biological molecules

Question 1

what is meant by hydrogen bonding?

Answer 1

as the electrons in a molecule are not evenly distributed but spend more time in one position this region is more negatively charged than the rest of the molecule. when a weak electrostatic attraction is formed between teh positive end of one moleculae and the negative end of another a weak electrostatic bond is formed, this is called an hydrogen bond.

Question 2

what is meant when a molecule is polarised?

Answer 2

it has a negative region and also a positive region.

Question 3

what is polymerisation?

Answer 3

polymerisation is process in which polymers are formed. polymers are long chains of monomers, these are usually are based on carbon.

Question 4

what is a condensation reaction?

Answer 4

in the formation of polymers from polymerisation a water molecule is produced each time a new sub-unit is attached

Question 5

what is hydrolisation?

Answer 5

polymers can be broken down by the addition of water. they break the bonds in between the sub units, in polysaccharides these are called glycosidic bonds.

Question 6

what is a molar solution?

Answer 6

a solution that contains one mole of solute in each liter of solution.

Question 7

what is the basic monomer unit of carbohydrates?

Answer 7

a sugar unit. this is also known as a saccharide. a single monomer is therefor called a monosaccharide, two are a disaccharide, and more than two is a polysaccharide.

Question 8

what is a monosaccharide?

Answer 8

a monosaccharide are soluble substances that have the general formula (CH2O)n where n can be any number from 3 to 7.

Question 9

what is a reducing sugar?

Answer 9

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

Question 10

wha is the test for a reducing sugar?

Answer 10

the benedicts test. benedict’s is an alkaline solution of copper (II) sulphate. when a educing sugar is heated with benedicts it gives off an insoluble red precipitate of copper(I) oxide

Question 11

what are the 3 examples of disaccharides?

Answer 11

glucose joins to glucose to form maltose.
glucose joins to fructose to form sucrose
glucose joins to galactose to form lactose

Question 12

what is the bond between two monosaccharides called?

Answer 12

a glycodic bond

Question 13

what is the test for non reducing sugars?

Answer 13

firstly carry out the test for non educing sugar. if the result is negative then add 2cm3 of the sample to 2cm3 of dilute HCL and then place the solution in a gently boiling water bath for 5 min. (the HCL will hydrolyse any disaccharide present). slow add some sodium hydrogen carbonate to neutralise the HCL. re test the resulting solution for reducing sugars.

Question 14

what are polysaccharides?

Answer 14

polysaccharides are polymers, formed by combining together many monosaccharides molecules.

Question 15

what is the test for starch?

Answer 15

place the sample being tested into a test tube add two drops of iodine solution and stir. if starch is present then the solution will go blue-back.

Question 16

what is starch?

Answer 16

starch is a polysaccharide that is sound in many parts of a plant in forms of small grains. it forms a major component if food and is the major energy source in most diets.

Question 17

why does starches structure make it great for energy storage?

Answer 17

it is insoluble and therefor doesn’t affect water potential s water is not drawn into the cell by osmosis
being large and insoluble, it does not defuse out of cells
it is compact, so a lot of it can be stored in a small space
when hydrolysed it forms alpha glucose, which is both easily transported and also 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 easily and very rapidly

Question 18

what is glycogen?

Answer 18

glycogen is a polysaccharide that is found in animal and bacteria but never in plant cells. it is similar to starch but is shorter and is more highly branched. in animals it is mainly stored as granules in the muscles and the liver.

Question 19

why does glycogens structure suit it for storage?

Answer 19

it is insoluble and their for does not tend to draw water in to the cell via osmosis
being, insoluble it does not diffuse out of cells
it is compact so a lot can be stored in a small space
it is more branched than starch so has more ends that can be acted on simultaneously by enzymes. it is therefor more rapidly broken down to form glucose monomers, which are used in reparation. important in animals which have a high metabolic rate.

Question 20

what is cellulose?

Answer 20

cellulose unlike both starch and glycogen uses beta glucose instead of alpha, this produces fundamental differences in the structure and the function of this polysaccharide. cellulose does not have a coil structures inside it has straight unbranched chain. these run parrealel to each other allowing hydrogen bonds to form between them. while each inividua hydrogen bind adds very little to the strength of the molecule, the sheer overall number of the, makes a considerable contribution to strengthening the the cellulose

the cellulose molecules group to gather to form microfibrils which are arranged in parallel groups called fibres. cellulose provides rigidity to the cell. stops the cell bursting as water enters by osmosis (exerts an inward pressure)

Question 21

why does the structure of cellulose make it suitable to its job?

