H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
Assignment 10B: Respiratory pathways
Respiratory pathway
The term, respiratory pathway, can be defined as the route taken by the
respiratory system in relation to the process of aerobic and anaerobic
respiration. The main respiratory pathways are classed as aerobic and anaerobic
respiratory pathways which will be discussed in more detail over the next few
pages of this assignment. The term aerobic means with oxygen and the term
anaerobic means without oxygen. The stages of the aerobic respiratory
pathways are glycolysis, Link reaction, Krebs cycle, electron transport chain and
chemiosmosis whereas the stages of the anaerobic respiratory pathway are
glycolysis and alcoholic/lactic fermentation.
Aerobic respiratory pathway
Figure 1- Flow diagram of the
Glycolysis
process of glycolysis
The process of glycolysis is the initial stage of aerobic
respiration which takes place in the cytoplasm of cells.
This process can be referred to as an anaerobic process
due to no oxygen being required.
Glycolysis involves converting one molecule of glucose
(which has 6 carbon atoms) into two molecules of
pyruvate (which has 3 carbon atoms). This process
needs a coenzyme known as NAD (nicotinamide-
adenine dinucleotide) to help enzymes carry out the
removal of hydrogen atoms from molecules (oxidation)
and also helps them to catalyse oxidation reactions by
accepting and carrying the hydrogen atoms that have
been removed.
The process of glycolysis can be separated into 3
stages:
- Phosphorylation of glucose
- Splitting of hexose biphosphate
- Oxidation of triose phosphate
In the first stage, phosphorylation of glucose, the
process starts off with a molecule of glucose (as shown
in Figure 1) and 2 phosphate molecules are added in order to produce hexose
biphosphate- this allows glucose to be made more reactive so that it can split
easily. The 2 phosphate molecules are taken from 2 ATP molecules that are
hydrolysed to obtain the phosphates needed. Figure 1 shows the hydrolysis of
ATP as ADP and Pi (inorganic phosphate) are produced to phosphorylate glucose.
1
, H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
In the second stage of glycolysis (see Figure 1), splitting of hexose biphosphate,
2 molecules of triose phosphate (each contain 3 carbon atoms) are produced by
splitting hexose biphosphate.
In the final stage of glycolysis, oxidation of triose phosphate, enzymes known as
dehydrogenase are involved as they remove a hydrogen atom from each of the
triose phosphate molecules, hydrogen atoms become hydrogen ions, and each of
the hydrogen ions are accepted by a molecule of NAD. As shown in Figure 1, 2
NAD molecules with hydrogen atoms are reduced and these 2 reduced NAD
molecules will be of use later on. The phosphates from each triose phosphate
molecule are then used to produce 2 molecules of ATP each, forming a net of 4
molecules of ATP as a result- as shown in Figure 1. 4 molecules of ATP are
produced, however 2 were used up in stage 1, therefore there is a net gain of 2
ATP. At the end of this stage, 2 molecules of pyruvate are produced from 2
triose phosphate molecules.
Overall, the products made from glycolysis are:
- 2 pyruvate molecules
- 2 reduced NAD (NADH) molecules
- 2 ATP molecules
The importance of glycolysis is that it produces 2 pyruvate molecules that are
actively transported into the matrix of the mitochondria for the Link reaction-
the next stage of aerobic respiration. In addition to this, the process of glycolysis
takes place in all cells of the body, acting as an energy source for all cells in the
body.
Furthermore, the amount of energy released at this stage is significant as it is
used to synthesise 2 molecules of ATP from the phosphates in triose phosphate.
Link reaction
The second stage of aerobic respiration is the Link reaction Figure 2- Flow diagram of the
and this is when pyruvate is converted to acetyl Link reaction
coenzyme A (acetyl CoA) in the mitochondrial
matrix.
Before the Link reaction occurs, pyruvate is
actively transported across the mitochondrial
envelope and into the matrix by the transport
protein, pyruvate H+ symport.
