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A Level Biology > 2.1.2 Biological Molecules (Foundations in Biology) > Flashcards

2.1.2 Biological Molecules (Foundations in Biology) Flashcards

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1
Q

What’s the role of water in the body?

A
  • provide a medium for reactions to occur
  • transport medium e.g. blood
  • maintain osmotic balance
  • cooling mechanism i.e. sweating
  • waste removal
  • formation of urine
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2
Q

What are the roles of carbohydrates in the body?

A

Simple Sugars (monosaccharides and disaccharides):

  • use in respiration to provide energy for cells
  • other roles e.g. attracting animals to eat fruit

Complex Carbohydrates (polysaccharides):

  • starch and glycogen are energy stores
  • cellulose: plant cell walls
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3
Q

What are the roles of lipids in the body?

A

Fats and Oils (triglycerides):

  • insulation
  • protection of organs
  • stored energy

Cholesterol:

  • component of cell membranes

Steroid Hormones:

  • testosterone, oestrogen, progesterone (sex hormones)
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4
Q

What are the roles of proteins in the body?

A
  • enzymes
  • some hormones
  • antibodies
  • blood clotting
  • muscles
  • structural roles e.g. keratin in hair and collagen in skin
  • channel protein and protein pumps
  • haemoglobin (transports oxygen)
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5
Q

What are the role of nucleic acids in the body?

A

DNA: - stores genetic info

  • codes for proteins

RNA: - protein synthesis

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6
Q

Draw a water molecule

A
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7
Q

What are hydrogen bonds?

A
  • a weak interaction which happens between slightly negatively charged atom (O, N, F) and slightly positively charged hydrogen
  • they form between adjacent water molecules
  • weaker than covalent bonds
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8
Q

Draw how water molecules are joined by hydrogen bonds

A
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9
Q

Name six properties of water, related to its importance for organisms

A
  • liquid at room temperature
  • ideal density
  • ideal solvent
  • cohesion and surface tension
  • high specific heat capacity
  • high latent heat of vaporisation
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10
Q

Describe and Explain why water being a liquid of room temperature is important to organisms

A
  • as the water molecules move, they continually make and break hydrogen bonds
  • the hydrogen bonds make it more difficult for them to escape to become a gas
  • even with H bonds, water has quite a low viscosity so flows easily

water:

  • provides habitats
  • provides a reaction medium for chemical reactions
  • forms a major component of tissues in organisms
  • provides an effective transport medium (e.g. blood)
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11
Q

Describe and explain why the density of water is important to organisms

A
  • water behaves differently from other liquids
  • when most liquids get colder, they become more dense
  • however, as water goes from 4 degrees Celsius to freezing point, due to its polar nature, the water molecules align themselves in a structure which is less dense than liquid water

due to this:

  • aquatic animals live in a stable environment
  • bodies of water are insulated against extreme cold, layers of ice reduce rate of heat loss
  • organisms can live on ice
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12
Q

Describe and Explain why water being a solvent is important to organisms

A
  • water is a good solvent for many substances found in living things (e.g. ionic solutions NaCl)
  • since water is polar, positive and negative parts of water molecules are attracted to the negative and positive parts of the solute
  • water molecules cluster around these parts of the solute molecules or ions and will help separate them and keep them apart
  • so they dissolve and a solution is formed
  • molecules and ions can move around and react together in water e.g. in the cytoplasm of the cell
  • molecules and ions can be transported around living things whilst dissolved in water
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13
Q

Describe and Explain why cohesion and surface tension of water is important to organisms

A
  • water molecules show cohesion, which is when H bonds between them pull them together
  • this happens at the surface of the water as well:
  • at the surface, water contracts as molecules are pulled inwards and gives the surface of the water the ability to resist force applied to it
  • this is surface tension

because of cohesion and surface tension:

  • transport in the xylem relies on cohesion between water molecules sticking together
  • surface tension allows small insects to walk on water
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14
Q

Describe and Explain why high specific heat capacity of water is important to organisms

A
  • water require a lot of energy to increase its temperature
  • a lot of energy is needed to break the hydrogen bonds between water molecules
  • this means that water does not change temperature easily
  • organisms need a stable temperature for enzyme-controlled reactions to happen properly
  • aquatic organisms need a stable environment to live
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15
Q

Describe and Explain why high latent heat of vaporisation of water is important to organisms

A
  • when water evaporates, heat energy, the latent heat of vaporisation, helps the molecules to break away from each other to become a gas
  • because the molecules are held together by hydrogen bonds, a relatively large amount of energy to needed fro water molecules to evaporate
  • water can help to cool living things and keep their temperature stable
  • liquid water remains as liquid despite temperature changes e.g. oceans exist
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16
Q

What are carbohydrates?

