Chapter 9: Cell Cycle and Cell Reproduction

Why do cells need to divide? Growth and development You started as 1 cell and now you’re made up of roughly 40 TRILLION cells Repair and regeneration of tissue Reproduction

What happens when cells divide? We go from one functional cell to two functional and identical cells All the organelles need to double All the genetic material needs to be replicated The plasma membrane needs to encapsulate both cells All of these events are controlled in the cell cycle

What is the cell cycle? Cell cycle – orderly set of stages that take place between the time a eukaryotic cell divides and the time the resulting two daughter cells divide Cells are always at some stage of the cell cycle

Stages of the cell cycle Interphase – cell performs usual functions and prepares for division Longest stage at about 20 hours, or 90% of cell cycle Consists of three separate phases: G1 – growth phase after previous division, organelles replicate and proteins are translated for DNA synthesis S phase – DNA is synthesized, or copied G2 –cell continues to grow and replicate organneles, translation of proteins necessary for mitosis

Mitotic Stage Mitosis – Nuclear division Division of nucleus and DNA Cytokinesis – Division of cytoplasm

Mitosis Mitosis is nuclear division Nuclear division means we need to create two identical nuclei, including all the genetic material inside of them Genetic material = DNA DNA is wrapped around histones, or proteins that help store the DNA Chromosomes-strands of packaged DNA Eukaryotic cells contain roughly 2m of DNA and pack it into a nucleus that is only 6um in diameter!

Cytokinesis in animals SEM 140 Daughter cells Cleavage furrow Contracting ring of microfilaments Cytokinesis in animals Cleavage furrow- indentation of membrane between the two daughter nuclei Contractile ring – Actin filaments that tighten around the cell

Cytokinesis in animals where the cell pinches in “belt” made of microfilaments (actin)

Cell Cycle Regulation Signals – Agent that influences cell growth Checkpoints occur at G1, G2 and Mitosis If the cell is ready to proceed, the appropriate signals are released If not, it stops

Apoptosis Apoptosis – Programmed cell death Normal development To make complicated structures from a single cell, some cells have to die in the process Prevention of the spread of disease Cells are constantly becoming damaged and usually they die when they are beyond repair, but sometimes they ignore these cues and replicate uncontrollably Apoptosis in Normal Development Apoptosis Overview

Cancer Cancer – cell growth disorder that occurs when cells divide uncontrollably Happens through a series of mutations that disrupt cell cycle checkpoints and apoptosis Normal cells cooperate to benefit the whole organism, cancer cells compete to benefit only themselves

Characteristics of cancer cells Cancer cells are no longer specialized cells they do not perform any useful function Cancer cells have large nuclei due to extra chromosomes Cancer cells do not undergo apoptosis they don’t die when they should Cancer cells form tumors, or abnormal growths Cancer cells trigger blood vessel growth (angiogenesis) and travel throughout the body (metastasis) Essentially, normal cells cooperate to help the body function. Cancer cells only care about themselves and compete with everything