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OCR AS/A Level Biology Context > module 2.1.2 - biological molecules > Flashcards

module 2.1.2 - biological molecules Flashcards

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1
Q

what is a monosaccharide

A

these are the single sugar units that are used as monomers. they are soluble and sweet reducing sugars

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2
Q

what is glucose

A

it is a hexose sugar, C6H12O6. it is used for respiration
–> used as a respiratory substrate to provide energy for the formation of atp

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3
Q

what is a pentose pentose sugar

A

contains 5 carbons
eg. deoxyribose and ribose

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4
Q

what are the 2 types of glucose molecules

A

alpha and beta

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5
Q

draw both alpha and beta glucose

A

same but they differ by flipping the -OH and -H

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6
Q

what are dissacharrides

A

2 monosaccharides bonded by glycosidic bonds. they are soluble and sweet. most are reducing sugars except sucrose

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7
Q

what is the most common bond found in carbohydrates

A

1,4 glycosidic bonds

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8
Q

what does glucose and fructose form and what bonds are in between them

A

sucrose - 1,6 glycosidic bond

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9
Q

what do 2 glucose molecules formand briefly describe the components of its structure

A

maltose
- contains alpha glucose with alpha glycosidic bonds
- same direction
- 1,4 glycosidic bond

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10
Q

what does glucose and galactose form

A

lactose
- beta glucose
- beta glycosidic bonds
- sugars in opposing orientation
- 1,4 glycosidic bonds

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11
Q

how are disaccharides converted back to monosaccharides

A

by hydrolysis

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12
Q

what is a polysaccharide

A

large insoluble molecules consisting of many monosaccharides joined together via condensation reaction

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13
Q

what are the 3 examples of polysaccharides

A

starch, cellulose and glycogen

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14
Q

what is starch made up of

A

it is made up of 2 molecules
amylose and amylopectin

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15
Q

what is the structure of amylose

A

consists of a long, unbranched chain of alpha glucose subunits joined by 1,4 glycosdic bonds and all have same orientation
the chain of subunits coil up
the -OH group on the 2nd carbon of each subunit is hidden in the coil
- makes it less insoluble
- prevents amylose from affecting the water potential of the cell
- doesnt affect osmosis

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16
Q

what happens when an amylase-iodine complex is heated

A

when an iodine-amylose complex is heated to 60 degrees,the hydrogen bonds break, the helix unravels, and the iodine is released

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17
Q

what is the function of amylose

A

used for the storage of glucose subunits and energy in plants
- stored as grains within the cell
it is compact
glucose subunits can be easily removed from the molecule
- can be used as building blocks for other substances or as a substrate in respiration to release stored energy

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18
Q

describe the structure of amylopectin and glycogen

A

amylopectin and glycogen are made up of a glucose subunits bonded by 1,4 and 1,6 glycosidic bonds
- means they are branched and non-helical
- consists of 1 chain with no crosslinks between molecules
amylopectin branches form per 20 subunits and form per 10 subunits for glycogen

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19
Q

describe the function and properties of amylopectin

A

amylopectin is used for storage for glucose subunits and energy in plant cells. it is insoluble and compact. stored as granules and have all the glucose units in the same orientation

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20
Q

describe the function and properties of glycogen

A

use for storage for glucose subunits and energy in animal cells. it is insoluble and compact. stored as granules and have all the glucose units in the same orientation
has more 1,6 glycosidic bonds so it is more branched and there is more space where the enzymes can attach
- increase SA so that the molecule can be hydrolysed quickly

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21
Q

describe the structure of cellulose

A

consists of a long unbranched chain of β-glucose subunits
- the subunits are joined by 1,4 glycosidic bonds
- its beta glucose monomers alternate at 180 degrees to each other
- the chain of β-glucose subunits form a straight chain

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22
Q

state and explain the properties of cellulose

A

it is fibrous
- the hydroxyl groups on carbon 2 of each subunit are exposed, allowing hydrogen bonds to form between adjacent cellulose molecules
- some 60–70 molecules bind together to form a cellulose microfibril and many microfibrils join together to form macrofibrils

