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BIOLOGY A LEVEL > 2.2 Biological Molecules > Flashcards

2.2 Biological Molecules Flashcards

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1
Q

Why is water of great biological importance?

A
  • It is the medium in which all metabolic reactions take place
  • 71% of the earth is water, so it is a major habitat fro organisms
  • 70-95% of the mass of a cell is water
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2
Q

What is the electrical configuration of water like?

A
  • It is in the from of H2O in a covalent bond, with 2 hydrogens and one oxygen
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3
Q

What is a dipole (in water molecules)?

A
  • a dipole is the separation of charge due to electrons in covalent bonds being unevenly shared
  • the sharing of electrons is uneven in water as the oxygen atom attracts electrons more strongly than the hydrogen atoms
  • this leads to a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms (δ+)
  • this also results in the asymmetrical shape
  • the electrons are closer to the oxygen atom than the hydrogen
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4
Q

What is a polar molecule (and is water one?)

A

A polar molecule is a molecule with one end negatively charged and one end positvely charged (water is one)

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5
Q

What type of bonds form between water molecules? (and how strong are they?)

A
  • hydrogen bonds form between water molecules due to their polarity between positvely and negatively charged regions of adjacent water molecules
  • Hydrogen bonds are weak in small numbers, so will constantly break and reform, while in larger numbers they are strong
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6
Q

What important properties of water do hydrogen bonds contribute to?

A
  • excellent solvent
  • acts as a transport medium
  • relatively high specific heat capacity
  • relatively high specifc latent heat of vapourisation
  • becomes less dense as a solid and can act as a habitat
  • high surface tension and cohesion
  • acts as a reagent
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7
Q

Why is water good as a solvent and what does it do?

A
  • because water is a polar molecule many polar covalent substances and ion will disolve into it
  • this allows it to carry out chemical reactions (because dissolved solutes are more reactive when they are free to move)
  • metabolites which are polar can be transported more efficiently
  • allows prokaryotic cells to exchange substances with surroundings via diffusion
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8
Q

What is a metabolite?

A

A chemical substance involved in metabolism

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9
Q

What is osmosis?

A

Osmosis is the diffusion of water through a partially permeable membrane from an area of high water potential to an area of low water potential

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10
Q

What is the specific heat capacity of water and why?

A
  • SHC is the amount of energy required to raise 1kg of a substance by 1 degree and water has a SHC of 4200 J/kg OC
  • It has a relatively high SHC due to the large number of hydorgen bonds which require large amounts of thermal energy to break
  • this means the temperature of water does not fluctuate a lot
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11
Q

Why is the high SHC of water good for organisms?

A
  • provides a suitable habitat for many animals
  • can absorb large amounts of heat without large heat fluctuations (constant temp)
  • that is used for maintaning temperatures that are optimal for enzyme activity in eukaryotes and prokaryotes
  • water in blood plasma is also used to transfer heat around the body to help mantain a constant temperature
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12
Q

What is water in blood plasma used for?

A
  • Water in blood plasma is used to transfer heat around the body as when blood passes through warmer parts of the body it will absorb the heat energy but not increase temperature much
  • water in tissue fluid also has a regulatory role in maintaining constant body temp
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13
Q

What is the latent heat of vapourisation of water and why is it useful?

A
  • latent heat of vapourisation for water states that in order to change from a liquid to a gas, large amounts of thermla energy are needed to break hydrogen bonds
  • this is good for organisms as only a little water needs to evaporate for the organism to lose large amounts of heat (e.g sweating)
  • acts as a coolant
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14
Q

What is water cohesion?

A
  • hydrogen bonds between water molecules allow strong cohesion (sticking together) which allows columns of water to travel (e.g up xylem)
  • this cohesion also creates surface tension where a body of water meets air so the top layer of water molecules acts as a film
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15
Q

What is water adhesion?

A
  • water is able to hydrogen bond to other molecules such as cellulose (known as adhesion)
  • also enables water to move up xylem due to transpiration
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16
Q

What are the 5 key molecules required for organisms’ structures?

A
  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water
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17
Q

What are monomers?

A

Monomers are smaller units from which large molecules are made

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18
Q

What are Polymers?

A

Polymers are molecules made from a large number of monomers in a chain

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19
Q

What are macromolecules?

