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AS Biology > Module 2.2 - Biological Molecules > Flashcards

Module 2.2 - Biological Molecules Flashcards

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1
Q

What are 5 things that make water vital to living organisms?

A

1) It’s a reactant in lots of important chemical reactions, including hydrolysis reactions.
2) Water is a solvent, which means some substances dissolve in it. Most biological reactions take place in solution (cytoplasm) making it essential.
3) Water transports substances because its a liquid and a solvent, can transport all sorts of materials like glucose and oxygen in plants and animals.
4) Water helps with temperature control for it has a high specific heat capacity and high latent heat of evaporation.
5) Water is a habitat (temp. control, solvent and less dense when it freezes), means many organisms can survive and reproduce in it.

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2
Q

Describe the structure of water?

A

> Water is a polar molecule that has shared electrons between O and 2H and these electrons are pulled towards the O atom giving it a slight/delta negative charge and a delta positive charge on the H.
The partially negatively charged O atoms attract the delta positive H atoms of other water molecules.
This attraction is called hydrogen bonding.

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3
Q

What are the five main properties of water?

A

1) High specific heat capacity (because of hydrogen bonds).
2) High Latent Heat of Evaporation (because of hydrogen bonds).
3) Very cohesive (because of water’s polarity).
4) Good solvent (because of water’s polarity).
5) Water’s less dense when it’s a solid.

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4
Q

Explain what cohesion is?

A

Cohesion is the attraction between molecules of the same type, they tend to stick together.

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5
Q

How does water being very cohesive aid it’s function?

A

Helps water to flow, making it great for transporting substances. It also helps water to be transported up plant stems in the transpiration stream.

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6
Q

Explain how water is a good solvent?

A

A lot of important substances in biological reactions are ionic and because water is polar, the delta + end of a water molecule will be attracted to the negative ion and vice versa. This means the ions will get totally surrounded by water molecules, they’ll dissolve.

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7
Q

Give an example of how water being a good solvent helps it’s function?

A

In humans, important ions can dissolve in the water in blood and then be transported around the body.

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8
Q

Why are water molecules less dense when solid than as a liquid?

A

Water molecules are held further apart in ice than they are in liquid water because each water molecule forms 4 hydrogen bonds to other water molecules, making a lattice shape. This makes ice less dense than liquid water which is why ice floats.

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9
Q

Why does water being less dense in solid form than liquid make it useful for aquatic organisms?

A

In cold temperatures ice forms an insulating layer on top of water so the water below doesn’t freeze can still move around. So organisms that live in water, like fish, don’t freeze and can still move around.

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10
Q

What is a polymer?

A

A polymer is a molecule made up of many similar, smaller molecules (called monomers) bonded together.

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11
Q

What is glucose’s structure?

A

Glucose is a monosaccharide with 6 carbon atoms, meaning it’s a hexose monosaccharide.

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12
Q

Why is glucose’s structure useful for it’s function?

A

Main energy source in animals and plants so it’s structure makes it soluble so it can be easily transported. It’s chemical bonds contain lots of energy.

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13
Q

What elements are all carbohydrates made of?

A

C, H and O.

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14
Q

What bonds join together monosaccharides?

A

Glycosidic bonds.

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15
Q

During synthesis, a hydrogen atom on one monosaccharide bonds to a hydroxyl group (OH) group on the other, releasing a molecule of water. What kind of reaction is this?

A

A condensation reaction.

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16
Q

Describe a hydrolysis reaction?

A

A molecule of water reacts with the glycosidic bond, breaking it apart.

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17
Q

Starch is a mixture of 2 polysaccharides of alpha glucose, what are they called?

A

Amylose and amylopectin.

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18
Q

What is the structure of amylose?

A

A long, unbranched chain of alpha glucose. The angles of the glycosidic bonds give it a coiled structure, almost like a cylinder. This makes it compact and good for storage because you can fit more in a small space.

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19
Q

What is the structure of amylopectin?

A

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. This means that the glucose can be released quickly.

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20
Q

What’s another property of starch that makes it good for storage?

A

Starch is insoluble in water, so it doesn’t cause water to enter cells by osmosis which would make them swell.

