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AQA A Level Biology flashcards > 1A - Biological Molecules > Flashcards

1A - Biological Molecules Flashcards

1
Q

What type of molecule are carbohydrates?

A

Polymers

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2
Q

What are polymers?

A

Large complex molecules made up of long chains of repeating monomers joined together.

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3
Q

What are monomers?

A

Small, basic molecular units.

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4
Q

Give some examples of monomers.

A
  • Monosaccharides
  • Amino acids
  • Nucleotides
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5
Q

What elements do all carbohydrates contain?

A
  • Carbon
  • Hydrogen
  • Oxygen
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6
Q

What are monomers in carbohydrates called?

A

Monosaccharides

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7
Q

What are some examples of monosaccharides?

A
  • Glucose
  • Fructose
  • Galactose
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8
Q

What are some examples of disaccharides?

A
  • Maltose
  • Sucrose
  • Lactose
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9
Q

What type of sugar is glucose?

A

Hexose - it contains 6 carbon atoms.

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10
Q

What are the types of glucose?

A

Alpha (α) and Beta (β)

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11
Q

What can alpha and beta glucose be referred to as?

A

Isomers

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12
Q

What are isomers?

A

Molecules with the same molecular formula as each other but with the atoms arranged differently.

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13
Q

Give an example of isomers.

A

Alpha and beta glucose are isomers.

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14
Q

Remember to practice drawing out the structure of alpha and beta glucose.

A

Pg 2 of revision guide.

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15
Q

Describe the difference between an alpha and beta glucose molecule.

A

The position of the hydroxyl group
In beta glucose its positioned on the right but on top
In Alpha glucose its positioned on the right but on the bottom

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16
Q

What is a condensation reaction?

A

When two molecules join together with the formation of a new chemical bond, and a water molecule is released.

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17
Q

What type of reaction is two monosaccharides joining together?

A

Condensation

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18
Q

What type of bond is formed between two monosaccharides when two monosaccharides join in a carbohydrate?

A

Glycosidic

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19
Q

What is formed when two monosaccharides join?

A

Disaccharide

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20
Q

What monosacchaides join to form maltose?

A

Glucose + Glucose

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21
Q

What monosacchaides join to form sucrose?

A

Glucose + Fructose

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22
Q

What monosacchaides join to form lactose?

A

Glucose + Galactose

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23
Q

What monosacchaides join to form maltose, sucrose and lactose?

A 
Maltose = Glucose + Glucose
Sucrose = Glucose + Fructose
Lactose = Glucose + Galactose
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24
Q

What type of glucose is found in maltose?

A

Alpha

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25
Q

What is found in the middle of a glycosidic molecule?

A

An oxygen atom

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26
Q

Remember to practise drawing a glycosidic bond.

A

Pg 2 of revision guide.

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27
Q

What type of reaction is used to break down a polymer?

A

Hydrolysis reaction

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28
Q

What type of reaction is used to break down and form polymers?

A

Breaking down -> Hydrolysis

Forming -> Condensation

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29
Q

What is a hydrolysis reaction?

A

When a chemical bond is broken by a water molecule.

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30
Q

Remember to practise drawing hydrolysis reactions.

A

Pg 3 of revision guide.

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31
Q

What does the term sugar refer to?

A

Monosaccharides and disaccharides

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32
Q

What is the difference between sugars and carbohydrates?

A
  • Sugars -> Monosaccharides and disaccharides

- Carbohydrates -> Polysaccharides

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33
Q

What is the test for sugars called?

A

Benedict’s test

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34
Q

What are the two types of sugar?

A

Reducing and non-reducing

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35
Q

What are the reducing sugars?

A
  • All monosaccharides

- Some disaccharides (e.g. maltose and lactose)

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36
Q

What are the non-reducing sugars?

A
  • Most disaccharides (e.g. sucrose)
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37
Q

Give some examples of reducing disaccharides.

A

Maltose and lactose

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38
Q

Give some examples of non-reducing disaccharides.

A

Sucrose

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39
Q

Describe the test for reducing sugars.

A
  • Add Benedict’s reagent (blue) to a sample
  • Heat in a water bath that’s been brought to boil
  • If the test is positive -> Orange precipitate
  • If the test is not positive -> Stays blue
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40
Q

Describe how the colour of the precipitate in the test for reducing sugars changes with concentration of the sugar.

