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

Biological Molecules Flashcards

1
Q

define what is meant by a monomer

A

a small repeating unit from which larger molecules are made

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2
Q

define what is meant by a polymer

A

a molecule made from a long chain of monomers bonded together

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3
Q

give three examples of monomers

A

amino acids
monosaccharides
nucleotides

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4
Q

what is the monomer for a carbohydrate?
what is the polymer?
what elements are present?

A

monosaccharide
polysaccharide
carbon, hydrogen, oxygen

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5
Q

what is the monomer for a protein?
what is the polymer?
what elements are present?

A

amino acid
polynucleotide
carbon, hydrogen, oxygen, nitrogen, sulfur

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6
Q

what is the monomer for a nucleic acid?
what is the polymer?
what elements are present in this compound?

A

nucleotide
polynucleotide
carbon, hydrogen, oxygen, phosphorous, nitrogen

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7
Q

what is a condensation reaction?

A

a reaction that joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

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8
Q

what is a hydrolysis reaction?

A

a reaction that breaks a chemical bond between two molecules and involves the insertion of a molecule of water

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9
Q

what is a monosaccharide?

A

monomers from which larger carbohydrates are made

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10
Q

name three examples of monosaccharides

A

glucose
fructose
galactose

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11
Q

what type of sugar is glucose?

A

a hexose sugar

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12
Q

draw and name the two isomers of glucose

A

alpha and beta glucose

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13
Q

define what is meant by an isomer

A

compounds with the same molecular formula but a different arrangement of atoms

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14
Q

what type of bond joins monosaccharides together?

A

a glycosidic bond

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15
Q

how is a disaccharide formed?

A

condensation reaction between two monosaccharides

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16
Q

how is maltose formed?

A

condensation reaction that forms a glycosidic bond between two alpha glucose units

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17
Q

how is lactose formed?

A

condensation reaction that forms a glycosidic bond between galactose and alpha glucose

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18
Q

how is sucrose formed?

A

a condensation reaction that forms a glycosidic bond between alpha glucose and fructose

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19
Q

give three examples of reducing sugars

A

alpha glucose
galactose
fructose

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20
Q

describe the benedict’s test for reducing sugars

A
  • add benedicts reagent to sample and heat in a water bath
  • if reducing sugar is present, sample will form a coloured precipitate eg. red, orange, yellow, green or blue
  • colour of precipitate depends on the concentration of reducing sugar
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21
Q

why would the use of a colorimeter improve the repeatability of an experiment

A
  • colour change is subjective
  • colorimeter produces quantitative data that standardises the method
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22
Q

describe a more accurate way to compare the amount of reducing sugar in a solution than comparing the colour of precipitate formed

A
  • filter the solution to separate the precipitate
  • weigh the precipitates
  • compare the different weights
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23
Q

why should excess benedicts solution always be used when testing for sugars?

A

to make sure all the sugar reacts

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24
Q

describe the benedicts test for non-reducing sugars

A
  • add benedicts reagent to sample and heat in water bath
  • wait for negative result (no coloured precipitate forms or blue precipitate forms)
  • boil solution with acid HCl and neutralise with NaHCO3
  • add benedicts solution and heat in a water bath
  • if non reducing sugar is present, red precipitate will form
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25
Q

what is a polysaccharide

A

a polymer formed when more than two monosaccharides join together by condensation reactions that form glycosidic bonds

(a long chain of monosaccharides)

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26
Q

why cant excess glucose be stored as glucose?

A

glucose is soluble
this would enable it to dissolve into the cells cytoplasm, increasing the concentration of the cell solution and also lowering the cells water potential
this would cause water to flow into the cell by osmosis, causing the cell to swell and eventually burst

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27
Q

how do plants store glucose?

A

as starch

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28
Q

how do animals store glucose?

