Unit 1: Biological Molecules Flashcards
Define a monomer - with examples
Monomers are small, basic molecular units. They can join together to form larger molecules (polymers)
Examples: monosaccharides (glucose, fructose and galactose), amino acids and nucleotides
Define polymers - with examples
Polymers are large, complex molecules composed of long chains of monomers joined together.
Examples: polysaccharides, proteins, DNA/RNA and most carbohydrates.
What happens in a condensation reaction?
A chemical bond forms between 2 molecules and a molecule of water is produced.
What happens in a hydrolysis reaction?
A water molecule is used to break a chemical bod between 2 molecules.
What are the 3 heroes monosaccharides?
- glucose
- fructose
- galactose
All have the molecular formula: C6H12O6
What type of bond is formed when monosaccharides react?
(1,4 or 1,6) glycosidic bond.
2 monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide
What are 3 disaccharides and how are they formed?
- maltose: glucose + glucose
- sucrose: glucose + fructose
- lactose: glucose + galactose
A condensation reaction forms glycosidic bond between two monosaccharides.
All have the molecular formula: C12H22O11
What elements do all carbohydrates contain?
C, H and O
What type of sugar is glucose?
Hexose
What are the two types of glucose?
Alpha and beta
They are isomers (molecules with the same molecular formula as each other, but with the atoms connected in a different way)
What the difference between alpha and beta glucose?
Alpha glucose has H on top and OH at bottom at right group
Beta glucose has OH on top and H at bottom at right group
What’s the test for presence of sugars?
Benedict’s test
Describe the test for presence of reducing sugars
- Reducing sugars include all monosaccharides and some disaccharides (e.g. maltose and lactose).
- Add Benedict’s reagent (blue) to a sample and heat it in a water bath that has been brought to a boil (100 degrees for 5 mins).
- If test is positive it will form a coloured precipitate (solid particles suspended in the solution)
-> colour of precipitate changes from: blue - green - yellow - orange - brick red - The higher the conc of reducing sugar, the further the colour change goes - you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weight the precipitate.
always use an excess of Benedict’s solution - this makes sure that all the sugar reacts
Describe the test for the presence of non-reducing sugars
- If result of reducing sugars is negative, non-reducing sugars could still be present, such as sucrose. To test for them you have to break them down into monosaccharides.
- You do this by getting a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in water bath that’s been brought to a boil (100 degrees for 5 mins). You then neutralise it with sodium hydrogen-carbonate. Then just carry out the Benedict’s test as you would for a reducing sugar.
- If the test is positive it will form a coloured precipitate (as it did for reducing sugars). If test is negative the solution will stay blue, which means it doesn’t contain sugar (either reducing or non-reducing).
Describe the structure and functions of starch
Storage polymer of a-glucose in plant cells
- insoluble = no osmotic effect on cells
- large = doesn’t diffuse out of cells
Made from amylose:
- 1,4 glycosidic bonds
- unbranched chain of a-glucose
- helix (coiled) with intermolecular H-bonds = compact -> good for storage - fit more in smaller space.
Made from amylopectin:
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis into glucose
What’s the test for presence of starch?
The iodine test
Describe the test for the presence of starch
- Add iodine dissolved in potassium iodide solution to the test sample.
- If starch is present, the sample changes colour from browny-orange to a blue-black colour.
- If starch isn’t present the colour remains browny-orange.
Describe the structure and functions of glycogen
Main storage polymer of a-glucose in animal cells (but also found in plant cells)
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis, stored glucose can be released quickly -> important for energy release in animals
- insoluble = no osmotic effect & does’t diffuse out of cells
- compact -> good for storage
Describe the structure and functions of cellulose
Polymer of B-glucose gives rigidity to plant cells walls (prevents bursting under turgor pressure, holds stem up)
- 1,4 glycosidic bonds
- straight-chain, unbranched molecule
- alternate glucose molecules are rotated 180 degrees
- H-bonds crosslinks between parallel strands form microfibrils = high tensile strength (structural support for cells e.g. plant cell walls)
Outline how colorimetric 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 calibrations curve: absorbance or % transmission (y-axis), concentration (x-axis)
- Record abundance or % transmission values of unknown samples. Use calibration curve to read off concentration
What’s the structure of a triglyceride?
One molecule of glycerol with three fatty acids attached to it
Fatty acid molecules have long ‘tails’ made up of hydrocarbons - they’re ‘hydrophobic’ (repel water molecules). They make lipids insoluble in water.
All fatty acids have the same basic structure, but hydrocarbon tail varies (variable ‘R’ group)
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 temp
- found in animal fats
- ‘saturated’ with hydrogen
Unsaturated:
- contain C-C double bonds
- ‘Kinked’ molecules have fewer contact points
- lower melting point = liquid at room temp
- found in plant oils
Relate the structure of triglycerides to their functions
- long hydrocarbon tail contain lots of chemical energy = load of energy is released when they’re broken down.
- high energy: mass ratio = high calorific value from oxidation (energy storage)
- insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing. The triglycerides clump together as insoluble droplets in cells because the fatty acid tails = hydrophobic - they face inwards, shielding themselves from water with there glycerol heads
- 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 phosphate head.
- forms phospholipid bilayer in water = component of membranes
- tails can splay outwards = waterproofing
How does the structure of phospholipids relate to their functions?
- make up the bilayer of cell membranes = which control what enters and leaves a cell
- heads are hydrophilic and tails are hydrophobic = they form a double layer with their heads facing out towards the water on either sides.
- centre of bilayer is hydrophobic = water-soluble substances cant easily pass through - membrane act as a barrier to those substances
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)
Are phospholipids and triglycerides polymers?
No: they aren’t made from small repeating units. They are macromolecules.
What’s the test for the presence of lipids?
The Emulsion test
Describe the test for the presence of lipids
- Shake the test substance with ethanol for about a minute so it dissolves.
- Add an equal volume of water and shake again
- If lipids are present, a milky white emulsion forms
- The more lipid there is, the more noticeable the milky colour will be
