1. biological molecules

how can you test for reducing sugars?

(typical) Benedict’s test:

• place 2 cm³ of liquid testing substance in a boiling tube (if not liquid, first crush w/ pestle and mortar and add distilled water, then use filter paper and funnel to create a filtrate)

• add 10 drops of Benedict’s

• place in a boiling water bath for 3-5 mins

• if positive - blue → green/yellow/orange/brick red precipitate (depending on conc of reducing sugar)

how can you test for non reducing sugars?

(altered) Benedict’s test:

• boil in diute HCl (to hydrolyse the non-reducing sugar)

• add sodium hydrogen carbonate (to neutralise solution)

• place 2 cm³ of liquid testing substance in a boiling tube (if not liquid, first crush w/ pestle and mortar and add distilled water, then use filter paper and funnel to create a filtrate)

• add 10 drops of Benedict’s

• place in a boiling water bath for 3-5 mins

• if positive - blue → green/yellow/orange/brick red precipitate (depending on conc of non reducing sugar)

name the reducing sugars:

• (all monosaccharides)

  • glucose

  • galactose

  • fructose

• maltose

• lactose

name a non reducing sugar:

lactose

what is the difference between a reducing and a non reducing sugar?

reducing sugars act as reducing agents in chemical reactions, whereas non reduicng sugars do not

how can you test for starch?

iodine test:

• place 3 cm³ of liquid testing substance in a boiling tube (if not liquid, first crush w/ pestle and mortar and add distilled water, then use filter paper and funnel to create a filtrate)

• add 1 cm³ of iodine solution (containing iodine and potassium iodide)

• if positive - orange → blue black

how can you test for lipids?

emulsion test:

• add ethanol then water and shake

• if lipid present, white emulsion should form

why do we not filter the lipid solution when testing for lipids?

lipids may stick to filter paper

how can you test for proteins?

biuret test:

• place 3 cm³ of liquid testing substance in a boiling tube (if not liquid, first crush w/ pestle and mortar and add distilled water, then use filter paper and funnel to create a filtrate)

• add 3 cm³ of dilute NaOH solution and mix

• add 10 drops of dilute copper (II) sulfate solution and mix

• (this is biuret solution - may be premixed)

• if positive - blue → violet

why would you get a negative result in the biuret test for a solution w/ just amino acids (and not proteins)?

tests for peptide bonds (which would not be present)

what is a calibration curve used for?

to demonstrate the conc of a substance in an unknown sample

creatinine detecting solution reacts w/ creatinine to produce an orange colour - how could you produce a calibration curve for creatinine?

• use distilled water and creatinine solutio to produce a serial dilution

• add creatinine detecting solution to each soltuion

• use a known/specified/constant vol of a soltuion (e.g. diluted creatinine solution)

• record absorbance/transmission of solution(s)using a colourimeter

• plot dilution/conc of creatinine solution against absorbance/transmission

summarise how a colourimeter works

• colourimeter detects how much light is absorbed by solution (how much of the light that is travelling through the solution is being stopped by the solution)

• the more concentrated the solution, the more light it will absorb

• we can use this to determine to conc of a solution

what is a macromolecule?

a molecule built up from much smaller molecules

why are all polymers macromolecules, but not all macromolecules monomers?

• a polymer always consists of many monomers

• whereas a macromolecule is simply a giant molecule which may or may not contain repeating units

what is a monomer? what is a polymer?

• monomer: subunits of life - many can bond together to form a polymer

• polymer: many monomers bonded together

what is a condensation reaction?

• reaction which joins 2 molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

• enzymes are required!

what is a hydrolysis reaction?

• reaction which breaks a chemical bond between two molecules and involves the use of a water molecule (e.g. when breaking polymers into monomers)

• enzymes are required!

what is hydrogen bonding? how are hydrogen bonds formed?

• type of intermolecular attraction (NOT a covalent bond!)

