Nucleic Acids

RNA - Ribonucleic acid 

DNA - Deoxyribonucleic acid 

Nucleotide Structure: 

• a pentose sugar 
• a phosphate group 
• nitrogen containing organic base (adenine, thymine, guanine , cytosine and uracil) 

- Joined as a result of a condensation reaction to form a single nucleotide (mononucleotide) 

- The bond formed between them is phosphodiester bond

RNA - a polymer made up of nucleotide. A single short polynucleotide chain (mRNA tRNA rRNA) bases = adenine uracil guanine and cytosine 

DNA structure: 

• pentose sugar = deoxyribose 
• organic bases = adenine, thymine, guanine and cytosine 
• two DNA strands (made of two nucleotides) is extremely long which are joined by hydrogen bonds (the double helix)

Base pairing: A&T G&C and A&U (only in RNA structure) These are said to be complementary to each other. 

the stability of the DNA  - 

• phosphodiester backbone protects the more chemically reactive organic bases inside the double helix 
• there are three hydrogen bonds between  G - C the higher the proportion the more stable the DNA molecule. 

• Cytokinesis: follows nucler divison and is the process which the whole cell divides 
• Nuclear Division: the process which the nucleus divides - mitosis and meiosis 

Semi- conservative replication:

• DNA helicase casues the two DNA strands to seperate by breaking the hydrogen bonds that hold the complementary bases together. 
• DNA helicase completes the seperation of the strand and free nucleotides bind to their complementary bases. 
• Once the activated nucleotides are bound, they are joined together by DNA polymerase which causes the formation of phosphodiester bonds. The remaining unpaired bases continue to attract their complementary nucleotides. 
• All nucleotides are joined to form a complete polynucleotide chain using DNA polymerase. Two DNA molecules are formed both which have half the original molecule and half the new molecule. 

• it is very stable structure which normally pases from generation to generation without change- only rarely mutates. 
• two seperate strands are joined by hydrogen bonds - this allows them to be seperated during DNA replication. 
• extremely large molecule  - contains large amounts of infomation 
• base pairing leads to DNA being able to replicate and transfer infomation - mRNA

Structure of ATP:

• adenine - nitrogen containing base
• ribose - pentose sugar
• three phosphate groups - chain of three phosphate groups 

How ATP stores energy:

• bonds between phosphate groups are unstable and has low activation energy - these are easily broken 
• ATP + H_²0 = ADP + Pi + E  (Hydrolysis reaction and is catalysed by ATP Catalyse)

Synthesis of ATP:

• the conversion is reversible reaction - energy can be used to add inorganic phosphate to ADP to reform ATP this is catalysed by the enzyme ATP Synthase (this reaction is condensation as water is removed) 

• good energy donor
• instability of phosphate bonds is why it is not a good long term store
• ATP is the immediate energy source of a cell 
• ATP only contains a small supply of energy 
• ATP is rapidly reformed from ADP 

better immediate energy source than glucose: 

• it releases less energy than each glucose molecule - released in easier more management quantities 
• hydrolysis of ATP - ADP is a single reaction and releases immediate energy. (the breakdown of glucose is a long series of reactions and takes longer) 

ATP cannot be stored so it has to be continuously made within the mitochondria of the cells that need it 

Metabolic processes: ATP provides the energy needed to build up macromolecules from their basic units 

Movement: ATP provides energy for muscle contraction which ATP provides the energy for the filaments of muscle fibres to slide past one another and therefore shorten the overall length of a muscle fibre 

Active transport: ATP provides the energy to change of carrier proteins in plasma memebrane 

Secretion: ATP is needed to form lymosomes necessary for the secretion of cell products 

Activation of molecules: the inorganic phosphate released during the hydrolysis of ATP can be used to phosphorolayte other compounds in order to make them more reactive. 

• dipolar molecule:- oxygen has a slight positve charge, hydrogen has a slight negative one (it has both positive and negative poles) 
• the attractive force between the opposite poles is hydrogen bonds
• the bonds are weak but together they form important forces that causes the water molecule to stick together - gives it unusual properties

specific heat capacity of water 

• it takes more energy to heat a given mass of water, that is water has a high specific heat capacity 
• water therefore acts as a buffer against sudden temperature change, making the aquatic environment a stable one. As organisms are mostly water it also buffers them against sudden temperature changes. 

not easily compressed - provides support     transparent - photosynthesis can still occur

latent heat of vapourisation 

• hydrogen bonding between water molecules means that it requires a lot of energy to evapourate 1 gram of water
• evapouration of water is an effective means of cooling because body heat is used to evapourate the water (importance of water)

cohesion and surface tension

• the tendency of molecules to stick together is known as cohesion 
• hydrogen bonding = large cohesive forces which allows it to be pulled up through a tube (eg xylem vessel in plants)
• surface tension = when water molecules meet air they tend to be pulled back into the body of water rather than escaping from it - surface acts like skin and is strong enough to support small organisms. 

• major component of cells , raw material in photosynthesis

metabolism:

-used to break down many complexes molecules by hydrolysis

- water is also used in condensation reactions 

water as a solvent: - rapidly dissolves other substances 

- gases such as carbon dioxide, oxygen can dissolve 

- wastes such as urea and ammonia 

- inorganic ions and enzymes 

• found in the cytoplasm 
• inorganic = does not contain carbon 
• anions = negative charge (cl)
• cations = positive charge (na)

phosphate ions -  structural roles in DNA&RNA and storing energy in ATP

sodium ions - transport of amino acids and glucose across plasma memebranes 

iron ions - haemoglobin for the transport of oxygen in the blood

hydrogen ions - determines and provides the basis for pH