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)
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
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
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
What are plasmids?
Plasmids are small, circular, extrachromosomal DNA molecules
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
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)
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
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
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