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21
Q

What is the main energy storage material in animals?

A

Glycogen.

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22
Q

Describe the structure of cellulose?

A

Cellulose is made from long, unbranched chains of beta - glucose and when they bond, they form straight cellulose chains. These chains are linked together by hydrogen bonds to form strong fibres called microfibrils. These strong fibres means cellulose provides structural support for cells (e.g. in plant cell walls).

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23
Q

What are macromolecules?

A

They’re complex molecules with a relatively large molecular mass.

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24
Q

What is the structure of a triglyceride?

A

1 glycerol molecule and 3 fatty acids.

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25
Q

What is the structure of fatty acid molecules?

A

Have long ‘tails’ made of hydrocarbons. The tails are hydrophobic (they repel water molecules).

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26
Q

What is esterification?

A

The formation of an ester bond formed by a condensation reaction.

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27
Q

What is the difference between unsaturated and saturated fatty acids?

A

The difference is their hydrocarbon tails.
>Saturated F.A don’t have any double bonds between their C atoms. The F.A is saturated with H.
>Unsaturated F.A have at least 1 double bond between C atoms, which causes the chain to kink.

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28
Q

How do phospholipid and triglyceride structures compare?

A

They’re pretty similar but in phospholipids one F.A is replaced by a phosphate group.

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29
Q

Why are triglycerides good as energy storage molecules?

A

> The long hydrocarbon tails of the F.A contain lots of chemical energy causing lots of energy to be released when they’re broken down.
They’re insoluble, don’t cause water to enter the cell by osmosis making them swell (impacting the water potential of the cell).

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30
Q

How does the phospholipid bilayer help the function as a cell membrane?

A

> Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on both sides.
The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it, the membrane acts as a barrier to those substances.

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31
Q

What is the structure of cholesterol?

A

It has a hydrocarbon ring structure attached to a hydrocarbon tail . The ring structure has a polar hydroxyl (OH) group attached to it. It has a small size and flattened shape allowing cholesterol to fit between the phospholipids molecules in the membrane.

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32
Q

What is the function of cholesterol?

A

In eukaryotic cells, cholesterol molecules help strengthen the cell membrane by interacting with the phospholipid bilayer. Cholesterol binds to the hydrophobic tails of the phospholipids causing them to pack closer together making the membrane more rigid.

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33
Q

What are the monomers in proteins?

A

Amino acids.

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34
Q

What are the chemical elements all amino acids have?

A

C, O, H and N. Some also contain S.

35
Q

What is the general structure of an amino acid?

A

A carboxyl group (-COOH) and an amine group (-NH2) attached to a C atom. The difference between different amino acids is the variable group (R) they contain.

36
Q

What type of bonds and reaction form amino acids?

A

Amino acids are linked together by peptide bonds to form dipeptides and polypeptides. It’s a condensation reaction.

37
Q

What are the four structure levels of proteins?

A

Primary, secondary, tertiary and quaternary structure.

38
Q

What is the primary structure?

A

The sequence of amino acids in the polypeptide chain.

39
Q

What is the secondary structure?

A

The polypeptide chain doesn’t remain flat and straight. Hydrogen bonds form between nearby amino acids in the chain. This makes it automatically coil into an alpha helix or fold into a beta pleated sheet.

40
Q

What is the tertiary structure?

A

The coiled/folded chain of amino acids is often then coiled/folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

41
Q

What is the quaternary structure?

A

Some proteins are made from several different polypeptide chains and it’s the way these chains are assembled together.

42
Q

What bonds hold together the proteins in the primary structure?

A

Peptide bonds.

43
Q

What bonds hold together the proteins in the secondary structure?

A

Hydrogen bonds.

44
Q

What bonds hold together the proteins in the tertiary structure?

A

> Ionic bonds - These attractions between (- charged) R groups and (+ charged) R groups on different parts of the molecule.
Disulphide bonds - 2 molecules of the amino acid cysteine come close together, the S atom in one bonds to the S atom in the other.
Hydrophobic and Hydrophilic interactions - When hydrophobic R groups are close together in the protein they tend to clump together. This means that the hydrophilic R groups tend to be pushed to the outside impacting the how the protein folds and its structure.
Hydrogen bonds - these weak bonds form between delta + charged H atoms in some R groups and delta -atoms in other R groups on the polypeptide chain.

