Cell Growth & Division Chapter 5

8b - describe the cell cycle; AKS Standards: 8b - describe the cell cycle; 9e - compare the advantages of sexual reproduction and asexual reproduction in different situations

Functions of Cell Division Reproduction of cells all cells come from pre-existing cells results in two identical cells except for size Growth and Development of Organisms tadpoles become frogs, ivy vines get longer Tissue renewal skin cells are being replaced, cuts and bruises heal

Stages of the Cell Cycle During the cell cycle, a cell grows, prepares for division, and divides to form 2 identical daughter cells, where each one of which begins a new cycle. The 5 phases of the cell cycle are: Interphase (G1, S, G2) – period of rest between cell division Prophase Metaphase Anaphase Telophase 6. Cytokinesis - division of the cytoplasm phases of nuclear division (MITOSIS) The cell cycle is a regular pattern of growth, DNA replication, and cell division that occurs in eukaryotic cells.

Events of the Cell Cycle Gap 1 (G1): Cell carries out normal functions. It also increases in size and organelles increase in number. Synthesis (S): Cell makes a copy of nuclear DNA. Gap 2 (G2): Cells continue to carry out normal functions and prepares for Mitosis. Mitosis (M): Includes nuclear division and cytokinesis. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

Cells Divide at Different Rates Rates of cell division vary widely, and each is linked to a body’s need for those cells: In human cells, the G1, S, G2 and M stages together take about 12 hours.

Limits to Cell Size Why can’t organisms just be one giant cell? Cells have upper and lower size limits. If they were too small, they could not contain all of the necessary organelles and molecules. For example, a cell with only a few mitochondria would not have enough energy to live. If they were too big, necessary nutrients and wastes could not be transported efficiently into and out of cells. For example, wastes would collect inside the cell and poison it; and nutrients could not reach organelles in a timely manner, so cells would die. Also, information overload would occur. DNA makes copies as a cell divides, and there must be enough DNA blueprint to allow for protein production. Why can’t organisms just be one giant cell?

As the length of a cell increases, its volume increases faster than its surface area. The resulting decrease in the cell’s ratio of SA to V makes it more difficult for the cell to move needed materials in and waste products out. Volume is a three-dimensional unit – length X width X height Surface Area is a two-dimensional unit – length X width SO VOLUME INCREASES AT A FASTER RATE THAN DOES SURFACE AREA…Thus, SURFACE AREA IS THE LIMITING FACTOR IN THE SIZE OF A CELL: SMALLER CELLS HAVE A MORE FAVORABLE SA: V RATIO, AND THEREFORE THEIR DIFFUSION EFFICIENCY IS MUCH FASTER!

Review | Critical Thinking Activities The following activities are highly recommended by your teacher. Each activity will allow you to (1) review main concepts; (2) apply what you have learned; and (3) think critically and analytically in such a way that allows you to form your own conclusions in novel applications: Section 5.1 Assessment Questions (textbook pp. 137). Section 5.1 Concept Map: The Cell Cycle – accessed via the virtual textbook at classzone.com. Section 5.1 Virtual Quiz - accessed via the virtual textbook at classzone.com.

8b - describe the cell cycle; AKS Standards: 8b - describe the cell cycle; 9e - compare the advantages of sexual reproduction and asexual reproduction in different situations

Cell Division: Distributing Identical Sets of Chromosomes to Daughter Cells Cell division is the copying and equal separation of chromosomes. Chromosomes are long continuous threads of DNA that consists of numerous genes along with regulatory information: made up of DNA and protein cells of every organism have a specific number of chromosomes not visible in cells except during cell division

Chromosome Structure Before cell division, each chromosome is replicated and consists of 2 identical “sister” chromatids Each pair of chromatids is attached at an area called the centromeres Chromosomes spend most of their time as chromatin – long strands of DNA that are relaxed. When cells get ready to divide, chromatin condenses into chromosomes.

