Unit 7- Cell Cycle, DNA, and Protein Synthesis 7a- Cell Cycle

Bellwork Get out poster worksheet, we are going to discuss correct answers

Bellwork Remember, Photosynthesis Poster Due Tmrw.

Bellwork What are the three tenants of cell theory (try to remember!) Why is cell division important for life?

Cell Review Cell Theory: –All living things are composed of cells –The cell is the basic unit of life –All cells come from preexisting cells Cell Reproduction- aka cell division; process by which cells produce offspring cells –Differs in prokaryotes and eukaryotes

Important Vocabulary Chromosomes: rod-shaped structures made of DNA & proteins. –Each chromosome is a single DNA molecule associated with proteins –Eukaryotic DNA wraps tightly around proteins called histones Histones help maintain the shape of the chromosome

Important Vocabulary Chromatid- form as the DNA makes a copy of itself before cell division Chromatin- the less tightly coiled DNA-protein complex; substance that composes chromosomes Diploid Cells- cells with two sets of chromosomes Haploid cells- cells with one set of chromosomes

Cell Division in Eukaryotes Both the cytoplasm and the nucleus divide Two kinds: –Mitosis: results in new cells that are identical to the original cell Occurs in organisms undergoing growth, development, repair, or asexual reproduction –Meiosis: occurs during the formation of gametes (reproductive cells) Reduces the chromosome number by half

The Cell Cycle Cell Cycle: the repeated pattern of growth and division that occurs in eukaryotic cells Most of the cell’s life is spent in the growth phase known as interphase –made up of three phases: G1, S, and G2 The shortest phase in the cycle is the cell division phase known as mitosis & cytokinesis.

The Cell Cycle (see diagram on page 228) G1 – GAP 1 – Chromosomes are not visible (chromatin) Cell is rapidly growing and synthesizing proteins for daily functions S Stage - Synthesis Cell’s DNA is copied. G2 – Gap 2 - Cell is growing & producing proteins needed for division Cytokinesis- Division of cytoplasm Mitosis – Division of the nucleus

Mitosis The purpose of mitosis is the division of the nucleus –Produces two identical nuclei, each with the same number of chromosomes All somatic cells (cells other than the sex cells that make eggs and sperm) undergo mitosis. Four phases of mitosis: –Prophase –Metaphase –Anaphase –Telophase

Prophase First & longest phase in mitosis Chromatin coils to become visible chromosomes –The two identical halves of the doubled structure are called sister chromatids. –Held together by the centromere Nuclear envelope breaks down & disappears By the end of prophase, the centrosomes (organelles that produce spindle fibers) have separated and have moved to opposite poles of the cell. –Start to form spindle fibers

Metaphase 2 nd & shortest phase in mitosis Spindle fibers attach to the centromere Chromosomes are pulled to the middle of the cell & line up on the midline or equator, held in place by the spindle fibers Sister chromatids point to opposite poles

Anaphase The centromeres split & the sister chromatids are pulled to opposite poles of the cell. After the chromatids separate, they are considered to be individual chromosomes.

Telophase Spindle fibers break down and dissolve Chromosomes uncoil (chromatin) A nuclear envelope forms around each set of chromosomes Cytokinesis begins

Cytokinesis Cytoplasm is split forming two daughter cells each with its own nucleus & organelles –In animals: the cell membrane forms a cleavage furrow that eventually pinches the cell into two nearly equal parts. –In plants: a structure known as a cell plate forms midway between the divided nuclei, which gradually develops into a separating membrane. The cell wall forms in the cell plate Cell Plate

Name the Phase Prophase Metaphase Anaphase Metaphase Telophase Anaphase

Controlling the Cell Cycle The cell cycle is driven by a chemical control system telling the cell when to turn on and off cell division –Internal signals – cell senses the presence of enzymes produced within the cell –External signals – cell senses the presence of chemicals (such as growth factors) produced by other specialized cells Cells also respond to physical signals –When cells are packed in too closely, division is turned off –When cells are not in contact with other cells, division is turned on

Controlling the Cell Cycle Proteins regulate the progress of cell division at certain checkpoints –Checkpoint- a critical control point where stop & go signals can regulate the cycle –The cell division mechanism in most animal cells is in the “off” position when there is no stimulus present. Specific stimuli are required to start the processes.

Controlling the Cell Cycle 3 checkpoints: –Cell Growth (G1) Checkpoint – makes sure conditions are favorable & cell is big enough for division –DNA synthesis (G2) Checkpoint – DNA repair enzymes check the results of DNA replication –Mitosis Checkpoint – cell makes sure chromosomes & spindle are arranged properly to exit mitosis. If a cell passes this checkpoint, it will enter the G1 phase.

Mitosis Out of Control Cancer cells are an example of cells that do not respond normally to the body’s control mechanisms. Cancer cells keep dividing even when they are densely packed and/or if the proteins that regulate cell division are not functioning properly due to a mutation.

Mitosis Out of Control Cancer begins when a single cell is transformed into a cancer cell- one that does not listen to the regulation mechanism. This cell is normally found & destroyed by the body’s immune system. If not, this cell will continue to divide by mitosis and each daughter cell will be a cancer cell.

Mitosis Out of Control A mass of these cells that invades & impairs the functions of 1 or more organs is called a malignant tumor. A benign tumor is a mass of abnormal cells that remains at the original site. Cancer cells may also separate from the original tumor, enter the blood vessels of the circulatory systems, & invade other parts of the body, where they grow to form new tumors.