of oxygen, resulting in the production of carbon dioxide, water, and ATP.
• 🔍 Aerobic respiration is divided into four stages: glycolysis, link reaction, citric acid cycle (also known as Krebs cycle or TCA cycle), and oxidative phosphorylation along with chemiosmosis.
• 📍 Glycolysis occurs in the cytoplasm, the link reaction and citric acid cycle take place in the mitochondrial matrix, while oxidative phosphorylation and chemiosmosis happen in the inner mitochondrial membrane.
• 🍬 Glycolysis is the initial step of aerobic respiration, involving the breakdown of a glucose molecule into two molecules of pyruvate.
• ⚡ To initiate glycolysis, glucose is phosphorylated using two ATP molecules, making it more reactive and transforming it into fructose 1,6-bisphosphate.
• 🔄 The process of isomerization converts glucose into fructose 1,6-bisphosphate without the need for the student to memorize the intermediate steps.
• 💥 Fructose 1,6-bisphosphate is then split into two three-carbon sugars, or triose phosphates, during glycolysis.
• 🔋 Glycolysis results in a net gain of two ATP molecules after the initial investment of two ATP, as four ATP are produced during the substrate-linked reaction.
• 🌀 Oxidation, or dehydrogenation, occurs during glycolysis, where hydrogen atoms are released and carried by NAD+ to become reduced NADH.
• 🔑 The end products of glycolysis are two molecules of pyruvate, two NADH molecules, and a net gain of two ATP molecules.
• 🚫 It's important to note that students should not abbreviate 'substrate-linked reaction' as 'SLR' in exams but should write out the full name.

Q & A

What is aerobic respiration?

Aerobic respiration is the process of breaking down organic molecules, such as glucose (C6H12O6), in the presence of oxygen to produce carbon dioxide, water, and ATP (energy).

How many stages are there in aerobic respiration?

Aerobic respiration is divided into four main stages: glycolysis, link reaction, citric acid cycle (also known as Krebs cycle or TCA cycle), and oxidative phosphorylation along with chemiosmosis.

Where does glycolysis occur within a cell?

Glycolysis takes place in the cytoplasm of the cell.

What is the purpose of adding a phosphate group to glucose during glycolysis?

Adding a phosphate group to glucose makes it more reactive and less stable, facilitating its breakdown in the glycolysis process.

What molecule is formed after glucose is phosphorylated and undergoes isomerization?

After glucose is phosphorylated and undergoes isomerization, it becomes fructose 1,6-bisphosphate.

What happens to fructose 1,6-bisphosphate during glycolysis?

Fructose 1,6-bisphosphate breaks down into two molecules of glyceraldehyde 3-phosphate (triose phosphates).

What is the net gain of ATP molecules from glycolysis?

The net gain of ATP molecules from glycolysis is two, as two ATP are used at the beginning and four ATP are produced at the end.

What is the role of NAD in glycolysis?

NAD acts as a hydrogen carrier in glycolysis, accepting hydrogen atoms released during the oxidation of triose phosphates and becoming reduced to NADH.

What is the end product of glucose after glycolysis?

The end product of glucose after glycolysis is two molecules of pyruvate.

What are the four steps of glycolysis?

The four steps of glycolysis are phosphorylation using two ATP molecules, lysis to break it down into triose phosphates, substrate-linked reaction (SLR), and oxidation or dehydrogenation.

Why is glucose considered an energy storage molecule?

Glucose is considered an energy storage molecule because it is quite stable and not easily broken down, making it a good candidate for storing energy in a form that can be later released during cellular respiration.