Chapter 8 - Nucleic Acids

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Our DNA carries the genetic code - a set of instructions telling the cell the sequence in which to link amino acids when proteins are being synthesised.

DNA is made up of a double helix.

DNA molecule is made up of two long chains of nucleotides molecules. Each chain is called a polynucleotide.

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Structure of DNA

DNA stands for Deoxyribonucleic Acid.

Each DNA molecule contains:

- Phosphate 
- Deoxyribose - 5 carbon
- Nitrogenous Base - Adenine, Guanine, Thymine, Cytosine

Adenine & Guanine - contain 2 rings = Purine Bases

Thynine and Cytosine - contain 1 ring = Pyrimidine Bases 


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Structure of DNA

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Structure of DNA

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Nucleotides to Polynucleotides


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Nucleotides to Polynucleotides

Nucleotides can form together to create long chains of polynucleotides.

2 chains of polynucleotides lie side by side. Going in different directions, leading strand goes from 5 prime to 3 prime, laging strand goes 3 prime to 5 prime.

2 chains of polynucleotides goes oppoiste ways and are described as anti-parrallel.

Bases join together by hydrogen bonding.

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Direction of a Polynucleotide

5 - carbon sugar - each carbon has a number.

Top phosphate is connected to carbon 5. So at the 5' end.

Bottom phosphate is connected to carbon 3. So at the 3' end.

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Code Making

Ability of DNA to hold and pass on coding to make proteins, is the pattern of the bases.

Adenine only links to Thymine

Cytosine only links to Guanine

The base pairings are called complementary base pairing.

Complementay base pairings allow the code can be copied perfect again and again. It is also the code for creating different amino acids.

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Hydrogen Bondings

A-T = 2 hydogen bonds

C-G = 3 hydrogen bonds

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DNA Replication

DNA gets replicated during interphase of cell cycle.

One copy is passed onto to each daughter cell.

Method of DNA is called semi-conservative replication - Each of the new DNA molecules is made up of one old strand and one new strand.

1. DNA helicase starts to unzip the double helix breaking the hydrogen bonds.
2. Leading strand is synthesised by the polymerase matching the bases.
3. It is easy and is continuous as the DNA goes from 5' to 3'
4. On the lagging strand, small okazaki fragments are made as the opposite DNA chain runs from 3' to 5'
5. Ligase is added to join up the okazaki fragments
6. Hydrogen bonds form again 

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Role of DNA

DNA carries a code that is used by the cel when making proteins.

Sequence of bases determine the sequence of amino acids.

Length of DNA that codes a polypeptide is a Gene. 30,000 genes in our cells

Bases are read every 3

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Structure of RNA

Some nucleotides contain ribose rather than deoxyribose.

They therefore are called ribosenucleic acid.

RNA is single stranded, DNA = Double strands

RNA contains Uracil instead of thymine

RNA involved in making proteins, DNA stores genetic information

Sequence of bases on part of a DNA molecule - a gene - is used to build a RNA with the complementary base sequence.

RNA then travels out in the cytoplasm and attatches to ribosome. Working with other RNA molecules with the complementary base pairings is used to determine the sequence of amino acids.

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DNA is transcripted in the Nucleus and forms RNA.

RNA is transcripted in the cytoplasm and forms proteins.

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