Chapter 3 - Biological Molecules Flashcards
(371 cards)
1
Q
how are atoms bonded in water
A
with covalent bonds
2
Q
why is water a polar molecule
A
electrons are not shared equally between atoms, the atom with a greater share of electrons will be slightly negative and the other slightly positive
3
Q
what atom in water is SLIGHTLY positive
A
hydrogen - a smaller share of electrons in covalent bonds
4
Q
what atom in water is SLIGHTLY negative
A
Oxygen has the greater share of electrons in covalent
5
Q
why are many organic molecules polar
A
molecules contain hydroxyl (OH) group
6
Q
how are hydrogen bonds formed
A
o the polar water molecules interact as the + and – regions of the molecule attract each other and from hydrogen bonds
7
Q
characteristics of hydrogen bonds
A
- quite weak
-they break and reform between constantly moving water molecules - viscous
8
Q
characteristics of water (8)
A
- solvent
- cohesive
- adhesive
- has surface tension
- high SHC
- high latent heat of vaporisation
- density
- colourless/ transparent
9
Q
why is water a good solvent
A
o because water is polar, it is attracted to other covalently bonded polar molecules and ions
o The +ve and -ve regions of water molecules are attracted to the -ve and +ve parts of solutes/ions.
o Water molecules cluster around these charged parts and help them separate + stay apart.
10
Q
example of an ion
A
sodium chloride
11
Q
example of a covalently bonded polar molecule
A
glucose
12
Q
why is water being a good solvent significant for life
A
- allows chemical reactions to occur within cells - as the dissolved solutes are more chemically reactive when they are free to move about
- polar molecules (amino acids, nucleic acids) can dissolve in the cytosol
- Metabolites// solutes can be transported efficiently in and out of cells
13
Q
what is the cytosol
A
cell liquid if eukaryotic and prokaryotic cells
14
Q
what is cohesion
A
o Hydrogen bonds pull molecules towards each other // moves as one mass as molecules are attracted to each other
15
Q
why is cohesion significant for life
A
plants can draw water through roots/xylem in transpiration
16
Q
how is surface tension formed
A
at air-water surface, the cohesion between water molecules produces surface tension as the hydrogen bonds also pull the molecules inwards
17
Q
how is surface tension significant for life
A
surface tension is strong enough for some insects e.g., Pond skaters to inhabit
18
Q
what is adhesion
A
water molecules can be attracted to surfaces such as narrow tubes
19
Q
how is adhesion significant for life
A
- causes water to exhibit capillary action
- water can rise up narrow tubes = transpiration
20
Q
define specific heat capacity
A
the amount of energy needed to raise the temperature by 1 degree Celsius of a 1kg substance, without changing state
21
Q
why does water have a high SHC
A
- due to the many hydrogen bonds present in water.
- a relatively large amount of energy is required to raise its temperature
22
Q
SHC of water
A
4200 J/kg°C
23
Q
why is having a high SHC significant for life
A
- Important in habitats as provides a stable environment eg. for fish
- maintaining temperatures that are optimal for enzyme activity
24
Q
define the latent heat of vaporisation
A
the amount of energy needed to change the state (liquid to gas, vice versa) of 1kg a substance without changing its temp
25
why does water have a high latent heat of vaporisation
o takes a lot of thermal energy to break hydrogen bonds and a lot of energy to build them
o absorbs a large amount of heat before it turns into gas
26
why is having a high latent heat of vaporisation significant for life
– reduces evaporation from ocean
- provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin
27
which is more dense - ice or water
water
28
why is ice less dense than water
due to the hydrogen bonds
- when water is cooled below 4 degrees Celsius, the hydrogen bonds fix the polar molecules slightly further apart than the average distance in liquid state,
- forming a giant, rigid, open structure which is less dense than liquid water
29
what type of bonding is hydrogen bonds
intermolecular bonds
30
at what point when cooling down does water start becoming less dense, instead of more
4 degrees Celsius
31
structure of ice
a giant, rigid, open structure
- Every oxygen at the centre of a tetrahedral arrangement of hydrogen atoms
32
why is the anomaly in density of water significant for life
- insulates ponds/lakes
- stops organisms freezing underneath // only surface freezes not whole of ocean
33
what is a condensation reaction
