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Transcript of Biological Molecules
Biochemical Test for molecules
The simplest carbohydrate - monosaccharide.
Solid = Fat
Liquid = Oil
Unevenly shared electrons because oxygen pulls the shared electrons towards itself - slightly negative. Hydrogen gets the shared electrons pulled away from itself - slightly positive.
This results in a polar molecule.
water - liquid and ice
At lower temperatures more hydrogen bonds form but they don't break as easily. As water becomes a solid the hydrogen bonds hold the structure in a semi-crystalline form.
Liquid - molecules form hydrogen bonds with each other which are continuously making and breaking as they move around. This makes it difficult for a molecule of water to escape to become a gas.
Hydrogen bonds restrict movement of water molecules. Large amounts of energy is needed to increase temperature of water, this means that the temperature of large bodies can remain fairly stable.
Density and freezing
Ice - less dense than water. As water decreases temperature, density increases until 4°C then density decreases. Ice float on water and insulates water below.
Cohesion and surface tension
This results in surface tension.
Hydrogen bonds pull water molecules in at the surface - cohesion.
Any molecule that is polar can dissolve in water.
Once in solution, molecules can move around and react with other molecules.
Water molecule will cluster around slightly charged parts of the solute and separates the molecules (dissolves).
Movement of materials around organisms both in cells and on a large scale in multicellular organisms requires a liquid transport medium
Blood in animals and the vascular tissues in plants use water as a liquid transport medium
Large bodies have fairly constant temperatures.
Evaporation of water can cool surfaces by removing heat
Oceans provide relatively stable environments in terms of temperatures.
Many land-based organisms use evaporation as a cooling mechanism, for example in panting or sweating.
Water freezes forming ice on the surface. Water beneath the surface becomes insulated and less likely to freeze.
Organisms such as polar bears live in an environment of floating ice packs.
Lakes tend not to freeze completely so aquatic organisms are not killed as temperature fall.
Water molecules stick to each other creating surface tension on the water surface.
Cohesion also makes long, thin water columns very strong and difficult to break.
Transport of water in the xylem relies on water molecules sticking to each other as they are pulled up the xylem in the transpiration stream.
Some small organisms make use of the surface tension to walk on water.
Metabolic processes in all organisms rely on chemicals being able to react together in solution.
Dissolved chemicals take part in processes such as respiration and photosynthesis in living organisms.
Monosaccharides have similar properties such as:
-Soluble in water
3-carbon monosaccharides - triose sugars
5-carbon monosaccharides - pentose sugars
6-carbon monosaccharides - hexose sugars
Hexoses - most common (incl. glucose and fructose)
a-glucose ----- OH at C1 is below the plane of the ring
B-glucose ---- OH at C1 is above the plane of the ring
Condesation - forms disaccharide molecule & glycosidic bond forms between them - water given off.
Hydrolysis reaction - molecule of water is used to give glycosidic bond.
Glucose has a large number of bonds that can be broken down, it's used to make ATP.
The breaking down of glucose is driven by specific enzymes
a-glucose can be broken down, B-glucose cannot
(By plants an animals with enzymes)
Stores of potential energy
two a-glucose -- maltose
A repeating condensation reaction created amylose. The glycosidic bond between C1 of the first molecule and C4 of the next - 1,4 glycosidic bond
Coils into compact springs because of the shape of the glucose molecules.
Iodine becomes trapped in the coils of the spring. Brown to black in starch test.
Energy-storage polysaccharide in plants.
Consists of straight chain amylose and branched amylopectin.
It's stored in chloroplasts and in membrane bound starch grains.
Energy-storage polysaccharide in animals.
Made with a-glucose -- branched.
Glycogen differs to amylopectin, the 1,4 bonds are shorter and have more branching.
Glycogen is more compact than starch -- forms glycogen granules in animal cells
Features of starch and glycogen
Both starch & glycogen made from a-glucose
They don't dissolve. So storage does not affect W.P this feature is vital in both plant and animals as glucose stored in a cell as free molecules would dissolve and dramatically reduce the water potential.
Glucose molecules can be broken off the chain for respiration when required
B-glucose - when condensed, long straight chains are formed because of the way they're shaped.
B-glucose polymer chain
Fibres are arranged in a specific way to form plant cell walls. Hydrogen bonds form between them (cross linking) which forms bundles called micro fibrils.
When hydrogen bonds form between micro fibrils, this forms large bundles called macro fibrils.
These have great mechanical strength which is embedded in a polysaccharides glue of substances called pectins to form cell walls.
Structure and function of a plant cell wall
Arrangement of micro fibrils allow water to move through and along cell walls and in and out of cells easily.
Water moving in doesn't cause cells to burst. Wall prevents bursting and in turgid cells it helps to support the whole plant
Arrangement of macro fibrils determines how cells can grow or change shape.