A
  • they are molecules made up of sugar units
  • general formula: CnH2nOn
  • include sugars, starch/glycogen and cellulose

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17
Q

What are monosaccharides?

A
  • carbohydrates whose molecules contain just one sugar unit
  • monosaccharides are the monomers of carbohydrates
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18
Q

How are larger carbohydrates made?

A
  • by joining monomers, the monosaccharides, together
  • a condensation reaction occurs to form a glycosidic bond
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19
Q

Why is it called a condensation reaction?

A
  • a water molecule is formed as one of the products of the reaction
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20
Q

What are the properties and functions of monosaccharides?

A
  • sweet-tasting
  • soluble in water
  • insoluble in non-polar solvents
  • crystalline
  • can exist as straight chains or in rings or cyclic forms
  • they are a source of energy due to having a large number of carbon-hydrogen bonds
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21
Q

How are monosaccharides grouped?

A
  • grouped according to the number of carbon atoms in the molecules
  • e.g. triose sugars have 3 carbon atoms
  • pentose 5
  • hexose 6
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22
Q

What is the most common monosaccharide group?

A
  • hexoses
  • includes glucose, fructose and galactose
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23
Q

What is the role of alpha-glucose?

What is its displayed formula?

A
  • energy source
  • component of starch and glycogen, which act as energy stores
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24
Q

What is the function of beta-glucose?

What is its displayed formula?

A
  • energy source
  • component of cellulose, which provides structural support in plant cell walls
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25
Q

Explain the difference between alpha and beta glucose and draw one out

A
  • in α glucose, the OH at C1 is below plane
  • in β glucose, the OH at C1 is above the plane
  • leads to very different properties
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26
Q

What is the role of the monomer, fructose?

A
  • in fruit and nectar: attracts animals to disperse seeds/pollen
  • used by plants to make sucrose (glucose and fructose)
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27
Q

Give examples of two important pentose sugars and their roles

A
  • ribose: component of RNA, ATP and NAD
  • deoxyribose: component of DNA
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28
Q

Draw deoxyribose

A
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29
Q

What are disaccharides?

A
  • two monosaccharide molecules joined together in a condensation reaction to form a disaccharide
  • a new covalent bond called a glycosidic bond is formed and water is removed
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30
Q

What are the properties of disaccharides?

A
  • soluble in water
  • taste sweet
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31
Q

Which disaccharide is made from α glucose + α glucose?

A
  • maltose
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32
Q

What is ß-glucose + galactose?

A
  • lactose
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33
Q

What disaccharide is made from α glucose + fructose?

A
  • sucrose
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34
Q

What is an alpha/beta 1,4-glycosidic bond?

A
  • the glycosidic bond is between carbon atom 1 of one molecule and carbon atom 4 of the other
  • alpha is when the OH on C1 is below the ring
  • beta is when the OH on C1 is above the plane
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35
Q

Through what reaction are carbohydrates broken?

A
  • disaccharides and polysaccharides are broken into monosaccharides by a hydrolysis reaction
  • it requires the addition of water
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36
Q

Define hydrolysis

A
  • a chemical reaction where the covalent bond between two molecules is broken with the addition of a water molecule, separating the two molecules
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37
Q

What are polysaccharides?

A
  • large complex organic molecules made up of many hundred monosaccharide subunits

there are two types:

  • homopolysaccharides: made solely of one kind of monosaccharide (e.g. starch)
  • heteropolysaccharides: made of more than one monosaccharide (hyaluronic acid)
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38
Q

What differs in polysaccharides from monosaccharides and disaccharides and why?

A
  • they are insoluble in water
  • due to their size
  • also because regions that could H-bond with water are hidden away inside the molecule
  • or the molecule (e.g. amylose) may form a double helix, which has a hydrophobic surface
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39
Q

What roles do polysaccharides provide in plants and animals

A
  • energy storage and structural roles
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40
Q

What are the stores of potential energy for plants and animals?

A
  • Glycogen: in animals
  • Starch: in plants
  • starch is made of amylose and amylopectin
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41
Q

What is starch?

