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AS Biology Biological molecules. OBJECTIVES All should : be able to describe the structure of a water molecule,the H bonds that hold them together & and.

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Presentation on theme: "AS Biology Biological molecules. OBJECTIVES All should : be able to describe the structure of a water molecule,the H bonds that hold them together & and."— Presentation transcript:

1 AS Biology Biological molecules

2 OBJECTIVES All should : be able to describe the structure of a water molecule,the H bonds that hold them together & and understand this is responsible for its unusual properties. Be able to describe some of the properties of water and link some to its structure and importance to living organisms All should : be able to describe the structure of a water molecule,the H bonds that hold them together & and understand this is responsible for its unusual properties. Be able to describe some of the properties of water and link some to its structure and importance to living organisms Some may: be able to take this a stage further and give detailed explanations of how the H bonds in water control the properties that are so important for living organisms Some may: be able to take this a stage further and give detailed explanations of how the H bonds in water control the properties that are so important for living organisms

3 Unit 2 Module 1 Biological molecules l

4 Proteins enzymes structural proteins lipids transport protein phospholipids triglycerides cholesterol carbohydrates saccharides polysaccharides structural storage water nucleic acids DNA RNA

5

6 The Elements of life 92 naturally occurring elements 92 naturally occurring elements The atoms of only 16 are commonly found in living organisms The atoms of only 16 are commonly found in living organisms 4 account for 99% of the atoms found in living organisms,these are in order of abundance: 4 account for 99% of the atoms found in living organisms,these are in order of abundance: H hydrogen H hydrogen C carbon C carbon O oxygen O oxygen N nitrogen N nitrogen This is because living organisms are made up of organic molecules This is because living organisms are made up of organic molecules Others are calcium(Ca),iron(Fe),potassium(K),sodium(Na), chlorine(Cl),sulphur(S) & magnesium(Mg) Others are calcium(Ca),iron(Fe),potassium(K),sodium(Na), chlorine(Cl),sulphur(S) & magnesium(Mg)

7 Bonding Atoms are joined together to make molecules and compounds Atoms are joined together to make molecules and compounds This is done by chemical bonds This is done by chemical bonds Most of the molecules making up living organisms have atoms joined by covalent bonds Most of the molecules making up living organisms have atoms joined by covalent bonds Covalent bonds are shown by lines.They can be single,double or treble.They are formed by sharing electrons Covalent bonds are shown by lines.They can be single,double or treble.They are formed by sharing electrons Glycine – an amino acid

8 Covalent bonding Carbon always has 4 covalent bonds with other atoms. Terrestrial life forms are carbon based. This multiple bonding allows carbon to be a framework atom Carbon always has 4 covalent bonds with other atoms. Terrestrial life forms are carbon based. This multiple bonding allows carbon to be a framework atom All the biological molecules we will learn about use carbon as a framework atom. All the biological molecules we will learn about use carbon as a framework atom. Other bonds formed are: Oxygen 2,hydrogen 1 & nitrogen 3 Other bonds formed are: Oxygen 2,hydrogen 1 & nitrogen 3 ethanol ethene

9 Covalent bonding

10 The building blocks of life Living organisms are mainly made up of macromolecules (giant molecules) Living organisms are mainly made up of macromolecules (giant molecules) These are polymers made up of many smaller monomers by a process called polymerisation These are polymers made up of many smaller monomers by a process called polymerisation The main macromolecules are: The main macromolecules are: Polysaccharides Polysaccharides Nucleic acids Nucleic acids Proteins (polypeptides) Proteins (polypeptides) Lipids (fats) Lipids (fats)

11 The Building Blocks of life MONOMER POLYMER MONOMER POLYMER monosaccharide Organic base, sugar & phosphate Amino acids Fatty acids & glycerol polysaccharide Nucleic acids proteins lipids nucleotides

12 Carbohydrates All contain the elements carbon, hydrogen & oxygen All contain the elements carbon, hydrogen & oxygen The name comes from hydrated carbon! The name comes from hydrated carbon! For every carbon atom there is a water For every carbon atom there is a water General formula for carbohydrate is General formula for carbohydrate is C n (H 2 O) n C n (H 2 O) n Q. Fructose has 6 carbons, what is it formula? What about ribose which is a pentose sugar? Q. Fructose has 6 carbons, what is it formula? What about ribose which is a pentose sugar? There are 2 types of carbohydrate: There are 2 types of carbohydrate: 1. Simple sugars: Monosaccharide & Disaccharides 1. Simple sugars: Monosaccharide & Disaccharides 2. Polysaccharides 2. Polysaccharides