Answer 21

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

Question 22

what are lipids?

Answer 22

lipids are a group of substances that share the following characteristics
they contain hydrogen, carbon, oxygen
the the proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
they are insoluble in water
they are soluble in organic solvents

the main group of lipids are triglycerides and phospholipids.

Question 23

what are the roles of lipids?

Answer 23

source of energy - when oxidised, lipids provide more than twice the same mass or carbohydrate and release valuable water
waterproofing - lipids are insoluble in water and therefore useful in water proofing
insulation - fats are slow conductors of heat and when stored beneath the body surface help to retain body fat. 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 24

what are triglycerides?

Answer 24

a molecule that contains there fatty acids combine with a glycerol. each fatty acid forms an ester bind with the glycerol. as glyceride is alwase the same the variation in the molecule come from the fatty acids. there are over 70 different fatty acids

Question 25

what is the structure of a fatty acid?

Answer 25

all fatty acids have a carboxyl (–COOH) group, if this has no double bonds then the fatty acid is described as saturated.

Question 26

how is the structure of phospholipids related to there properties?

Answer 26

triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and are therefore an excellent source of energy
triglyceride molecules have a low mass to energy ratio meaning that they are good storage molecules as they can store lots of energy in a small volume
being large, non-polar molecules, triglycerides are insoluble in water, as a result their storage does not affect the water potential of the cell
as they have a high ratio of hydrogen to oxygen atoms they release water water when oxidised.

Question 27

what are phospholipids?

Answer 27

phospholipids are similar t lipids except that one of the fatty acid molecules is replaced by a phosphate molecule. where as fatty acid molecules repel water, phosphate molecules attract it
a phospholipid is therefore made up of two parts - a hydrophilic head and a hydrophobic tail.

Question 28

how is the structure of phospholipids related to their properties?

Answer 28

phospholipids are polar molecules. this means that in an aqueous environment they form a bilayer
the hydrophilic phosphate heads of phospholipid molecules help to hold at the surface pf the cell-surface membrane
the phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane.

Question 29

what is the test for lipids?

Answer 29

1) take a completely dry grease fleetest tube
2) to 2cm3 of the sample being tested add 5cm3 of ethanol
3) shake the tube thoroughly to dissolve any lipid in the sample
4) add 5cm3 of water and shake gently
5) a cloudy white colour indicates the presence of a lipid
6) as a control use water instead of the sample

the cloudy colour is due to the lipid in the sample being dispersed in the later to form an emulsion, light passing through the emulsion is refracted as it passes from oil droplet to water droplet, making it appear cloudy.

Question 30

what are amino acids?

Answer 30

amino acids are the basic monomer that make up the polymer called a polypeptide. polypeptides can be combined to form proteins. there are 20 amino acids that occur in all living organisms.

Question 31

what is the structure of an amino acid?

Answer 31

every amino acid has a central carbon atom to which re attached four different chemical groups:
the amino group (-NH2) a basic group from the name of amino acid is derived
carboxyl group (-COOH) an acid group
hydrogen atom
R (side) group- a variety of different chemical groups, each amino acid ha a different R group

Question 32

how is a peptide bond formed?

Answer 32

amino acid monomers can bind to form a peptide bond. the bond forms between the carboxyl group on one and the nitrogen on the other amino acid. the reaction is a condensation reaction so the OH from the carboxyl group and the H from the amino group bind to form water.

Question 33

what its the primary structure if proteins?

Answer 33

the sequence of amino acids in the polypeptide chain

Question 34

what is the secondary structure of a protein?

Answer 34

the polypeptide chain does not remain flat and straight. hydrogen bonds form between the amino acids in the chain, this makes it automatically coil into a alpha helix or a beta pleated sheet

Question 35

what is the tertiary structure of a protein?

Answer 35

the coiled or folded chain is often folded or coiled further. more bonds form between the. more binds form between different parts of the chain form, including hydrogen binds and ionic bonds. disulphide bridges also form whenever two molecules of the amino acid cysteine come close together. for proteins made up of a singular polypeptide chain the tertiary structure arms their final 3D structure

Question 36

what is the quaternary structure of a protein?

Answer 36

some proteins are made up of several polypeptide chains. the way that these assemble is the quaternary structure

Question 37

what is the test for proteins?

Answer 37

place a sample of the solution to be tested I’m a test tube and add an equal volume of sodium hydroxide at rom temperature
add a few drops of very dilute copper(II)sulphate solution and mix gently.
a purple colorisation indicates the presence of peptide bonds and hence a protein, if no protein is present then the solution remains blue.