Lecture 6 Cycle 3: Inheritance of Sameness and DNA Synthesis

A collection of vocabulary flashcards covering key concepts related to DNA synthesis, cell cycle, and associated mechanisms.

DNA synthesis

is the biological process of producing two identical replicas of DNA from one original DNA molecule. This fundamental process ensures that genetic information is faithfully passed from a parent cell to its daughter cells during cell division, occurring primarily during the S phase of the cell cycle

Semiconservative replication

is the mechanism by which DNA is replicated. In this method, each new DNA molecule consists of one original (parental) strand and one newly synthesized strand. This ensures that half of the original DNA molecule is 'conserved' in each new double helix, maintaining genetic integrity across generations of cells

Genome copy number

specifies the total number of complete genomes present within a given cell. In diploid organisms, a cell typically has one genome copy before the S phase (when ploidy is 2n2n but genome copy is 1), and after DNA replication in the S phase, it has two genome copies (ploidy remains 2n2n, but the cell is 4C4C chromatid content). This metric is crucial for understanding the cell's genetic content at different stages of the cell cycle

Leading strand

During DNA replication, the leading strand is the DNA template strand that is synthesized continuously in the 5′5′ to 3′3′ direction. It is oriented towards the replication fork, allowing DNA Polymerase to add nucleotides without interruption as the DNA unwinds. This results in a single, long daughter strand

Lagging strand

is the DNA template strand synthesized discontinuously during DNA replication. Because DNA Polymerase can only synthesize in the 5′ to 3′ direction, and the lagging strand template is oriented 3′ to 5′ with respect to the replication fork, synthesis occurs in short segments called Okazaki fragments, moving away from the fork.

Okazaki fragments

are short, newly synthesized DNA fragments that are formed on the lagging strand during DNA replication. These fragments, typically 100-200 nucleotides long in eukaryotes, require their own RNA primer for initiation and are later joined together by DNA ligase to form a continuous DNA strand

DNA polymerase

is an enzyme essential for DNA replication that synthesizes new DNA strands. It adds deoxyribonucleotides one by one to a growing DNA chain, complementary to a template strand, always in the 5′ to 3′

Primase

is a specialized RNA polymerase enzyme that synthesizes a short RNA primer. These RNA primers provide a free 3′ hydroxyl group, which is required by DNA polymerase to begin the synthesis of a new DNA strand, as DNA polymerase cannot initiate DNA synthesis without an existing strand

Telomeres

Repetitive DNA sequences at the ends of eukaryotic chromosomes that protect genes from degradation.

Telomerase

A ribonucleoprotein enzyme that extends the telomeres by adding repeated DNA sequences to ends of chromosomes utilizing RNA template and is active in stem cells and germ cells.

Chemo-therapy

A cancer treatment that targets rapidly dividing cells, often by interfering with DNA synthesis.

Ligase

An enzyme that joins DNA fragments together by forming phosphodiester bonds.

Replication fork

The Y-shaped region where the DNA double helix is unwound and replicated.

Hayflick limit

describes the finite number of times that normal human somatic cells can divide in vitro (in cell culture) before cell division ceases. This biological phenomenon is primarily attributed to telomere shortening with each successive cell division. Once telomeres become critically short, cells enter a state of irreversible growth arrest called senescence or undergo apoptosis (programmed cell death)

Topoisomerase

An enzyme that regulates the overwinding or underwinding of DNA during replication by cutting, twisting, and rejoining DNA strands.

Helicase

An enzyme that unwinds the DNA double helix at the replication fork, separating the two strands to allow for replication.