• Joins two molecules together with the formation of a chemical bond, and involves the elimination of a molecule of water
34
what is a hydrolysis reaction
• Breaks a chemical bond between two molecules and involves the use of a molecule of water
35
what type of reactions are condensation and hydrolysis
reversible reaction
36
What do carbohydrates contain
Carbon, Hydrogen and Oxygen
37
General formula of a carbohydrate
Cx(H2O)y
38
Glucose formula
C6H1206
39
What is a monosaccharides
1 unit
40
What is a disaccharide
2 units
41
What is a polysaccharide
Many units
42
Examples of monosaccharides (3]
glucose, fructose, ribose
43
Examples of disaccharides
lactose, sucrose, maltose
44
Examples of polysaccharides
glycogen, starch, cellulose
45
What is a monosaccharide of 6 carbons called
hexose monosaccharide
46
Example of a become monosaccharide
Glucose
47
How are carbons numbered in a structure diagram
carbons are numbered clockwise, beginning with the carbon to the right of oxygen
48
Is glucose soluble in water
Yes
49
Why is glucose soluble in water
due to the hydrogen bonds that form between the hydroxyl groups and water molecules.
50
Why is solubility for glucose important
as it means glucose is dissolved in the cytosol of cell
51
What are the two isomers of glucose
Alpha (α) glucose and Beta (β) glucose
52
What is an isomer
molecules with the same molecular formula but with different structural arrangements of atoms.
53
What’s the difference between alpha and beta glucose
o Alpha has the OH below the C1
o Beta has the OH above the C1
54
Draw alpha glucose
55
Draw beta glucose
56
What is special about monosaccharides
• Same no. of C as O atoms
57
General formula of monosaccharides
(CH2O)n
58
General properties of monosaccharides
• White crystalline solids
• Dissolve in water to form sweet tasing solutions
59
What can monosaccharides be categorised into
Trioses
Tetroses
Pentoses
Hexoses
60
How many carbons does trioses have
3
61
How many carbons does tetroses have
4
62
How many carbons does pentoses have
5
63
How many carbons does hexoses have
6
64
Example of a triose
Glyceraldehyde
65
Properties of trioses
Intermediates in respiration and photosynthesis
66
Properties of tetroses
Rare
67
Example of pentoses
RIBOSE or ribulose
68
Properties of pentoses (ribose)
Used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP
69
Example of hexoses
Glucose or Fructose
70
Properties of hexoses
Used as a store of energy in respiration and as building blocks for larger molecules
71
How to break down polysaccharides
Hydrolysis
72
How to synthesise polysaccharides / disaccharides
Condensation reaction
73
How do two glucose molecules form a disaccharide
Condensation reaction
74
Describe the process of the condensation reaction of two alpha glucose molecules
• When two alpha glucose molecules (monosaccharides) are side by side, two hydroxyl groups interact, bonds are broken and new bonds reform to produce different molecules (disaccharides)
• 2 hydrogen atoms and 1 oxygen atom are removed to form water
• A bond forms between carbons 1 and 4 and the molecules are now joined
75
What type of bond is formed between a carbon 1 and a carbon 4 in a condensation reaction
Covalent - 1,4 glycosidic bond
76
What molecule is made when two alpha glucose react
Maltose
77
What is requires for a hydrolysis reaction
• Requires one water molecule to supply the H and the OH to the sugars formed
78
Constituent monomers of sucrose
a- glucose + fructose
79
Constituent monomers of maltose
a glucose + a glucose
80
Constituent monomers of lactose
Glucose + galactose
81
What is starch
• Main storage polysaccharide in plants
82
Properties of starch
• Pure starch is white, tasteless, and odourless
• It is insoluble in cold water or alcohol
83
How is starch formed
when alpha glucose monomers are joined together by glycosidic bonds during condensation reactions
84
What are the two constituents of starch
Amylose + amylopectin
85
Approx how much starch is made from amylose
o 20-30%
86
How is amylose formed
o Formed by alpha glucose molecules joined only by 1,4 glycosidic bonds
87
Properties of amylose
o long unbranched chains
88
What specific about the angle of the bond in amylose
o angle of bond means that the long chain of glucose twists into a helix, further stabilised by hydrogen bonds
89
What important about amylose twisting into a helix
o makes it more compact and less soluble in comparison to the glucose molecules
90
How is amylopectin formed
o Formed when glycosidic bonds form in condensation reactions between carbon 1 and 6.
