myasbiology-blog

[myasbiology-blog]

Carbohydrates

They are energy and structural materials made up of Carbon, Hydrogen and Oxygen. There are monosaccharides (e.g. glucose, fructose), disaccharides (e.g. maltose, sucrose) and polysaccharides (e.g. starch, glycogen and starch).

Monosaccharides

(C H2 O)n is their general formula (n is the number of carbon molecules). e.g. pentose sugars where n=5. Other examples are ribose and deoxyribose. 

They are soluble so they can be carried in the blood. They are small so they can move across membranes. More complex carbohydrates are often broken down to monosaccharides for respiration. 

The hexose sugar: glucose (alpha) - energy source

The structure of Beta glucose is similar (difference is the right side has OH on top and H on the bottom). It is a component of cellulose. 

Disaccharides

When two monosaccharides join by a condensation reaction they release a molecule of water and forms a disaccharide. 

Examples include Maltose (a-glucose + a-glucose) and sucrose (a-glucose + fructose). 

Polysaccharides 

This is when there are more than 2 sugars/monosaccharides joined together. They have 2 main functions: storage (starch and glycogen) and structural (cellulose). 

Starch

They are insoluble, compact and stored as granules. It is a polmer made up of approximately 1000 a-glucose units. It's a mixture of 2 polysaccharides: amylose: forms straight chains that are unbranched. It forms a spiral (coiled like a helix). amylopectin: they have many branches providing a greater surface area making it easier to be broken down by enzymes. 

Glycogen

A storage carbohydrate found in animals and fungus. It's a polymer formed of around 2000-6000 a-glucose molecules. It has a large number of branches and is helical. It's found in liver and muscle cells. It has more branched ends than starch allowing for faster hydrolysis when conditions demand.

Cellulose

This is found in cell walls. It's a structural polymer of B-glucose that are used in the formation of cell walls. It forms long, straight chains with no branches. They're cross-linked by hydrogen bonds. This gives it strength as it doesn't have to be broken down for usage. The B-glucose have to alternate due to the different structure (right hand side OH and H). The cellulose chains are group together in microfibrils. Plant cell walls are formed of the cellulose microfibrils arranged into many planes in a lattice structure to further increase its tensile strength.

Hydrolysis: adding water resulting in the breaking down of molecules.

Condensation: combining two simple molecules to form a complex one with the release of water.

[myasbiology-blog]

Water and its Properties

Water is an ion meaning it is hydrated in an aqueous solution. 

Substances that dissolve in water are polar / hydrophilic. 

Substances that don't dissolve in water are non-polar / /hydrophobic.

 Water is a Universal biological solvent.

The properties of water:

solvent properties: they allow the water to act as a transport medium for polar solutes.

Transpiration stream: water can move up the xylem because of the cohesion between the water molecules and the adhesion between the water and the walls of the xylem vessels.

Metabolic functions: used in photosynthesis and hydrolysing macromolecules. It's also the medium for many biochemical reactions to take place. 

Supporting role: the cohesive forces means it is not easily compressed so it is good for support like in the hydro-skeleton of the earthworm. It also provides support in the form of turgor pressure and amniotic fluid.

Lubricant properties: the cohesive and adhesion properties make it viscous making it a good lubricant.

Thermoregulation: it has a high specific heat capacity which makes the bodies made up of around 70-80% water very thermostable making them less prone to heat damage. The high latent heat of vaporisation means the body is cooled with minimal loss of water e.g. sweating.

Transparency: visible light can pass through allowing photosynthesis in shallow aquatic environments.