General Biology I: DNA, Central Dogma, Mitosis, and Meiosis

Comprehensive practice flashcards covering DNA structure and history, DNA replication models, transcription, translation, mitosis, cell cycle checkpoints, cyclins/Cdks, and meiosis.

What three chemical components make up a nucleotide monomer?

A phosphate group, a pentose sugar, and a nitrogenous base.

How does a phosphodiester bond form during nucleic acid polymer formation?

The phosphate group of one nucleotide binds to the hydroxyl group of the pentose sugar of another nucleotide through a dehydration reaction.

In a DNA strand, what chemical group defines the $3^\prime$ end, and what group defines the $5^\prime$ end?

The $3^\prime$ end terminates with a hydroxyl ($\text{-OH}$) group, and the $5^\prime$ end terminates with a phosphate ($\text{-PO}_4$) group.

What major contribution did Rosalind Franklin make to discovering DNA structure in 1952?

She found the structure of a DNA strand, the double helix, through X-Ray diffraction.

According to Chargaff's rules, what are the base composition equalities and the hydrogen bonding patterns between base pairs in DNA?

$\%\,\text{of } \text{A} = \%\,\text{of } \text{T}$ and $\%\,\text{of } \text{C} = \%\,\text{of } \text{G}$. Adenine forms $2$ hydrogen bonds with thymine, and guanine forms $3$ hydrogen bonds with cytosine.

If a double-stranded DNA molecule contains $30\%$ thymine, what percentage of guanine will it contain?

$20\%$ guanine (since $\text{T} = 30\%$, $\text{A} = 30\%$, totaling $60\%$; the remaining $40\%$ is divided equally between cytosine and guanine).

What are the three proposed models of DNA replication shown from left to right in this diagram?

The conservative model, the semiconservative model, and the dispersive model.

How does the dispersive model describe the composition of newly replicated DNA molecules?

The daughter DNA copies consist of a hybrid mixture containing patches of both parental (old) and newly synthesized DNA.

What is the difference between the DNA template (antisense) strand and the DNA coding (sense) strand during transcription?

The template (antisense) strand is read by RNA polymerase to synthesize complementary mRNA

The coding (sense) strand is not transcribed and matches the mRNA sequence (except DNA has $\text{T}$ instead of $\text{U}$).

Which process of the Central Dogma converts an mRNA nucleotide code into a polypeptide sequence?

Translation.

What constitutes a codon, and how is the reading frame established in mRNA translation?

A codon consists of $3$ RNA nucleotides coding for an amino acid; the reading frame is set by the position of the start codon ($\text{AUG}$).

What is a frameshift mutation, and how does it affect the resulting protein?

An insertion or deletion of a number of nucleotides that is not a multiple of three; it alters the reading frame and changes all amino acids downstream of the mutation.

What RNA secondary structure is shown here, and what is its role in prokaryotic transcription?

A hairpin loop; its formation causes RNA polymerase to pause and release both the DNA and the RNA transcript, terminating transcription.

What does it mean that transcription and translation are coupled in prokaryotes?

Translation begins before transcription has completed; ribosomes load onto the mRNA strand as soon as it emerges from RNA polymerase.

What occurs during eukaryotic transcription initiation as shown in this diagram?

Transcription factors recognize and bind the TATA box of the promoter, recruiting additional factors and RNA polymerase II to form the preinitiation complex.

What two post-transcriptional modifications are added to the ends of eukaryotic precursor mRNA, and what is their primary function?

A $5^\prime$ cap ($7$-methylguanosine) and a $3^\prime$ poly-A tail ($100\text{--}200$ adenines); they stabilize mRNA, protect it from enzymatic degradation, and assist translation initiation.

What occurs during eukaryotic pre-mRNA splicing as illustrated here?

Introns (non-coding sequences) are cut out and removed, while exons (protein-coding sequences) are joined together to form the mature mRNA.

What are the roles of the acceptor stem and the anticodon loop on a transfer RNA (tRNA)?

The acceptor end attaches to a specific amino acid, while the anticodon loop contains a $3$-nucleotide sequence that base-pairs with the complementary mRNA codon.

What are the specific functions of the A, P, and E tRNA binding sites on the large ribosomal subunit?

The A site binds incoming aminoacyl-tRNA carrying the next amino acid; the P site binds tRNA attached to the growing peptide chain; the E site binds and ejects uncharged tRNA.

How is translation terminated at a stop codon in prokaryotes?

A release factor protein enters the A site, recognizes the stop codon, triggers the release of the polypeptide, and dissociates the ribosomal complex.

How does cell division in prokaryotes differ fundamentally from eukaryotic cell division?

Prokaryotes replicate their circular DNA and divide via binary fission by building a septum; eukaryotes replicate linear chromosomes and divide via mitosis and cytokinesis.

What is the chromosomal composition of the human karyotype?

$22$ pairs of autosomal chromosomes and $1$ pair of sex chromosomes ($\text{XX}$ or $\text{XY}$), giving a diploid number ($2n$) of $46$ and a haploid number ($n$) of $23$.

What is the structural difference between homologous chromosomes and sister chromatids?

Homologous chromosomes are pairs consisting of one maternal and one paternal chromosome; sister chromatids are identical replicated copies of a chromosome held together by cohesin proteins.

What are the three stages of Interphase, and what major event characterizes the $S$ phase?

$G_1$ (gap phase 1), $S$ (synthesis phase), and $G_2$ (gap phase 2). In $S$ phase, DNA is replicated to produce two identical sister chromatids.

What mitotic phase is shown in this diagram, and what key event defines it?

Metaphase; all chromosomes align along the equator of the cell (metaphase plate) under tension from opposite spindle poles.

What primary mechanical event triggers the transition into anaphase during mitosis?

Proteins (cohesins) holding sister chromatids together at the centromere are degraded, allowing spindle microtubules to pull separated chromatids to opposite poles.

How does cytokinesis differ between animal cells and plant cells?

Animal cells divide by pinching inward with a cleavage furrow, whereas plant cells construct a cell plate that develops into a dividing cell wall.

How does the binding of a cyclin regulate a Cyclin-Dependent Kinase (Cdk) as shown in this diagram?

Binding of a cyclin converts inactive Cdk into an active Cdk-cyclin complex, which phosphorylates target proteins to advance the cell cycle into the next phase.

What are the three primary cell cycle checkpoints, and at what points do they act?

The $G_1/S$ checkpoint (prior to S Phase), the $G_2/M$ checkpoint (prior to M Phase), and the Spindle checkpoint (Prior to Anaphase).

The Spindle Checkpoint checks to see if every chromatid is attached to the spindle.

What is the function of the p53 tumor suppressor protein when unfixable DNA damage occurs?

It halts the cell cycle at the $G_1/S$ checkpoint for DNA repair, and if the damage cannot be repaired, it initiates apoptosis (programmed cell death).

What are synapsis and crossing over, and when do they take place during meiosis?

They take place during Prophase I; synapsis is the pairing of homologous chromosomes into tetrads via synaptonemal complexes

Crossing over is the exchange of genetic segments between homologs at chiasmata(crossing over point).

How does chromosome segregation during Anaphase I of meiosis differ from segregation during anaphase of mitosis?

In Anaphase I of meiosis, homologous chromosomes are pulled apart while sister chromatids remain attached at the centromere; in mitosis, sister chromatids are pulled apart.

What causes independent assortment of maternal and paternal chromosomes during meiosis?

The random orientation of paired homologous chromosomes along the metaphase plate during Metaphase I, which leads to their random segregation in Anaphase I.