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Biology - Module 2 > Chapter 3 - Biological Molecules > Flashcards

Chapter 3 - Biological Molecules Flashcards

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1
Q

how are atoms bonded in water

A

with covalent bonds

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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

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3
Q

what atom in water is SLIGHTLY positive

A

hydrogen - a smaller share of electrons in covalent bonds

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4
Q

what atom in water is SLIGHTLY negative

A

Oxygen has the greater share of electrons in covalent

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5
Q

why are many organic molecules polar

A

molecules contain hydroxyl (OH) group

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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

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7
Q

characteristics of hydrogen bonds

A
  • quite weak
    -they break and reform between constantly moving water molecules - viscous
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8
Q

characteristics of water (8)

A
  • solvent
  • cohesive
  • adhesive
  • has surface tension
  • high SHC
  • high latent heat of vaporisation
  • density
  • colourless/ transparent
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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.

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10
Q

example of an ion

A

sodium chloride

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11
Q

example of a covalently bonded polar molecule

A

glucose

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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
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13
Q

what is the cytosol

A

cell liquid if eukaryotic and prokaryotic cells

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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

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15
Q

why is cohesion significant for life

A

plants can draw water through roots/xylem in transpiration

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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

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17
Q

how is surface tension significant for life

A

surface tension is strong enough for some insects e.g., Pond skaters to inhabit

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18
Q

what is adhesion

A

water molecules can be attracted to surfaces such as narrow tubes

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19
Q

how is adhesion significant for life

A
  • causes water to exhibit capillary action
  • water can rise up narrow tubes = transpiration
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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

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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
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22
Q

SHC of water

A

4200 J/kg°C

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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
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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

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25
Q

why does water have a high latent heat of vaporisation

A

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

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26
Q

why is having a high latent heat of vaporisation significant for life

A

– 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
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27
Q

which is more dense - ice or water

A

water

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28
Q

why is ice less dense than water

A

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
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29
Q

what type of bonding is hydrogen bonds

A

intermolecular bonds

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30
Q

at what point when cooling down does water start becoming less dense, instead of more

A

4 degrees Celsius

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31
Q

structure of ice

A

a giant, rigid, open structure

  • Every oxygen at the centre of a tetrahedral arrangement of hydrogen atoms
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32
Q

why is the anomaly in density of water significant for life

A
  • insulates ponds/lakes
  • stops organisms freezing underneath // only surface freezes not whole of ocean
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33
Q

what is a condensation reaction

A

• Joins two molecules together with the formation of a chemical bond, and involves the elimination of a molecule of water

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34
Q

what is a hydrolysis reaction

A

• Breaks a chemical bond between two molecules and involves the use of a molecule of water

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35
Q

what type of reactions are condensation and hydrolysis

A

reversible reaction

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36
Q

What do carbohydrates contain

A

Carbon, Hydrogen and Oxygen

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37
Q

General formula of a carbohydrate

A

Cx(H2O)y

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38
Q

Glucose formula

A

C6H1206

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39
Q

What is a monosaccharides

A

1 unit

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40
Q

What is a disaccharide

A

2 units

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41
Q

What is a polysaccharide

A

Many units

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42
Q

Examples of monosaccharides (3]

A

glucose, fructose, ribose

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43
Q

Examples of disaccharides

A

lactose, sucrose, maltose

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44
Q

Examples of polysaccharides

A

glycogen, starch, cellulose

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45
Q

What is a monosaccharide of 6 carbons called

A

hexose monosaccharide

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46
Q

Example of a become monosaccharide

A

Glucose

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47
Q

How are carbons numbered in a structure diagram

A

carbons are numbered clockwise, beginning with the carbon to the right of oxygen

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48
Q

Is glucose soluble in water

A

Yes

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49
Q

Why is glucose soluble in water

A

due to the hydrogen bonds that form between the hydroxyl groups and water molecules.

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50
Q

Why is solubility for glucose important

A

as it means glucose is dissolved in the cytosol of cell

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51
Q

What are the two isomers of glucose

A

Alpha (α) glucose and Beta (β) glucose

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52
Q

What is an isomer

A

molecules with the same molecular formula but with different structural arrangements of atoms.