A

Blue -> Green -> Yellow -> Orange -> Brick red

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41
Q

Instead of looking at colour change, what is a more accurate way of measuring the sugar concentration?

A

Filtering the solution and weighing the copper oxide precipitate.

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42
Q

Describe the test for non-reducing sugars.

A
  • Add dilute hydrochloride acid to the sample.
  • Heat in a water bath that’s been brought to boil
  • Neutralise with sodium hydrogencarbonate.
  • Carry out normal Benedict’s test for reducing sugars.
  • If test is positive -> Orange precipitate -> Non-reducing sugar present
  • If test is not positive -> Stays blue -> No sugars present at all
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43
Q

Why are two separate tests needed for reducing and non-reducing sugars?

A

A non-reducing sugar will not react with Benedict’s reagent, but it can be hydrolysed into reducing sugars which will react with Benedict’s reagent.

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44
Q

How are polysaccharides formed?

A

When two or more monosaccharides are joined by condensation reactions.

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45
Q

How do plants use starch to store glucose?

A
  • Excess glucose is stored as starch

* When a plant needs glucose, it breaks down the starch into glucose

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46
Q

What are the two types of starch?

A
  • Amylose

* Amylopectin

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47
Q

What are amylose and amylopectin?

A

Polysaccharides of alpha glucose.

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48
Q

What is amylose?

A
  • Type of starch
  • Long, unbranched chains of alpha glucose
  • Coiled structure
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49
Q

Describe the structure of amylose and relate it to its function.

A
  • Long, unbranched chains of alpha glucose.

* Angles of glycosidic bonds give it a coiled structure -> This makes it compact and good for storage.

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50
Q

What type of glucose is starch made up of?

A

Alpha

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51
Q

What is amylopectin?

A
  • Type of starch

* Long, branched chain of alpha glucose

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52
Q

Describe the structure of amylopectin and relate it to its function.

A
  • Long, branched chains of alpha glucose
  • Its side branches allow enzymes that break down the molecule to get to the glycosidic bonds easily -> Energy can be released quickly.
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53
Q

What is the difference between amylose and amylopectin?

A
  • Amylose -> Unbranched, spiral

* Amylopectin -> Branched

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54
Q

How does the structure of starch relate to its function?

A
  • Made of alpha glucose -> Store of glucose for energy
  • Insoluble -> Many glycosidic bonds
  • Spiral shape (amylose) -> Compact
  • Branched (amylopectin) -> More SA for enzymes to release glucose
  • Doesn’t affect osmotic potential -> Water doesn’t enter cells by osmosis, which would cause them to swell
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55
Q

What is the test for starch?

A
  • Add iodine dissolved in potassium iodide solution to sample
  • If starch present -> Turns blue-black
  • If no starch present -> Remains browny-orange
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56
Q

What is the function of glycogen?

A

Excess glucose is stored as glycogen in animal cells.

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57
Q

What type of glucose is starch made up of?

A

Alpha glucose

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58
Q

Describe the structure of glycogen.

A

Highly-branched, long chains of glucose.

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59
Q

How does the structure of glycogen relate to its function?

A
  • Made of alpha glucose -> Store of glucose for energy
  • Insoluble -> Many glycosidic bonds
  • Highly branched -> More SA for enzymes to release glucose
  • Compact -> Efficient storage
  • Doesn’t affect osmotic potential -> Water doesn’t enter cells by osmosis, which would cause them to swell
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60
Q

What is the function of cellulose?

A

Structure in plants -> It is found in cell walls.

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61
Q

What type of glucose is cellulose made up of?

A

Beta glucose

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62
Q

Describe the structure of cellulose.

A
  • Long unbranched chains of beta glucose.

* Chains are linked together by hydrogen bonds -> This forms microfibrils

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63
Q

How does the structure of cellulose relate to its function?

A
  • Insoluble -> Many glycosidic bonds
  • Doesn’t affect osmotic potential -> Water doesn’t enter cells by osmosis, which would cause them to swell
  • Hydrogen bonds -> Cumulative strength
  • Microfibrils -> Cumulative strength
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64
Q

What are the types of lipids?

A
  • Triglycerides

* Phospholipids

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65
Q

Are fatty acids hydrophilic or hydrophobic?