  • cellulose is strong (high tensile strength) -because of the the hydrogen bonds that can form between adjacent fibrils- and completely insoluble
  • it is used in plant cell walls and provides enough strength to support the whole plant
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23
Q

describe the function of cellulose

A

used in plant cell walls and provides enough strength to support the whole plant

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24
Q

name roles of lipids in living organisms

A
  • as thermal insulation
  • as an energy store
  • to protect organs from mechanical damage
  • in the membranes around cells to control the exit and entry of molecules into the cells
  • as a component of steroid hormones such as testosterone
  • for buoyancy
  • to waterproof parts of the body (i.e skin)
  • as a source of water via respiration
  • as electrical insulation around neurones
  • to aid the absorption, storage, and production of fat-soluble vitamins A, D, E, and K
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25
Q

what is a lipid and name a property

A

lipids are a large compound. are insoluble in water but soluble in organic solvent (ethanol)

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26
Q

what are the elements that make up lipids

A

C, H and O

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27
Q

name 3 examples of lipids

A

triglycerides, phospholipids and steroids

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28
Q

what is a triglyceride

A

a macromolecule containing 1 glycerol molecule, 3 fatty acid chains. the bonds between the glycerol and fatty acid is ester bonds

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29
Q

comment on the energy aspect of triglycerides and explain

A

are rich in energy and used to store excess energy
- can be broken down in aerobic respiration to release this energy
- water is also released, which can be useful for animals that live in dry environments — hence camels store fat in their humps
- the stores can be held under the skin and around major organs. it has the benefit of protecting the major organs from physical shock

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30
Q

comment on the insulation aspect of glycerides and explain

A

are also good insulators
- insulate animals that live in cold environments such as polar bears and aquatic mammals such as whales
- provide buoyancy for these mammals

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31
Q

what is a saturated fatty acid and where it is found

A

when each carbon atom has 2 H atoms attached so there is no double or triple bonds and found in animal fats

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32
Q

what is the melting point of saturated fatty acid and where is it found

A

they have a high melting point and more solid at room temp (eg. butter)

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33
Q

what happens when saturated fatty acids is eaten

A

can cause an increase in low density lipoprotein (LDL)

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34
Q

how does mycoprotein help with saturated fatty acid

A

has less lipid than meat from animals and more of it is unsaturated
- results in less of an increase in LDL

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35
Q

what is an unsaturated fatty acid

A

when there is less than 2 H atoms per carbon, there will be double or even triple bonds between adjacent
- may be called polyunsaturated

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36
Q

where are unsaturated fatty acids found

A

found in plant fats and oils

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37
Q

comment on the melting points of the unsaturated fatty acids

A

have lower melting points and more likely to be liquid at RTP (eg. spread and vegetable oil)

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38
Q

describe the structure of phospholipids

A

has 2 fatty acids and a phosphate group
- tails are hydrophobic (insoluble in water)
- head is hydrophilic (soluble in water)

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39
Q

explain how it forms a phospholipid bilayer

A
  • phospholipids form bilayers with the hydrophobic ‘tails’ in the centre and the hydrophilic ‘heads’ pointing outwards to interact with the surrounding aqueous solution
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40
Q

what does the middle of the bilayer being hydrophobic mean

A

makes it difficult for polar molecules to pass through

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41
Q

what is a protein

A

are polymers consisting of long, unbranched chains of amino acids, which are held together by peptide bonds

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42
Q

how are the bonds between amino acids formed

A

by condensation reaction and occurs between the amine group of 1 amino acid and the carboxylic acid of another

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43
Q

how do 2 amino acids form. what do multiple amino acids form

A

dipeptide and polypeptide

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44
Q

name the 4 types of structure

A

primary, secondary, tertiary and quaternary structure

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45
Q

describe the primary structure

A
  • sequence of amino acids, held together in a chain by covalent bonds called peptide bonds
  • peptide bonds occur between the amine group of one amino acid and the carboxyl group of another
  • the H from the amine group combines with the OH from the carboxyl group in a condensation reaction, with a molecule of water being produced.
46
Q

describe the secondary structure

A

when the chain of amino acids becomes folded and coiled into regions with repeating patterns. two shapes are formed:
* alpha (α) helix — shaped like a coil spring
* beta (β) sheets — pleated like a folded sheet of paper
hydrogen bonds hold the folds and coils in place

47
Q

describe the tertiary structure

A

final folds and coils are caused by the interactions between the R groups on the amino acids. some R groups attract or repel each other, and so interact to form a range of bonds that hold the 3D shape. these bonds include:
* hydrogen bonds between polar R groups
* ionic bonds between R groups with opposite charges
* covalent disulfide bonds between two sulfur-containing R groups
R groups are hydrophobic and twist away from water into the centre of the molecule and vice versa

