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Bio- moleculesGrade 12 Structures and Properties of Water

We are accustomed to good old H2O, but we will now examine water a bit more closely.

Water consists of two hydrogen atoms bonded to an oxygen atom. The bonds are shared electrons between oxygen and hydrogenWater molecules have a bent geometry because of the presence of non bonding electrons pairs.

The non bonding electrons repel the electrons in the bond, giving water bent, instead of linear geometry.

Water molecules are neutral in charge, and are usually unreactive (inert).** Water however has partial charges which give it very useful properties.

Electrons ( negatively charged) are attracted to the oxygen atom, causing a partial negative charge to develop on the oxygen atom

Hydrogen atoms are left with a corresponding partial positive charge

The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. ** Note water is used as a reagent, for photosynthesis, and also in hydrolysis reactions.

This attractive force known as hydrogen bonding is what gives water its cohesive properties.

This has several biological implications such as the fact that water has a high surface tension, because molecules are held so tightly together by hydrogen bonds.

Because of this some animals such as the Jesus lizard , and the Water strider can walk on waterHydrogen Bonding in WaterThe Jesus Lizard- using surface tension

Because of the partial charges , water can become attracted to the walls of narrow vessels and ascend . This is called capillary action

What is happening is that the water molecules are attracted to the straw molecules.

When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw.

Plant roots take up water from the soil via capillary action. Water travels up xylem of plants due to high cohesive nature.

The partial charge that develops across the watermoleculehelps make it an excellentsolvent. Water dissolves many substances by surrounding charged particles and "pulling" them into solution.

For example, common tablesalt, sodium chloride, is an ionic substance that contains alternating sodium and chlorineions.

When table salt is added to water, the partial charges on the water moleculeare attracted to the Na+and Cl-ions, and surround them, hence causing them to dissolve.

Water dissolves many other substrates which are essential to life.Water readily dissolves other substrates and this attribute is used in transport through the body.

Water is a fundamental component of blood plasma, tissue fluid and lymph and are used to dissolve a wide range of substances such as red blood cells that carry oxygen, platelets used for clotting, as well as minerals, which can then be easily transported and made available to the cells.

Metabolic waste products such as ammonia and urea are removed from the body in a water solution. Most digestive juices have salts and enzymes in solution, tears consist largely of water. These are used for cleaning the surface of the eye to avoid infections.

Water is also important at the cellular level, for delivering nutrients and oxygen to cells, in solution, and for removing waste such as CO2 form cellsWater in heat regulation

Water has a high specific heat, which means that it resists temperature changes when it absorbs or releases heat.As a result of hydrogen bonding among water molecules, it takes a relatively large heat loss or gain for each 1 degree C change in temperature.Hydrogen bonds must absorb heat to break, and they release heat when they form.

Water in heat regulationMuch absorbed heat energy is used to disrupt hydrogen bonds before water molecules can move faster (increase temperature).

Water helps to regulate temperature in biological systems by resisting change (i.e. Constant body temperature

Large bodies of water also help regulate environmental temperature.Water in heat regulationWater has a high heat of vaporisation

Large amount of heat needed to break hydrogen bonds in order for individual molecule to escape as gas. When water evaporates it removes a large amount of heat from the surface it leaves.

The principle by which animals and plants are cooled through transpiration and perspiration.

Density and freezing properties of Water

Below 4oC the density of water decreases

This means that ice is less dense than water, and hence will float

This is essential for aquatic life , as when lakes, seas, freeze over, only the surface is frozen, and plant and animal life can still survive at lower depths.

Density and freezing properties of Water

CarbohydratesContain carbon, hydrogen, and oxygenGeneral formula Cx(H2O)y Are all aldehydes or ketones around which their chemistry is based.

Divided into Monosaccharides, disaccharides and polysaccharides

MonosaccharidesSingle sugar units.General formula (CH2O)nClassified according to # of carbon atomsTriose, tetrose, pentose , hexose, heptoseOne C atom has an aldehyde group (aldose) or ketone group (ketoses0 attached. All other C atoms have OH groups attached.

Monosaccharides Aldehydes and ketones reduce blue Cu(II) ions to red Cu(I) ions forming the red precipitate Cu2O- reducing sugar tests.

Cu(II) + e- Cu(I)

Glucose -Structure and Function

Open Chain form

Ring formThe OH group at C 5 attaches to C 1 leading to the closing of the ring.

The process is easily reversed, so glucose exists as a mixture of open chain and ring forms. (inverting sugar)Glucose is a monosaccharide (single sugar)

Glucose is used as a source of energy in cells. The process by which glucose is broken down to yield energy in cells is called glycolysis.

Alpha and beta glucoseThe position of the OH group at C 1 is different.ATPADP

Glucose Structure and FunctionYOU ONLY NEED TO KNOW THAT GLUCOSE IS THE SUBSTRATE FOR GLYCOLYSIS.Glycolisis involves the ring form of glucose.

Under the action of the enzyme hexokinase, the OH group attached to C 6 is phosphorylated by ATP.

Due to the loss of one phosphate group, ATP is reduced to ADP. This is the first step in the glycolsis of glucose.

Glucose-6-phospahte, remains in the cell, and undergoes glycolysis to yield energy, or is converted to glycogen.Sucrose- structure and function

Sucrose, (table sugar) is a disaccharide (double sugar).

It is composed of one molecule of glucose and one molecule of fructose

Water is eliminated in the formation of sucrose from the ring forms of fructose and glucose

Glucose Fructose- H2OSucrose- structure and function

In biological systems, the reverse occurs.

Under the direction of the enzyme sucrase, glucose is hydrolysed to yield glucose and fructose.

The monosaccharides are then metabolised through glycolisis.

Other double sugars include maltose, lactose

Glucose Fructose+ H2OStarch- Structure and function

Starch is a polysaccharide, i.e. its has a large number of monomer units in a chain.

Monomer units e.g. glucose are bonded together at the OH groups, with the elimination of water.

Starch is manufactured by plants to store glucose.

Starch can occur in long continuos chains of 200- 200 000 glucose units

Amylopectin has side chains which make it more complex and insoluble. This type of starch can have over 2 000 000 glucose moleculesamylose (a simple soluble starch)Amylopectin

Starch coils are arranged in precise way, for enzymes to act on them.

Starch can be hydrolysed when necessary, by plants, or animals to glucose, which then undergoes glycolysis to yield energy.

In hydrolysis water is added across glycosidic bonds to regenerate the OH groupsGlycosidic linkage + n H2O

The hydrolysis of glucose is controlled by enzymes in both plants and animals.+GlycogenAnimals can use starch made by plants, but cannot synthesise it themselves.

Instead, excess glucose** is converted to glycogen, for storage in animals. Glycogen is stored largely in muscle and liver cells, and is degraded to glucose when there is a demand.

Glycogen is made by an enzymes glycogen synthase, in conjuction with a protein called glycogenin. The starting material is glucose-6-phpospahte, and glycogen is degraded on demand to this same compound by the enzyme glycogen phosphorylase.

glucose-6-phpospahte

Glycogen.CelluloseWhile starch is a polymer of a-D-glucose, cellulose is constructed by b-D-glucose

CelluloseAmylose starch

-D-Glucose-D-Glucose

Because of the alternating positions of the groups in cellulose, different chains are able to fit closer together.

Allows greater interaction between chains, through hydrogen bonds.

Chains are held in place making cellulose very rigid.

Good for plant cell walls, and overall support of plantsSeparate cellulose chains