y5 bio: cluster 5 (cell and nuclear division)

what is the main role of mitosis in eukaryotes?

to produce two genetically identical diploid daughter nuclei for cell proliferation, growth, tissue repair, and asexual reproduction

what occurs during the S-phase of interphase prior to mitosis or meiosis?

DNA replication occurs, producing identical sister chromatids held together at the centromere

what are the four phases of mitosis in sequential order and in which phase of the cell cycle do they occur in?

prophase, metaphase, anaphase, and telophase. all + cytokinesis occur in the M phase of cell cycle

what happens during prophase of mitosis?

1. chromosomes condenses and becomes shorter and fatter

2. centrioles go to different poles of the cell

3. spindle microtubules form mitotic spindle

4. the nuclear membrane breaks down into smaller vesicles

what is the role of microtubules and kinetochores during metaphase?

kinetochores attach chromosomes to spindle microtubules at the centromere, aligning chromosomes along the cell equator in a single file

what occurs during anaphase of mitosis?

spindle microtubules shorten, pulling apart sister chromatids to opposite poles of the cell, led by their centromeres

what occurs during telophase of mitosis?

1. chromosome decondenses to become longer and thinner chromatin

2. spindle microtubules begin to break down

3. nuclear membrane fuses back tgt

how does cytokinesis differ between animal and plant cells?

animal cells divide via an actin ring forming a cleavage furrow, whereas plant cells construct a cell plate formed by fusing Golgi vesicles

what is unequal cytokinesis and where does it occur in human biology?

unequal distribution of cytoplasm resulting in one large cell and smaller polar bodies, occurring during human oogenesis

how do you calculate the mitotic index of a tissue micrograph?

(number of cells in mitosis/total number of cells) x 100

what is the function of cyclins in cell cycle regulation?

cyclins bind to cyclin-dependent kinases (CDKs) to activate them, where CDKs adds phosphate tag to other proteins to drive it to next stage of cell cycle

which phase, CDK and cyclin goes tgt?

G1 phase- CDK4/6, cyclin D AND CDK2, cycline E

[G1/S CHECKPOINT]

S phase - CDK2, cyclin A

G2 phase - CDK1, cyclin A

[G2/S CHECKPOINT, DNA replication done]

M phase - CDK1, cyclin B

[M/G1 CHECKPOINT]

how do proto-oncogenes and tumor suppressor gene mutations lead to cancer development?

mutated proto-oncogenes become overactive oncogenes that continuously drive cell division, while mutated tumor suppressor genes lose their ability to halt the cell cycle or repair DNA. this causes uncontrolled proliferation and cancer development

benign tumors VS malignant tumors

benign is non-cancerous, it does not spread, it grows slowly, and does not metastasise or create secondary tumors. malignant tumors are cancerous, invades nearby tissues and has the potential to spread to form secondary tumors.

what is the difference between a primary tumor, secondary tumor, and metastasis?

a primary tumor forms at the original site, metastasis is the spread of cancer cells through blood/lymph, forming secondary tumors elsewhere

why is meiosis I referred to as a reduction division?

it reduces the chromosome number from diploid (2n) to haploid (n) by separating homologous chromosomes.

what is a bivalent (tetrid) and when does it form?

a pair of homologous chromosomes formed during prophase I of meiosis

what occurs during crossing over in prophase I and what is its consequence?

non-sister chromatids exchange DNA segments at chiasmata, producing recombinant chromatids and increasing genetic variation

how does independent assortment generate genetic diversity in meiosis?

homologous chromosome pairs align randomly at the metaphase plate in metaphase I, creating 2^n possible gamete combinations

what is non-disjunction and what condition can it cause?

the failure of homologous chromosomes or sister chromatids to separate properly during anaphase I or II, causing aneuploidy such as trisomy 18 (Edward’s syndrome) and 21 (Down syndrome)