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OCR Biology Paper 1 > 2.2 - Biological Molecules > Flashcards

2.2 - Biological Molecules Flashcards

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1
Q

Define the structure of water

A
  • Two hydrogen atoms covalently bonded to one oxygen atom.
  • Polar molecule
  • Hydrogen bonds form between electronegative oxygen atoms and electropositive hydrogen
    atoms on adjacent water molecules
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2
Q

Water has important solvent properties. Explain these properties using an example to illustrate your answer

A
  • Water is polar
  • Substances that dissolve in water are hydrophilic
  • Water forms hydrogen bonds with polar substances
  • Positive pole of water attracted to negative pole of molecules
  • e.g. Glucose dissolves because it is polar
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3
Q

Which properties explain the ability of water to dissolve solutes?

A
  • Polarity of water molecules
  • Hydrogen bonding
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4
Q

Which property of water accounts for its moderating effects on the Earth’s atmosphere?

A

Thermal properties

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5
Q

Explain the reasons for the unique thermal properties of water

A
  • Water is polar and exhibits dipolarity
  • Causes strong hydrogen bonds to form between the molecules
  • Requires more energy to overcome hydrogen bonds
  • Increases the melting point
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6
Q

Define specific heat capacity

A

Heat energy required to raise the temperature of 1Kg of a substance by 1°C

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7
Q

Define latent heat of vaporisation

A

Heat energy required to change the state of a substance from liquid to gas

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8
Q

Why does water act as an adhesive?

A

Water is a polar molecule allowing it to ‘stick’ to other substances

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9
Q

Why is water cohesive?

A

Hydrogen bonds between molecules allow them to ‘stick’ together

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10
Q

Why does water act as a coolant?

A

Hydrogen bonds between water molecules must be broken when water evaporates - removes heat energy from body

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11
Q

Outline the properties of water molecules that permit them to move upwards in plants

A
  • Water molecules are polar and can form hydrogen bonds.
  • Cohesion between water molecules allows transpiration stream to form in xylem.
  • Adhesion of water to the walls of xylem vessel helps water rise.
  • Water evaporates at environmental temperatures allowing transpiration pull.
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12
Q

Why is water’s/ice’s density a benefit to living organisms?

A

Ice is less dense than water and floats on top of it, creating an insulating layer and preventing animals in large bodies of water from freezing

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13
Q

Why is water being a solvent a benefit to living organisms?

A

Allows many metabolic reactions occur

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14
Q

How does water having a high specific heat capacity benefit living organisms?

A

Lots of energy required to warm water up, minimising temperature fluctuations

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15
Q

Define condensation reaction

A
  • Reaction which involves the elimination of a small molecule e.g. water
  • Occurs when two molecules chemically bond together
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16
Q

Define polymer

A
  • Very large molecule formed by the joining together of smaller subunits (monomers)
  • Formed by condensation reactions
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17
Q

Define hydrolysis reaction

A
  • Reaction that breaks a chemical bond between two molecules
  • Involves the use of a water molecule
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18
Q

Define anabolism

A
  • Synthesis of complex molecules from simpler molecules
  • Includes the formation of polymers from monomers by condensation reactions
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19
Q

Define catabolism

A
  • Breakdown of complex molecules into simpler molecules
  • Includes the hydrolysis of polymers into monomers
  • e.g. amylose (polymer) into maltose (monomer) by amylase (enzyme)
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20
Q

List the elements found in carbohydrates

A

Carbon, hydrogen, oxygen

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21
Q

List the elements found in lipids

A

Carbon, hydrogen, oxygen

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22
Q

List the elements found in proteins

A

Carbon, oxygen, hydrogen, nitrogen (+ sometimes sulfur)

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23
Q

List the elements found in nucleic acids

A

Carbon, oxygen, hydrogen, nitrogen, phosphorous

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24
Q

Define monosaccharide

A

Simple carbohydrates consisting of one subunit (monomer)
- e.g alpha (α)-glucose, beta (β)-glucose

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25
Q

What type of bond forms between monosaccharides?

A

Glycosidic bonds

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26
Q

Define disaccharide

A
  • Carbohydrate consisting of two subunits (monomers)
  • Glycosidic bonds formed by condensation reactions
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27
Q

What is maltose made of?

A

Maltose formed from two glucose monomers

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28
Q

What is lactose made of?

A

Lactose formed from one glucose and one galactose monomer

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29
Q

What is sucrose made of?

A

Sucrose formed from one glucose and one fructose monomer

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30
Q

Define polysaccharide

A

Complex carbohydrates consisting of more than two subunits (monomers)
- e.g. glycogen, cellulose, starch

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31
Q

Describe the structure of starch

A
  • Polymer
  • Formed from α-glucose
  • Two forms - amylose and amylopectin
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32
Q

Describe the structure of cellulose

A
  • Unbranched polymer
  • Formed from β-glucose monomers
  • Long straight chains linked together by many hydrogen bonds to form fibrils
  • Provides high tensile strength to plant cell walls
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33
Q

Describe the structure of amylose

A
  • Polysaccharide
  • Formed from α-glucose
  • 1,4 linkages → unbranched (linear)
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34
Q

Describe the structure of amylopectin

A
  • Polysaccharide
  • Formed from α-glucose
  • 1,4 and 1,6 linkages → branched
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35
Q

What is the function of starch?

