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Module 2- Foundations in biology > 2.2 Biological molecules > Flashcards

2.2 Biological molecules Flashcards

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1
Q

What’s a condensation reaction?

A

Reaction that occurs when two molecules are joined together with the removal of water.

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2
Q

What’s a hydrogen bond?

A

A weak interaction that can occur whenever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen atom.

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3
Q

What’s a hydrolysis reaction?

A

Reaction that occurs when two molecules are split into smaller molecules with the addition of water.

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4
Q

What’s a monomer?

A

A small molecule which binds to many other identical molecules to form a polymer.

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5
Q

What’s a polymer?

A

A large molecule made from many smaller molecules called monomers.

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6
Q

What’s a covalent bond?

A

By sharing electrons with other atoms, the atom’s outermost shell can be ‘filled’ and it becomes strongly bonded with the other atom- this is called a covalent bond.

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7
Q

What are condensation and hydrolysis reactions responsible for?

A

They’re responsible for bonding and splitting apart biological molecules.

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8
Q

What is the monomer and polymer of a carbohydrate?

A

Monomer- monosaccharides (e.g. glucose)
polymer- polysaccharides (e.g. starch)

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9
Q

What is the monomer and polymer of proteins?

A

Monomer- Amino acids
Polymer- polypeptides and proteins

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10
Q

What is the monomers and polymers of nucleic acid?

A

Monomer- nucleotide
Polymer- DNA and RNA

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11
Q

How does hydrogen bonding in water occur?

A

Water consists of two hydrogen atoms, each contently bonded to one oxygen atom. However, because the oxygen atom has a greater number of positive protons in it’s nucleus, this exerts a stronger attraction for the shared electrons. This means the oxygen atom becomes slightly positive. When this happens, we say the molecule is polar.

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12
Q

What are the properties of water?

A

. Liquid
. Density
. Solvent
. Cohension and surface transport
. High specific heat capacity
. High latent heat of vapourisation
. Reactant

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13
Q

Why is this property of water important to living organisms? -Liquid

A

Because water is liquid at room temperature-
. Provides habitats for living things in rivers, lakes, ponds, etc.
. Form major component of tissues in living organisms.
. Provides a reaction medium for chemical reactions.
. Provide an effective transport system, e.g. in blood and vascular tissue.

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14
Q

Why is this property of water important to living organisms? -Density

A

.If water was less dense aquatic animals would find it difficult to float.

.Water becomes more dense as it cools till it reaches around 4 degrees- from there, to freezing point, because of waters polar nature, the molecules align themselves in a structure which is less dense than liquid water- therefore ice is less dense than water.
.Ice can provide a habitat because it floats.
.Aquatic animals have a stable environment in which to live during the winter.
.Ponds and bodies of water are insulated against the extreme cold as the layer of ice reduces the rate of heat loss from the rest of the pond.

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15
Q

Why is this property of water important to living organisms? -Solvent

A

.Molecules and ions can move around and react together in water. Many such reactions happen in the cytoplasm of cells, which is over 70% water.
.Molecules and ions can be transported around living things whilst dissolved in water.

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16
Q

Why is this property of water important to living organisms? -Cohesion and surface tension

A

.Column of water in plant vascular tissue are pulled up the xylem tissue together from the roots.
.Insects like pond skaters can walk on water.

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17
Q

Why is this property of water important to living organisms? -High specific heat capacity

A

.Living things, including prokaryotes and eukaryotes, need a stable temperature for enzyme- controlled reactions to happen properly.
.Aquatic organisms need a stable environment in which to live.

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18
Q

Why is this property of water important to living organisms? -High latent heat of vaporisation

A

Water can help living things keep their temperature stable. e.g. mammals are cooled when their sweat evaporates and plants are cooled when water evaporates from mysolphyll cells.

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19
Q

Why is this property of water important to living organisms? -Reactant

A

Water’s role as a reactant is extremely important for digestion and synthesis of large biological molecules.

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20
Q

What is cohension?

A

A drop of water does not spread out on a flat surface, but almost looks spherical. This is because the hydrogen bonding between molecules pull them together. The water molecules demonstrate cohesion.

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21
Q

What is surface tension?

A

The water molecules at the surface are all hydrogen-bonded to the molecules beneath them, and hence are more attracted to the water molecules beneath them to the air molecules above. this means the water contracts , and gives the surface of the ability to resist a force applied to it.

