Biological Molecules

Question 1

define monomer and give some examples

Answer 1

small units that join together to form larger molecules
-monosaccharides (glucose, fructose, galactose)
-amino acids
-nucleotides

Question 2

define polymer and give some examples

Answer 2

molecules formed when many monomers join together
-polysaccharides
-proteins
-DNA/RNA

Question 3

what happens in a condensation reaction?

Answer 3

a chemical bond forms between to molecules and a molecule of water is produced

Question 4

what happens in a hydrolysis reaction?

Answer 4

a water molecule is used to break a chemical bond between 2 molecules

Question 5

name 3 hexose monosaccharides

Answer 5

-glucose
-fructose
-galactose
all have the molecular formula C6H12O6

Question 6

name the type of bond formed when monosaccharides react

Answer 6

(1,4 or 1,6) glycosidic bond
if there are 2 monomers there’s 1 chemical bind and it’s called a disaccharide
if there are multiple monomers there will be many chemical bonds so it’s called a polysaccharide

Question 7

name 3 disaccharides and describe how they form

Answer 7

-maltose: glucose + glucose
-sucrose: glucose + fructose
-lactose: glucose + galactose
a condensation reaction forms a glycosidic bond between 2 monosaccharides
they all have the formula C12H22O11

Question 8

draw the structure of alpha glucose

Answer 8

now google it to check you did it right :)
(going round clockwise, the OH should be down down up down)

Question 9

draw the structure of beta glucose

Answer 9

now google it to check you did it right
(going clockwise the OH should be up down up down)

Question 10

describe the structure and functions of starch

Answer 10

starch is a storage polymer of alpha glucose in plant cells
- it’s insoluble so it has no osmotic effect on plants
- its large so it doesn’t diffuse out of cells

starch is made from amylose:
- 1,4 glycosidic bonds
- helix structure with intermolecular H-bonds so it is is compact

and from amylopectin:
- 1,4 and 1,6 glycosidic bonds
- is branched so it has many terminal ends for hydrolysis into glucose

Question 11

describe the structure and functions of glycogen

Answer 11

it’s the main storage polymer of alpha glucose in animal cells (but it is also found in plant cells)
- 1,4 and 1,6 glycosidic bonds
- is branched so it has many terminal ends for hydrolysis
- it is insoluble so there is no osmotic effect and it does not diffuse out of cells
- it is compact

Question 12

describe the structure and functions of cellulose

Answer 12

it is a polymer of beta glucose which gives righty to plant cell walls (prevents bursting under turgid pressure and holds stem up)

-1,4 glycosidic bonds
- straight chain in branched molecule
- Hbond cross links between parallel strands from microfibrils so it has high tensile strength

Question 13

describe the benedict’s test for reducing sugars

Answer 13

1) add an equal volume of benedict’s reagent to a sample
2) heat the mixture in an electric water bath at 100 degrees C for 5 mins
3) positive result: colour change from blue to orange and brick red precipitate forms

Question 14

describe benedict’s test for non reducing sugars

Answer 14

1) negative result: benedict’s reagent remains blue
2) hydrolyse non-reducing sugars (eg sucrose) into their monomers by adding 1cm cubed of HCl. heat in boiling water bath for 5 mins
3) neutralise mixture using sodium carbonate solution
4) proceed with benedict’s test as usual

Question 15

describe the test for starch

Answer 15

1) add iodine solution
2) positive result: colour change from orange to blue-black

Question 16

outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

Answer 16

1) make standard solutions with known concentrations. record absorbance or % transmission values
2) plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis)
3) record absorbance or % transmission values of unknown samples. use calibration curve to read off concentration

Question 17

describe how to test for lipids in a sample

Answer 17

1) dissolve solid samples on ethanol
2) ass an equal volume of water and shake
3) positive result: milky while emulsion forms

Question 18

how do triglycerides form

Answer 18

condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds

Question 19

contrast saturated and unsaturated fatty acids

Answer 19

saturated
-contain only single bonds
-straight chain molecules have many contact points
-higher melting point (solid at room temperature)
-found in animal fats

unsaturated
-contain carbon carbon double bonds
-‘kinked’ molecules have fewer contact points
-lower melting point (liquid at room temperature)
-found in plant oils

Question 20

relate the structure to function of triglycerides

Answer 20

-high energy to mass ratio so there is high calorific value from oxidation
-insoluble links hydrocarbon chain so no effect in water potential of cells and used for waterproofing
-slow conductor of heat so has thermal insulation
-less dense than water so helps buoyancy of aquatic animals

Question 21

describe the structure and function of phospholipids

Answer 21

amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophobic polar phosphate head
- forms phospholipid bilayer which is the component of membranes
- the tails can go outwards which makes it waterproof

Question 22

compare phospholipids and triglycerides

Answer 22

• both have glycerol back bone
• both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids
• both contain the elements C, H, O
• both formed by condensation reactions

Question 23

contrast phospholipids and triglycerides

Answer 23

phospholipids
- 2 fatty acids and 1 phosphate group attached
-hydrophilic head and hydrophobic tail
- used primarily in membrane formation

triglycerides
- 3 fatty acids attached
- entire molecule is hydrophobic
- used primarily as a storage molecule

Question 24

are phospholipids and triglycerides polymers?

Answer 24

NO; they are not made from a small repeating unit. they are macromolecules

Question 25

why is water a polar molecule?

Answer 25

oxygen is more electro negative than hydrogen so it attracts the electron density in the covalent bond more strongly
forms oxygen delta negative (slightly negative charge) and hydrogen delta positive (slightly positive charge)

Question 26

state 4 biologically important properties of water

Answer 26

due to polarity and intermolecular hydrogen bonds
- metabolite/ solvent for chemical reactions in the body
- high specific heat capacity
- high latent heat of vaporisation
- cohesion between molecules

Question 27

explain why water is significant to living organisms

Answer 27

• solvent for polar molecules during metabolic reactions
• enables organisms to avoid fluctuations in core temperature
• cohesion-tension of water molecules in transpiration stream

Question 28

what are inorganic ions and where are they found in the body?

Answer 28

• ions that do not contain carbon atoms
• found in cytoplasm and extra cellular fluid
• may be in high or very low concentrations

Question 29

explain the role of hydrogen bonds in the body

Answer 29

• high concentration of H+ ions means there is a low (acidic) pH
• H+ ions interact with H-bonds and ionic bonds in tertiary structure of proteins, which can cause them to denature

Question 30

explain the role of iron ions in the body

Answer 30

• Fe2+ binds to porphyria ring to form haem group in haemoglobin
• haem group has binding site to transport 1 molecule of O2 around the body in the blood stream
• 4 haem groups per haemoglobin molecule

Question 31

explain the role of sodium ions in the body

Answer 31

• involved in cotransport for absorption of glucose and amino acids in lumen of gut
• involved in propagation of action potentials in neurons

Question 32

explain the role of phosphate ions in the body

Answer 32

component of:
- DNA
- ATP
- NADP
- cAMP