A

Used by plants as a storage of glucose/energy

36
Q

How are starch molecules adapted for their function in plant cells?

A
  • Insoluble - do not affect water potential
  • Helical/spirals - compact
  • Large molecule - cannot leave cell
  • Branched amylopectin can load and unload glucose more quickly than unbranched
    amylose - more exposed subunits for enzymes to act upon
37
Q

Which type of reaction is the breakdown of starch into sugars?

A

Hydrolysis

38
Q

Describe the role of glycogen

A
  • Used by animals and fungi as a storage of glucose
  • Stored in animal liver cells and muscle
39
Q

Describe the structure of glycogen

A
  • Formed from α-glucose
  • Highly branched
  • Branched structure allows fast loading and unloading of glucose
  • Insoluble - does not affect water potential of cell
40
Q

Why is glycogen more branched than starch?

A
  • Animals require more energy than plants (for movement, digestion etc.)
41
Q

Which sugars are reducing sugars?

A
  • All monosaccharides
  • Some disaccharides (e.g. maltose and lactose)
  • All others are non-reducing sugars
42
Q

What is the test for reducing sugars?

A

Benedict’s reagent (copper(II) sulfate)
- Place sample in water
- Add equal amount of Benedict’s reagent
- Heat gently in water bath for five minutes
- Positive result: Brick red precipitate forms

43
Q

What is the test for non-reducing sugars?

A
  • Perform test for reducing sugar
  • If solution remains blue:
  • Boil sample with HCl
  • Neutralise with sodium hydrogen carbonate
  • Add equal amount of Benedict’s reagent
  • Heat gently in water bath for five minutes
  • Positive result: Brick red precipitate forms
44
Q

Why is hydrochloric acid added when testing for non-reducing sugars?

A

Hydrolyses glycosidic bonds

45
Q

Describe how to measure the change in concentration of the reducing sugar maltose as the enzyme amylase breaks down starch into maltose

A
  • Take samples at a range of times
  • Same volumes of solutions removed each time
  • Heat samples with Benedict’s solution
  • Colour changes from blue → green → yellow → orange → brick red
  • Colour change depends on concentration of maltose in solution
  • Calibrate a colorimeter using unreacted Benedict’s solution
  • Record the absorbance of each sample
  • Less absorbance = more maltose present
  • Using known concentrations of maltose, plot a calibration curve
  • Plot absorbance against reducing sugar concentration
  • Use graph to read off concentration of maltose
46
Q

What are reagent strips?

A

Paper strips that can detect the presence of reducing sugars

47
Q

What is the advantage of reagent strips?

A

Concentration of the sugar can be easily determined

48
Q

What is the test for starch?

A
  • Iodine solution added to sample
  • Positive result: Brown solution turns blue/black
49
Q

What are the three major types of lipid?

A
  • Phospholipids
  • Triglycerides
  • Steroids
50
Q

Describe the structure of a triglyceride

A

Three fatty acids, one unit of glycerol

51
Q

What type of bond forms between glycerol and a fatty acid?

A

Ester

52
Q

Describe the structure of a phospholipid

A
  • Two fatty acids, phosphate, glycerol
  • Heads are hydrophilic
  • Tails are hydrophobic
53
Q

Describe the structure of a steroid

A
  • Four fused rings
  • e.g. cholesterol, progesterone, estrogen, testosterone
54
Q

Define saturated

A

All carbon bonds are single

55
Q

Define unsaturated

A

Contains one or more carbon-carbon double bond

56
Q

Define monounsaturated

A

Contains only one carbon-carbon double bond

57
Q

Define polyunsaturated

A

Contains two or more carbon-carbon double bonds

58
Q

Describe the difference in appearance between saturated and unsaturated lipids at room temperature

A
  • Saturated - solid (e.g. animal fats)
  • Unsaturated - liquid (e.g. plant oils)
59
Q

What is the role of fats and oils?

A

Concentrated, long-term energy store

60
Q

What is the advantage of using lipids as an energy store over carbohydrates?

A
  • Amount of energy released per gram of lipids is double that of carbohydrates
  • Insoluble - do not affect water potential of the cell
61
Q

What is the role of phospholipids?

A
  • Form phospholipid bilayer cell membranes
  • Hydrophilic head faces outwards
  • Hydrophobic tail faces inwards
62
Q

What are the roles of steroids?

A
  • Hormones
  • Vitamins
  • Cholesterol adds stability to cell membranes
  • Keeps membranes fluid at low temperatures
  • Prevents membranes becoming too fluid at high temperatures
63
Q

What medical conditions are associated with increased blood cholesterol levels?

A
  • Coronary heart disease
  • Atherosclerosis
  • Stroke
  • Type 2 diabetes
64
Q

What is the test for lipids?