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22
Q

What is specific heat capacity?

A

The amount of heat energy required to raise 1kg of a material by 1 degrees.

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23
Q

What is latent heat of vaporisation?

A

The amount of heat energy required to change water from a liquid to a gas.

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24
Q

Why is water a good solvent?

A

Because water is polar, the positive and negative parts of the water molecules are attracted to the negative and positive parts of the solute.

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25
Q

What is a carbohydrate?

A

A group of molecules containing carbon, hydrogen and oxygen. Carbohydrates are ‘hydrated carbon’ meaning, for every carbon there are two hydrogen atoms and one oxygen atom.

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26
Q

What are carbohydrates for?

A

.Source of energy
.Store of energy
.Structural units

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27
Q

What are the main groups of carbohydrates.

A

.Monosaccharides
.Disaccharides
.Polysaccharies

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28
Q

What is a monosaccharide?

A

.The simplest carbohydrates- they are particularly important in living things a as source of energy..They are sugars..Large numbers of carbon-hydrogen atoms.
.Exist as straight lines or in ring or cyclic structures..They have a backbone of single-bonded carbon atoms, with one double-bonded to an oxygen atom to form a carboxyl group.
.Different sugars have different can have different numbers of carbon atoms e.g. hexose sugars have six carbon atoms (e.g. glucose).

Monosaccharide hexose sugars, like glucose, are the monomers of more complex carbohydrates, they bond together to form diasaccharides or polysaccarides.

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29
Q

What is a triose, tetrose, pentose and hexose sugar?
And what form would u expect to find them?

A

Triose- 3 carbon
Tetrose- 4 carbon
Pentose- 5 carbon
Hexose- 6 carbon

In solution, triose and tetrose sugars exist as straight chains. However, pentose and hexose are more likely to be found in ring or cyclic form.

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30
Q

What are the characteristics of a monosaccharide?

A

.Taste sweet
.Soluble in water
.Insoluble in non-polar solvcents

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31
Q

Characteristics of disaccharides?

A

.Taste sweet
.Soluble in water
.In soluble in non-polar solvents

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32
Q

What is a diasccharide?

A

When two monosaccharides join together a disaccharide is formed.

When they form, a condensation reaction occurs to form a glycosidic bond.

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33
Q

Explain what alpha glucose is?

A

.C6H12O6
.Monosaccharide
.Energy store
.Component of starch and gycogen (energy stores)

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34
Q

How are gycosidic bonds formed?

A

When they join, a condensation reaction occurs to form a glycosidic bond. Two hydroxyl groups line up next to each other, from which a water molecule is removed- this leaves an oxygen atom acting as a link between two monosaccharide units.

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35
Q

How are disaccharides broken up into monosaccharides?

A

Disaccharides are broken into monosaccharides by a hydrolysis reaction, which requires the addition of water. The water provides the hydroxyl group and a hydrogen, which helps to break the gycosidic bond.

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36
Q

What is a polysaccharide?

A

Polysaccharides are polymers of monosaccharides. They’re made up of hundreds of thousands of monosaccharide monomers bonded together. They’re stores of energy.

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37
Q

What are polysaccharides made up of solely one type of monosaccharide called?

A

homopolysaccharides

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38
Q

What are polysaccharides made up of more than one type of monosaccharide called?

A

heteropolysaccharides

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39
Q

What is an example of a homopolysaccharide?

A

Starch

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40
Q

Why are polysaccharides good energy stores?

A

.Glycogen and starch are compact, which means they do not occupy a large amount of space. They both occur in dense granules within the cell.

.Polysaccharides hold glucose molecules in chains, so they can be easily ‘snipped off’ from the end of the chain by hydrolysis when needed for respiration.

.Some chains are unbranched while some are branched. Branched chains tend to be more compact, but also offer the chance for lots of glucose molecules to be ‘snipped off’ by hydrolysis at the same time, when lots of energy is needed quickly.

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41
Q

Why is a polysaccharides solubility important?

(and what structural point makes it this way)

A

Polysacchararides are less soluble in water than monosaccharides. This is because of their size and also because the regions which could hydrogen-bond with water are hidden away inside the molecule inside it’s spiral structure.

If many glucose molecules did dissolve in the cytoplasm, the water potential would reduce, and excess water would diffuse in, disrupting the normal working of cell.