Diploid v. Haploid Cells DIPLOID CELLS UNDERGO MITOSIS…HAPLOID CELLS UNDERGO MEIOSIS. Diploid cells are somatic – the cells of the body. Haploid cells are sex cells – egg and sperm. HAPLOID CELLS - gametes (single set of chromosomes) DIPLOID CELLS - offspring (full set of chromosomes)

Cell Division Before it becomes too large, a growing somatic cell divides forming 2 “daughter” cells by a process known as cell division: The combined processes of mitosis and cytokinesis produce two genetically identical daughter cells. Each daughter cell gets 1 complete set of genetic information during cell division and therefore will be IDENTICAL TO THE MOTHER CELL! A somatic cell is a non sex cell!

Review: Events of the Cell Cycle Interphase is divided into 3 phases: G1 – cell growth S – DNA replication G2 – preparation for Mitosis During Interphase, chromosomes are in their “uncondensed” form and are called chromatin Mitosis (nuclear division) is the division of the nucleus and it occurs in 4 phases: P = prophase – chromatin condenses into chromosomes, the centrioles separate & nuclear membrane breaks down M = metaphase – chromosomes line up across center of cell and each chromosome is connected to a spindle fiber at its centromere A = anaphase – sister chromatids separate into individual chromosomes and are pulled apart T = telophase – chromosomes gather at opposite ends of the cell and 2 new nuclear membranes form around them Cytokinesis – division of cytoplasm

INTERPHASE Interphase is very long (cells spend most of time here): Nucleus well defined bounded by nuclear envelope. Easily identifiable nucleolus. Genetic material in uncondensed form of chromatin – chromosomes cannot be seen. Interphase is very long (cells spend most of time here): G1 phase – cell growth; cells increase in size and synthesize new proteins and organelles S phase – chromosomes are replicated and the synthesis of DNA molecules takes place; key proteins associated with the chromosomes are synthesized during this time G2 phase – shortest of 3 phases; many of the organelles and molecules required for cell division are produced

M phase: Mitosis - PMAT Nuclear Division (Mitosis) is divided into four phases: Prophase Metaphase Anaphase Telophase USEFUL ANIMATION: http://www.sumanasinc.com/webcontent/animations/content/mitosis.html

PROPHASE Chromatin coils and condenses; becomes visible as chromosomes. Centrioles separate and take up positions on opposite sides of the nucleus. Chromosomes become attached to spindle fibers. Nucleolus disappears, nuclear membrane breaks down

Chromosome Duplication and Distribution During Mitosis A duplicating chromosome consists of 2 sister chromatids, which narrow at their centromeres. The DNA molecules of sister chromatids are identical. Chromosomes normally exist in the highly condensed state shown here only during the process of mitosis.

METAPHASE This is the shortest phase of mitosis. Chromosomes line up in center of cell along metaphase plate. For each chromosome, the kinetochores of the sister chromatids are attached to microtubules coming from opposite poles of the cell.

ANAPHASE Anaphase begins suddenly when the paired centromeres that join the sister chromatids separate from each other. NOW EACH CHROMATID IS A SEPARATE CHROMOSOME….they begin moving toward opposite poles of the cell. Chromosomes continue to move until they have separated into two groups near the poles of the spindle. Anaphase is over when the chromosomes stop moving!

TELOPHASE Two daughter nuclei form at the two poles of the cell. Chromosomes begin to relax back down into chromatin. Nuclear envelope re-forms around each cluster of chromatin. Spindle begins to break apart and nucleolus reappears in each daughter cell. NUCLEAR DIVISION IS NOW COMPLETE, BUT NOT CELL DIVISION!

Phases of Mitosis

Cytokinesis Cytokinesis is the division of the cytoplasm itself. It can take place in a number of ways: In animal cells – “draw-string” effect forms cleavage furrow (which pinches the cell into two parts). In plant cells – cell plate forms from inside out, and cell wall begins to appear .

