Metabolic Pathways (b) State 2 ways metabolic pathways are controlled State the role of intra- and extra-cellular signal molecules State how a sequence of reactions can be driven in a particular direction

Control of Metabolic Pathways Metabolic pathways consist of several stages Metabolic pathways are controlled by: the absence or presence of particular enzymes the regulation of the rate of reaction of key enzymes within the pathway Regulation can be controlled by intra and extracellular signal molecules Most metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction. Alternative pathway X Causes the reaction to reverse Lots of Substrate 3 Increases the rate of reaction here

Example of metabolic pathways in the body Making Melanin: What characteristics of metabolic pathways can you see? It consists of several stages Each stage is controlled by enzymes

Control of Metabolic Pathways Metabolic pathways consist of several stages Metabolic pathways are controlled by the absence or presence of particular enzymes They are also controlled through the regulation of the rate of reaction of key enzymes within the pathway Regulation can be controlled by intra and extracellular signal molecules Most metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.

Example of metabolic pathways in the body Phenylketonuria (PKU): X X Toxins produced Phenylketonuria is a genetic disorder cause by a missense substitution mutation to a gene on chromosome 12 that normally codes for enzyme 1 in the pathway. The person is unable to make the essential enzyme that converts phenylalanine to tyrosine. Instead an alternative metabolic pathway occurs that produces toxins that limit metal development and cause epilepsy.

Example of metabolic pathways in the body Phenylketonuria (PKU): In the UK, PKU occurs in about 1:10000 people. Babies are screened at birth for the condition. Their blood is tested for excess phenylalanine, if the condition is present it can be controlled with a special low-protein diet. PKU sufferers have lighter skin than normal as they still get some tyrosine from their diet so are still able to produce some melanin (skin pigment).

Example of metabolic pathways in the body Albinism: X X Albinos are unable to make the enzyme that allows the synthesis of melanin. Provided they avoid any exposure to UV radiation they have no medical problems.

Control of Metabolic Pathways Metabolic pathways consist of several stages Metabolic pathways are controlled by the absence or presence of particular enzymes They are also controlled through the regulation of the rate of reaction of key enzymes within the pathway Regulation can be controlled by intra and extracellular signal molecules Most metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.

Control of Metabolic Pathways Genes for some enzymes are continuously expressed. These enzymes are always present in the cell and their control involves regulation of their rate of reaction. This can be through: intra and extracellular signal molecules switching genes on or off

Epinephrine is released by adrenal glands It binds to receptors on liver cell membranes This triggers the a series of events that activate an enzyme to convert glycogen into glucose and release it into the blood stream. Epinephrine acts a signal molecule

Control of Metabolic Pathways 1. Intracellular signal molecules: Signals that originate within the cell and affect metabolism 2. Extracellular signal molecules: Signals that come from the cells environment (other cells) and affect metabolism An example of this would be epinephrine (AKA adrenaline)

Control of Metabolic Pathways 3. Switching genes on or off Some metabolic pathways are only required to operate under certain circumstances. Therefore in order to regulate the metabolic pathway, the genes which code for the enzymes can either be switched on or off. An example of this is found in the bacteria E coli.

Escherichia coli produces the enzyme -galactosidase to digest the substrate lactose, to release the glucose that it needs for respiration. The enzyme is only made if lactose is present. When no lactose is present the gene that codes for the synthesis of -galactosidase is switched off. This ensures that resources are not wasted in the production of an enzyme when it is not needed.

+ Lactose = Lactose (a sugar found in milk) Glucose Galactose Glucose Enzyme that catalyses the breakdown of lactose Glucose β - Galactosidase Galactose + Lactose

Tasks: Complete the “Investigating the control of metabolic pathways in E coli“ sheet

Investigating the lac operon in E coli ANSWERS ONPG is a colourless synthetic chemical that can be broken down by the enzyme B-galactosidase as follows: ONPG galactose + yellow compound The presence of yellow indicates activity by B-galactosidase.

Investigating the lac operon in E coli ANSWERS Method:

Investigating the lac operon in E coli ANSWERS Results:

Investigating the lac operon in E coli ANSWERS Results & conclusion: Test tube 1 Test tube 2 Test tube 3 Test tube 4 Colour of solution Reason the solution turned this colour Yellow Yellow Colourless Colourless Presence of lactose induced E. coli to produce B- galactosidase. The substrate ONPG was not present, so the yellow colour could not be produced The enzyme B- galactosidase acted on substrate ONPG forming the yellow compound The substrate ONPG was not present, so the yellow colour could not be produced