Module 2.2 - Biological Molecules

Question 1

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

Answer 1

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.

Question 2

Describe the structure of water?

Answer 2

> 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.

Question 3

What are the five main properties of water?

Answer 3

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.

Question 4

Explain what cohesion is?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

Explain how water is a good solvent?

Answer 6

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.

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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.

Question 9

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

Answer 9

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.

Question 10

What is a polymer?

Answer 10

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

Question 11

What is glucose’s structure?

Answer 11

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

Question 12

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

Answer 12

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.

Question 13

What elements are all carbohydrates made of?

Answer 13

C, H and O.

Question 14

What bonds join together monosaccharides?

Answer 14

Glycosidic bonds.

Question 15

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?

Answer 15

A condensation reaction.

Question 16

Describe a hydrolysis reaction?

Answer 16

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

Question 17

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

Answer 17

Amylose and amylopectin.

Question 18

What is the structure of amylose?

Answer 18

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.

Question 19

What is the structure of amylopectin?

Answer 19

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.

Question 20

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

Answer 20

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

Question 21

What is the main energy storage material in animals?

Answer 21

Glycogen.

Question 22

Describe the structure of cellulose?

Answer 22

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).

Question 23

What are macromolecules?

Answer 23

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

Question 24

What is the structure of a triglyceride?

Answer 24

1 glycerol molecule and 3 fatty acids.

Question 25

What is the structure of fatty acid molecules?

Answer 25

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

Question 26

What is esterification?

Answer 26

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

Question 27

What is the difference between unsaturated and saturated fatty acids?

Answer 27

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.

Question 28

How do phospholipid and triglyceride structures compare?

Answer 28

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

Question 29

Why are triglycerides good as energy storage molecules?

Answer 29

>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).

Question 30

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

Answer 30

>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.

Question 31

What is the structure of cholesterol?

Answer 31

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.

Question 32

What is the function of cholesterol?

Answer 32

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.

Question 33

What are the monomers in proteins?

Answer 33

Amino acids.

Question 34

What are the chemical elements all amino acids have?

Answer 34

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

Question 35

What is the general structure of an amino acid?

Answer 35

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.

Question 36

What type of bonds and reaction form amino acids?

Answer 36

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

Question 37

What are the four structure levels of proteins?

Answer 37

Primary, secondary, tertiary and quaternary structure.

Question 38

What is the primary structure?

Answer 38

The sequence of amino acids in the polypeptide chain.

Question 39

What is the secondary structure?

Answer 39

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.

Question 40

What is the tertiary structure?

Answer 40

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.

Question 41

What is the quaternary structure?

Answer 41

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

Question 42

What bonds hold together the proteins in the primary structure?

Answer 42

Peptide bonds.

Question 43

What bonds hold together the proteins in the secondary structure?

Answer 43

Hydrogen bonds.

Question 44

What bonds hold together the proteins in the tertiary structure?

Answer 44

>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.

Question 45

What bonds hold together the proteins in the quaternary structure?

Answer 45

Tends to be determined by the tertiary structure.

Question 46

What differs between carbohydrates and lipids?

Answer 46

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.

Question 47

What are globular proteins?

Answer 47

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.

Question 48

What are fibrous proteins?

Answer 48

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

Question 49

What are three globular proteins?

Answer 49

Haemoglobin, insulin and amylase.

Question 50

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

Answer 50

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.

Question 51

Describe the globular protein amylase?

Answer 51

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.

Question 52

What are three examples of fibrous proteins?

Answer 52

Collagen, keratin and elastin.

Question 53

Describe collagen and where it is found in the body?

Answer 53

>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.

Question 54

Where is keratin found in organisms?

Answer 54

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

Question 55

Describe elastin and examples in the body?

Answer 55

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.

Question 56

What is an inorganic ion?

Answer 56

One which doesn't contain C.

Question 57

What are 5 inorganic cations?

Answer 57

Calcium, sodium, potassium, hydrogen and ammonium.

Question 58

What are 5 inorganic anions?

Answer 58

Nitrate, hydrogen carbonate, chloride, phosphate and hydroxide.

Question 59

What is the role of calcium in biological processes?

Answer 59

>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.

Question 60

What is the role of sodium in biological processes?

Answer 60

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

Question 61

What is the role of potassium in biological processes?

Answer 61

>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.

Question 62

What is the role of hydrogen in biological processes?

Answer 62

>Affects the pH of substances. | >Important for photosynthesis reactions that occur in the thylakoid membranes inside the chloroplasts.

Question 63

What is the role of ammonium in biological processes?

Answer 63

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

Question 64

What is the role of nitrate in biological processes?

Answer 64

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

Question 65

What is the role of hydrogen carbonate in biological processes?

Answer 65

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

Question 66

What is the role of chloride in biological processes?

Answer 66

>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.

Question 67

What is the role of phosphate in biological processes?

Answer 67

>Involved in photosynthesis and respiration reactions. | >Needed for the synthesis of many biological molecules, such as nucleotides, phospholipids and calcium phosphate.

Question 68

What is the role of hydroxide in biological processes?

Answer 68

>Affects the pH of substances

Question 69

What is the biochemical test for reducing sugars?

Answer 69

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)

Question 70

What is the biochemical test for non-reducing sugars?

Answer 70

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.

Question 71

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

Answer 71

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.

Question 72

Describe the 2 stages of the Biuret test?

Answer 72

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.

Question 73

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

Answer 73

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

Question 74

What is a colorimeter?

Answer 74

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.

Question 75

What is colorimetry used to determine?

Answer 75

The concentration of a glucose solution.

Question 76

What are the steps of a colorimetry experiment?

Answer 76

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.

Question 77

What is a biosensor?

Answer 77

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

Question 78

How does a biosensor work?

Answer 78

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.

Question 79

In chromatography, what is the mobile phase?

Answer 79

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

Question 80

In chromatography, what is the stationary phase?

Answer 80

Where the molecules can't move. | >In paper chromatography the stationary phase is a piece of chromatography paper.

Question 81

Describe the experiment to identify unknown amino acids?

Answer 81

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.

Question 82

What is the Rf value?

Answer 82

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

Question 83

How do you calculate the Rf value?

Answer 83

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

Question 84

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

Answer 84

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.