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53
Q

What’s the difference between alpha and beta glucose

A

o Alpha has the OH below the C1
o Beta has the OH above the C1

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54
Q

Draw alpha glucose

A
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55
Q

Draw beta glucose

A
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56
Q

What is special about monosaccharides

A

• Same no. of C as O atoms

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57
Q

General formula of monosaccharides

A

(CH2O)n

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58
Q

General properties of monosaccharides

A

• White crystalline solids
• Dissolve in water to form sweet tasing solutions

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59
Q

What can monosaccharides be categorised into

A

Trioses

Tetroses

Pentoses

Hexoses

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60
Q

How many carbons does trioses have

A

3

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61
Q

How many carbons does tetroses have

A

4

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62
Q

How many carbons does pentoses have

A

5

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63
Q

How many carbons does hexoses have

A

6

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64
Q

Example of a triose

A

Glyceraldehyde

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65
Q

Properties of trioses

A

Intermediates in respiration and photosynthesis

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66
Q

Properties of tetroses

A

Rare

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67
Q

Example of pentoses

A

RIBOSE or ribulose

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68
Q

Properties of pentoses (ribose)

A

Used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP

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69
Q

Example of hexoses

A

Glucose or Fructose

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70
Q

Properties of hexoses

A

Used as a store of energy in respiration and as building blocks for larger molecules

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71
Q

How to break down polysaccharides

A

Hydrolysis

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72
Q

How to synthesise polysaccharides / disaccharides

A

Condensation reaction

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73
Q

How do two glucose molecules form a disaccharide

A

Condensation reaction

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74
Q

Describe the process of the condensation reaction of two alpha glucose molecules

A

• 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

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75
Q

What type of bond is formed between a carbon 1 and a carbon 4 in a condensation reaction

A

Covalent - 1,4 glycosidic bond

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76
Q

What molecule is made when two alpha glucose react

A

Maltose

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77
Q

What is requires for a hydrolysis reaction

A

• Requires one water molecule to supply the H and the OH to the sugars formed

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78
Q

Constituent monomers of sucrose

A

a- glucose + fructose

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79
Q

Constituent monomers of maltose

A

a glucose + a glucose

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80
Q

Constituent monomers of lactose

A

Glucose + galactose

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81
Q

What is starch

A

• Main storage polysaccharide in plants

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82
Q

Properties of starch

A

• Pure starch is white, tasteless, and odourless
• It is insoluble in cold water or alcohol

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83
Q

How is starch formed

A

when alpha glucose monomers are joined together by glycosidic bonds during condensation reactions

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84
Q

What are the two constituents of starch

A

Amylose + amylopectin

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85
Q

Approx how much starch is made from amylose

A

o 20-30%

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86
Q

How is amylose formed

A

o Formed by alpha glucose molecules joined only by 1,4 glycosidic bonds

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87
Q

Properties of amylose

A

o long unbranched chains

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88
Q

What specific about the angle of the bond in amylose

A

o angle of bond means that the long chain of glucose twists into a helix, further stabilised by hydrogen bonds

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89
Q

What important about amylose twisting into a helix

A

o makes it more compact and less soluble in comparison to the glucose molecules

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90
Q

How is amylopectin formed

A

o Formed when glycosidic bonds form in condensation reactions between carbon 1 and 6.
o Has both 1,4 and 1,6 glycosidic bonds

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91
Q

What types of bonds make up amylopectin

A

1,4 and 1,6 glycosidic bonds

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92
Q

What does the 1,6 bonds mean in amylopectin

A

Means it has a branched structure with 1,6 branching points occurring approx. 1 in 25 glucose subunits

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93
Q

How often do branching points occur in amylopectin

A

approx. 1 in 25 glucose subunits

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94
Q

How is a branching point formed in amylopectin

A

From 1,6 glycosidic bonds

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95
Q

Why is it important to have branching points

A

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

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96
Q

Where is glycogen found

A

in dense granules in liver cells

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97
Q

What percentage of the mass of a liver does glycogen take up

A

7%

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98
Q

What is glycogen

A

• Main storage polysaccharide in animals and fungi (animal equivalent of starch)

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99
Q

How is glycogen formed

A

when alpha glucose monomers are joined together by glycosidic bonds during condensation reactions