13 Simple sugars: Monosaccharides Sugars – all end in -ose Sugars – all end in -ose White,crystalline substances,dissolve easily in water to give sweet solutions. White,crystalline substances,dissolve easily in water to give sweet solutions. Single sugar molecule – mono = one Single sugar molecule – mono = one General formula (C H 2 O)n where n is the number of carbon atoms General formula (C H 2 O)n where n is the number of carbon atoms So if 6 carbon atoms(a hexose sugar) the molecular formula is C 6 H 12 O 6 So if 6 carbon atoms(a hexose sugar) the molecular formula is C 6 H 12 O 6 What about pentose sugars(C5) or triose sugars(C3)? What about pentose sugars(C5) or triose sugars(C3)?

14 Glucose Most important and widespread monosaccharide. Most important and widespread monosaccharide. Hexose sugar Hexose sugar The 6 carbons are numbered The 6 carbons are numbered Function:Transported around in the blood and used in cells as a source of energy in respiration. The energy is released in the form of ATP Function:Transported around in the blood and used in cells as a source of energy in respiration. The energy is released in the form of ATP Structural formula Molecular formula C 6 H 12 O

15 The ring form of glucose The chain of carbons in hexose(and pentose) sugars is long enough to close up and form a more stable ring structure The chain of carbons in hexose(and pentose) sugars is long enough to close up and form a more stable ring structure Carbon atom 1 joins to the oxygen on carbon atom 5 Carbon atom 1 joins to the oxygen on carbon atom 5

16 Glucose isomers The new OH formed in the reaction can be above the ring - β glucose or below - α glucose The new OH formed in the reaction can be above the ring - β glucose or below - α glucose These are isomers-two forms of the same chemical. These are isomers-two forms of the same chemical.

17 Triose,pentose & hexose sugars

18 Roles of monosaccharides in living organisms A source of energy for respiration. A source of energy for respiration. Due to large number of C-H bonds which when broken release a lot of energy Due to large number of C-H bonds which when broken release a lot of energy This energy is used to make ATP(adenine triphosphate) from ADP(adenine diphosphate) This energy is used to make ATP(adenine triphosphate) from ADP(adenine diphosphate) Also used as building blocks to make larger molecules for example: Also used as building blocks to make larger molecules for example: Deoxyribose(pentose) used to make DNA Deoxyribose(pentose) used to make DNA Ribose used to make RNA and ATP Ribose used to make RNA and ATP Glucose makes up starch,cellulose and glycogen. Glucose makes up starch,cellulose and glycogen.

19 Disaccharide formation Two glucose molecules are held close together by an enzyme. Two glucose molecules are held close together by an enzyme. Water is lost and a 1-4 glycosidic bond(link) formed. Water is lost and a 1-4 glycosidic bond(link) formed. This is a condensation reaction This is a condensation reaction The new molecule is a disaccharide - maltose The new molecule is a disaccharide - maltose

20 A disaccharide - maltose 1-4 glycosidic link

21 Common Disaccharides

22 Hydrolysis of maltose – by enzyme maltase

23 Chemical test for saccharides(sugars) Reducing Sugars Reducing Sugars Heat the sugar solution with an equal volume of blue benedict's solution for 2-3 minutes at about 90°C Heat the sugar solution with an equal volume of blue benedict's solution for 2-3 minutes at about 90°C A positive result is a brick red precipitate A positive result is a brick red precipitate Benedicts solution contains blue Cu 2 + ions, the sugar reduces this to the insoluble brick red Cu+ compound Benedicts solution contains blue Cu 2 + ions, the sugar reduces this to the insoluble brick red Cu+ compound Cu 2 + Cu+ Cu 2 + Cu+ Electron From sugar

24 Non reducing sugar test Some sugars are non reducing. Some sugars are non reducing. They do not reduce benedict's solution They do not reduce benedict's solution One example is sucrose, it must be hydrolysed(broken-down by adding water) to form glucose and fructose One example is sucrose, it must be hydrolysed(broken-down by adding water) to form glucose and fructose This can be done by heating with a few drops of acid at 90°C for a few minutes. Then neutralising the solution with an equal amount of sodium hydroxide solution This can be done by heating with a few drops of acid at 90°C for a few minutes. Then neutralising the solution with an equal amount of sodium hydroxide solution You will then get a positive result when repeating the benedict's test You will then get a positive result when repeating the benedict's test

