CARBOHYDRATES

CARBOHYDRATES

CARBOHYDRATES contain 3 elements:

1. Carbon (C)
2. Hydrogen (H)
3. Oxygen (O)

CARBOHYDRATES are found in one of three forms:

1. Monosaccharides
2. Disaccharides (both sugars)
3. Polysaccharides

General formula:.MONOSCHARIDES

(CH2O)n where n is a number between 3 and 9. They are classified according to the number of carbon atoms. The monosaccharides you will have to know fall into these categories:

C = 3 = triose

C = 4 = tetrose

C = 5 = pentose

C = 6 = hexose

Trioses: (e.g. glyceraldehydes), intermediates in respiration and photosynthesis.

Tetroses: rare.

Pentoses: (e.g. ribose, ribulose), used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP.

Hexoses: (e.g. glucose, fructose), used as a source of energy in respiration and as building blocks for larger molecules.

All but one carbon atom have an alcohol (OH) group attached. The remaining carbon atom has an aldehyde or ketone group attached.

Chain form:

Ring form:

Due to the bond angles between the carbon atoms, it is possible for pentoses and hexoses to form stable ring structures. The carbon atoms are numbered 1 to 5 in pentoses and 1 to 6 in hexoses.

Depending on the orientation of the OH group on carbon 1, the monosaccharide can have either α or β configurations.

Disaccharides AND GLYCOSIDIC BOND

These are formed when two monosaccharides are condensed together. One monosaccharide loses an H atom from carbon atom number 1 and the other loses an OH group from carbon 4 to form the bond.

The reaction, which is called a condensation reaction, involves the loss of water (H2O) and the formation of an 1,4-glycosidic bond. Depending on the monosaccharides used, this can be an α-1,4-glycosidic bond or a β-1,4-glycosidic bond.

The reverse of this reaction, the formation of two monosaccharides from one disaccharide, is called a hydrolysis reaction and requires one water molecule to supply the H and OH to the sugars formed.

Examples of Disaccharides

Sucrose: glucose + fructose,

Lactose: glucose + galactose,

Maltose: glucose + glucose.

Maltose: glucose + glucose.

Sucrose is used in many plants for transporting food reserves, often from the leaves to other parts of the plant. Lactose is the sugar found in the milk of mammals and maltose is the first product of starch digestion and is further broken down to glucose before absorption in the human gut.

Biochemical tests

All monosaccharides and some disaccharides including maltose and lactose are reducing sugars. These can be tested for, by adding Benedict's reagent to the sugar and heating in a water bath. If a reducing sugar is present, the solution turns green, then yellow and finally produces a brick red precipitate. Non-reducing sugars can also be tested for using Benedict's reagent but first require addition of an acid and heating to hydrolyse (break apart) the sugar. The acid must then be neutralised using an alkali like sodium hydroxide before carrying out the test as described above.

PolysaccharideS

Polysaccharide:	Function:	Structure:	Relationship of structure to function:
Starch	Main storage polysaccharide in plants.	Made of 2 polymers - amylose and amylopectin. Amylose: a polymer of glucoses joined by α-1,4-glycosidic bonds. Forms a helix with 6 glucose molecules per turn and about 300 per helix. Amylopectin: a polymer of glucoses joined by α-1,4-glycosidic bonds but with branches of α-1,6-glycosidic bonds. This causes the molecule to be branched rather than helical	Insoluble therefore good for storage. Helix is compact. The branches mean that the compound can easily hydrolysed to release the glucose monomers.
Glycogen	Main storage polysaccharide in animals and fungi	Similar to amylopectin but with many more branches which are also shorter.	The number and length of the branches means that it is extremely compact and very fast hydrolysis.
Cellulose	Main structural constituent of plant cell walls	Adjacent chains of long, unbranched polymers of glucose joined by β-1,4-glycosidic bonds hydrogen bond with each other to form microfibrils.	The microfibrils are strong and so are structurally important in plant cell walls.