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100
Q

What types of bonds are in glycogen

A

1,4 and 1,6 glycosidic bonds

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101
Q

Which type of bond is responsible for branching

A

1,6

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102
Q

Which forms more branches glycogen or amylopectin

A

Glycogen

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103
Q

Why does glycogen form more branches

A

more compact and less space needed for it to be stored, important as animals are mobile

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104
Q

Properties of glycogen

A

• Insoluble, branched, compact

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105
Q

What is cellulose

A

• Main structural constituent of plant cell walls

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106
Q

Why is it important for plants to have cellulose

A

• 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

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107
Q

What is cellulose made from

A

Beta glucose molecules

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108
Q

Why can’t beta glucose molecules join in the same way alpha can

A

the hydroxyl group on carbon 1 and 4 are too far to react

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109
Q

How do plants solve the problem of beta glucose

A

alternate beta glucose molecules are turned upside down

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110
Q

Properties of cellulose

A

• Unable to coil or form branches – a straight chain is produced (cellulose)

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111
Q

What two types of bonds are formed in cellulose

A

1,4 glycosidic bonds and hydrogen bonds

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112
Q

How are hydrogen bonds formed in cellulose

A

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

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113
Q

What is a cellulose chain called

A

Microfibril

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114
Q

What do microfibrils join together to form

A

Cellulose fibres

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115
Q

Properties of cellulose fibres

A

strong, insoluble, used to make cell walls

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116
Q

What makes up lipids

A

Carbon oxygen and hydrogen

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117
Q

Difference between Lipoids and carbohydrates

A

Lipids have a lot less oxygen

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118
Q

Solubility of lipids

A
  • Insoluble in water = because they are non polar
  • soluble in organic solvents
  • hydrophobic
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119
Q

What is lipids made from

A

3 Fatty acids + 1 glycerol

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120
Q

Do lipids form polymers

A

NO

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121
Q

Examples of lipids

A

Fats
Oils
Cholesterol
Steroids
Phospholipids

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122
Q

Difference between fats and oils

A

• Fats = solid at RT // oils = liquid at RT

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123
Q

What type of molecule are lipids

A

• Macromolecules = large complex molecules

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124
Q

What are the functions of lipids [6]

A

• Energy storage
• Metabolic water source
• Membrane structure
• Water proofing
• Insulation
• Produces hormones

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125
Q

Types of lipids with fatty acids

A

o Triglycerides / Phospholipids / Waxes

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126
Q

Types of lipids without fatty acids

A

o Steroids / cholesterol

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127
Q

How are triglycerides mace

A

made from combining one glycerol molecule with 3 fatty acids, in a condensation reaction

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128
Q

Functional group of glycerol

A

Alcohol

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129
Q

Functional group of fatty acids

A

Carboxylic acid

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130
Q

What is needed when triglycerides are broken down

A

three water molecules need to be supplied to reverse the reaction that formed the triglyceride = hydrolysis reaction

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131
Q

Why is it called triglycerides

A

There are three fatty acids

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132
Q

What bond does triglycerides produce when forming from condensation reaction

A

And ester bond

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133
Q

What else does glycerol + three fatty acids produce in a condensation reaction

A

Three water molecules

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134
Q

What is a saturated fatty acid chain

A

the hydrocarbon chain has only single bonds

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135
Q

What is an unsaturated fatty acid

A

• The hydrocarbon chain consists of at least 1 double bond

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136
Q

What is the name when the lipid has 1 double bond

A

monosaturated

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137
Q

What is the name when the lipid has 2+ double bonds

A

polysaturated

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138
Q

What does the presence of a double bond cause in a lipid

A

causes molecules to bend = therefore not compact = therefore they are liquids/oils rather than fats

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139
Q

Draw a saturated and mono saturated and poly saturated chain

A
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140
Q

Types of unsaturated fat

A

• Unsaturated fat can be either cis or trans

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141
Q

What does cis and trans fat refer to

A

the arrangement of the two hydrogen atoms bonded on to the carbon chain involved in a double bond

