7.1 DNA Structure Flashcards
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 C1and the phosphate group attached to C5
- Nucleotides are joined by a covalent phosphodiester bonds between the C5phosphate group and the C3hydroxyl 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
2
State the number of hydrogen bonds between G and C
3
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