Genetics and Gene Expression Lecture Notes

Flashcards covering the central dogma, RNA types, gene regulation, chromatin structure, and chromosome ploidy.

Which two cell types in the human body are exceptions to having the exact same DNA as all other cells?

Red blood cells (which lack a nucleus) and gametes (sex cells: sperm and egg).

What are the two primary processes that constitute the central dogma of molecular biology?

Transcription, where DNA is copied into mRNA, and translation, where mRNA is read to assemble amino acids into a protein.

What role does tRNA perform during translation?

tRNA acts as a transfer or "taxicab" RNA that brings specific amino acids to the ribosome by matching its anticodon to the mRNA codon.

What is the function of siRNA (simple interference RNA) in cells?

siRNA binds complementarily to target mRNA to recruit enzymes that degrade the RNA, helping regulate gene expression and break down viral RNA.

How does an enzyme retain a "memory" after breaking down RNA targeted by an siRNA?

The enzyme forms an RNA-protein complex that holds onto a retained piece of RNA to recognize and break down more of that specific mRNA in the future.

How can scientists use siRNAs in knockout experiments?

By introducing siRNA to degrade the mRNA of a specific gene, scientists can stop its expression and observe cellular function without that gene to deduce what it does.

What role does snRNA (small nuclear RNA) play prior to mRNA exiting the nucleus?

snRNA is involved in cleaning up and splicing mRNA, keeping introns inside the nucleus and allowing exons to exit.

How do retroviruses such as HIV serve as an exception to the central dogma?

Retroviruses carry RNA and perform reverse transcription to go backwards from RNA to DNA, integrating that DNA into the host genome.

What is the difference between a genotype and a phenotype?

A genotype is the underlying genetic sequence/makeup in DNA, whereas a phenotype represents the physical characteristics or traits produced by proteins.

How does a single mutation lead to the physical traits of sickle cell anemia?

A single base change in DNA causes a single base change in mRNA, replacing one amino acid in hemoglobin; this alters protein folding, creating a sickle shape instead of a donut shape.

What are the two main regions of a gene and what are their functions?

Structural regions, which code for the functional protein or RNA formed, and regulatory regions, which act like on/off switches or volume knobs to determine when and how much is made.

What is an allele?

An allele is a specific version of a gene that arises from mutations.

Approximately what percentage of its DNA does a typical human cell express?

About $20\%$ to $40\%$, with specialized cells expressing even less.

What structural components make up a single nucleosome?

Eight histone proteins assembled into a spool wrapped with double-stranded DNA.

How does histone acetylation affect chromatin packaging and gene expression?

Acetylation modifies nucleosomes so they push away from each other, opening chromatin into loosely packed euchromatin and making DNA accessible for transcription.

How does methylation affect chromatin and gene expression?

Methylation condenses chromatin tightly into heterochromatin, blocking enzyme access and making transcription and translation difficult or impossible.

What defines homologous chromosomes (homologs)?

Pairs of matching chromosomes that share the same size, shape, and gene locations, though they may carry different alleles.

How many total chromosomes and homologous pairs are found in typical human somatic cells?

Humans have $46$ total chromosomes arranged into $23$ pairs (one set from mom and one set from dad).

What are duplicated chromosomes called while they remain attached at the centromere, and how are they counted?

They are called sister chromatids, and they are counted as one single chromosome as long as they remain hooked together at the centromere.

What is the difference between haploid and diploid ploidy levels in humans?

Haploid cells (gametes: sperm and egg) contain one copy of each chromosome ($23$ total), while diploid cells (somatic body cells) contain two copies of each chromosome ($46$ total).

In a human karyotype, what distinguishes autosomes from sex chromosomes?

Pairs $1$ through $22$ are autosomes that express general traits, while pair $23$ consists of sex chromosomes carrying genes contributing to sex characteristics.