A

as glycogen

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29
Q

what are glycogen and starch examples of

A

storage polysaccharides

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30
Q

what is starch a mixture of

A

amylose and amylopectin

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31
Q

describe the structure of amylose and an advantage of its structure

A

amylose is a long, unbranched chain of alpha glucose, that contains (1-4) glycosidic bonds
this makes it form a straight chain which coils into a helix.
this coiled structure makes it good for storage as it is compact

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32
Q

describe the structure of amylopectin and an advantage of its structure

A

amylopectin is a long, branched chain of alpha glucose, that contains (1-4) and (1-6) glycosidic bonds
the branches allow glucose to be hydrolysed from the ends of the chains faster for respiration and ATP production.

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33
Q

where can glycogen be found

A

liver and muscle cells

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34
Q

describe how the structure of glycogen is related to its function

A
  • helical, so compact for storage
  • polymer of glucose so easily hydrolysed
  • (1-6) glycosidic bonds form branches, so there are more ends for faster hydrolysis of glucose for respiration and ATP production
  • insoluble so does not affect water potential of the cell
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35
Q

what is cellulose a polymer of?

A

beta glucose

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36
Q

what type of polysaccharide is cellulose

A

structural polysaccharide

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37
Q

what are cellulose chains linked together by?
what is the name of the structures formed?

A

hydrogen bonds
fibrils/microfibrils

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38
Q

describe a process by which you would test for the presence of starch

A
  • add iodine and potassium iodide to solution containing starch
  • positive result is colour change from orange/brown to blue/black
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39
Q

what are the two main types of lipid?

A

triglycerides
phospholipids

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40
Q

what do triglycerides contain?

A

one molecule of glycerol and three molecules of fatty acid

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41
Q

what are fatty acid tails made up of

A

hydrocarbon chains of varying lengths

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42
Q

are fatty acid tails hydrophobic or hydrophillic?
what does this mean?

A

hydrophobic
they repel water

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43
Q

draw the basic structure of a fatty acid using displayed formula

A
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44
Q

draw the structure of glycerol using displayed formula

A
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45
Q

how are triglycerides formed?
what types of bonds are created?

A

condensation reactions that eliminate three molecules of water between glycerol and three fatty acids
-ester bonds are formed

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46
Q

draw and label the condensation reaction for the formation of a triglyceride

A
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47
Q

what may the R group of a fatty acid be

A

saturated or unsaturated

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48
Q

what does saturated mean?
what does unsaturated mean?

A
  • contains no double bonds between carbon atoms
  • contains at least one double bond between carbon atoms
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49
Q

what are the differences between a triglyceride and a phospholipid

A
  • phospholipids contain a phosphate group, whereas triglycerides do not
  • triglycerides contain three fatty acid tails, whereas phospholipids only contain two
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50
Q

is the phosphate head in a phospholipid hydrophillic or hydrophobic

A

hydrophillic

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51
Q

what are triglycerides mainly used as?
what properties of a triglyceride make this possible?

A
  • mainly used as energy storage molecules
  • -the long hydrocarbon tails of the fatty acid contain lots of chemical energy that is released when theyre broken down
    -theyre insoluble, so dont affect the water potential of cells and cause water to enter cells by osmosis
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52
Q
  • what are phospholipids mainly used for?
  • what properties of phospholipids makes this possible?
A
  • make up the bilayer of cell membranes that control what enters and leaves the cell
  • -their heads are hydrophillic and their tails are hydrophobic, so they form a double layer ‘phospholipid bilayer’ with their heads facing outwards towards the water on the other side
    -the centre of the bilayer is hydrophobic, so water soluble substances cannot easily pass through it. the membrane acts as a barrier to those substances.
53
Q

what test tests for the presence of lipids?
how would you carry out this test

A
  • emulsion test
  • shake sample with ethanol
    add water
    if lipid present, a white emulsion will form
54
Q

what are the monomers of proteins?
what are the polymers of proteins?

A

amino acids
polypeptides

55
Q

how is a dipeptide formed?

A

condensation reaction that forms a peptide bond between two amino acids and eliminates a molecule of water

56
Q

how is a polypeptide formed?

A

condensation reactions between more than two amino acids to form peptide bonds, that eliminates molecules of water

57
Q

what are functional proteins made up of

A

more than one polypeptide chain

58
Q

draw the structure of an amino acid (spec version)

A
59
Q

what do the different groups in an amino acid represent

A

NH2 - amine group
COOH - carboxyl group
R - side chain

60
Q

how many different types of amino acid are there?
how do they differ?

