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Biology A-Level > Biological Molecules (Chapter 2) > Flashcards

Biological Molecules (Chapter 2) Flashcards

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1
Q

What is a biochemical?

A

A chemical involved in a life process

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2
Q

What is metabolism?

A

The name for all biochemical reactions in a living organism

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3
Q

What are anabolic reactions?

A

Reactions that build up more complex molecules

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4
Q

What are catabolic reactions?

A

Reactions that break bigger molecules into smaller components

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5
Q

What is an organic compound?

A

A compound containing carbon and hydrogen as well as other elements

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6
Q

What is the monomer for carbohydrates?

A

Monosaccharide

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7
Q

What is the suffix that suggests a substance is a sugar?

A

-ose

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8
Q

What are carbohydrates made up of?

A

C, H and O

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9
Q

What ratio are H and O present in carbohydrates?

A

2:1

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10
Q

What is the general molecular formula for a carbohydrate?

A

Cx(H2O)y

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11
Q

What is the general molecular formula of a monosaccharide?

A

(CH2O)x

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12
Q

What is a residue?

A

What’s left of monomer when it has joined up with other monomers to make a polymer

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13
Q

Give examples of types of monosaccharides

A

Triose e.g. aldotriose
Pentose e.g. ribose
Hexose e.g. glucose, fructose

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14
Q

What characteristics do monosaccharides have?

A

Polar and sweet

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15
Q

What are the main functions of carbohydrates?

A

Cellular respiration, storage, cell structure

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16
Q

What are the main functions of monosaccharides?

A

They act as respiratory substrates and as monomers for the anabolic synthesis of more complex molecules

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17
Q

What is a respiratory substrate?

A

A molecule that can be used to release energy from respiration

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18
Q

What are the three forms of glucose (learn diagrams as well)?

A

Straight chain, alpha ring, beta ring

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19
Q

What makes alpha and beta glucose different structurally?

A

The position of the OH group on the carbon-1 atom - if it is below the plane, it is alpha glucose, if it is above the plane it is beta glucose

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20
Q

What is maltose made up of?

A

Glucose and glucose

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21
Q

What is sucrose made up of?

A

Glucose and fructose

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22
Q

What is lactose made up of?

A

Glucose and galactose

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23
Q

What is the reaction that combines monosaccharides called?

A

Condensation reaction / condensation polymerisation

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24
Q

Why is a condensation reaction called so?

A

Because a water molecule is formed

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25
Q

What is the bond between two monosaccharides called?

A

A glycosidic bond

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26
Q

When is a glycosidic bond formed?

A

When two adjacent OH groups on different monosaccharides line up and one of them takes an O atom from the other to release a water molecule and then remaining O forms the glycosidic bond

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27
Q

How are polysaccharides formed?

A

Many condensation reactions taking place (condensation polymerisation), making many glycosidic bonds

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28
Q

What is the reverse reaction of condensation?

A

Hydrolysis - the addition of a water molecule

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29
Q

What is the bond in maltose?

A

alpha 1,4 glycosidic bond

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30
Q

What is starch made from?

A

Amylose (most common) and amylopectin (less common

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31
Q

What is amylose and so what is it made up of?

A

poly(alpha 1,4) glucose - made up of poly-alpha-1,4 glucose residues, forming a cylindrical molecule made of a coil of glucose residues
- a polysaccharide

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32
Q

What is amylopectin and how is it made?

A

poly (alpha 1,4) (alpha 1,6) glucose - the majority of the bonds are alpha 1,4 but some are between carbon-1 and carbon-6 which forms side brances
- a polysaccharide

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33
Q

What is starch?

A

The main long term energy store in plants

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34
Q

What benefit is there of starch being largely insoluble?

A

It can be stored in large quantities in cells (in organelles called amyloplasts) without having a significant impact on the water potential of the cell, avoiding osmotic problems

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35
Q

Why is starch less reactive than individual glucose molecules?

A

Because it needs to be hydrolysed to its glucose monomers before chemical reactions occur

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36
Q

Why is glycogen a suitable molecule for storing energy?

A
  • It can be hydrolysed as it is made up of glucose molecules - these molecules can then be used in respiration to release energy
  • It is not water soluble because it is a polysaccharide
  • It is energy dense
  • It is highly branched and compact so can be stored in granules
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37
Q

What is glycogen used for and where is it found?

A

It is a medium-term store of energy

- Mainly stored in muscle and liver cells in animals

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38
Q

What is glycogen made up of?

