week 2 - DNA, Chromosomes, and Cell Division

Week 2

What are the key components and phases involved in DNA replication?

DNA helicases, single-strand binding proteins, topoisomerase, and the processes of unwinding, complementary strand synthesis, and the overall cell cycle.

What is the significance of DNA replication in cellular function?

Is crucial for maintaining genetic integrity and ensuring that new cells receive identical DNA strands during cell division.

What is the first step of DNA replication?

Unwinding, which involves breaking the hydrogen bonds between the DNA strands.

Which enzymes are involved in the unwinding step of DNA replication?

DNA helicase unwinds the DNA strands, single-strand binding proteins keep the strands separated, and topoisomerase relieves stress on the DNA molecule.

What is a replication fork?

Is a Y-shaped structure at the active region of DNA separation during replication.

What are replication bubbles?

Are structures where replication forks originate, located at DNA sequences called replication origins.

How are daughter strands produced during DNA replication?

By using the separated strands of DNA as templates, following Chargaff's rules of base pairing.

In which direction is the new DNA strand built during replication?

In a 5' to 3' direction.

What is the leading strand in DNA replication?

A single strand from the point of origin toward the opening replication fork.

What is the role of RNA primers in DNA replication?

Are necessary to start the addition of new nucleotides for forming new DNA strands.

Which enzyme synthesizes the RNA primer during DNA replication?

DNA primase

What is the central dogma of life?

The flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation).

What processes are involved in the central dogma of life?

DNA replication, transcription, and translation.

What is the significance of errors and mutations in DNA processes?

Can impact cellular function and genetic stability, potentially leading to diseases such as cancer.

What phase of the cell cycle does DNA replication occur?

S phase of interphase.

What is the role of topoisomerase during DNA replication?

Prevents super-coiling of DNA by relieving stress on the DNA molecule as it separates.

What are single-strand binding proteins?

Proteins attach to separated DNA strands to keep them untwisted and prevent re-annealing.

What is Chargaff's rule?

That in DNA, the amount of adenine equals thymine, and the amount of cytosine equals guanine.

What happens to DNA strands during the unwinding step?

The hydrogen bonds between the DNA strands are broken, allowing the strands to separate.

What is the importance of maintaining genetic integrity during DNA replication?

Ensures that cells function properly and that genetic information is accurately passed on.

How do prokaryotic and eukaryotic cells differ in DNA replication?

Prokaryotic cells typically have a single circular DNA molecule and replicate it from a single origin, while eukaryotic cells have multiple linear chromosomes and multiple origins of replication.

What is the overall goal of DNA replication?

Is to produce two identical copies of DNA for cell division.

What is the structure of DNA strands?

Anti-parallel and highly coiled, with nucleotides bonded from phosphate to sugar between the 3′ and 5′ carbons.

What enzyme facilitates the addition of complementary nucleotides to the 3' end of a newly forming strand of DNA?

DNA polymerase III

What does DNA polymerase III require to add further nucleotides?

The 3'-hydroxyl end of a base-paired strand.

How is the Lagging Strand synthesized during DNA replication?

Discontinuously against the overall direction of replication.

What are Okazaki Fragments?

Short segments on the lagging strand.

What enzyme joins Okazaki fragments together?

Ligase.

What is the process of DNA replication described as?

Semiconservative, resulting in two identical DNA molecules, each with a parent strand and a newly synthesized strand.

What is the first step in protein synthesis?

Transcription.

What is the role of RNA polymerase in transcription?

To link ribonucleotides together in a sequence complementary to the DNA template strand.

What happens to part of the DNA during transcription?

It temporarily unzips and is used as a template to assemble complementary nucleotides into mRNA.

What are promoters in the context of transcription?

Regions on DNA where RNA polymerase must bind to begin transcription.

What is the TATA box?

A specific promoter region on DNA.

What is the purpose of the termination signal in transcription?

To signal the end of transcription.

What is RNA capping?