o Has both 1,4 and 1,6 glycosidic bonds
91
What types of bonds make up amylopectin
1,4 and 1,6 glycosidic bonds
92
What does the 1,6 bonds mean in amylopectin
Means it has a branched structure with 1,6 branching points occurring approx. 1 in 25 glucose subunits
93
How often do branching points occur in amylopectin
approx. 1 in 25 glucose subunits
94
How is a branching point formed in amylopectin
From 1,6 glycosidic bonds
95
Why is it important to have branching points
o Branching means there are many free ends where glucose molecules can be added/removed, speeds up processes of storing/releasing glucose molecules required by the cell
96
Where is glycogen found
in dense granules in liver cells
97
What percentage of the mass of a liver does glycogen take up
7%
98
What is glycogen
• Main storage polysaccharide in animals and fungi (animal equivalent of starch)
99
How is glycogen formed
when alpha glucose monomers are joined together by glycosidic bonds during condensation reactions
100
What types of bonds are in glycogen
1,4 and 1,6 glycosidic bonds
101
Which type of bond is responsible for branching
1,6
102
Which forms more branches glycogen or amylopectin
Glycogen
103
Why does glycogen form more branches
more compact and less space needed for it to be stored, important as animals are mobile
104
Properties of glycogen
• Insoluble, branched, compact
105
What is cellulose
• Main structural constituent of plant cell walls
106
Why is it important for plants to have cellulose
• As plants do not have a rigid skeleton like the one found in animals, a cell wall needs to be strong enough to enable each cell to support the whole plant
107
What is cellulose made from
Beta glucose molecules
108
Why can’t beta glucose molecules join in the same way alpha can
the hydroxyl group on carbon 1 and 4 are too far to react
109
How do plants solve the problem of beta glucose
alternate beta glucose molecules are turned upside down
110
Properties of cellulose
• Unable to coil or form branches – a straight chain is produced (cellulose)
111
What two types of bonds are formed in cellulose
1,4 glycosidic bonds and hydrogen bonds
112
How are hydrogen bonds formed in cellulose
bonds form between the rotated beta glucose molecules on the same cellulose chain and between the rotated beta glucose on cellulose chains that lie alongside each other
113
What is a cellulose chain called
Microfibril
114
What do microfibrils join together to form
Cellulose fibres
115
Properties of cellulose fibres
strong, insoluble, used to make cell walls
116
What makes up lipids
Carbon oxygen and hydrogen
117
Difference between Lipoids and carbohydrates
Lipids have a lot less oxygen
118
Solubility of lipids
- Insoluble in water = because they are non polar
- soluble in organic solvents
- hydrophobic
119
What is lipids made from
3 Fatty acids + 1 glycerol
120
Do lipids form polymers
NO
121
Examples of lipids
Fats
Oils
Cholesterol
Steroids
Phospholipids
122
Difference between fats and oils
• Fats = solid at RT // oils = liquid at RT
123
What type of molecule are lipids
• Macromolecules = large complex molecules
124
What are the functions of lipids [6]
• Energy storage
• Metabolic water source
• Membrane structure
• Water proofing
• Insulation
• Produces hormones
125
Types of lipids with fatty acids
o Triglycerides / Phospholipids / Waxes
126
Types of lipids without fatty acids
o Steroids / cholesterol
127
How are triglycerides mace
made from combining one glycerol molecule with 3 fatty acids, in a condensation reaction
128
Functional group of glycerol
Alcohol
129
Functional group of fatty acids
Carboxylic acid
130
What is needed when triglycerides are broken down
three water molecules need to be supplied to reverse the reaction that formed the triglyceride = hydrolysis reaction
131
Why is it called triglycerides
There are three fatty acids
132
What bond does triglycerides produce when forming from condensation reaction
And ester bond
133
What else does glycerol + three fatty acids produce in a condensation reaction
