Exam 4 Flashcards
4 events in cell division
- Reproductive signal: initiates cell division, can be intracellular or extracellular
- Replication of DNA
- Segregation: distribution of DNA into each of the two new cells
- Cytokinesis: separation of cellular material into the two new cells
Prokaryotic cell division
Also called binary fission, prokaryotes only have one chromosome, folded and circular.
- ori (origin): where replication starts
- ter (terminus): where replication ends
DNA moves through replication of proteins, in rapidly dividing prokaryotes, DNA replication occupies entire time between cell divisions
Reproductive signals in prokaryotes
External factors (e.g., nutrient concentration and environmental conditions)
Ori regions
When replication is complete, the ori regions move toward opposite ends of the cell, segregating the daughter DNA molecules
Reproductive signals in eukaryotes
related to the needs/function of the entire organism
Sister chromatids
newly replicated chromosomes closely associated with one another
Homologous pairs
two chromosomes that are the same size and shape, and contain the same genes in the same order
Mitosis
process that segregates newly replicated chromosomes into two new nuclei
Somatic cells
any cell in the body of a multicellular organism that is not a reproductive cell
Meiosis
a type of cell division that occurs in sexually reproducing organisms to produce gametes, or sex cells (sperm and eggs)
3 broad stages of cell cycle
interphase, mitosis and cytokinesis, 23
hours in interphase, 1 hour in mitosis/cytokinesis
3 subphases of interphase
G1, S, and G2
G1
Chromosomes are single and associated with proteins
- Duration can be minutes or years
- G0: inactive resting phase, Cells enter if not preparing for cell division, cells must be stimulated by growth factors to divide
S
DNA replicates: sister chromatids remain together
G2
cell prepares for mitosis
Restriction (R) point (aka G1‐to‐S
transition)
commitment to DNA replication and subsequent cell division
Kinase
enzyme that catalyzes transfer of a phosphate group from ATP to a
target protein
Cdks
Cyclin‐dependent kinases, control progress through the cell cycle
Cyclins
allosterically regulates cdks
Phosphorylation
addition of a phosphate group
Cyclin cdks
act as cell cycle checkpoints – they regulate progression, e.g., at checkpoint R, if DNA is damaged, p21 protein is made
* p21 binds to G1 cdks, preventing their activation
* Cell cycle pauses while DNA is repaired
RB
retinoblastoma protein, progress past restriction point depends on this, RB normally inhibits cell cycle, when RB is phosphorylated by cyclin‐cdk, it becomes inactive and no longer blocks cell cycle
Nucleosomes
beadlike units formed by the interaction of the histones and DNA, has 8 histone proteins: 2x H2A, H2B, H3, and H4
Chromatin
DNA molecules bound to proteins
Cohesins
proteins that hold together sister chromatids during G2, except at centromere - DNA sequence that joins sister chromatids together, creating a short arm and a long arm on the chromatids
Apoptosis
Programmed cell death, cells may no longer be needed or are prone to genetic damage that can lead to cancer
What initiates apoptosis
hormones, growth factors, viral infections, toxins, extensive DNA damage
Tumors
large mass of cells
Benign vs. malignant tumor
Benign tumors: grow slowly, resemble the tissue they grow from, are encapsulated and remain localized
Malignant tumors: do not resemble the parent tissue
Oncogene
positive regulators in cancer cells
- Normal regulators mutated to be overactive or present in excess
Tumor suppressor
negative regulators such as RB are
inactive in cancer cells
