section 1: biological molecules Flashcards
1
Q
test for reducing sugars
A
- all monosaccharides and some disaccharides are reducing sugars
- add 2cm of the food sample to be tested in a test tube
- add an equal volume of Benedict’s reagent
- heat the mixture in a water bath for 5 minutes
- if reducing sugar is present there will be a colour change to red/brown
- different colours can show different amounts of reducing sugar : blue = none, green = very low, yellow = low, orange = medium, red = high
2
Q
test for non-reducing sugars
A
- add 2cm of the food sample being tested to 2cm of Benedict’s reagent in a test tube and filter
- put test tube in water bath for 5 minutes, if no colour change then reducing sugar is not present
- add another 2cm of the food sample to 2cm of dilute hydrochloric acid in a test tube and place in water bath for 5 minutes, the hydrochloric acid will hydrolyse any disaccharide present into its monosaccharides
- slowly add some sodium hydrogencarbonate solution to the test tube to neutralise the acid
- re test the solution by heating it with 2cm of Benedict’s reagent in a water bath for 5 minutes
- if a non-reducing sugar was present in the original sample then the Benedict’s solution will now turn orange/brown due to reducing sugars that have been produced
3
Q
test for starch
A
- place 2cm of sample being tested into a test tube
- add two drops of iodine solution and shake
- if starch is present there will be a colour change to blue/black
4
Q
what does saturated mean ?
A
no double bonds between carbon atoms
5
Q
what does unsaturated mean?
A
there is double bond between carbon atoms
6
Q
test for lipids
A
- known as the emulsion test
- take a completely dry and grease free test tube and add 2cm of the sample being tested
- add 5cm of ethanol
- shake thoroughly to dissolve any lipid in the sample
- add 5cm of water and shake gently
- a cloudy-white colour indicates the presence of a lipid
7
Q
test for proteins
A
- the Biuret test which detects peptide bonds
- put a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
- add a few drops of very dilute copper sulfate solution and mix gently
- a colour change to purple indicates peptide bonds are present, if it remains blue there are none
8
Q
what bond is between 2 monosaccharides
A
glycosidic bonds
9
Q
monomers
A
are the smaller repeating units from which larger molecules are made to by joining them to make polymers
10
Q
polymers
A
a molecule made from a large number of monomers joined together
11
Q
condensation reaction
A
removing water from something to make new bonds
12
Q
hydrolysis reaction
A
adding water to something to break it’s bonds
13
Q
monosaccharides
A
- glucose
- galactose
- fructose
14
Q
disaccharides
A
- maltose (glucose + glucose)
- sucrose (glucose + fructose)
- lactose (glucose + galactose)
15
Q
polysaccharides
A
- starch
- glycogen
- cellulose
16
Q
cellulose
A
- made of beta glucose
- has straight, unbranched chains, that run parallel to each other
- makes it straight and strong so is good for cell walls
- many chains are cross linked by hydrogen bonds to form microfibrils which help strengthen the walls
17
Q
starch
A
- made of alpha glucose linked by 1-4 glycosidic bonds
- branched or unbranched
- arranged in a helix shape
- insoluble so doesn’t effect water potential
- large molecule so can’t diffuse out of cell
- compact so can store large amounts of energy in small space
- energy storage in plants
18
Q
glycogen
A
- made of alpha glucose
- more branched than starch (speeds up enzyme reaction)
- compact so can store a lot of energy in a small space
- large so can’t diffuse out of cell
- insoluble so doesn’t effect water potential
- in shorter chains than starch
- energy storage in animals
19
Q
roles of lipids
A
- energy stores
- insulation
- substrate for respiration
- protection of organs
- buoyancy
- cell membranes
20
Q
how does structure of triglycerides relate to their properties ?
A
- have a high ratio of carbon-hydrogen bonds to carbon atoms so are very good source of energy
- low mass to energy ratio so are good storage molecules as they can store a lot of energy in a small volume (less mass to carry around with them)
- insoluble in water so don’t effect water potential
- high number of hydrogen-oxygen atoms so they release water when oxidised so are source of water
21
Q
how does the structure of phospholipids relate to its properties?
A
- them being polar means in an aqueous environment they can form a bilayer
- the hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane
- their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition
22
Q
explain the complementary base pairing rules
A
- adenine pairs with thymine (A+T)
- cytosine pairs with guanine (C+G)
- in RNA uracil replaces thymine (A+U)
23
Q
type of sugar in DNA
A
deoxyribose
24
Q
type of sugar in RNA
A
ribose
25
how is DNA structure related to it’s function?
- phosphodiester backbone protects the organic bases inside of the double helix
- it coils up into a double helix so that it is more compact and lots of information can be stored in a small space
- it’s very long so can store a lot of information
26
how is ATP converted to ADP?
* ATP is hydrolysed to form ADP and a phosphate molecule
| * this reaction is catalysed by ATP hydrolase
27
how is ATP resynthesised from ADP ?
* ATP is resynthesised by a condensation reaction
* this reaction is catalysed by ATP synthase
* requires energy (endergonic reaction)
28
semi-conservative DNA replication
1. the enzyme DNA helicase breaks the hydrogen bonds and separates the two strands of DNA
2. each exposed strand can now act as a template
3. free nucleotides are attracted to their complimentary base pairs and line up
4. DNA polymerase catalyses the polymerisation of nucleotides to become a polynucleotide chain - reforms sugar phosphate backbone
5. each new strand contains half of the original maternal and half newly synthesised
29
properties of water?
* surface tension - the uneven distribution of force at a boundary interface caused by molecular bonding, so the surface of water forms a skin which can support aquatic organisms
* density - water freezes from the top down, so organisms can survive below the surface of the ice which acts as an insulating layer
* solvent - this allows water to act as a transport medium for polar molecules
* cohesion - the tendency of molecules of a substance to attract one another, molecules are pulled inward causing it to move upwards through xylem tissue
30
explain how water hydrogen bonds
there is an uneven distribution of charge so one end of the molecule is more positive than the other so then hydrogen bonding can occur in the water molecules
31
functions of proteins
- structure e.g. collagen or keratin
- enzymes
- hormones
- maintains pH
- assist transport of molecules
32
primary structure of proteins
- amino acids join together (polymerisation)
- chain/sequence of amino acids
- peptide bonds
33
secondary structure of proteins
- alpha helix or pleated sheet
- hydrogen bonds form causing the chain to twist into a 3D structure
- peptide bonds + hydrogen bonds
34
tertiary structure of proteins
- becomes folded even more
- more complex 3D structure
- disulfide, ionic, hydrogen and peptide bonds
35
quaternary structure of proteins
- large complex molecules
- contains 2 or more polypeptide chains
- all 4 types of bonds
36
what are the two types of proteins
* fibrous - collagen, structure
| * globular - enzymes, haemoglobin
37
what are competitive enzyme inhibitors?
bind to the enzyme active sight
compete with the substrate so slows rate of reaction
if substrate concentration is increased then the rate of reaction will still increase
38
what are non-competitive enzyme inhibitors?
binds to the allosteric site and changes the shape of the enzyme active site
so substrate is no longer complementary as doesn't fit
even if the concentration of the substrate is increased it will no longer have an affect on the rate of reaction
39
what are enzymes?
biological catalysts
| they speeds up or direct chemical reactions