Three water molecules
134
What is a saturated fatty acid chain
the hydrocarbon chain has only single bonds
135
What is an unsaturated fatty acid
• The hydrocarbon chain consists of at least 1 double bond
136
What is the name when the lipid has 1 double bond
monosaturated
137
What is the name when the lipid has 2+ double bonds
polysaturated
138
What does the presence of a double bond cause in a lipid
causes molecules to bend = therefore not compact = therefore they are liquids/oils rather than fats
139
Draw a saturated and mono saturated and poly saturated chain
140
Types of unsaturated fat
• Unsaturated fat can be either cis or trans
141
What does cis and trans fat refer to
the arrangement of the two hydrogen atoms bonded on to the carbon chain involved in a double bond
142
What is cis fat
hydrogens are on the same side of the double bond
143
What is trans fat
hydrogens are on opposite side of the double bond
144
Draw a cis fatty acid
145
Draw a trans fatty acid
146
What are phospholipids
• Modified triglycerides containing phosphorus, carbon, oxygen and hydrogen
147
How is the phosphate group added into a phospholipid
• One of the fatty acid chains is replaced with a phosphate group
148
Where are inorganic phosphate ions found
In the cytoplasm of every cell
149
Are phospholipids soluble in water
Yes
150
Why are phospholipids soluble in water
o Have extra electrons = soluble in water
151
Sketch the chemical structure of a phospholipid
152
The structure of phospholipids
• Have a non-polar fatty acid tail and a charged phosphate head
153
Property of phospholipid fatty acid tail
Non-polar
154
Significance of phospholipid non-polar tail
repelled by water = hydrophobic
155
Significance of phospholipid charges head
interacts/attracted to water = hydrophilic
156
Significance of BOTH non-polar tail and charged head
• They form a layer on the surface of water with the phosphate heads in the water and the fatty acid tails sticking out of the water
• Can form structured based on 2 layered sheet formations (bilayers), with all the hydrophobic tails pointing towards the centre of the sheet, protected by the hydrophilic heads
157
Significance of phospholipids forming bilayers
• Able to separate an aqueous environment in which cells usually exist from the aqueous cytosol within
158
What are peptides
• polymers made up of amino acid molecules (monomers)
159
What does a protein consist of
• 1+ polypeptides arranged as complex macromolecules and have specific biological functions
160
What do all proteins contain (biological elements)
• carbon, hydrogen, oxygen and nitrogen
161
What is the general structure of an amino acid
o An amine group -NH2
o A carboxylic acid group -COOH
o A hydrogen atom
o An R group
162
Draw the general structure of an amino acid
163
What do different R groups result in
Different amino acids
164
How many amino acids are there
20
165
What is formed when 2 amino acids bond
Dipeptide
166
What is formed when 3 amino acids bond
Tripeptide
167
What is formed when many amino acids bond
Polypeptide
168
How are peptides made - overall reaction
Condensation reaction
169
How are peptides made - detailed
• Amino acids join when amino and carboxylic acid groups connected to the central carbon atom react.
• The R-groups are not involved at this point.
• The hydroxyl in the carboxylic acid group of one amino acid reacts with the hydrogen in amine group of another amino acid.
• The remaining carbon atom (with the double-bonded oxygen) from the first amino acid bonds to the nitrogen atom of the second amino acid
• Peptide bond is formed between the amino acids and water is produced (condensation reaction).
• Resulting compound: dipeptide
170
What is specifically not involved in the formation of peptides
R groups
171
What type of bonds are peptides bonds
Covalent
172
What is the reaction forming peptides catalysed by
by enzyme peptidyl transferase
173
Where is peptidyl transferease found
present in ribosomes.