45
Q

What bonds hold together the proteins in the quaternary structure?

A

Tends to be determined by the tertiary structure.

46
Q

What differs between carbohydrates and lipids?

A

Lipids contain large amounts of C, H and smaller amounts of O. They are insoluble in water because they are not polar but do dissolve in alcohol. They are not polymers but they do have different components bonded together. They are example of macromolecules.

47
Q

What are globular proteins?

A

Has molecules of a relatively spherical shape, which are soluble in water, so they’re easily transported in fluids and often have metabolic roles within the organism.

48
Q

What are fibrous proteins?

A

Has a repetitively, long, thin structure, is insoluble in water and metabolically inactive, often having a structural role within an organism.

49
Q

What are three globular proteins?

A

Haemoglobin, insulin and amylase.

50
Q

How does the structure of haemoglobin relate to it’s function?

A

It’s a globular protein that carries oxygen around the body in red blood cells. It’s known as a conjugated protein which means it’s a protein with a non-protein group attached called a prosthetic group. Each of the 4 polypeptide chains in haemoglobin has a prosthetic group called harm which contains iron which O binds to.

51
Q

Describe the globular protein amylase?

A

Amylase is an enzyme that catalyses the breakdown of starch in the digestive system. Made of a single chain of amino acids and its secondary structure contains both alpha helix and beta-pleated sheet sections. Most enzymes are globular proteins.

52
Q

What are three examples of fibrous proteins?

A

Collagen, keratin and elastin.

53
Q

Describe collagen and where it is found in the body?

A

> It is a very strong molecule and minerals can bind to the protein to increase it’s rigidity.
Found in animal connective tissues, such as bone, skin and muscle.

54
Q

Where is keratin found in organisms?

A

It can either be flexible like skin, hair and feathers. Or can be hard and tough like nails and horns.

55
Q

Describe elastin and examples in the body?

A

It’s elastic so it allows tissues to return to their original shape after they have been stretched.
>Found in elastic connective tissue, such as skin, large blood vessels and some ligaments.

56
Q

What is an inorganic ion?

A

One which doesn’t contain C.

57
Q

What are 5 inorganic cations?

A

Calcium, sodium, potassium, hydrogen and ammonium.

58
Q

What are 5 inorganic anions?

A

Nitrate, hydrogen carbonate, chloride, phosphate and hydroxide.

59
Q

What is the role of calcium in biological processes?

A

> Involved in the transmission of nerve impulses and the release of insulin from the pancreas.
Acts as a cofactor to enzymes.
Important for bone formation.

60
Q

What is the role of sodium in biological processes?

A

> Important for generating nerve impulses, for muscle contraction and for regulating fluid balance in the body.

61
Q

What is the role of potassium in biological processes?

A

> Important for generating nerve impulses, for muscle contraction and for regulating fluid balance in the body.
Activates essential enzymes needed for photosynthesis in plant cells.

62
Q

What is the role of hydrogen in biological processes?

A

> Affects the pH of substances.

>Important for photosynthesis reactions that occur in the thylakoid membranes inside the chloroplasts.

63
Q

What is the role of ammonium in biological processes?

A

> Absorbed from the soil by plants and is an important source of nitrogen, used to make amino acids.

64
Q

What is the role of nitrate in biological processes?

A

Same as ammonium. Absorbed from the soil by plants and is an important source of nitrogen, used to make amino acids.

65
Q

What is the role of hydrogen carbonate in biological processes?

A

> Acts as a buffer, helps to maintain the pH of blood.

66
Q

What is the role of chloride in biological processes?

A

> Involved in the ‘chloride shift’ helping to maintain the pH of the blood during gas exchange.
Acts as a cofactor for enzymes amylase.
Involved in some nerve impulses.

67
Q

What is the role of phosphate in biological processes?

A

> Involved in photosynthesis and respiration reactions.

>Needed for the synthesis of many biological molecules, such as nucleotides, phospholipids and calcium phosphate.

68
Q

What is the role of hydroxide in biological processes?

