Biological Molecules

Question 1

What is covalent bonding

Answer 1

Atoms share a pair of elections in their outer shell and as a result the outer shells of both atoms are filled and a more stable compound is nade

Question 2

What is ionic bonding

Answer 2

Ions with opposite charge attract one another
The electrostatic attraction is known as an ionic bond

Question 3

What is hydrogen bonding

Answer 3

The electrons within a molecule are not evenly distributed but tend to spend more time at one position
This reigon is more negatively charged than the rest of the molecule
A molecule with an uneven distribution of charge is said to be polarised
The negative region of one polarised molecule and the positively charged region of another attract each other
A week electrostatic bond is formed between the two
However they can collectedly form important forcesthat after the physical properties of molecules

Question 4

What is a monomer

Answer 4

Small molecules that can be linked together to form chains

Question 5

What are polymers And polymerisation

Answer 5

A polymer is along chain of monomer sub - units
The process of polymer formation is called polymerisation

Question 6

What are condensation and hydrolysis reactions

Answer 6

the formation of polymers through polymerisation is called a condensation reaction
With each new attached sub unit a molecule of water is formed

Polymers are broken down through the addition of water. These molecules use used when breaking the glycosidicbonds that link sub units

Question 7

What molecules can go through hydrolysis

Answer 7

Hydrolysis
Polypeptide to amino acid
Polysaccharide starch to monosaccaride glucose
Lipids into fatty acid + glycerol
Polynucleotides into nucleotides
And the opposite for condensation

Question 8

What is metabolism

Answer 8

All the chemical processes that take place in living organisms one collectively called metabolism

Question 9

How is life based on carbon

Answer 9

Carbon contains molecules are known as organic molecules In living organisms there are relatively few other atoms that attach to carbon life is the reform based on a small number of chemical elements

Question 10

What is a reducing sugar

Answer 10

A reducing sugar is a sugar that can donate electrons to another chemical

Question 11

What sugars are reducing sugars

Answer 11

All monosaccharides and some disaccharides c.g. Maltose

Question 12

Reducing sugars test method + results

Answer 12

Benedict’s reagent is un alkaline solution of copper II sulphate when a reducing sugar is heated with Benedict’s reagent it forms an insoluble red precipitate of copper oxide

• Add 2 cm’ of the food sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water.
• Add an equal volume of Benedict’s reagent.
• Heat the mixture in a gen tly boiling water bath for five minutes.

Question 13

Disaccharides

Answer 13

• Glucose joined to glucose forms maltose.
• Glucose joined to fructose forms sucrose.
• Glucose joined to galactose forms lactose.
. The bond that is formed in a condensation reaction is glycosidic bond

Question 14

Describe the test for non reducing sugars

Answer 14

If the sample is not already in liquid form, it must first be ground up in water.
• Add 2cm’ of the food sample being tested to 2 cm’ of Benedict’s reagent in a test tube and filter..
• Place the test tube in a gently boiling water bath for 5 minutes. If the Benedict’s reagent does not change colour (the solution remains blue), then a reducing sugar is not present.
• Add another 2cm’ of the food sample to 2cm’ of dilute hydrochloric acid in a test tube and place the test tube in a gently boiling water bath for five minutes. The dilute hydrochloric acid will hydrolyse any disaccharide present into its constituent monosaccharides.
• Slowly add some sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid. (Benedict’s reagent will not work in acidic conditions.) Test with pH paper to check that the solution is alkaline.
• Re-test the resulting solution by heating it with 2 cm? of Benedict’s reagent in a gently boiling water bath for five minutes.
• If a non-reducing sugar was present in the original sample, the Benedict’s reagent will now turn orange-brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.

Question 15

Polysaccharides

Answer 15

Polysaccharides are polymers, formed by combining together many monosaccharide molecules.

As polysaccharides are very large molecules, they are insoluble. This feature makes them suitable for storage. When they are hydrolysed, polysaccharides break down into disaccharides or monosaccharides

Question 16

Starch and polysaccharides

Answer 16

Starch is a polysaccharide that is found in many parts of plants in the form of small granules or grains, for example starch grains in chloroplasts. It is formed by the joining of between 200 and 100 000 a-glucose molecules by glycosidic bonds in a series of condensation reactions.

Question 17

Test for starch

Answer 17

Starch is easily detected by its ability to change the colour of the iodine in potassium iodide solution from yellow to blue-black
The test is carried out at room temperature. The test is carried out as follows:
• Place 2 cm’ of the sample being tested into a test tube (or add two drops of the sample into a depression on a spotting tile).
• Add two drops of iodine solution and shake or stir.
• The presence of starch is indicated by a blue-black coloration.

Question 18

Starch

Answer 18

Starch is a polysaccharide found in parts of a plant in the form of small grains. large amounts occur in seeds and storage organs, such as potato tubers. It forms an important component of food and is the major energy source in most diets.
Starch is made up of chains of a-glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions.
The chains may be branched or unbranched. The unbranched chain is wound into a tight coil that makes the molecule very compact.

Question 19

How is starch’s structure suited for its structure

Answer 19

it is insoluble and doesn’t affect water potential, so water is not drawn into the cells by osmosis
• being large and insoluble, does not diffuse out of cells
• it is compact, so a lot can be stored in a small space
• when hydrolysed it forms a-glucose, which is both easily transported and readily used in respiration
• the branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly.

