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A-level Biology > 3 - Biological Molecules > Flashcards

3 - Biological Molecules Flashcards

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1
Q

What makes up molecules?

A

Atoms

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2
Q

What are different types of atoms called?

A

Elements

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3
Q

What distinguishes different elements from one another?

A

the number of protons in their atomic nuclei

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4
Q

How many bonds can carbon make?

A

4

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5
Q

How many bonds can nitrogen make?

A

3

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6
Q

How many bonds can oxygen make?

A

2

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7
Q

How many bonds can hydrogen make?

A

1

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8
Q

What is methane’s formula?

A

CH4

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9
Q

What is ammonia’s formula?

A

NH3

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10
Q

What are ions in solutions called?

A

electrolyte

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11
Q

Cations

What is calcium necessary for?

Ca2+

A
  • nerve impulse transmission
  • muscle contraction
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12
Q

Cations

What is sodium necessary for?

Na+

A
  • nerve impulse transmission
  • kidney function
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13
Q

Cations

What is potassium necessary for?

K+

A
  • nerve impulse transmission
  • stomatal opening
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14
Q

Cations

What is hydrogen necessary for?

H+

A
  • catalysis of reactions
  • pH determination
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15
Q

Cations

What is ammonium necessary for?

NH4 +

A
  • production of nitrate ions by bacteria
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16
Q

Anions

What are nitrate ions necessary for?

NO3 -

A
  • nitrogen supply to plants for amino acid and protein fomration
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17
Q

Anions

What are hydrogen carbonate ions necessary for?

HC03 -

A
  • maintenance of blood pH
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18
Q

Anions

What are chloride ions necessary for?

Cl-

A
  • balance positive charge of sodium and potassium ions in cells
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19
Q

Anions

What are phosphate ions necessary for?

PO4 3-

A
  • cell membrane formation
  • bone formation
  • nucleic acid and ATP formation
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20
Q

Anions

What are hydroxide ions for?

OH-

A
  • catalysis of reactions
  • pH determination
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21
Q

What elements are present in carbohydrates?

A

carbon, hydrogen and oxygen

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22
Q

What elements are present in lipids?

A

carbon, hydrogen and oxygen

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23
Q

What elements are present in proteins?

A

carbon, hydrogen, oxygen, nitrogen and sulfur

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24
Q

What elements are present in nucleic acids?

A

carbon, hydrogen, oxygen, nitrogen and phosphorus

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25
Q

What monomers make up carbohydrates?

A

sugars (saccharides)

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26
Q

What monomers make up proteins?

A

amino acids

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27
Q

Define polarity

A

The uneven distribution of charges

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28
Q

How is water a polar molecule?

A
  • oxygen has a negative charge
  • two hydrogen have two positive charges
  • positive and negative regions of the molecule attract each other and form hydrogen bonds
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29
Q

Define a hydroxyl group (OH)

A

Organic molecules containing oxygen and hydrogen bonded together

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30
Q

Why is water’s bp unusual?

A

Very hugh

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31
Q

Why is water a liquid at room temp. despite being a small molecule?

A

due to hydrogen bonding between water molecules - takes a lot of energy to increase the temp

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32
Q

What is water’s density when it freezes?

A

Less dense as ice

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33
Q

What happens as water cools below 4°C?

A

hydrogen bonds fix the positions of polar molecules slightly further apart than normal

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34
Q

What is made when water cools below 4°C?

A

A giant, rigid, but open structure with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms

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35
Q

Why does water move as one mass?

A

Due to cohesion as molecules are attracted to one anofjer

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36
Q

Why is water attracted to other molecules?

A

Adhesion

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37
Q

What is a property of water from strong cohesion?

A

gives water a “skin” of surface tension

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38
Q

Why is water an efficient transport medium in living things?

A

cohesion between water molecules means that water and molecules stick together

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39
Q

What are the effects of adhesion and cohesion on water?

A

Capillary action - process by which water can rise up a narrow tube against the force of gravity

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40
Q

Why is water important for temperature?

A

Acts as a coolant so controls organisms temperature as it is a stable substance

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41
Q

Why is surface tension important on water?

A

Provides a habitat to support small insects such as pond skaters

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42
Q

What is the general formula for carbohydrates?

A

Cx(H2O)y

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43
Q

What is a single sugar unit called?