Cytokinesis in Animal and Plant Cells CLEAVAGE OF AN ANIMAL CELL: Cleavage furrow forms just inside plasma membrane and deepens until the cell is pinched in half. CELL PLATE FORMATION IN A PLANT CELL: Here we see the two daughter nuclei and vesicles from the Golgi apparatus that are coming together to form a cell plat at the middle of the cell. A cell wall between the daughter cells will form from the contents of the cell plate.

The stages of Mitotic Cell Division in an Animal Cell: G2 phase; Prophase; Prometaphase

The Stages of Mitotic Cell Division in an Animal Cell: Metaphase; Anaphase; Telophase and Cytokinesis. Refer to text page 141.

Review | Critical Thinking Activities The following activities are highly recommended by your teacher. Each activity will allow you to (1) review main concepts; (2) apply what you have learned; and (3) think critically and analytically in such a way that allows you to form your own conclusions in novel applications: Section 5.2 Assessment Questions (textbook pp. 142). Animated Biology Activity: Mitosis Stage Matching Game – accessed via the virtual textbook. Section 5.2 Concept Map: Mitosis – accessed via the virtual textbook at classzone.com. Section 5.2 Virtual Quiz - accessed via the virtual textbook at classzone.com.

8b - describe the cell cycle; AKS Standards: 8b - describe the cell cycle; 9e - compare the advantages of sexual reproduction and asexual reproduction in different situations

Regulation of the Cell Cycle Cell cycle regulation is necessary for healthy growth. Cell growth and division are regulated by both external factors, such as hormones and growth factors, and internal factors, such as proteins known as cyclins and kinases. When proper regulated of cell growth is disrupted, a cell may become cancerous. Cancer cells grow more rapidly than do normal cells and form clumps called tumors that may metastasize to other regions of the body. External factors include: cell-cell contact and growth factors, a group of proteins that stimulates cell division. Internal factors include: responses to external factors using a group of proteins called kinases and cyclins. These two factors help a cell advance to different stages of the cell cycle. When a cell needs to die, apoptosis occurs. This is programmed cell death whereby external and internal factors activate genes that help produce self-destructive enzymes.

Cell Division is Uncontrolled in Cancer Cancer is a common name for a class if diseases characterized by uncontrolled cell division. Cancer cells form disorganized clumps called tumors. Cancer cells come from normal cells that have suffered damage to the genes that help make proteins involved in cell-cycle regulation. These mutations may be inherited, or they may be caused by carcinogens (substances known to produce or promote the development of cancer). http://www.youtube.com/watch?v=Rfm6RJlasj4 In a benign tumor, the cancer cells typically remain clustered together. This means that the tumor is relatively harmless. In a tumor that is malignant, some of the cancer cells can break away, or metastasize, from the tumor and be carried by the bloodstream or lymph system to other parts of the body where they can form more tumors. Standard cancer treatment includes radiation and chemotherapy. Radiation therapy is the use of radiation to kill cancer cells and shrink tumors. It works by damaging a cell’s DNA so much that the cell cannot divide. This type of cancer treatment is usually localized – targeted to a specific region, because it can hurt healthy cells as well. Chemotherapy uses certain drugs, often in combination, to kill actively dividing cells. It can kill both cancerous and healthy, but chemotherapy is not targeted – drugs travel throughout the entire body.

Review | Critical Thinking Activities The following activities are highly recommended by your teacher. Each activity will allow you to (1) review main concepts; (2) apply what you have learned; and (3) think critically and analytically in such a way that allows you to form your own conclusions in novel applications: Section 5.3 Assessment Questions (textbook pp. 147). WebQuest: Skin Cancer– accessed via the virtual textbook. Section 5.3 Concept Map: Cell Cycle Regulation – accessed via the virtual textbook at classzone.com. Section 5.3 Virtual Quiz - accessed via the virtual textbook at classzone.com.