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42
Q

What sort of molecule is cellulose?

A

Polysaccharide

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43
Q

What are the characteristics of cellulose?

A

.Forms cell walls
.Tough
.Insoluble
.Fibrous substance
.Homopolysaccharide

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44
Q

What is cellulose made up of?

A

Long chains up to 15000 beta glucose molecules bonded together through condensation reactions to form glycosidic bonds.

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45
Q

What is the structure of cellulose like?

A

.Cellulose is straight (it doesn’t spiral)

.Hydrogen and hydroxyl groups on carbon 1 are inverted in beta glucose. This means that every other beta-glucose molecule in the chain is rotated by 180 degree. This beta-1-4 glycosidic bond helps prevent the chain spiraling.

.Hydrogen bonding between the rotated beta-glucose molecule in each chain also gives the chain additional strength, and stops spiralling.

Hydrogen bonding between the rotated beta-glucose molecules in different chains the whole structure additional strength.

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46
Q

What is a mirofibril?

A

When 60-70 cellulose chains are bound together, they form microfibrils (They’re 10-30nm in diameter).

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47
Q

What’s macrofibrils?

A

400 microfibrils bundle together to form a macrofibril, which are imbedded in pectins (like glue) to form plant cell walls. Macrofibrils run in all directions criss-crossing the wall for extra strength.

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48
Q

Function of cellulose?

A

.Excellent material for plant cell walls
.High tensile strength
.Difficult to digest
.Support the whole plant
.Allows the cell wall to be fully permeable

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49
Q

Structure of plant cell walls?

A

.Microfibrils and macrofibrils have very high tensile strength, both because of the strength of their glycosidic bonds between chains.

.Macrofibrils run in all directions, criss-crossing for extra stregth.

.Difficult to digest as the glycosidic bonds between the glucose molecules are less easy to break and most animals don’t even have an enzyme to catalyse the reaction.

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50
Q

What are the key features of cellulose that helps the plant wall do it’s job?

A

.Because plants don’t have a rigid skeleton, each cell needs to have strength to support the whole plant.

.There is space between macrofibrils for water and mineral ions to pass on their way into and out of the cell. This makes the cell fully permeable.

.Wall has high tensile strength which prevents the cell from bursting.

.The macrofibril structure can be reinforced with other substances for extra support or to make the cell wall waterproof. For example, cutin and suberin are waxes that block spaces in the cell wall, making in waterproof.

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51
Q

What are lipids?

A

A group of substances that are soluble in alcohol rather than water (they’re not polar). They incude triglycerides, phospholipids and cholesterol.
Lipids are examples of macromolcules.

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52
Q

What is a macromolecule?

A

A very large, organic molecule.

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53
Q

What is a phospholipid?

A

Molecule consisting of glycerol, two fatty acids and one phosphate group.

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54
Q

What is the structure of a triglyceride?

A

Triglycerides are made up of glycerol and fatty acids.

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55
Q

What is the structure of glycerol?

A

Glycerol has three carbon atoms. It is an alcohol, which means it has free -OH groups. There are three -OH groups, which are important to the structure of triglycerides.

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56
Q

What makes up a fatty acid?

A

Fatty acids have a carboxyl group (-COOH) on one end, attached to a hydrocarbon tail, made of only carbon and hydrogen atoms. This may be anything from 2 to 20 carbons long. The carboxyl group ionises into H+ and a -COO- group. This structure is therefore an acid because it can produce free H+ ions.

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57
Q

What does it mean if an acid is saturated?

A

If a fatty acid is saturated, it mean s there is no C=C bonds (no double bonds) in the molecule. Animal lipids contain lots of saturated fatty acids, which are solid at room temperature (20 degrees)- If there’s more unsaturated fats, the melting point is lower.

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58
Q

What does it mean is a fatty acid is unsaturated?

A

If a fatty acid is unsaturated, is a double bond (C=C) between two of the carbon atoms instead, which means the fewer hydrogen atoms can be bonded to the molecule.

A single C=C bond makes a fatty acid monosaturated, while more than one C=C bond makes it polysaturated.

The C=C bond causes a kink in the hydrocarbon chain- because these kinks push the molecules apart slightly, it makes then more fluid.

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59
Q

What sort of bond forms in a triglyceride and why?