A
  • Emulsion test
  • Mix sample with ethanol, then water
  • Positive test: Milky white emulsion forms
65
Q

What is the basic building block of a protein called?

A

Amino acid

66
Q

How many different amino acids exist?

A

20

67
Q

Describe the structure of an amino acid

A
  • Amine group (NH2)
  • Carboxyl group (COOH)
  • Central carbon atom
  • R group (variable depending on the amino acid)
68
Q

Define polypeptide

A

Long unbranched chain formed of many amino acids

69
Q

What type of bond forms between amino acids?

A

Peptide bonds

70
Q

How are amino acids joined together to form a polypeptide?

A
  • Condensation reactions
  • Peptide bond forms between amine group of one amino acid and carboxyl group of another
71
Q

Outline the general structure of a protein

A

Primary structure
- Order of amino acids

Secondary structure
- Folding of polypeptide into alpha-helix or beta-sheet
- Held in position by hydrogen bonds

Tertiary structure
- Folding of polypeptide chain in 3D space
- Held in position by hydrogen bonds, ionic bonds, hydrophobic and
hydrophilic interactions and disulfide bridges between amino acids

Quaternary structure
- Joining of two or more polypeptides to form a functioning protein

72
Q

Explain how the secondary structure is held in position

A
  • Hydrogen bonds
  • Between amino (N-H) and carboxyl (C=O) groups on different amino acids
73
Q

Explain how alpha helices/beta pleated sheets are formed

A
  • Hydrogen bonds form between N-H and C=O groups
74
Q

What type of interactions form between R-groups?

A
  • Ionic interactions between positively charged and negatively charged R-groups
  • Hydrogen bonds between polar R-groups
  • Covalent disulphide bridges between cysteine R-groups
  • Hydrophobic (non-polar) amino acids orientate themselves towards centre of polypeptide
  • Hydrophilic (polar) amino acids orientate themselves towards outside of polypeptide
75
Q

Outline the importance of polar and non-polar amino acids in proteins

A
  • Polar and non-polar amino acids help determine protein structure
  • Polar amino acids on the outside of proteins make them soluble in water
  • Polar amino acids in channels in membranes allow passage of polar substances
  • Polarity or non-polarity of surface amino acids on proteins determines their interaction with
    other molecules (e.g substrates, hormones, signalling molecules)
76
Q

Provide examples of different roles and types of proteins

A

Enzymes
- Globular proteins
- e.g. rubisco which catalyses photosynthesis

Hormones
- Globular proteins
- e.g. insulin triggers conversion of glucose to glycogen to lower blood glucose levels

Structural
- Fibrous proteins
- e.g. keratin found in hair, collagen found in skin

77
Q

Distinguish between fibrous and globular proteins

A

Fibrous - Linear / long chains
Globular - Spherical

Fibrous - Usually insoluble
Globular - Usually soluble

Fibrous - Provide strength
Globular - Forms hydrogen bonds with water

Fibrous - Structural roles
Globular - Catalysis/transport roles

78
Q

What is a conjugated protein?

A

Globular protein with a prosthetic group
- e.g. haemoglobin - protein combined with iron

79
Q

Describe the structure of collagen

A
  • Peptide bonds between amino acids
  • Every 3rd amino acids is the same (glycine)
  • Forms left-handed helix
  • Glycine allows polypeptide chains to pack close together
  • Forms fibrils
  • Hydrogen bonds between three polypeptide chains
  • Few hydrophilic R groups on outside of molecule
80
Q

Describe the quarternary structure of haemoglobin

A
  • 4 polypeptide subunits
  • 1 haem group (a prosthetic group, contains Fe2+) per polypeptide
81
Q

Describe the ways in which the structure of collagen is similar to the structure of haemoglobin

A
  • Both made from amino acid chains
  • Peptide bonds between amino acids
  • Disulfide bridges, ionic bonds, hydrogen bonds and hydrophobic/hydrophilic interactions
    form tertiary structure
  • Both contain more than one polypeptide in quaternary structure
82
Q

Define denaturation

A
  • A deformation of 3D structure of proteins (tertiary structure)
  • In enzymes can cause change in shape of active site
  • Substrate can no longer bind
83
Q

What causes denaturation?

A
  • High temperature (usually irreversible)
  • Changes in pH (usually reversible)
84
Q

How does high temperature alter the protein’s structure?

A
  • Intermolecular bonds break altering the protein’s 3D structure
  • Usually irreversible
85
Q

What is the test for protein?

A
  • Biuret test
  • Place liquid sample in equal volume of 10% sodium hydroxide solution
  • Add 1% copper sulphate solution
  • Mix and leave for 5 minutes
  • Positive result: blue solution turns purple/lilac
86
Q

Describe how thin layer chromatography can be used to separate amino acids

A
  • Amino acids added to one end of layer of silica gel (stationary phase)
  • This end is submerged in organic solvent
  • Solvent moves through silica gel (mobile phase)
  • Different components of the mixture travel at different speeds, causing them to separate
  • The more soluble the amino acid, the further it will travel through the gel
  • An Rf value can be calculated and compared to data tables

OCR Biology Paper 1 (20 decks)

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