Cell Growth and Division

Things to ponder When living things grow, what happens to its cells?? OR?

Things to ponder When living things grow, what happens to its cells? For example: When a 7lb baby grows into a 70lb child is it because its cells grow bigger or because it made more cells?

Things to ponder When living things grow, what happens to its cells? For example: When a 7lb baby grows into a 70lb child is it because its cells grow bigger or because it made more cells? What would happen if a cell where just split into two without any preparation? Would the two new cells have everything they would need to survive??

Objectives Describe the stages of the cell cycle, including DNA replication and mitosis, and the importance of the cell cycle to the growth of organisms (TEKS 5A) Describe how cell division solves the problems of cell growth. Name the main events and components of the cell cycle Describe what happens during the 4 phases of mitosis Recognize that disruptions of the cell cycle lead to diseases such as cancer (TEKS 5D)

Limits to Cell Growth The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane. If cells just grew larger DNA would get overloaded As a cell increases in size, it usually doesn t make more DNA. The same amount of DNA would then be forced to control a much larger cell causing an information crisis

Limits to Cell Growth The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane. If cells just grew larger Exchanging materials would also become more difficult Food, oxygen, and water enter a cell through the cell membrane and wastes exit through this same membrane The cells surface area and volume are critical to the cells ability to efficiently do this. As a cell grows, its volume increases more rapidly than its surface area limiting what can come into or out of the cell. It s like a highway in Houston vs a highway in Huntsville.

Made more cells Cell Division! When a 7lb baby grows into a 70lb child is it because its cells grow bigger or because it made more cells?

Cell division, however, is just one small part of the cell cycle

The 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. Interphase-The longest part of the cell cycle. It has 3 phases. G1 phase- a growth phase. Cells increase in size and synthesize new proteins and organelles. S phase- Chromosomes (DNA) are replicated G2 phase- another growth phase. Organelles are duplicated and the cell prepares for cell division Cell Division Also called M phase. Has 2 phases. Mitosis- First stage of cell division. It s made up of 4 stages Cytokinesis- Final stage of division when the cytoplasm divides and separates to form two daughter cells.

Cell Division: Background Info The who, what, where, when, why, and how of cell division Who s dividing: The cell, specifically somatic or asexual cells Where does it start: When does it divide: The nucleus During mitosis (M phase) Why does it divide: To make more cells (to grow) How does this happen: I m glad you asked

Cell Division: How it happens Every cell must copy its genetic information before cell division can begin. In prokaryotes (aka bacteria) cells undergo a much simpler version of cell division called binary fission but we won t focus on this today. In eukaryotes, cell division is more complex mainly due to the complexity of cell itself (more organelles, more DNA, etc) The two main stages of cell division are mitosis and cytokinesis Do you remember at what stage of the cell cycle is genetic information copied?

Cell Division: What s a chromosome? Every cell must copy its genetic information before cell division can begin. Chromosomes contain that genetic information. Chromosomes are simply DNA wound up into a threadlike structure found in the nucleus. Chromosomes are not visible in most cells except during cell division. During S phase, each chromosome is duplicated or copied creating an identical sister chromatid. At the end of cell division, the two new daughter cells will each have one of those sister chromatids; thereby making two cells with identical chromosomes.

Humans have 46 chromosomes, or 23 pairs. One chromosome is paternal (means it comes from the father) One chromosome is maternal (means it comes from the mother) The figure below is called a karyotype. It s a set of human chromosomes arranged in order from 1-22 with the sex chromosomes being last.

Interphase This is NOT cell division!! Before cell division occurs, cells are in Interphase. Interphase is the longest stage of the cell cycle; most cells spend their time in interphase. Three stages to interphase: G1 (a growth stage) S (when the DNA duplicates the S stands for synthesis) G2 (another growth stage Chromosomes are not visible at this time. They will not become visible until M phase (aka cell division, aka mitosis) occurs.

Cell Division: Mitosis There are 4 main stages of mitosis

PROPHASE 1st dividing phase DNA thickens and becomes visible Centrioles appear in centrosome region & move to poles Nuclear membrane & nucleolus disappear Spindle fibers form & attach to chromosomes

Spindle MICROTUBULES are part of cytoskeleton

METAPHASE Chromosomes line up in middle

ANAPHASE Centromeres split Centrioles pull chromatids apart Each chromatid is now its own chromosome

TELOPHASE See two nuclei Nuclear membrane & nucleolus return Chromosomes spread out at opposite ends of the cell Spindle fibers disappear Images from: Pearson Eduction Ince; Publishing as Pearson Prentice Hall http://www2.bc.cc.ca.us/cnewton/biology%2011/mitosis.html

Final stage of cell division is: CYTOKINESIS Cytoplasm splits into 2 cells

Cancer Video Cancer is when someone s own cells go through the cell cycle unchecked and cells begin to grow and divide uncontrollably. The rapid growth causes cells to amass into tumors. Not all tumors are cancerous. Benign tumors are masses of cells, but they do not spread and infect surrounding healthy tissue. Malignant tumors, on the other hand, are cancerous, and invade healthy tissue, absorb the nutrients the normal cells need, and prevent organs from functioning properly. Cancerous cells that reach the bloodstream can travel to other parts of the body and spread cancer to many organs. This process is called metastasis and is very difficult to treat.

Cancer The Cause It is not always known what causes disruptions in the cell cycle; however, it is often the result of a random mutation. Often, these mutations involve check points during the cell cycle process. A high number of cancer cells have defective p53 genes. This gene helps to regulate the cell cycle, and when it s mutated, the cell cycle losses the ability to control normal cell growth. Other external factors such as viruses, extreme physical or emotional stress, and aging can all cause the cell cycle to go haywire. Toxins, or poisons, that mutate cells and result in cancerous cell cycles are called carcinogens. Common carcinogens include tobacco smoke, asbestos, radiation from X rays and microwaves, and smog.

Cancer - Treatment Since cancer can spread so easily, it must be treated immediately. The most common treatments are surgery, radiation, and chemotherapy. Surgery: remove tumors from the body to prevent the cancer cells from metastasizing. Not always possible. Radiation: malignant tumors are blasted with concentrated beams of radiation that are targeted to destroy the cancer cells. Chemotherapy: usually accompanies surgery and radiation. Uses powerful drugs that target rapidly dividing cells. Radiation and chemotherapy tend to also damage healthy cells, leaving the patient with side effects such as weakness, hair loss, and skin rashes. Ongoing research: Gene therapy is one of the recent advancements in cancer treatment. Genes, often from stem cells, are injected into patients in place of damaged DNA to produce the necessary proteins for fighting infection. Also, damaged genes are completely replaced with healthy, normal functioning genes.

Summary Cell Cycle: -Interphase G1, S (DNA synthesis), G2 -M phase (Cell division) Mitosis (PMAT) know these stages!! cytokinesis Facts about Mitosis: only occurs in somatic (body cells). We ll talk about meiosis (how sperm and egg are created later) Diploid cell makes 2 diploid cells (called daughter cells) The daughter cells are identical to the original cell Cancer Unregulated cell division Cancer is your own cells that just keep dividing, making more and more (cancer) cells