DNA Replication, Mitosis, & Meiosis

Helicase

Enzyme that opens DNA at the replication fork.

Topoisomerase

prevents DNA double helix ahead of replication fork from getting too tightly wound.

Primase

Enzyme that forms RNA primers, required to initiate DNA synthesis.

DNA Polymerase

Enzyme responsible for adding nucleotides to the 3’ end of the growing DNA strand.

DNA Lipase

seals any gaps that remain after removal of primers in newly synthesized strands.

Mitosis

Form of cell division resulting in 2 daughter cells with identical chromosomes and organelles with the parent cell.

What are the stages of mitosis?

Prophase, prometaphase, metaphase, anaphase, & telophase/cytokinesis

Mitosis: Prophase

Chromosomes condense and become more tightly coiled. Forms 2 sister chromatids bound at the centrosome, mitotic spindle fibers begin to appear and nucleolus disappears.

Mitosis: Prometaphase

Nuclear envelope fragments and microtubules surrounding spindle enter nuclear area and attach to condensed chromosomes, moving them towards the cell’s equator.

Mitosis: Metaphase

Longest mitotic stage: all chromosomes align at metaphase plate (cell’s equator).

Mitosis: Anaphase

Sister chromosomes separate from each other and are pulled towards opposite ends of the cell.

Mitosis: Telophase/Cytokinesis

Nuclear envelopes are formed around each of the newly separated sets of chromosomes. Cytokinesis divides the cytoplasm to produce 2 new cells.

Meiosis

2-stage process of cell division for production of gametes (sperm & eggs). 

What are the 2 stages of meiosis?

Meiosis l & Meiosis ll

Prophase l

Chromosomes condense and pair, becoming closely entwined. Then the chromosomes cross over one another, exchanging genetic information. Requires longest amount of time - 90%

Metaphase l

Pairs of chromosomes align along metaphase plate.

Anaphase l

Chromosomes separate and each move towards opposite pole, with centromere leading the way.

Telophase/Cytokinesis l

Chromosomes arrive at opposite poles, dividing the cell; forms 2 daughter cells

Prophase ll

Chromosomes condense and nuclear envelope breaks down.

Metaphase ll

Chromosomes consisting of non-identical sister chromatids are positioned along metaphase plate.

Anaphase ll

Sister chromatids separate as centromeres separate and move towards opposite ends of the cell.

Telophase/Cytokinesis ll

Nuclei form and cells divide

Result of Mitosis

2 daughter cells with identical DNA

Result of Meiosis

4 daughter cells with unique genetic codes