S1) Introduction to DNA Flashcards
What is the role of nucleic acids?
Nucleic acids are required for the storage and expression of genetic information
Identify the two types of nucleic acid
- Deoxyribonucleic acid (DNA)
- Ribonucleic acid (RNA)
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Describe the structure of DNA
- DNA is a polymer of deoxyribonucleoside monophosphates covalently linked by 3’→5’–phosphodiester bonds
- DNA exists as a double-stranded (ds) molecule, forming a double helix
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Describe the bonds formed in the DNA molecule
Phosphodiester bonds join the 3’ end of one nucleotide to the 5’ end of an adjacent nucleotide through a phosphate group
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Describe the polarity of the overall DNA chain
The resulting chain has polarity, with both a 5’-end (free phosphate) and a 3’-end (free hydroxyl) that are not attached to other nucleotides
How are bases in DNA written?
Bases are written in sequence from the 5’-end of the chain to the 3’-end
Compare and contrast the DNA found in eukaryotes with that found in prokaryotes
- Eukaryote: many chromosomes, linear molecule of dsDNA, bound to a complex of proteins to form chromatin
- Prokaryote: single circular and supercoiled chromosome, associated with non-histone proteins that condense the DNA to form a nucleoid
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What are plasmids?
Plasmids are small, circular, extrachromosomal DNA molecules
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What do plasmids do?
- Carry genes that convey antibiotic resistance to the host bacterium
- Facilitate the transfer of genetic information from one bacterium to another
Describe the structure of the double helix in the DNA molecule
- Two chains are coiled around an axis of symmetry in an anti-parallel manner
- The hydrophilic deoxyribose–phosphate backbone is on the outside and the hydrophobic bases are stacked inside
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Describe base pairing in a DNA molecule
Bases of one strand are paired with the bases of the second strand:
- Adenine is always paired with a thymine (two H2 bonds)
- Cytosine is always paired with a guanine (three H2 bonds)
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Explain how the separation of the DNA strands in a double helix might occur
- The two strands separate when hydrogen bonds between the paired bases are disrupted
- Disruption occurs if pH of the DNA solution is altered or if the solution is heated
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What are telomeres?
Telomeres are complexes of noncoding DNA and proteins located at the ends of linear chromosomes
Describe the structure of telomeres
The single-stranded region folds back on itself, forming a loop structure that is stabilized by protein
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What do telomeres do?
- Maintain the structural integrity of the chromosome, preventing attack by nucleases
- Allow repair systems to distinguish a true end from a break in dsDNA
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