A

20 different types
differ in their side chains

61
Q

draw a condensation reaction between two amino acids to form a dipeptide

A
62
Q

what is the primary structure of a protein?

A

the sequence of amino acids in the polypeptide chain

63
Q

what is the secondary structure of a protein?
what are the structures formed held together by?

A
  • when the polypeptide chain folds or twists into beta pleated sheets or alpha helices
  • hydrogen bonds between the amino acids
64
Q
  • what is the tertiary structure of a protein?
  • what is this held together by?
A
  • when the polypeptide chain folds or twists even more to form a 3D structure
  • held in place by hydrogen bonds, disulphide bridges or ionic bonds between the R groups
65
Q

what is the name of the amino acid that disulphide bridges form between?

A

cysteine

66
Q

what is the quarternary structure of a protein

A

more than one polypeptide chain bonded together

67
Q

state 4 uses of proteins

A

antibodies
enzymes
structural proteins eg keratin in nails and hair
transport proteins eg carrier and channel

68
Q

what are globular proteins

A

soluble proteins that have biochemical functions eg hormones and enzymes

69
Q

what are fibrous proteins

A

insoluble proteins that have structural functions eg keratin in nails and hair

70
Q

describe how cellulose molecules are adapted for their function in plant cells

A
  • long and straight chains of beta glucose
  • linked by hydrogen bonds to form fibrils
  • that provide strength to the cell wall
71
Q

what do enzymes act as?

A

biological catalysts

72
Q

how do enzymes speed up the rate of reaction?

A

by lowering the activation energy

73
Q

what must the active site be to the substrate

A

complementary

74
Q

when an enzyme and a substrate bind, what is formed

A

enzyme-substrate complex

75
Q

how does the formation of the enzyme substrate complex lower the activation energy?

A
  • it reduces the natural repulsion between substrate molecules by holding them close together, allowing them to bond more easily
  • fitting into the active site puts a strain on the bonds in the substrate and bends them, so the substrate molecules break more easily
76
Q

describe the lock and key model of enzyme action

A

this model states that the active site is a perfect complementary fit to the substrate

77
Q

describe the induced fit model of enzyme action

A
  • model states that the active site is complementary to the substrate but not perfectly
  • so when the substrate binds, it induces a slight change in the active site’s shape
  • this change in shape bends the bonds in the substrate, putting a strain on them and thus causing them to break more easily
78
Q

what is the active site of an enzyme determined by

A

its tertiary structure

79
Q

how can the tertiary structure of an enzyme (shape of the active site) be altered?

A

increasing temperature
changes in pH
addition of a non competitive inhibitor

80
Q

what is the primary structure of an enzyme determined by?
how can mutations affect this?

A

a gene
if a mutation occurs in this gene, it could change the tertiary structure of the enzyme produced.

81
Q

why do some enzymes only work of a non-protein molecule is added to the active site

A

enzymes have a specific tertiary structure
without the part, the active site is not complimentary to the substrate
so with the part, enzyme substrate complex can be formed.

82
Q

describe how two enzymes with different amino acid sequences can catalyse the same reaction

A
  • both active sites have similar tertiary structures
  • so form enzyme substrate complexes with the same substrate
83
Q

how does temperature affect enzyme activity

A

the rate of enzyme controlled reactions increases when the temperature increases
this is because the kinetic energy of the enzymes and the substrates increases
which in turn causes them to collide with each other more, so more enzyme substrate complexes form. this increases the rate of reaction.
however above the optimum temperature, the hydrogen bonds in the tertiary structure of the enzyme begin to break
this causes the active site to change shape, causing the enzyme to denature, meaning it is no longer complementary to the substrate.
rate of reaction decreases.

84
Q

how does pH affect enzyme activity

A

deviation away from the optimum pH can cause the H+ and OH- ions found in acids and alkalis to change the ionic and hydrogen bonds between R groups in the enzyme’s tertiary structure
this causes the active site to change shape and the enzyme to denature, so enzyme substrate complexes can no longer form
this decreases the rate of reaction

85
Q

how does enzyme concentration affect enzyme activity?

