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biological molecules (topic 1) Flashcards

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1
Q

benedicts reagent + heat: tests for and what they do

A

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)

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2
Q

sugars formula

A

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

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3
Q

sugar condensation reaction - products and bond formed

A

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

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4
Q

3 common disaccharides:
maltose
sucrose
lactose

A

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

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5
Q

benedicts test method

A
  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
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6
Q

non reducing sugars method

A
  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.
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7
Q

monosaccharides definition

A

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

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8
Q

disaccharides

A

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

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9
Q

polysaccharides def

A

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

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10
Q

starch diagram and function

A

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

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11
Q

glycogen diagram and function

A

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)

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12
Q

cellulose diagram and function

A

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)

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13
Q

what are the 2 groups of lipids

A

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

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14
Q

how are triglycerides formed

A

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

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15
Q

a condensation reaction between glycerol and a fatty acid form

A

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

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16
Q

acidic carboxyl group

A

COOH

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17
Q

hydroxyl group

A

OH

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18
Q

fatty acids R-group (hydrocarbon part) may be

A

saturated (animals) or unsaturated (plants)

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19
Q

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

A

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

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20
Q

monounsaturated vs polyunsaturated

A

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

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21
Q

fats vs oils (in terms of structure)

A

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

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22
Q

why do lipids make excellent energy reserves

A

can store the same amount of energy in half the mass

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23
Q

triglycerides vs phospholipids

A

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

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24
Q

structure of a phosphate group

A

.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

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25
Q

simplified phospholipids

A

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

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26
Q

phospholipids as cell membranes form what

A

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

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27
Q

phosphate group in a phospholipid…polar or non polar

A

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

28
Q

emulsion test

A
  • 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
29
Q

different properties of triglycerides and phospholipids

A

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

30
Q

protein structure

A

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

31
Q

protein bond between 2 amino acids

A

peptide bond

32
Q

protein condensation reaction

A

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

33
Q

how do amino acids differ in structure

A

the R group is different

34
Q

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

A

…dipeptide
…polypeptide

35
Q

protein: primary structure

A

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

36
Q

protein: secondary structure

A
  • 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
37
Q

protein: tertiary structure (3D)

A
  • 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

38
Q

protein: quaternary structure

A
  • 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
39
Q

protein structure and bonds in it

A

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

40
Q

biuret A and B are called

A

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

41
Q

biuret test

A
  • 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
42
Q

what do enzymes do in reactions

A

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

43
Q

what type of protein are enzymes

A

globular proteins
they are also tertiary structure proteins

44
Q

anabolic reactions

A

enzymes bring the substrate molecules together

45
Q

catabolic reaction

A

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

46
Q

conditions needed for an enzyme reaction

A

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

47
Q

enzymes: activation energy def

A

the minimum amount of energy needed to activate a reaction

(enzymes lower this AE so reactions can take place at a much lower temp)

48
Q

what do enzymes form

A

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

49
Q

induced fit model of enzyme action

A

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))

50
Q

factors affecting enzyme activity:
substrate concentration

A

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

51
Q

factors affecting enzyme activity:
enzyme concentration

A

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

52
Q

factors affecting enzyme activity:
temperature

A

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)

53
Q

factors affecting enzyme activity:
pH

A

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

54
Q

factors affecting enzyme activity:
inhibitors

A

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

55
Q

how to work out pH

A

on calculator:
— log [conc hydrogen ions]

56
Q

water being dipolar (hydrogen bonds)

A

slightly negative oxygen bonds to slightly positive hydrogens of other water molecule

so hydrogen bonds form between water molecules

57
Q

water property: cohesion

A

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)

58
Q

water property: surface tension

A

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

59
Q

water property: as a solvent

A

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

60
Q

water property: non-compressible

A

watee in plants helps the stem resist external pressure

good support system

61
Q

water property: transparency

A

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

62
Q

water property: latent heat of vaporisation

A

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

63
Q

water property: high specific heat capacity

A

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)

64
Q

water property: metabolite

A

is one in metabolic reactions eg condensation and hydrolysis

65
Q

water property: ice less dense

A

provides habitat for eg polar bears
allows them to escape predators

a biology (19 decks)

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