174
What is the primary structure of a protein
• sequence of amino acids joined by peptide bonds
175
What determines the primary structure of proteins
DNA
176
What is the secondary structure of proteins
• occurs when the sequence of amino acids are linked by hydrogen bonds in an alpha helix or beta helix pleated sheet
177
What interacts to form the secondary structure
• the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form hydrogen bonds
178
What type of bonds make up the secondary structure
Hydrogen bonds
179
What two types of shapes can be made in the secondary structure
o α-helix
o β-pleated sheet
180
When does the α-helix shape occur
• when the hydrogen bonds form between every fourth peptide bond (between the oxygen of the carboxyl group and the hydrogen of the amine group)
181
When does the β-pleated sheet occur
• when the protein folds so that two parts of the polypeptide chain are parallel to each other enabling hydrogen bonds to form between parallel peptide bonds
182
What type of protein mostly has a secondary structure
• Most fibrous proteins have secondary structures (e.g. collagen and keratin)
183
What is the secondary structure also known as
The protein backbone
184
Why is the secondary structure known as the portion backbone
only relates to hydrogen bonds forming between the amino group and the carboxyl group
185
What can hydrogen bonds be broken by in the secondary structure
• high temperatures and pH changes
186
What is the tertiary structure in proteins
describes the folding of a polypeptide chain, due to the molecular interactions among the R groups of the amino acids
187
What are these molecular interactions in the tertiary structure
o Hydrogen (these are between R groups)
o Disulphide (only occurs between cysteine amino acids)
o Ionic (occurs between charged R groups)
o Weak hydrophobic interactions (between non-polar R groups)
188
What protein is tertiary structure common in
Globular
189
What type of bond is disulphide bond
Covalent bond
190
What does disulphide bonds form between
two cysteine R groups
191
Why do disulphide bonds only form between two cysteine R groups
as this is the only amino acid with a sulphur atom
192
Which type of R group interaction is the strongest
Disulphide
193
What can disulphide bonds be broken by
Oxidation
194
What do ionic bonds in the tertiary structure form between
• form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
195
What are ionic bonds broken by
Changes in pH
196
What do hydrogen bonds form between in the tertiary structure
form between strongly polar R groups.
197
What is the weakest type of R group interaction
Hydrogen bonds
198
What do hydrophobic interactions form between
• form between the non-polar (hydrophobic) R groups within the interior of proteins
199
What is the quaternary structure in a protein
• arrangement of two or more polypeptide chains working together as a functional macromolecule
200
Example of a protein with a quaternary structure
Haemoglobin
201
What is each polypeptide chain in the quaternary structure referred to as
The subunit of the protein
202
Summary table of bonds in the different levels of proteins structures
203
Properties of globular proteins
• compact, roughly spherical (circular) in shape and soluble in water
204
Why do globular proteins form a spherical shape
o their non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings and
o their polar hydrophilic R groups orientate themselves on the outside of the protein
205
What causes globular proteins to be soluble in water
Its arrangement
• the water molecules can surround the polar hydrophilic R groups
206
Example of a globular protein
Insulin
207
What is a conjugated protein
Globular proteins which contain a prosthetic group.
208
What are prosthetic groups
can be lipoproteins, glycoproteins, metal ions or minerals from vitamins.