A

Hydrophobic

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66
Q

What is a triglyceride made of?

A
  • 1 glycerol molecule
  • 3 fatty acid molecules

(See pg 6 of revision guide)

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67
Q

Describe the structure of a fatty acid.

A
  • Carbon
  • O and OH attached to the carbon
  • R group hydrocarbon chain attached to the carbon

(See pg 6 of revision guide)

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68
Q

What makes various fatty acids different?

A

The length of the hydrocarbon tail.

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69
Q

What type of bond is formed when a fatty acid joins onto a glycerol molecule (in a triglyceride)?

A

Ester bond

70
Q

How is a triglyceride formed?

A
  • 3 fatty acids join to the glycerol molecule through condensation reactions
  • Ester bonds form

(See diagram pg 6)

71
Q

What are the two types of fatty acid?

A
  • Saturated

* Unsaturated

72
Q

What is a saturated fatty acid?

A

One which does not have any double bonds BETWEEN CARBON ATOMS in the hydrocarbon chain.

73
Q

What is an unsaturated fatty acid?

A

One which has at least one double bond BETWEEN CARBON ATOMS in the hydrocarbon chain.

74
Q

Why are lipids insoluble?

A

The fatty acids in them are hydrophobic.

75
Q

What is a phospholipid?

A

A type of lipid, like a triglyceride except one of the fatty acids is replaced by a phosphate group.

76
Q

What are the parts of a phospholipid molecule?

A
  • 1 glycerol molecule
  • 2 fatty acids
  • 1 phosphate group
77
Q

Which parts of a phospholipid are hydrophobic and hydrophilic?

A
  • Phosphate head -> Hydrophilic

* Fatty acid tail -> Hydrophobic

78
Q

What is the function of triglycerides?

A

Energy storage.

79
Q

What is the function of phospholipids?

A

Bilayers of cell membranes.

80
Q

Describe how the structure of triglycerides relates to their function.

A

Function: Energy storage molecules.
• Long hydrocarbon tails of fatty acids -> Contain lots of chemical energy
• Insoluble -> Don’t affect water potential and cause water to enter by osmosis
• Clump together as insoluble droplets due to hydrophobic fatty acid tails

81
Q

How do triglyceride molecules arrange themselves in water?

A

Form insoluble droplets due to the fatty acid tails repelling water and facing inwards.

(See diagram pg 7 of revision guide)

82
Q

Describe how the structure of phospholipids relates to their function.

A

Function: Bilayers in cell membranes
• Hydrophilic heads and hydrophobic tails cause a double layer to form
• Centre of layer is hydrophobic -> Water-soluble substances cannot pass through easily

83
Q

How do phospholipid molecules arrange themselves in water?

A

Form a double layer with the hydrophilic heads facing out and the hydrophobic tails facing in.

(See diagram pg 7 of revision guide)

84
Q

What is the test for lipids called?

A

The emulsion test.

85
Q

Describe the emulsion test for lipids.

A
  • Shake the sample with ethanol for 1 minute until it dissolves.
  • Pour the solution into water.
  • If lipid present -> Milky emulsion
  • If no lipid present -> No emulsion
86
Q

What are the monomers of proteins?

A

Amino acids

87
Q

What is formed when two amino acids join together?

A

A dipeptide.

88
Q

What is formed when two or more amino acids are joined together?

A

A polypeptide.

89
Q

What are the parts of an amino acid?

A
  • Central carbon atom
  • Hydrogen atom
  • Amino group (NH2)
  • Carboxyl group (COOH)
  • Variable R group
90
Q

How many different amino acids are there in living organisms?

91
Q

What is the difference between various amino acids?

A

The R group

92
Q

What type of bond is formed when two amino acid molecules join (in a polypeptide)?

A

A peptide bond.

93
Q

How is a polypeptide formed?

A
  • Amino acids are joined by condensation reactions

* Peptide bonds are formed

94
Q

Describe the formation of a peptide bond.

A
  • The OH from the carboxyl group and the H from the amino group join to form a water molecule, which is released.
  • A peptide bond is formed between the C and N.

(See diagram pg 8 of revision guide)

95
Q

Describe the formation of an ester bond.