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142
Q

What is cis fat

A

hydrogens are on the same side of the double bond

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143
Q

What is trans fat

A

hydrogens are on opposite side of the double bond

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144
Q

Draw a cis fatty acid

A
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145
Q

Draw a trans fatty acid

A
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146
Q

What are phospholipids

A

• Modified triglycerides containing phosphorus, carbon, oxygen and hydrogen

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147
Q

How is the phosphate group added into a phospholipid

A

• One of the fatty acid chains is replaced with a phosphate group

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148
Q

Where are inorganic phosphate ions found

A

In the cytoplasm of every cell

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149
Q

Are phospholipids soluble in water

A

Yes

150
Q

Why are phospholipids soluble in water

A

o Have extra electrons = soluble in water

151
Q

Sketch the chemical structure of a phospholipid

A
152
Q

The structure of phospholipids

A

• Have a non-polar fatty acid tail and a charged phosphate head

153
Q

Property of phospholipid fatty acid tail

A

Non-polar

154
Q

Significance of phospholipid non-polar tail

A

repelled by water = hydrophobic

155
Q

Significance of phospholipid charges head

A

interacts/attracted to water = hydrophilic

156
Q

Significance of BOTH non-polar tail and charged head

A

• 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
Q

Significance of phospholipids forming bilayers

A

• Able to separate an aqueous environment in which cells usually exist from the aqueous cytosol within

158
Q

What are peptides

A

• polymers made up of amino acid molecules (monomers)

159
Q

What does a protein consist of

A

• 1+ polypeptides arranged as complex macromolecules and have specific biological functions

160
Q

What do all proteins contain (biological elements)

A

• carbon, hydrogen, oxygen and nitrogen

161
Q

What is the general structure of an amino acid

A

o An amine group -NH2
o A carboxylic acid group -COOH
o A hydrogen atom
o An R group

162
Q

Draw the general structure of an amino acid

A
163
Q

What do different R groups result in

A

Different amino acids

164
Q

How many amino acids are there

A

20

165
Q

What is formed when 2 amino acids bond

A

Dipeptide

166
Q

What is formed when 3 amino acids bond

A

Tripeptide

167
Q

What is formed when many amino acids bond

A

Polypeptide

168
Q

How are peptides made - overall reaction

A

Condensation reaction

169
Q

How are peptides made - detailed

A

• 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
Q

What is specifically not involved in the formation of peptides

A

R groups

171
Q

What type of bonds are peptides bonds

A

Covalent

172
Q

What is the reaction forming peptides catalysed by

A

by enzyme peptidyl transferase

173
Q

Where is peptidyl transferease found

A

present in ribosomes.

174
Q

What is the primary structure of a protein

A

• sequence of amino acids joined by peptide bonds

175
Q

What determines the primary structure of proteins

A

DNA

176
Q

What is the secondary structure of proteins

A

• occurs when the sequence of amino acids are linked by hydrogen bonds in an alpha helix or beta helix pleated sheet

177
Q

What interacts to form the secondary structure

A

• the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form hydrogen bonds

178
Q

What type of bonds make up the secondary structure

A

Hydrogen bonds

179
Q

What two types of shapes can be made in the secondary structure

A

o α-helix
o β-pleated sheet

180
Q

When does the α-helix shape occur

A

• 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
Q

When does the β-pleated sheet occur

A

• 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
Q

What type of protein mostly has a secondary structure

A

• Most fibrous proteins have secondary structures (e.g. collagen and keratin)

183
Q

What is the secondary structure also known as

A

The protein backbone

184
Q

Why is the secondary structure known as the portion backbone

A

only relates to hydrogen bonds forming between the amino group and the carboxyl group

185
Q

What can hydrogen bonds be broken by in the secondary structure

A

• high temperatures and pH changes

186
Q

What is the tertiary structure in proteins

A

describes the folding of a polypeptide chain, due to the molecular interactions among the R groups of the amino acids

187
Q

What are these molecular interactions in the tertiary structure

A

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
Q

What protein is tertiary structure common in

A

Globular

189
Q

What type of bond is disulphide bond

A

Covalent bond

190
Q

What does disulphide bonds form between

A

two cysteine R groups

191
Q

Why do disulphide bonds only form between two cysteine R groups

A

as this is the only amino acid with a sulphur atom

192
Q

Which type of R group interaction is the strongest

A

Disulphide

193
Q

What can disulphide bonds be broken by

A

Oxidation

194
Q

What do ionic bonds in the tertiary structure form between

A

• form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups

195
Q

What are ionic bonds broken by

A

Changes in pH

196
Q

What do hydrogen bonds form between in the tertiary structure

A

form between strongly polar R groups.