48
Q

describe the quaternary structure

A

consist of more than one polypeptide chain

49
Q

describe the structure and properties of globular proteins

A

proteins that are highly folded to form a spherical shape
- these proteins are water soluble as they are folded so that the hydrophobic groups are on the inside and the hydrophilic are on the outside, so they can form hydrogen bonds with water
- they are active in metabolism and their activity relies on their three-dimensional shape
- their shape and activity are sensitive to temperature changes
- higher temperatures can cause distortion of their shape

50
Q

describe the structure of haemoglobin

A

haemoglobin contains four polypeptide chains called subunits — two alpha (α) chains and two beta (β) chains
- haemoglobin is a conjugated protein as each subunit has a non-protein prosthetic group attached, called a haem group, which contains a single iron ion (Fe2+)
- one oxygen molecule can attach to each haem group, so a haemoglobin molecule can carry four oxygen molecules

51
Q

describe the function of haemoglobin

A

is used to transport O2 in the form of oxyhaemoglobin

52
Q

name an enzyme

A

amylase

53
Q

describe the function and structure of amylase

A

hydrolyses the bonds between glucose subunits in amylose
- the molecule has regions that are coiled in an alpha (α) helix and other regions that are folded into beta (β) sheets
- the compact globular shape contains an active site that has a specific shape that is complementary to the shape of the substrate (in this case, amylose)
- the active site holds at least one calcium ion that acts as a cofactor — it is essential for the correct action of the enzyme

54
Q

name a hormone

A

insulin

55
Q

describe the function and structure of insulin

A

used to stimulate removal of excess glucose from the blood
- there are two polypeptides held together by disulfide bridges
- one polypeptide is 21 amino acids long and the second is 30 amino acids long
- the molecule has a specific three-dimensional shape that is complementary to the shape of a glycoprotein receptor on the surface of cells in the liver

56
Q

describe the properties and structure of fibrous proteins

A
  • have a regular sequence of amino acids that is repeated many times
  • they are less soluble in water (usually totally insoluble) as they have few hydrophilic groups
  • they have a quaternary structure, and tend to form fibres that have structural functions
  • they are strong due to the bonding between their polypeptide chains
57
Q

describe the function and structure of collagen

A

has three polypeptide chains wound around one another, forming a left handed helix
it contains C, H, O, and N. Its chains when adjacent are joined together by covalent bonds otherwise known as crosslinks
the crosslinks are staggered to avoid weak points in the molecule
collagen contains a high proportion of glycine (which is small, and is every 3rd amino acid in its structure) so its chains can lie close together and to twist. Its monomers are amino acids, which are not identical, and they are joined together by peptide bonds
it is not easily stretched as it is not elastic, however it is flexible
it provides strength in the walls of arteries to withstand the high blood pressure. it is found in tendons, which hold muscle to bone, and in bone, where it is hardened by calcium phosphate. it it also found in cartilage, ligaments, connective tissue, the bronchi, bronchioles, and trachea, and in skin
- it is insoluble as it only has a few hydrophilic R-groups on the outside of its molecules. many collagen fibres can join together via hydrogen bonding to form a fibril

58
Q

what is the structure of keratin

A

has 2 polypeptide chains coiled together

59
Q

what is the function of keratin

A

strong and is used for protecting delicate parts of the body (eg. fingernails, claws, hooves, horns, scales, hair and feathers)
the cells in the outer layer of skin also contain keratin, which makes them impermeable to water

60
Q

what is the structure of elastin

A

linked by tropoelastin
- coiled like a spring and can stretch and recoil

61
Q

what is the function of elastin

A

used whenever stretching and recoil is required
- eg. in the walls of arteries and airways, alveoli, skin and the wall of the bladder

62
Q

what is an inorganic ions

A

are charged particles that have a number of important roles
these roles range from creating skeletal structures to nervous conduction and activating enzymes

63
Q

what is the use of NH4+ (ammonium)

A

a component of amino acids, proteins and nucleic acids Involved in the:
* nitrogen cycle
* maintenance of pH

64
Q

what is the use of Ca2+

A

increases the hardness of bones, teeth and the exoskeletons of crustaceans. it is also found in the middle lamella between plant cells, and:
* a factor in blood clotting
* involved in the control of muscle contraction and synaptic action
* activates enzymes such as amylase and lipase