A

A covalent bond is found between the glycerol and each fatty acid which is called an ester bond.
A condensation reaction happens between the -COOH group of the fatty acid and the -OH group of the glycerol. Because there are three -OH groups, three fatty acids will bond, hence the name triglyceride. Because it is a condensation reaction, a water molecule will be produced and the ester bond will form.

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60
Q

What are the functions of triglycerides?

A

.Energy source- triglycerides can be broken down in respiration to provide energy and generate ATP. Respiration of a lipid produces more water than respiration of sugar.

.Energy store- because they are insoluble in water, they can be stored without affecting the water potential of the cell.

.Insulation

.Buoyancy- fat is less dense than water, it is used by aquatic animals to help them to stay afloat.

.Protection- Humans have fat around delicate organs to act as a shock absorber.

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61
Q

What is an example of a polysaccharide?

A

.Starch (store of energy)(found in plants)
.Glycogen (store if energy)(found in animals)

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62
Q

What is starch made up of?

A

Starch is made up of amylose and amylopectin.

Amylose is made up of alpha-glucose monomers are held together with glycosidic bonds between 1-4.

Amylopectin is made up of alpha-glucose monomers and are held together with glycosidic bonds between 1-4 and 1-6 because it is a branched structure.

Both amylose and amylopectin coil up and are held together with hydrogen bonds.

63
Q

What is glycogen made up of?

A

Glycogen is made up of alpha-glucose monomers held together with 1-4 and 1-6 glycosidic bonds. its more branched than starch but less coiled.

64
Q

Which bits of a phospholipid is polar and non polar? What word can we use to describe this?

A

When surrounded by water, the phosphate group has a negative charge, making it polar. however, the fatty acid tails are non polar so are repelled by water. The head is hydrophilic and the tail is hydrophobic.
This means the phospholipid molecule is amphipathic.

65
Q

What is the structure of a phospholipid?

A

Phosopholipids are made up of a glycerol molecule, 2 fatty acids and a phosphate molecule. The 2 fatty acid tails are bonded to the glycerol by an ester bond while the phosphate is bonded to the glycerol is bonded to the glycerol by a phosphate ester bond.

66
Q

How do phospholipids behave in water?

A

.They may from a layer on the surface of the water with heads in the water and tails sticking up out of the water.

.They may form micelles- tiny balls with the tails tucked away inside, and the heads pointing outwards into the water.

67
Q

Where are phospholipids found in membranes around cells and organelles?

A

The phospholipids form a bilayer, with two rows of phopholipids, tails pointing inwards and heads pointing outwards into the solution.

68
Q

why is it good the phophlipds make up most of a cell membrane?

A

.The individual phospholipids are free to move in their layer, but will not move into any position where their hydrophobic tails are exposed to water. this gives the membrane some stability.

.The membrane is selectively permeable.It is only possible for small and non-polar molecules to move through the tails in the bilayer, such as oxygen and carbon dioxide. This lets the membrane control what goes in and out of the cell, and keeps the cell functioning properly.

69
Q

What is cholesterol?

A

Cholesterol is a steroid alcohol- a type of lipid. It is a small and hydrophobic molecule, meaning it can sit in the middle of the hydrophobic part of the bilayer,

70
Q

What is cholesterol made up of?

A

Cholesterol consists of four carbon-based rings or isoprene units.

71
Q

What is cholesterol’s function in s cell membrane?

A

Cholesterol regulates the fluidity of the membrane preventing it from becoming too fluid or stiff.

72
Q

Where is cholesterol made in animals?

A

The liver

73
Q

What is cholesterol in plant membranes called and whats the difference between it and cholesterol in an animals cell membrane?

A

Plants have cholesterol derivative in their membranes, called stigmasterol.
Stigmasterol is different to cholesterol because, stigmasterol has a double bond between carbon 22 and carbon 23.

74
Q

What is some examples of molecules made of cholesterol?

A

The steroid hormones, testosterone, oestrogen and vitamin D are all made from cholesterol.

75
Q

What is the monomers of all proteins?

A

amino acids.

76
Q

What bond holds amino acids together?

A

peptide bond.

77
Q

What are proteins?

A

Proteins are large polymers comprised of long chains of amino acids.

78
Q

What are some functions of protein?

A

.They form structural components.
.They have a tendency to adopt specific shapes which make them important as enzymes, antibodies and hormones..Membranes have protein constituents that act as carriers and pores for active transport and facilitated diffusion.

