Bio102: Introduction to Cell Biology and Genetics

Cell Cycle and Cell Division

Key Terms:

Interphase / Checkpoints / Spindle / Anaphase / Meiosis
Mitosis / G0 / Centrosome / Telophase / Homologous pair
G1 and G2 / Sister chromatid / Prophase / Cytokinesis / Crossing over
S phase / Centromere / Prometaphase / Metaphase plate
M phase / Telomere / Metaphase

Key Questions:

·  What happens in each of the stages of mitosis?

·  Which cells of the body undergo mitosis? Which undergo meiosis?

·  Why are two divisions needed in meiosis?

·  What key event occurs in prophase of meiosis I that did not occur in mitosis?

·  Why is it more difficult to divide up the genetic material between the daughter cells than to divide up the cytoplasmic enzymes, ribosomes, mitochondria, etc.?

·  Why is it important that the two sister chromatids remain attached after DNA replication is complete? At what point in meiosis is a haploid cell produced?

Lecture Outline:

Mitosis (M phase) is when chromosomes become visible and get separated to the daughter cells

the rest of the time is Interphase (composed of G1, S and G2 phases)

DNA is synthesized in S phase only

during duplication, the chromosome goes from having one chromatid to two chromatids

still just one single chromosome

sister chromatids are connected at the centromere

Nondividing cells are in G0. May enter G1 only if appropriate external signals are provided

Checkpoints in late G1, late G2 and M phases

M phase can be separated to Prophase, Prometaphase, Metaphase, Anaphase, Telophase&Cytokinesis

Prophase: DNA condenses and become visible to the microscope. Spindle forms

Prometaphase: Nuclear membrane breaks down. Centrosomes on chromosomes attach to spindle

Metaphase: chromosomes align in the middle of the cell

Anaphase: sister chromatids separate and begin moving to the poles

Telophase and cytokinesis: more movement of chromatids

nuclear membrane re-forms. chromosomes de-condense

cells splits down the middle (cytokinesis)

result of mitosis is two identical, diploid cells

Meiosis is used to create haploid gametes

replication still happens, followed by two cell divisions (Meiosis I and Meiosis II)

very similar to mitosis, except for the arrangement of the chromosomes in Metaphase I

homologous pairs of chromosomes pair up together

Meiosis I separates homologous pairs. Meiosis II separates sister chromatids