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AQA A Level Biology 2018 > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

What are Monomers?

A

The smaller units from which larger molecules are made.

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2
Q

What are Polymers?

A

Molecules made from a large number of monomers joined together.

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3
Q

Give 4 examples of Monomers:

A
  • Amino Acids
  • Nucleotides.
  • Monosaccharides.
  • Glucose.
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4
Q

Glucose =

A

C (6) H (12) O (6)

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5
Q

What does a Condensation reaction do?

A

It joins two molecules by forming a chemical bond and it involves the elimination of a water molecule.

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6
Q

What does a Hydrolysis reaction do?

A

It seperates two molecules by breaking a chemical bond and it involves the use of a water molecule.

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7
Q

What are Monosaccharides?

A

The monomers from which larger carbohydrates are made.

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8
Q

Give 3 common Monosaccharides:

A
  • Glucose
  • Galactose
  • Fructose
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9
Q

What does a condensation reaction between two Monosaccharides form?

A

A glycosidic bond which forms Disaccharides.

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10
Q

What are Disaccharides formed by?

A

The condensation of two Monosaccharides.

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11
Q

What is Maltose and how is it formed?

A
  • A Disaccharide

- the condensation of two glucose molecules

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12
Q

What is Sucrose and how is it formed?

A
  • A Disaccharide

- the condensation of a glucose molecule and a fructose molecule

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13
Q

What is Lactose and how is it formed?

A
  • A Disaccharide

- formed by the condensation of a glucose molecule and a galactose molecule.

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14
Q

Why are Carbohydrates considered organic compounds?

A

Because they only contain C, H and O and are made by plants (living things.)

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15
Q

How are Polysaccharides formed?

A

By the condensation of many glucose units.

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16
Q

Give 3 examples of Polysaccharides:

A
  • Glycogen
  • Starch
  • Cellulose
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17
Q

How are Glycogen and Starch formed?

A

By the condensation of (A) - Glucose.

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18
Q

How is Cellulose formed?

A

By the condensation of (B) - Glucose.

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19
Q

Are Monosaccharides soluble?

A

Yes.

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20
Q

What is the general formula for Monosaccharides?

A

(CH (2) O) n

n = any number 3-7

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21
Q

Give 2 examples of reducing sugars:

A
  • All Monosaccharides

- Some Disaccharides (maltose)

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22
Q

What is Reduction?

A

A chemical reaction involving the gain of electrons or hydrogen.

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23
Q

What is a reducing sugar?

A

A sugar that can donate electrons to another chemical (or reduce it).

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24
Q

What is Benedict’s reagent?

What happens when a reducing sugar is heated with it?

A

An alkaline solution of copper sulfate.

It forms an insoluble red precipitate of copper oxide.

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25
Q

Give the 3 steps to testing for a reducing sugar using Benedict’s reagent:

A
  • Add 2cm cubed of the food sample - make sure it’s in liquid form.
  • Add an equal amount of Benedict’s reagent.
  • Heat the mixture in a water bath for 5mins.
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26
Q

How would you know if a reducing sugar is present after using the Benedict’s test?

A

The solution turns orange-brown.

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27
Q

Are Polysaccharides soluble?

A

No because they are very large molecules , they’re suitable for storage though.

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28
Q

Give the first 3 steps to testing for a NON reducing sugar:

A
  • Add 2cm cubed of the food sample being tested to 2cm cubed of Benedict’s reagent (in liquid form)
  • put in a water both for 5mins and if the colour doesn’t change then a reducing sugar is not present.
  • Add another 2cm cubed of the food sample to 2cm cubed of dilute hydrochloric acid in a test tube and put this in a water bath for 5mins.
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29
Q

What is the purpose of the Hydrochloric acid which you add to the test tube in the case of a non reducing sugar?

A

It will hydrolyse any Disaccharide present into monosaccharides.

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30
Q

Give the final 3 steps to testing for a Non Reducing sugar: (the hydrochloric acid has been added)

A
  • slowly add sodium hydrogencarbonate solution to the test tub - neutralise acid .
  • use the Benedict’s test again - Heat solution with 2cm cubed of Benedict’s reagent in a waterbath.
  • if a non reducing sugar is present, it will turn orange-brown.
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31
Q

Why does Bendict’s reagent turn orange-brown in the presence of the non reducing sugar now?

A

Because reducing sugars were produced from the hydrolysis of the non reducing sugar.

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32
Q

What is Starch?