79
Q

How do animals get the amino acids they need to form proteins?

A

Animals can make some amino acids , but must ingest others (called essential amino acids).

80
Q

How do plants get the amino acids they need to form proteins?

A

Plants can make all the amino acids they need, but only if they can access fixed nitrogen.

81
Q

What does every amino acid contain?

A

Each amino acid contains the elements carbon, hydrogen, oxygen and nitrogen.
Some contain sulfur.

82
Q

How many amino acids are there?
How many of these are found in proteins?

A

There are over 500 amino acids, but only 20 of them are found in proteins.

83
Q

What groups make up an amino acid?

A

Each protein chain of amino acids has an amine group (-NH2) at one end, a carboxyl group (-COOH) at the other end and a R group in the middle).

84
Q

What is the R group?

A

The R group doesn’t stand for a particular element however, in every amino acid it is different.

85
Q

What is the amino acid in glycine?

A

H (hydrogen atom)

86
Q

What is the amino acid in alanine?

A

CH3 (methyl group)

87
Q

What is the amino acid in cytosine?

A

CH3S

88
Q

What bond keep amino acids together?

A

peptide bonds.

89
Q

What are two amino acids joined together called?

A

depetide.

90
Q

What are a chain of amino acids joined together called?

A

polypeptide.

91
Q

What reaction joins two amino acids together?

A

A condensation reaction

92
Q

What reaction breaks up two amino acids?

A

A hydrolysis reaction.

93
Q

What are the stages of the structure of proteins in order of simplest to a complete perotein?

A

.Primary structure
.Secondary structure
.Tertiary structure
.Quaternary structure

94
Q

What is the primary structure of a protein?

A

The sequence of amino acids in a protein chain is called the primary structure.

95
Q

What is the secondary structure of a protein?

A

The chain of amino acids is not straight, but twists into a shape called the secondary structure. Some chain into an alpha-helix and others fold with a zigzag structure called a beta-pleated sheet.
Hydrogen bonds are found.

96
Q

What is the tertiary structure?

A

When these coils themselves start to fold, along areas of straight chains of amino acids, this forms the tertiary structure. The tertiary structure is a very precise shape which is held together firmly in place amino acids which lay close to each other.
Bonds found in the tertiary structure include hydrogen, ionic, hydrophobic and hydrophilic interactions and disulfide links.

97
Q

What is the quaternary structure of a protein?

A

The quaternary structure descries how multiple chains are arranged to make the complete protein molecule.
Bonds found in the quaternary structure include hydrogen, ionic, hydrophobic and hydrophilic interactions and disulfide links.

98
Q

How does a hydrogen bond form?

A

Hydrogen bonds form between hydrogen atoms with a slight positive charge and other atoms with a slightly negative charge.

99
Q

How do hydrogen bonds form in amino acids?

A

Hydrogen bonds form between in hydroxyl, carboxyl and amine groups.

100
Q

What is a disulfide link?

A

The R group of the amino acid cytosine contains sulphur. Disulfide bridges are formed between the R groups of two cytesine’s. these are strong covalent bonds.

101
Q

Which two main categories do the three-dimensional tertiary structure of proteins fall into?

A

.Fibrous proteins
.Globular proteins

102
Q

What are the features of fibrous proteins?

A

.Has a relatively long, thin structure.Has regular, repetitive sequences of amino acids
.Insoluble in water.metabolically inactive
.often has a structural role within an organism

103
Q

Examples of fibrous proteins?

A

.Collagen
.Keratin
.Elastin

104
Q

What are the features of globular proteins?

A

.Tend to roll up into an almost spherical shape.Any hydrophobic R groups are turned inwards and any Hydrophilic R groups are on the outside. This makes the protein water soluble, because water molecules can easily cluster round and bind to them.
.They often have specific shapes, which helps them to take up roles as enzymes, hormones and haemoglobin.

105
Q

Examples of globular proteins?

A

.Haemoglobin
.Insulin
.Pepsin

106
Q

What is the function of collagen?

A

To provide mechanical strength

107
Q

Where is collagen found in the body and what does it do there?

A

.In artery walls, a layer of collagen prevents the artery bursting when withstanding high pressure from blood being pumped by the heart.
.Tendons are made from collagen and connect muscles to bones, allowing them to pull on bones..Bones are made from collagen, and then reinforced with calcium phosphate, which makes them hard..Cartilage and connective tissue are made from collagen.

