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AQA A Level Biology > 3.1.1 Biological Molecules > Flashcards

3.1.1 Biological Molecules Flashcards

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1
Q

What is a polymer?

A

Molecule made of large number of monomers joined together

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2
Q

What are monomers?

A

Small, basic molecular units

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3
Q

Name the 3 elements all carbohydrates contain

A

C, H & O

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4
Q

What are the monomers in carbohydrates?

A

Monosaccharides

(e.g. glucose, fructose, galactose)

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5
Q

What type of sugar is glucose?

A

Hexose sugar (monosaccharide with 6 carbon atoms in each molecule)

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6
Q

Name the 2 types of glucose

A

alpha (α) & beta (β)

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7
Q

Draw the skeletal structure for α-glucose

A
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8
Q

Draw the skeletal structure for β-glucose

A
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9
Q

In alpha glucose the OH is…

A

below the plane of the ring

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10
Q

In beta glucose the OH is…

A

above the plane of the ring

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11
Q

What is a condensation reaction?

A

Joining together of molecules with a chemical bond & the elimination of a water molecule (it’s released)

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12
Q

How are monosaccharides joined together?

A

By condensation reactions

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13
Q

What type of bond is formed between the 2 monosaccharides as molecule of water is released?

A

A glycosidic bond

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14
Q

What is formed when 2 monosaccharides join together?

A

A disaccharide

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15
Q

How is sucrose formed?

A

Formed from condensation reaction between α-glucose molecule and fructose molecule

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16
Q

What is lactose formed from?

A

From glucose molecule & galactose molecule

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17
Q

What is maltose formed from?

A

From 2 α-glucose molecules

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18
Q

What is hydrolysis?

A

Breaking of the chemical bond between monomers using a water molecule

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19
Q

When are polysaccharides formed?

A

When more than 2 monosaccharides are joined together by condensation reactions

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20
Q

Where is starch located in organisms?

A

Many parts of plants in the form of small grains + large amounts found in seeds & storage organs

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21
Q

What is the purpose of starch?

A

Plants store excess glucose as starch

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22
Q

How is starch produced?

A

Condensation of many α-glucose sub units, which then form hydrogen bonds with molecules in the same chain

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23
Q

Starch is a mixture of…

A

2 polysaccharides of alpha-glucose

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24
Q

Name the 2 polysaccharides of alpha-glucose found in starch

A
  • Amylose
  • Amylopectin
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25
Q

Describe the structure of amylose

A

Long, unbranched chain of α-glucose

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26
Q

Describe how the structure of amylose relates to its function

A

Angles of the glycosidic bonds = coiled structure → makes it compact = can fit more into a small space (= good for storage)

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27
Q

Describe the structure of amylopectin

A

Long, branched chain of α-glucose

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28
Q

Describe the structure of amylopectin relates to its function

A

Its side branches allow the enzymes that break down starch to get at the glycosidic bonds easily = glucose can be released quickly

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29
Q

α-glucose molecules are formed by what type of glycosidic bonds?

A

1,4 & 1,6 glycosidic bonds

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30
Q

Where is glycogen located in organisms?

A

Stored as small granules mainly in liver and some in muscles

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31
Q

What is the purpose of glycogen?

A

In animals: excess glucose is stored as glycogen

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32
Q

Glycogen is a p______…

A

Polysaccharide of α-glucose

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33
Q

Describe glycogen’s structure

A

Very similar to amylopectin BUT has lots more side branches coming off it + shorter chains

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34
Q

Describe how glycogen’s structure relates to its function

A
  • Loads of branches & shorter chains = stored glucose can be released even quicker than in starch → important for energy releases in animals
  • Very compact molecule, making it good for storage
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35
Q

Why is starch suited for its role? 3x

A
  1. Insoluble in water = doesn’t affect water potential (doesn’t cause water to enter cells by osmosis)
  2. Compact = lots of it can be stored in small space
  3. When hydrolysed, alpha glucose can be easily transported & used in respiration
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36
Q

Describe the test for starch

A
  1. Add iodine dissolved in potassium iodide solution to test sample
  2. If starch present = sample changes from browny-orange to blue-black colour

(Carried out at room temp.)

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37
Q

Describe the structure of cellulose

A
  • Long, unbranched chains of beta-glucose
  • Straight cellulose chains run parallel to each other in cell walls = allows hydrogen bonds to form cross-linkages between chains
  • Result: formation of bundles called micro fibrils which then join together to make macro fibrils
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38
Q

What is the purpose of cellulose?

A

To provide rigidity to plant cells

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39
Q

How does cellulose prevents the cell from bursting as water enters it by osmosis?