A
  • The H from the OH on one side of the glycerol molecule joins with the OH on the end of the fatty acid to form a water molecule.
  • An ester bond forms with an oxygen in the middle between two carbons.

(See diagram pg 6 of revision guide)

96
Q

What is the primary structure of a protein?

A

The sequence of amino acids in the chain.

97
Q

What is the secondary structure of a protein?

A
  • The coiling of the polypeptide chain due to hydrogen bonding.
  • This can cause it to coil into an alpha helix or fold into a beta pleated sheet.
98
Q

What is the tertiary structure of a protein?

A
  • The more complicated coiling or folding of the polypeptide chain as a result of hydrogen bonding, ionic bonding and disulfide bridges.
  • For proteins made from only a single polypeptide chain, this forms the final 3D structure.
99
Q

What is a disulfide bridge and when is it formed?

A
  • When two molecules of the amino acid cysteine are close together
  • The sulfur atoms in each bond together
  • This is a very strong bond
100
Q

What is the quaternary structure of a protein?

A

The way in which several polypeptide chains are arranged and held together by bonds.

101
Q

What are the main functions of proteins?

A
  • Transport proteins
  • Antibodies
  • Structural proteins
  • Enzymes
102
Q

Describe the structure of enzymes and how this relates to their function.

A

• Usually spherical -> Soluble

Function: Metabolism and synthesis of molecules

103
Q

Describe the structure of antibodies and how this relates to their function.

A

• Made up of two heavy and two light polypeptide chains bonded together
• Have a variable region where the amino acids vary greatly
Function: Immune response

104
Q

Why are enzymes roughly spherical?

A

Due to the tight folding of the polypeptide chains.

105
Q

Describe the structure of transport proteins and how this relates to their function.

A

• Channel proteins contain hydrophilic and hydrophobic amino acids -> Fold protein and allow a channel to form
Function: Transport molecules and ions across membranes

106
Q

Describe the structure of structural proteins and how this relates to their function.

A

• Made of long polypeptide chains, parallel to each other with cross-links -> Strong
Function: Provide strength in tissues

107
Q

Give two examples of structural proteins and where they are found.

A
  • Keratin - Hair and nails

* Collagen - Connective tissue

108
Q

What is the test for proteins called?

A

Biuret test

109
Q

Describe the test for proteins.

A
  • Add a few drops of sodium hydroxide to the sample
  • Add some copper (II) sulphate solution
  • If protein present -> Purple
  • If no protein -> Stay blue
110
Q

What is the positive result for proteins in the Biuret test?

A

The solution turns purple.

111
Q

What is the negative result for proteins in the Biuret test?

A

The solution stays blue.

112
Q

Why is sodium hydroxide added at first during the Biuret test?

A

The test solution needs to be alkaline.

113
Q

What are enzymes?

A

Biological catalysts that speed up chemical reactions.

114
Q

At what level do enzymes act?

A
  • Cellular level

- For the organism as a whole

115
Q

Give an example of when enzymes catalyse a reaction at a cellular level.

A

Respiration

116
Q

Give an example of when enzymes catalyse a reaction in the organism as a whole.

A

Digestion in mammals

117
Q

Do enzymes act only within cells?

A

No, they can catalyse extracellular or intracellular reactions.

118
Q

What two things can enzymes affect within an organism?

A
  • Structures

- Functions

119
Q

Give an example of when enzymes affect structure within an organism.

A

Production of collagen (an important protein in connective tissue of animals)

120
Q

What type of molecule are enzymes?

121
Q

What is the active site of an enzyme?

A

The part where the substrate molecules bind to. It is highly specific.

122
Q

In short, why are enzymes highly specific?

A

Due to their tertiary structure.

123
Q

What is the activation energy of a reaction?

A

The amount of energy that must be supplied to the reactants before the reaction will start.

124
Q

In general, how do enzymes speed up a reaction?

A
  • Lower the activation energy
  • This means the reaction can happen at a lower temperature
  • This increases the rate of reaction
125
Q

What is formed when a substrate binds to the active site of an enzyme?

A

Enzyme-substrate complex

126
Q

How do enzymes lower the activation energy in a reaction where two substrate molecules join?

A

The enzyme holds the molecules together, reducing any repulsion between the molecules so they can bond more easily.

127
Q

How do enzymes lower the activation energy in a breakdown reaction?

