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*AQA A-Level Biology* > Chapter 1: Biological Molecules > Flashcards

Chapter 1: Biological Molecules Flashcards

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1
Q

Define covalent bonding:

A

The sharing of outer shell electrons between atoms, forming a stable molecule.

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2
Q

Define ionic bonding:

A

The (electrostatic) attraction of oppositely charged ions in an “ionic bond”. This bond is weaker than covalent bonds.

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3
Q

Define hydrogen bonding:

A

When the electrons within a molecule are not evenly distributed so there are areas with more negative charge than the rest if the molecule. This molecule is said to be “polarised” and the negative region of one polar molecule and the positive region of another polar molecule attract via weak electrostatic bonds.

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4
Q

Define a monomer:

A

A single repeating unit which can be linked together to form long chains.

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5
Q

Define a polymer:

A

A chain of monomers/ groups of monomers forming repeating units.

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6
Q

Give 4 examples of monomer units:

A
  • Monosaccharides
  • Fatty acids and glycerol
  • Amino acids
  • Nucleotides
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7
Q

Give 4 examples of polymer units:

A
  • Polysaccharides (carbohydrates)
  • Lipids
  • Polypeptides (proteins)
  • Polynucleotides (nucleic acids e.g. DNA or RNA)
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8
Q

Define hydrolysis:

A

Adding water to break a bond

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9
Q

Define condensation:

A

Joining molecules, which releases water.

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10
Q

Define metabolism:

A

The sum of the chemical reactions that occur in cells.

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11
Q

Define atomic number:

A

The number of protons in an atom.

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12
Q

Define mass number:

A

The total number of protons and neutrons in an atom.

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13
Q

What is an isotope?

A

Different types of an element that exist due to a variation the the number of neutrons present.

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14
Q

What is an ion?

A

A charged atom (gained or lost electrons).

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15
Q

What is OILRIG?

A

Oxidation

Is

Loss of electrons

Reduction

Is

Gain of electrons

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16
Q

What is a carbohydrate?

A

A molecule made of carbon, hydrogen and oxygen.

Monomer unit: sugar/ monosaccharide.

Polymer unit: disaccharide/ polysaccharide.

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17
Q

Name 4 carbohydrates:

A
  • Sugar
  • Starch
  • Cellulose
  • Glycogen
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18
Q

Name 3 monosaccharides:

A
  • Glucose
  • Galactose
  • Fructose
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19
Q

glucose+glusose=

A

Maltose

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20
Q

glucose+fructose=

A

Sucrose

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21
Q

glucose+galactose=

A

lactose

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22
Q

Compare alpha and beta glucose:

A
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23
Q

Define a reducing sugar:

A

A sugar that can donate electrons to another chemical.

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24
Q

How can you test for reducing sugars?

A

1) Add Benedict’s solution to sample in a 1:1 ratio
2) Heat the mixture in a gently boiling water bath for 5 mins
3) Look for a colour change from blue to brick red/ orange precipitate.

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25
Q

Why does a colour change occur in the test for reducing sugars?

A

Insoluble red precipitate of copper (I) oxide has formed.

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26
Q

How can the Benedict’s test become semi-quantitative?

A

Use the colours as an approximate amount of reducing sugar:

Blue= none

Green= very low

Yellow= low

Orange= medium

Brick red= high

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27
Q

How are disaccharides/polysaccharides formed?

A

A condensation reaction occurs between monosaccharides which forms a glycosidic bond. They can be broken down via hydrolysis.

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28
Q

How can you test for non-reducing sugars?

A

1) Add sample to dilute hydrochloric acid in a 1:1 ratio
2) Heat the mixture in a gently boiling water bath for 5 minutes
3) Slowly add sodium hydrogencarbonate solution to neutralise the acid
4) Add Benedict’s solution to the sample in a 1:1 ration
5) Heat the mixture in a gently boiling water bath for 5 minutes
6) Look for a colour change from blue to brick red/ orange precipitate

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29
Q

Define a polysaccharide:

A

A very large, insoluble carbohydrate molecule.

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30
Q

How can you test for starch?

A

1) Place 2cm3 of sample being tested into a test tube
2) Add 2 drops of iodine solution and stir
3) Look for a colour change from yellow to blue-black

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31
Q

What is starch?

A

A polysaccharide made of alpha glucose, found as small grains in storage organs. It can be found in branched or unbranched chains.

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32
Q

Outline the structure of starch:

A
  • Insoluble (doesnt affect water potential)
  • Large (no diffusion)
  • Compact (storage)
  • Forms alpha glucose when hydrolysed (respiration and transport)
  • Branched chains with many ends (all acted on by enzymes to release glucose monomers)
33
Q

Define branched chains:

A

A polymer chain with many ends for conversion into monomer units.

34
Q

Define unbranched chains:

A

A chain wound into a tight coil, making it very compact.

35
Q

What is glycogen?

A

A polysaccharide that is found in animals and bacteria (but not plant cells). It has a similar structure to starch but has shorter chaibs and is more highly branched. In humans, it is mainly found in muscle and liver cells.

36
Q

Outline the structure of glycogen:

A
  • Insoluble (doesnt affect water potential)
  • Large (diffusion)
  • Compact (storage)
  • Highly branched (many ends to be acted on by enzymes: more transport and respiration than plants)
37
Q

What is cellulose?

A

A polysaccharide made of beta glucose monomers. It forms straight, unbranched chains which run parallel to one another with hydrogen cross-linkages beween adjacent chains (making it a valuable structural material).

38
Q

How are cellulose fibres made? What do they do?

A

Cellulose molecules group together to form microfibrils which are arranged parallel to one another in fibres.