A

the more enzyme molecules there are in a solution, the more likely they are to collide with substrate molecules and form enzyme substrate complexes - this increases the rate of reaction
however, at a point the amount of substrate becomes limiting, so adding more enzymes will have no effect

86
Q

how does substrate concentration affect enzyme activity

A

the higher the concentration of substrate, the faster the rate of reaction, as the substrates and the enzymes are more likley to collide, causing more enzyme substrate complexes to form
however, once the substrate concentration increases to a certain point, the active site availability of enzymes becomes limiting, as there are not enough enzymes for the amount of substrates.

87
Q

what is an inhibitor

A

a molecule that reduces the rate of an enzyme controlled reaction

88
Q

how do competitive inhibitors reduce the rate of reaction?
how can this be overcome?

A

have a similar shape to the substrate
this means they cant fit into the active site and block the substrate from binding
thus reducing the number of enzyme substrate complexes that can form.
however, if the substrate concentration is higher than the competitive inhibitor concentration, the substrate is more likely to bind to the enzyme’s active site - so the effect of the inhibitor can be overcome.

89
Q

how do non-competitive inhibitors reduce the rate of reaction

A

molecules that bind away from the active site (in the allosteric site)
the binding of this molecule changes the tertiary structure of the active site, causing it to change shape
this means substrate molecules will no longer be complementary, so enzyme substrate complexes can no longer form.
increasing the concentration of substrate will not make a difference here, as the active site of the enzyme is no longer complementary.

90
Q

what does dna stand for?
what does it store?

A

deoxyribonucleic acid
genetic material

91
Q

what does rna stand for?

A

ribonucleic acid

92
Q

what is the function of rna

A

to transfer genetic material from the dna to the ribosomes

93
Q

what are ribosomes formed from?

A

rna and proteins

94
Q

what are dna and rna polymers of

A

nucleotides

95
Q

draw the general structure of a nucleotide

A
96
Q

what are the components of a dna nucleotide

A
  • the pentose sugar deoxyribose
  • a phosphate group
  • a nitrogen containing base that is either adenine, guanine, cytosine or thymine
97
Q

what are the components of an rna nucleotide

A
  • the pentose sugar ribose
  • a phosphate group
  • a nitrogen containing base either adenine, guanine, cytosine or uracil
98
Q

what type of bond does a condensation reaction between two nucleotides form

A

a phosphodiester bond

99
Q

what parts of the nucleotides are phosphodiester bonds formed between

A

the phosphate of one nucleotide and the sugar of another

100
Q

what is the chain of sugars and phosphates in dna called

A

the sugar phosphate backbone

101
Q
  • how many polynucleotide chains does dna contain?
A

2

102
Q

what is the structure of dna called

A

double helix structure

103
Q

what are the polynucleotide strands in dna in relation to eachother

A

antiparralel

104
Q

what type of bond forms between complementary bases

A

hydrogen bonds

105
Q

what bases are complementary?
how many hydrogen bonds form between these complementary base pairs?

A

adenine = thymine/uracil = 2 hydrogen bonds
cytosine = guanine = 3 hydrogen bonds

106
Q

why did scientists doubt dna could carry the genetic code?
what did they argue it carried instead?

A
  • doubted it could carry the genetic code as it has a relativley simple chemical composition
  • argued genetic material must be carried by proteins as they are much more chemically varied
107
Q

who was the double helix structure devised by

A

watson and crick

108
Q

how many polynucleotide chains does rna have?
longer or shorter than most dna polynucleotides?

A

1
shorter

109
Q

which stage of the cell cycle does dna replication occur in

A

interphase (s phase)

110
Q

by which method of replication does dna replicate

A

semi-conservative replication

111
Q

what are the names of the enzymes required for dna replication?
what are the functions of these enzymes?