A

The enzyme puts a strain on the bonds in the substrate, so the molecule breaks up more easily.

128
Q

What are the two models of enzyme action?

A
  • Lock and Key

- Induced Fit

129
Q

Describe the lock and key model of enzyme action.

A
  • The enzyme’s active site and substrate are complementary
  • The enzyme and substrate come together and bind to form an enzyme-substrate complex, without the enzyme changing shape
  • The products are formed
130
Q

Why was the lock and key model eventually dismissed?

A

The enzyme was found to change shape slightly to bind more tightly to the substrate once an enzyme-substrate complex was formed.

131
Q

Give two reasons why enzymes are so specific.

A

1) Their active site has to be of a near-complementary shape in order for substrate to fit into it
2) The substrate and active site must interact in such a way that the enzyme fits more tightly around the substrate

132
Q

Describe the induced fit model of enzyme action.

A
  • At first the enzyme’s active site and the substrate are not complementary, only near-complementary
  • When the enzyme and substrate come together, they interact so that the active site changes shape slightly and fits more tightly around the substrate
  • This gives a more tight enzyme-substrate complex
  • The products are formed
133
Q

What does an enzyme being specific mean?

A

Only one complementary substrate will fit into the enzyme’s active site.

134
Q

What determines the shape of the active site?

A

The tertiary structure, which is determined by the primary structure.

135
Q

How may the tertiary structure of an enzyme be altered?

A
  • pH
  • Temperature
  • Mutation of a gene that determines the primary structure of the enzyme
136
Q

What factors affect enzyme activity?

A
  • Temperature
  • pH
  • Enzyme concentration
  • Substrate concentration
137
Q

Explain how temperature affects the rate of an enzyme-controlled reaction.

A
  • Up to a point, ROR increases due to the increased kinetic energy -> Collisions are more likely + more of them are likely to happen with sufficient energy to form an E-S complex.
  • After this optimum temperature, ROR decreases due to denaturing of the enzymes, when the active site changes shape due to bonds breaking.
138
Q

Explain how pH affects the rate of an enzyme-controlled reaction.

A
  • The ROR increases up to an optimum pH and then decreases after the optimum pH.
  • Above and below the optimum temperature, the H+ and OH- ions (found in acids and alkalis) affect ionic and hydrogen bonds -> The enzymes are denatured.
139
Q

Explain how enzyme concentration affects the rate of an enzyme-controlled reaction.

A
  • As concentration increases, so does the ROR -> This is because the likelihood of a substrate molecule colliding with an enzyme increases
  • Eventually, the substrate concentration becomes the rate limiting factor -> Every substrate is already in an enzyme
140
Q

Explain how substrate concentration affects the rate of an enzyme-controlled reaction.

A
  • As concentration increases, so does the ROR -> This is because the likelihood of a substrate molecule colliding with an enzyme increases
  • Eventually, the enzyme concentration becomes the rate limiting factor -> Every enzyme is already taken by a substrate
141
Q

Remember to revise the graphs of factors affecting enzyme controlled reactions.

A

Pg 12 of revision guide.

142
Q

What are enzyme inhibitors?

A

Molecules that bind to an enzyme and prevent it catalysing its usual reaction.

143
Q

What are the two types of inhibitor?

A
  • Competitive

* Non-competitive

144
Q

What is a competitive inhibitor and how does it work?

A
  • Competitive inhibitor have a similar shape to that of the substrate molecules
  • They compete with the substrate molecules to bind to the active site (but NO reaction takes place)
  • This blocks the active site so no substrate molecules can fit in
145
Q

Does a reaction take place when a competitive inhibitor binds to an enzyme?

146
Q

Explain how substrate concentration effects the rate of a reaction inhibited by a competitive inhibitor.

A
  • As substrate concentration increases, the effectiveness of the inhibitor decreases and so the ROR increases
  • On a graph, this results in a curve slightly below the normal curve
147
Q

What determines the effectiveness of a competitive inhibitor and why?

A

The relative concentrations of the inhibitor and the substrate -> Because they COMPETE for the active site

148
Q

Describe the graph for the ROR with a competitive inhibitor against substrate concentration.

A

• Like the normal graph, except slightly below it. • The curve reaches the plateau later.

