Unit 2 - biological molecules

These cards cover every learning objective of the second module on the biology AS specification. They were made to help me revise so they are in a format which makes sense to me, but I hope they can help other people too!  

What are the 2 general uses for biological molecule?
Broken down into smaller molecules then rebuilt to form new parts of an organism, and used to provide energy for metabolic reactions.
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Name the 6 biological molecules needed for life?
Carbohydrates, proteins, lipids, vitamins and minerals, nucleic acids and water.
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What are the functions of carbohydrates in the body?
Energy storage and supply, and sometimes structure.
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What are the functions of proteins in the body?
Structure, transport, enzymes, antibodies and most hormones.
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What are the functions of lipids in the body?
Membranes, energy supply, thermal insulation, protective layers/padding, electrical insulation in neurones and some hormones.
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Whats are the functions of vitamins and minerals in the body?
Form parts of lager molecules, take part in metabolic reactions and act as coenzymes.
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What are the functions of nucleic acids in the body?
Information molecules.
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What are the functions of water in the body?
Take part in reactions, support in plants, solvent and medium for metabolic reactions and transport.
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Define metabolism?
Is the sum total of all the biochemical reactions taking place in the cells of an organism.
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What are anabolic reactions?
Reactions that involve building smaller molecules into larger ones, e.g. muscle growth.
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What are catabolic reactions?
Reactions that involve breaking larger molecules into smaller ones, e.g. digestion.
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What are the 4 elements found in biological molecules?
Carbon, hydrogen, oxygen and nitrogen.
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What percentage of a cell is water?
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What makes up the remaining 30% of a cell?
DNA, phospholipids, polysaccarides, ions, RNA and proteins.
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What are the monomers and polymers of carbohydrates?
Monosaccharides, and polysaccharides
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What are the monomers and polymers of proteins?
Amino acids, and polypeptides and proteins.
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What are the monomers and polymers of Nucleic acids?
Nucleotides, and DNA and RNA.
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Why are molecules made from carbon atoms stable?
Because each atom in the molecule is sharing in the electrons to give a stable, full outer energy level.
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What takes place a condensation reaction?
A water molecule is released, a new covalent bond is formed and a new larger molecule is formed.
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What takes place in a hydrolysis reaction?
A water molecule is used, a covalent bond is broken and smaller molecules are formed.
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What is the difference between the structure of alpha-glucose and beta-glucose?
In alpha-glucose, the OH at C1 is below the plane of the ring, in beta-glucose, the OH at C1 is above the plane of the carbon ring.
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Properties of carbohydrates?
Soluble in water, sweet tasting and form crystals.
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The name of carbohydrates?
They are named after the number of carbon atoms, e.g. tri, pent or hex, and then add 'so' on the end.
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General formula for carbohydrates?
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The bonds that carbohydrates make when they join in a condensation reaction?
1-4 glycosidic bonds.
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When forming branches, what type of bonds form?
1-6 glycosidic bonds.
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How is a glycosidic bond formed?
The two hydroxyl groups at C1 and C4 line up along side each other, one combines with a H atom to form water and the other forms an oxygen bridge between the two molecules.
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Why do alpha-glucose chains form a coil shape?
The alpha-glucose molecules form long chains, bonded with 1-4 glycosidic bonds, resulting in a long and straight structure. It is long enough to coil
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Why do beta-glucose gains form straight chains?
When beta-glucose molecules join in a condensation reaction, one of the molecules rotates 180 degrees, resulting in a straight chain.
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Equation for respiration?
Glucose + oxygen ----> carbon dioxide + water + energy used to form of ATP.
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Why can't animals and plants respire beta-glucose?
Because they have enzymes that break down alpha-glucose only. The two forms of glucose are different shapes, and therefore the enzymes cannot act on both.
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Two alpha-glucose molecules bonded together forms what?
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What does many maltose bonded together form?
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How does the test for starch with iodine work?
Amylose coils into a spring shape, the iodine molecules get trapped in the coils and causes the colour of the iodine to change from yellow/brown to blue/black.
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What is the energy storage polysaccharide in plants?
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What is the structure of starch?
Mixture of long straight-chained amylose and branched amylopectin.
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What is the functions of starch?
Stored in chloroplasts and elsewhere in membrane bound starch grains, can be broken down into glucose molecules which can be used for respiration.
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What is the energy storage polysaccharide in animals?
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What is the structure of glycogen?