197
Q

What is the weakest type of R group interaction

A

Hydrogen bonds

198
Q

What do hydrophobic interactions form between

A

• form between the non-polar (hydrophobic) R groups within the interior of proteins

199
Q

What is the quaternary structure in a protein

A

• arrangement of two or more polypeptide chains working together as a functional macromolecule

200
Q

Example of a protein with a quaternary structure

A

Haemoglobin

201
Q

What is each polypeptide chain in the quaternary structure referred to as

A

The subunit of the protein

202
Q

Summary table of bonds in the different levels of proteins structures

A
203
Q

Properties of globular proteins

A

• compact, roughly spherical (circular) in shape and soluble in water

204
Q

Why do globular proteins form a spherical shape

A

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
Q

What causes globular proteins to be soluble in water

A

Its arrangement

• the water molecules can surround the polar hydrophilic R groups

206
Q

Example of a globular protein

A

Insulin

207
Q

What is a conjugated protein

A

Globular proteins which contain a prosthetic group.

208
Q

What are prosthetic groups

A

can be lipoproteins, glycoproteins, metal ions or minerals from vitamins.

209
Q

Examples of conjugated proteins

A

Haemoglobin + catalase

210
Q

What prosthetic group does haemoglobin have

A

Haem

211
Q

What is haemoglobin

A

• a globular protein which is an oxygen-carrying pigment found in vast quantities in red blood cells

212
Q

What type of structure is haemoglobin

A

Quaternary

213
Q

How many polypeptide chains does haemoglobin have

A

4

214
Q

What types of polypeptide subunits does haemoglobin have

A

two α–globins and two β–globins

215
Q

What does each subunit in haemoglobin have

A

A prosthetic haem group

216
Q

How are the four subunits held together in haemoglobin

A

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
Q

What makes haemoglobin soluble

A

hydrophilic R groups are facing outwards

218
Q

What does the prosthetic haem group contain

A

iron II ion (Fe2+)

219
Q

What’s the purpose of the iron II ion (Fe2+) in haemoglobin

A

• able to reversibly combine with an oxygen molecule forming oxyhaemoglobin and results in the haemoglobin appearing bright red

220
Q

How many oxygen molecules can each haemoglobin molecule carry

A

• Each haemoglobin with the four haem groups can therefore carry four oxygen molecules (eight oxygen atoms)

221
Q

Why can oxygen be carried round more efficiently when bound to haemoglobin

A

• 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
Q

What is catalase

A

Globular conjugated protein

223
Q

What type of structure does catalyse have

A

Quatenaryb

224
Q

How many prosthetic haem groups does catalase have

A

4

225
Q

What does the presence of iron II in the haem group in catalase allow

A

• allow catalase to interact with hydrogen peroxide and speed up its breakdown.

226
Q

What is hydrogen peroxide

A

• a common by-product of metabolism but is damaging to cells and cell components if allowed to accumulate.

227
Q

What does catalase do

A

Stops hydrogen peroxide accumulating

228
Q

What is insulin

A

Globular protein

229
Q

Where is insulin produced

A

In the pancreas

230
Q

Why must insulin be soluble

A

Hormones transported in bloodstream

231
Q

Why does insulin need a specific shape

A

fits into receptors on cell surface membranes to cause more/less glucose production

232
Q

What does insulin consist of

A

• Consists of 2 polypeptide chains held together by 3 disulphide bridges

233
Q

What are fibrous proteins

A

• long strands of polypeptide chains that have cross-linkages due to hydrogen bonds

234
Q

Properties of fibrous proteins

A

• have little or no tertiary structure
Insoluble in water
Suitable,e for structural roles