A

dna helicase unzips the dna strands and breaks the hydrogen bonds between complementary base pairs

dna polymerase catalyses the condensation reactions that join adjacent nucleotides together forming phosphodiester bonds

112
Q

describe the process of dna replication

A

dna helicase breaks the hydrogen bonds between complementary bases in the polynucleotide strands. this causes the helix to unwind and form two single strands

each single strand acts as a template for a new strand, and free floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand (adenine with thymine and cytosine with guanine)

condensation reactions join the nucleotides of the new strands together, and these reactions are catalysed by DNA polymerase. hydrogen bonds form between the complementary bases of the original and new strands, and phosphodiester bonds form between the adjacent nucleotides on the new strands.

each new dna molecule contains one strand of the original dna molecule and one new strand - semi conservative replication.

113
Q

what is the active site of dna polymerase specific to?

A

the 3’ end of the polynucleotide strand

114
Q

in which direction are new strands of dna made? why?

A

5’ end
dna polymerase moves down the template strand from the 3’ end to the 5’ end (as this is the direction it is specific to)
but, because the strands in the double helix are anti-parallel, the new strand of dna is made with the 3’ end at the bottom and the 5’ end at the top.
so, the dna polymerase working on the new strand travels up from the 3’ end at the bottom to the 5’ end at the top.
and, since it is now the 5’ end that is at the top, we say the new strand of dna is made in the 5’ direction

115
Q

state the names of the three methods of dna replication that were considered

A

conservative
semi conservative
dispersive

116
Q

what is meant by conservative, semi conservative and dispersive

A

conservative - both parent dna molecules act as templates during replication. daughter molecules contain two identical strands.

semi conservative - parent dna molecule separates into two strands, and each strand acts as a template during replication. daughter molecules contain one parent strand and one new strand

dispersive - parent dna molecule breaks into segments and new nucleotides fill the gaps. daughter molecules are a mixture of old parent nucleotides and new nucleotides.

117
Q

what did meselson and stahl prove?

A

that dna replicates semi conservativley
(read over notion page regarding their method and results)

118
Q

what are the components of atp

A

adenine base
ribose sugar
three phosphate groups

119
Q

what does atp stand for

A

adenosine triphosphate

120
Q

draw the structure of atp

A
121
Q

what enzyme is atp hydrolysed by?
what are the products of this hydrolysis?
what bond breaks as a result?
what does this bond breaking release?

A

atp hydrolase
adp and pi
phosphate bond
energy

122
Q

state 4 examples of reactions that the energy provided by atp can be used for

A

active transport
nerve impulses
protein synthesis
musicle contraction

123
Q

what can the inorganic phosphate formed from the hydrolysis of atp do?
what does this do?

A
  • phosphorylate other compounds
  • makes them more reactive
124
Q

how can atp be resynthesised?
what enzyme catalyses this reaction?
when does this reaction occur?

A

condensation of adp and pi to form atp and water
atp synthase
respiration and photosynthesis

125
Q

state 5 advantages of using atp as an energy source/ 5 reasons why atp is used in many biological processes

A
  • releases energy in small amounts
  • is easily hydrolysed in one step by just one enzyme to release adp pi and energy
  • rapidly resynthesised using atp synthase
  • cannot leave cells through cell membranes as is too large
  • phosphorylates other compounds, making them more reactive
126
Q

explain six properties of water that make it important for organisms

A

water is a metabolite in metabolic reactions, such as condensation reactions and hydrolysis reactions

is a solvent in which metabolic reactions occur

has a relatively high specific heat capacity, to buffer changes in temperature

has a relatively large latent heat of vapourisation, which provides a cooling effect and reduces the amount of water lost by evaporation

cohesion between water molecules supports columns of water eg the transpiration stream

cohesion between water molecules provides surface tension for small organisms

127
Q

where are inorganic ions usually found?
what do they usually not contain

A

cytoplasm and bodily fluids
carbon

128
Q

recall 4 types inorganic ions and how they are important

A
  • iron ions are an important part of haemoglobin binding to oxygen
  • sodium ions are used in the co transport of glucose and amino acids
  • phosphate ions are important components of dna, rna, atp and phospholipids
  • hydrogen ions lower pH
129
Q

when drawing a graph, which axis does the independent variable go on?
which axis does the dependent variable go on?

A

x axis
y axis

A-Level Biology AQA Year 1 (4 decks)

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