25 Sugar Type of saccharide? Result of benedicts test for reducing sugar Result of non- reducing sugar test Reducing or non-reducing sugar? Reducing or non-reducing sugar? lactose fructose glucose sucrose maltose

26 Quantitative Estimation of glucose concentration in a solution Glucose solution(%) Weight of precipitate (g) Light Transmission of filtrate (%)

27 Sugars homework a. Glyceraldehyde – C3 Triose Ribose C5 Pentose Ribose C5 Pentose Glucose & Fructose C6 Hexose Glucose & Fructose C6 Hexose b. Glucose is an aldose sugar H-C=O is on C 1 c.

28 d

29 e alpha glucose OH below the ring e alpha glucose OH below the ring beta glucose OH above ring beta glucose OH above ring f alpha galactose f alpha galactose

30 Polysaccharide- Structure & Function Polysaccharides are polymers made up of monosaccharide subunits Polysaccharides are polymers made up of monosaccharide subunits The polymers can be many thousand monosaccharides – making macromolecules The polymers can be many thousand monosaccharides – making macromolecules Most important are starch,glycogen & cellulose Most important are starch,glycogen & cellulose All are polymers of glucose All are polymers of glucose They are insoluble in water and do not taste sweet. They are insoluble in water and do not taste sweet.

31 Starch Made up of a mixture of two macromolecules Made up of a mixture of two macromolecules Amylose (20%) and amylopectin (80%) Amylose (20%) and amylopectin (80%)

32 Amylose Amylose is formed by condensation of a long chain of α glucose using 1α – 4 glycosidic bonds Amylose is formed by condensation of a long chain of α glucose using 1α – 4 glycosidic bonds

33 Amylose α helix The 1α – 4 glycosidic links in amylose mean the glucose monomers are at a slight angle to each other The 1α – 4 glycosidic links in amylose mean the glucose monomers are at a slight angle to each other This causes a helix to form This causes a helix to form This is stabilised by hydrogen bonds This is stabilised by hydrogen bonds

34 Amylopectin Branching chains of α glucose Branching chains of α glucose Branches about once every 25 glucose Branches about once every 25 glucose Branches formed by 1-6 glycosidic bonds Branches formed by 1-6 glycosidic bonds The branching structure gives many ends to attach new glucose or to remove it. So it is ideal for storing glucose The branching structure gives many ends to attach new glucose or to remove it. So it is ideal for storing glucose

35 Starch – Role in living organisms Starch is a store of glucose in plants Starch is a store of glucose in plants Plants cannot store sugars as this would increase the osmotic potential (low water potential) of the cells,the solution inside the cells would be too concentrated. Plants cannot store sugars as this would increase the osmotic potential (low water potential) of the cells,the solution inside the cells would be too concentrated. This would lead to …. This would lead to …. Starch is insoluble and has no osmotic effect Starch is insoluble and has no osmotic effect

36 Starch Grains In plants starch is stored as starch grains In plants starch is stored as starch grains These are most often found in chloroplasts or in specialised plant structures such as seeds or tubers eg potatoes These are most often found in chloroplasts or in specialised plant structures such as seeds or tubers eg potatoes The helical shape of amylose means it can be packed tightly The helical shape of amylose means it can be packed tightly

37 Chemical test for Starch Add iodine solution to the material Add iodine solution to the material Iodine solution is orange brown Iodine solution is orange brown A blue black colour is produced on contact with starch A blue black colour is produced on contact with starch This is because the iodine molecules fit into the amylose helix giving the colour This is because the iodine molecules fit into the amylose helix giving the colour

38 Glycogen Starch is not found in animal cells Starch is not found in animal cells Glycogen is used to store glucose in animal cells Glycogen is used to store glucose in animal cells It is very similar to amylopectin but more branched It is very similar to amylopectin but more branched It branches every 8-10 glucoses,again giving plenty of ends to add extra glucose It branches every 8-10 glucoses,again giving plenty of ends to add extra glucose It forms granules which can be seen in muscle & liver cells It forms granules which can be seen in muscle & liver cells

39 Cellulose Cellulose makes up plant cell walls Cellulose makes up plant cell walls It is a structural polysaccharide It is a structural polysaccharide It is made up of β glucose where OH is above the ring It is made up of β glucose where OH is above the ring In order to form a glycosidic bond the other glucose must be upside down. In order to form a glycosidic bond the other glucose must be upside down. The bond formed is a β1-4 glycosidic bond The bond formed is a β1-4 glycosidic bond

40 Cellulose cross links Cellulose cannot form a helix Cellulose cannot form a helix It exists in long chains It exists in long chains Chains lie side by side and hydrogen bonds form between them Chains lie side by side and hydrogen bonds form between them These form between adjacent glucose molecules and between the chains. These form between adjacent glucose molecules and between the chains.