To start off the Link reaction, a pyruvate molecule
is decarboxylated and dehydrogenated by the
large multi-enzyme complex pyruvate
dehydrogenase. The decarboxylation of pyruvate
removes a carboxyl group and produces CO2 while
the dehydrogenation of pyruvate removes
hydrogen atoms that are accepted by NAD, producing reduced NAD (NADH)- as
2
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
Assignment 10B: Respiratory pathways
Respiratory pathway
The term, respiratory pathway, can be defined as the route taken by the
respiratory system in relation to the process of aerobic and anaerobic
respiration. The main respiratory pathways are classed as aerobic and anaerobic
respiratory pathways which will be discussed in more detail over the next few
pages of this assignment. The term aerobic means with oxygen and the term
anaerobic means without oxygen. The stages of the aerobic respiratory
pathways are glycolysis, Link reaction, Krebs cycle, electron transport chain and
chemiosmosis whereas the stages of the anaerobic respiratory pathway are
glycolysis and alcoholic/lactic fermentation.
Aerobic respiratory pathway
Figure 1- Flow diagram of the
Glycolysis
process of glycolysis
The process of glycolysis is the initial stage of aerobic
respiration which takes place in the cytoplasm of cells.
This process can be referred to as an anaerobic process
due to no oxygen being required.
Glycolysis involves converting one molecule of glucose
(which has 6 carbon atoms) into two molecules of
pyruvate (which has 3 carbon atoms). This process
needs a coenzyme known as NAD (nicotinamide-
adenine dinucleotide) to help enzymes carry out the
removal of hydrogen atoms from molecules (oxidation)
and also helps them to catalyse oxidation reactions by
accepting and carrying the hydrogen atoms that have
been removed.
The process of glycolysis can be separated into 3
stages:
- Phosphorylation of glucose
- Splitting of hexose biphosphate
- Oxidation of triose phosphate
In the first stage, phosphorylation of glucose, the
process starts off with a molecule of glucose (as shown
in Figure 1) and 2 phosphate molecules are added in order to produce hexose
biphosphate- this allows glucose to be made more reactive so that it can split
easily. The 2 phosphate molecules are taken from 2 ATP molecules that are
hydrolysed to obtain the phosphates needed. Figure 1 shows the hydrolysis of
ATP as ADP and Pi (inorganic phosphate) are produced to phosphorylate glucose.
1
, H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
In the second stage of glycolysis (see Figure 1), splitting of hexose biphosphate,
2 molecules of triose phosphate (each contain 3 carbon atoms) are produced by
splitting hexose biphosphate.
In the final stage of glycolysis, oxidation of triose phosphate, enzymes known as
dehydrogenase are involved as they remove a hydrogen atom from each of the
triose phosphate molecules, hydrogen atoms become hydrogen ions, and each of
the hydrogen ions are accepted by a molecule of NAD. As shown in Figure 1, 2
NAD molecules with hydrogen atoms are reduced and these 2 reduced NAD
molecules will be of use later on. The phosphates from each triose phosphate
molecule are then used to produce 2 molecules of ATP each, forming a net of 4
molecules of ATP as a result- as shown in Figure 1. 4 molecules of ATP are
produced, however 2 were used up in stage 1, therefore there is a net gain of 2
ATP. At the end of this stage, 2 molecules of pyruvate are produced from 2
triose phosphate molecules.
Overall, the products made from glycolysis are:
- 2 pyruvate molecules
- 2 reduced NAD (NADH) molecules
- 2 ATP molecules
The importance of glycolysis is that it produces 2 pyruvate molecules that are
actively transported into the matrix of the mitochondria for the Link reaction-
the next stage of aerobic respiration. In addition to this, the process of glycolysis
takes place in all cells of the body, acting as an energy source for all cells in the
body.
Furthermore, the amount of energy released at this stage is significant as it is
used to synthesise 2 molecules of ATP from the phosphates in triose phosphate.
Link reaction
The second stage of aerobic respiration is the Link reaction Figure 2- Flow diagram of the
and this is when pyruvate is converted to acetyl Link reaction
coenzyme A (acetyl CoA) in the mitochondrial
matrix.
Before the Link reaction occurs, pyruvate is
actively transported across the mitochondrial
envelope and into the matrix by the transport
protein, pyruvate H+ symport.
To start off the Link reaction, a pyruvate molecule
is decarboxylated and dehydrogenated by the
large multi-enzyme complex pyruvate
dehydrogenase. The decarboxylation of pyruvate
removes a carboxyl group and produces CO2 while
the dehydrogenation of pyruvate removes
hydrogen atoms that are accepted by NAD, producing reduced NAD (NADH)- as
2