• formed by a H atom covale ntly bonded to a very electronegative atom (such as an N, O or F atom) and another electronegative atom

• this is made possible due to the partial charges of the atoms

• single hydrogen bonds are weak, but many hydrogen bonds are strong

how do we represent partial +ve/-ve charge on an atom?

𝛿+/𝛿-

why is water a dipole?

charge of the water molecule is unevenly distributed

rank the strength of single bonds of hydrogen, covalent and ionic bonds

strongest to weakest: covalent, ionic, hydrogen

what are some examples of monosaccharides?

glucose, galactose, fructose

what is a disaccharide?

two monosaccharides joined together

what are some examples of disaccharides?

• maltose

• lactose

• sucrose

what is a polysaccharide?

• polymers, made up of repeating units of monosaccharides

• joined by glycosidic bonds

• formed by condensation reactions

H bonds between molecules of water

H bonds between molecules of ammonia

α-glucose

β-glucose

condensation reaction to form maltose

hydrolysis of maltose (w/ alpha-glucose)

amylose

amylopectin

glycogen

cellulose

unsaturated triglyceride

polysaturated triglyceride

triglyceride condensation/hydrolysis

unsaturated phospholipid

polysaturated phospholipid

saturated fatty acid

unsaturated fatty acid

phosphate group

glycerol

amino acid (general structure)

amine group

carboxyl group

dipeptide

polypeptide

give the equation for aerobic respiration (not including carrier molecules):

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

give the equation for aerobic respiration (including carrier molecules):

C₆H₁₂O₆ + 6O₂ + 38ADP + 38Pi → 6CO₂ + 6H₂O + 38ATP

what is ATP?

• adenosine triphosphate - energetic molecule w/ a high energy, unstable phosphoanhydride bond in which energy is released through respriation

• energy from condensation reaction between ADP and Pi comes from breaking down glucose in respiration

• phosphoanhydride bond broken through hydrolysis → Pi + ADP

why is ATP a good/bad energetic molecule?

• releases relatively small amount of E

• releases E instantaneously

• phosphorylates other compounds

• can be rapidly resynthesised

• is not lost from/does not leave cells

BUT:

• can’t be stored in last quantities as lowers water potential due to its -ve charges

• this means it will attract water through osmosis, causing cells to lyse

• a cell must have lots of mitochondria to release lots of ATP (as only a small amount can be released each time)

what is phosphorylation?

transferring/attaching Pi to target molecule, activating/energising target molecule and inducing a conformational change

what is dephosphorylation?

removing the Pi from the target molecule, causing the target molecule to become inactive

give some examples where phosphorylation may occur:

• active transport pumps

• sliding proteins in muscle cells (allowing muscles to contract

• cytoskeleton proteins needed to move vesicles in cells

• enzymes (e.g. protein synthesis)

• making compounds more reactive (e.g. glucose is phosphorylated in first stage of respiration to synthesise starch)

the addition of a respiratory inhibitor stops the absorption of amino acids - use the diagram to explain why (3)

• no/less ATP produced → no/less active transport

• Na⁺ not moved out of cell

• no conc grad for Na⁺ to move into cell w/ amino acid

describe how an ATP molecule is formed from its component molecules (4)

what is DNA a polymer of?

nucleotides

what are the main functions of the genetic information in DNA?

• acts as a info carrying molecule of inheritance

• used to make proteins and functional RNAs

what is a nucleotide made up of?

(don’t need to be able to draw!)

• deoxyribose

• phosphate group

• nitrogenous organic base

how do the 3 components of a nucleotide join together?

via condensation reaction

name the 4 nitrogenous organic bases present in DNA:

• adenine

• thymine

• guanine

• cytosine

what do adenine and guanine have in common (in terms of their structure)?

both purines

(this is why adenine only bonds to guanine)

what do cytosine, thymine and uracil have in common (in terms of their structure)?

all pyramidines

how are the strands arranged in a dsDNA?

anti parallel

what is the bond between nucleotides called? how is it formed?