A

It is a mixture of poly alpha 1,4 glucose and alpha 1,6 glucose but with a higher proportion of branches than amylopectin as it has more alpha 1,6 glucose linkages, making it form granules

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39
Q

Where is cellulose found?

A

In plant cell walls (and photosynthetic protoctists) and is the most abundant organic molecule on the planet

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40
Q

What does cellulose do?

A

It provides strength to the cell and allows cells to support multicellular plants through turgor as a consequence

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41
Q

What is the key difference between cellulose and the other polysaccharides?

A

It is a polymer of beta glucose

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42
Q

Describe the structure of the glucoses in cellulose

A

Successive beta glucose residues are orientated at 180 degrees to allow glycosidic bonds to form between carbon-1 and carbon-4 of adjacent molecules

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43
Q

Why is cellulose so strong?

A

Because of the beta glucose orientations, the H atoms of OH groups are weakly attracted to neighbouring O atoms in the ring of glucose.
The individual H bonds are weak but collectively they provide strength, allowing 60-70 cellulose molecules to align in parallel forming microfibrils.
The microfibrils are bundled into fibres also held together by hydrogen bonds.
Cell walls have many of these fibres, orientated at different angles within several planes, providing greater strength

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44
Q

What is a bonus of cellulose for plants?

A

The beta 1,4 linkages cannot be digested by amylase, cellulase is needed to digest cell walls, which relatively few organisms possess

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45
Q

What is cellulose a major component of in humans?

A

Dietary fibre or roughage

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46
Q

What is the difference between a fat and an oil?

A

Fat is a solid lipid at 25 degrees and oil is a liquid lipid at 25 degrees

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47
Q

What is the structural difference between a fat and an oil?

A

The more H atoms and therefore the more saturated, the more likely it is to be a fat
Oils are more likely to be made up of unsaturated molecules which have one C=C double bond(s)

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48
Q

What are the two types of unsaturated molecule?

A

Monosaturated (one c=c double bond)

Polysaturated (more than one c=c double bond)

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49
Q

What are the two general characteristic of lipids?

A

They are generally hydrophobic and non-polar

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50
Q

What is the basic lipid?

A

A triglyceride

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51
Q

What is the main function of lipids?

A

They act as a long-term energy store in animals

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52
Q

Why are lipids good long term energy stores?

A

The molecules are ‘energy dense’ releasing almost twice as much energy per gram when respired than protein or carbohydrate
This is because they have few oxygen atoms (highly reduced) meaning they can be more fully oxidised during respiration
More potential energy

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53
Q

What are 4 other functions of lipids?

A

Protection - cushioning internal organs from physical impact
Insulation - a layer of fat under the skin (subcutaneous fat) or a thicker layer (blubber) in marine mammals
Buoyancy - mainly in marine mammals
Sources of water - when respired, releasing water as a product, e.g. a camel’s hump stores fat

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54
Q

What examples are there for lipids acting a precursor for the production of other kinds of molecules?

A

Triglycerides can be changed into phospholipids which are essential components of biological membranes
Cholesterol is a precursor used to make hormones such as oestrogen and testosterone

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55
Q

Are triglycerides polymers?

A

No

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56
Q

What is a triglyceride made up of?

A

Several molecules joined together - three fatty acid residues and one glycerol molecule

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57
Q

What is glycerol?

A

An alcohol

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58
Q

How is a triglyceride formed?

A

Each OH group combines with the COOH acid part of a fatty acid and forms an ester bond, releasing water (condensation reaction)

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59
Q

What is the fatty acid part of the triglyceride?

A

It contains an organic acid group COOH at one end and the rest is a long hydrocarbon chain (unsaturated or saturated)

60
Q

What effect does the double bond in an unsaturated fatty acid have?

A

Each double bond introduces a kink in the chain, meaning atoms are further apart, the chemical less dense and more likely to be a liquid (oil) at room temperature

61
Q

What are examples of structural proteins?

A

Fibrous proteins e.g. collagen, keratin, actin and myosin (in muscles), cytoskeleton
They provide support for tissues

62
Q

What are examples of globular proteins?

A

Enzymes, haemoglobin, antibodies, some hormones (e.g. adrenaline and insulin)

63
Q

What are the monomers for protein?

A

Amino acids

64
Q

How many types of amino acid are there?

