7.1 DNA Structure Flashcards Preview

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Flashcards in 7.1 DNA Structure Deck (10):

Describe the structure of DNA including the antiparallel strands, 3' - 5' linkages and hydrogen bonding between purines and pyrimidines

• The carbon atoms in deoxyribose are numbered, with the nitrogenous bases attached to C1 and the phosphate group attached to C5
• Nucleotides are joined by a covalent phosphodiester bonds between the C5 phosphate group and the C3 hydroxyl group
• The chain is constructed 5' - 3', as new nucleotides bond to the exposed C3 hydroxyl group
• The nitrogenous bases interact via hydrogen bonding (complementary base pairing)
• In order for the bases to associate one strand must run antiparallel to the other (3' - 5')


State the number of hydrogen bonds between A and T



State the number of hydrogen bonds between G and C



Outline the structure of nucleosomes

• The DNA of eukaryotes associates with proteins called histones
• DNA is wound around an octamer of histones (8 histones)
• The octamer and DNA combination is secured to a H1 histone, forming a nucleosome


Outline the function of nucleosomes

Nucleosomes serve two main functions
• They protect DNA from damage
• They allow long lengths of DNA to be packaged (supercoiled) for mobility during mitosis/meiosis
• When supercoiled, DNA is not accessible for transcription


Define exon

The part of the gene which codes for a protein (expressed sequence)


Define intron

A non coding sequence of DNA within a gene which is cut out by enzymes when RNA is made into mature mRNA (interrupting sequence)


Outline the features of exons (unique or single copy genes)

• Smaller proportion of genome
• Occur once in the genome
• Long base sequences
• Usually genes
• May be translated
• Low rate of mutation
• Very similar between individuals
• Not used for DNA profiling


Outline the features of introns (repetitive sequences)

• Larger proportion of genome
• Occur many times in the genome
• Short base sequences
• Not genes
• Never translated
• Higher rate of mutation
• Varies greatly between individuals
• Used for DNA profiling


Distinguish between eukaryotic and prokaryotic DNA with regards to introns

Eukaryotic DNA contains introns but prokaryotic DNA does not