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Summary DNA, RNA and Meiosis
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Summaries of DNA and RNA, as well as meiosis. All work covered as specified by the subject assessment guidelines
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Topic 1: DNA, the code of lifeThere are two types of nucleic acid:
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)
We also know that cells replicate by mitosis. During interphase of the cell cycle, the DNA in the
nucleus replicates itself exactly so that each daughter cell that is formed, receives an identical
copy of the DNA.
Unit 1 : Deoxyribonucleic acid
Location of DNA in the cell ---> found in form of chromosomes in the nucleus of eukaryotic cells.
Chromosomes carry the hereditary information in the form of genes. The tangle of
chromosomes is known as the chromatin network.
DNA is also found inside the mitochondria and chloroplasts of eukaryotic cells. DNA found
inside outside the nucleus is known as extracellular DNA.
Chromosome: a threadlike molecule of DNA made up of many genes
Gene: a specific part of a strand of DNA that codes for a particular characteristic, for
example eye color.
The structure of DNA
• Carbon
• Hydrogen
• Oxygen
• Nitrogen
• Phosphorous
,DNA is a double stranded polynucleotide. A polynucleotide chain is a very long molecule made
up of string of repeating units called nucleotides.
Each DNA nucleotide consists of three parts:
1. A deoxyribose sugar molecule
2. A phosphate group
3. A nitrogen containing base
The phosphate group is joined to the deoxyribose sugar that is joined to the base. The bonds
create a L-shaped nucleotide.
There are four possible bases that can form part of a nucleotide:
• Adenine (A) --> PURINE BASE
• Thymine (T) --> PYRIMADINE BASE
• Guanine (G) --> PURINE BASE
• Cytosine (C) --> PYRIMADINE BASE
Purines are larger molecules because they consist of a double ring.
Nucleotides join to form a polynucleotide chain when the deoxyribose sugar of one nucleotide
joins to the phosphate group of the next nucleotide. This forms the sugar-phosphate backbone
of the polynucleotide chain.
Each DNA molecule consists of two polynucleotide chains (parallel) that lie with bases on each
strand or chain facing each other. Hydrogen bonds hold these two chains to form a ladder like
structure.
, • Adenine joins to thymine by two hydrogen bonds
• Cytosine joins to guanine by three hydrogen bonds
These bases are said to be complimentary bases. This means that only two complimentary
bases can join to form a complete ‘rung.’
DNA molecule is twisted to form a 3D shape --> DOUBLE HELIX. There are 10 base pairs for
every complete twist of the helix.
Complementary bases: nucleotide bases that are able to be joined by hydrogen bonds and
therefore hold the double stranded nucleic acid together.
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