Biology by Bradford
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The subtopic in the middle and twelve tasks round it: label four diagrams, complete two tables, put a process in order and fill 60 gaps. Every standard level statement has a box; the four boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
| Process | Anabolic or catabolic? | What happens |
|---|---|---|
| Protein synthesis | amino acids joined into polypeptides | |
| Glycogen formation | glucose monomers joined by | |
| Photosynthesis | sugars built from carbon dioxide and water | |
| Digestion | macromolecules split into monomers by | |
| Respiration | glucose and other substrates |
Anabolism builds macromolecules from monomers; catabolism breaks them down.
The inhibitor on the left is : it resembles the substrate and binds where the substrate would. The one on the right is : its binding changes the enzyme's , so the substrate no longer fits. Both bind reversibly. Adding more substrate the first kind of inhibition but not the second. , which lower blood cholesterol, work like the one on the left.
Isoleucine is made from by a chain of five enzymes. When isoleucine builds up, it binds to an on the first enzyme and inhibits it: the end product controls its own production by . As isoleucine is used up it , and the pathway runs again.
Penicillin binds to the active site of , a bacterial enzyme that builds cross-links in the cell . The binding is : it chemically changes the active site, so the enzyme never works again. Walls weaken and growing bacteria . Resistant bacteria make a version of the enzyme whose active site has a different , so penicillin no longer binds.
Enzymes are biological : they speed up reactions without being used up, so cells get fast reactions at body temperature. is the web of interdependent chemical reactions in an organism. Each enzyme is , catalysing just one reaction, so a cell needs many different enzymes and can steer the whole web by controlling them.
| Factor | Shape of the graph | Why |
|---|---|---|
| Temperature | rises to an , then falls steeply | more kinetic energy, so more frequent collisions, until heat denatures the enzyme |
| pH | a peak, falling away on | changed charges in the active site alter its shape, so fewer substrates bind |
| Substrate concentration | rises, then levels off at a | more collisions, until every active site is |
Sketch graphs like these are : they can be tested against the results of enzyme experiments.
Rate is the amount of product made per unit . A tangent drawn at the start of the curve gives the rate: here 24 cm³ in 60 s, or cm³ s⁻¹. The curve levels off as the runs out.
Energy is needed to bonds in the substrate, and energy is as the bonds of the products form. An enzyme the energy that must be put in to start the reaction, so more collisions succeed at body temperature.
The pocket where substrates bind is lined by only a few , but its shape and chemistry depend on how the whole protein folds. Only a substrate that matches both can bind, so each enzyme is . Heat or extreme pH can change the pocket for good, so the substrate no longer fits: the enzyme is .
Number the steps in order.
Collisions need movement: usually the substrate moves, but a large substrate may be , and some enzymes are held still by being embedded in .
Glycolysis and the Krebs cycle are catalysed by enzymes; the enzymes of chemical digestion are , working in the gut once secreted. Glycolysis is a pathway, but in the Krebs and Calvin cycles the last step regenerates the molecule the first step uses. No reaction transfers energy with 100% efficiency, so metabolism always releases , which mammals and birds use to keep their body temperature constant.
1234Enzymes are biological catalysts: they speed up reactions without being used up, so cells get fast reactions at body temperature. Metabolism is the web of interdependent chemical reactions in an organism. Each enzyme is specific, catalysing just one reaction, so a cell needs many different enzymes and can steer the whole web by controlling them.
| Process | Anabolic or catabolic? | What happens |
|---|---|---|
| Protein synthesis | anabolic | amino acids joined into polypeptides |
| Glycogen formation | anabolic | glucose monomers joined by condensation |
| Photosynthesis | anabolic | sugars built from carbon dioxide and water |
| Digestion | catabolic | macromolecules split into monomers by hydrolysis |
| Respiration | catabolic | glucose and other substrates oxidised |
Anabolism builds macromolecules from monomers; catabolism breaks them down.
The pocket where substrates bind is lined by only a few amino acids, but its shape and chemistry depend on how the whole protein folds. Only a substrate that matches both can bind, so each enzyme is specific. Heat or extreme pH can change the pocket for good, so the substrate no longer fits: the enzyme is denatured.
Collisions need movement: usually the substrate moves, but a large substrate may be immobilised, and some enzymes are held still by being embedded in membranes.
| Factor | Shape of the graph | Why |
|---|---|---|
| Temperature | rises to an optimum, then falls steeply | more kinetic energy, so more frequent collisions, until heat denatures the enzyme |
| pH | a peak, falling away on either side | changed charges in the active site alter its shape, so fewer substrates bind |
| Substrate concentration | rises, then levels off at a plateau | more collisions, until every active site is occupied |
Sketch graphs like these are models: they can be tested against the results of enzyme experiments.
Rate is the amount of product made per unit time. A tangent drawn at the start of the curve gives the initial rate: here 24 cm³ in 60 s, or 0.4 cm³ s⁻¹. The curve levels off as the substrate runs out.
Energy is needed to break bonds in the substrate, and energy is released as the bonds of the products form. An enzyme lowers the energy that must be put in to start the reaction, so more collisions succeed at body temperature.
Glycolysis and the Krebs cycle are catalysed by intracellular enzymes; the enzymes of chemical digestion are extracellular, working in the gut once secreted. Glycolysis is a linear pathway, but in the Krebs and Calvin cycles the last step regenerates the molecule the first step uses. No reaction transfers energy with 100% efficiency, so metabolism always releases heat, which mammals and birds use to keep their body temperature constant.
The inhibitor on the left is competitive: it resembles the substrate and binds where the substrate would. The one on the right is non-competitive: its binding changes the enzyme's shape, so the substrate no longer fits. Both bind reversibly. Adding more substrate overcomes the first kind of inhibition but not the second. Statins, which lower blood cholesterol, work like the one on the left.
Isoleucine is made from threonine by a chain of five enzymes. When isoleucine builds up, it binds to an allosteric site on the first enzyme and inhibits it: the end product controls its own production by feedback inhibition. As isoleucine is used up it leaves, and the pathway runs again.
Penicillin binds to the active site of transpeptidase, a bacterial enzyme that builds cross-links in the cell wall. The binding is irreversible: it chemically changes the active site, so the enzyme never works again. Walls weaken and growing bacteria burst. Resistant bacteria make a version of the enzyme whose active site has a different shape, so penicillin no longer binds.