Mixture of alpha-glucose subunits, but the 1-4 glucose chains are shorter and have more branches extending from them.
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What is the function of glycogen?
More compact than starch, from glycogen granules in liver and muscle cells and can be broken down into glucose which can be respired.
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Features of energy storage molecules?
Made by bonding 1000s of alpha-glucose, do not dissolve so don't affect the water potential of the cell, they hold glucose molecules in chains that can be easily broken off from the ends.
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Similarities of amylose and cellulose?
Both contain molecules bonded together by condensation reactions, insoluble in water and contain the elements carbon, hydrogen and oxygen.
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Differences of amylose and cellulose?
Amylose is made of alpha-glucose and cellulose is beta-glucose. Amylose forms compact coils, cellulose form long straight chains. Amylose is an energy storage molecule, cellulose is structural. Amylose found in plants & animals, cellulose in plants.
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How are cellulose fibres arranged?
Because glucose monomers contain OH groups hydrogen bonds form between them. 60-70 cellulose molecules become cross linked by H bonds to form microfibrils. These are then linked by H bonds to form macrofibrils.
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How does the arrangement of cellulose fibres help its function in plant walls?
Gives great strength, allows water to move through and along cell walls, cell does not burst if water moves in, keeps cell turgid, determine how a cell grows or changes shape and can be reinforced to make waterproof.
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The 3 parts of an amino acid are?
The amino group (N and 2H), the R group (central C) and acid group (C=O and OH group).
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Sources of essential amino acids?
Meat and soya.
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The bonds that form when two amino acids join together in a condensation reaction?
Peptide bonds.
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When two amino acids join they form what type of molecule?
A dipeptide.
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When many amino acids join together what type of molecules do they form?
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Define primary structure of a protein?
Is given by the specific sequence of amino acids that make up the protein.
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Define secondary structure of a protein?
The coiling and pleating of parts of the polypeptide molecule to form an alpha helix or beta pleated sheet. Hydrogen bonds hold the coils in place, and give stability to the molecule.
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Define tertiary structure of a protein?
The overall 3D structure of the final polypeptide or protein molecule. It is held in place by a number of different types of bonds, including disulphide, hydrogen and ionic bonds.
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Explain disulphide bonds in proteins?
They form between R-groups containing -SH groups. The amino acid cystine contains sulfur, so two cysteines close to each other will form disulphide bonds.
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Explain ionic bonds in proteins?
They form between two ionised R-groups. R groups sometimes carry charge, either +ve or -ve. When oppositely charged amino acids are close to each other they form ionic bonds.
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Explain hydrogen bonds in proteins?
They form wherever there are slightly positively charged atoms next to slightly negatively charge atoms.
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Explain hydrophilic and hydrophobic interactions in proteins?
They form between amino acids with hydrophilic side chains and amino acids with hydrophobic side chains.
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How does heat effect the structure of a protein?
It increases the kinetic energy in the molecule, causing the molecule to vibrate. This breaks some of the bonds holding the tertiary structure in place as they are weak. The tertiary structure will unravel and the protein will be denatured.
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Differences between globular and fibrous proteins?
Globular roll up to form balls, are usually soluble (hydrophilic R groups are on outside) and have roles in metabolic reactions. Fibrous proteins form fibres, insoluble and have structural roles.
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Define quaternary structure?
Protein structure where a protein consists of more than one polypeptide chain. Haemoglobin and insulin both have quaternary structures.
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Structure of haemoglobin?
Consists of four polypeptide subunits. Two are alpha-chains and two are beta-chains. These give it a specific shape so it can carry out a specific function.
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How is haemoglobin's structure specialised?
Each polypeptide contains a haem group (Fe2+) which the oxygen can bind to.
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Describe the structure of a collagen molecule?
Made up of three polypeptide chains, wound around each other. Each of the three chains are coils made of of around 1000 amino acids. Hydrogen bonds form between chains.
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Where is collagen used in the body?
Provides strength in walls of arteries, forms strong connections in tendons, bones, cartilage and connective tissue and cosmetic procedures.
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Differences between haemoglobin and collagen?
Haemoglobin is a globular protein, soluble in water, wide rage of amino acid constituents, contains a prosthetic group and wound into alpha helix structures. Collagen is a fibrous protein, insoluble in water, 35% same constituents, no prosthe
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Define lipids?
A diverse group of chemicals that dissolve in organic solvents, such as alcohol, but not water. They include fatty acids, triglycerides and cholesterol.
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What is a triglyceride made up of?
One glycerol and three fatty acids.
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What type of bonds form in the condensation of fatty acids and the OH group of a glyceride?
Ester bond.
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Why do triglycerides and water not mix?
