BI111 Lecture Notes - Lecture 1: Dna Replication, Polynucleotide, Cytosine

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5 Jan 2017
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DNA is encoded in polynucleotide chains
DNA consists of 3 main components
- Bonding occurs between Adenine and Thymine
- Bonding occurs between Cytosine and Guanine
DNA has a semi conservative replication process
- Originating helix: zipped and unzipped by several enzymes
- Another batch of enzymes come in and use the old strand of DNA to construct a new
strand
o This can occur only due to the fact that C&G bond; A&T bond
- DNA replication is accurate because of the specific binding and also because cell is
chalked full of proof readers
o Enzymes that come in and correct mistakes in genetic coding
- Has to be accurate because if it was inaccurate: all the essential information would be
corrupted
o Life wouldn’t be as it was if gene replication was inaccurate
o On the other hand, life wouldn’t be the same if replication was 100% accurate
Mutations are essential for the evolution of life
Some species are more likely to mutate than others
Mutation rates
Mutation rates vary based on the environment one is found in
Higher mutation rates in RNA (single stranded) viruses in comparison to DNA viruses
WHY?
- RNA is single stranded so if you have a mutation there is no template to check against
- DNA has the duplicate template to catch errors easier
Higher in mitochondrial DNA than in genomic DNA
Higher in asexual species than sexual species
Whenever a cell needs to build something; it will unzip a specific region of DNA (gene). The
gene contains the necessary information to build one strand. Once a new RNA strand is made; it
peels of DNA. The RNA can be processed edited to remove unnecessary regions. The end
product is a sequence of bases which is then translated.
The translation phase is the “decoding” phase
- For every conceivable combination of letters (codons); it corresponds to a specific amino
acid
There is a start codon that says where to start making the polypeptide and a stop codon that says
where to stop making the polypeptide
Missense Mutation
- Single change in single letter that might change the amino acid that was initially to be
coded
- Instead of proline; code for cysteine
Nonsense mutation
- Codon appears to be a stop codon
- Premature termination of polpeptide
Silent Mutation
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