108
Q

What is the structure of keratin?

A

Keratin is rich in cysteine so lots of disulfide bridges form between the polypeptide chains . Alongside hydrogen bonding, this makes the molecule very strong.

109
Q

Where is keratin found?

A

Keratin is found wherever a body part needs to be hard and strong. It is found in finger nails, hair, claws, hoofs, scales, fur and feathers.

110
Q

What does keratin provide?

A

It provides mechanical protection, but also provides an impermeable barrier to infection and, being waterproof, also prevents entry of water-born pollutants.

111
Q

What is the structure of elastin?

A

Cross-linking and coiling make the structure of elastin strong and extensible.

112
Q

Where is elastin found?

A

It is found in living things where they need to stretch or adapt there shape as part of life processes.
For example, skin stretched around our bines and muscles, because without elastin, skin would not go back to normal after being pinched.
Other examples of where elastin is found includes, our lungs, bladder and blood vesicles.

113
Q

What is the structure of hemoglobin?

A

The quaternary structure of haemoglobin, is made up of four polypeptide chains: two alpha-globin chains and two beta-globin chains. Each of there has its own tertiary structure, but when fitted together, they form one haemoglobin molecule.
At one position on the outside of each chain, there is a space in which a haem group is held (prosthetic group). The haem group contains an iron ion.

114
Q

What is a protein associated with a prosthetic group called?

A

A conjugated protein.

115
Q

What is the function of haemoglobin?

A

To carry oxygen from the lungs to the tissues. In the lungs, an oxygen molecule binds to the iron in each of the four haem groups in the haemoglobin molecule.
When it binds, the haemoglobin turns from a purple colour to bright red.
Oxygen is then released when it reached the tissues.

116
Q

What is the structure of insulin?

A

Insulin is made up of two polypeptide chains. The A chain begins with a section of alpha-helix, and the B chain ends with a section of beta-pleat. Both chains fold into a tertiary structure, then are joined together by disulfide links. Amino acids with hydrophilic R groups are found on the outside of the molecule, therefor making it soluble in water.

117
Q

What is the function of insulin?

A

Insulin binds to glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose.

118
Q

What is the function of pepsin?

A

Pepsin is an enzyme that digests protein in the stomach.

119
Q

What is the structure of pesin?

A

The enzyme pepsin, is made up of a single polypeptide chain of 327 amino acids, but it folds into a symmetrical tertiary structure. pepsin has few amino acids with basic R groups (only 40) Whereas it has 43 amino acids with acidic R groups- which explains why it is so stable in the environment in the stomach, as there is few R groups to accept H+ ion (so there can be little effect on the molecules structure). The tertiary structure is also held together via hydrogen bonds and 2 disulfide bridges.

120
Q

What is the molecular structure of alpha-glucose?

A
121
Q

What is the molecular structure of beta-glucose?

A
122
Q

What is the molecular structure of a triglyceride?

A
123
Q

what is the molecular structure of a fatty acid?

A
124
Q

What is the molecular structure of glycerol?

A
125
Q

What is the molecular structure of a phospholipid?

A
126
Q

What is the molecular structure of an amino acid?

A
127
Q

What is the molecular structure of cholesterol?

A
128
Q

How do you test for starch? And what would a positive result look like?

A

Add iodine solution (in potassium iodide) to a sample. If starch is present, there will be a colour change of yellow-brown to blue-black.

129
Q

Why does the sample change colour in the starch test?

A

When dissolved in potassium iodide, the iodine (I2) forms a triiodide ion I3-, which slips into the middle of the amylose helix. This causes the colour change.

130
Q

What are some examples of reducing sugars?

A

Reducing sugars include all monosaccharides and disaccarides.

131
Q

What are reducing sugars called reducing sugars?

A

They’re known as reducing sugars because the can reduce, or give electrons to, other molecules.

132
Q

How do you test for reducing sugars and what would a positive result look like?

A

Add Benedict’s solution to the sample then, heat in a water bath at 80degrees for 3 minutes. If reducing sugar is present, there will be a colour change from blue to green to yellow to orange-red (the amount of colour change is proportional to the amount if reducing sugars in the solution).

133
Q

Why does testing for reducing sugars change colour when it is positive?

A

Benedict’s solution contains Cu2+ ions, which are reduced to Cu+ ion, forming orange-red copper oxide (Cu2O). This is called a precipitate.

