Biological molecules

Question 1

What is the test for protein

Answer 1

Biuret reagent is added, no heating is required, a purple colour develops if there is protein

Question 2

What is the test for lipids

Answer 2

Emulsion test, the substance is shaken with ethanol. The ethanol is then poured into a test tube containing water. If there is lipid then the water turns cloudy.

Question 3

What is the test for starch

Answer 3

Add Iodine to the substance, a blue-black colour is produced when there is starch

Question 4

What is the test for reducing sugars

Answer 4

Add benedicts solution to the substance which is heated in a water bath. If a reducing sugar is present it will turn brick red.

Question 5

What is the test for non-reducing sugars

Answer 5

Heat the sugar solution with hydrochloric acid. You need to add an alkali such as sodium hydroxide. Add benedicts solution and gently heat. If the solution goes red now but not in the initial step then there is a non-reducing sugar is present.

Question 6

How to use colour standards to estimate the concentration of reducing sugars

Answer 6

The intensity of the red colour in the benedicts test can be used to estimate the concentration of the reducing sugars. You can estimate the concentration using colour standards made by comparing the colour of the unknown concentration against the colours obtained in tests done with reducing sugar solutions of known concentrations.

Question 7

Monomer

Answer 7

A relatively simple molecule used as a building block to make polymers.

Question 8

Polymer

Answer 8

A giant molecule made from monomers joined together in a chain.

Question 9

Macromolecule

Answer 9

A large biological molecule such as a protein, polysaccharide or nucleic acid

Question 10

Monosaccharide

Answer 10

They are sugars with the general formula (CH2O)n and consist of a single sugar unit

Question 11

How are monosaccharides classified

Answer 11

They are classified according to how many carbon atoms are in each molecule. There are trioses (3C), pentoses (5C) and hexoses (6C)

Question 12

Disaccharide

Answer 12

A sugar molecule consisting of two monosaccharides joined together by a glyosidic bond

Question 13

Polysaccharide

Answer 13

A polymer whose subunits are monosaccharides joined together by glycosidic bonds.

Question 14

How are disaccharides formed

Answer 14

Two monosaccharides are joined by a condensation reaction to form a glycosidic bond. An -OH is lost from one sugar and H from another -OH group. If two alpha monosaccharides are joined up its with their 1 and 4th carbons. It is possible for any two possible -OH groups to line up but only a few actually exist in nature. Many thousands monosaccharides can join up into polysaccharide as each successive monosaccharide is joined by a glycosidic bond.

Question 15

Hydrolyses

Answer 15

The breakage of glycosidic bonds in polysaccharides and saccharides by hydrolyses. In reducing sugars this occurs.

Question 16

Why are polysaccharides used in storage

Answer 16

They are compact, inert and insoluble.

Question 17

Starch

Answer 17

Made of Amylose and Amylopectin. Amylose is made by condensation between alpha glucose molecules, they are linked between 1 and 4 of successive glucose units. The chains coil into a helical structure making the final molecule more compact. Amylopectin is also made of many 1,4 linked alpha glucose molecules, but the chains are shorter then in amylose and branch out to the sides. Starch is never found in animal cells .

Question 18

Glycogen

Answer 18

Like amylopectin it is made of chains of 1,4 linked alpha glucose with 1,6 linkage forming branches. It is more branched then amylopectin, these branches can be broken down easily which is useful when there is a sudden need for energy. It is less compact then starch.

Question 19

Cellulose

Answer 19

Mechanically strong. Successive beta glucose molecules are linked at 180 degrees to each other. The hydrogen atoms of the -OH group are weakly attracted to oxygen atoms in the same cellulose molecule and also to oxygen of -OH groups in neighbouring molecules. These hydrogen bonds are collectively very strong. The bundles form microfibrils which are in turn held together in bundles called fibres by hydrogen bonding. A cell wall has several layers of fibres running in different directions to increase strength. Strength means that it doesn’t burst when osmosis happens.

Question 20

Triglycerides

Answer 20

Forms when glycerol reacts with 3 fatty acid tails in a condensation reaction to form a ester. They are insoluble in water as the fatty acid tail is not polar.

Question 21

Roles of triglycerides

Answer 21

An excellent energy reserve as it is rich in carbon hydrogen bonds so will yield more energy on oxidation. It is also a metabolic source of water, when oxidised CO2 and water is produces which is useful for animals which live in dry climates.

Question 22

Phospholipids

Answer 22

When one of the fatty acid tails in triglycerides is replaced by a phosphate group. The head containing the phosphate group is hydrophilic whereas the two fatty acid tails are hydrophobic. It can form a membrane around a cell where the hydrophilic head lies in the watery surroundings on the outside of the membrane and the hydrophobic tails form a layer which is impermeable to hydrophilic substances

Question 23

Amino acid

Answer 23

H R =O
N—C—C
H H OH

They have a central carbon which is bonded to an amine group -NH2 and a carboxylic acid group -COOH, a hydrogen is also bonded to the central carbon. There is also an R group bonded to the central carbon which varies in each amino acid.

