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Biology 201 Enzymes

Biology 201 Enzymes

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Biology 201 Enzymes

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  1. Biology 201 Enzymes

  2. What are Enzymes? • Enzymes are catalysts. • A catalyst is a substance which increases the rate of chemical reaction • Catalysts themselves are NOT used up • Used in living organisms • Reactions must occur at body temp and atmospheric pressure (LOW)‏ • Without catalysts reactions would be too slow • Needed to sustain life

  3. What are Enzymes? • Metabolism is just the cummulation of reactions • 1000's of different reactions in an organism • Each reaction requires a unique catalyst • These catalysts are called enzymes • Enzymes act upon a substance called its substrate (reactant) • Metabolism is a chain of reactions • Product of one reaction is substrate for the next • A different enzyme for each step in the chain • This is called the metabolic pathway • enzyme1 enzyme2 enzyme3 enzyme4 • A ---------> B ---------> C ---------> D ---------> E

  4. How Enzymes Work • Each reaction requires a specific enzyme • Enzymes must be made of something that can take many different shapes • Proteins • There is a small part of the enzyme that contacts the substrate called the active site • Like a small cleft or indent on the surface • Substrate fits into active site and interacts with exposed amino acids by ionic or hydrogen bonding • Forms enzyme-substrate complex • Reaction then occurs

  5. How Enzymes Work • This is known as the lock and key model • Specific substrate fits specific enzyme

  6. How Enzymes Work • Induced fit model is an alternate mechanism • Enzyme's active site does not fit the substrate until the substrate actually enters the enzyme • The enzyme is not active until this happens

  7. How Enzymes Work • Enzyme-catalysed reactions are reversible • Direction of reaction depends on concentrations • Enzymes don't effect the point of equilibrium • Enzymes only change the time to equilibrium • In cells this in not important because products become substrates for new reactions or used up • Reactions will always go forward

  8. Added Molecules • molecules or ions other than proteins may associate with an enzyme to aid in its function • cofactor • coenzyme • prosthetic group

  9. Energy Changes • During a chemical reaction bonds must be broken and new bonds are remade to form products • Breaking bonds required energy endergonic • Making bonds releases endergy exergonic • These energies are not equal • Reaction can create a net increase of energy • Reaction can require an external source of energy • Anabolic reactions build large complex molecules built up from smaller ones • These reactions are endergonic (requires energy)‏ • Protein synthesis • Photosynthesis uses light energy

  10. Energy Changes Catabolic reactions break down large complex molecules into smaller, simpler ones These reactions are exergonic (releases energy)‏ Respiration releases chemical energy All reactions begin by breaking bonds which requires an activation energy to start Enzymes work by lowering the activation energy This is done by the enzyme-substrate complex This complex has lower activation energy Makes the reaction proceed quicker and easier Without enzyme activation is too high to occur

  11. Energy Changes

  12. Enzyme Activity Factors The activity of an enzyme is a measure of how well it catalyses its reaction Temperature Increase temperature --> Increase kinetic energy More collisions between substrate and enzyme More successful conversions Moving higher than optimum temp reduces activity Enzyme is made of protein High temperatures can denature the enzyme Tertiary structure is changed 3D structure of enzyme changes too much for substrate to fit Most enzymes in the human body have an optimum temperature around 40 C

  13. Temperature

  14. Enzyme Activity Factors pH A change of pH means a change in H+ ions in surrounding Affects the bonding of R-groups Affects the shape of the enzyme Most human enzymes have optimum at 7 (neutral)‏ Stomach enzymes (pepsin) have optimum at 2 Liver enzymes arginase has optimum at 10

  15. pH

  16. Enzyme Activity Factors Enzyme concentration Enzymes are not used up during reactions Can work effectively at low concentrations Usually substrate molecules are in excess Reaction rate is limited by enzyme concentration Increased concentration --> increased reaction rate

  17. Enzyme Concentration

  18. Enzyme Activity Factors Substrate concentration If substrate concentration is low some enzyme sites empty Rate of reaction will be lower If substrate conc. is then increased --> rate increases This increase continues until substrate is in excess Reaction rate approaches maximum called Vmax Enzyme active sites are saturated with substrate

  19. Substrate Concentration

  20. Enzymes- quiz (open book) • 1.What is an enzyme?- identify 4 properties (4 marks) • 2. Name the two different theories that attempt to explain how enzymes work (2 marks) • 3. Describe how each theory above works (4 marks) • 4. What do enzymes do to help a chemical reactions- think energy. (2 marks) • 5. Name 4 factors that can effect enzyme effectiveness (4 marks) • 6. Choose two and explain how these factors effect enzymes. Include a rough graph to support your answer (4 marks) • 7. What word do you use to describe an enzyme that has changed shape and no longer functions (1 mark).

  21. Co-factors & Co-enzymes • Enzymes often need “helpers”.  • Sometimes ions or metal atoms are used. These helpers are called cofactors (e.g. iron in haemoglobin, calcium in nerve signalling, nickel in urease etc.) • Small molecule helpers are called coenzymes. • Coenzymes that we can't build ourselves, that we need to get from our food in their working form, are called vitamins.  (e.g. vitamin B in respiration, vitamin C for turning genes “on”)

  22. Co-factors & Co-enzymes

  23. Inhibitors Inhibitors are chemicals which reduce the rate of enzyme catalyzed reactions Alter the shape of the active site directly or indirectly Non-reversible bind permanently disabling enzyme Permanent change of tertiary structure (break disulfide bond)‏ Always non-competitive Reversible inhibitors bind temporarily to enzyme Competitive inhibitors Similar shape to substrate and fit into active site Prevents substrate from entering enzyme Non-competitive inhibitors Bind to other parts of the enzyme altering shape of enzyme Active site no longer fits substrate

  24. Inhibitors

  25. Examples • Heavy metals (such as Pb, Hg, Ag and Cu). • These are non-competitive inhibitors and bid to the enzyme altering the shape. This is non-verseable • Reversible competitive inhibitors: • Antiviral drugs used to treat HIV bind to the enzymes which start DNA replications. • This stops the virus from reproducing