A
  • the energy storage polysaccharide in plants
  • glucose made by photosynthesis in plant cells is stored as starch
  • a chemical energy store
  • a polymer of α-glucose
  • it is actually a mixture of two different polysaccharides: amylose and amylopectin
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42
Q

How is amylose formed?

A
  • amylose is formed by a series of condensation reactions that bond alpha glucose molecules together into a long chain
  • forms many alpha 1, 4-glycosidic bonds
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43
Q

Describe the detailed structure of amylose

A
  • once the amylose chain is formed, the angle of the bond means that the long chain of glucose coils into a helix
  • this is further stabilised by hydrogen bonding within the molecule
  • this makes the polysaccharide more compact than glucose molecules
  • OH groups on carbon 2 are situated inside the coil, making the molecule less soluble
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44
Q

What is amylopectin?

A
  • forms glycosidic bonds between carbons 1 and 4 but in addition it has glycosidic bonds between carbons 1 and 6
  • amylopectin also coils into a spiral shape like amylose, held together by H bonds, but with branches emerging from the spiral
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45
Q

How is starch made?

A
  • the highly branched amylopectin is wrapped around the amylose to make up starch
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46
Q

Where in plants is starch stored?

A
  • root tubers e.g. potatoes
  • leaf cells
  • chloroplasts
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47
Q

What is glycogen?

A
  • the energy storage polysaccharide in animals
48
Q

Describe the structure of glycogen

A
  • like amylopectin, with glycosidic bonds between carbon 1 and 4, and carbon 1 and 6
  • the 1-4 bonded chains tend to be smaller than in amylopectin, so glycogen has less tendency to coil
  • however, it does have more branches, which makes it more compact
  • it is easier to remove monomer units as there are more ends
49
Q

Where is glycogen stored?

A
  • muscles: needs to be used when glucose runs out and needs to be converted
  • liver: many reactions so needs a lot of glucose
50
Q

Explain the importance of the difference in structure between glycogen and starch

A
  • glycogen is more space efficient than starch: due to more branching
  • more glucose can be released from glycogen than the same amount of starch: so more energy is obtained from it, advantage in animals as they are more metabolically active
51
Q

What makes starch and glycogen good storage materials?

A
  • compact due to helix form and doesn’t take much space.
  • occurs in dense granules within the cell
  • insoluble: keep glucose in the right place (i.e. not used or transported). glucose is stored in a cell as a free molecule would dissolve and reduces the water potential of the cell which would affect osmotic balance
  • easily hydrolysed by enzymes to release glucose when needed
  • branched structure provides easy access for enzymes to ‘strip off’ glucose when needed
52
Q

If glucose is needed for fuel, why store it as glycogen?

A
  • compact due to helix form and doesn’t take much space.
  • insoluble: keep glucose in the right place (i.e. not used or transported). glucose is stored in a cell as a free molecule would dissolve and reduces the water potential of the cell which would affect osmotic balance
  • easily hydrolysed by enzymes to release glucose when needed
  • branched structure provides easy access for enzymes to ‘strip off’ glucose when needed
  • glycogen is insoluble so doesn’t affect the water potential of cell
  • our muscles and over cells need a store of glucose to use even if we haven’t recently eaten sugar
53
Q

What is cellulose?

A
  • found in plants, forming the cell walls
  • a polymer of beta glucose units where each glucose molecule is inverted with respect to its neighbour
  • the orientation of the beta glucose units places many hydroxyl (OH) groups on each side of the molecule
54
Q

Describe the structure of cellulose

A
  • every other beta-glucose molecule is rotated by 180 degrees
  • the two beta-glucose molecules join together to form a beta-1-4-glycosidic bond
  • it is unable to coil or form branches, so a straight-chain molecule is formed
  • H-bonding between the rotated b-glucose molecules in different chains gives additional strength
  • when 60-70 cellulose chains are bound together in this way, they form microfibrils, which are 10-30nm in diameter
  • these then bundle together into macrofibrils containing up to 400 microfibrils, which are embedded in pectins to form plant cells
  • macrofibrils run in all directions, criss-crossing the wall for extra strength
55
Q

Why is cellulose an excellent material for plant cell walls?

A

cellulose is excellent for cell walls because:

  • microfibrils and macrofibrils have very high tensile strength, both because of the strength of the glycosidic bonds, but also because of H-bonding between chains
  • macrofibrils are stronger than steel wire of the same diameter
  • macrofibrils run in all directions, criss-crossing the wall for extra strength
  • it is difficult to digest cellulose because glycosidic bonds between glucose molecules are hard to break
56
Q

How do features of cellulose allow the plant cell wall to do its job?