They provide rigidity (as they make the cell turgid) and prevent the cell form bursting by exerting pressure on the cell. This turgidity also provides the maximum surface area for photosynthesis.

39
Q

Outline the structure of cellulose:

A
  • Long, straight, unbranched chains (beta glucose)
  • Strength (parallel cross linked chains)
  • Strengh (microfibrils and fibre groups)
40
Q

What molecules are lipids made of?

A

Carbon, hydrogen and oxygen

41
Q

Lipids are ____ when solid and ____ when liquid.

A

Fats

Oils

42
Q

Lipids are _____ in water and _____ in organic solvents.

A

Insoluble

Soluble

43
Q

Which as a higher oxygen:carbon + hydrogen ratio, lipids or carbohydrated?

A

Lipids

44
Q

What are the 2 main lipid groups?

A

Triglycerides

Phospholipids

45
Q

What are 5 roles of lipids?

A
  • Cell membranes
  • Waterproofing (insoluble in water, oily seretions, waxy cuticle layer)
  • Insulation (slow heat conductors, heat retention, electrical insulators)
  • Protection (surrounds organs)
  • Energy (2x that of carbs, release water)
46
Q

What is a trygliceride?

A

A lipid made of three fatty acids and glycerol joined together in an ester bond (condensation reation).

47
Q

What is the general formula for a triglyceride?

A

-COOH (carboxyl) group

Hydrocarbon chain attached

48
Q

How woud you hydrolyse a triglyceride?

A

Add 3 molecules of water

49
Q

Define a saturated fatty acid chain:

A

A fatty acid with no carbon-carbon double bonds

50
Q

Define an unsaturated fatty acid chain:

A

Mono-unsaturated: A fatty acid chain with one carbon-carbon double bond

Poly-unsaturated: A fatty acid with two or more carbon-carbon double bonds

51
Q

Describe the strucure of triglycerides and the uses of this structure.

A
  • 3 non-polar/ uncharged, hydrophobic fatty acid molecues
  • Low mass:energy ratio for comact storage
  • Can be oxidised to release water
52
Q

What is a phospholipid?

A

A lipid with one fatty acid replaced by a phosphate group

53
Q

What is the general formula for a phospholipid?

A
54
Q

Describe the polarity of phospholipids:

A

Phospholipids are non-polar (as faty acids are uncharged) but they have a polar phosphate ‘head’.

55
Q

How do phospholipids interact with water?

A

Phosphate ‘head’: Hydrophilic

Fatty acid: Hydrophobic

56
Q

Where are phospholipids found?

A

Cell membranes in a phospholipid bilayer

57
Q

What is a glycolipid?

A

A phospholipid with an attatched carboydrate

58
Q

How do you test for lipids?

A

1) Add 5cm3 of ethanol to 2cm3 of food sample.
2) Shake thoroughly to dissolve any lipid.
3) Add 5cm3 of water and shake gently.
4) A cloudy white colour indicates the presence of a lipid.

59
Q

What is the name of the lipids test?

A

The emulsion test.

This is because an emulsion is formed when the sample finely disperses, causing the light to refract and appear cloudy.

60
Q

Define a protein

A

A very large, polymer molecule made of amino acid monomers

61
Q

Describe a basic amino acid monomer

A
63
Q

How many naturally occurring amino acid monomers are there?

A

20

64
Q

What reactions occur between amino acids? Which bonds form?

A

Condensation reaction

Dipeptide: 2 amino acids

Polypeptide: 3+ amino acids

A peptide bond is formed

65
Q

Which elements are peptide bonds between?

A

Carbon (from CO of one amino acid) Nitrogen (from HN of another amino acid)

66
Q

Describe a test for proteins:

A

Biuret test for proteins 1) Add biuret solution to sample and shake. 2) A positive result is indicated by a colour change from blue to lilac. Biuret solution consists of sodium hydroxide and copper sulfate.

67
Q

What is the primary structure of a protein?

A

The sequence/ number of amino acids in a polypeptide chain (generally non functional).

68
Q

What is the secondary structure of a protein?

A

The twisting/ folding of a primary polypeptide chain to become a 3D shape due to the formation of hydrogen bonds.

69
Q

Name 2 secondary protein structures.

A

Alpha helix (spiral) Beta pleated sheet (zig zag)

70
Q

Why do secondary protein structures form?

A

Opposing charges on either side of the peptide bonds

71
Q

What is the tertiary structure of a protein?

A

The further twisting/ folding of the secondary structure. This is generally the stage of globular proteins.

72
Q

Give an example of tertiary structure proteins.

A

Enzymes

73
Q

What are the 3 tertiary structure bonds in proteins?

A

-Hydrogen bonds (weak and easily broken but numerous) -Disulfide bridges (fairly strong so not easily broken) -Ionic bonds (weaker bonds than disulfide bridges. Easily broken by changes in pH)

74
Q

Where are ionic bonds formed in proteins?

A

Between carboxyl and amine groups

75
Q

What is the quaternary structure of a protein?

A

Multiple polypeptide chains and often additional prosthetic groups.

76
Q

Give an example of a quaternary structure protein.

A

Haemoglobin- multiple polypeptide chains and haem groups

77
Q

Give a way in which amino acids can be separated from their structure.

A

Chromatography

78
Q

What is a fibrous protein?

A

Proteins with structural functions which run in long chains parallel to each other. E.g. collagen, keratin, silk

79
Q

What is a globular protein?

A

Proteins with a spherical shape due to tightly folded chains which have metabolic functions. E.g. transport proteins, enzymes, hormones

*AQA A-Level Biology* (6 decks)

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