biological molecules Flashcards
Define monomer. Give some examples.
smaller units that join together to form larger molecules
● monosaccharides (glucose, fructose, galactose)
● amino acids
● nucleotides
Define polymer. Give some examples.
molecules formed when many monomers join together
● polysaccharides
● proteins
● DNA / RNA
What happens in a condensation reaction?
A chemical bond forms between 2 molecules & a molecule of water is produced.
What happens in a hydrolysis reaction?
A water molecule is used to break a chemical bond between 2 molecules.
Name the 3 hexose monosaccharides.
● glucose
● fructose
● galactose
all have the molecular formula C6H12O6
Name the type of bond formed when monosaccharides react.
glycosidic bond
2 monomers = 1 chemical bond = disaccharide
multiple monomers = many chemical bonds = polysaccharide
Name 3 disaccharides. Describe how they form.
condensation reaction forms glycosidic bond between 2 monosaccharides
● maltose: glucose + glucose
● sucrose: glucose + fructose
● lactose: glucose + galactose
all have molecular formula C12H22O11
Draw the structure of ⍺-glucose.
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Draw the structure of 𝛽-glucose.
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Describe the structure and functions of starch.
storage polymer of 𝛼-glucose in plant cells
● insoluble = no osmotic effect on cells
● large = does not diffuse out of cells
made from amylose:
● 1,4 glycosidic bonds
● helix with intermolecular H-bonds = compact
and amylopectin:
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal ends for hydrolysis into glucose
Describe the structure and functions of glycogen.
main storage polymer of 𝛼-glucose in animal cells ( but also found in plant cells)
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal ends for hydrolysis
● insoluble = no osmotic effect & does not diffuse out of cells
● compact
Describe the structure and functions of cellulose.
polymer of 𝛽-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)
● 1,4 glycosidic bonds
● straight-chain, unbranched molecule
● alternate glucose molecules are rotated 180°
● H-bond crosslinks between parallel strands form microfibrils = high tensile strength
Describe the Benedict’s test for reducing sugars.
- Add an equal volume of Benedict’s reagent to a sample.
- Heat the mixture in an electric water bath at 100°C for 5 mins.
- Positive result: colour change from blue to orange & brick-red precipitate forms.
Describe the Benedict’s test for non-reducing sugars.
- Negative result: Benedict’s reagent remains blue
- Hydrolyse non-reducing sugars e.g. sucrose into their
monomers by adding 1cm3 of HCl. Heat in a boiling water bath for 5 mins. - Neutralise the mixture using sodium carbonate solution.
- Proceed with the Benedict’s test as usual.
Describe the test for starch.
- Add iodine solution.
- Positive result: colour change from
orange to blue-black.
Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch.
- Make standard solutions with known concentrations. Record absorbance or % transmission values.
- Plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis).
- Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration.
Describe how to test for lipids in a sample.
- Dissolve solid samples in ethanol.
- Add an equal volume of water and
shake. - Positive result: milky white emulsion
forms
How do triglycerides form?
condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds
Contrast saturated and unsaturated fatty acids.
Saturated:
● Contain only single bonds
● Straight-chain molecules have many contact points
● Higher melting point = solid at room temperature
● Found in animal fats
Unsaturated:
● Contain C=C double bonds
● ‘Kinked’ molecules have fewer contact points
● Lower melting point = liquid at room temperature
● Found in plant oils
Relate the structure of triglycerides to their functions.
● High energy:mass ratio = high calorific value from oxidation (energy storage).
● Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.
● Slow conductor of heat = thermal insulation e.g. adipose tissue.
● Less dense than water = buoyancy of aquatic animals.
Describe the structure and function of phospholipids.
Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head.
● Forms phospholipid bilayer in water = component of membranes.
● Tails can splay outwards = waterproofing
Compare phospholipids and triglycerides.
● Both have glycerol backbone.
● Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids.
● Both contain the elements C, H, O.
● Both formed by condensation reactions.
Contrast phospholipids and triglycerides.
phospholipids:
● 2 fatty acids & 1 phosphate group attached
● Hydrophilic head & hydrophobic tail
● Used primarily in membrane formation
triglycerides:
● 3 fatty acids attached
● Entire molecule is hydrophobic
● Used primarily as a storage molecule (oxidation releases energy)