A

20

65
Q

Describe the basic structure of an amino acid (also learn diagram)

A

An amino acid has an amine group (NH2) and at the other end a carboxylic acid (COOH) and on the middle carbon there is a hydrogen and an ‘R’ group

66
Q

What happens to amino acids in water?

A

The NH2 gains a H+ making this end of the molecule positively charged whilst the COOH loses a H+ forming COO-, making this end negatively charged

67
Q

What is the word for having oppositely charged ends?

A

Amphoteric

68
Q

Do amino acids dissolve in water?

A

Yes and they are ionized

69
Q

What is the ‘R’ group?

A

It is what makes the 20 amino acids different from each other e.g. the simplest is one H atom, but more complex amino acids have complex organic structures
The ‘R’ groups influence the overall solubility and other chemical properties of the amino acids e.g. electrically charged, fully polar, less polar

70
Q

What is the bond in a condensation reaction between amino acids called?

A

A peptide bond

71
Q

How does the peptide bond form?

A

The bond forms between two adjacent amino acids in which the NH2 loses one H atom and the COOH loses the OH, which combine to form water
The remaining link between the two amino acid residues is made up of a C=O and N-H (the peptide bond)

72
Q

What is a dipeptide?

A

The result of a single peptide bond forming between two amino acids

73
Q

What is a polypeptide?

A

A whole series of amino acids linked together by peptide bonds

74
Q

What is a protein?

A

A molecule made up of one or more polypeptide chains

75
Q

What is a macromolecule?

A

A large biological molecule e.g. protein, polysaccharide or nucleic acid

76
Q

What is a monomer?

A

A relatively simple molecule which is used as a basic building block for the synthesis of a polymer
Many monomers are joined together to make the polymer, usually by condensation reactions

77
Q

What is a polymer?

A

A giant molecule made from many similar repeating subunits joined together in a chain
The subunits are monomers

78
Q

What are monosaccharides?

A

Single sugar molecules - they dissolve easily in water to form sweet tasting solutions

79
Q

What are disaccharides?

A

Two monosaccharide residues joined together

80
Q

What are polysaccharides?

A

Polymers whose subunits (monomers) are monosaccharides

81
Q

What are reducing sugars?

A

All monsaccharides e.g. glucose

Some disaccharides e.g. maltose

82
Q

What is the only common non-reducing sugar?

A

Sucrose

83
Q

What test is used to detect reducing sugars?

A

Benedict’s test with Benedict’s reagent

84
Q

What are the colours for Benedict’s test?

A

Blue to brick red

85
Q

How would you carry out a Benedict’s test?

A

1) Add excess Benedict’s reagent to the solution and put it in a water bath (heat)
2) If a reducing sugar is present, the solution will gradually turn through green, yellow, orange to red-brown as the insoluble copper oxide forms as a precipitate
3) Then you can estimate the concentration using colour standards by comparing to the colour of known concentrations or by using a colorimeter

86
Q

What is the test for non-reducing sugars?

A

The disaccharide is first broken down into its two monosaccharide constituents by hydrolysis which can be brought about by HCl
The constituent monosaccharides will be reducing sugars and their presence can be detected by Benedict’s test after the acid has been neutralised

87
Q

How would you carry out a test for non-reducing sugars?

A

Heat the sugar solution with HCl, releasing free monosaccharides
Benedict’s reagent needs alkali conditions to work, so neutralise the solution by adding an alkali (e.g. NaOH)
Carry out Benedict’s test and look for a colour change
If the solution goes red now but didn’t when tested before hydrolysis, there is a non-reducing sugar
If both a reducing and non-reducing sugar are present, the precipitate obtained will be heavier than the one obtained in Benedict’s test

88
Q

How do you test for starch?

A

Add a drop of iodine solution to a solid or liquid sample

If starch is present the iodine solution will turn blue/black from orange/brown

89
Q

How does the iodine test work?

A

Starch molecules tend to curl up into long spirals
The hole that runs down the middle of the spiral is just the right size for iodine molecules to fit into
The starch-iodine complex that forms has a strong blue-black colour

90
Q

What is the primary structure of a protein?

A

The number, sequence and type of amino acids in polypeptide chain

91
Q

What are phospholipids?

A

A special type of lipid - one of the three fatty acid tails is replaced by a phosphate group which is hydrophilic whilst the two remaining tails are still hydrophobic
So one end is hydrophilic and the other is hydrophobic

92
Q

What is the secondary structure of a protein?

A

The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids, e.g. an alpha helix or beta pleated sheet

93
Q

What are the two types of secondary structure?