Functions of carbohydrateS

1. Substrate for respiration (glucose is essential for cardiac tissues).
2. Intermediate in respiration (e.g. glyceraldehydes).
3. Energy stores (e.g. starch, glycogen).
4. Structural (e.g. cellulose, chitin in arthropod exoskeletons and fungal walls).
5. Transport (e.g. sucrose is transported in the phloem of a plant).
6. Recognition of molecules outside a cell (e.g. attached to proteins or lipids on cell surface membrane).

Biochemical tesT

Iodine solution or potassium iodide solution can be used to test for the presence of starch. A positive result changes the solution from an orange-brown to a blue-black colour. - refer to gcse and title biochemical test for carboydrate.

WATER NOTES

water????what is water???? :)

Structure of a water molecule

• A water molecule consist of an oxygen atom and two hydrogen atom
• The two hydrogen atoms are combined with the oxygen atom by sharing of electrons
• The three atoms form a triangle, not a straight line

• The water molecule is electrically neutral but there is a net negative charge on the oxygen atom and a net positive charge on both hydrogen atoms.
• A molecule carrying such an unequal distribution of electrical charge is called a polar molecule.
• The positively charged hydrogen atoms of one water molecule are attracted to the negatively charged oxygen atoms of nearby water molecules by forces called hydrogen bonds.
• Hydrogen bonds largely account for the unique properties of water. weaker than covalent bonds.
• But -> strong enough to hold water molecules together.
• Because of their hydrogen bonds, water molecules are attracted to charged particles or charged surfaces.
  
  
  Properties of water
• polar molecule acts as universal solvent
• Low viscosity of water
• High specific heat capacity
• Latent heat of vaporization of water
• Effect of temperature on water density
• High Surface Tension - adhesive and cohesive forces
  

DNA VS RNA

Comparison chart

DNA versus RNA comparison chart

	DNA	RNA
Stands For	DeoxyriboNucleicAcid.	RiboNucleicAcid.
Definition	A nucleic acid that contains the genetic instructions used in the development and functioning of all modern living organisms. DNA's genes are expressed, or manifested, through the proteins that its nucleotides produce with the help of RNA.	The information found in DNA determines which traits are to be created, activated, or deactivated, while the various forms of RNA do the work.
Function	The blueprint of biological guidelines that a living organism must follow to exist and remain functional. Medium of long-term, stable storage and transmission of genetic information.	Helps carry out DNA's blueprint guidelines. Transfers genetic code needed for the creation of proteins from the nucleus to the ribosome.
Structure	Double-stranded. It has two nucleotide strands which consist of its phosphate group, five-carbon sugar (the stable 2-deoxyribose), and four nitrogen-containing nucleobases: adenine, thymine, cytosine, and guanine.	Single-stranded. Like DNA, RNA is composed of its phosphate group, five-carbon sugar (the less stable ribose), and four nitrogen-containing nucleobases: adenine, uracil (not thymine), guanine, and cytosine.
Base Pairing	Adenine links to thymine (A-T) and cytosine links to guanine (C-G).	Adenine links to uracil (A-U) and cytosine links to guanine (C-G).
Location	DNA is found in the nucleus of a cell and in mitochondria.	Depending on the type of RNA, this molecule is found in a cell's nucleus, its cytoplasm, and its ribosome.
Stability	Deoxyribose sugar in DNA is less reactive because of C-H bonds. Stable in alkaline conditions. DNA has smaller grooves, which makes it harder for enzymes to "attack."	Ribose sugar is more reactive because of C-OH (hydroxyl) bonds. Not stable in alkaline conditions. RNA has larger grooves, which makes it easier to be "attacked" by enzymes.
Propagation	DNA is self-replicating.	RNA is synthesized from DNA when needed.
Unique Features	The helix geometry of DNA is of B-Form. DNA is protected in the nucleus, as it is tightly packed. DNA can be damaged by exposure to ultra-violet rays.	The helix geometry of RNA is of A-Form. RNA strands are continually made, broken down and reused. RNA is more resistant to damage by Ultra-violet rays