The charges on the triglyceride molecule are evenly distributed around the molecule. This means hydrogen bonds cannot form with the water molecules, so they do not mix.
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How is a triglyceride similar to a phospholipid?
Both contain fatty acids and glyceride.
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How is a triglyceride different to a phospholipid?
Triglyceride contains three fatty acids and a glycerol, phospholipids contain two fatty acids, a phosphate group and a glycerol. Triglycerides are insoluble and a compact energy store. Phospholipids are part hydrophilic, used in cell membranes.
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Structure of cholesterol?
Made of four carbon based rings. Small, narrow and hydrophobic molecule.
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How do cholesterols properties help its function?
Allow it to sit between the phospholipid hydrocarbon tails and regulate the fluidity and strength of the membrane. Steroid hormones are made from cholesterol and means they can pass through phospholipid bilayer to reach target receptor.
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Define hydrogen bond?
Is a weak interaction that can occur wherever molecules contain a slightly negatively charges atom bonded to a slightly positively charged hydrogen. Water molecules hydrogen bond with each other extensively.
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List the seven properties of water?
It's a solvent, liquid, cohesion, it freezes, thermal stability and metabolic.
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How is water being a solvent of use in the natural world?
Metabolic processes rely on chemicals being able to react in solution.
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How is water being a liquid of use in the natural world?
It is used in the movement of materials around organisms.
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How is water having cohesion of use in the natural world?
Creates surface tension, makes long thin water columns that are difficult to break.
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How is water freezing of use in the natural world?
Forms ice on the surface of lakes, insulates water below.
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How is water having thermal stability of use in the real world?
Large water bodies have stable temperature providing a stable environment. Evaporation can also cool surfaces.
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What is the test for starch?
Add a few drops of iodine and if starch is present it will turn from yellow/brown to blue/black.
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What is the test for a reducing sugar?
Add Benedict's solution and heat to 80 degrees in a water bath. It will turn from blue to orange-red.
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What is the test for a non-reducing sugar?
If reducing sugar test is negative, boil with HCl, cool and neutralise with sodium hydrogen carbonate solution, then repeat Benedict's test. Blue to orange-red on second test.
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What is the test for a protein?
Add biuret reagent. It will turn blue to lilac.
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What is the test for a lipid?
Add ethanol to dissolve lipid, and pour alcohol into water in another test tube. A white emulsion will form near the top.
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What is DNA?
A polynucleotide, usually double stranded, made up of the bases adenine, thymine, cytosine and guanine.
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What is RNA?
A polynucleotide, usually dingle stranded, made up of nucleotides containing the bases adenine, uracil, cytosine and guanine.
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What are the three parts of a nucleotide?
A phosphate, a sugar (deoxyribose in DNA, ribose in RNA) and an organic base.
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Organic bases are purines or pyrimidines, what are the differences?
Purines are larger, pyrimidines are smaller.
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Which of the organic bases are purines?
Adenine and guanine.
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Which of the organic bases are pyrimidines?
Thymine, uracil and cytosine.
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How are the double helix DNA strands held together?
By hydrogen bonds between
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Why is DNA a double helix?
A pyrimidine will pair with a purine. Base-pairing rules apply, AT and CG. The sugars point inwards with the phosphate groups forming a backbone on the outside. The antiparallel chains twist, forming a double helix.
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How does DNA copy itself?
The double helix untwists, hydrogen bonds brake, unzips the DNA, free DNA nucleotides are hydrogen bonded to exposed bases according to base pair rules. Covalent bonds are then formed between the phosphate group and the sugar of the next nucleotide.
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Define gene?
A length of DNA that codes for one (or more) polypeptide. Each gene occupies a specific place on a chromosome. Different versions of the same gene are called alleles.
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Role of RNA?
Messenger RNA, copy of the other DNA strand, ribosomal RNA, found in ribosomes and transfer RNA, carries amino acids to the ribosomes.
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Role of DNA?
(needs to be completed)
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In what ways are all enzymes similar?
They are all globular proteins, they act as catalysts, they are specific, contain inactive site and their activity is affected by temperature and pH.
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Define enzyme?
Enzymes are biological catalysts.
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Define catalyst?
A molecule that speeds up a reaction by providing an alternative pathway with a lower activation energy. It is not used up in the reaction, and at the end of the reaction, remains unchanged.
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To function properly and enzyme needs to be at?
It's optimum temperature and pH.
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During digestion which bonds are broken?
Glycosidic (carbohydrates), peptide (proteins) and ester bonds (lipids).
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Explain extracellular?
Enzymes catalyse reactions outside the cell.
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Explain intracellular?