A

Alpha helix or beta pleated sheet

94
Q

What happens to form an alpha helix?

A

A polypeptide chain coils into a corkscrew shape due to hydrogen bonding between the O of the CO group of one amino acid and the H of the NH group of the amino acid four places ahead of it

95
Q

What happens to form a beta pleated sheet?

A

Hydrogen bonds between amino acids that are further apart, resulting in a looser, straighter shape

96
Q

What are characteristics of hydrogen bonds?

A

Strong enough to hold the secondary structures in place but are easily broken by high temperatures and pH changes

97
Q

What is the tertiary structure?

A

The compact structure of a protein molecule resulting from the three-dimensional coiling of the already folded chain of amino acids

98
Q

What kinds of protein need a tertiary structure?

A

Proteins with complex functions e.g. enzymes, membrane proteins and myoglobin

99
Q

What are the four times of bonds between non-adjacent amino acids that stabilise the tertiary structure?

A

Hydrogen bonds
Disulfide bonds
Ionic bonds
Weak hydrophobic interactions

100
Q

Describe hydrogen bonding in the tertiary structure

A

Hydrogen bonds form between strongly polar groups e.g. NH, CO and OH

101
Q

Describe disulfide bonding in the tertiary structure

A

Disulfide bonds form between cysteine molecules (which contain sulfur in their R groups) - they are strong covalent bonds and can be broken by reducing agents

102
Q

Describe ionic bonding in the tertiary structure

A

Ionic bonds form between ionised amine (NH3+) groups and ionised carboxylic acid (COO-) groups - they can be broken by pH changes

103
Q

Describe weak hydrophobic interactions in the tertiary structure

A

Weak hydrophobic interactions occur between non-polar R groups - although the interactions are weak, the groups tend to stay together because they are repelled by the watery environment around them

104
Q

What is the quaternary structure?

A

The association of different polypeptide chains - the chains are held together by the same four types of bond as in the tertiary structure

105
Q

What is a globular protein?

A

A protein whose molecules curl up into a ‘ball’ shape, normally so that their non-polar hydrophobic R groups point into the centre of the molecule, away from watery surroundings
Hydrophilic R groups are on the outside of the molecule so globular proteins are usually soluble

106
Q

What is haemoglobin?

A

A globular protein that is the oxygen carrying pigment found in red blood cells

107
Q

Describe the basic structure of haemoglobin

A

It is made up of four polypeptide chains so it has a quaternary structure
Each chain itself is a protein known as globin
The two types of globin used to make haemoglobin are alpha-globin and beta-globin
Two of the haemoglobin chains (alpha chains) are made from alpha globin and the other two chains (beta chains) are made from beta globin

108
Q

Describe the shape of haemoglobin

A

The haemoglobin molecule is nearly spherical - the four polypeptide chains pack closely together, the hydrophobic R groups pointing in towards the centre of the molecule and the hydrophilic ones pointing outwards

109
Q

Why are the interactions between the hydrophobic R groups in haemoglobin important?

A

They hold it in its correct 3D shape

110
Q

Why are the outward pointing hydrophilic R groups on the surface of the molecule important?

A

They maintain its solubility

111
Q

What does each polypeptide chain of haemoglobin contain?

A

A haem group

112
Q

What is a prosthetic group?

A

An important, permanent part of a protein but is not made of amino acids e.g. a haem group

113
Q

What is the haem group and what does it do?

A

Each haem group contains an iron atom
One O2 molecule can bind with each iron atom
So a complete haemoglobin molecule, with four haem groups, can carry four O molecules (eight O atoms) at one time

114
Q

What else is the haem group responsible for?

A

The colour of haemoglobin - the colour changes depending on whether or not the iron atom are combined with oxygen, if they are the molecule is called oxyhaemoglobin and is bright red, if not the colour is purplish

115
Q

What is collagen?

A

The most common protein found in mammals

It is an insoluble fibrous protein and an important structural protein

116
Q

Where is collagen found?

A

Skin, tendons, cartilage, bones, teeth and the walls of blood vessels

117
Q

Describe the basic structure of collagen

A

Three polypeptide chains, each in the shape of a helix, are wound round each other, forming a three-stranded ‘rope’ or ‘triple helix’

118
Q

How are the three chains in a collagen molecule held together?

A

Hydrogen bonds and some covalent bonds

119
Q

Why is almost every third amino acid in each polypeptide glycine, the smallest amino acid?