A

monosaccharide

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44
Q

Give examples of monosaccharides

A

glucose, fructose, ribose

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45
Q

What are two monosaccharides called?

A

disaccharide

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46
Q

Give examples of disaccharides

A

lactose, sucrose

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47
Q

What are more than two monosaccharides joined together called?

A

polysaccharide

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48
Q

Give examples of polysaccharides

A

glycogen, cellulose, starch

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49
Q

Formula of glucose

A

C6H12O6

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50
Q

In molecular structured diagrams, how are the carbon atoms numbered?

A

clockwise, beginning with the carbon to the right of the oxygen atom within the ring

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51
Q

What are the types of glucose and how do they vary?

A

Alpha and beta glucose vary in their position of the OH group on carbon 1

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52
Q

Properties of glucose

A

polar, soluble due to hydrogen bonds between hydroxyl group

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53
Q

What happens when 2 alpha glucose molecules are side by side?

A

two hydroxyl groups interact, breaking bonds and reforming them in different places = produces new molecules

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54
Q

What happens in a condensation reaction?

A
  • 2 hydrogen atoms and 2 oxygen atoms are removed from glucose monomers and join to form water
  • bond forms between carbons 1 and 4 on glucose for example, joining molecules
  • ## covalent bond called glycosidic bond forms between two glucose
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55
Q

Define a condensation reaction

A

when a water molecule is formed as one of the products of the reaction

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56
Q

Give examples of hexose monosaccharides

A

fructose, galactose, glucose

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57
Q

What forms the disaccharide lactose (milk)?

A

galactose and glucose

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58
Q

What forms the disaccharide sucrose (cane sugar)?

A

fructose and glucose

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59
Q

What is ribose present in?

A

ribose is sugar in RNA nucleotides and deoxyribose is the sugar in DNA nucleotides

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60
Q

What are pentose monosaccharides?

A

sugars containing 5 carbon atoms

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61
Q

What is starch?

A

Glucose made by plants is stored as starch as it isa chemical energy store

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62
Q

Name a polysaccharide in starch

A

amylose

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63
Q

How is amylose formed?

A

by alpha glucose molecules joined together only by 1-4 glycosidic bonds

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64
Q

What makes amylose more compact and less soluble than glucose?

A

angle of 1-4 glycosidic bond means long chain of glucose twists to form a helix, which is stabilised by hydrogen bonding

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65
Q

Which starch polysaccharide is made by 1-4 glycosidic bonds between alpha glucose molecules, but formed by condensation reactions?

A

Amylopectin

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66
Q

Where are the condensation reactions on amylopectin and how does this affect it?

A

between carbon 1 and carbon 6 on two glucose molecules, meaning it has a branched structure

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67
Q

What is the animals and fungi equivalent to starch?

A

glycogen

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68
Q

How is glycogen’s branching imporant in its storage?

A

it can be coiled very compactly, meaning less sace is needed to store it

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69
Q

What are the key properties of amylopectin and glycogen?

A

insoluble, branched and compact

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70
Q

Why does the branching glycogen help?

A

means there are many free ends where glucose molecules can be added or removed, speeding up the process of storing or releasing glucose

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71
Q

How is starch/glycogen released for respiration?

A

in a hydrolysis reaction, requring the addition of water molecules

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72
Q

What catalyses hydrolysis reactions?

A

enzymes

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73
Q

Can beta glucose molecules join in the same way as alpha glucose?

A

No, the only way that beta glucose molecules can join together and form a polymer is if alternate beta glucose molecules are turned upside down

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74
Q

What is a straight chain molecule of beta glucose called, and what are its properties?

A

cellulose - it is unable to coil or form branches

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75
Q

How are microfibrils formed?

A

when cellulose molecules make hydrogen bonds with each other

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76
Q

What happens when microfibrils join together?

A

macrofibrils are formed, which combine to produce fibres

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77
Q

Why is cellulose imporant to our diet?

A

it is hard to break down, and forms fibre necessary for healthy digestive system

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78
Q

What is the chemical test for sugar?

A

Benedict’s reagent, an alkaline solution of copper(II) sulfate

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79
Q

How is a Benedict’s reagent test carried out?

A
  • place sample in a boiling tube (grind it up or blend in water if its a solid)
  • add an equal volume of Benedict’s reagent
  • heat the mixture gently in boiling water bath for 5 mins
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80
Q

How will reducing sugars react in Benedict’s reagent?