Cell walls can be reinforced with other substances to provide extra support or to make the walls waterproof.
Small, soluble sweet and crystalline
Provides energy via respiration
Small, soluble, sweet and crystalline
A sugar obtained when starch is broken down in hydrolysis reactions. It can be split further to glucose for respiration
Starch and glycogen
Large molecules of many a-glucose joined by condensation reactions.
Insoluble in water.
Energy-storage carbohydrates - starch in plants; glycogen in animals and fungi.
Large molecules of many B-glucose molecules joined by condensation reactions.
Insoluble in water.
Structural carbohydrate. Found in plants where it forms cell walls
Add a few drops of iodine solution
Brown to blue/black
Add Benedict's solution and heat to 80°C in a water bath.
Blue to orange - red
If a reducing sugar is negative, boil with hydrochloric acid, cool and neutralise with sodium hydrogencarbonate solution or sodium carbonate solution; repeat Benedict's test.
Blue to orange-red
(on second test)
Add biuret reagent
Blue to lilac
Add ethanol to extract lipid and pour alcohol into water in another test tube
White emulsion forms near the top of the water
Source of energy, can be respired to release energy to generate ATP
Biological membranes are made from lipids
Insulation - heat & electrical
Protection - i.e. cuticle oil
Hormones - i.e. steroids
Composition: carbon, hydrogen and oxygen (much less than that found in carbohydrates)
Glycerol & Fatty acids
Glycerol molecule is always the same - fatty acids differ.
Fatty acids - acid group at one end. The rest of the molecule consists of a hydrocarbon chain.
Unsaturated changes shape of the chain, molecules in a lipid push apart - makes them more fluid.
Lipids containing many unsaturated fats are mostly oils. Saturated fatty acids are often fats.
A condensation reaction between the acid group of a fatty acid molecule and one of the OH groups of the glycerol molecules forms a covalent bond (ester bond). Water is given off - this reaction forms a monoglyceride, this happens two more times to form a triglyceride molecule.
They're insoluble in water - hydrophobic - charges on molecules are disturbed evenly around the molecule - non polar.
Heads - hydrophilic :. soluble (ability to form membranes)
Tails - hydrophobic - insoluble
Fluidity of the phospholipid is determined by saturated or unsaturated fatty acids. Organisms can control fluidity using this feature.
Cholesterol - lipid - small molecule made from four carbon - based rings
Hydrophobic and so it can sit between phospholipid hydrocarbon tails. Regulates fluidity and strength of the membrane.
Cells make cholesterol because it's vital. When in excess (in bile) cholesterol can stick together to form lumps- gallstones. In blood, cholesterol can be deposited in inner linings of blood vessels - athersclerosis.
Steroids such as Oestrogen, testosterone are made from cholesterol
The lipid nature of the hormones means they can pass directly through phospholipid bilayer in order to reach target receptor. They can pass through the nuclear envelope.
Respiration of lipids requires hydrolysis of ester bonds. The breaking down of glycerol and fatty acids forms carbon dioxide and water which releases energy used to generate ATP.
Respiration of 1g of lipid gives twice the amount of energy than 1g of carbohydrate. It also produces more metabolic water than carbohydrates
Lipids are insoluble, they can be stored in a compact way. They don't affect W.P so they're an excellent energy storage molecule.
Glycerol + 3 Fatty acids
Compact energy store, insoluble in water so doesn't affect water potential
Stored as a fat - thermal and electrical insulation and protective properties
Glycerol + 2 fatty acids + Phosphate group
Forms a molecule that is part hydrophilic and part hydrophobic, ideal basis for cell membranes.
Phosphate group may have carbohydrate parts attached - these glycolipids are involved in cell signaling
Four carbon-based ring structures joined together
Forms a small, thin molecule that fits into the lipid bilayer giving strength and stability
Used to form the steroid hormones
Large molecules made up of carbon, hydrogen, oxygen and nitrogen.
Structural components, membrane carriers and pores, enzymes, hormones, antibodies...
Provide building materials important for the growth and repair.
Necessary for most metabolic activity
Proteins are made up from polymers consisting of a chain of amino acid monomers.
There are 20 types of naturally occurring AA
Some R-groups are +vely charged, some are -vely charged. Some hydrophobic/phillic.
Plants make amino acids with nitrates from soil, they're converted into amino acids and bonded with organic groups made from products from photosynthesis.
Proteins from diet are digested into amino acids. Some essential amino acids found in meat, less found in plants.
When amino acids are surplus they're too toxic if present - deamination - converted to urea
Joined by condensation reaction between acid of one AA and amino of another. Forms covalent bond (peptide bond) water is given off.
Two amino acids = dipeptide. Which can be broken by hydrolysis.
Uses of molecule of water to break the bond.
The making and breaking of peptide bonds is required in making and rebuilding pro