Enzymes catalyse reactions inside the cell.
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Give an example of when enzymes are used as a defence mechanism?
In phagocytic white blood cell, the pathogen is digested.
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What are the organelles called in our cells that produce enzymes?
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Define activation energy?
The amount of energy needed to start a reaction by the breaking of bonds.
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What effect do enzymes have on activation energy?
They reduce the activation energy.
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What term is used to describe the method by which enzymes fit certain molecules?
The lock-and-key model.
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What are the basic principle of the lock-and-key method?
An enzyme has a specifically shaped active site, it is complementary to the substrate involved. The substrate fits into the active site and held in place so the reaction can go ahead.
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What are the basic principle of the induced-fit hypothesis?
When the substrate and active site collide, the enzyme changes shape slightly. This makes the active site fit more closely around the substrate. Produces a strain on the substrate, destabilising the substrate. Reaction occurs more easily.
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What is the optimum temperature of a human enzyme?
37 degrees.
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What is the effect of increasing temperature on enzyme activity?
Molecules have kinetic energy, increasing heat increases the kinetic energy. Molecules move around more quickly, making the chances of molecules colliding more likely. They are also moving with greater speed so they collide with greater force.
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What effect does temperature have on the rate of reaction of an enzyme?
Molecules have more kinetic energy so there are more random collisions between enzymes and substrate, meaning the rate increases and more product is formed.
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Define denaturation?
Changes the tertiary structure of an enzyme such that it cannot function and its function cannot be restored.
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What happens if too much heat is applied?
The molecule vibrate and place a strain on the bonds holding the molecules together. It breaks weaker bonds, like H bonds. These hold the tertiary structure in place, so when they break the tertiary structure unravels and the enzymes is denatured.
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What is the common range for optimum temperature in enzymes?
40 - 50 degrees.
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What is pH?
The measure of H+ ions concentration.
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How does pH affect enzyme activity?
H ions have a + charge so will be attracted towards - charged ions, or parts of molecules. H and ionic bonds hold the active site in shape. H+ ions interfere with the H bonds and ionic bonds, active site changes shape, substate no longer fits.
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Where would the optimum pH for an enzyme be higher than usual?
In the stomach because it contains HCl, e.g. pepsin has an optimum pH of 2.
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What is the effect of an increase of substrate on enzyme activity?
Collisions occur more often, more enzyme-substrate complexes form, so more product formed.
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What is the effect of an increase of enzyme on enzyme activity?
More active sites available, more enzyme-substrate complexes form, so more product is formed.
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Define enzyme inhibitor?
Any substance or molecule that slows down the rate of an enzymes controlled reaction by affecting the enzyme molecule in some way.
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What are the three types of inhibitor?
Competitive, non-competitive and permanent inhibitors.
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How do competitive inhibitors work?
The inhibitor has a similar shape to the substrate. They occupy the active site, forming enzyme-inhibitor complexes. This means the real substrate cannot enter, so the number of enzyme-substrate complexes is reduced.
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How do non-competitive inhibitor work?
They do not compete with a substrate for the active site, they attach to the enzyme in a region away form the active site. Distorts tertiary structure of the enzyme, leading to change in shape of active site. Enzyme-substrate complexes cannot form.
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How do permanent inhibitor work?
They bind permanently to the enzyme. Most competitive inhibitors are non-permanent, but non-competitive inhibitors are permanent.
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Define cofactor?
Any substance that must be present to ensure enzyme controlled reactions take place at the appropriate rate.
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Define coenzyme?
An inorganic non-protein molecule that binds temporarily with substrate to an enzyme active site. It is essential for enzyme activity.
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How do enzyme inhibitors sometimes act as poisons?
They can inhibit process vital to life, like respiration or digestion.
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An example of an inhibitor poison?
Potassium cyanide inhibits cell respiration. Acts on enzyme called cytochrome ozidase, reducing oxygen use, meaning less ATM is produced.
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How do enzyme inhibitors act as medical drugs?
They inhibit certain processes which could have harmful or unwanted effects.
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An example of an inhibitor medicinal drug?
In the treatment of HIV chemicals are used that act on protease inhibitors, preventing viruses from replicating.
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Other cards in this set

Card 2


Name the 6 biological molecules needed for life?


Carbohydrates, proteins, lipids, vitamins and minerals, nucleic acids and water.

Card 3


What are the functions of carbohydrates in the body?


Preview of the front of card 3

Card 4


What are the functions of proteins in the body?


Preview of the front of card 4

Card 5


What are the functions of lipids in the body?


Preview of the front of card 5
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