2.1.2 AS OCR biology

DNA-Deoxyribonucleic acid

• Has two complimentary nucleotides-double stranded
• Nucleotide: made up of a deoxyribose sugar, phosphate group and a nitrogenous base
• Each nucleotide has the same sugar and phosphate group but its the base that varies

For DNA there are four possible bases: A,T,C,G

• Adenine
• Thymine
• Cytosine
• Guanine

• Adenine+Guanine= Purine
  
• Thymine+ Cytosine= Pyrimidine (think Top Cat)

RNA-Ribonucleic acid

Similar structure to DNA:

• Has one polynucleotide- Single stranded
• Has phosphate group, nitrogenous base but a ribose sugar- note that its not deoxyribose sugar
• Makes proteins using the instructions from the DNA

• Sugar in RNA is ribose and not deoxy ribose like DNA

• Has only polynucleotide so its single stranded, whereas DNA has two polynucleotides therefore double stranded

• RNA's pyrimidine consists of Adenine and Uracil
• And its purine Cytosine and Guanine

• DNA nucleotides join together and become polynucleotides
• The nucleotide joins between its own phosphate group and the sugar of another nucleotide
• 2 DNA polynucleotides are joined together by Hydrogen bonding between the bases

To form the double helix:

• Adenine always pairs with Thymine (A-T)
• Cytosine always pairs with Guanine (C-G)
• 2 hydrogen bonds form between A-T
• and 3 hydrogen bonds between C-G
• 2 Antiparallel polynucleotides twist and form a double helix

To form the double helix complimentary pairing happens

A-T 2H bonds

C-G 3H bonds

The two antiparralel polynucleotides twist and form a double helix

The DNA copies itself before cell division

• The hydrogen bonds break between the two strands- The DNA unzips to form two single strands
• Free floating nucleotides join to exposed bases on template strand by complimentary pairing A-T, C-G
• Nucleotides of the new and old strand are joined together by DNA polymerase (an enzyme) this enzyme also checks for any errors.
• The two DNA strands one original and one new are joined by Hydrogen bonding between the bases.

• This process is known as semiconservative replication

Gene: A length of DNA that codes for a polypeptide

• Proteins are made up of amino acids
• Different proteins = different numbers and order of amino acids
• Each amino acid is coded by 3 bases in a gene, so different bases codes for different Amino acids
• Guanine, Thymine, Cytosine (GTC) makes valine
• Thymine, Cytosine, Adenine (TCA) makes serine

DNA- Deoxyribonucleic acid

• Contains the cell's genetic information to grow and develop
• Its long and tightly coiled together and fits into the nucleus
• The molecules paired structure makes it easier for cell replication- this makes it easier for cell division and passing on the genetic information down generations
• DNA can be specific and form specific amino acids needed for a particular protein

All reactions and processes in living organisms need proteins

• DNA carries instructions to make proteins (in the form of genes) and its located in the nucleus

• The DNA undergoes transcription where the instructions to make the protein is now in the form of mRNA
• Once the mRNA leaves the nucleus through the nuclear pores it heads to the ribosome where a 3 step process with tRNA synthesises the protein
• This protein is then packed off to the Golgi apparatus via vesicles, where it is further modified and processes