A

will react with copper ions, resulting in the addition of electrons to the blue Cu2+ ions, reducing them to brick red

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81
Q

What is the result of a reducing sugar test?

A

a brick-red precipitate is formed - the higher the conc. of reducing sugar, the less blue Cu2+ ions left

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82
Q

What is the most common non-reducing sugar

A

Sucrose

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83
Q

What is the test for non-reducing sugars

A
  • first boil sugar with dilute HCL
  • this will give it a positive result when then mixed with benedicts
  • this is because the sugar has been hydrolysed by the acid to its monosaccharides
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84
Q

What is the test for starch?

A

Iodine test - add a few drops of iodine dissolved in potassium iodide solution

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85
Q

What is the result for the iodine test for starch?

A

yellow/brown to purple/black

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86
Q

Why are manufactured reagent strips good?

A

the concentration of the sugar can be determined using the colour-coded chart

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87
Q

What are biosensors?

A

use biological components to determine the presence and conc. of molecules such as glucose

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88
Q

How does a colorimeter work?

A

quantitatively measures the absorbance, or transmission of light by a coloured solution

more conc a solution = more light it will absorb

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89
Q

What are the building blocks of proteins?

A

Amino acids

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90
Q

What does every amino acid possess in its structure?

A

An amino group and a carboxylic acid group

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91
Q

How many naturally occurring amino acids are there?

A

20

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92
Q

What bond is formed when amino acids join together?

A

Peptide bond

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93
Q

What is formed when two amino acids bond during a condensation reaction?

A

A dipeptide molecule

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94
Q

What enzymes catalyse the condensation reaction of amino acids to form peptides?

A

Peptidyl transferase found in ribosomes

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95
Q

What enzyme catalysed the hydrolysis reaction, turning peptides back into amino acids?

A

Proteases

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96
Q

What are R groups in proteins?

A

A variable group

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97
Q

How can amino acids be neutral molecules?

A

When the amino acids possesses one acid (carboxylic acid) and one basic group (amino group)

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98
Q

How can amino acids be acidic molecules?

A

When the R group is a carboxylic acid group. It thus has 2 acidic and 1 basic group

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99
Q

How can amino acids be basic molecules?

A

When the R group is an amino group. It thus has 2 basic groups and 1 acidic hroup

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100
Q

Name the two sulphur-containing amino acids

Sulfur is in the R-group

A

Cysteine and Methionine

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101
Q

Define hydrogen bonds in proteins

A

Formed between R-groups; easily broken but numerous

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102
Q

Define disulphide bonds in proteins

A

Formed between sulfur-containing amino acids; strong bonds important in structural proteins (eg.skin/hair)

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103
Q

What are long, thin proteins called that are insoluble and structural?

A

Fibrous

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104
Q

What are proteins rolled into a ball, that are soluble and important in metabolism called?

A

Globular

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105
Q

Protein Structure

What is the primary structure?

A

Is the number, type, order and sequence of amino acids that make up this linear chain together with peptide bonds

106
Q

Protein Structure

Define the general secondary structure

A

The arrangement in space of the atoms that form the backbone or linear chain of the protein

107
Q

Protein Structure

What is the alpha helix secondary structure?

A
  • Amino acid chain coils into a right handed helix
  • hydrogen bonds form between oxygen and hydrogen atoms that have been brought into close proximity
  • hydrogen bonds stabilise structure
108
Q

Protein Structure

What is the beta-pleased secondary structure?

A
  • amino acid folds back upon itself lots forming anti-parallel chains
  • oxygen and hydrogen atoms brought into close proximity form hydrogen bonds
  • hydrogen bonds stabilise structure
109
Q

Which proteins display tertiary structure?

A

Globular proteins

110
Q

Protein Structure

What is the tertiary structure?

A

Folding of a protein into its final shape

Once the secondary structures have formed, the molecule bends and folds into a 3D globular shape

111
Q

Define ionic bonds in proteins

A

Stronger than hydrogen bonds and fork between oppositely charged R-groups

112
Q

Define hydrolysis

A

The type of reaction that occurs when water is added to break a bond in a molecule

113
Q

Define hydrophilic

A

The phosphate group of a phospholipid that readily attracts water molecules

114
Q

Define hydrophobic

A

Substances that can’t become part of water’s hydrogen-bonded structure will not dissolve

115
Q

Protein Structure

When is quaternary structure shown?