A
  • Macromolecules are very larger molecules containing more than1000 atoms
  • Polymers can be macromolecules if they have the same repeating units
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20
Q

What is the difference between a nonpolar and polar covalent bond?

A
  • A non-polar covalent bond is a colavent bond where the electrons are shared equally
  • A polar covalent bond is a bond where the electrons are shared unequally (where an atom is more electronegative)
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21
Q

Why are covalent bonds very stable?

A

Becayse they require large amounts of energy to break their bonds

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22
Q

How does polymerisation start?

A
  • When two monomers are close enough that their outer orbitals overlap this results in a covalent bond (electrons are shared)
  • if more monomers are added this leads to polymerisation and possibly macromolecules
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23
Q

What is condensation polymerisation?

A
  • known as dehydration synthesis
  • occurs when polymers or macromolecules are formed and water is removed
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24
Q

What is hydrolysis?

A
  • In hydrolysis, covalent bonds are broken when water is added
  • They produce monomers
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25
Q

what covalent bonds are present in carbohydrates?

A
  • glycosidic
  • 2 carbons, one oxygen, single bonds
    -C- O - C
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26
Q

what covalent bonds are present in proteins?

A
  • peptide
  • oxygen carbon double bond, carbon nitrogen single bonds, nitrogen hydrogen single bond
  • O = C - N - H
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27
Q

what covalent bonds are present in lipids?

A
  • ester
  • oxygen carbon double bond, carbon oxygen single bond, carbon oxygen single bond
  • O = C - O - C
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28
Q

what covalent bonds are present in nucleic acids?

A
  • phospodiester
  • see diagrams
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29
Q

What does something need to have to be an organic compound?

A
  • for something to be an organic compound it must have carbon and hydrogen
  • carbohydrates, proteins, lipids and nucelic acids are organic compounds
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30
Q

Why are carbon atoms the key to organic compounds?

A
  • each carbon atom can form 4 covalent bonds which makes compounds extremely stable
  • Carbon atoms can from straight chains, branched chains or rings
  • Carbons atoms can form covalent bonds with oxygen, nitrogen and sulfur
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31
Q

What are the chemical properties of carbohydrates?

A
  • All carbohydrates contain the chemical elements C, H and O
  • as H and O atoms are always present in the ratio 2:1 (where hydrate comes from) the formula is Cx(H20) y
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32
Q

What is the formula for carbohydrates?

A

Cx(H20)y

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33
Q

What are the 3 types of carbohydrates?

A

monosaccharides, disaccharides and polysaccharides

34
Q

What are the functions of carbohydrates?

A
  • source of energy - (glucose is used for energy release during cellular respiration)
  • store of energy - (glycogen is stored in the muscles and liver of animals)
  • structurally important - (cellulose in the cell walls of plants)
35
Q

What is the definition of a monosaccharide?

A
  • A single sugar monomer which are all reducing sugars (can act as a reducing agent)
36
Q

What are the functions and examples of monosaccharides?

A
  • they are sources of energy in respiration
  • they are used as building blocks for polymers
  • glyceraldehyde (3C)
  • ribose (5C)
  • glucose (6C)
37
Q

What does the 6C in glucose (6C) mean?

A
  • means there are 6 carbon atoms
38
Q

What is the definition of a disaccharide bond?

A
  • a sugar formed by 2 monosaccharides joined by a glycosidic bond in a condensation reaction
39
Q

What are some examples of disaccharides?

A
  • maltose (2 alpha glucose)
  • sucrose ( alpha glucose and fructose)
  • lactose (alpha glucose and beta galactose)
40
Q

What is the function of a disaccharide?

A
  • sugar found in germinating seeds (maltose)
  • mammal milk sugar (lactose)
  • sugar in sugar cane (scurose)
41
Q

What are polysaccharides?

A
  • a polymer of many monosaccharides joined by glycosidic bonds in a condensation reaction
42
Q

What are some examples of polysaccharides?

A
  • cellulose (beta glucose)
  • starch (alpha glucose in the from of amylose and amylopectin)
  • glycogen (alpha glucose)
43
Q

What are the functions of polysaccharides?

A
  • energy storage (starch in plants and glycogen in animals)
  • structural (cell wall )
44
Q

What is the difference between alpha and beta glucose?