235
Q

Why are fibrous proteins insoluble in water

A

Due to a large number of hydrophobic R groups

236
Q

Why are fibrous proteins suitable for structural roles

A

• 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
Q

Examples of fibrous proteins

A

Keratin + elastin + collagen

238
Q

What does keratin make up

A

Hair, nail, horns, feathers

239
Q

Where is elastin found

A

connective tissue, tendons, skin and bone

240
Q

Where is collagen found

A
  • skin, tendons and ligaments
241
Q

Both elastin and collagen are examples of what

A

Connective tissue

242
Q

What is the structure of collagen

A

• 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
Q

How many polypeptide chains in collagen

A

3

244
Q

What are the polypeptide chains held together by in collagen

A

Hydrogen bonds

245
Q

What is the properties of collagen

A
  • forms connective tissue
  • strong + tensile strength
  • stable
  • insoluble
246
Q

Why does collagen have great tensile strength

A

• presence of the many hydrogen bonds within the triple helix structure of collagen results in great tensile strength.

247
Q

Why is collagen strong

A

• The staggered ends of the collagen molecules within the fibrils provide strength

248
Q

Why is collagen stable

A

• 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
Q

Why is collagen insuluble

A

The length of collagen molecules means they take too long to dissolve in water

250
Q

Properties of keratin

A

Strong
Flexible
Insoluble

251
Q

Why is keratin flexible

A

• 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
Q

What determines flexibility

A

Degree of disulphide bonds

253
Q

Why is there an unpleasant smell when hair / skin is burnt

A

Due to larger quantities of sulphur

254
Q

Where is elastin found specifically

A

• in elastic fibres (along with small protein fibres).

255
Q

Where are elastic fibres found

A

in walls of blood vessels and in the alveoli of the lungs

256
Q

What do elastic fibres do

A

• they give these structures flexibility to expand when needed, but also contract to normal size.

257
Q

What structure does elastic have

A

Quaternary

258
Q

Compare globular and fibrous proteins

Mention shape / amino acid sequence / function / examples / solubility

A
259
Q

Compare collagen and haemoglobin

Include number of polypeptide chain / shape / type of protein / function / amino acid sequence / prosthetic group / solubility

A
260
Q

What test is needed for reducing / non-reducing sugars

A

Benedict’s test

261
Q

Difference between reducing + non reducing sugars

A

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
Q

Examples of reducing sugars

A

Galactose

Glucose

Fructose

Maltose

263
Q

Examples of non - reducing sugars

A

Sucrose

264
Q

What colour is Benedict’s Reagent

A

Blue

265
Q

What does Benedict’s reagent contain

A

copper (II) sulphate ions (CuSO4 )

266
Q

What happens to the copper (II) sulphate ions (CuSO4 ) in Benedict’s solution, when in contact with reducing sugars

A

• copper (I) oxide forms

267
Q

Why does copper (I) oxide form a precipitate

A

Not soluble in water

268
Q

Method to test for reducing sugars

A

• 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
Q

Positive test - reducing sugar

A

If a reducing sugar is present, a coloured precipitate will form

270
Q

Why will a coloured precipitate form if a reducing sugar is present in Benedict’s test

A

• as copper (II) sulfate is reduced to copper (I) oxide which is insoluble in water – reduce copper 2+ ions to Cu+ ions

271
Q

Why is it important to add an excess of Benedict’s solution

A

• so that there is more than enough copper (II) sulfate present to react with any sugar present

272
Q

What is the colour change for reducing sugars

A

• 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
Q

Why is the reducing sugar test described as semi - quantitative

A

o as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present

274
Q

Is there’s more reducing sugar…

A

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
Q

Method for test for non-reducing sugar

A

• 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
Q

Why do we add a little more sodium hydrogen carbonate in the non-reducing sugars test

A

o as the conditions need to be slightly alkaline for the Benedict’s test to work

277
Q

Why do we add hydrochloric acid in the non-reducing sugars test

A

• 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
Q

Colour change for Benedict’s test reducing + non-reducing

A
279
Q

What test is used to identify starch

A

Iodine test

280
Q

Method to test for starch

A

• add a few drops of orange/brown iodine in potassium iodide solution to the sample

281
Q

Why do we use potassium iodide when testing for starch

A

Because iodine by itself is insoluble in water

282
Q

Positive result - iodine starch test

A

• 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
Q

What are reagent strips

A

• can be used to test for the presence of reducing sugars, most commonly glucose.

