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What is the cell cycle?
The life of a cell from its formation until its own division into two cells.
What are the main functions of mitosis?
Growth, tissue repair, and asexual reproduction.
What is a genome?
A cell’s endowment of DNA (genetic information).
What must happen before a cell divides?
The genome must be copied.
What is the chromosome number in human somatic cells?
46 chromosomes (diploid number).
What is the chromosome number in human gametes?
23 chromosomes (haploid number).
What type of cell division produces gametes?
Meiosis.
What is a duplicated chromosome composed of?
Two sister chromatids attached by a centromere.
Are sister chromatids identical?
Yes, they have identical DNA sequences.
What happens to sister chromatids during mitosis?
They separate and become individual chromosomes in two new cells.
What is mitosis?
The division of a cell’s nucleus.
What is cytokinesis?
The division of the cytoplasm, following mitosis.
What is the outcome of mitosis?
Two genetically identical daughter cells.
What are the two major phases of the cell cycle?
Interphase and the mitotic phase.
What percentage of the cell cycle is interphase?
About 90%.
What happens during the G1 phase?
The cell grows and carries out normal functions.
What happens during the S phase?
DNA replication (chromosome duplication).
What happens during the G2 phase?
The cell prepares for mitosis by growing and carrying out functions.
What are the five stages of mitosis?
Prophase, prometaphase, metaphase, anaphase, telophase.
What happens during prophase?
Chromatin condenses into chromosomes
Nucleoli disappear
Mitotic spindle begins to form
What happens during prometaphase?
Nuclear envelope fragments
Microtubules attach to kinetochores of chromatids
What happens during metaphase?
Chromosomes align at the metaphase plate
Sister chromatids attach to spindle fibers from opposite poles
What happens during anaphase?
Sister chromatids separate
Motor proteins pull chromatids toward opposite poles
What happens during telophase?
Nuclear envelopes reform
Chromosomes decondense into chromatin
What happens during cytokinesis in animal cells?
A cleavage furrow forms, dividing the cytoplasm.
What happens during cytokinesis in plant cells?
A cell plate forms, dividing the cytoplasm.
How do prokaryotes divide?
By binary fission.
Do prokaryotes use mitosis?
No, they do not perform mitosis.
What controls the progression of the cell cycle?
The cell cycle control system.
What are the major cell cycle checkpoints?
G1, G2, and M phase checkpoints.
Which checkpoint is the most important?
The G1 checkpoint.
What happens if a cell does not receive a go-ahead signal at the G1 checkpoint?
It enters the G0 phase (non-dividing state).
What types of cells remain in the G0 phase permanently?
Nerve and muscle cells.
Which human cells can re-enter the cell cycle from G0?
Liver cells, if signaled
What are kinases?
Enzymes that regulate the cell cycle.
When are kinases active?
Only when bound to cyclin proteins.
What are CDKs?
Cyclin-dependent kinases that give go-ahead signals at checkpoints.
What are growth factors?
Molecules that stimulate cell division.
What is density-dependent inhibition?
When crowded cells stop dividing.
What is anchorage dependence?
Normal cells must be attached to a surface to divide.
Do cancer cells exhibit density-dependent inhibition?
No, they continue dividing regardless of crowding.
Do cancer cells exhibit anchorage dependence?
No, they can divide without attachment.
Why does cancer become more common with age?
Mutations accumulate over time.
What is a tumor?
A mass of abnormal cells in normal tissue.
What is a benign tumor?
A non-invasive, non-spreading tumor.
What is a malignant tumor?
A tumor that invades other tissues and spreads.
What is metastasis?
The spread of cancer cells to other parts of the body.
Cyclin levels fluctuate
Cyclin proteins regulate CDKs, and their concentrations vary throughout the cycle, influencing progression through checkpoints.
MPF (Maturation-Promoting Factor)
A specific cyclin-CDK complex that triggers the cell’s passage into mitosis.
Chromatin vs. Chromosomes:
DNA is found as chromatin (loose and accessible) during interphase and condenses into chromosomes during mitosis.
Histones & Nucleosomes
DNA wraps around histone proteins, forming nucleosomes, which help with chromosome structure and gene regulation.
Steps of Binary Fission
DNA Replication begins at the origin of replication
The chromosome copies move to opposite sides
The cell elongates, and the membrane pinches inward
A new cell wall forms, producing two identical daughter cells
Unlike mitosis, binary fission does not involve spindle fibers or mitotic phases.