41 This gives the cellulose molecule great mechanical strength This gives the cellulose molecule great mechanical strength They are insoluble,tough,durable and slightly elastic, ideal structural components They are insoluble,tough,durable and slightly elastic, ideal structural components chains are strongly linked together to form bundles called microfibrils chains are strongly linked together to form bundles called microfibrils Microfibrils are held together in fibres Microfibrils are held together in fibres Fibres make up the plant cell wall Fibres make up the plant cell wall

42 Structure of cellulose

43 Cellulose fibres are laid down in layers to form the cell wall Cellulose fibres are laid down in layers to form the cell wall Fibres are at right angles to increase strength Fibres are at right angles to increase strength Other molecules help cross linking Other molecules help cross linking Older cell walls are reinforced with lignin Older cell walls are reinforced with lignin A glue like matrix(pectins) is laid down in between the fibres to increase strength A glue like matrix(pectins) is laid down in between the fibres to increase strength Similar to reinforced concrete Similar to reinforced concrete

44 Cellulose – structure & function High tensile strength of cellulose fibres means they are difficult to break if pulled at both ends High tensile strength of cellulose fibres means they are difficult to break if pulled at both ends Allows the cell to withstand the pressure caused when water enters by osmosis. Allows the cell to withstand the pressure caused when water enters by osmosis. Gives plant cells strength and rigidity Gives plant cells strength and rigidity Provides support Provides support Despite strength they are freely permeable Despite strength they are freely permeable Even though cellulose contains glucose it cannot be digested by most animals as they do not have the required enzyme cellulase Even though cellulose contains glucose it cannot be digested by most animals as they do not have the required enzyme cellulase

45 Other structural polysaccharides Chitin Chitin Exoskletons of arthropods Exoskletons of arthropods Peptidoglycan Peptidoglycan Cell wall of bacterial cells Cell wall of bacterial cells

46

47

48 Lipids This group contains a wide range of molecules ranging from fats,oils,phospholipids,waxes & steroids This group contains a wide range of molecules ranging from fats,oils,phospholipids,waxes & steroids They all contain the elements C,H & O They all contain the elements C,H & O Normally much less O Normally much less O The most widespread are TRIGLYCERIDES also known as fats or oils The most widespread are TRIGLYCERIDES also known as fats or oils

49 Triglyceride structure Made up of 3 FATTY ACID molecules Made up of 3 FATTY ACID molecules And 1 GLYCEROL molecule And 1 GLYCEROL molecule

50 Fatty Acid structure Stearic acid an example of a saturated fatty acid. Stearic acid an example of a saturated fatty acid. All the carbon atoms in the tail are full,saturated with hydrogen All the carbon atoms in the tail are full,saturated with hydrogen Can also be written as CH 3 (CH 2 ) 16 COOH

51 The COOH group is called a CARBOXYLIC ACID group The COOH group is called a CARBOXYLIC ACID group The long tail of the molecule is called a HYDROCARBON TAIL The long tail of the molecule is called a HYDROCARBON TAIL This hydrocarbon chain will not dissolve in water it is said to be non-polar or hydrophobic(water hating) This hydrocarbon chain will not dissolve in water it is said to be non-polar or hydrophobic(water hating)

52 The carboxylic acid group is polar or hydrophilic(water loving) The carboxylic acid group is polar or hydrophilic(water loving)

53 Unsaturated Fatty Acids These fatty acids contain a double bond These fatty acids contain a double bond It causes a kink in the tail It causes a kink in the tail These fatty acids melt more easily These fatty acids melt more easily One double bond is monounsaturated One double bond is monounsaturated More than one are called polyunsaturated More than one are called polyunsaturated

54 Glycerol structure Glycerol is a type of alcohol with 3 alcohol groups. Glycerol is a type of alcohol with 3 alcohol groups.