A

A polysaccharide found in plants in the form of small grains.

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33
Q

What is Starch made up from?

A

Alpha Glucose linked by glycosidic bonds formed by condensation reactions.

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34
Q

What’s the structure of Starch like?

A

Unbranched chain which is in a tight coil making it compact.

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35
Q

What are three features of Starch?

A
  • insoluble so won’t draw water and is also good for storage.
  • when hydrolysed, forms Alpa Glucose which is easily transported and readily used in respiration.
  • it is compact so a lot can be stored in a small space.
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36
Q

What 2 things is Starch made up from:

A
  • Amylose.
  • Amylopectin.

Two polysaccharides of alpha glucose.

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37
Q

Give 2 facts about Amylose:

A

It is a long unbranched chain of alpha glucose molecules.

The angles of the glycosidic bond give it a coiled structure which makes it compacts so it is really good for storage.

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38
Q

Give 2 facts about Amylopectin:

A

It is a long branched chain of alpha glucose.
It’s side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily - glucose can be released quickly.

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39
Q

The structure of Cellulose: (2)

A
  • straight, unbranched chains which runnparallel to one another and the hydrogen bonds form cross linkages.
  • lots of H bonds make them strong.
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40
Q

Cellulose molecules form…

A

Microfibrils which are arranged into parallel groups - Fibres. Adds to the strength.

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41
Q

Give 3 ways Cellulose is suitable for its use in Cell Walls:

A
  • exerts an in are pressure that stops any further influx of water - prevents cell from bursting because of osmosis.
  • very strong.
  • plant cells are more turgid and push on eachother making the non- Woody parts semi turgid which is important in maintaining stems.
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42
Q

Structure of Gylcogen:

A
  • similar to Starch but shorter branches and highly branched.
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43
Q

Glycogen is stored in…

A

Muscle and liver as small granules.

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44
Q

Storage adaptations of Glycogen: (3)

A
  • insoluble so doesn’t diffuse out or draw water.
  • highly branched meaning it is more rapidly broken down to form glucose monomers which is needed for respiration.
  • compact.
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45
Q

What are amino acids?

A

The monomers from which proteins are made.

46
Q

Are the 20 amino acids in all organisms the same?

A

Yes but they have different side groups.

47
Q

What does a condensation reaction between two amino acids form?

A

A peptide bond - forms Dipeptides.

48
Q

How are Dipeptides formed?

A

By the condensation of two amino acids.

49
Q

How are Polypeptides formed?

A

By the condensation of many amino acids.

50
Q

How can you reverse a condensation reaction?

A

Add water and protease (hydrolysis)

51
Q

What is a Protein?

A

One or more polypeptide chains folded into its final functional and highly specific 3D shape.

52
Q

Proteins have a variety of functions…

Structural proteins:

A

They are physically strong as they consist of long polypeptide chains lying parallel to each other.

53
Q

Give 2 examples of Structural Proteins:

A
  • Keratin

- Collagen

54
Q

Proteins have a variety of functions…

Antibodies:

A

They are involved in the immune response and are made up of two light polypeptide chains and two heavy polypeptide chains bonded together.

55
Q

Proteins have a variety of functions…

Transport proteins:

A

Channel proteins contain hydrophobic and hydrophilic amino acids which causes the protein to fold up and form a channel - these proteins transport molecules and ions across membranes.

56
Q

Proteins have a variety of functions…

Enzymes:

A

They’re usually roughly spherical in shape due to the tight folding of the polypeptide chains. They’re soluble and often have roles in metabolism (e.g. digestive enzymes) and other help to make large molecules.

57
Q

Proteins are big complicated molecules. How do we separate them?

A

They have 4 ‘levels’

Primary, Secondary, Tertiary and Quaternary.

58
Q

What is the significance of the Primary Structure in a protein?

A

This is the sequence of amino acids in the polypeptide chains and it determines its ultimate shape and function - even a small change here can change the whole shape and function of the protein.

59
Q

What is the significance of the Secondary Structure of a protein?
What does this cause?

A

Weak hydrogen bonds are formed here because of the positive NH and negative C—O on each side of the peptide bond.

Causes long polypeptide bond to be twisted into a 3D alpha helix or fold into a beta pleated sheet.

60
Q

What is the significance of the Tertiary Structure?

A

The coiled or folded amino acids are often coiled/folded even more into an even more complex 3D shape maintained by different bonds.

