biological molecules (topic 1)

Question 1

benedicts reagent + heat: tests for and what they do

Answer 1

reducing sugars (all monosaccharides and some disaccharides)
they donate an electron to the benedicts reagent (copper sulfate)
when a reducing sugar is added and heated it forms insoluble red precipitate (copper oxide)

Question 2

sugars formula

Answer 2

(CH2O)n
eg if n=6, then C6H12O6 (glucose)

Question 3

sugar condensation reaction - products and bond formed

Answer 3

a molecule of water is produced as two monosaccharides form a disaccharide with a glycosidic bond

Question 4

3 common disaccharides:
maltose
sucrose
lactose

Answer 4

α-glucose + α- glucose -> maltose + water
α-glucose + fructose -> sucrose + water
α-glucose + galactose -> lactose + water

Question 5

benedicts test method

Answer 5

1. add 2cm3 of the food sample to be tested (needs to be in liquid form to begin with).
2. add 2cm3 of Benedict’s Reagent.
3. heat the mixture gently in a water bath for five minutes. If the solution turns green to brick red then a reducing sugar is present and it is a positive result

Question 6

non reducing sugars method

Answer 6

1. 2cm3 liquid food sample is added to 2cm3 of Benedict’s Reagent. Place in a water bath for 5 minutes to gently warm (reducing sugars test)
2. expect negative result
3. Another 2cm3 of the same food sample is then taken and 2cm3 of dilute hydrochloric acid is added. add test tube back to water and boil. the dilute HCl will hydrolyse the disaccharides into their constituent monosaccharides
4. After this ass sodium hydrogencarbonate to neutralise the test tube as the Benedict’s Reagent will not work in acidic conditions. check with pH paper.
5. The solution can now be retested by adding 2cm3 of Benedict’s Reagent to the solution and placing in a water bath for 5 minutes.
6. If non reducing sugar is present in the original sample then a colour change from the blue Benedict’s Reagent to brick red will be observed.

Question 7

monosaccharides definition

Answer 7

the monomers from which larger carbohydrates are made
(glucose, galactose, fructose)

Question 8

disaccharides

Answer 8

formed by the condensation of two monosaccharides
maltose = glucose + glucose
sucrose = glucose + fructose
lactose = glucose + galactose

Question 9

polysaccharides def

Answer 9

formed by the condensation of many glucose units
glycogen and starch: α-glucose
cellulose: β-glucose

Question 10

starch diagram and function

Answer 10

d: coiled and branched
f: energy store in plants
- insoluble - doesn’t affect water potential so water isn’t drawn into cells - osmosis
- large + insoluble - doesn’t diffuse out cells
- compact - lots of it can be stored in a small space
- when hydrolysed, forms α-glucose (easily transported + readily used in respiration)
- branched - has many ends so enzymes can simultaneously act on it, glucose monomers are released very rapidly

Question 11

glycogen diagram and function

Answer 11

d: more highly branched than starch
f: energy store in animals
- insoluble - doesn’t tend to draw water into cells by osmosis
- insoluble - doesn’t diffuse out of cells
- compact - lots of it can be stored in a small space
- more highly branched, more ends to be acted on by enzymes simultaneously, more rapidly broken down into glucose monomers used in respiration (important for animals w higher metabolic rate (= respiratory rate) as they are more active)

Question 12

cellulose diagram and function

Answer 12

d: straight, unbranched chains, that run parallel to each other, hydrogen bonds form cross linkages between the chains. cellulose molecules grouped together form microfibrils.
f: hydrogen bonds form collective strength which helps cell wall provide rigidity to cell.
- cell wall prevents cell bursting during osmotic pressure (exerts inward pressure preventing further influx of water)

Question 13

what are the 2 groups of lipids

Answer 13

triglycerides and phospholipids
- triglycerides are fats and oils
- phospholipids are cell membrane

Question 14

how are triglycerides formed

Answer 14

condensation reaction between one molecule of glycerol and three molecules of fatty acid

Question 15

a condensation reaction between glycerol and a fatty acid form

Answer 15

an ester bond (between the O of glycerol and C of fatty acid)

Question 16

acidic carboxyl group

Answer 16

COOH

Question 17

hydroxyl group

Answer 17

OH

Question 18

fatty acids R-group (hydrocarbon part) may be

Answer 18

saturated (animals) or unsaturated (plants)