The addition of Guanosine triphosphate to the 5' end of the RNA shortly after transcription begins.

What is the function of the 5' cap on mRNA?

It serves as a recognition signal for ribosomes to bind to the mRNA.

What is polyadenylation?

The modification of the 3' end of the primary transcript by adding a string of adenine nucleotides.

What is the role of the poly(A) tail in mRNA?

It helps in the transport of mRNA molecules to the cytoplasm and plays a role in mRNA stability.

What are introns?

Non-functional segments of DNA that are snipped out of the chain during mRNA processing.

What are exons?

Segments of DNA that code for proteins and are rejoined after introns are removed.

What is translation in the context of protein synthesis?

The process of decoding mRNA into a polypeptide chain.

How do ribosomes read mRNA during translation?

They read mRNA triplets or codons one at a time to construct proteins.

What is the role of transfer RNA (tRNA)?

It carries amino acids and has an anticodon that is complementary to the mRNA codon.

What happens during the initiation step of translation?

The mRNA start codon AUG attaches to the small ribosomal subunit.

What occurs during the elongation step of translation?

The ribosome catalyzes the formation of peptide bonds as tRNA pairs with each codon.

What is the termination step in translation?

At the stop codon, a release factor binds to the A site, hydrolyzing the polypeptide from tRNA and disassembling the translation complex.

What are the main phases of Interphase in the cell cycle?

Gap 1 (G1), Synthesis (S), and Gap 2 (G2).

What happens during the S phase of Interphase?

DNA synthesis occurs, resulting in chromosomes consisting of two identical sister chromatids.

What occurs during interphase?

The cell prepares to undergo cell division.

What marks the end of interphase?

The completion of Gap 2 (G2).

What happens to chromosomes during prophase?

They begin to coil, become more condensed, and become visible as discrete structures.

What happens to nucleoli during prophase?

Nucleoli are visible early in prophase but disappear as the stage progresses.

What occurs during prometaphase?

The nuclear membrane disappears and spindle fibers begin to appear; chromosomes attach to spindle fibers at their kinetochores.

What characterizes metaphase?

The mitotic spindle is completed, centrioles move to opposite poles, and chromosomes line up on the equatorial plate.

Why are metaphase chromosomes significant?

They are traditionally studied in cytogenetics.

What occurs during anaphase?

Centromeres divide longitudinally, sister chromatids separate, and migrate to opposite poles.

What happens during telophase?

Chromosomes uncoil, nucleoli reform, and the nuclear membrane is reconstructed; usually followed by cytokinesis.

Where does meiosis take place?

Only in the ovaries and testes.

What is the process of meiosis?

It involves one duplication of DNA and two cell divisions, reducing the diploid number (2n = 46) to the haploid number (n = 23).

What is the result of fertilization in terms of chromosome number?

It restores the diploid number in the zygote.

What are the stages of prophase I in meiosis?

Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

What occurs during leptotene?

Chromosomes begin to condense but are not yet visible by light microscopy.

What is synapsis in prophase I?

The pairing of homologous chromosomes locus for locus.

What is the synaptonemal complex?

A tripartite structure necessary for crossing-over during prophase I.

What happens during pachytene?

Synapsis is complete, chromosomes condense further, and crossing over occurs.

What is crossing over?

The exchange of homologous segments of DNA between nonsister chromatids of bivalents.

What are chiasmata?

Points where homologous chromosomes are held together after crossing over.

What occurs during metaphase I?

The nuclear membrane disappears, meiotic spindle forms, and bivalents line up on the equatorial plate.

What happens during anaphase I?

The centromeres of each bivalent separate and migrate to opposite poles.

What is the outcome of telophase I?

Two haploid sets of chromosomes reach opposite poles, and the cytoplasm divides, resulting in two cells with 23 chromosomes each.

What distinguishes meiosis II from mitosis?

Meiosis II proceeds without intervening interphase or prophase and each cell contains only 23 chromosomes.