Genetics test 3

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Key Definitions

1. DNA: Deoxyribonucleic acid, the molecule that carries the genetic instructions in living organisms.
2. RNA: Ribonucleic acid, involved in protein synthesis and regulation of gene expression.
3. Nucleotides: The basic building blocks of nucleic acids, consisting of a sugar, a phosphate group, and a nitrogenous base.
4. Nucleoside: A compound consisting of a sugar and a nitrogenous base.
5. Purines: Nitrogenous bases with a double-ring structure (adenine and guanine).
6. Pyrimidines: Nitrogenous bases with a single-ring structure (cytosine, thymine, and uracil).
7. Bacteriophages: Viruses that infect bacteria.
8. Chargaff’s rule: The observation that in DNA, the amount of adenine equals thymine, and the amount of guanine equals cytosine.
9. Complementary chain: The matching of base pairs across two strands of DNA or RNA.

Structural Features of DNA

10. Antiparallel: Referring to the orientation of the two DNA strands running in opposite directions.
11. Base stacking: A stabilizing interaction between adjacent base pairs in the DNA double helix.
12. Major and minor groove: The regions of accessibility on the DNA helix where proteins can bind.

DNA Modifications

13. Methylation: The addition of a methyl group to DNA, influencing gene expression.
14. Phosphodiester bond: A covalent bond linking two nucleotides in a DNA or RNA strand.
15. Base pairs: Pairs of nitrogenous bases (A-T and G-C) in a DNA molecule.
16. Chromosomes: Structures made of DNA and proteins that contain genetic information.
17. Genome: The complete set of genetic material in an organism.

Genetic Elements and Regions

18. Transposable element: DNA segments that can change position within the genome.
19. Intergenic region: Non-coding regions between genes.
20. Origin of replication: The site where DNA replication begins.
21. Moderately and highly repetitive sequences: DNA sequences that are repeated many times in the genome.
22. Sequence complexity: A measure of the variety of sequences present in a genome.

DNA Topology and Structure

23. Topoisomerase: An enzyme that alters the supercoiling of DNA.
24. Topoisomers: Variants of DNA that differ in their supercoiling.
25. Microdomain and macrodomain: Structural levels within the DNA organization in cells.
26. Nucleoid: The region in a prokaryotic cell where the DNA is located.
27. Nucleosome: The basic unit of chromatin, consisting of DNA wrapped around histone proteins.

Chromatin Organization and Dynamics

28. Loop domain: A structural arrangement in which a segment of DNA is looped out from the main DNA strand.
29. DNA gyrases: Enzymes that introduce negative supercoils into DNA.
30. Supercoiling: Tightly coiling of DNA due to overwinding or underwinding.
31. Introns: Non-coding regions within a gene that are removed during RNA processing.
32. Exons: Coding regions of a gene that remain in the final mRNA.

Repetitive Sequences and Transposition

33. Direct repeats: Sequences that are repeated in the same orientation.
34. Inverted repeats: Sequences that are repeated in opposite orientations.
35. Autonomous and non-autonomous element: Types of transposable elements where autonomous elements can transpose independently, while non-autonomous require help from other elements.
36. Transposition: The process by which a transposable element moves from one location to another in the genome.
37. Reverse transcriptase: An enzyme that synthesizes DNA from an RNA template.
38. Integrase: An enzyme that integrates viral DNA into the host genome.
39. LINEs (Long Interspersed Nuclear Elements): A type of transposable element that can copy and paste itself into different genome locations.
40. SINEs (Short Interspersed Nuclear Elements): Shorter transposable elements that rely on LINEs for their transposition.
41. Exon shuffling: A process that leads to the rearrangement of exons in different genes.
42. Hybrid dysgenesis: Disturbances in reproductive success due to the presence of transposable elements.
43. LTRs (Long Terminal Repeats): Sequences repeated at both ends of some retrotransposons.
44. Simple and retrotransposons: Types of transposable elements based on their replication mechanisms.
45. Zigzag model: A proposed model for the organization of chromatin.
46. SMC protein: Structural maintenance of chromosome proteins involved in chromatin organization.
47. CCCTC binding: A domain important for chromatin structure and regulation.
48. Condensin I and II: Protein complexes that play roles in chromosome compaction during mitosis.
49. Cohesin: A protein complex that holds sister chromatids together during cell division.
50. Histone: Proteins around which DNA is wrapped to form nucleosomes.
51. Heterochromatin: Highly condensed form of chromatin, generally not active in transcription.
52. Euchromatin: Less condensed form of chromatin, active in transcription.
53. Topologically associating domain: Structural units in the genome that organize chromatin interactions.

Short Answer Responses

1. The medium-sized human chromosome contains 100 million bp. If the DNA of this chromosome was stretched out in a linear manner, it would measure approximately 0.034m, calculated as follows:

• Length = (100 million bp) x (0.34 nm/bp) = 0.034m

1. The AT/GC rule applies only to double-stranded DNA molecules; thus, the relationships of base pairs do not necessitate equivalence in single-stranded forms.