Question 19

what do unsaturated fatty acids have that saturated ones don’t

Answer 19

a C=C double bond
- which allows them to bend

Question 20

monounsaturated vs polyunsaturated

Answer 20

mono = only one C=C double bond
poly = two or more C=C double bond

Question 21

fats vs oils (in terms of structure)

Answer 21

fats have a greater proportion of saturated fatty acids
oils have a greater proportion of unsaturated fatty acids

Question 22

why do lipids make excellent energy reserves

Answer 22

can store the same amount of energy in half the mass

Question 23

triglycerides vs phospholipids

Answer 23

in phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group

Question 24

structure of a phosphate group

Answer 24

.p has double bond O, C has single bond H
R - O - P - O - C - H
.p has single bond O-, C has single bond C for glycerol

Question 25

simplified phospholipids

Answer 25

O |[ (second one is unsaturated) head and a tail head = hydrophilic - interacts with water, attracted to it tail = hydrophobic - repels water

Question 26

phospholipids as cell membranes form what

Answer 26

a phospholipid bilayer (tails are protected against water, heads orientated towards water O |[ |[ O

Question 27

phosphate group in a phospholipid…polar or non polar

Answer 27

polar (dissolves in water) (tails are non-polar)

Question 28

emulsion test

Answer 28

- take a dry and grease free test tube - put 2cm of sample in test tube - add 2cm of ethanol - shake thoroughly to dissolve any lipid in the sample - add 2cm water and shake gently - a cloudy-white colour indicates presences of lipid

Question 29

different properties of triglycerides and phospholipids

Answer 29

T are non polar, P are polar T hydrophobic, P heads hydrophilic and tails hydrophobic (form bolsters)

Question 30

protein structure

Answer 30

(R) (amine group) H2N - C - COOH (carboxyl group) (H)

Question 31

protein bond between 2 amino acids

Answer 31

peptide bond

Question 32

protein condensation reaction

Answer 32

OH from the carboxyl group H from the amine group forms water and dipeptide

Question 33

how do amino acids differ in structure

Answer 33

the R group is different

Question 34

two amino acids form a … many amino acids form a …

Answer 34

…dipeptide …polypeptide

Question 35

protein: primary structure

Answer 35

the no and sequence of amino acids in the chain determines eventual shape of the protein, therefore function

Question 36

protein: secondary structure

Answer 36

- amino acids in primary structure of a protein don’t lie flat and straight - HYDROGEN bonds form between amino acids makes the protein COIL into an α helix or FOLD into a β pleated sheet

Question 37

protein: tertiary structure (3D)

Answer 37

- the coiled or folded chain often coil/fold further - more bonds form due to interactions between R-GROUPS of the polypeptide chain - for proteins formed from a single polypeptide chain, this is the final 3D structure of the protein BONDS: - disulphides : strong and not easily broken down. between 2 amino acids which both contain S - ionic : easily broken down by changes in pH. between carboxyl/amine groups which aren’t involved in peptide bond - hydrogen : numerous but very easily broken down. between +ve and -ve charged -NH and -C=O

Question 38

protein: quaternary structure

Answer 38

- large complex proteins containing a number of individual polypeptide chains - also contain some ‘non-protein’ groups - eg haemoglobin, made of 4 polypeptide chains bonded together - there may also be non protein groups added in (prosthetic groups) eg haemoglobin has haem containing iron

Question 39

protein structure and bonds in it

Answer 39

P - peptide S - hydrogen T - disulphide bridges, ionic, hydrogen Q - depends on tertiary, influenced by all bonds

Question 40

biuret A and B are called

Answer 40

A: sodium hydroxide (hydrolyse protein sample to expose peptide bonds) B: copper sulphate

Question 41

biuret test

Answer 41

- 2cm3 food sample in a test tube. add equal vol Biuret A (sodium hydroxide) to test tube at room temp - add 3 drops of Biuret B (copper sulfate) to test tube - shake gently to mix - note any colour change

Question 42

what do enzymes do in reactions

Answer 42

biological catalyst - lowers activation energy of the reaction it catalyses catalyst: alter the rate of a chemical reaction without undergoing permanent changes themselves