61
Q

What are the 3 bonds that are found in the Tertiary Structure of a Protein?

A

Hydrogen bonds

Iconic bonds

Disulfide bridges

62
Q

What are hydrogen bonds like?

A

There are lots of them but they are easily broken.

63
Q

What are ionic bonds like and how are they formed?

A

Formed between the negative and positive charges on the different parts of the molecule.

Weaker than disulfide bridges and are easily broken by changes in pH.

64
Q

What are Disulfide Bridges like?

A

Fairly strong and not easily broken.

65
Q

What is the significance of the Quaternary Structure?

A

Some proteins are made of different polypeptide chains held together by bonds - this structure is how these chains are assembled.

66
Q

3D Structure is important in a protein but…

A

It is the sequence of amino acids that determines the 3D shape in the first place.

67
Q

How can you test if protein is present in a sample?

A

Use the Biuret test.

68
Q

Give the 2 steps to the Biuret Test:

A
  • place a sample of the solution to be tested in a tube and add equal volume of sodium hydroxide solution at room temp.
  • add a few drops of very dilute copper sulfate solution and mix gently.
69
Q

How do you know if a Protein is present after using the Biuret test?

A

A purple coloration indicates the presence of peptide bonds and hence a protein. If no Protein is present, the solution will remain blue.

70
Q

What characteristics do lipids share?

A
  • C, H and O molecules
  • proportion of oxygen to carbon and hydrogen is smaller than in carbs
  • insoluble
  • soluble in organic solvents e.g. alcohol and acetone.
71
Q

2 main groups of Lipids:

A
  • Triglycerides

- Phospholipids

72
Q

Give 4 roles of Lipids:

A
  • insulation as fats are slow conductors of heat when stored beneath the body surface , they retain body heat.
  • protection e.g. fat is stored near kidney (delicate organs)
  • source of energy as when oxidised they provide 2X energy as the same mass of carbohydrate and release valuable water.
  • waterproofing as they are insoluble in water.
73
Q

Fats at room temp?
(10 - 20 degrees)
Oils at room temp?

A

Fats are solids

Oils are liquid

74
Q

How are Triglycerides formed?

A

From condensation reactions and they form Ester Bonds.

75
Q

What are Triglycerides made up from?

A

One Glycerol and 3 fatty acids.

76
Q

All the glycerol molecules in Triglycerides are the same. So what causes the difference in their properties?

A

The carboxyl group because it has a hydrocarbon chain attached - if depends on the bond between the carbons.

77
Q

If the hydrocarbon chain has no carbon- carbon double bonds then…

A

The fatty acid is then described as saturated because all the carbon atoms are linked to the maximum possible number of hydrogen atoms.

78
Q

If there is a single double bond in the hydrocarbon chain then…

A

It is mono-unsaturated

79
Q

If there is more than one double bond present in the hydrocarbon chain then…

A

It is polyunsaturated.

80
Q

Why are Triglycerides a good source of energy?

A

Because they have a high ratio of energy storing carbon-hydrogen bonds to carbon atoms.

81
Q

Why does the storage of Triglycerides not affect osmosis in cells?

A

Because they are large non polar molecules and are insoluble.
And also have low mass to energy ratio meaning lots can be stored in a small volume.

82
Q

What is the structure of Phospholipids like?

A

Similar to Triglycerides except one of the fatty acids is replaced by a phosphate molecule.

83
Q

Why is a Phospholipid made up of two parts?

A

Because the fatty acid molecules repel water while the phosphate molecules attract water.

84
Q

Molecules that have two ends that behave differently are said to be..

A

Polar, meaning when these polar phospholipid molecules are placed in water, they position themselves so that the hydrophilic heads are as close to the water as possible while the hydrophobic tails are as far away as possible.

85
Q

What can Phospholipids do because of their structure?

A
  • they can form Glycolipids by combining with carbohydrates within the cell sufrace membrane - these are important in cell recognition.
86
Q

Give the 3 steps to testing if a Lipid is present:

A
  • put 2cm cubed of the sample being tested into a test tube and add 5cm cubed of ethanol.
  • shake to dissolve any lipid in the sample.
  • Add 5cm cubed of water and shake gently.
87
Q

How do you know if a lipid is present?

A

A cloudy white colour indicates the presence of a lipid.

88
Q

Why does the sample go cloudy if a lipid is present?

A

Due to any lipid in the sample being finely dispersed in the water to form an emulsion - light passing through this emulsion is refracted as it is passed from oil droplets to water droplets making it appear cloudy.