209
Examples of conjugated proteins
Haemoglobin + catalase
210
What prosthetic group does haemoglobin have
Haem
211
What is haemoglobin
• a globular protein which is an oxygen-carrying pigment found in vast quantities in red blood cells
212
What type of structure is haemoglobin
Quaternary
213
How many polypeptide chains does haemoglobin have
4
214
What types of polypeptide subunits does haemoglobin have
two α–globins and two β–globins
215
What does each subunit in haemoglobin have
A prosthetic haem group
216
How are the four subunits held together in haemoglobin
by disulphide bonds and arranged so that their hydrophobic R groups are facing inwards (helping preserve the three-dimensional spherical shape) and the hydrophilic R groups are facing outwards (helping maintain its solubility)
217
What makes haemoglobin soluble
hydrophilic R groups are facing outwards
218
What does the prosthetic haem group contain
iron II ion (Fe2+)
219
What’s the purpose of the iron II ion (Fe2+) in haemoglobin
• able to reversibly combine with an oxygen molecule forming oxyhaemoglobin and results in the haemoglobin appearing bright red
220
How many oxygen molecules can each haemoglobin molecule carry
• Each haemoglobin with the four haem groups can therefore carry four oxygen molecules (eight oxygen atoms)
221
Why can oxygen be carried round more efficiently when bound to haemoglobin
• As oxygen is not very soluble in water and haemoglobin is, oxygen can be carried more efficiently around the body when bound to the haemoglobin
222
What is catalase
Globular conjugated protein
223
What type of structure does catalyse have
Quatenaryb
224
How many prosthetic haem groups does catalase have
4
225
What does the presence of iron II in the haem group in catalase allow
• allow catalase to interact with hydrogen peroxide and speed up its breakdown.
226
What is hydrogen peroxide
• a common by-product of metabolism but is damaging to cells and cell components if allowed to accumulate.
227
What does catalase do
Stops hydrogen peroxide accumulating
228
What is insulin
Globular protein
229
Where is insulin produced
In the pancreas
230
Why must insulin be soluble
Hormones transported in bloodstream
231
Why does insulin need a specific shape
fits into receptors on cell surface membranes to cause more/less glucose production
232
What does insulin consist of
• Consists of 2 polypeptide chains held together by 3 disulphide bridges
233
What are fibrous proteins
• long strands of polypeptide chains that have cross-linkages due to hydrogen bonds
234
Properties of fibrous proteins
• have little or no tertiary structure
Insoluble in water
Suitable,e for structural roles
235
Why are fibrous proteins insoluble in water
Due to a large number of hydrophobic R groups
236
Why are fibrous proteins suitable for structural roles
• have a limited number of amino acids with the sequence usually being highly repetitive
• The highly repetitive sequence creates very organised structures that are strong and this along with their insolubility property, makes fibrous proteins very suitable for structural roles
237
Examples of fibrous proteins
Keratin + elastin + collagen
238
What does keratin make up
Hair, nail, horns, feathers
239
Where is elastin found
connective tissue, tendons, skin and bone
240
Where is collagen found
- skin, tendons and ligaments
241
Both elastin and collagen are examples of what
Connective tissue
242
What is the structure of collagen
• formed from three polypeptide chains closely held together by hydrogen bonds to form a triple helix (known as tropocollagen)
• Along with hydrogen bonds forming between the three chains there are also covalent bonds present
• Covalent bonds also form cross-links between R groups of amino acids
• The cross-links hold the collagen molecules together to form fibrils
• The collagen molecules are positioned in the fibrils so that there are staggered ends
• When many fibrils are arranged together they form collagen fibres
• Collagen fibres are positioned so that they are lined up with the forces they are withstanding
243
How many polypeptide chains in collagen
3
244
What are the polypeptide chains held together by in collagen
Hydrogen bonds
245
What is the properties of collagen
- forms connective tissue
- strong + tensile strength
- stable
- insoluble
246
Why does collagen have great tensile strength
• presence of the many hydrogen bonds within the triple helix structure of collagen results in great tensile strength.
247
Why is collagen strong
• The staggered ends of the collagen molecules within the fibrils provide strength
248
Why is collagen stable
• due to the high proportion of proline and hydroxyproline amino acids present. These amino acids increase stability as their R groups repel each other
249
Why is collagen insuluble
The length of collagen molecules means they take too long to dissolve in water
250
Properties of keratin
Strong
Flexible
Insoluble
251
Why is keratin flexible
• Large proportion of sulphur – containing amino acid, cysteine.
• Degree of disulphide bonds determine flexibility – hair contains fewer bonds making it more flexible than nails which contains more bonds.
