2.1.2 AS OCR biology
EVERYTHING IN 2.1.2 BY SPECIFICATION
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- Created by: Maryan
- Created on: 31-03-12 15:22
The structure of DNA
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
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For DNA there are four possible bases: A,T,C,G
- Adenine
- Thymine
- Cytosine
- Guanine
- Adenine+Guanine= Purine
- Thymine+ Cytosine= Pyrimidine (think Top Cat)
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Structure of RNA
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
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Differences between RNA and 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
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Formation of a DNA molecule
- 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
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Formation of a DNA- Pairings of the strands
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
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Anti parallel visual aid
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DNA replication
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
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Genes
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
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Roles of DNA and RNA in living organisms
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
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Outline of protein synthesis
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
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