A
  • because plant cells do not have a rigid skeleton, so it requires a cell wall to provide support
  • there is space between the macrofibrils to allow ions and water to get into and out of the cell, making it fully permeable
  • the wall has high tensile strength, so it prevents the cells from bursting when they are turgid to help support the plant
  • the wall also protects the delicate cell membrane
  • macrofibril structure can be reinforced with other substances for extra support or to make the cell walls waterproof
  • cutin and suberin are waxes that block the spaces in the cell wall and make it waterproof
57
Q

What are the properties and functions of cellulose?

A
  • provides great tensile strength to cell wall:
  • prevents cell bursting
  • enables turgidity: keeps plant upright when hydrated
  • cell wall is permeable
  • role in guard cells: opening and closing stomata
  • can be reinforced to make it more waterproof of for extra support (e.g. cutin, suberin, lignin)
58
Q

What are lipids?

A
  • a group of substances that are soluble in alcohol rather than water
  • non-polar molecules
  • they are large complex molecules known as macromolecules, which are not built from repeating units
  • includes triglycerides, phospholipids, glycolipids and cholesterol
59
Q

What are triglycerides and describe its components?

A
  • a lipid made by combining one glycerol molecule with three fatty acids
  • glycerol is an alcohol
  • fatty acids are carboxylic acids
60
Q

What are the fatty acid molecules made of?

A
  • they have a carboxyl group at the end, attached to a hydrocarbon tail
  • this may be anything from 2 to 20 carbons long
  • the carboxyl group ionises into H+ and COO-, so it is an acid due to the H+
  • fatty acids can be saturated or unsaturated
61
Q

Draw a glycerol molecule

A
62
Q

What are the properties of fatty acids?

A
  • the tails are hydrophobic (repel water molecules)
  • they make lipids insoluble in water
63
Q

Why can the shape of the hydrocarbon chain in fatty acids kink and how does this affect the properties of a triglyceride?

A
  • having one or more C=C bond changes the shape and forms a kink
  • these kinks push the molecules apart slightly, making them more fluid
64
Q

How are triglycerides formed?

A
  • triglycerides are synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule
  • each ester bond is formed by a condensation reaction (in which a water molecule is released)
  • the process of triglyceride synthesis is called esterification
  • triglycerides break down when the ester bonds are broken
  • each ester bond is broke in a hydrolysis reaction (water molecule is used up)
65
Q

What are the functions of triglycerides?

A
  • energy source: triglycerides can be broken down in respiration to release energy and generate ATP
  • first, hydrolyse ester bonds, then both glycerol and fatty acids can be broken down to CO2 and water. respiration of lipid produces more water than respiration of a sugar
  • energy store: insoluble in water, so can be stored without affecting the water potential of the cell
  • 1g of fat releases twice as much energy as 1g of glucose due to a higher proportion of H atoms
  • insulation: adipose tissue a storage location for whales
  • lipids in nerve cells act as an electrical insulator.
  • buoyancy: fat is less dense than water, helps aquatic mammals stay afloat
  • protection: humans have fat around delicate organs, such as kidneys, to act as a shock absorber
  • peptidoglycan cell wall of some bacteria is covered in the lipid-rich outer coat
66
Q

What are phospholipids and describe its structure?

A
  • they are also macromolecules
  • similar to triglycerides except one fatty acid molecule is replaced by a phosphate group
  • a condensation reaction between an OH group on a phosphoric acid molecule (H3PO4) and one of the OH on glycerol
  • most fatty acids found in phospholipids have an even number of C atoms (often 16 or 18)
  • commonly one of these chains is saturated and the other unsaturated
67
Q

What is the behaviour of phospholipids in water?

A
  • the phosphate group is polar and the fatty acid tails are non-polar
  • this is known as amphipathic
  • in water, they form a later on its surface, with the phosphate heads in the water and the tails sticking out
  • they are called surface-active agents, or surfactants
  • they can also form a phospholipid bilayer with all their hydrophobic tails pointing toward the centre of the sheet, protected from the water by the hydrophilic heads
  • they can also form micelles
68
Q

How does the phospholipid bilayer play a key role in cell membranes?