284
Q

What type of molecules are lipids

A

Non-polar

285
Q

Why do we add ethanol when identifying lipids

A

Cause ethanol is non-polar, so lipids (being non-polar) will dissolve in it

286
Q

What test do we use to identify lipids

A

Emulsion test

287
Q

Method of emulsion test

A

• Add ethanol to the sample to be tested
• Shake to mix
• Add the mixture to a test tube of water

288
Q

Emulsion test - positive result

A

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
Q

Emulsion test - negative result

A

Solution remains clear

290
Q

Limitations of emulsion test

A

• This test is qualitative - it does not give a quantitative value as to how much lipid may be present in a sample

291
Q

What test is used to identify proteins

A

Biuret test

292
Q

What does biuret reagent contain

A

• an alkali and copper (II) sulphate which react in the presence of peptide bonds

293
Q

Method for biuret test

A

• 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
Q

Positive result - biuret test

A

colour change is observed from blue to lilac/mauve

295
Q

The colour change for biuret test can be very subtle - how do we help this

A

o hold the test tubes up against a white tile when making observations

296
Q

Limitations of biuret test

A

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
Q

What is an inorganic ion

A

• an ion that does not contain carbon

298
Q

Where are inorganic ions found

A

• occur in solution in the cytoplasm and body fluids of organisms

299
Q

What do inorganic ions act as

A

Co-factors

300
Q

What are cofactors

A

o non-protein chemical compounds that are required for a protein to function

301
Q

How many bonds does carbon form

A

4

302
Q

How many bonds does nitrogen form

A

3

303
Q

How many bonds does oxygen form

A

2

304
Q

How many bonds does hydrogen form

A

1

305
Q

What does valency mean

A

• Number of covalent bonds an atom can make.

306
Q

Cations we need to know

A

Hydrogen ions
Calcium ions
Iron ions
Sodium ions
Potassium ions
Ammonium ions

307
Q

Chemical symbol + function of hydrogen ions

A
308
Q

Chemical symbol + function of calcium ions

A
309
Q

Chemical symbol + function of iron ions

A
310
Q

Chemical symbol + function of sodium ions

A
311
Q

Chemical symbol + function of potassium ions

A
312
Q

Chemical symbol + function of ammonium ions

A
313
Q

Anions we need to know

A

Nitrate ions
Hydrogen carbonate ions
Chloride ions
Phosphate ions
Hydroxide ions

314
Q

Chemical symbol + function of nitrate ions

A
315
Q

Chemical symbol + function of hydrogen carbonate ions

A
316
Q

Chemical symbol + function of chloride ions

A
317
Q

Chemical symbol + function of phosphate ions

A
318
Q

Chemical symbol + function of hydroxide ions

A
319
Q
A
320
Q
A
321
Q
A
322
Q
A
323
Q
A
324
Q
A
325
Q
A
326
Q
A

B

327
Q
A

A

328
Q
A

D

329
Q
A
330
Q
A
331
Q
A
332
Q
A
333
Q
A
334
Q
A

A

335
Q
A

C

336
Q
A

A

337
Q
A

C

338
Q
A

A

339
Q
A

A

340
Q
A
341
Q
A
342
Q
A
343
Q
A
344
Q
A
345
Q
A
346
Q
A
347
Q

Two similarities + two differences between this and glycogen

A
348
Q
A
349
Q
A
350
Q
A
351
Q

What is special about collagen

A

Every 3rd amino acid is the same

352
Q

Benefit of glycogen being insoluble

A

Has no effect upon water potential

353
Q

What makes up lactose

A

Beta glucose + galactose

354
Q

Which proteins are held together by disulphide bridges = quaternary

A

Insulin + haemoglobin

355
Q
A

B

356
Q
A

C

357
Q
A

C

358
Q
A
359
Q
A
360
Q
A
361
Q
A
362
Q
A
363
Q
A

C

364
Q
A

D

365
Q
A
366
Q
A
367
Q
A
368
Q
A
369
Q
A
370
Q

Colour change for iodine test

A

Orange / brown to black

371
Q

Is amylose soluble

A

No

Biology - Module 2 (6 decks)

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