OCR f212 enzymes

notes about enzymes in line with the specification

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  • Created by: sophie
  • Created on: 13-12-11 18:04

Basics

Enzymes are globular proteins

They have a specific tertiary structure

They catalyse metabolic reaction (by lowering the actiation energy)

Enzyme action can be intracellular (withn cells) or extracellular (between cells)

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Key features of enzymes

Specificity: Enzymes catclyse only a few reactions due to the precise tertiary shape so only certain substrates fit into the active site

Active site: Cleft where substrate binds and reaction takes place.Complimentary to substrate

Lock and Key hypothesis: Proposed by Fischer. Only a single substrate fits into an active site

Induced fit hypothesis: Proposed by Koshland. Active site moulds to substrate as it enters. Bonds form between substrate and R-group to induce a better fit

Eenzyme Substrate/Product complex: In catabolic reaction, strains increase likelihood of breakage. In anabolic reaction, substrates are brought closer together. The enzyme is released unchanged

Lowering of activation energy: Enzymes increase likelyhood of reaction by lowering activation energy so more substrates can react that wouldnt have before

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Factors affecting enzyme activity

pH

Enzymes have an optimum pH. Lower pH's lower the rate of reaction, slowing it. A higher pH affects the ability to form hydrogen and ionic bonds so change the 3D shape of the protein. Extreme pH change denatures enzymes so activity stops.

Temperature

Increasing temperature inccreases the KE of molecules, meaning they collide with the enzyme more frequently and forcefully. A tohigh temperature vibrates the enzyme, putting strain on and breaking weaker H and ionic bonds. This affects the tertiary structure and active sit, reducing enzyme activity

Substrate concentration

Higher change of substrate colliding with enzyme. Above a certain concentration, all active sites are occupied so rate levels off

Enzyme concentration

Increasing concentration increases rate - higher chance of substrate entering active site

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Investigating the effect of factors

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Inhibitors

Competative

similar shape to substrate to fits into active site

prevents substrate from entering active site

reversible: enters then leaves site, not strongly bound

Non-competative

Doesnt bind to the active site

changes the 3D shape and distorts the active site so the substrate no longer fits

reversible: inhibitor leaves the enzyme and functions normally. irriversable: inhibitor firmly bound in the enzyme so enzyme is denatured

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Cofactors + Coenzymes

Cofactor

Ions/non-protein molecules asocciated with enzymes to make them work properly

Include inorganic ions, prosthetic groups and coenzymes

Prosthetic Group

These cofactors are tightly bound to the enzyme and form a permenant part of it

Coenzyme

Organic cofactors that are loosely associated with enzymes

Transfer chemical groups, atoms or electrons from one molecule to another

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Metabolic Poisons

Metabolic poisosns may be enzyme inhibitors

Cyanide

Attaches strongly to copper containing prosthetic group of cytochrome c oxydase, which stops respiration

Without an antidote, unconsciousmess, come and death

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Medicinal Drugs

Some medicinal drugs work by inhibiting enzyme action

Penicillin

Binds to active site of enzyme that links molecules in bacterial cell wall. The cell bursts and absorbs water

Ethanol

If antifreeze is ingested, it is converted to toxic acids. Alcohol competes with the anti-freeze for enzymes active site.

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Comments

Chloe Thorn

methanol ( alcohol you shouldn't drink we drink ethanol) posining is also treated with ethanol  - just a random fact :)

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