• phosphodiester bond

• condensation reaction

which bonds join DNA strands together? why is this significant?

• H bonds

• strong - lots of H bonds together are strong (although they are individually weak)

state Chargraff’s Rule

complementary base pairing rule - in a sample, amount of adenine = amount of thymine found in a sample and the amount of cytosine is always = to amount of guanine found in a sample

why did many scientists initially doubt that DNA carried genetic code?

its structure was relatively simple

what is RNA?

relatively short polynucleotide chain

what are the components of RNA?

ribose sugar, Pi group and organic nitrogenous base of adenine/uracil/guanine/cytosine

what is the overall function of RNA?

transfers genetic info from DNA to ribosomes

compare the structure of DNA to the structure of RNA:

• DNA has the base thymine, RNA has the base uracil

• DNA has a deoxyribose sugar, DNA has a ribose sugar

• DNA is double stranded, RNA is single stranded

describe the structure of DNA and the structure of a chromosome (6)

• polymer of nucleotides

• nucleotide consists of deoxyribose, phosphate and organic/nitrogenous base

• phosphodiester bonds between nucleotides

• DNA double helix held by H bonds

• complementary base pairing and H bonds between adenine, thymine pairs and cytosine, guamine pairs

• DNA is associated w/ histone proteins

• during mitosis (when visible) - chromosome consists of 2 chromatids joined at a centromere

name the two groups of lipids:

• phospholipids

• triglycerides

what is the main function of phospholipids?

make up cell (plasma) membrane

what is the main function of triglycerides?

act as fats and oils

what are the main features of lipids:

• insoluble in water

• soluble in organic solvents

• contain C, H and O, but proportions are less than in carbs

what are the main roles of lipids?

• energy source

• waterproofing

• insulation

• waxy cuticle

• protecting

how do lipids act as an energy source?

lipids provide more than 2x the energy as the same mass of carbohydrates

how do lipids act as a means of waterproofing?

insoluble in water

how does the lipid waxy cuticle aid a plant/insect?

helps to conserve water

how do lipids act as a means of insulation?

• lipids are slow conductors of heat

• so can help to retain body heat

how do lipids act as protection?

stored around delicate organs (e.g. kidneys)

how are triglycerides formed?

• condensation of one molecule of glycerol and three molecules of fatty acid

• ester bond and molecule of water formed (for every condensation reaction that occurs)

what are esters? why are they significant?

• organic compounds formed by the reaction of an alcohol w/ a carboxylic acid

• all have thefunctional group -COO

• all lipids are esters

what are the two main properties of esters?

• volatile

• distinct fruity smell

what is glycerol?

• an alcohol

• C₃H₈O₃

  

what is a fatty acid?

• all have a carboxyl group (-COOH)

• can vary in length and saturation/double bonds

what is a saturated fatty acid?

• have no double bonds (C-C)

• so no of H bonds on fatty acid tail is maximised/saturated

• higher melting point → solid at room temp

what is an unsaturated fatty acid?

• have no double bonds (C=C)

• so no of H bonds on fatty acid tail is not maximised/saturated

• lower melting point → liquid at room temp

what are the main properties of triglycerides?

• high ratio of C-H to C atoms

• low mass to energy ratio

• large, non polar molecules

why do triglycerides have a high ratio of C-H to C atoms?

• so lots can be stored in a small volume

• reduces mass that needs to be carried as they move

why do triglycerides have a low mass to energy ratio?

excellent store of energy

why are triglycerides large, non polar molecules?

so as not to affect water potential

how are phospholipids formed?

• condensation of one molecule of glycerol, two molecules of fatty acids and one phosphate group

• ester bond and molecule of water formed (for every condensation reaction that occurs)

  

what are the polarities and affiliation to water of the different parts of a phospholipid?

• hydrophilic, partially negative head

• hydrophobic, partially positive tails

what is the general formula of a carbohydrate?

(CH2O)n