Section Objectives Sequence the events of the cell cycle. Relate the function of a cell to its organization in tissues, organs, and organ systems.

Cell Size Limitations Cells come in a wide variety of sizes and shapes. Review: Considering this wide range of cells sizes, why then can’t most organisms be just one giant cell? (hint: cell size lab) ____________________________________ ____________________________________ ____________________________________ ____________________________________ ________

Diffusion limits cell size Although diffusion is a fast and efficient process over short distances, it becomes slow and inefficient as the distances become larger. Because of the slow rate of diffusion, organisms can’t be just one giant-sized cell.

Surface area-to-volume ratio As a cell’s size increases, its volume increases much faster than its surface area If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete. The surface area, however, would increase by a factor of only four. The cell would either starve to death or be poisoned from the buildup of waste products. Surface area = 6 mm2 Volume = 1 mm3 Surface area = 24 mm2 Volume = 8 mm3 2 mm 1 mm 2 mm 4 mm

Cell Reproduction Cell division is the process by which new cells are produced from one cell. Cell division results in two cells that are identical to the original, parent cell. REVIEW: Levels of Organization Cells -  _______ -  _________--  _________--  __________

chromosomes Structures, which contain DNA and become darkly colored when stained, are called chromosomes. Chromosomes are the carriers of the genetic material that is copied and passed from generation to generation of cells. Accurate transmission of chromosomes during cell division is critical.

The large, complex chromosomes of eukaryotes duplicate with each cell division Chromosomes contain a very long DNA molecule with thousands of genes –Individual chromosomes are only visible during cell division –They are packaged as chromatin Before a cell starts dividing, the chromosomes are duplicated –This process produces sister chromatids Sister chromatids Centromere

double-stranded human chromosomes ready for mitosis

The Cell Cycle The cell cycle is the sequence of growth and division of a cell. The majority of a cell’s life is spent in the growth period known as interphase. Interphase

The Cell Cycle Following interphase, a cell enters its period of nuclear division called mitosis. Following mitosis, the cytoplasm divides, separating the two daughter cells. Mitosis

Interphase: A Busy Time Interphase, the busiest phase of the cell cycle, is divided into three parts: G 1, S, & G 2 Rapid growth and metabolic activity DNA synthesis and replication cell prepares for division Interphase

Interphase: A Busy Time During the first part,(G 1 ) the cell grows and protein production is high. Rapid growth and metabolic activity Interphase

Interphase: A Busy Time In the next part of interphase, (S) the cell copies its chromosomes. DNA synthesis and replication Interphase

Interphase: A Busy Time After the chromosomes have been duplicated, the cell enters another shorter growth period (G2) in which mitochondria and other organelles are manufactured and cell parts needed for cell division are assembled cell prepares for division Interphase

Biology is the only subject in which multiplication is the same thing as division…

MITOSIS: Making New Cells Making New DNA during S phase of interphase

Where it all began… You started as a cell smaller than a period at the end of a sentence…

Going from egg to baby…. the original fertilized egg has to divide… and divide… Getting from there to here…

Why do cells divide…  One-celled organisms  for reproduction  asexual reproduction (clones)  Multi-celled organisms  for growth & development  from fertilized egg to adult  for repair & replacement  replace cells that die from normal wear & tear or from injury amoeba starfish

The Phases of Mitosis The phases of mitosis are, prophase, metaphase, anaphase, and telophase. PMAT PLEASE MEET AT TIM’S Mnemonics?

Prophase: The first phase of mitosis During prophase, the chromatin coils to form visible chromosomes. Spindle fibers Disappearing nuclear envelope Doubled chromosome

Prophase: The first phase of mitosis The two halves of the doubled structure are called sister chromatids. Sister chromatids are held together by a structure called a centromere, which plays a role in chromosome movement during mitosis. Centromere Sister chromatids

Metaphase: The second stage of mitosis During metaphase, the chromosomes move to the equator of the spindle.

Anaphase: The third phase of mitosis During anaphase, the centromeres split and the sister chromatids are pulled apart to opposite poles of the cell.

Telophase: The fourth phase of mitosis During telophase, two distinct daughter cells are formed. The cells separate as the cell cycle proceeds into the next interphase. Nuclear envelope reappears Two daughter cells are formed

Cytokinesis Following telophase, the cell’s cytoplasm divides in a process called cytokinesis. Cytokinesis differs between plants and animals. Toward the end of telophase in animal cells, the plasma membrane pinches in along the equator.

Cytokinesis Plant cells have a rigid cell wall, so the plasma membrane does not pinch in. A structure known as the cell plate is laid down across the cell’s equator A cell membrane forms around each cell, and new cell walls form on each side of the cell plate until separation is complete.

Results of Mitosis When mitosis is complete, unicellular organisms remain as single cells. In multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function. Tissues organize in various combinations to form organs that perform more complex roles within the organism. Multiple organs that work together form an organ system.

Mitosis in whitefish blastula

Mitosis in plant cell

onion root tip

Onion root tip

Section Objectives Describe the role of enzymes in the regulation of the cell cycle. Distinguish between the events of a normal cell cycle and the abnormal events that result in cancer. Identify ways to potentially reduce the risk of cancer.

Mitosis & Cancer: When Making New Cells Goes Terribly Wrong!

When is mitosis a good thing? When you have to add or replace cells –growth & development –repair –replacement

When is mitosis a BAD thing When cells reproduce & they are not needed –these cells take over organs, but don’t do the right job –they just keep making copies –cancer damages organs

Why would cells just make copies? If DNA gets damaged, cells stop listening to correct instructions –mutations Causes of mutations:  UV radiation  chemical exposure  radiation exposure  heat  cigarette smoke  pollution  age  genetics

Normal Control of the Cell Cycle Proteins and enzymes control the cell cycle The cell cycle is controlled by proteins called cyclins and a set of enzymes that attach to the cyclin and become activated. Occasionally, cells lose control of the cell cycle.

Normal Control of the Cell Cycle This uncontrolled dividing of cells can result from the failure to produce certain enzymes, the overproduction of enzymes, or the production of other enzymes at the wrong time. Cancer is a malignant growth resulting from uncontrolled cell division.

Normal Control of the Cell Cycle Enzyme production is directed by genes located on the chromosomes. A gene is a segment of DNA that controls the production of a protein. REVIEW: AN ENZYME LOWERS THE ______________ ENERGY IT WORKS VIA THE ___________ AND ____________ MODEL

Cancer: A mistake in the Cell Cycle Currently, scientists consider cancer to be a result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle. Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients

Cancer: A mistake in the Cell Cycle In later stages, cancer cells enter the circulatory system and spread throughout the body, a process called metastasis, forming new tumors that disrupt the function of organs, organ systems, and ultimately, the organism.

The causes of cancer The causes of cancer are difficult to pinpoint because both genetic and environmental factors are involved. Environmental factors, such as cigarette smoke, air and water pollution, and exposure to ultraviolet radiation from the sun, are all known to damage the genes that control the cell cycle. Cancer may also be caused by viral infections that damage the genes.

Cancer prevention Physicians and dietary experts agree that diets low in fat and high in fiber content can reduce the risk of many kinds of cancer. Vitamins and minerals may also help prevent cancer. In addition to diet, other healthy choices such as daily exercise and not using tobacco also are known to reduce the risk of cancer.