A

By exerting inward pressure that stops any influx (inrush) of water = makes plant cells turgid

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40
Q

Why is it important that stems & leaves are in a turgid state?

A

To provide maximum surface area for photosynthesis

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41
Q

Name the 2 types of sugars

A

Reducing and non-reducing

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42
Q

What is a reducing sugar?

A

Sugars that can donate electrons to another chemical e.g. Benedict’s reagent

i.e. all monosaccharides and some disaccharides (e.g. maltose and lactose)

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43
Q

Describe Benedict’s test for reducing sugars

A
  1. Add Benedict’s reagent (blue) to sample & heat it in water bath that’s been brought to a boil (for 5 mins)
  2. Test’s positive = orange/red precipitate
  3. Higher the concentration of reducing sugar = further the colour change goes
44
Q

Benedict’s Test for Reducing Sugars:

The colour of the precipitate changes from…

A
45
Q

Benedict’s Test for Reducing Sugars:

What’s a more accurate way of comparing the amount of reducing sugar in different solutions (than colour change)?

A

Filter solution & weigh precipitate

46
Q

What does it mean if the result of the reducing sugars test is negative (i.e. no precipitate is formed)?

A

Means a non-reducing sugar present (disaccharides)

47
Q

Describe the test for non-reducing sugars

A
  1. Boil supernatant (new test sample) with dilute hydrochloric acid (in water bath)
  2. Then neutralise it with sodium hydrogencarbonate
    1. Check solution is alkaline (with pH paper)
  3. Carry out Benedict’s test as you would for a reducing sugar
    1. If test’s positive = orange/red precipitate
    2. If test’s negative = solution remains blue = no sugar present
48
Q

In the test for non-reducing sugars, why is dilute hydrochloric acid added?

A

To hydrolyse, break down, the non-reducing sugar (disaccharide) into monosaccharides

49
Q

Name 5 roles of lipids

A
  1. Energy source
  2. Flexibility in plasma membranes
  3. Protection
  4. Insulation
  5. Waterproofing
50
Q

Elaborate on lipids’ role as a energy source

A

When oxidised, lipids = more than twice as much energy per gram as carbohydrates

51
Q

Elaborate on lipids’ role in plasma membranes

A

Phospholipids contribute to flexibility of membranes & transfer of lipid-soluble substances across them

52
Q

Elaborate on lipids’ role in protection

A

Stored around delicate organs

53
Q

Elaborate on lipids’ role in insulation

A

Fats = slow conductors of heat = help retain body heat

54
Q

Elaborate on lipids’ role in waterproofing

A

Lipids are insoluble in water ∴ waterproof material

  • In plants & insects: waxy cuticle to conserve water
  • In mammals: produce oil secretion from sebaceous glands in skin
55
Q

Describe the structure of a triglyceride

A

One molecule of glycerol with 3 fatty acids attached to it

56
Q

What do fatty acids have?

A

Have long ‘tails’ made from hydrocarbons

57
Q

Properties in triglycerides differ due to variations in ___ __

A

fatty acids

58
Q

Name 2 kinds of fatty acids

A
  • Saturated
  • Unsaturated
59
Q

Draw a saturated fatty acid

A
60
Q

Draw a unsaturated fatty acid

A
61
Q

What does the double carbon bond causes the chain to do?

A

Causes it to kink

62
Q

Define mono-unsaturated

A

Single double bond

63
Q

Define polyunsaturated

A

More than one double bond

64
Q

Describe how a triglycerides forms

A
  1. A fatty acid joins to a glycerol molecule
  2. When ester bond is formed = molecule of water is released - condensation reaction
  3. Process happens twice more = form a triglyceride
65
Q

Why are triglycerides good energy storage molecules?

A

Long hydrocarbon tails of fatty acids contains lots of chemical energy = lot of energy released when they’re broken down

∴ contain twice as much energy per gram as carbohydrates

66
Q

Describe how the structure of a triglyceride makes them insouble

A
  • Triglycerides clump together as insoluble droplets in cells ∵ fatty acid tails = hydrophobic
  • = tails face inwards = shielding themselves from water with their glycerol heads
67
Q

Where are phospholipids found?