8b - describe the cell cycle; AKS Standards: 8b - describe the cell cycle; 9e - compare the advantages of sexual reproduction and asexual reproduction in different situations

Asexual Reproduction Many organisms reproduce by cell division. Most prokaryotes reproduce through a process known as binary fission, in which a cell divides into two approximately equal parts. This is a type of asexual reproduction whereby the offspring are genetically identical to the parent organism, except when mutation occurs. Advantages of Asexual Reproduction: if favorable environments do not change, asexual reproduction can be more efficient than sexual reproduction. However, asexual reproduction can be a disadvantage in changing conditions because genetically identical offspring will respond to the environment in the same way. Sexual reproduction increases genetic variation, which raises the chance that at least a few individuals will survive or even thrive in changing conditions. BUT – the cost of sexual reproduction is greater. This is because sexually reproducing organisms must attract a mate. This effort involves using energy to find and attract the mate – both of which are timely activities. Organisms that reproduce asexually do not have this cost or time commitment.

Review | Critical Thinking Activities The following activities are highly recommended by your teacher. Each activity will allow you to (1) review main concepts; (2) apply what you have learned; and (3) think critically and analytically in such a way that allows you to form your own conclusions in novel applications: Section 5.4 Assessment Questions (textbook pp. 150). Virtual Lab: Investigating Bacterial Growth – accessed via the virtual textbook. Section 5.4 Concept Map: Asexual Reproduction – accessed via the virtual textbook at classzone.com. Section 5.4 Virtual Quiz - accessed via the virtual textbook at classzone.com.

8b - describe the cell cycle; AKS Standards: 8b - describe the cell cycle; 9e - compare the advantages of sexual reproduction and asexual reproduction in different situations

Multicellular Life Cells work together to carry out complex functions. Within multicellular organisms, cells form tissues, tissues form organs, and organs form organ systems. The cells differentiate to perform specific functions – and much of this specialization is determined by a cell’s location within the developing embryo.

Cell Differentiation Cell differentiation is the process by which unspecialized cells develop into their mature forms and functions. While most cells of the body have a full set of DNA, each type of cell uses only the specific genes it needs to carry out its functions. A cell’s location within the embryo helps determine how it will differentiate.

Stem Cells Stem cells are a unique type of body cell that have the ability to (1) divide and renew themselves for a long period of time, (2) remain undifferentiated in form, and (3) develop into a wide variety of specialized cell types. Stem cells can be classified by their ability, or potential, to develop into the differentiated cell types of different tissues. They can also be classified by their origin, as either adult or embryonic stem cells. Adult stem cells are partially undifferentiated cells located among the specialized cells of many organs and tissues. They are found all over the body. They are also found in children and umbilical cord blood, so the term somatic stem cell is more accurate. Advantage – they can be taken from a patient, grown in culture, and returned to a patient. This reduces transplant rejection and avoids ethical issues. Disadvantage – they are few in number, difficult to isolate, and tricky to grow. They are also likely to contain more DNA abnormalities than embryonic stem cells. Embryonic stem cells come from donated embryos grown in a clinic. These are usually the result of in vitro fertilization. Advantage - they can generally form any of the 200 cell types of the body, can be grown indefinitely in culture and are at the forefront of curing many debilitating diseases. Disadvantage – these cells are often rejected by the immune system as foreign material, can lead to tumor growth if unchecked by normal cell cycle mechanisms, and raise ethical questions because getting embryonic stem cells requires destruction of the embryo.

Review | Critical Thinking Activities The following activities are highly recommended by your teacher. Each activity will allow you to (1) review main concepts; (2) apply what you have learned; and (3) think critically and analytically in such a way that allows you to form your own conclusions in novel applications: Section 5.5 Assessment Questions (textbook pp. 155). Section 5.5 Concept Map: Multicellular Life – accessed via the virtual textbook at classzone.com. Section 5.5 Virtual Quiz - accessed via the virtual textbook at classzone.com. Reviewing Vocabulary & Main Ideas (textbook pp. 159). Critical Thinking & Connecting Concepts (textbook pp. 160) GEORGIA Standards-Based Assessment (textbook pp. 161).