A

A level of structure displayed by proteins that consist of more than one polypeptide chain

116
Q

Give an example of a protein with quaternary structure?

A

Haemoglobin

  • consists of 4 polypeptide chains that are held together by weak forces
117
Q

In haemoglobin, what does each polypeptide chain contain?

A

an iron containing a haem group that binds to molecules of oxygen

118
Q

What happens with hydrophobic R groups in proteins?

A

Tend to cluster towards the interior of the protein mowlcule

119
Q

Name a protein that has tertiary structures & where is it found?

A

Myoglobin is found in muscle cells

120
Q

Give examples of biological processes requiring energy

A

Muscle contraction, cell division, the transmission of nerve impulses, memory formation

121
Q

Cell require energy for what 3 main types of activity

A
  • synthesis
  • transport
  • movement
122
Q

How is energy supplied inside cells in a way it can be used?

A

Adenosine triphosphate (ATP)

123
Q

What composed an ATP molecule?

A

A nitrogenous base, a pentose sugar and 3 phosphate groups - it is a nucleotide

124
Q

What is the base and the sugar in ATP?

A

Base = adenine
Sugar = ribose

125
Q

What is ATP known as?

A

Universal energy currency

126
Q

How much energy is released to break the bond holding the last phosphate group in ATP?

A

Small amount of energy as the bond is weak

127
Q

How much energy is released when the free phosphate in ATP undergoes other reactions involving bond formation?

A

A large amount of energy

128
Q

Overall, how much more energy is released than used in ATP?

A

30.6 kJ / mol

129
Q

Why is the removal of the phosphate group in ATP a hydrolysis reaction?

A

As water is a reactant

130
Q

Where does the hydrolysis of ATP happen?

A

In association with energy-requiring reactions - reactions are said to be “coupled” as they happen simultaneously

131
Q

What are the products of the hydrolysis of ATP?

A

Adenosine diphosphate (ADP) + a phosphate ion + energy

132
Q

Why is ATP not a good long-term energy source, and what is a better source?

A

The phosphate bonds are too unstable. A better source would be fats and carbs

133
Q

What is phosphorylation?

A

Reattaching a phosphate group to an ADO molecule to create ATP. It is a condensation reaction as water is removed

134
Q

Why is ATP a good immediate energy source?

A

The inter conversion of ATP and ADP is rapid and constant in living cells

135
Q

What are the properties of ATP?

A
  • small = moves easily in/out of cells
  • soluble
  • easily regenerated
  • releases energy in small quantities
  • contains bonds between phosphates with intermediate energy = large enough to be useful but not so large that energy is wasted
136
Q

What will affect how amino acids and proteins ionise?

A

The hydrogen ion concentration (pH)

137
Q

What type of ions are most amino acids?

A

Cations

138
Q

Define an Iso-electric point (IEP)

A

the pH at which the amino acids or proteins carry no net charge

139
Q

What state are different lipids at room temperature?

A

Fats = solid
Oils = liquid

140
Q

What are macromolecules?

A

Large, complex molecules which are not built from repeating units or monomers

Eg. Lipids

141
Q

Are lipids polar molecules?

A

No as the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar molecules

142
Q

What makes up a triglyceride?

A

One glycerol molecules and 3 fatty acids

143
Q

Which group does glycerol beli to?

A

Alcohols

144
Q

Which group do fatty acids being to?

A

Carboxylic acids

145
Q

How does esterification (condensation) occur in lipids?

A

Hydroxyl groups interact, producing 3 waters and ester bonds between fatty acids and glycerol

146
Q

What is it called when a fatty acid chain has no double bonds with carbon atoms, and is full of hydrogen?

A

Saturated

147
Q

What is it called when a fatty acid has double bonds between some of the carbon atoms?

A

Unsaturated

148
Q

What is it called if a fatty acid has only 1 double bonds

A

Monounsaturated

149
Q

What is it called when a fatty acid has 2 or more double bonds?

A

Polyunsaturated

150
Q

What does the presence of double bonds in fatty acids cause?

A

The molecule can’t link or bend, so they can’t pack closely together = why they are liquid at room temp

151
Q

What lipids do plants contain?

A

Unsaturated triglycerides (healthy oils)

152
Q

What can excess saturated fats in a diet lead to?

