Nucleotides and Nucleic Acid Revision Notes

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Nucleotides and Nucleic Acids
Nucleic acids are essential to heredity in living organism. Understanding the structure of
nucleotides and nucleic acids allows an understanding of their roles in the storage of genetic
information and cell metabolism.
Nucleotide Structure
Made from pentose sugar, nitrogenous base and phosphate group. All nucleotides contain the
elements C, H, O, N and P.
Nucleotides are monomers that make up DNA and RNA which are types of nucleic acid. They are in
ALL living cells.
DNA stores genetic info and RNA is used to make proteins from instructions in DNA.
DNA Nucleotides ­
Pentose sugar = deoxyribose.
Each DNA nucleotide has same phosphate group.
Four bases = A ­ Adenine, T ­ Thymine, C ­ Cytosine and G ­ Guanine.
Molecule of DNA contains 2 polynucleotide chains each made up of lots of nucleotides joined
RNA Nucleotides ­
Nucleotides with ribose sugar.
Four bases like DNA but U ­ Uracil replaces T ­ Thymine.
Purines and Pyrimidines ­
2 bases
Each bases present in DNA or RNA are either purines or pyrimidines
A and G are purines.
C, T and U are pyrimidines
Purines contain 2 carbonnitrogen rings joined together whereas pyrimidines only contain one so
pyrimidine base is smaller than purine.
Formation of Polynucleotides ­
Nucleotides joined together.
Join by forming bond between phosphate group of one nucleotide and pentose sugar of another.
This is a phosphodiester bond. Chain of sugars and phosphates is called a sugarphosphate

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They are broken by breaking phosphodiester bonds.
ADP and ATP ­
Phosphorylated nucleotides.
To phosphorylate a nucleotide you add one or more phosphate group to it.
ADP has 3 base A, sugar ribose and 2 phosphate groups.
ATP has base A, sugar ribose and three phosphate groups.
Making and Using ATP ­
In respiration energy from glucose is used to make ATP and then ATP provides energy for chemical
reactions in cell.
ATP synthesised from ADP and inorganic phosphate.…read more

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DNA SemiConservative Replication ­
Copies itself before cell division so each new cell has full amount of DNA. Called SemiConservative
because half of each strand in each new DNA molecule is from original DNA.
1) DNA helicase breaks H bonds between 2 polynucleotide strands. Helix unzips to form 2
single strands.
2) Each original single strand acts as template. Free floating DNA Nucleotides join exposed
bases on templates and match up complimentary.
3) Nucleotides on new strand joined by DNA polymerase which forms sugarphosphate
backbone.…read more

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Genetic code is universal which means same specific base triplets code for same amino acids in all
living things.
Transcription ­
1st stage of protein synthesis. mRNA copy of gene is made in nucleus.
1) RNA polymerase attaches to DNA ­ H bonds break which separate 2 strands and DNA
uncoils. One strand then used as template for mRNA to copy.
2) Complimentary mRNA formed ­ RNA polymerase line up free RNA nucleotides alongside
template strand. Once paired, joined forming mRNA molecule.…read more


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