134
Q

What is a precipitate?

A

A precipitate is a solid suspended in a reaction mixture.

135
Q

What is an easier way to test for reducing sugars?

A

It is possible to use commercially manufactured test strips to test for reducing sugars. You just dip the strip into the test solution, and compare the colour with the calibration card supplied. (These are often used to test for glucose in the urine of diabetic patients).

136
Q

How do you test for non-reducing sugars?

A

First test for reducing sugars then if there’s none, carry on to test for non-reducing sugars. We have to hydrolyse the bond first, to ‘free up’ these ‘reducing groups’ then test for reducing sugars as normal. To hydrolyse the bonds you have to:

  • boil the sample with hydrochloric acid to hydrolyse the sucrose and fructose.
  • cool the solution and used sodium hydrogencarbonate solution to neutralise it.
  • test for reducing sugars again.
137
Q

What should you do if you get a positive result for reducing sugars?

A

You can go on and also test for non-reducing sugars in an equal sized sample. If present, the precipitate from this second sample will have more mass than the precipitate than the first sample. You can extract this precipitate by filtration.

138
Q

How to test for lipids and what is a positive result?

A

The emulsion test is used to test for lipids:

  • take a sample and mix it thoroughly with ethanol. Any lipid will go into solution with the ethanol.
  • filter.
  • pour the solution into water in a clean test tube.
  • A cloudy white emulsion indicates the presence of lipids.
139
Q

What is an emulsion?

A

This is made up of a 2 liquids that wont mix. It is ma\de up of tiny droplets (e.g.oil) that come out of solution when mixed with water.

140
Q

How do you test for proteins and what does a positive result look like?

A

For this you use the biuret test. Add biuret solution and if proteins are present, the colour changes from light blue to lilac.

141
Q

How does the biuret test work?

A

The colour is formed by a complex between nitrogen atoms in a peptide bonds and Cu2+ ions, which is why this test really detects the presence of peptide bonds.

142
Q

How can we find a quantitative test for biological molecules?

A

We can asses the concentration of a substrate by testing for the molecule then, putting the sample in a colorimeter.

143
Q

How can you predict the shape of a protein molecule?

A

Computer modelling of protein structure.

144
Q

What are the two broad approaches to computer modelling of protein structure?

A
  • Ab initio protein modelling
  • Comparative protein modelling
145
Q

What id Ab initio protein modelling?

A

A model is built based on the physical and electrical properties of the atoms in each amino acid in the sequence. With this technique, there can be multiple solutions, and other method’s sometimes need to be applied to reduce the number of solutions.

146
Q

What is comparative protein modelling?

A

One approach is protein threading, which scans the amino acid sequence against a database of solved structures and produces a set of possible model which would match that sequence.

147
Q

What does benedict’s reagent detect the presence of?

A

Reducing sugars.

148
Q

When testing for reducing sugars, what would you expect to see if there there is more sugar present?

A
  • The amount of precipitate will increase.
  • The amount of copper (II) ions remaining in the solution will increase.
149
Q

What technique can we use to get a quantitative quantity the find the concentration of sugar in a solution?

A

Colourimetry (using a colourimeter)

150
Q

Before using a colourimeter, how can we separate the solution and any unwanted precipitate left in the solution.

A

Using a centrifuuge.

151
Q

How does a colourimeter work?

A

A colourimeter works by shining light through a sample.

  • Using a pipette, we can take the supernatant and place it in a cuvette, which is then places in the colourimeter.
152
Q

What must you make sure you do when using a colourimeter?

A
  • Zero the apparatus each time you take a reading by putting a cuvette of distilled water (called a blank) in before doing the test. This resets the 100% transmission/ absorption.
  • Make sure you do not leave greasy finger prints on surface of the cuvette as it could affect the transmission of light.
153
Q

How does a colourimeter work to test the percentage transmission on a benedict’s test?

A

A red colour filter is used. WE shine red light through the solution, and detect how much passes through (percentage transmission). The solution reflects blue light but absorbs red light.

  • If there is lots of unreacted copper sulphate, the supernatant is still quite blue, absorption of the red light is high and percentage transmission is low.
  • If there is little unreacted copper sulphate, the supernatant is less blue, absorption of red light is low and percentage transmission is high.

Module 2- Foundations in biology (4 decks)

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