A

Coronary heart disease / obesity

153
Q

What are phospholipids?

A

modified trig. and contain phosphorus, carbon, hydrogen, and oxygen

154
Q

Where can you find organic phosphate ions in a cell?

A

In the cytoplasm

155
Q

Why are phosphate ions soluble in water?

A

the have extra electrons and so are negatively charged

155
Q

Why are phosphate ions soluble in water?

A

the have extra electrons and so are negatively charged

156
Q

How is a phospholipid structurally formed?

A

One of the fatty acid chains in a trig. is replaced with a phosphate group

157
Q

What is the non-polar end (tail) of a phospholipid and what does this mean?

A

Tail = fatty acids chain
Repelled by water = hydrophobic
Mix readily with fat

158
Q

What is the charged end (head) of a phospholipid and what does this mean?

A

Charged head = phosphate group
Interacts with water = hydrophilic

159
Q

How do phospholipids interact with water due to their hydrophobic/hydrophilic structure?

A

Form a layer on surface of water with the phosphate heads, with the fatty acids tail sticking out of the water

160
Q

What are phospholipids called because of their reaction with water?

A

Surface active agents / surfactants

161
Q

How is a phospholipid bilayer formed in water?

A

Two-layered sheer formation (bilayer) with hydrophobic tails pointing towards centre of sheet, protected from water by hydrophilic heads

162
Q

How are phospholipids important in playing a key role in forming cell membranes?

A

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

It is thought this is how first cells were formed

163
Q

What are the biological roles of lipids due to their non-polar nature?

A
  • membrane formation + creation of hydrophobic barriers
  • hormone production
  • electrical insulation = impulse transmission
  • waterproofing (birds’ feathers/leaves)
164
Q

What is the role of triglycerides stores under the skin and around vital organs?

A
  • thermal insulation
  • cushioning to protect vital organs
  • buoyancy for aquatic animals
165
Q

What is manufactured using cholesterol?

A

Vitamin D, steroid hormones, bile

166
Q

Where does the body manufacture the sterol Cholesterol?

A

primarily in the liver and intestines

167
Q

What is the role of cholesterol?

A

Formation of cell membranes, becoming positioned between the phospholipids with the hydroxyl group at the periphery of the membrane

168
Q

Why is cholesterol important in cell membranes?

A

Adds stability and regulates their fluidity by keeping membrane fluid at low temps

169
Q

What is the structure of sterols aka steroid alcohols?

A

Complex alcohol molecules, based on a 4 carbon ring structure with a OH group at one end

170
Q

How are sterols similar to phospholipids?

A

Dual hydrophilic/hydrophobic

Hydroxyl group in sterols is polar = hydrophilic and rest of molecule is hydrophobic

171
Q

What is the test for lipids?

A

Emulsion test

  1. Mix sample with ethanol
  2. Mix solution with water
  3. White emulsion forms = lipids are present
172
Q

What is food synergy?

A

Nutrients do not work in isolation but as part of the combined effect of a whole range of nutrients

173
Q

Define cohesion

A

Water is attracted to water

174
Q

Define adhesion

A

Water is attracted to other substances

175
Q

What 3 components are in a nucleotide?

A
  • a pentose monosaccharide
  • a phosphate group
  • a nitrogenous base
176
Q

How does a condensation reaction occur in a nucleotide?

A

phosphate group at carbon 5 of sugar forms a covalent bond with the hydroxyl group at the third carbon of an adjacent nucleotide

177
Q

What bond forms between nucleotides?

A

a phosphodiester bond

178
Q

What are pyrimidines?

A

1 nitrogen-containing ring

179
Q

What are purines?

A

2 nitrogen-containing rings

180
Q

Which bases are pyrimidines?

A

Thymine and Cytosine

181
Q

Which bases are purines?

A

Adenine and Guanine

182
Q

What bonds are between bases?

A

Hydrogen bonds

183
Q

What are DNA strands said to be?

A

Anti-parallel

184
Q

How many hydrogen bonds do C and G form?

A

3 hydrogen bonds

185
Q

Why is there a constant distance between the DNA backbones?

A

The complementary base pairing means that a small pyrimidine base always binds to a larger purine base

186
Q

What carries the genetic info of an organism?

A

The sequence of bases along a strand in the form of a code

187
Q

Why is DNA unable to leave the nucleus?