89
Q

What do enzymes do?

A

They speed up reactions by acting as biological catalysts.

90
Q

Many reactions require an initial amount of…

A

Energy to start - called the activation energy.

91
Q

How do enzymes work?

A

They lower the activation energy level by providing an alternative reaction pathway. Without them, reactions would be too slow to sustain life.

92
Q

What is the active site in an enzyme made of?

A

Amino acids.

93
Q

The molecule on which the enzymes acts is called…

A

The substrate which fits in neatly into the depression which is the active site and forms an enzyme substrate complex.

94
Q

How is the substrate molecule held within the active site?

A

By bonds that temporarily form between certain amino acids of the active site and groups on the substrate molecule.

95
Q

How does the mechanism of enzyme action work?

A

The substrate goes into the active site and the enzyme changes shape slightly as the substrate bonds with its active site. Breaks the substrate into its products and enzyme returns to its original shape.

96
Q

What does the lock and key model say?

A

That the shape of the substrate fits exactly into the active site.

97
Q

One limitation of the lock and key model is that…

A

The enzyme is considered to be a rigid structure. However enzymes shapes are altered by the binding molecule so it becomes flexible - known as the induced fit model.

98
Q

What does Collagen do?

Where can it be found?

A

Supports the skin and internal organs as it can be found in connective tissues, it makes up the structure of bones and cartilage.

99
Q

What’s the structure of Collagen like?

A

The 3D Protein is made up of long fibers of 3 polypeptide chains wound around each-other and each of the 3 chains it coils.

100
Q

What amino acids does Collagen contain and what is the most important?

A

Glycine is the most important (35%) as it has a small H side chain which can fit into every Collagen at every third helix.
Also made of proline & hydroxyproline.

101
Q

What are the Polypeptide chains in Collagen held by?

A

Covalent bonds as molecules form cross links with eachother and this improves stability.

102
Q

Brittle Bones is caused by…

A

A defect in the gene which produces type 1 (Collagen)

103
Q

How does temperature affect enzyme activity?

A

The rise makes them move more but if it gets too high, this vibration breaks the bonds holding the enzyme in shape = denatures.

104
Q

How does pH affect enzyme activity?

What happens above and below the optimum pH?

A

All enzymes have their optimum pH value e.g. pepsin works at 2.

Above and below this opitimum pH, the H+ and OH- ions found in acids and alkali can mess up the ionic bonds and hydrogen bonds that hold the enzyme’s Tertiary Structure in place = denatures.

105
Q

How does enzyme concentration affect the rate of reaction?

A

The more enzyme molecules in a solution, the more likely a substrate will collide with one and form an enzyme substrate complex = increases rate as long as there’s an excess of substrate too.

106
Q

How does substrate concentration affect the rate of a reaction?

A

The higher substrate number , the faster reaction. This is only true until a ‘saturation’ point though because after that all the enzyme’s active sites are full and can’t cope with more.

107
Q

How does substrate concentration change with time?

A

Decreases unless more substrate is added to the reaction mixture so rate of reaction also decreases with time.

108
Q

How does Competitive Inhibition affect enzyme activity?

A

They are molecules which have a similar shape to substrate and basically block the active site.

High concentration of inhibitor = block all them and slow enzyme activity unless there are more substrates than inhibitors.

109
Q

How does Non Competitive Inhibition affect enzyme activity?

A

They bind to the enzyme away from its active site causing the site to change shape so substrates can’t bind to it.

Enzyme activity will be inhibited even if you add more substrate.

110
Q

How can you measure how fast a substrate is broken down by an enzyme?

A

Put a drop of iodine in potassium iodide on a spotting tile. Mix analyse and starch in a test tube and add a drop onto the sporting tile - goes blue black.

Record how long it takes for the iodising solution to no longer turn blue/black when the Starch mix is added.

111
Q

Required practical 1

Investigating the effect of temperature on the rate of an enzyme controlled reaction:

A
  • write an X on three test tubes filled with 10cm cubed of milk powder.
  • Add 2cm cubed of trypsin solution to 2cm cubed of ph7 buffer in another 3 tubes & put all 6 in a water bath (20-60 degrees) for 10mins.
  • pour one trypsin tube into the milk powder tube = time how long it takes for the milk to go clear, how long X disappears.
  • repeat with all temps & make graph.

AQA A Level Biology 2018 (17 decks)

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