252
What determines flexibility
Degree of disulphide bonds
253
Why is there an unpleasant smell when hair / skin is burnt
Due to larger quantities of sulphur
254
Where is elastin found specifically
• in elastic fibres (along with small protein fibres).
255
Where are elastic fibres found
in walls of blood vessels and in the alveoli of the lungs
256
What do elastic fibres do
• they give these structures flexibility to expand when needed, but also contract to normal size.
257
What structure does elastic have
Quaternary
258
Compare globular and fibrous proteins
Mention shape / amino acid sequence / function / examples / solubility
259
Compare collagen and haemoglobin
Include number of polypeptide chain / shape / type of protein / function / amino acid sequence / prosthetic group / solubility
260
What test is needed for reducing / non-reducing sugars
Benedict’s test
261
Difference between reducing + non reducing sugars
Reducing sugars are carbohydrates that can act as reducing agents due to the presence of free aldehyde groups or free ketone groups.
Nonreducing sugars are carbohydrates that cannot act as reducing agents due to the absence of free aldehyde groups or free ketone groups.
262
Examples of reducing sugars
Galactose
Glucose
Fructose
Maltose
263
Examples of non - reducing sugars
Sucrose
264
What colour is Benedict’s Reagent
Blue
265
What does Benedict’s reagent contain
copper (II) sulphate ions (CuSO4 )
266
What happens to the copper (II) sulphate ions (CuSO4 ) in Benedict’s solution, when in contact with reducing sugars
• copper (I) oxide forms
267
Why does copper (I) oxide form a precipitate
Not soluble in water
268
Method to test for reducing sugars
• Add Benedict's reagent (which is blue as it contains copper (II) sulfate ions) to a sample solution in a test tube – an equal volume of sample
• Heat the test tube in a water bath or beaker of water that has been brought to a boil for a few minutes
Observe colour
269
Positive test - reducing sugar
If a reducing sugar is present, a coloured precipitate will form
270
Why will a coloured precipitate form if a reducing sugar is present in Benedict’s test
• as copper (II) sulfate is reduced to copper (I) oxide which is insoluble in water – reduce copper 2+ ions to Cu+ ions
271
Why is it important to add an excess of Benedict’s solution
• so that there is more than enough copper (II) sulfate present to react with any sugar present
272
What is the colour change for reducing sugars
• from blue (no reducing sugar), through green, yellow and orange (low to medium concentration of reducing sugar) to brown/brick-red (a high concentration of reducing sugar)
273
Why is the reducing sugar test described as semi - quantitative
o as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present
274
Is there’s more reducing sugar…
o more precipitate formed = less Cu blue ions left.
o Hence, the actual colour is a mix of the brick-red precipitate and unchanged blue copper ions, so colour will be different depending on reducing sugar concentration, thus test is qualitative.
275
Method for test for non-reducing sugar
• Add dilute hydrochloric acid to the sample and heat in a water bath that has been brought to the boil
• Neutralise the solution with sodium hydrogencarbonate
o Use a suitable indicator (such as red litmus paper) to identify when the solution has been neutralised, and then add a little more sodium hydrogencarbonate as the conditions need to be slightly alkaline for the Benedict’s test to work
• Then carry out Benedict’s test as normal
Add Benedict’s reagent to the sample and heat in a water bath that has been boiled
276
Why do we add a little more sodium hydrogen carbonate in the non-reducing sugars test
o as the conditions need to be slightly alkaline for the Benedict’s test to work
277
Why do we add hydrochloric acid in the non-reducing sugars test
• The addition of acid will hydrolyse any glycosidic bonds present in any carbohydrate molecules
• The resulting monosaccharides left will have an aldehyde or ketone functional group that can donate electrons to copper (II) sulfate (reducing the copper), allowing a precipitate to form
278
Colour change for Benedict’s test reducing + non-reducing
279
What test is used to identify starch
Iodine test
280
Method to test for starch
• add a few drops of orange/brown iodine in potassium iodide solution to the sample
281
Why do we use potassium iodide when testing for starch
Because iodine by itself is insoluble in water
282
Positive result - iodine starch test
• If starch is present, iodide ions in the solution interact with the centre of starch molecules, producing a complex with a distinctive blue-black/purple-black colour
283
What are reagent strips
• can be used to test for the presence of reducing sugars, most commonly glucose.
