A level Biology Transition lesson 1 ENZYMES AQA

A level Biology Transition lesson 1 ENZYMES

AQA GCSE Biology Specification It is really important that your GCSE knowledge is good going into A level Biology as you can see there is a big step up. . AQA A level Biology Specification Learning objectives - To review and consolidate GCSE enzymes knowledge - To describe how starch is broken down into glucose - To describe the induced fit model of enzyme action - To understand why and how enzymes are denatured.

STARTER 1) (5 minutes) Create a mind map including everything you remember from studying Enzymes in GCSE Biology without using any resources. 2) (5 minutes) Watch the following video and add anything to your mind map you didn’t include https: //www. youtube. com/watch? v=smt. CH 5 HX 44 o

What is an enzyme? Enzymes are proteins! Proteins are long chains of amino acids that fold and form bonds to give a specific 3 D structure (depending on the sequence of amino acids). Enzymes are Biological catalysts – they speed up the rate of chemical reactions in living organisms. You will discuss more about protein structure in A level biology Not all proteins are enzymes but ALL enzymes are proteins!

TASK 1 (5 minutes) Match the terms to their correct definitions. Copy of the key words and write the correct definitions next to them 1. Active site A substance which changes the rate of a chemical reaction without being changed or used up 2. Catalyst A molecule upon which an enzyme act. Its shape is complementary to an enzymes active site. 3. Activation energy The special site in the structure of an enzyme where the substrate binds. 4. Substrate The energy needed for a chemical reaction to take place. Extension add any other key words and definitions you recall from this topic at GCSE

TASK 1 Self assess your answers 1. Active site 2. A substance which changes the rate of a chemical reaction without being changed or used up 2. Catalyst 4. A molecule upon which an enzyme act. Its shape is complementary to an enzymes active site. 3. Activation energy 1. The special site in the structure of an enzyme where the substrate binds. 4. Substrate 3. The energy needed for a chemical reaction to take place.

TASK 2 (5 minutes) Digestive enzymes – copy and complete the following table (use your GCSE revision guide if you need to) Name of enzyme Amylase Lipase Protease Where is it produced? What Name of the substrate does product it act upon?

TASK 2 Self assess your answers Name of enzyme Where is it produced? What substrate does it act upon? Name of the product Amylase Salivary glands, Small intestine, pancreas Starch Maltose Lipase Pancreas and small intestine Lipids (fats) Fatty acids and Glycerol Protease Small intestine pancreas and stomach Proteins Amino acids These monomers (single units) are now small enough to be absorbed into the small intestine wall. BUT WHAT ABOUT MALTOSE?

New A level terminology is in blue – you may want to consider creating a glossary of new key words) What about maltose? ? 1. Starch is a polymer (lots of repeating units), it is a big long chain of glucose molecules joined together by glyosidic bonds 3. Maltose is a sugar made up of 2 units of glucose 2. Amylase catalyses the hydrolysis (breaking down using water) of starch in to maltose 4. The enzyme maltase hydrolyses (breaks) the bond to release 2 glucose molecules 5. The enzyme maltase hydrolyses (breaks) the bond to release 2 glucose molecules 6. The glucose molecules are monomers (single units) small enough to be absorbed through the walls of the small intestine

TASK 3 (5 minutes) 1. Copy out the diagram below illustrating enzyme action and add labels 2. In your own words using the diagram below and the GCSE revision guide describe the ‘lock and key hypothesis’ Use the GCSE revision guide to help if you need it. + ↔ ↔ +

Self assess Enzyme-Substrate complex Active site + Enzyme ↔ Substrate Products + ↔ Enzyme The lock and key theory The substrate is complementary to the active size and fits exactly into the active site, like a key into a lock. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).

Activation energy Reactions usually need an input of energy to get them going; this is called the activation energy. For example the gas in a Bunsen burner doesn’t burn until you provide heat from a match • Enzymes bring reactants together in the correct sequence (forming an enzyme substrate complex), keep them close together & put strain on the bonds making them easier to break • All of this lowers the activation energy so reactions can happen at a lower temperature.

TASK 4 (6 minutes) Watch the following and answer the following questions. 1. 2. 3. 4. 5. 6. What do we mean by induced fit? Which 3 letters do the names of sugars usually end in? Which 3 letters do the names of enzymes usually end in? Name the enzyme that breaks down lactose? Name factors that effect enzyme activity What does denatured mean? https: //www. youtube. com/watch? v=qg. VFk. Rn 8 f 10

Self assess 1) Induced fit means the active site changes it shape slightly when the substrate enters (see diagram) 2) 3) 4) 5) OSE (Glucose, lactose, maltose) ASE (lipase, Protease) Lactase p. H, temperature (substrate concentration, enzyme concentration and inhibitors are also valid answers here) 6) The active site had changed shape so the substrate no longer fits (enzyme substrate complex cannot be formed)

Why are enzymes denatured? • Remember we said that enzymes are proteins…. • When the chain of amino acids folds to form a 3 D shape bonds are formed between the amino acids that give it its specific shape. • If the temperature is too high (too much kinetic energy) of the p. H isn’t optimum (too many OH- or H+ Ions are present) some of these bond break. This causes the active site to change shape so the substrate can no longer fit. The enzyme has been denatured

TASK 5 (15 minutes) • Use your knowledge from task 1 -4 and the extra information on the slides provided to attempt the A level exam questions. You do not need to print these off you can just type or write your responses.

Self assess Qu 1 (a) Protein; Catalyst; Accept speeds up a reaction (but is not changed by the reaction) (For reaction involving a) specific substrate; Lowers activation energy; 2 max (b) Enzyme D binds/collides with substrate E; Active site forms/changes shape to fit substrate/E; Max 2 if no reference to letters Please note – you would not be allowed (By) induced fit; lock and key theory here as the active side is not exactly complementary to the (As) enzyme-substrate complex forms; substrate so it is showing induced fit (Breaks down to give) products F and G; Enzyme is unchanged (at end); 3 max [5]

Self assess Q 2. (a) Amylase; Please note – as this is an A level question the new terminology is important. (Starch) to maltose: Remember hydrolysis (breaking bond using Maltase; water ) is how the bond is broken and glyosidic is the name of the specific bond Maltose to glucose; formed between glucose molecules Hydrolysis; (Of) glycosidic bond; (5) Q 3. (a) 1. (before reaction) active site not complementary to/does not fit substrate; 2. Shape of active site changes as substrate binds/as enzyme-substrate complex forms; Note. Points 1 and 2 may be made in one statement and ‘complementary’ introduced at any point. Points 1&2 – active site mentioned once applies for both points (2)

Plenary (5 minutes) • Read through the pages from ‘CGP head start to A level Biology’ most of which we have covered today. • Complete the 3 questions at the bottom of pg 4 and 5

Self assess Pg 4 1. Increase the rate of/speed of biochemical reactions. / Act as biological catalysts 2. Activation energy is the energy required to get a reaction started 3. Break down food into smaller molecules Pg 5 1. The substrate molecules must be the correct shape to fit into the active site 2. The shape of the active site has changed and the substrate will no longer fit 3. Acids and alkalis can denature enzymes by disrupting the weak hydrogen bonds in enzymes tertiary (3 D) structure and changing the shape of their active sites.

Other videos you may find useful for this topic. . • https: //www. youtube. com/watch? v=VNX 9 UQ 08 f. Z 4 • https: //www. youtube. com/watch? v=qq 1 fo. Xn v. Jao • https: //www. youtube. com/watch? v=rl. H 1 ym 9 16 Fo Any issues or questions please email Mrs Abbott (s. abbott@jths. co. uk)