149
Q

Why does an enzyme denature at high temperatures?

A

The bonds in it are broken.

150
Q

What is the optimum pH of most enzymes?

151
Q

What is the optimum pH of pepsin?

152
Q

What is a non-competitive inhibitor and how does it work?

A
  • A molecule that binds to the enzyme away from its active site
  • This changes the active site’s shape so it can no longer fit around a substrate
153
Q

Explain how substrate concentration effects the rate of a reaction inhibited by a competitive inhibitor.

A
  • As substrate concentration increases, the ROR increases, but at a slower rate than without the inhibitor
  • The graph plateaus at a lower ROR and earlier -> Increasing the substrate concentration has no effect since the enzyme activity will still be inhibited
154
Q

How and why are competitive and non-competitive inhibitors affected by an increased substrate concentration?

A
  • Competitive -> Effect is reduced, since it depends on the relative inhibitor and substrate concentrations
  • Non-competitive -> No effect, since the inhibitor and the substrate do not compete for the active site and so inhibition happens equally
155
Q

Describe the graph for the ROR with a non-competitive inhibitor against substrate concentration.

A
  • Below the normal graph

* Plateaus at a much lower ROR

156
Q

Remember to revise competitive and non-competitive inhibitor graphs.

A

Pg 13 of revision guide.

157
Q

What are the two ways of measuring the rate of an enzyme-controlled reaction?

A

1) Measure how fast the product is made

2) Measure how fast the substrate is broken down

158
Q

The rate of a reaction can be measured by looking at how fast the product is made. Give an example of a reaction like this.

A

The breakdown of hydrogen peroxide -> Collecting the volume of oxygen gas produced

159
Q

What is hydrogen peroxide broken down into?

A

Water and oxygen

160
Q

What enzyme catalyses the breakdown of hydrogen peroxide?

161
Q

Describe the experiment by which the rate of the breakdown of hydrogen peroxide can be measured.

A

1) Set up a boiling tube with a delivery tube connected through water to an upturned measuring cylinder.
2) Prepare boiling tubes with the same volume and concentration of H2O2. Add equal volumes of buffer solution.
3) Put each boiling tube and another one containing catalase in a water bath at various temperatures (e.g. 10C, 20C, 30*C, etc.)
4) Add the same volume of catalase to each boiling tube and then attach it to the apparatus set up.
5) Record the volume of oxygen produced in 60s. Repeat at each temperature 3 times and find an average.
6) Calculate the ROR by dividing the volume by the time taken. Units: cm3/s
(See diagram pg 14)

162
Q

The rate of a reaction can be measured by looking at how fast the substrate is broken down. Give an example of a reaction like this.

A

The breakdown of starch to maltose -> Checking if any starch is left

163
Q

What is starch broken down into?

164
Q

What enzyme catalyses the breakdown of starch?

165
Q

Describe the experiment by which the rate of the breakdown of starch can be measured.

A

1) Put a drop of iodine in potassium iodide solution into each well on a spotting tile
2) Mix a certain concentration of amylase and starch in a test tube
3) At regular intervals, put a drop of this into a well
4) Do this until the iodine no longer turns dark blue-black but remains browny-orange (This indicates that no starch remains)
5) Repeat this experiment using different concentrations of amylase, 3 times at each concentration.
(See diagram pg 14)

166
Q

Remember to revise interpreting graphs of enzyme-controlled reactions.

A

Pg 15 of revision guide

167
Q

Describe how to interpret graphs of enzyme-controlled reactions.

A
  • Look at the start of the graph and compare the ROR at different pHs/temperatures
  • Look at the rest of the graph and compare the lines for different pHs/temperatures
168
Q

How can the rate of reaction be calculated from a curved graph of volume of product produced against time?

A
  • Draw a tangent at the right time

* Calculate the gradient of the tangent

169
Q

What is the name for the process when the final product in an enzyme-controlled production sequence inhibits the first enzyme?

A

End product inhibition

170
Q

What is end product inhibition and why is it useful?

A
  • In an enzyme-controlled production sequence, the final product inhibits the first enzyme
  • This ensures that the necessary amount of the product is made
171
Q

Remember to practice drawing out the formation of a triglyceride.

A

Diagram pg 6 of revision guide.

AQA A Level Biology flashcards (19 decks)

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