A

Its smalls size allows the three strands to lie close together, forming a tight coil - any other amino acid would be too large

120
Q

How do fibrils form?

A

Each complete, three-stranded molecule of collagen interacts with other collagen molecules running parallel to itself
Covalent bonds form between the R groups of amino acids lying next to each other
These cross-links hold many collagen molecules side by side, forming fibrils

121
Q

Why are the ends of parallel collagen molecules staggered?

A

If they were not, there would be a weak spot running right across the collagen fibril

122
Q

What are fibres?

A

Strong bundles formed by many fibrils lying alongside each other

123
Q

What is the advantage of the structure of collagen?

A

It is flexible but has tremendous tensile strength, meaning it can withstand large pulling forces without breaking

124
Q

How do collagen fibres line up?

A

According to the forces they must withstand

125
Q

How do collagen fibres line up in tendons?

A

In parallel bundles along the length of the tendon, the direction of tension

126
Q

How are collagen fibres arranged in skin?

A

They may form layer, with the fibres running in different layers, like cellulose in cells walls, resisting tensile forces from many directions

127
Q

What is the test for proteins?

A

Biuret test

128
Q

How would you carry out the Biuret test?

A

Biuret reagent is added to the solution
A purple colour indicated that protein is present
The colour develops slowly after a few minutes

129
Q

What is an ester?

A

A chemical produced by the reaction if an acid and an alcohol

130
Q

What is a glyceride?

A

An ester formed by the fatty acid combining with the alcohol glycerol (which has 3 hydroxyl groups)

131
Q

What is an ester bond?

A

The chemical link between the acid and the alcohol

132
Q

When are lipids insoluble?

A

In water

133
Q

When are lipids soluble?

A

In ethanol, ether and chloroform

134
Q

What is the test for lipids?

A

The emulsion test

135
Q

How would you carry out the emulsion test?

A

1) Shake the substance vigorously with some absolute ethanol - this allows any lipids in the substance to dissolve in the ethanol
2) The ethanol is then poured into a tube containing water - if lipid is present, a cloudy white suspension is formed

136
Q

Why is water a good solvent for polar molecules and ions?

A

The water molecules are attracted to them and so collect around the polar or ionic molecules, separating them

137
Q

What happens to non-polar, hydrophobic molecules in water?

A

If surrounded by water, they push together as the water molecules are attracted to each other - increases the stability of membrane structures

138
Q

How is water used as a transport medium?

A

Water is the transport medium in the blood, the lymphatic, excretory and digestive system of animals, and the vascular tissue of plants

139
Q

Why does water have a high specific heat capacity?

A

Because the hydrogen bonds between water molecules must be broken to allow free movement and this requires a high amount of energy
So hydrogen bonding allows water to store more energy than would be possible for the given temp rise

140
Q

Why is the high specific heat capacity of water useful?

A

1) It makes water more resistant to changes in temp - so the temp within cells and the bodies of organisms tend to be more constant than that of the air around them
2) Biochemical reactions operate at relatively constant rates and are less likely to be adversely affected by extremes of temperature
3) Large bodies of water (lakes, oceans) are slow to change temperature as environmental temp changes - provides more stable habitats for aquatic organisms

141
Q

Why does water have a high latent heat of vaporisation?

A

Because of its high heat capacity - the fact that water molecules stick together by hydrogen bonds means that relatively large amounts of energy are needed for vaporisation to occur, because the bonds have to be broken before molecules can escape as a gas
It also means that the energy transferred to water molecules during vaporisation means a loss of energy from their surroundings, cooling it down

142
Q

Why is the high latent heat of vaporisation of water important?

A

Living organisms can use evaporation as a cooling mechanism (sweating or panting in mammals)
Large amounts of heat energy can be lost for relatively little loss of water, reducing the risk of dehydration e.g. cooling of leaves during transpiration

143
Q

What bonds are there between water molecules?

A

Hydrogen bonds

144
Q

Why does water have hydrogen bonds?

A

In water, the O with a slight negative charge of one molecule is attracted to the slight positive charge of hydrogen on another molecule

145
Q

Why is water a polar molecule?

A

H2O has a dipole - the O atom has a slight negative charge because it is more electronegative, so the electrons in the covalent bond are more attracted to the O and therefore the H atoms have a slight positive charge

146
Q

What does the cohesive nature of water mean?

A

That it is a liquid at room temperature and can contain life and other molecules, making it a suitable external and internal environment

Biology A-Level (44 decks)

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