65
Q

what is the use of Na+

A

involved in:
* the regulation of water potentials in cells and body fluids
* the selective reabsorption of sugars and amino acids in the kidney
* the reabsorption of water in the kidney
* nervous transmission and muscle contraction

66
Q

what is the use of K+

A

improves growth of leaves and flowers in plants involved in the:
* regulation of water potentials in cells and body fluids
* nervous transmission and muscle contraction

67
Q

what is the use of Mg2+

A

absorbed by soil via active transport, found at the centre of chlorophyll as a component for absorbing light during photosynthesis

68
Q

what is the use of H+

A

involved in:
* oxidative phosphorylation in respiration
* photophosphorylation in photosynthesis
* the transport of carbon dioxide in the blood
* the regulation of blood pH
* reduction reactions in metabolism

69
Q

what is the use of Cl-

A

a cofactor in amylase and is involved in the:
* reabsorption of water in the kidney
* regulation of water potentials in cells and body fluids
* transport of carbon dioxide in the blood
* production of hydrochloric acid in the stomach

70
Q

what is the use of OH-

A

involved in the regulation of blood pH

71
Q

what is the use of PO4 3-

A

a component of phospholipids, ATP and nucleic acids
* increases the hardness of bones, teeth and the exoskeletons of crustaceans
* improves root growth in plants

72
Q

what is the use of HCO3 -

A

Involved in the:
* regulation of blood pH
* transport of carbon dioxide in the blood

73
Q

what is the use of NO3 -

A

absorbed by plants from the soil to be used as a component of amino acids, proteins and nucleic acids Involved in the nitrogen cycle

74
Q

what is the test for proteins

A

biuret test
- dissolve in water . add Biuret
- colour change from blue to purple
biuret solution contains copper sulfate and sodium hydroxide
- if no protein is present, the mixture stays blue

75
Q

what is the test for reducing sugars

A

eg. glucose
benedicts test
- dissolve in water. add Benedict’s reagent. heat at 80-90 degrees
- a precipitate forms. colour change from blue to brick red

76
Q

what is the test for non reducing sugars

A

benedicts test
- test it for a reducing sugars to ensure none are present. then dissolve in water
- add a few drops of dilute HCl and boil for 2 mins
- neutralise by adding dilute NaOH. add benedicts reagent and reheat for 2 mins
- precipitate. goes from blue to brick red

77
Q

what is the test for starch

A

iodine solution test
- dissolve in water. add iodine solution
- changes to black (if not present, remains orange

78
Q

what is the test for lipids

A

emulsion test
- dissolve in alcohol and filter and add water to filtrate
- when water is added to filtrate, it will turn clooudy/milky

79
Q

what is the purpose of a biosensor

A

converts a chemical variable into an electrical signal
- when the biosensor is dipped into a solution, the glucose diffuses towards immobilised enzymes
- these catalyse a reaction that releases hydrogen peroxide
- the hydrogen peroxide reacts with a platinum electrode to generate a current
- the current generated is proportional to the glucose concentration

80
Q

how is a biosensor made

A

you would immobilise an enzyme/antibody/single strand of DNA, add your sample, and then if it (for DNA) hybridized, or forms a complex (for enzymes or antibodies) then a transducer would convert it into an electrical signal and this signal would be sent to a display where a quantitative concentration would be shown

81
Q

what is meant by chromatography

A

a process used to separate mixtures of coloured compounds

82
Q

what is meant by mixture

A

contains more than one compound, with compounds not being chemically bonded to each other, each of which has a different solubility in a given solvent

83
Q

what are the stages of chromatography

A
  • placing a small concentrated sample of the mixture solution onto a pencil line drawn above the bottom of the strip of chromatography paper
  • the paper is then placed with one end in a shallow layer of solvent below said pencil line
  • the solvent rises up through the paper by capillary action. when it passes the sample of mixture, the molecules in the mixture start to travel up the paper with the solvent
  • the more soluble a compound is, the further it will travel in the mobile phase, so compounds separate in order of their solubility. non-polar substances move more quickly up the paper strip
  • the paper acts as the stationary phase, and the solvent acts as the mobile phase
  • if the compounds in the mixture are colourless, then you will need to stain them (i.e: ninhydrin for amino acids)
  • whichever way you do chromatography, the stationary phase should be suspended in the mobile phase such that it does not touch the bottom of the container (i.e: clipped to some string hung over the container)
  • you also want to stop the chromatography before the mobile phase reaches the top so that you can mark in pencil where the mobile phase got up to in order to measure Rf values for the compounds present
  • the solvent front is the total distance moved by the solvent
84
Q

what is the difference between paper chromatography and thin layer chromatography