A
  • The difference between alpha and beta glucose is the orientation of the hydroxyl (-OH) and hydrogen group (-H) on carbon 1
  • The beta glucose has the hydroxyl group above the ring while the alpha glucose has its hydroxyl group below the ring
45
Q

What are the 4 functions of lipids?

A
  • source of energy - can be respired (lipids have high energy yield)
  • store of energy - stored in animals as fats in adipose tissues and in plants as lipid droplets
  • insulating layer - thermal insulation under animal skin and electrical insulation around nerve cells
  • component of biological membranes
46
Q

What are 4 example types of lipids?

A
  1. Triglycerides (fats and oils)
  2. phospholipids
  3. waxes
  4. steroids (e.g cholestrol)
47
Q

What is the chemical composition of lipids?

A
  • all lipids contain the chemical elements of C,H,O
  • the proportion of O is low compared to carbohydrates
48
Q

What is the chemical composition of proteins?

A
  • proteins contain C,H,O and N
  • some proteins also contain S (Sulphur)
49
Q

What are the functions of proteins?

A
  1. Required for cell growth, repair and replacement of biological materials
  2. Structurally Important - for muscles, collagen (bone and skin) and elastin (skin), keratin (hair)
  3. Proteins can also be carrier molecules in cell membranes, antibodies, enzymes or hormones
50
Q

What is the chemical composition of nucleic acids?

A
  • all nucleic acids contain C, H, O
  • They also contain Nitrogen in their bases and Phosphorus (P) in the form of phosphate grous
51
Q

What is the singular function of nucleic acids?

A
  • carrying genetic code in all living organisms
  • they are essential in the control of cellular processes such as protein synthesis
  • 2 main classesof nucleic acids are DNA and RNA
52
Q

What is the definition of a reducing sugar?

A
  • a reducing sugar can donate electrons (the carbonyl group becomes oxidised)
  • the sugars become the reducing agent
53
Q

How can you test for reducing sugars?

A
  • Reducing sugars can be tested for using Benedicts test
  • They will reduce the soluble copper sulphate into an insoluble brick red copper oxide
54
Q

What are 3 examples of reducing sugars?

A
  • glucose, fructose and galactose
  • all have the same molecular formula as glucose but have a different structural formula which means they have slightly different properties
55
Q

How do you test for non-reducing sugars?

A
  • non-reducing sugars cannot donate electrons so they cannot be oxidised
  • therefore they must be broken via hydrolysis from a disaccharide into 2 monosaccharides
  • Then Benedicts test can be carried out
  • e.g sucrose
56
Q

What are trioses?

A
  • Trioses are monosaccharides with 3 carbon atoms
  • e.g glyceraldehyde
57
Q

What are pentoses?

A
  • monosaccharides with 5 carbon atoms (per molecule)
  • e.g ribose
58
Q

What are hexoses?

A
  • Hexoses are monosaccharides formed from molecules with 6 carbon atoms
  • e.g glucose
59
Q

What is the molecular formula and functions of glucose?

A
  • C6H12O6
  • The most common monosaccharide
  • main function of glucose is as an energy source
  • the main substrate used in respiration (releases energy for the production of ATP)
  • It is soluble (monosaccharide) so can be transported in water
60
Q

What are the 2 forms of glucose?

A
  • 2 structurally different forms of glucose exists, alpha and beta glucose
61
Q

What is an isomer?

A
  • an isomer is an organic molecule with the same molecular formula but with different structures which results in different properties
62
Q

When is glucose in a straight chain vs when is it in a ring structure?

A
  • glucose is in a straight chain structure when not in an aqueous solution (there is no beta and alpha then, they are both same)
  • when in an aqueous solution alpha and beta glucose are in a ring structure
63
Q

What is the difference between alpha and beta glucose?

A
  • alpha glucose has the OH molecule under the carbon 1 in ring structure
  • beta glucose has the OH molecule over the carbon 1 molecule in ring structure
64
Q

What is the structure of alpha glucose?

A
  • 5 carbons and one oxygen in a hexagonal ring (carbons numbered from right to left)
  • carbon 1,2 and 4 have a hydrogen above bonded and an OH below
  • carbon 3 has an OH above the carbon and a H below
  • Carbon 5 has a H below and a CH2OH above (the carbon in this is numbered 6)
65
Q

What is the structure of beta glucose?

