Why do cells divide?. The Cell Cycle Why do cells divide? Repair Growth Reproduction Some organisms...
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Transcript of Why do cells divide?. The Cell Cycle Why do cells divide? Repair Growth Reproduction Some organisms...
Why do cells divide?
The Cell Cycle
Why do cells divide?
Repair Growth Reproduction
Some organisms reproduce by cell division (asexual)
Limit on size
Chromosomes Genetic material is composed of DNA Most of the time, DNA is in the form of
chromatin (unraveled; in use)
Chromosomes Before the cell divides,
chromatin is replicated and condensed to form chromosomes (humans have 46)
Each chromosome consists of 2 identical copies called sister chromatids joined by a centromere
The Cell Cycle
The cell cycle consists of 2 phases: Interphase
G1, S, G2 Mitotic Phase
Mitosis (4 stages) Cytokinesis
Interphase
Time in between cell divisions Interphase is broken into 3 sub-phases:
G1 – cell works and grows S – DNA (chromatin) duplicates G2 – cell prepares to divide
Mitotic Phase
Mitosis – Division of nucleus Prophase Metaphase Anaphase Telophase
Cytokinesis – Division of cytoplasm
The Mitotic Spindle
Microtubules that separate the sister chromatids
Grows from centrosomes
Chromosomes are separated into sister chromatids
Chromosomes form Spindle fibers attach to the
chromatids Chromosomes line up in the
middle of the cell Spindle elongates the cell by
pushing the poles apart Genetic material exists as
chromatin
Chromatids are separated and move towards the poles
Spindle disappears 2 nuclei reappear The cytoplasm splits,
forming 2 cells Nuclear envelope breaks
down Cell is growing & working;
genetic material replicates
Mitosis
Prophase Chromosomes form Nucleus breaks down Centrosomes move to poles Spindle fibers attach to the
chromosomes
Mitosis
Metaphase Chromosomes line up in the
middle of the cell
Mitosis
Anaphase Chromosomes are separated
into sister chromatids Spindle elongates the cell
Mitosis
Telophase Chromatids reach the poles Spindle disappears 2 nuclei reappear Cleavage furrow appears
Cytokinesis
Cytokinesis The cytoplasm
splits, forming 2 cells
Summary
The cell cycle begins with one cell The cell undergoes a series of steps:Interphase – Prophase – Metaphase –
Anaphase – Telophase – Cytokinesis 2 identical daughter cells have been
produced
Restriction Point
Cell Cycle Checkpoints
Restriction point (G1) Internal surveillance External surveillance
Density dependence Anchorage dependence
Cancer
Benign tumor Malignant tumor
Metastasis Treatment
Surgery Radiation therapy Chemotherapy
Meiosis
Diploid vs haploid
Cells with two sets of chromosomes are called diploid (2n)
Cells with one set of chromosomes are called haploid (n)
Homologous chromosomes
You inherit one chromosome of each type from each parent
Homologous chromosomes are the 2 matching chromosomes 44 autosomes 2 sex chromosomes
Meiosis
The process by which 4 haploid gametes are produced, each with half the number of chromosomes as the diploid parent Sperm – male gamete Egg – female gamete
If a human body cell has 46 chromosomes, how many does a human gamete have?
Meiosis
Meiosis involves 2 divisions Meiosis I – splits homologous pairs Meiosis II splits sister chromatids
Major Events
Prophase I Crossing over
Anaphase I Homologous pairs
separate Anaphase II
Sister chromatids separate
Meiosis promotes genetic diversity
Produces 4 genetically different daughter cells
During prophase 1, homologous chromosomes can exchange pieces of genetic material to form totally new chromosomes (crossing over)
Errors in Meiosis
A nondisjunction occurs when chromosomes or chromatids fail to split
Activity: Mitosis vs Meiosis
Fill in the chart to compare the two types of cell division.