Biological molecules A-level

Electrons unevenly distributed creating positive and negative poles in the molecule

Negative pole of one polar molecule and positive pole of another polar molecule form a weak electrostatic bond.

(CH2O)n (N is any number from 3-7)

Sweet tasting and soluble

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A sugar that can donate electrons to another chemical

An alkaline solution of copper (II) sulfate

-Add 2cm^3 of sample to a test tube as a liquid (or grind it up) -Add an equal amount of benedict's reagent -Heat the water gently for 5 mins -If a reducing sugar present, will change from blue -> red

Differences in color of results can be used to estimate the amount of reducing sugar present in the solution.

glucose + glucose

glucose + fructose

glucose + galactose

glycosidic bond

Breaks the glyosidic bonds to create monosaccharides (hydrolysis)

Benedict's test

When added to reagent doesn't change colour of the reagent when heated.

Hydrolyse it into into monosaccharides

1. equal amount of sample and benedict's reagent into a test tube and filter

2. gently heat the test in a water bath for 5mins ~ if the solution doesn't change colour than no reducing sugars present.

3. equal amount of sample and hydrochloric acid to new test tube and heat for 5mins

4. slowly add sodium hydrogencarbonate solution to neutralise the acid until it's alkaline (use pH paper)

5. repeat steps 1 and 2 and reagent should turn red/brown.

The dilute hydrochloric acid will hydrolyse the disaccharide

Benedict's reagent doesn't work in acidic conditions

makes them insoluble and so are suitable for storage.

structural support in plants

granules

Organic molecules that have the same chemical formulas but different structural formulas

glyosidic bonds formed by condensation reactions

add 2cm^3 of sample into test tube with 2 drops of iodine solution and shake. If colour changes from yellow to blue or black then starch is present

branched or unbranched unbranched is wound into a tight coil which makes it compact. insoluble contains alpha glucose

doesn't effect water potential so water not drawn into cells by osmosis doesn't diffuse out of cells (also caused by it being large)

When hydrolysed forms alpha glucose which is easily transported and readily used in respiration

Has many ends that enzymes can work on simultaneously so glucose monomers can be released quickly.

animal cells

animal and bacteria cells

As small granules mainly in the muscles and liver

because fat is the main storage molecule in animals.

-insoluble ~ doesn't draw water into cells or diffuse out of cells

• compact

• more highly branched than starch so has more space for enzymes so rapidly broken down into glucose molecules for respiration

alpha glucose

beta glucose

straight, parallel unbranched chains hydrogen bond cross-links

between the -OH group of the beta glucose molecules.

microfibrils which then form fibres

-provides rigidity -prevents cell from bursting due to water intake from osmosis

exerts an inward pressure that stops any further influx of water

to provide the maximum surface area for photosynthesis

provides strength

-contain carbon, oxygen and hydrogen -insoluble in water -soluble in organic substances like alcohol and acetone

-phospholipids make membrane flexible and transport lipid soluble substances across the membrane -energy source -waterproofing -insulation -protection

When oxidised lipids provided twice as much energy as carbohydrates due to a higher ratio of H atoms

insoluble in water

good conductors of heat and when stored beneath the body surface, help to retain body heat. Also are electrical insulators in the myelin sheath.

Fat is often stored around delicate organs, such as the kidney

3 fatty acids and glycerol

ester bonds formed by condensation

unsaturated has double carbon bonds

a high ratio of hydrogen-carbon bonds to carbon atoms which contain a lot of energy.

Low mass to energy ratio so a lot of energy can be stored in a small volume.

Makes them insoluble so doesn't effect osmosis or water potential.

Have a high ratio of hydrogen to oxygen atoms so release water when oxidised.

1 of the fatty acids is replaced by a phosphate molecule

phosphate head

-polar (hydrophilic and hydrophobic ends) -form a bilayer which creates a hydrophobic barrier in membrane

glycolipids

1. 2cm^3 of sample to 5cm^3 of ethanol in a dry and grease free tube

2. shake to dissolve lipids

3. Add 5cm^3 of water and shake gently

4. will turn milky-white if a lipid is present

lipid is finely dispersed to form an emulsion. As light passes through the emulsion it is refracted as it passes from oil droplets to water droplets, making it appear cloudy.

replace the sample with water and the solution should stay clear.

Polypeptide

-Central carbon atom -hydrogen -R group -Carboxyl group -amino group

dipeptides

condensation reaction Water comes from OH of carboxyl group and H of amino group

peptide bonds between carbon atom of 1 amino acid and nitrogen atom of another.

Joining of amino acids into a polypeptide

sequence of amino acids in a polypeptide chain determined by DNA

weak hydrogen bonds between H of NH and O of C=O making the protein twist into a 3D shape (alpha helix)

Further folding to create a complex 3D structure. Maintained by various bonds.

Disulfide bridges Hydrogen bonds Ionic bonds

strong and not easily broken

Form between carboxyl and amino groups not involved in forming peptide bonds Weaker than disulfate bridges easily broken by changes in pH

determines the function of the protein and allows them to be distinctive and to be recognized by, and to recognize, other molecules.

Polypeptide chains bonded in various ways with non-protein parts associated with the molecule.

Biuret test

1.Add equal volume of sample and sodium hydroxide to test tube at room temp 2.Add a few drops of very dilute copper (II) sulfate solution and mix gently 3.If solution changes from blue to purple then peptide bonds present and so proteins present.