A

> Affects the pH of substances

69
Q

What is the biochemical test for reducing sugars?

A

1) Add Benedict’s reagent to a sample and heat it in a water bath thats been brought to boil.
2) If the sample does have reducing sugars it will form a coloured precipitate dependent on the concentration of them. (blue to brick red)

70
Q

What is the biochemical test for non-reducing sugars?

A

1) Add dilute HCI acid and heat in water bath.
2) Then neutralise it with sodium hydrogen carbonate.
3) Carry out the Benedict’s tests like for reducing sugars.

71
Q

What test can you use for determining if glucose is present and what would it be used for in practice?

A

Use test strips coated in a reagent which will change colour if glucose is present. Useful for testing a person’s urine for glucose which may indicate if they have diabetes.

72
Q

Describe the 2 stages of the Biuret test?

A

1) The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
2) Then add some copper sulphate solution, if protein is present turns purple, if not stays blue.

73
Q

What are the steps and observations you should see in the emulsion test?

A

After shaking the sample with ethanol for about a minute, pour the solution into water.
>If lipid is present, the solution will turn milky.

74
Q

What is a colorimeter?

A

A device that measures the strength of a coloured solution by seeing how much light passes through it. Measures absorbance and the higher the absorbance is, the more concentrated the colour.

75
Q

What is colorimetry used to determine?

A

The concentration of a glucose solution.

76
Q

What are the steps of a colorimetry experiment?

A

Have to make several glucose solutions of different known concentrations:
1) Add 10cm3 of the initial glucose solution to the 1rst tube and 5cm3 of distilled water to the other 4 test tubes.
2)Then using a pipette draw 5cm3 of the glucose solution from the 1rst test tube and add it to the distilled water in the 2nd test tube and mix thoroughly.
4) Repeat this process three more times to create solutions of 20, 10, 5 and 2.5mM.
Once you have your glucose solutions you need to make calibration curve:
1) Do a Benedict’s test on each.
2) Remove any precipitate - either leave for 24 hours or centrifuge them.
3) Use a colorimeter to measure the absorbance of the Benedict’s test remaining in each tube.
4) Use the results to make a calibration curve showing absorbance against glucose concentration.
Test the unknown solution in the same way and use the calibration curve to find it’s concentration.

77
Q

What is a biosensor?

A

A device that uses a biological molecule, such as an enzyme to detect a chemical.

78
Q

How does a biosensor work?

A

The biological molecule produces a signal (e.g. chemical signal) which is converted to an electrical signal by a transducer. The electrical signal is then processed and can be used to work out other info.

79
Q

In chromatography, what is the mobile phase?

A

Where the molecules can move.

>In both paper and thin-layer chromatography the mobile phase is a liquid solvent, such as ethanol or water.

80
Q

In chromatography, what is the stationary phase?

A

Where the molecules can’t move.

>In paper chromatography the stationary phase is a piece of chromatography paper.

81
Q

Describe the experiment to identify unknown amino acids?

A

1) Draw a pencil line near the bottom of the chromatography paper and put a concentrated spot of the mixture of amino acids on it,
2) Add a small amount of prepared solvent to a beaker and dip the bottom of the paper into it. Should be done in a fume cupboard and cover with a lid to stop the solvent evaporating.
3) As the solvent spreads up the paper, the different amino acids move with it at different rates so spread out.
4) When the solvents nearly reached the tip, take the paper out and mark the solvent front with pencil. Leave the paper to dry out before analysis.
5) Amino acids aren’t coloured which means you won’t be able to see them on the paper. So before analysis spray its ninhydrin solution to make the amino acids purple and able to be seen/calculated.

82
Q

What is the Rf value?

A

The ratio of the distance travelled by a spot to the distance travelled by the solvent.

83
Q

How do you calculate the Rf value?

A

Rf value of amino acid = distance travelled by spot / distance travelled by solvent.

84
Q

How does cohesion cause surface tension so organisms like pond skaters can walk on water?

A

The water molecules at the surface are all hydrogen-bonded to the molecules beneath them meaning the surface of the water contracts and gives the surface of the water an ability to resist the force applied to it, this is surface tension.

AS Biology (12 decks)

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