A
  • between 20-80% of membranes in plants and animal cells are made of phospholipids
  • bacterial membranes tend to contain a higher proportion of protein
  • the individual phospholipids are free to move around in their layer, but will not move into any position where their hydrophobic tails are exposed to water
  • this gives the membrane some stability
  • the membrane is selectively permeable
  • it is only possible for small and non-polar molecules to move through the tails in the bilayer such as oxygen and carbon dioxide
  • this lets the membrane control what goes in and out of the cell and keeps it functioning properly
69
Q

What are sterols?

A
  • steroid alcohols
  • another type of lipid
  • they are complex alcohol molecules, based on a four-carbon ring structure (isoprene units) with a -OH group on one end
  • they are amphipathic
70
Q

What is cholesterol, its structure and where is it made?

A
  • cholesterol is a sterol
  • it is a small and hydrophobic molecule
  • mainly made in the liver in animals
  • plants also have a cholesterol derivative in their membranes, called stigmasterol (it has a double bond between carbon 22 and 23)
71
Q

What hormones are made from cholesterol and why is that helpful?

A
  • steroid hormones such as testosterone, oestrogen, vitamin D
  • they are small and hydrophobic, so can pass through the hydrophobic part of the cell membrane
72
Q

What is the function of cholesterol?

A
  • due to being small and hydrophobic, it can sit in the middle of the hydrophobic part of the bilayer
  • it regulates the fluidity of the membranes, preventing it from becoming too fluid or stiff
  • steroid hormones testosterone, oestrogen, vitamin D and bile are made from cholesterol
  • since they are hydrophobic, they can pass through the hydrophobic part of the cell membrane and any other membrane inside the cell
73
Q

What are proteins?

A
  • they are large polymers comprised of long chains of amino acids
74
Q

What chemical elements are in amino acids?

A
  • all contain carbon, oxygen, hydrogen and nitrogen
  • some contain sulfur
75
Q

Draw the structure of an amino acid

A
76
Q

How many naturally occurring amino acids are there?

A
  • 20
77
Q

How are peptides synthesised?

A
  • they are linked together by peptide bonds to form dipeptides and polypeptides
  • the carboxyl group from one amino acid bond with the amine group from another to form a peptide bond
  • a molecule of water is released during the reaction, called a condensation reaction
  • when many amino acids are joined together, a polypeptide is formed
  • this is catalysed by the enzyme peptidyl transferase present in ribosomes
78
Q

Which enzymes catalyse the breakdown of polypeptides in humans?

A
  • small intestine: trypsin
  • stomach: pepsin
79
Q

Describe the primary structure of proteins

A
  • the sequence of amino acids in a protein chain is its primary structure
  • this is determined by the sequences of bases on a gene
  • the particular amino acids in the sequence will influence how the polypeptide folds to give the protein’s final shape
  • which in turn will determine its function
  • a change in one amino acid could lead to a different protein/prevent protein function
80
Q

Describe the secondary structure of proteins

A
  • formed when amino acid chain coils or folds
  • may form an α helix or ß-pleated sheet, or they may not adopt a regular structure, or even have more than one secondary structure
  • hydrogen bonds holds the structures in place
  • they are weak bonds, but there are many, so give great stability
  • these bonds form between different amino acids in the chain
81
Q

Describe the structure of alpha helixes and beta-pleated sheets

A

alpha-helix:

  • 36 amino acids per 10 turns of the helix
  • helix is held together by the hydrogen bonds between the NH group of one amino acid and the -CO group of another four places ahead of it

Beta-pleated sheet:

  • a very slight zig-zag structure
  • hydrogen bonds between the -NH group of one amino acid and the -CO group of another further down the strand hold the sheet together
82
Q

Describe the tertiary structure of proteins

A
  • the coiled or folded chain of amino acids is often coiled and folded further to form the final 3D shape of the protein
  • the coiling or folding of proteins in their secondary structures brings R-groups of different amino acids closer together so they can interact and fold further

interactions that may occur:

  • hydrophobic and hydrophilic interactions: weak interactions between polar and non-polar R-groups
  • hydrogen bonds: weakest of the bonds formed
  • ionic bonds: stronger than H bonds and form between oppositely charged R-groups
  • disulfide bonds: these are covalent and the strongest of the bonds, but only form between R-groups that contain sulfur atoms
83
Q

Describe the quaternary structure of proteins

A
  • some proteins are made of several different polypeptide chains held together by bonds
  • quaternary structure is the way polypeptide chains are assembled together
  • it is the interaction between R groups on different chains that hold the quaternary structure in place
84
Q

What kind of bonds hold together the primary structure of proteins?