A

Each chromosome is a very long molecule which can’t be transported through nucleic pores

188
Q

How is DNA changed to be able to leave the nucleus?

A

short section of the long DNA corresponding to a single gene is transcribed into a mRNA

189
Q

How is RNA different to DNA?

A

RNA has ribose, DNA has deoxyribose
RNA has uracil, DNA has thymine

190
Q

What happens to RNA after protein synthesis?

A

The RNA molecules are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused

191
Q

Globular protein properties

A

Compact, water soluble, spherical

192
Q

How do globular proteins form?

A

When proteins fold into 3Y in a way that the hydrophobic R groups are kept away from the aq environment

193
Q

Where are the hydrophilic R groups on globular proteins and what does this mean?

A

On the outside of the protein = soluble

194
Q

What type of protein is insulin?

A

A globular hormone - alpha helix -

195
Q

Why is it important hormones are globular?

A

Transported in the bloodstream so need to be soluble, and hormones must fit into specific receptors on cell-surface membranes, so must be precise shapes

195
Q

Why is it important hormones are globular?

A

Transported in the bloodstream so need to be soluble, and hormones must fit into specific receptors on cell-surface membranes, so must be precise shapes

196
Q

What are conjugated proteins?

A

Globular proteins that contain a non-protein component called a prosthetic group

197
Q

What are proteins that don’t have prosthetic groups called?

A

Simple proteins

198
Q

What is an example of a prosthetic group in conjugated proteins?

A

Haem groups - contain iron 2+

199
Q

What is haemoglobin’s structure?

A

4Y made from 4 polypeptides, two alpha and two beta units

200
Q

What enables haemoglobin to transport oxygen around the body?

A

Each subunit contains a haem group, with the iron ions present in it are able to combine reversible with O2 (associate/dissociate)

201
Q

What is Catalase’s structure?

A

4Y conjugated protein containing 4 haem groups

202
Q

How does the presence of iron 2+ in Catalase’s haem group help it’s function?

A

Allows catalase to interact with hydrogen peroxide and speed up its breakdown

203
Q

What is hydrogen peroxide (that is broken down by catalase)?

A

A common byproduct of metabolism but is damaging to cells if allowed to accumulate

204
Q

What are fibrous proteins properties?

A

Long, insoluble molecules that are not folded into complex 3D shapes

205
Q

Why are fibrous proteins insoluble?

A

Due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structure

206
Q

Where is keratin found?

A

In hair, skin and nails

207
Q

What sulfur-containing amino acid does keratin contain?

A

Cysteine

208
Q

What does the presence of cysteine in keratin result in?

A

Many strong disulphide bonds (bridges) forming strong, inflexible and insoluble materials

209
Q

What is the unpleasant smell when hair/skin is burnt?

A

Large quantities of sulfur in keratin

210
Q

Give examples of fibrous proteins?

A

Keratin, elastin and collagen

211
Q

What does the degree of disulphide bonds determine in keratin?

A

The flexibility

212
Q

What makes hair more flexible than nails?

A

Contains fewer disulfide bonds making it more flexible

213
Q

Where are elastic fibres containing elastin found?

A

In the walls of blood vessels and in the alveoli of the lunhs

214
Q

What is elastin’s structure?

A

4Y made from stretchy molecules called tropoelastin - gives flexibility

215
Q

Where is collagen found?

A

Skin, tendons, ligaments and the nervous system

216
Q

What is tropoelastin?

A

Wiggly fibres that straighten when stretched

217
Q

How is collagen used artificially?

A

Cosmetics - in lip fillers

218
Q

Collagen is in a number of different forms, but all are made from…?

A

3 polypeptides wound together in a long, strong, rope-like structure with covalent bonds

219
Q

Collagen has a lot of what amino acid every 3rd a.a.?

A

Glyceine

220
Q

How do the 3 polypeptides in collagen form a beta-pleated structure?

A

Forms a triple helix - 3 fibres twisted together are staggered at their ends to avoid weak points

221
Q

How many strands do DNA and RNA have?

A

DNA = 2
RNA = 1

222
Q

DNA + RNA summary of use

A

DNA = stores generic blueprint - stable
RNA = transfers genetic info for decoding

223
Q

What are the 2 covalent bonds called between 2 nucleotides in a condensation reaction?

A

phosphodiester linkage

224
Q

What did Watson and Crick notice as a copying mechanism?