284
What type of molecules are lipids
Non-polar
285
Why do we add ethanol when identifying lipids
Cause ethanol is non-polar, so lipids (being non-polar) will dissolve in it
286
What test do we use to identify lipids
Emulsion test
287
Method of emulsion test
• Add ethanol to the sample to be tested
• Shake to mix
• Add the mixture to a test tube of water
288
Emulsion test - positive result
If lipids are present, a milky emulsion will form (the solution appears ‘cloudy’); = on the top layer
the more lipid present, the more obvious the milky colour of the solution
289
Emulsion test - negative result
Solution remains clear
290
Limitations of emulsion test
• This test is qualitative - it does not give a quantitative value as to how much lipid may be present in a sample
291
What test is used to identify proteins
Biuret test
292
What does biuret reagent contain
• an alkali and copper (II) sulphate which react in the presence of peptide bonds
293
Method for biuret test
• Add sodium hydroxide to the food solution sample to make the solution alkaline
• Add a few drops of copper (II) sulfate solution (which is blue) to the sample
o Biuret ‘reagent’ contains an alkali and copper (II) sulfate
• Repeat steps 1 and 2 using the control solution
• Compare the colours of the control solution and the food sample solution
294
Positive result - biuret test
colour change is observed from blue to lilac/mauve
295
The colour change for biuret test can be very subtle - how do we help this
o hold the test tubes up against a white tile when making observations
296
Limitations of biuret test
o For this test to work, there must be at least two peptide bonds present in any protein molecules, so if the sample contains amino acids or dipeptides, the result will be negative
• The Biuret test is qualitative - it does not give a quantitative value as to the amount of protein present in a sample
297
What is an inorganic ion
• an ion that does not contain carbon
298
Where are inorganic ions found
• occur in solution in the cytoplasm and body fluids of organisms
299
What do inorganic ions act as
Co-factors
300
What are cofactors
o non-protein chemical compounds that are required for a protein to function
301
How many bonds does carbon form
4
302
How many bonds does nitrogen form
3
303
How many bonds does oxygen form
2
304
How many bonds does hydrogen form
1
305
What does valency mean
• Number of covalent bonds an atom can make.
306
Cations we need to know
Hydrogen ions
Calcium ions
Iron ions
Sodium ions
Potassium ions
Ammonium ions
307
Chemical symbol + function of hydrogen ions
308
Chemical symbol + function of calcium ions
309
Chemical symbol + function of iron ions
310
Chemical symbol + function of sodium ions
311
Chemical symbol + function of potassium ions
312
Chemical symbol + function of ammonium ions
313
Anions we need to know
Nitrate ions
Hydrogen carbonate ions
Chloride ions
Phosphate ions
Hydroxide ions
314
Chemical symbol + function of nitrate ions
315
Chemical symbol + function of hydrogen carbonate ions
316
Chemical symbol + function of chloride ions
317
Chemical symbol + function of phosphate ions
318
Chemical symbol + function of hydroxide ions
319
320
321
322
323
324
325
326
B
327
A
328
D
329
330
331
332
333
334
A
335
C
336
A
337
C
338
A
339
A
340
341
342
343
344
345
346
347
Two similarities + two differences between this and glycogen
348
349
350
351
What is special about collagen
Every 3rd amino acid is the same
352
Benefit of glycogen being insoluble
Has no effect upon water potential
353
What makes up lactose
Beta glucose + galactose
354
Which proteins are held together by disulphide bridges = quaternary
Insulin + haemoglobin
355
B
356
C
357
C
358
359
360
361
362
363
C
364
D
365
366
367
368
369
370
Colour change for iodine test
Orange / brown to black
371
Is amylose soluble
No
