Biological Molecules

Question 1

What are monomers?

Answer 1

Smaller units from which larger molecules are made

Question 2

What are polymers?

Answer 2

Molecules made from a large number of similar monomers joined together

Question 3

What is a condensation reaction?

Answer 3

Joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

Question 4

What is a hydrolysis reaction?

Answer 4

Breaks a chemical bond between two molecules and involves the use of a water molecule

Question 5

What elements do carbohydrates contain?

Answer 5

Carbon, hydrogen and oxygen

Question 6

Describe the properties of monosaccharides and disaccharides

Answer 6

Small, soluble molecules that are easy to transport and sweet-tasting

Question 7

Describe what monosaccharides are and their purpose

Answer 7

Basic molecular units of carbohydrates. Mainly used in respiration to provide energy and in growth during the formation of larger carbohydrates. They: include glucose, fructose and galactose (isomers), are reducing sugars: they give a positive Benedict’s test result

Question 8

What are the two isomers of glucose?

Answer 8

Alpha glucose and beta glucose

Question 9

Describe how a disaccharide is formed and give examples

Answer 9

When two monosaccharides are joined together by a glycosidic bond formed in a condensation reaction. Glucose and glucose makes maltose, glucose and fructose makes sucrose, glucose and galactose makes lactose

Question 10

How can disaccharides be hydrolysed?

Answer 10

Heating with acid e.g. dilute HCl or by an enzyme

Question 11

Explain the Benedict’s test for reducing sugars

Answer 11

1. A small amount of the sample is placed in a test tube with the same volume of Benedict’s solution 2. This is heated to 95 degrees in a water bath 3. A brick red or orange ppt is a positive result 4. If the Benedict’s solution remains blue, no reducing sugar is present

Question 12

Explain why the Benedict’s test for reducing sugars is a qualitative test

Answer 12

Does not allow you to compare results from different samples - it simply gives a positive or negative result

Question 13

How is the semi-quantitative Benedict’s test useful?

Answer 13

Useful for comparing the concentration of reducing sugar in different solutions/samples

Question 14

How are control variables in the semi-quantitative Benedict’s test standardised?

Answer 14

Using the same volume of Benedict’s solution, the same volume of the sample solutions and the samples must be heated for the same period of time at the same temperature.

Question 15

How is the semi-quantitative Benedict’s test used to compare the concentration of reducing sugar in different samples and what is the issue with this?

Answer 15

An intense brick-red colour indicates a high concentration of reducing sugar whereas a yellow or green colour shows a low concentration is present. A problem with this method is it can be difficult to judge colour - it is subjective

Question 16

What is the quantitative Benedict’s test used for?

Answer 16

To obtain numerical data to compare the concentration of reducing sugar in different samples - objective. This method can also be used to find the concentration of an unknown sample

Question 17

How can we use the quantitative Benedict’s test to figure out the concentration of an unknown sample?

Answer 17

1. Perform test on reducing sugar solutions of known concentrations 2. Control variables must be standardised 3. Use a colorimeter to measure the absorbance of each of the known solutions 4. Plot a graph of known concentration against absorbance value. This is called a calibration curve, add a line of best fit 5. Repeat the Benedict’s test with the unknown sample 6. Use the absorbance value of the unknown to read off the calibration curve to find its concentration

Question 18

Describe the test for a non-reducing sugar

Answer 18

1. Take a small sample and heat in a 95 degrees celcius water bath with Benedict’s solution to confirm a negative result 2. Hydrolyse another sample of the sucrose by heating in a 95 degrees celcius water bath with dilute acid 3. When cooled, neutralise the acid with an alkali 4. Add the same concentration of Benedict’s solution and heat in a 95 degrees celcius water bath 5. A positive brick red colour indicates a non-reducing sugar (sucrose) was originally present

Question 19

What are three properties of polysaccharides?

Answer 19

1. Do not taste sweet and are relatively insoluble in water 2. Are non-reducing - giving a negative result in the Benedict’s test 3. Function as storage (starch and glycogen) or structural molecules (cellulose)

Question 20

What is starch?

Answer 20

Storage carbohydrate found in plants, consisting of long, branched chains of alpha glucose molecules linked together by glycosidic bonds as a result of condensation reactions.

Question 21

How is starch stored?

Answer 21

In starch grains in the cytoplasm of plant cells

Question 22

What are 4 ways starch is suited to its function as a storage compound?

Answer 22

1. Large so cannot cross cell-surface membrane and leave cell 2. Insoluble so osmotically inactive 3. Has a helical shape which forms a compact store 4. Branched so glucose is easily released for respiration

Question 23

How can starch be detected in a sample using the iodine test?

Answer 23

1. Add 2-3 drops of iodine solution 2. If starch is present a blue/black colour is produced 3. If no starch is present the iodine solution remains orange/yellow

Question 24

What is glycogen?

Answer 24

Storage carbohydrate found in cytoplasm of animal cells, formed by the condensation of alpha glucose.

Question 25

Where is glycogen stored?

Answer 25

In large amounts in liver and muscle tissues

Question 26

What are two ways glycogen is suited to its function as a storage molecule?

Answer 26

1. Insoluble so is osmotically inactive 2. Similar structure to starch but with more branches which means it can be hydrolysed more rapidly to release glucose for respiration

Question 27

What is cellulose?

Answer 27

A polymer of beta glucose molecules joined together by glycosidic bonds, these bonds are formed in condensation reactions to produce long, straight chains of beta glucose molecules

Question 28

Where is cellulose found and what is it's significance?