Question 43

what type of protein are enzymes

Answer 43

globular proteins they are also tertiary structure proteins

Question 44

anabolic reactions

Answer 44

enzymes bring the substrate molecules together

Question 45

catabolic reaction

Answer 45

enzyme active site affects bonds in substrates so they are easier to break

Question 46

conditions needed for an enzyme reaction

Answer 46

enzyme substrate complex is needed to form for a reaction to happen to increase likelihood of this forming, increase kinetic energy

Question 47

enzymes: activation energy def

Answer 47

the minimum amount of energy needed to activate a reaction (enzymes lower this AE so reactions can take place at a much lower temp)

Question 48

what do enzymes form

Answer 48

they are specific to a certain type of substrate, when they bind together they form an enzyme-substrate complex temporary bonds form between the substrate molecule and specific amino acids in the active site. these hold the substrate within the active site

Question 49

induced fit model of enzyme action

Answer 49

in an enzyme-substrate complex, structure of the enzyme is altered so the active site of the enzyme fits around the substrate (prior to binding, active site and substrate are not precisely complementary ((but not dissimilar))

Question 50

factors affecting enzyme activity: substrate concentration

Answer 50

as SC increases, ROR increases proportionally until all enzymes are saturated, then it will level off. increasing amount of substrate increases collisions, assuming enough enzymes present

Question 51

factors affecting enzyme activity: enzyme concentration

Answer 51

increasing EC will increase ROR, but this is limited by the amount of substrate present - enzymes are reused, substrate is not

Question 52

factors affecting enzyme activity: temperature

Answer 52

as temp increases, KE of enzyme and substrate molecules increases and they move faster increases likelihood enzyme and substrate will collide a rise of 10° usually doubles the ROR (below the optimum) above optimum, hydrogen bonds break (denatured)

Question 53

factors affecting enzyme activity: pH

Answer 53

changing pH changes conc of hydrogen or hydroxyl ions in the surrounding solution a small change alters the charges on the amino acids that make up the active site, so substrate molecule is unable to bind large change in pH breaks bonds that hold the tertiary structure together. affects formation of hydrogen bonds and ionic bonds between -NH2 and -COOH groups so affects shape of active site

Question 54

factors affecting enzyme activity: inhibitors

Answer 54

slow down the rate of enzyme controlled reactions attach to enzymes if forms covalent bonds that is permanent inhibition (irreversible) competitive inhibition: have similar shape to substrate, so block the active site and substrate can’t bind. increasing number of substrates lessens effect non-competitive inhibition: binds somewhere other than the active site and alters shape of enzyme adding more substrate doesn’t change ROR

Question 55

how to work out pH

Answer 55

on calculator: — log [conc hydrogen ions]

Question 56

water being dipolar (hydrogen bonds)

Answer 56

slightly negative oxygen bonds to slightly positive hydrogens of other water molecule so hydrogen bonds form between water molecules

Question 57

water property: cohesion

Answer 57

water molecules are known to stick together (one molecule can have 4 others stick to it because of the hydrogen bonds between the molecules) also adhesion: attraction to unlike molecules (not other waters)

Question 58

water property: surface tension

Answer 58

due to cohesion, when water meets air it gets pulled back into the body of water instead of escaping from it this force is called surface tension - water surface is strong enough to support smaller organisms

Question 59

water property: as a solvent

Answer 59

lots of things dissolve in water: gases (CO2 and O2) waste (urea/ammonia) inorganic ions and small hydrophilic molecules (amino acids, monosaccharides, ATP) some enzymes so good for transporting things in the body

Question 60

water property: non-compressible

Answer 60

watee in plants helps the stem resist external pressure good support system

Question 61

water property: transparency

Answer 61

allows aquatic plants to photosynthesise and grow allows animals to see (fluid in eye allows light rays to reach the retina)

Question 62

water property: latent heat of vaporisation

Answer 62

hydrogen bonding between the molecules means it requires a lot of energy to evaporate 1g of water energy known as latent heat of vaporisation mammals sweat: body heat used to evaporate water resulting in body cooling

Question 63

water property: high specific heat capacity

Answer 63

4.2kJ/kg/°C a lot of energy needs to be gained or lost to change the temp of water therefore acts as a buffer against temperature change aquatic environment is very stable (also means enzymes won’t be denatured by a change in temp)

Question 64

water property: metabolite

Answer 64

is one in metabolic reactions eg condensation and hydrolysis

Question 65

water property: ice less dense

Answer 65

provides habitat for eg polar bears allows them to escape predators