Chapter 8 Cell Reproduction

Chromosome Structure Chromosomes are made of DNA and proteins Each eukaryotic chromosome is a single DNA molecule associated with histone proteins

Between cell divisions, DNA is not so tightly coiled and is called chromatin Prokayotic DNA is simpler. It consists of only one chromosome which is circular.

Chromosome Numbers Sex chromosomes are either the X or Y Autosomes are all of the other chromosomes in an organism. Every cell has two copies of each autosome. Each pair is called a homologous chromosome. Homologous chromosomes carry the same genetic information. A photomicrograph of all of the chromosomes in a cell is called a karyotype

Human Karyotype

Diploid vs Haploid Cells with two sets of chromosomes are diploid Two of each autosome and a pair of sex chromosomes. These are referred to as 2n Sperm and eggs have only a single copy of each autosome and only one of the sex chromosomes Those cells are referred to as haploid or 1n

Cell Division All cells come from preexisting cells through cell division Cell division differs in prokaryotes and eukaryotes but the result if the same---two cells from one. Prokaryotic cell division is call binary fission

Cell Division in Eukaryotes Mitosis: results in cells identical to original cell, used for growth development, repair or asexual reproduction Meiosis: produces gametes (sex cells) which are haploid. Cell Cycle: the repeating set of events in the life of a cell. Includes: Cell Division: Mitosis (PMAT) and Cytokinesis Interphase: G1, S, G2

Stages of Mitosis Mitosis is the division of the nucleus It is a continuous process that allows for the organized distribution of the cell’s copied DNA. Observe in the lab the different phases of this process. Keep in mind that this process is critically important and so is the order of the events.

Cut the drawings you made of onion root tip cells apart. What order do you think they should go in? Remember we know that this is process is very precise and controlled. Review the order you have placed them in and look at the following pictures:

What are the major events in each Phase? Interphase: wait and look at next slide. Prophase: chromosomes begins to condense, nuclear membrane disappears, centrioles split and spindle begins to form Metaphase: chromosomes move to equator of the cell Anaphase: centromers split and chromosomes begin to move apart Telophase: chromosomes move to opposite poles of cell Cytokinesis: division of the cytoplasm

Events in the Cell Cycle The Cell Cycle is a set of events in the life of a cell Interphase Longest period G1: a period of growth following cell division S: DNA is copied G2: cell prepares for cell division G0: cells sometimes exit from the cell cycle and go into an extended state of interphase. They do not copy their DNA or prepare for cell division. EX. Neurons.

Cytokinesis Plant Cells Animal Cells

Control of Cell Division What triggers a cell to begin to divide? The cell cycle is controlled by regulatory proteins both inside and outside of the cell. Internal regulators: respond to events occurring inside the cell. Three checkpoints are discussed on following slide. External regulators: can speed up or slow down the cell cycle. Growth factors: during development and during healing

In eukaryotes there are checkpoints which regulate cell division. Cell growth (G1): is the cell healthy and grown to a suitable size. DNA Synthesis (G2) : The results of the DNA replication are checked. If all is good, the cell is signaled to continue into mitosis. Mitosis: was cell division successful, if so, go into G1 phase.

Apoptosis Cell death: can be accidental due to damage or injury. Can be “programmed” to die: apoptosis Important during development to shape the structure of tissues and organs.

Cancer: uncontrolled cell growth Cancer cells don’t respond to the signals that regulate the growth of most cells. As a result, the cells divide uncontrollably. A mass of cells is called a tumor Causes: environmental, genetics (p53 defect), viral infections Treatments: removal of tumor, treatments that target rapidly dividing cells (both radiation and chemical).