Cell Cycle

The Cell Division Cells are constantly trying to keep up with changes in the environment. Cells must go through these changes to maintain homeostasis.

Cell Cycle Broken down into interphase and cell division Interphase – Period of the cell cycle between cell divisions – G1, S, and G2 phase Cell division – Mitosis – Cytokinesis *

Cell Cycle During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. Four phases – G1 phase – S phase – G2 phase – M phase (Mitosis and Cytokinesis)

Interphase G1- Cell growth – Cells do most of their growing – Increase in size – Synthesize new proteins and organelles S phase- Synthesis – Chromosomes synthesized forming sister chromatids – Usually once cell enters S phase it completes the rest of the cell cycle G 2 – More growth – Cell synthesizes proteins needed during mitosis and cytokinesis – Preparation for mitosis

Interphase

Cell Regulation Cyclin – a protein responsible for advancing a cell through the phases of the cell cycle. Tells the cell when it is time to divide – Internal regulators- regulates what is going on inside the cell i.e.- make sure all chromosomes have been replicated before entering mitosis – external regulators- regulates what is going on outside the cell- speed up or slow down the cell cycle i.e. – growth factors – embryonic development and wound healing

Cell Regulation Checkpoints- 3 critical regulation points or CHECKPOINTS in eukaryotic cells G1- checkpoint (restriction pt) G2- checkpoint Metaphase- checkpoint Checkpoint proteins act as sensors to determine if the cell is in proper condition to divide. Cell cycle will be delayed or until problems are fixed or prevents division entirely Loss of checkpoint function can lead to mutation and cancer

Cell Regulation Cancer – These cells don’t respond to the signals that regulate the growth of most cells – Some causes: smoking tobacco, radiation exposure, sun damage. – Defect in a gene called p53- normally halts the cell cycle until all chromosomes have been replicated Disease of the cell cycle

Cell Cycle

Interphase

Mitosis Four phases – Prophase – Metaphase – Anaphase – Telophase  Cytokinesis – cell completes cell division - two cells are formed Mitosis can last anywhere from a few minutes to several days depending upon cell type.

Prophase Longest phase % of total time Chromatin condenses into chromosomes The centrioles separate A spindle begins to form Nuclear envelope begins to break down

Prophase

Metaphase Chromosomes line up across the center of the cell Each chromosome is connected to a spindle fiber at its centromere

Metaphase

Anaphase The sister chromatids separate into individual chromosomes and are moved apart Continue to move until they have separated into two groups near the poles of the spindle

Anaphase

Telophase The chromosomes gather at opposite ends of the cell Lose their distinct shapes Two new nuclear envelopes will form

Telophase

Cytokinesis Usually occurs at the same time as telophase Cytoplasm pinches in half- taking organelles and proteins with it Each daughter cell has an identical set of duplicate chromosomes – Animal cell- cleavage furrow – Plant cell- cell wall grows between

Cytokinesis

MITOSIS hill.com/olc/dl/120073/bio14.swf hill.com/olc/dl/120073/bio14.swf Mitosis process