55 Forming a triglyceride When glycerol combines with a fatty acid it forms a glyceride When glycerol combines with a fatty acid it forms a glyceride When it combines with 3 fatty acids it is a triglyceride When it combines with 3 fatty acids it is a triglyceride They combine in a condensation reaction, losing water They combine in a condensation reaction, losing water Forming an ester link Forming an ester link

56 Properties Triglycerides are insoluble in water, they are non-polar molecules Triglycerides are insoluble in water, they are non-polar molecules The more unsaturated fatty acids the lower the melting point making these oils at room temperature, normally found in plants The more unsaturated fatty acids the lower the melting point making these oils at room temperature, normally found in plants Animal fats have a higher melting point and are generally solid at room temperature due to saturated fatty acids Animal fats have a higher melting point and are generally solid at room temperature due to saturated fatty acids

57 Roles of triglycerides ENERGY RESERVES- high number of C-H bonds so much more energy content than carbohydrate-so you need to store less to get the same energy ENERGY RESERVES- high number of C-H bonds so much more energy content than carbohydrate-so you need to store less to get the same energy In humans stored around organs and under the skin In humans stored around organs and under the skin

58 Stored in adipose tissue Stored in adipose tissue

59 Under the skin it is also INSULATION eg blubber in sea mammals Under the skin it is also INSULATION eg blubber in sea mammals It can also produce metabolic water when used in respiration by desert animals such as camels It can also produce metabolic water when used in respiration by desert animals such as camels Insoluble: so no osmotic effect Insoluble: so no osmotic effect

60 Phospholipids In this molecule the glycerol has two fatty acids attached In this molecule the glycerol has two fatty acids attached On the 3 rd carbon is a phosphate group On the 3 rd carbon is a phosphate group

61 Phospholipid examples

62 Phospholipid properties and roles These molecules have a hydrophobic tail and hydrophilic head These molecules have a hydrophobic tail and hydrophilic head They form the membranes of living cells They form the membranes of living cells

63 Cholesterol Not formed from fatty acids and glycerol Not formed from fatty acids and glycerol 4 carbon based rings 4 carbon based rings Small hydrophobic molecule Small hydrophobic molecule Found between phospholipid tails in membranes Found between phospholipid tails in membranes Controls membrane fluidity and mechanical strength Controls membrane fluidity and mechanical strength

64 Excess cholesterol Many cells make cholesterol from saturated fats Many cells make cholesterol from saturated fats Especially liver cells Especially liver cells Excess can be deposited in artery walls Excess can be deposited in artery walls Causing atherosclerosis Causing atherosclerosis

65 Excess cholesterol is removed in bile Excess cholesterol is removed in bile It can form gallstones in the gall bladder It can form gallstones in the gall bladder

66 Steroid hormones These are made from cholesterol and include: These are made from cholesterol and include:

67 Chemical test for Lipids Emulsion test Emulsion test Add ethanol to the suspect material and mix well (any fat will dissolve in the alcohol) Add ethanol to the suspect material and mix well (any fat will dissolve in the alcohol) Filter off the ethanol Filter off the ethanol pour the ethanol into water pour the ethanol into water A milky emulsion will form if fat was present(fat can no longer dissolve and forms small droplets A milky emulsion will form if fat was present(fat can no longer dissolve and forms small droplets

68 Proteins(Polypeptides) Proteins make up more than 50% of the dry mass of cells Proteins make up more than 50% of the dry mass of cells They have many important functions They have many important functions All proteins are made up of amino acids All proteins are made up of amino acids Functions of proteins Functions of proteins

69 Proteins in living organisms globular fibrous enzymes transport membrane blood channel protein active transport complex glycoprotein contractile structural blood collagen elastin keratin Fibrinogen (fibrin) Actin/myosin (muscles) Respiration/ photosynthesis Albumin/ globulin antibodies hormones haemoglobin intracellular (metabolic) Extracellular (digestive)

70 Proteins in living organisms

71 Amino Acid Structure NH 2 is the a amine or amino group NH 2 is the a amine or amino group COOH is the carboxylic acid group COOH is the carboxylic acid group The R group or amino acid side chain varies. The R group or amino acid side chain varies. There are 20 different R groups found in nature so giving 20 different naturally occuring amino acids There are 20 different R groups found in nature so giving 20 different naturally occuring amino acids

72 The 20 naturally occurring amino acids R groups The 20 naturally occurring amino acids R groups

73

74 Amino Acids

75 The Peptide Bond Amino acids are joined together by a peptide bond Amino acids are joined together by a peptide bond Two amino acids joined form a dipeptide Two amino acids joined form a dipeptide

