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The Cell Cycle
How cells replicate!
The Cell Cycle • The cell cycle is the repeated pa3ern of growth and division that occurs in eukaryo:c cells.
• There are three parts of the cell cycle: 1. Interphase: growth & copying DNA 2. Mitosis: Division of the nucleus 3. Cytokinesis: Division of cytoplasm
• Cells spend the majority of their :me in interphase
Interphase • Divided into three phases • G1 (Gap 1): • The cell grows and makes proteins (protein synthesis)
• S (Synthesis): • Chromosomes replicate (x2) • They form iden:cal sister chroma:ds held together by a centromere
• G2 (Gap 2): • Cell con:nues to grow • Produce proteins for division • Prepares for cell division
Interphase
Chromatin vs. Chromosome • During interphase, the cell’s gene:c material is visible as a stringy material called chroma:n
• During prophase, the chroma:n condenses and supercoils into chromosomes
• A chromosome consists of two iden:cal sister chroma:ds held together by a centromere.
centromere
chromosome
Sister chroma.d
DNA double helix
Mitosis • Begins with one cell and produces two iden:cal “daughter cells” that have the same DNA as the parent cell.
• For example: • A normal human skin cell has 46 chromosomes • If the skin cell undergoes mitosis, the result will be two new skin cells, each with 46 chromosomes
Mitosis • 4 strands (2 sister chroma:ds) break apart so each new cell has one double strand
• Mitosis follows interphase and is divided into 4 phases.
Phases of Mitosis • Consists of four phases:
• Remember: PMAT
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
Mitosis
Prophase • The chroma:n condenses into visible chromosomes
• The nuclear envelope disappears • Centrioles separate and move to opposite ends of the cell
• Spindle fibers form and spread out across the center of the cell
Prophase
Metaphase • Chromosomes line up across the middle of the cell
• Spindle fibers connect the centromere of each chromosome to the poles
• Shortest phase of mitosis
Anaphase • Centromeres that join the sister chroma:ds split
• The chroma:ds separate
• Separated chroma:ds move to opposite ends of the cell
Telophase • The chromosomes uncoil and become chroma:n once again
• The nuclear envelope reforms around the chroma:n at each end of the cell
• Spindle fibers dissolve
• Cytokinesis begins
Cytokinesis
In Animals In Plants
• The division of the cytoplasm
• A cleavage furrow forms
• The cell membrane “pinches” inward between the two nuclei
• The cell cannot “pinch” inward due to cell wall
• A cell plate forms between the two nuclei
Cytokinesis: Animals
Cytokinesis: Plants