DNA Replication, Sequencing, and Cell Division - Study Notes 9/11/25 genetics

Vocabulary flashcards covering key terms from the lecture on DNA replication, separation of chromosomes, and sequencing technologies.

Replication bubble

The unwound region of DNA that expands as helicase unwinds DNA from the origin, creating two replication forks.

Origin of replication

The specific DNA sequence where replication begins and forks are established.

Replication fork

The Y-shaped junction at which the two parental strands are being unwound and new strands are synthesized.

Leading strand

The DNA strand synthesized continuously in the 5' to 3' direction toward the replication fork.

Lagging strand

The DNA strand synthesized discontinuously in short segments (Okazaki fragments) away from the fork.

5' to 3' synthesis

Direction in which DNA polymerase adds nucleotides; growth occurs from the 5' end toward the 3' end.

Termination

The end of DNA elongation when the template is fully replicated or blocked by termination sequences.

Termination sequence

DNA sequence that blocks polymerase progression, signaling the end of replication.

Prokaryotes vs eukaryotes origins

Prokaryotes typically have a single origin per genome; eukaryotes have multiple origins per chromosome.

Origin licensing

Preparation by specialized proteins in G1 to ensure origins fire once per cell cycle.

DNA polymerase (leading vs lagging)

Enzymes that synthesize DNA; different polymerases act on the leading vs lagging strands and primer removal/replacement is performed.

End replication problem

Issue of replicating the ends of linear chromosomes, leading to shortening without telomere protection.

Telomeres

Repetitive DNA at chromosome ends that protect genes during replication.

Telomerase

Reverse transcriptase that extends telomeres using its own RNA template, active in proliferative cells.

Telomerase RNA template

RNA component of telomerase that serves as the template for adding telomere repeats.

Proliferative cells

Cells with high replication activity (e.g., fetal, germline, bone marrow) where telomerase is often active.

Polymerase chain reaction (PCR)

In vitro method to amplify a specific DNA segment through cycles of denaturation, primer annealing, and extension.

Primer design

Short DNA sequence (about 22 bases) that anchors amplification to a unique genomic location.

Denaturation

Heating step that separates the two DNA strands to serve as templates.

Primer annealing

Temperature-controlled binding of primers to complementary sequences on the templates.

DNA polymerase in PCR

Heat-stable enzyme (e.g., Taq) that extends primers to synthesize new DNA.

PCR cycles

Repeated rounds (roughly 30–35) to exponentially amplify the target DNA.

Gel electrophoresis

Technique that separates DNA fragments by size to analyze PCR products or STRs.

Short tandem repeats (STR) / microsatellites

Very short repeating DNA sequences whose copy number varies among individuals and can identify individuals.

Amplicon size

Length of the PCR product, determined by the number of repeats at the locus.

Sanger sequencing (dideoxy sequencing)

DNA sequencing method using chain-terminating ddNTPs to generate readable fragments.

Dideoxynucleotides (ddNTPs)

Nucleotides lacking a 3'OH that terminate DNA synthesis in Sanger sequencing.

Fluorescent sequencing / automated sequencing

Sanger sequencing with fluorescent labels read by a detector; enables automated base calling.

Reversible terminator sequencing

Sequencing-by-synthesis using reversible terminators to suspend and resume DNA synthesis cycle by cycle.

High-throughput / next-generation sequencing

Parallel sequencing technologies that read many DNA fragments simultaneously to sequence entire genomes.

Sequencing by synthesis on slides

Fragments bound to a slide are extended with labeled nucleotides and imaged to determine incorporated bases.

Locus

A specific position on a chromosome.

Sister chromatids

Two identical copies of a chromosome held together at the centromere after DNA replication.

Mitosis

Cell division phase where sister chromatids are separated into two nuclei and daughter cells.

Cohesin

Protein complex that holds sister chromatids together until anaphase.

Prometaphase

Mitotic stage where spindle fibers attach to chromosomes and promote chromosome movement.

Cytokinesis

Division of the cytoplasm; in animal cells via a contractile ring, in plant cells via a cell plate.

Telophase

Mitotic stage where chromosomes arrive at poles, de-condense, and the nucleus reforms.