Molecular Biology Quiz

DNA Structure and Function

• BI elements are scattered throughout human DNA.
• Hoogsteen base pairs are a type of non-standard base pair found in triplex DNA, where a C, A, or U binds sideways to a G and T.
• Ribozymes are part of certain enzymes, such as telomerase, enabling them to recognize specific short DNA sequences.

Genetic Code and Translation

• The genetic code is the set of rules for converting the base sequence in nucleic acids, read in groups of three, into the sequence of an amino acid.
• During termination, no tRNA can bind to a stop codon, so the ribosome disassembles, releasing the polypeptide.

DNA Enzymes and Topology

• DNA gyrase is an enzyme that introduces negative supercoils into DNA, a member of the type II topoisomerase family.
• Supercoiling refers to the higher-level coiling of DNA that is already composed of complementary strands.
• Catenanes are circular molecules of DNA that may become interlocked during transcription or recombination.

Gene Regulation and Expression

• An open reading frame is a sequence of bases in DNA or RNA that can be translated to give a protein.
• Constitutive genes have -10 and -35 region promoter sequences close to consensus, but are repressed under rare conditions.
• Enhancers are regulatory sequences that bind transcription factors, often located far away from the promoter region.
• The 5'-UTR is the region of an mRNA between the 5'-end and the translation start site.
• Primary transcripts are the original RNA molecules obtained by transcription from a DNA template, before any processing or modification.
• Housekeeping genes are genes that are switched on some of the time because they are needed for essential life functions.
• The Pribnow box is a region of bacterial promoters recognized by RNA polymerase, located 10 bases back from the start of transcription.

Cell Cycle Regulation

• There are two models for ordering cell-cycle events: the dependent pathway model, where a central clock triggers successive events, and the independent pathway model, where early events provide the substrate for and trigger later events.
• Kinetochore are disc-shaped structures present on the sides of centromeres.

Embryological Development

• Luteolysis: The regression of the corpus luteum, a temporary endocrine structure that plays a crucial role in the female reproductive cycle.
• Corona radiata: A layer of cells that surrounds the zona pellucida, which is a glycoprotein shell surrounding the oocyte.
• Blastomeres: The resulting cells from the cleavage of a fertilized ovum, which eventually form the blastocyst.
• Blastoderm: A layer of cells that forms from the blastomeres and eventually gives rise to the embryoblast and trophoblast.
• Compaction morula: A stage in embryonic development where the blastomeres compact and adhere to each other, resulting in a more tightly packed cluster of cells.

Embryological Derivatives

Ectoderm Derivatives

• The derivatives of ectoderm include the epidermis, nervous system, sensory organs, and the epithelial lining of the respiratory and gut tracts.

Organogenesis

Formation of the Digestive System

• The digestive system is formed from the endoderm layer, which invaginates to form the archenteron, eventually giving rise to the digestive tract and associated organs.

Embryological Layers

Somatopleure and Splanchnopleure Composition

• Somatopleure is composed of ectoderm and lateral plate mesoderm, while splanchnopleure is composed of endoderm and lateral plate mesoderm.

Twin Development

Identical vs. Non-Identical Twins

• Identical twins form from the same fertilized ovum, which splits to form two separate embryos, while non-identical twins form from two separate ova, each fertilized by a different sperm.

Microbiology

Streptococcal Pathogenicity

• S. pyogenes is a highly pathogenic bacterium that can cause severe invasive infections, whereas S. viridans is a less pathogenic bacterium that typically causes milder infections.

Antimicrobial Testing

Sensitivity, MIC, and MBC Tests

• Sensitivity test: determines whether a microorganism is susceptible to a particular antibiotic.
• MIC (Minimum Inhibitory Concentration) test: determines the minimum concentration of an antibiotic required to inhibit the growth of a microorganism.
• MBC (Minimum Bactericidal Concentration) test: determines the minimum concentration of an antibiotic required to kill a microorganism.