76 Peptide bond formation

77 Polypeptide formation Adding more amino acids to the chain forms a polypeptide Adding more amino acids to the chain forms a polypeptide In cells this occurs in ribosomes In cells this occurs in ribosomes A protein molecule may contain many hundred AAs and sometimes more than one polypeptide chain A protein molecule may contain many hundred AAs and sometimes more than one polypeptide chain

78 Protein – Primary structure The sequence of the amino acids in the polypeptide is known as its primary structure The sequence of the amino acids in the polypeptide is known as its primary structure A protein of several hundred amino acids has a huge number of possible primary structures A protein of several hundred amino acids has a huge number of possible primary structures A change in one of the AAs can completely alter the properties of the protein A change in one of the AAs can completely alter the properties of the protein

79 Protein- Secondary Structure This is when parts of the polypeptide chain becomes twisted or folded This is when parts of the polypeptide chain becomes twisted or folded There are 2 main types of 2° structure: There are 2 main types of 2° structure: helix helix pleated sheet pleated sheet

80 Polypeptide α helix Proteins form this stable helix due to hydrogen bonding Proteins form this stable helix due to hydrogen bonding This takes place between –C=O of one A.A This takes place between –C=O of one A.A And the –N-H of the A.A 4 places ahead And the –N-H of the A.A 4 places ahead

81 Polypeptide - β Pleated Sheet This looser, straighter shape is also formed by H bonds. This looser, straighter shape is also formed by H bonds. This time between –C=O and –N-H of adjacent chains This time between –C=O and –N-H of adjacent chains

82 Proteins may contain both of these secondary structures Proteins may contain both of these secondary structures They are easily disrupted by heat & changes in pH They are easily disrupted by heat & changes in pH

83 Biological molecules chemical tests Reducing Sugars Reducing Sugars Heat the sugar solution with an equal volume of blue benedict's solution for 2-3 minutes at about 90°C Heat the sugar solution with an equal volume of blue benedict's solution for 2-3 minutes at about 90°C A positive result is a brick red precipitate A positive result is a brick red precipitate Non reducing sugar (sucrose) Non reducing sugar (sucrose) Collect some filtrate from the reducing sugar test Collect some filtrate from the reducing sugar test Add a few drops of acid and heat in a water bath for a few minutes Add a few drops of acid and heat in a water bath for a few minutes Neutralise with an equal amount of sodium hydroxide solution Neutralise with an equal amount of sodium hydroxide solution Repeat the benedicts test, a brick red ppt is a positive result Repeat the benedicts test, a brick red ppt is a positive result Starch Starch Add orange brown iodine solution to the material Add orange brown iodine solution to the material A blue black colour is produced on contact with starch A blue black colour is produced on contact with starch Protein Protein Biuret reagent is made by combining equal amounts of Sodium Hydroxide and Copper Sulphate Biuret reagent is made by combining equal amounts of Sodium Hydroxide and Copper Sulphate Add biuret reagent to the suspect food or add some dilute sodium hydroxide solution and mix followed by a little dilute copper sulphate solution. Add biuret reagent to the suspect food or add some dilute sodium hydroxide solution and mix followed by a little dilute copper sulphate solution. The copper ions interact with the amino groups in the protein to give PURPLE colour for a positive result The copper ions interact with the amino groups in the protein to give PURPLE colour for a positive result If the solution stays BLUE this is a negative result If the solution stays BLUE this is a negative result

84 Food Testing Starch Starch Add orange brown iodine solution to the material Add orange brown iodine solution to the material A blue black colour is produced on contact with starch A blue black colour is produced on contact with starch Protein Protein Biuret reagent is made by combining equal amounts of Sodium Hydroxide and Copper Sulphate Biuret reagent is made by combining equal amounts of Sodium Hydroxide and Copper Sulphate Add biuret reagent to the suspect food or add some dilute sodium hydroxide solution and mix followed by a little dilute copper sulphate solution. Add biuret reagent to the suspect food or add some dilute sodium hydroxide solution and mix followed by a little dilute copper sulphate solution. The copper ions interact with the amino groups in the protein to give PURPLE colour for a positive result The copper ions interact with the amino groups in the protein to give PURPLE colour for a positive result If the solution stays BLUE this is a negative result If the solution stays BLUE this is a negative result


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