Question 24

Making a peptide bond

Answer 24

Two amino acids join together, one looses an -OH from its carboxylic acid whilst the other looses a hydrogen from its amine group. It is a condensation reaction, the carbon of the carboxylic acid group bonds to the nitrogen. This forms a dipeptide, a polypeptide can be made and any number of amino acids can join.

Question 25

Breaking a peptide bond

Answer 25

Polypeptides can be broken down into amino acids by breaking the peptide bond. This is a hydrolysis reaction involving the addition by water. It happens naturally in the stomach and small intestine.

Question 26

Primary structure

Answer 26

The sequence of amino acids in a polypeptide or protein

Question 27

Secondary structure

Answer 27

The structure of a protein molecules resulting from the regular coiling or folding of the chain of amino acids e.g. alpha helix or beta pleated sheet. Caused by the hydrogen bonding between the amine and carboxylic acid groups

Question 28

Tertiary structure

Answer 28

The compact structure of a protein molecule resulting from the three dimensional coiling of the already folded chain of amino acids.

Question 29

Quaternary structure

Answer 29

The three dimensional arrangement of two or more polypeptides, or of a polypeptide and a non protein component such as a haem group.

Question 30

Alpha helix

Answer 30

This is due to the hydrogen bonding between the oxygen of the CO group of one amino acid and the hydrogen of the NH group of the amino acid 4 places ahead of it.

Question 31

Beta pleated sheet

Answer 31

Sometimes the hydrogen bonding results in a much looser straighter shape then the alpha helix.

Question 32

Hydrogen bonding in secondary structure

Answer 32

Are strong enough to hold the alpha helix and beta pleated sheet in place but are broken at high temperatures and ph change.

Question 33

How hydrogen bonding keeps folded proteins in their precise shape

Answer 33

They form between strongly polar groups i.e. NH, CO and OH groups

Question 34

How disulfide bonds keep folded proteins in their precise shape

Answer 34

Form between cysteine molecules. They are strong covalent bonds. They can be broken by reducing agents

Question 35

How ionic bonding keeps folded proteins in their precise shape

Answer 35

Form between ionised amine NH3+ groups and ionised carboxylic acid COO- groups. They can be broken by ph change

Question 36

How weak hydrophobic interactions keep folded proteins in their precise shape

Answer 36

Occur between non-polar R groups. Although the interactions are weak, the groups tend to stay together because they are repelled by the watery environment around them.

Question 37

Globular proteins

Answer 37

A protein where the molecule curls up so that their non-polar hydrophobic R groups point into the centre of the molecule away from the watery surroundings. The polar, hydrophilic R groups remain on the outside of the molecule. Normally soluble, many have roles in metabolic reactions such as enzymes.

Question 38

Fibrous proteins

Answer 38

Form long strands, not normally soluble in water and tend to have structural roles. For example collagen or keratin.

Question 39

Haemoglobin - a globular protein

Answer 39

It is made of four polypeptide chains so has a quaternary structure. There are two chains of beta globin and two chains of alpha globin. The hydrophobic R groups point inwards and the hydrophilic R groups point outwards. This is important in maintaining solubility. Each polypeptide chain contains a haem group. Each haem group contains an iron atom, one oxygen molecule O2 can bind with each Iron atom. A complete haemoglobin molecule with 4 haem groups can carry 4 oxygen molecules.

Question 40

Collagen - a fibrous protein

Answer 40

An insoluble structural protein. It has 3 polypeptide chains, each in the shape of a helix. They are wound around each other to form a tripe helix. The three strands are held together by hydrogen and some covalent bonds. Every third amino acid in a polypeptide is glycine, the smallest amino acid. Its small size allows the strands to lie close together and form a tight coil. These triple helixes lie side by side and link to each other by covalent cross links these form fibrils. The ends are staggered so that there is no weak spot. The fibrils lie alongside each other forming fibres. Very flexible. They line up according to the forces they must withstand.

Question 41

Specific heat capacity

Answer 41

How much energy is taken to heat something up

Question 42

Latent heat of vaporisation

Answer 42

How much energy is needed to evaporate a substance

Question 43

Water has a high specific heat capacity and latent heat of vaporisation

Answer 43

This is due to the many strong hydrogen bonds which are a type of intermolecular force which make water molecules difficult to separate. This means temperatures in cells rarely changes so which is helpful as the organelle don’t get harmed. Large bodies of water rarely change temperature meaning the organisms inside it don’t get harmed.

Question 44

Water is a good solvent

Answer 44

Can dissolve ions and polar molecules because different sides of the water molecule are slightly charged. The water molecule collects around the ions and separate them. Lipids are not soluble because they are not polar so the water molecule attracts other water molecules instead. This allows for separation.