A
  • 5 carbons and one oxygen in a hexagonal ring (carbons numbered from right to left)
  • carbon 2 and 4 have a hydrogen above bonded and an OH below
  • carbon 1,3 has an OH above the carbon and a H below
  • Carbon 5 has a H below and a CH2OH above (the carbon in this is numbered 6)
66
Q

Are different polysaccharides formed from two isomers of glucose?

A

YES

67
Q

What common polysaccharides contain alpha glucose? (and do not contain any beta glucose)

A
  • starch
  • glycogen
68
Q

What common polysaccharides contain beta glucose? (and do not contain any alpha glucose)

A
  • cellulose
69
Q

What are the 2 most important pentose sugars and why?

A
  • ribose and deoxyribose sugars
  • they make up RNA and DNA respectively
70
Q

What are the 2 most important pentose sugars and why?

A
  • ribose and deoxyribose sugars
  • they make up RNA and DNA respectively
71
Q

What are the structures of ribose and deoxyribose sugars?

A

RIBOSE:
- 4 carbons and one oxygen in a pentagon shape (numbered clockwise from the right)
- carbon 1 has OH above and H below
- carbon 2 and 3 have H above and OH below
- carbon 4 has H below and CH2OH above (the carbon is numbered 5)
DEOXYRIBOSE:
- same except on carbon 2 has H below and above (lost one oxygen)

72
Q

What is (a cell’s) osmolarity?

A
  • The total number of solute particles per litre
  • measure of concentration of a solution
73
Q

What is the difference between reducing and non-reducing sugars?

A
  • non reducing sugars cannot donate electrons, while reducing sugars can donate electrons and become oxidised
  • OILRIG
74
Q

What is Benedict’s reagent? (and what does this lead the test to do)

A
  • Benedict’s Reagent is a blue solution containing copper (ii) sulfate ions
  • In the presence of a reducing sugar copper (i) oxide forms
  • copper oxide is not soluble in water so it forms a precipitate
75
Q

What is the method for testing a sugar with Benedict’s?

A
  • Add benedicts to a sample solution in a test tube
  • Heat the test tube in a water bath (for 5 minutes)
  • If a reducing sugar is present a coloured precipitate will form as the copper sulfate is reduced into copper oxide via the reducing sugar donating electrons
  • An excess of Benedict’s must be used
75
Q

Why is the Benedicts Test semi quantitative and what is the scale of presence?

A
  • A positive test result is a colour change from blue to green, yellow and orange (low/medium concentrations of reducing sugar) all the way to brown/brick red which shows a high concentration of reducing sugar
  • It is semi quantitative as the degree of colour change can give an approximation of how much reducing sugar is present
76
Q

What are the safety precautions for Benedict’s Test?

A
  • Use safety goggles and heatproof gloves
  • Handle Test Tube with tongs
77
Q

What are 4 common reducing sugars?

A
  • Galactose
  • Glucose
  • Fructose
  • Maltose
78
Q

What is a non reducing sugar?

A

Sucrose

79
Q

What is the test for non reducing Sugars?

A
  • Add dilute hydrocloric acid to a sample and heat in a water bath (that has just been brought to boil)
  • Neutralise the solution with sodium hydrogencarbonate (use indicator to find when solution has been neutralised and add some more sodium hydrogencarbonate as condition need to be slightly alkaline for benedicts)
  • Then carry out benedicts as usual, and if colour change occurs a non-reducing sugar is present)
80
Q

Why does neutralising the non reducing sugars help to test them?

A
  • the acid hydrolyses any glycosidic bonds in any sugars/ carbs
  • The monosacharides remaining have aldehyde or ketone functional groups open to donate electrons to copper sulfate in benedicts
81
Q

What is the iodine test for starch?

A
  • To test for presence of starch add drops of orange brown iodine in postassium iodide solution to the sample
  • the iodine is in potassium iodide as iodine by itself is not soluble in water
  • If starch is present, iodide ions in the slution interact with centre of starch molecules producing a blue black complex
  • If not the colour stays brown orange
  • useful for showing when starch has been digested by enzymes

BIOLOGY A LEVEL (3 decks)

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