Higher Human Biology Subtopic 6 (b) Metabolic Pathways Higher Human Biology Subtopic 6 (b)

Learning Intentions Describe how gene expression and enzymes are regulated Discuss the role of extracellular and intracellular signal molecules Explain the difference between competitive and non-competitive inhibitors and describe their effect on enzyme activity

Control of Pathways Each step in a metabolic pathway is driven by a specific enzyme. Each enzyme is coded for by at least one gene. If one enzyme is absent, the pathway stops.

Pathways can be regulated through gene expression. Control of Pathways Pathways can be regulated through gene expression. Some pathways are needed at all times so are always turned on. Some are only needed at certain times. Stages (genes) are switched on and off to stop resources being wasted.

The Lac Operon Lactose is a sugar in milk Glucose Galactose E. coli (a bacteria) use lactose as an energy source for respiration but they must first break it down. Glucose Galactose Lactose molecule

The Lac Operon E. coli has a gene that codes for β galactosidase – an enzyme that breaks down lactose. E. coli only produce the enzyme when lactose is present β galactosidase glucose Lactose galactose

This process is called ENZYME INDUCTION. The Lac Operon E. coli switch the gene for β galactosidase on when lactose is present and off when it’s not. This process is called ENZYME INDUCTION.

The Lac Operon – How it works An operon is 1 or more structural genes that code for the enzyme + a neighboring operator gene that controls them. operon operator gene Controls the switching on and off structural gene

In the absence of lactose - genes turned off - no enzyme produced RNA polymerase repressor protein binds to operator cannot bind to promoter promoter no transcription of structural genes repressor gene operator no enzymes for lactose breakdown no translation of structural proteins produces (via transcription and translation) repressor protein

In the presence of lactose - genes turned on - enzyme produced - lactose broken down L RNA polymerase binds to promoter promoter transcription of structural genes repressor gene operator mRNA for structural proteins altered repressor cannot bind operator produces (via transcription and translation) repressor protein lactose binds to and alters repressor L enzymes for lactose breakdown produced

Investigating The Lac Operon β galactosidase ONPG yellow substance + galactose

Controlling Pathways - signal molecules Some pathways are always switched on. These are controlled in different ways : - signal molecules - inhibitors

Signal Molecules These molecules can be e.g. hormones. They trigger the activation of the enzymes. They are intracellular - the signal is released within the cell Or extracellular - the signal comes from the environment outside the cell

Inhibitors This is a substance that decreases the rate of the reaction. There are 2 types : - competitive - non-competitive

Competitive Similar shape to the substrate Competes for the active site Blocks the active site (substrate can’t bind) Reaction rate decreases Active site ISN’T damaged

Competitive Increasing the substrate concentration will increase the rate of reaction as the substrate outnumbers the inhibitor. Textbook page 93

NON - Competitive Doesn’t combine with the active site Attaches elsewhere to an allosteric site Indirectly changes the shape of the active site Substrate can’t bind

Non - Competitive These inhibitors change the active site so increasing substrate concentration makes no difference to activity.

NEGATIVE FEEDBACK CONTROL End Point Inhibition As the concentration of the end product increases it can bind to e.g. enzyme 1 in the pathway. Less B, C and D will be produced (saves waste). As levels of D fall, less enzyme 1 is affected so the reaction increases. Animation 2 NEGATIVE FEEDBACK CONTROL

Activators Enzymes can exist in inactive or active forms. A regulatory molecule can bind to an allosteric site to activate the enzyme. This increases the reaction rate. Textbook page 93

Expt - Phosphotase Textbook page 95 phosphatase Phenolphthalein phosphate phenolphthalein + phosphate

Learning Intentions Describe how gene expression and enzymes are regulated Discuss the role of extracellular and intracellular signal molecules Explain the difference between competitive and non-competitive inhibitors and describe their effect on enzyme activity

Q1. Enzymes… a) speed up reactions and remain unchanged d) slow down reactions and are used up in the reaction c) speed up reactions and are used up in the reaction b) slow down reactions and remain unchanged

Q2. What is an active site? a) The place on a substrate where the enzyme binds. d) The place on an enzyme where the substrate binds. c) The place on the product where the substrate binds. b) The place on the substrate where the product binds.

Q3. Which graph shows the effect of temperature on enzyme activity? d) c) b) a) activity activity temperature temperature activity activity temperature temperature

Q4. What will bind to an active site? a) All types of substrate molecule. d) One type of product molecule. c) One type of substrate molecule. b) All types of product molecule.

Q5. Enzymes will work at … a) only one pH d) acidic pHs c) a range of pHs b) all pHs

Q6. Which of the following is correct? a) Starch catalase maltose d) Starch catalase glucose c) Starch amylase glucose b) Starch amylase maltose

Q7. Which of the following is correct? Amylase is a synthesis enzyme. Catalase is a breakdown enzyme. d) Amylase is a synthesis enzyme. Phosphorylase is a breakdown enzyme. c) Catalase is a synthesis enzyme. Amylase is a breakdown enzyme. b) Phosphorylase is a synthesis enzyme.

Q8. Which term best describes a denatured enzyme? a) Its active site has changed shape. d) Attached to the substrate. c) Working at its fastest rate. b) Dead.