Respiration: Glycolysis | A-level Biology | OCR, AQA, Edexcel

Respiration: Glycolysis in a Snap! Unlock the full A-level Biology course at http://bit.ly/2VZhlik created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.

The key points covered of this video include:

1. Types of Respiration
2. Introduction to Glycolysis
3. The Stages of Glycolysis
4. The Final Products of Glycolysis

Types of Respiration

Respiration can occur in the presence of oxygen or without oxygen. When respiration occurs in the presence of oxygen, it is called aerobic respiration. When respiration occurs without oxygen, it is called anaerobic respiration. Aerobic respiration produces a greater number of ATP molecules than aerobic respiration. Aerobic respiration is therefore more desirable because the cell can produce more energy from it. Aerobic respiration occurs in both the cytoplasm and the mitochondria, whereas anaerobic respiration only occurs in the cytoplasm.

Introduction to Glycolysis

Glycolysis is the first stage of respiration and occurs in both aerobic and anaerobic respiration. In glycolysis a glucose molecule is converted to two molecules of pyruvate. Pyruvate is a three carbon molecule which is used differently in aerobic and anaerobic respiration. Glycolysis can be split into three stages: 1. The phosphorylation of glucose. 2. The splitting of the phosphorylated glucose. Oxidation of the split glucose to form pyruvate. To carry out these steps, glycolysis requires the help of a coenzyme called NAD. NAD helps enzymes carry out the removal of hydrogen atoms from molecules. The removal of hydrogen atoms is known as an oxidation reaction. NAD helps enzymes that catalyse oxidation reactions by accepting and carrying the hydrogen atoms that have been removed.

The Stages of Glycolysis

The first step of glycolysis involves adding two phosphate molecules to a glucose molecule to produce hexose biphosphate. This process is called glucose phosphorylation and makes the glucose more reactive so it can be split more easily. These two phosphate molecules are taken from two ATP molecules which are hydrolyzed to obtain the phosphates needed. The hexose biphosphate can then be split to produce two molecules of triose phosphate. Enzymes called dehydrogenase enzymes remove a hydrogen atom from each of the triose phosphate molecules. This removal of hydrogen atoms is called oxidation and each hydrogen atom is accepted by a molecule of NAD. These NAD molecules with hydrogen atoms are described as reduced - these reduced NAD molecules will be of use later in the respiration process. The phosphates from each triose phosphate molecule are then used to produce 2 ATP molecules each. Therefore in this reaction 4 ATP are produced altogether. During this step two molecules of pyruvate are also produced from two triose phosphate molecules.

The Final Products of Glycolysis

Each glucose molecule used up in glycolysis produces: 2 pyruvate molecules, 2 reduced NAD molecules, A net of 2 ATP molecules.

Summary

Aerobic respiration uses oxygen whereas anaerobic respiration does not
Glycolysis is the first stage of both types of respiration and takes place in the cytoplasm
Glycolysis involves converting one molecule of glucose to two molecules of pyruvate
In glycolysis glucose is phosphorylated to hexose bisphosphate using 2 ATP molecules
Hexose bisphosphate is then split into two triose phosphate molecules
The triose phosphate molecules are then oxidised by the dehydrogenase enzyme and hydrogen atoms are accepted by the NAD coenzyme
In glycolysis 2 pyruvate, 2 reduced NAD and a net of 2 ATP are produced