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Topics 3.3 & 7.1
Nucleic Acids
IB Biology
Where can you find it?
Inside the cell- nucleus, chloroplasts and mitochondria
Chromosomes are made of DNA
Nucleic AcidsPolymers:
DNA (deoxyribonucleic acid) RNA (ribonucleic acid)
Units: nucleotidesNucleotide: sugar + nitrogenous base + phosphate
Parts of a NucleotidePhosphateSugar: Ribose or Deoxyribose (both pentoses)Nitrogenous Bases:
- Purines (double rings): Adenine + Guanine- Pyrimidines (single ring): Cytosine, Thymine, Uracil (RNA only)
Structure of DNA Discovery of Double Helix: 1962 James Watson, Francis Crick and Maurice Wilkins
received a NOBEL PRIZE Watson, Crick and Wilkins used unpublished
data from Rosalind Franklin’s research obtained without her knowledge and used without her consent.- She was misrepresented and unrecognized - She died of cancer in 1958
We know now: DNA is a double helix made of... - 4 nucleotides - A, T, G, C - in 2 polynucleotide strands - strands run antiparallel - [5'-----3'] - held together via weak H-Bonds & complimentary base pairing (A-T and C-G)
DNA is double-stranded, with complementary base pairing
Observe - hydrogen bonds
- complementary base pairing :
A – TC – G
- covalent bonds between 2 nucleotides
(formed through condensation)
Counting Carbons...
Anti-parallel strandsOne side 5’ 3’Other side 3’ 5’
DNA StructureIn eukaryotes it is always associated with proteinsNUCLEOSOMES = DNA wrapped around 8 histones (proteins)Help compact DNA Help control DNA transcription
Single copy x Highly repetitive sequences
Much of DNA in eukaryotes = repetitive base sequences, which are not translated (satellite DNA) = 5-300 bases / repeated as many as 10,000x
5-45% of DNA = function not clear
Single copy/unique genes = actually code for something (small proportion)
DNA’s jobStores informationIt has the code for all 20 amino acidsMutation: changes in the base sequence primary structure of a protein is altered (changing its shape)Can be harmful, neutral or beneficial Important: create variation – basis of natural selection
RNADiscovered after DNASingle strand shorter than DNAContains Uracil instead of ThymineSugar = ribose (DNA contains deoxyribose)DNA: nucleus, mitochondria, chloroplastsRNA: nucleus, cytoplasm, part of ribosomes
Types:RNAm: messenger blueprint for proteinRNAr: ribosomal makes up ribosomesRNAt: transfer delivers the proper amino acid to the ribosome