Question 20

Glycogen

Answer 20

Glycogen is found in animals and bacteria never in plant cells.
Glycogen is very similar in structure to starch but has shorter chains and is more highly branched.
It is sometimes called ‘animal starch’ because it is the major carbohydrate storage product of animals.
In animals it is stored as small granules mainly in the muscles and the liver.
The mass of carbohydrate that is stored is relatively small because fat is the main storage molecule in animals.

Question 21

How is glycogen suited for its function

Answer 21

• it is insoluble and therefore does not tend to draw water into the cells by osmosis
• being insoluble, it does not diffuse out of cells
• it is compact, so a lot of it can be stored in a small space
• It is more highly branched than starch and so has more ends that can be acted on simultaneously by enzymes. It is therefore more rapidly broken down to form glucose monomers, which are used in respiration.

Question 22

Why is it important that glycogen rapid break down to form glucose monomers

Answer 22

This is important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active.

Question 23

Cellulose

Answer 23

Cellulose differs from starch and glycogen in one major way: made of monomers of B-glucose rather than a-glucose this produces fundamental differences in the structure and function of this polysaccharide
Rather than forming a coiled chain like starch, cellulose has straight, unbranched chains. These run parallel to one another, allowing-hydrogen bonds to form cross-linkages between adjacent chains.each individual hydrogen bond adds very little to the strength of the molecule, the overall number of them makes a big contribution to strengthening cellulose, making it a good structural material

Question 24

Cellulose in plants

Answer 24

Cellulose is a big component of plant cell walls and provides rigidity to the plant cell. The cellulose cell wall also prevents the cell from bursting as water enters it by osmosis. It does this by exerting an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another, making non-woody parts of the plant semi-rigid. This is important in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis.

Question 25

Cellulose structure and now its accipata tor its function

Answer 25

cellulose molecules are made up of B-glucose and so form long straight, unbranched chains
• these cellulose molecular chains run parallel to each other and are crossed linked by hydrogen bonds which add collective strength
• these molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provides yet more strength.

Question 26

Characteristics + properties of lipids

Answer 26

They contain carbon, hydrogen and oxygen.
• The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
• They are insoluble in water.
• They are soluble in organic solvents such as alcohols and acetone.
The main groups of lipids are triglycerides (fats and oils) and phospholipids.

Question 27

Main role of lipids + the other 4

Answer 27

one role of lipids is in the cell membranes
Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.

•source of energy. When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water.

• waterproofing. Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.

• insulation . Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells.

• protection. Fat is often stored around delicate organs, such as the kidney.

Question 28

Fats and oils temp

Answer 28

Fats are solid at room temperature (10-20°C) whereas oils are liquid.

Question 29

Triglycerides

Answer 29

Triglycerides are so called because they have three fatty acids combined with glycerol . Each fatty acid forms an ester bond with glycerol in a condensation reaction.Hydrolysis of a triglyceride therefore produces glycerol and three fatty acids.

Question 30

Saturated, mono- unsaturated,polyunsaturated

Answer 30

Saturated-no double bonds between carbon atoms
Mono unsaturated -1 double bond between carbon atoms
Polyunsaturated -more than 1 double bond between carbon atoms

Question 31

How does the structure of trigglycerides relate to their properties

Answer 31

• Triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and are therefore an excellent source of energy.

• Triglycerides have low mass to energy ratio, making them good storage molecules because much energy can be stored in a small volume. This is especially beneficial to animals as it reduces the mass they have to carry as they move around.

• Being large, non-polar molecules, triglycerides are insoluble in water. As a result their storage does not affect osmosis in cells or the water potential of them.

• As they have a high ratio of hydrogen to oxygen atoms, triglycerides release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts.

Question 32

Phospholipids

Answer 32

Phospholipids are similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule Whereas fatty acid molecules repel water (are hydrophobic), phosphate molecules attract water (are hydrophilic). A phospholipid is therefore made up of two parts:
• a hydrophilic ‘head’, which interacts with water (is attracted to it) but not with fat
• a hydrophobic ‘tail’, which orients itself away from water but mixes readily with fat.

Question 33

What is a polar molecule and how does it relate to phospholipids

Answer 33

Molecules that have two ends (poles) that behave differently in this way are said to be polar. This means that 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 and the hydrophobic tails are as far away from the water as possible

Question 34

How does the structure of phospholipids relate to their properties

Answer 34

Phospholipids are polar molecules, having a hydrophilic phosphate head and a hydrophobic tail of two fatty acids. This means that in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membranes. As a result, a hydrophobic barrier is formed between the inside and outside of a cell.
• The hydrophilic phosphate ‘heads’ of phospholipid molecules help to hold at the surface of the cell-surface membrane.
• The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane.
These glycolipids are important in cell recognition.

Question 35

How do you test for lipids

Answer 35

Take a completely dry and grease-free test tube.
2 To 2cm? of the sample being tested, add 5 cm? of ethanol.
3 Shake the tube thoroughly to dissolve any lipid in the sample.
4 Add 5 cm’ of water and shake gently.
5 A milky-white emulsion indicates the presence of a lipid.
6 As a control, repeat the procedures using water instead of the sample; the final solution should remain clear.

Question 36

Why does the sample go cloudy when testing lipids

Answer 36

The cloudy colour is 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 passes from oil droplets to water droplets, making it appear cloudy.