A

In cell membranes

68
Q

Describe the structure of a phospholipid

A

One molecule of glycerol with 2 fatty acids + a phosphate group attached to it

69
Q

Draw glycerol

A
70
Q

Draw the basic structure of a fatty acid

A
71
Q

Draw a triglyceride

A
72
Q 
Phospholipids:
Phosphate group (the 'head') is \_\_\_\_\_\_\_
A

hydrophilic (attracts water)

73
Q

Phospholipids:
Fatty acid tails is _______

A

hydrophobic (repel water)

74
Q

Describe how phospholipids’ structures relates to its function

A

Phospholipids make up the bilayer of cell membranes

  1. Heads are hydrophilic & tails are hydrophobic = form double layer with their heads facing out towards the water on either side
  2. Centre of bilayer = hydrophobic = water-soluble substances can’t easily pass through
    • Membrane acts as a barrier to those substances
75
Q

Describe the emulison test for lipids

A
  1. Shake test substance with ethanol for few minutes so that it dissolves & then pour solution into water
  2. Any lipid will show up as a milky emulsion
  3. More lipid there is = more noticeable milky colour will be
76
Q

What are the monomers in proteins?

A

Amino acids

77
Q

What is formed when 2 amino acids join together?

A

Dipeptide

78
Q

When is a polypeptide formed?

A

When more than 2 amino acids join together

79
Q

Proteins are made up of one or more ____

A

polypeptides

80
Q

What are 3 things all amino acids have? (structure wise)

A
  • Carboxyl group (-COOH)
  • Amine group (NH2)
  • R group (aka variable side group)
81
Q

All living things share bank of ___ amino acids

A

20

82
Q

What changes with each amino acid?

A

The R group

83
Q

What is glycine’s R group?

A

H

84
Q

Draw an amino acid

A
85
Q

How are polypeptides formed?

A

Formed by amino acids linking together by condensation reactions (molecule of water is released during reaction)

86
Q

What is the name of the bond formed between amino
acids?

A

Peptide bonds

(Combines -OH from carboxyl group and -H from amino acid)

87
Q

Draw a dipeptide

A
88
Q

What is the primary structure in proteins?

A

Sequence of amino acids in polypeptide chain

89
Q

What is the secondary structure in proteins?

A
  • Hydrogen bonds form between amino acids in chain
  • = makes it coil into alpha helix or fold into beta pleated sheet
90
Q

What is the tertiary structure in proteins?

A
  • Further folding of whole polypeptide chain
  • More bonds form between different parts (R groups) of polypeptide chain:
    • Hydrogen bonds
    • Ionic bonds
    • Hydrophobic interactions
    • Disulphide bonds
91
Q

Where do disulphide bonds form?

A

Between R-groups containing sulfur atoms

92
Q

Where do ionic bonds form?

A

Form between R groups with charges

93
Q

Describe hydrophobic interactions in proteins

A

When polypeptide chain folds:

  • hydrophobic R-groups are in the interior of the folded chain
  • whereas hydrophilic R-groups tend to be on the outside
94
Q

What is the quaternary structure in proteins?

A

Arrangement of 2 or more polypeptide chains in a protein

95
Q

For proteins made … the tertiary structure form their final 3D structure

A

proteins made from single polypeptide chain

96
Q

For proteins made from … the quaternary structure is protein’s final structure

A

proteins made from more than one polypeptide chain (e.g. haemoglobin, insulin, collagen)

97
Q

Describe the structure of an enzyme and a property of them

A
  • Roughly spherical in shape due to tight folding of polypeptide chains
  • Soluble (& often have roles in metabolism)
98
Q

Describe the structure of antibodies

A
  • Made up of 2 light (short) polypeptide chains & 2 heavy (long) polypeptide chains bonded together
  • Have variable regions: amino acid sequences in these
    regions vary greatly
99
Q

Describe the structure of channel proteins (present in cell membranes) and its function

A
  • Contain hydrophobic and hydrophilic amino acids = cause protein to fold up & form a channel
  • These proteins transport molecules and ions across membranes
100
Q

Why are structural proteins physically strong?

A

Consist of long polypeptide chains lying parallel to each other with cross-link between them

101
Q

Describe the biuret test for proteins

A
  1. Test solution needs to alkaline ∴ add few drops of sodium
    hydroxide solution
  2. Then add some dilute copper(II) sulfate solution
    1. Protein present = turns purple
    2. No protein = solution stays blue
    3. (Colours are pale so look carefully)
102
Q

Name the 2 types of proteins

A

Fibrous (strands) & Globular (spherical)

103
Q

Give 3 examples of fibrous proteins

A

Structural:

collagen, muscles (actin & myosin), keratin

104
Q

Give 3 examples of globular proteins

A

haemoglobin, enzymes, hormones, antibodies

105
Q

What bond/interaction helps in the tertiary structure helps to form the 3D shape of globular proteins?

A

Hydrophobic interactions (keep circular shape - hydrophobic centre and hydrophilic outside)

AQA A Level Biology (41 decks)

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