A

its stationary phase tends to be a thin layer of absorbent material, such as silica gel, which spread onto a glass sheet

85
Q

what does Rf stand for

A

retention factor

86
Q

what is the equation for the Rf value

A

= distance moved by molecule
————————————–
distance moved by solvent front

87
Q

explain how the students would use the calibration curve to estimate the glucose concentration (2)

A

– find the absorbance
– find the conc that corresponds to this absorbance
– by following the absorbance value across to line of best fit and then down to the conc

88
Q

describe how you would carry out a controlled experiment to test this hypothesis without using a colorimeter
‘the higher the conc of glucose in the fruit juice, the sweeter it will be’ (4)

A

– taste the juice to see how sweet they are
– place a sample of each juice in a biosensor and take reading
– obtain rank order for sweetness
– compare rank orders for sweetness and glucose conc
– blind taste test to avoid biased

89
Q

describe how a method that uses benedicts reagent and a colorimeter could be calibrated to measure the conc of lactose in an unknown conc (4)

A

– zero the colorimeter
– using a blank
– use red filter
– use known conc
– produce series dilutions
– construct calibration curve
– test unknown sample
– read from calibration curve to determine conc

90
Q

suggest how you can test for the presence of trehalose

A

– carry out benedicts test
– if the test for reducing sugar negative, boil with dilute HCl and retest with benedicts

91
Q

describe the specific heat capacity of water

A

water has a high specific heat capacity –> bc a lot of energy to overcome H bonds
- this means the water maintains a thermally stable environment for aquatic organisms and temperature of organisms change only slowly
- biological reactions functions correctly

92
Q

describe the freezing of water

A

ice is less dense than water as it forms an open lattice structure so it floats, forming an insulating layer on the water
- prevents the water below the ice from freezing
- this means that the organisms beneath the ice do not freeze and nutrients can still circulate
- the ice itself can also act as a habitat for organisms such as polar bears

93
Q

describe the evaporation of water

A

water has a high latent heat of vaporisation
- a lot of energy is needed to cause a liquid to change into a gas (evaporation), which is an efficient mechanism used to cool the surface of living things (eg. sweating)

94
Q

describe the cohesion of water

A

the attraction of water molecules to each other, and produces surface tension
- this creates a habitat on the surface for invertebrates such as pond skaters
- enables continuous columns of water to be pulled up the xylem

95
Q

describe the way water acts as a solvent

A

as the molecules are polar, water can dissolve a wide range of substances, and thus can transport substances around the body
- it allows ionic compounds like magnesium chloride to separate into their charged ions, and so dissolve in water as they are able to interact with it
- this allows organisms such as fish to take up said ions from the water
- water can thus act as both an external and an internal transport medium, and can be used to dilute toxic substances

96
Q

describe the incompressibility of water

A

water cannot be compressed into a smaller volume. this means it can be pressurised and pumped in transport systems or used for support in hydrostatic skeletons

97
Q

describe how water acts as a reactant

A

water molecules are used in a wide range of metabolic reactions such as hydrolysis and photosynthesis

98
Q

describe the usefulness of water being transparent

A

this allows aquatic plants to carry out underwater photosynthesis

99
Q

describe the usefulness of high density

A

this allows water to support organisms and allows for flotation

100
Q

what are the monomers of nucleic acids

A

nucleotides

101
Q

how many amino acids are there

A

20

102
Q

what are the monomers of polysaccharides

A

monosaccharides

103
Q

what are the monomers of proteins

A

amino acids

104
Q

what are the monomers in carbohydrates and proteins joined by

A

covalent bonds

105
Q

what is a condensation reaction

A

when 2 molecules join to become on larger molecule via the formation of a covalent bond and the release of a water molecule

106
Q

how are bonds broken

A

by hydrolysis

107
Q

what is a hydrolysis reaction

A

when molecules that were covalently bonded together are split apart using a water molecule

108
Q

what is a carbohydrate made up of

A

carbon, oxygen and hydrogen

109
Q

what is the general formula of carbohydrates

A

(CH2O)x

110
Q

what are the 3 groups that carbohydrates are put into

A

monosaccharides, disaccharides and polysaccharides

OCR AS/A Level Biology Context (24 decks)

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