L1 - nucleotides

• DNA has a double helix structure. A pairs with T. G pairs with C
• DNA stands for deoxyribonucleic acid
• RNA stands for ribonucleic acid
• Both DNA and RNA are polymers that are made up of many repeating units called nucleotides. Each nucleotide is formed from:

  -a pentose sugar (sugar with five carbon atoms)

  -a nitrogen containing organic base

  -a phosphate group
• The components of a DNA nucleotide are:

  -a deoxyribose sugar with hydrogen at the 2’ position

  -a phosphate group

  -one of four nitrogenous bases (adenine A, cytosine C, guanine G, or thymine T)
• Components of an RNA nucleotide are:

  -a ribose sugar with a hydroxyl (OH) group at the 2’ position

  -a phosphate group

  -one of four nitrogenous bases (adenine A, cytosine C, guanine G, uracil U)
• The presence of the 2’ hydroxyl group makes RNA more susceptible to hydrolysis. This is why DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan
• The nitrogenous base molecules that are found in the nucleotides of DNA (A, T, C, G) and RNA (A, U, C, G) occur in two structural forms: purines and pyrimidines
• Purines:

  -adenine and guanine

  -double ring structure

  -can form 2 hydrogen bonds
• Pyramidines:

  -cytosine, thymine and guanine

  -single ring structure

  -can form 3 hydrogen bonds
• Phosphodiester bonds:

  -DNA and RNA are polynucleotides, meaning they are made of nucleotides joined in long chains

  -separate nucleotides are joined via condensation reactions between the phosphate group of one nucleotide and the pentose sugar of the next

  -this condensation reaction forms a phosphodiester bond
• The chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds is known as the sugar-phosphate backbone (of the DNA or RNA molecule)
• DNA structure: the DNA molecule twists into a double helix with the nucleotide pairs on the inside and the sugar-phosphate backbones on the outside
• Phosphodiester bonds:

  -the sugar is the 3’ end and the phosphate is the 5’ end of each nucleotide

  -the phosphate group attached to the 5’ carbon on one nucleotide forms an ester bond with the free hydroxyl on the 3’ carbon of the next nucleotide

  -the sugar phosphate backbone is described as extending, or growing, in the 5’ to 3’ direction when the molecule is synthesised
• The backbones run anti parallel:

  -one strand runs in the 5’ to 3’ direction

  -the other runs in the 3’ to 5’ direction
• Comparing DNA and RNA:

  -both linear polymers consisting of sugars, phosphates and bases, but there are some differences
• Comparing functions:

  -DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism

  -RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories
• Comparing structures:

  -DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, 5 carbon sugar, and nitrogenous base

  -RNA has only one strand and is made of nucleotides also. RNA strands are shorter than DNA
• Comparing locations:

  -DNA is found in the nucleus with a small amount also present in mitochondria

  -RNA forms in the nucleolus and then moves to specialised regions of the cytoplasm depending on the type of RNA formed