Answer 28

Found in the cell wall of plants, which provides rigidity and shape to the cell, prevents the plant cell from bursting

Question 29

What is the significance of every other beta glucose molecule being inverted in cellulose?

Answer 29

Hydroxyl groups project from either side of the beta glucose chain and form hydrogen bonds with the hydroxyl groups of other adjacent chains, producing a 3D structure known as a microfibril, which provides strength

Question 30

What three elements do lipids contain?

Answer 30

Carbon, hydrogen and oxygen

Question 31

Are lipids insoluble or soluble?

Answer 31

Insoluble in water but are soluble in a range of organic solvents e.g. alcohol

Question 32

What are the two types of lipid?

Answer 32

Triglycerides and phospholipids

Question 33

What is a triglyceride?

Answer 33

3 fatty acids joined to one glycerol molecule, joined in three condensation reactions with the loss of three water molecules. A condensation reaction between glycerol and a fatty acid forms an ester bond. One triglyceride has 3 ester bonds

Question 34

True or False: Triglycerides and phospholipids are polymers

Answer 34

False - they are not made up from similar monomers

Question 35

What is the general formula of a fatty acid?

Answer 35

R-COOH. R represents a hydrocarbon chain and COOH is a carboxylic acid group

Question 36

What does saturated mean?

Answer 36

No double bonds between carbon atoms

Question 37

What does unsaturated mean?

Answer 37

One or more double bonds between the carbon atoms

Question 38

What are two ways lipids can be hydrolysed into glycerol and fatty acids?

Answer 38

1. Heating with acid or alkali 2. Using the enzyme lipase at its optimum temp and pH

Question 39

What is important about triglycerides having a high proportion of C-H bonds?

Answer 39

Release twice as much energy as carbohydrates during aerobic respiration

Question 40

What is important about triglycerides having a high ratio of H to O atoms?

Answer 40

Release water when respired (metabolic water) which is important for organisms in dry deserts

Question 41

What is important about triglycerides being non-polar?

Answer 41

Insoluble in water - ideal storage compounds as they are osmotically inactive

Question 42

Why are triglycerides present in the waxy cuticles of insects and plant leaves?

Answer 42

Insolubility helps to reduce water loss

Question 43

What does a phospholipid molecule consist of?

Answer 43

One glycerol, two fatty acids and a phosphate group joined by 3 condensation reactions to form 3 ester bonds

Question 44

Describe the polarity of the phosphate head and the two fatty acids in a phospholipid

Answer 44

Phosphate head is polar and hydrophillic, fatty acid tails are non-polar and hydrophobic

Question 45

Why is the structure of phospholipids important?

Answer 45

They form a phospholpid lipid bilayer due to the hydrophobic tails being repelled by water - forms the cell surface membrane

Question 46

Describe the emulsion test for lipids

Answer 46

1. A small amount of the sample is placed into a test tube with ethanol 2. Shake the mixture so that the fat dissolves 3. Add this to water in another test tube and mix the contents 4. A white emulsion of fat droplets indicates lipid present

Question 47

What are four similarities between triglycerides and phospolipids?

Answer 47

1. Insoluble in water 2. Contain glycerol 3. Contain ester bonds 4. Contain C, H and O but phospholipids also contain P

Question 48

What are two differences between triglycerides and phospholipids?

Answer 48

1. Triglycerides have three fatty acids and phospholipid has two fatty acids plus phosphate group 2. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region

Question 49

What elements does protein contain?

Answer 49

C, H, O, N and sometimes S

Question 50

What are the monomers for protein?

Answer 50

Amino acids

Question 51

How many different commonly occurring amino acids are there in living organisms?

Answer 51

20

Question 52

What 3 groups do amino acids contain?

Answer 52

1. Amine (NH3) 2. Carboxylic acid (COOH) 3. R group - differ in their carbon-containing side group

Question 53

How are amino acids joined together?

Answer 53

Peptide bonds (-CONH-) formed by condensation reactions

Question 54

How does a dipeptide form?

Answer 54

Two amino acids join together in a condensation reaction to form a peptide bond

Question 55

How does a polypeptide form?

Answer 55

Many amino acids join together in a chain to form many peptide bonds

Question 56

How can proteins be hydrolysed into amino acids?

Answer 56

Heating with acid or by using enzymes (proteases)

Question 57

Describe the primary structure of a protein

Answer 57

Specific sequence of amino acids in a polypeptide chain - determines the specific shape of a protein

Question 58

Describe the secondary structure of a protein?

Answer 58

Folding or coiling of the polypeptide chain as a result of hydrogen bonding between amino acids to form an alpha helix or beta pleated sheet

Question 59

Describe the tertiary structure of a protein

Answer 59

Formed by further folding and coiling of the secondary structure due to hydrogen bonds, ionic bonds and disulfide bridges. These bonds form in places determined by the sequence of amino acids in the primary structure. They form between the R groups of amino acids

Question 60

Explain why proteins have such a wide variety of roles

Answer 60

Due to their tertiary structures being so specific and unique

Question 61

What does the tertiary structure of an enzyme determine?

Answer 61

Shape of its active site and therefore its precise function

Question 62

What are globular proteins?

Answer 62

Soluble and consist of a highly folded and coiled polypeptide chain to produce a compact, complex tertiary structure. They include enzymes and antibodies

Question 63

What is the quaternary structure of a protein?

Answer 63

When proteins consist of more than one polypeptide chain. The polypeptide chains are held together by ionic bonds, hydrogen bonds and sometimes disulfide bridges

Question 64

What is denaturation and what can this result in?

Answer 64

Alteration in the tertiary structure of a protein. This loss of the 3D shape is often irreversible and the protein is no longer functional