A
  • peptide bonds between amino acids
85
Q

What kind of bonds hold together the secondary structure of proteins?

A
  • hydrogen bonds
86
Q

What kind of bonds hold together the tertiary structure of proteins?

A
  • ionic bonds: the attraction between negatively-charged R groups and positively-charged R groups on different parts of the molecule
  • disulfide bonds: the sulphur atom from one cysteine bond and another sulphur atom come close and form a disulphide bond
  • hydrophobic and hydrophilic interactions: when hydrophobic R groups are close together in the protein, they tend to clump together, meaning hydrophilic R groups are more likely pushed to outside, affecting how proteins fold up into its final structure
  • hydrogen bonds: weak bonds between slightly positively-charged hydrogen atoms in some R groups and slightly negatively charged atoms in other R groups
87
Q

What kind of bonds hold together the quaternary structure of proteins?

A
  • determined by the tertiary structure
  • can be influenced by all the other levels
88
Q

Describe globular proteins and their structure

A
  • they are compact, water-soluble and have a spherical shape
  • the hydrophilic R groups on the amino acids tend to be pushed outside the molecule due to hydrophobic and hydrophilic interactions
  • this makes the globular proteins soluble, so they’re easily transported in fluids
89
Q

What are conjugated proteins?

A
  • they are globular proteins that contain a non-protein component, called a prosthetic group
  • proteins without a prosthetic group are called simple proteins
  • prosthetic groups could include:
  • lipids
  • carbohydrates
  • metal ions
  • molecules derived from vitamins
  • haem groups
90
Q

Describe the structure and function of the haemoglobin protein

A
  • the quaternary structure of haemoglobin is made up of four polypeptides:
  • two alpha-globin chains
  • two beta-globin chains
  • on the outside of each chain, there is space for a haem group
  • the haem group contains an iron ion
  • in the lungs, an oxygen molecule binds to the iron in each of the four haem groups
  • when it binds, haemoglobin turns from a purple-red colour to bright red
  • the oxygen is released when it reaches the tissues
91
Q

Describe the structure and function of the protein hormone insulin

A
  • a globular protein made of two polypeptide chains
  • A chain begins with a section of alpha-helix and the B chain ends with a section of beta-pleat
  • both chains fold into a tertiary structure and are then joined together by disulfide links
  • amino acids with hydrophilic R groups are on the outside of the molecule, making it soluble in water
  • insulin binds to glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose
92
Q

Describe the function of the protein amylase

A
  • a globular protein
  • an enzyme that catalyses the breakdown of starch in the digestive system
  • made of a single chain of amino acids
  • secondary structure contains both alpha helix sections and beta pleated sheet section
93
Q

What are fibrous proteins?

A
  • have regular repetitive sequences of amino acids
  • usually insoluble in water
  • due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures
  • tend to have a structural function
94
Q

Describe the structure and function of the protein collagen

A
  • a fibrous protein
  • a connective tissue found in skin, tendons, ligaments and the nervous system
  • made up of three polypeptides wound together ina long and strong rope-like structure
  • bones are made of collagen and then reinforced with calcium phosphate to make them hard
95
Q

Describe the structure and function of the protein keratin

A
  • a group of fibrous proteins found in hair, skin, nails
  • has a large proportion of sulfur-containing amino acid, cysteine
  • this results in many strong disulfide bridges
  • the degree of disulfide bonds determines the flexibility
  • hair contains fewer bonds than nails, so is more flexible
  • the unpleasant smell when hair or skin is burnt is due to the presence of large quantities of sulfur
96
Q

Describe the function of elastin

A
  • a fibrous protein found in elastic fibres
  • elastic fibres are present in the walls of blood vessels and in the alveoli of lungs
  • they allow these structures to expand but also return to normal size
  • elastin is a quaternary protein made from many stretchy molecules called tropoelastin
97
Q

What is an inorganic ion

A
  • an ion that doesn’t contain carbon
98
Q

What is the role of calcium ions, Ca2+, in biological processes?

A
  • increases rigidity of bone, teeth and cartilage and is a component of the exoskeleton of crustaceans
  • important in clotting blood and muscle contraction
  • activator for several enzymes, such as lipase, ATPase and cholinesterase
  • stimulates muscle contraction and regulates the transmission of nerve impulses
  • regulates the permeability of cell membranes
  • important for cell wall development in plants and formation of middle lamella between cell walls
99
Q

What is the role of sodium ions, Na+, in biological processes?