A

Specific pairings of bases

225
Q

What happens to the hydrogen bonds connecting the DNA strands before replication? Okay

A

They are unzipped = H bonds break

226
Q

What is semi-conservative replication?

A
  • one original strand acts as a template
  • one strand is newly synthesised
  • hence semi-conservative
227
Q

What is the original DNA strand in replication called?

A

The template for the creation of a new double stranded molecule

228
Q

When does semi-conservative replication happen?

A

During interphase

229
Q

What determines the direction of replication?

A

The two strands run in anti-parallel directions (5prime and 3prime)

230
Q

What enzyme is used for unzipping DNA strands?

A

Helicase

231
Q

What does primase do?

A

Catalyses the formation of a primer from RNA nucleotides

232
Q

What is the role of a primer in DNA replication?

A

Marks the starting point for the construction of the new DNA strand

233
Q

DNA replication

What does helicase do?

A

Unwinds the double helix and separate the two polynucleotide strands that run anti parallel by unzipping the strand

234
Q

DNA replication

What happens once the DNA strands are unzipped?

A

Two strands acts as templates for activated free nucleotides to align opposite their complementary base partner

235
Q

DNA replication

What does DNA polymerase do?

A

Synthesises the new strands from 2 parental template strands by catalysing the formation of phosphodiester bonds between the aligned nucleotides

236
Q

DNA replication

What is the leading strand?

A

The strand that is unzipped from the 3’ direction can be continuously replicated as the strands unzip

237
Q

DNA replication

What is the lagging strand?

A

The other strand unzipped from 5’ end undergoes discontinuous replication

238
Q

DNA replication

Why does the lagging strand undergo discontinuous replication?

A

Because DNA polymerase has to wait until a section of the strand has unzipped and then work backwards along the strand

239
Q

DNA replication

What does discontinuous replication result in?

A

Sections of DNA called Okazaki fragments which then have to be joined with DNA ligase

240
Q

DNA replication

How does DNA ligase join okazaki fragments together?

A

By covalently joining the sugar-phosphate backbones together with a phosphodiester bond

241
Q

DNA replication

Where does DNA polymerase attach to the DNA strand?

A

Attaches to the 3’ hydroxyl end and covalently joins the free nucleotides togeher

242
Q

What is a mutation?

A

Replication errors that occur randomly and spontaneously when an incorrect sequence of nucleotides and bases aren’t matched

243
Q

What is genetic code?

A

The DNA blueprint that must code for a sequence of amino acids, to fold into complex structures and form proteins as the foundations of living things

244
Q

Where is a simple triplet code found?

A

The code in the base sequences of DNA along the chain of nucleotides that make 2 strands

245
Q

What is a codon

A

A sequence of 3 bases in a simple triplet code

Each codon codes for an amino acid

246
Q

What is a gene?

A

A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein

247
Q

What does it mean if genetic code is universal?

A

All organisms use the same code

248
Q

Why are there 64 different base triplets or codons possible?

A

4 bases

4 X 4 X 4 = 64

249
Q

How many stop codons are there and what do they do?

A

3 stop codons that do not code for any amino acids and signal the end of a sequence

250
Q

What does a start codon do?

A

Signals the start of a sequence that codes for a protein

251
Q

What does a start codon in the middle of a gene do?

A

It codes for the amino acid methionine

252
Q

What does having a single codon to signal the start of a sequence ensure?

A

That the triplets of bases (codons) are read ‘in frame’ = DNA base sequence is read from base 1, not base 2 or 3 = genetic code isn’t overlapping

253
Q

What is degenerate code?

A

When many amino acids can be coded for by more than one codon

254
Q

Why does degenerate code exist?

A

As there are only 20 different amino acids that regularly occur, but a lot more codons

255
Q

Remember the genetic code is a triplet code!

3 bases =

A

= 1 codon

One codon codes for one amino acid

256
Q

Where does protein synthesis occur in eukaryotes?

A

In the cytoplasm at ribosomes

257
Q

Define transcription

A

For a gene to produce a protein, the DNA within the gene must first be copied into RNA

258
Q

Define translation

A

The process by which a cell makes proteins using the genetic information carried in a messenger RNA

259
Q

Although transcription results in a different polynucleotide it has many similarities with dna replication…:.

A

Page 76

A-level Biology (23 decks)

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