A
  • involved in regulation of osmotic pressure, control of water levels in body fluid and maintenance of pH
  • affects the absorption of carbohydrate in the intestine and water in the kidney
  • contributes to the nervous transmission and muscle contraction
  • a constituent of the vacuole in plants which helps maintain turgidity
100
Q

What is the role of potassium ions, K+, in biological processes?

A
  • involved in the control of water levels in body gfluid and maintenance of pH
  • assists active transport of materials across the cell membrane
  • involved in synthesis of glycogen and protein, and breakdown of glucose
  • generates healthy leaves and flowers in flowering plants
  • contributes to nervous transmission and muscle contraction
  • component of vacuoles in plants, helping to maintain turgidity
101
Q

What is the role of hydrogen ions, H+, in biological processes?

A
  • involved in photosynthesis and respiration
  • involved in transport of oxygen and carbon dioxide in blood
  • involved in regulation of blood pH
102
Q

What is the role of ammonium ions, NH4+, in biological processes?

A
  • a component of amino acids, proteins, vitamins and chlorophyll
  • some hormones are made of proteins
  • an essential component of nucleic acids
  • involved in maintenance of pH in the human body
  • a component of the nitrogen cycle
103
Q

What is the role of nitrate, NO3-, in biological processes?

A
  • a component of amino acids, proteins, vitamins and chlorophyll
  • an essential component of nucleic acids
  • some hormones are made of proteins, which contain nitrogen
  • a component of the nitrogen cycle
104
Q

What is the role of hydrogencarbonate, HCO3-, in biological processes?

A
  • involved in regulation of blood pH
  • involved in transport of carbon dioxide into and out of blood
105
Q

What is the role of chloride ions, Cl-, in biological processes?

A
  • involved in the chloride shift, maintaining the pH of the blood during gas exchange
  • acts as a cofactor for the enzyme amylase
  • involved in some nerve impulses
106
Q

What is the role of phosphate ions, PO43-, in biological processes?

A
  • involved in photosynthesis and respiration reaction
  • needed for the synthesis of many biological molecules, such as nucleotides, phospholipids
  • bone formation
  • cell membrane formation
107
Q

What is the role of hydroxide ions, OH-, in biological processes?

A
  • affects the pH of substances (more OH-, more alkali)
  • catalysis of reactions
108
Q

What are reducing sugars and which sugars are reducing?

A
  • sugars that can reduce another molecule, or donate electrons
  • all monosaccharides and some disaccharides are reducing sugars
109
Q

How to test for reducing sugars?

A
  1. Place sample in boiling tube and add equal volume of Benedict’s reagent
  2. Heat mixture gently in a boiling water bath for five minutes
    - reducing sugars will react with the copper ions in Benedict’s (an alkaline solution of copper(II) sulfate)
    - this results in the blue Cu2+ being reduced to red Cu+
    - the more reducing sugar present, the more precipitate formed and the less blue Cu2+ ion are left in solution
    - this test is qualitative
110
Q

How to test for non-reducing sugars?

A
  • if the result for reducing sugars is negative, there could still be non-reducing sugars like sucrose
  • you have to break them down into monosaccharides
  • get a new sample of solution
  • add dilute HCl and heat in water bath that is boiling
  • neutralise with sodium hydrogencarbonate
  • carry out Benedict’s test like for reducing sugar
  • if it is positive, it will for coloured precipitate
111
Q

How to test for glucose?

A
  • test strips with reagent
112
Q

How to test for starch?

A
  • iodine test

add iodine dissolved in potassium iodide

  • if starch is present, sample changes from orange-brown to dark, blue-black colour
  • if not, it stays
113
Q

How to test for proteins?

A
  • biuret test
  • test solution needs to be alkaline, so first add a few drops of sodium hydroxide solution
  • then add copper(II) sulphate solution
  • if protein is present solution turns lilac
  • if no protein, solution stays blue
114
Q

How to test for lipids

A
  • emulsion test
  • test substance with ethanol then pour solution into water
  • if lipid present, solution will turn milky
  • more lipid, more milky
  • if no lipid, solution stays clear
115
Q

What is the Rf value?

A
  • distance travelled by spot / distance travelled by solvent

A Level Biology (25 decks)

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