BIOL 1030 Introduction to Biology: Organismal Biology. Fall 2009 Sections B & D Steve Thompson: stthompson@valdosta.edu http://www.bioinfo4u.net 1
The cell cycle and mitosis Now that we ve seen how DNA replicates, let s put it in context within the cell. And we ll get to the exam review at the end of the lecture today. 2
Cells divide and cells die. Each of an organism s cells (except red blood cells) retains the genetic information present in the fertilized egg (or parental cell for asexual reproduction). Every cell in an organism results from countless rounds of cell division. Cells also die in predictable ways. This is known as apoptosis (also called programmed cell death). Cell death is a normal part of development; a necessary part of life. Cell division and cell death must be in balance, or the organism dies. 3
Chromosome duplication The entire genome must be duplicated before cell division can occur. In prokaryotic cells, the genome is often a single circular DNA molecule. However,... In eukaryotic cells, the genome is divided and packaged among multiple chromosomes, all housed in the nucleus. For example, humans have 46 (23 pair), chickens 78 (39 pair, including microchromosomes ), rice 24 (12 pair), and zebrafish 50 (25 pairs) chromosomes. 4
Eukaryotic chromosomes Stretched end to end and unpackaged all the DNA in a human cell would be over two yards long. Chromatin DNA plus histone packaging and other associated proteins. Nucleosomes stretch of DNA wrapped around histones ( beads on a string ). Chromatin is barely visible when the cell is not dividing and the chromosomes have not condensed. So, much of the time... DNA is loosely packed and accessible for cellular activities like making RNA and more DNA. 5
We saw a nucleosome earlier. One more time: http://molbio.info.nih.gov/cgi-bin/moldraw?1eqz 6
And in preparation for cell division, it all packages up into chromosomes. DNA condenses into visible chromosomes before cell division. Chromatid one of two identical copies of a replicated chromosome. 7 Sister chromatids pair with identical DNA sequences. Centromere point of attachment.
Know the vocabulary. 8
Karyotype Most human cells have 46 chromosomes. 23 from each parent. Somatic or body cells. Diploid 2 full sets of genetic information. Pair members look alike (not genetically identical). Except sex chromosomes, X and Y. Produced by mitosis. 9 Sperm and egg cells (gametes) are haploid. They have 23 total chromosomes. Produced by meiosis in germ cells in testes and ovaries.
The Cell Cycle Includes all the events between one cell division and the next. Two major stages: Interphase cell not dividing but it is very active. Cell division mitosis and cytokinesis. 10
Here s another view No stage is discrete; they all blend from one the the next. 11
And an animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/ chapter2/animation how_the_cell_cycle_works.html 12
Interphase Very active time in cell cycle. G1 (gap 1) cell grows and carries out basic functions. Signals tell cell to divide, stop for repair of DNA, die or enter G0, a quiescent stage. S (synthesis) genetic material (DNA) replicates. G2 (gap 2) cell prepares to divide and chromosomes begin to condense. 13
Mitosis Overall, it separates the replicated genetic material from the S phase evenly between two daughter cells. The mitotic spindle pulls each half to each new cell. Centrosomes organize the mitotic spindle in many animal cells. Kinetochores attach the chromosomes to the spindle. 14
Again, the vocabulary matters 15
Here are the parts 16
And an animation http://highered.mcgraw-hill.com/olc/dl/120073/bio14.swf 17
The steps (but, remember, they re really not discrete steps) Prophase chromosomes condense, mitotic spindle begins to form. Prometaphase kinetochores grow on centromeres, nuclear envelop breaks down. Metaphase chromosomes line up on mitotic spindle on equator. Anaphase centromeres split, one chromatid of each pair pulled to opposite pole. Telophase mitotic spindle disassembles, chromosomes begin to unwind, nuclear envelope reforms. And the silly way I memorized it way back when: Prophase meta Anaphase, and called her up on the Telo, and said Hey, let s Interphase! 18
And in more detail 19
Continued 20
Cytokinesis Animal cells cleavage furrow results from contractile ring. Plant cells construct a new cell wall. 21
Cell cycle regulation Some cells divide more or less constantly, e.g. stem cells in bone marrow. Cells need to know whether to divide or not. The chemical signals to divide usually come from outside the cell. Growth factors proteins that stimulate cell division. Checkpoints ensure the cell does not enter the next stage until the previous stage is complete. 22
Here s some of the important checkpoints in the cell cycle. 23
And in animation http://highered.mcgraw-hill.com/sites/0072495855/ student_view0/chapter2/animation control_of_the_cell_cycle.html 24
Telomeres a cellular clock Located at tips of eukaryotic chromosomes They lose nucleotides and become shorter at each cell division. Cell division stops after about 50 cell divisions due to telomere loss. Some cell types express telomerase; it adds DNA to the telomeres, which... Allows cells to go beyond 50 divisions. It s present in some normal cells, e.g. sperm germ cells, intestinal lining cells, plant meristem tissue, and in most cancer cells. 25
Here s what happens 26
Cancer! Has affected most everybody s lives. Tumor an abnormal mass of tissue. It forms when the body somehow loses control of the balance between cell division and cell death. Benign tumor is usually slow-growing and harmless. Malignant tumor invades other tissues (metastasize) cancer. 27
Cancer cells are different. They: Are not normal cells; Look different; Essentially immortal; May produce their own signals to divide; Lack contact inhibition; May not undergo apoptosis when damaged; Send signals to stimulate growth of blood vessels. 28
Normal marrow cells on right versus leukemia cells on the left 29
Causes of cancer It is NEVER contagious, though some viruses can cause cancer, e.g. HPV (human papilloma virus). Oncogenes are abnormal variants of genes that normally control cell division. You may inherit them, or they may mutate within your body due to carcinogens. They may accelerate the cell cycle and cause cancer. Tumor suppressor genes encode proteins that normally block cancer development, e.g. BRCA1 & 2 (breast cancer 1 & 2). They promote normal cell death or prevent cell division. Inactivation, deletion, or mutation can cause loss of function. Again, this can be inherited or a somatic mutation. Harmful chemicals, radiation, and viruses can all alter DNA. There are many risk factors, such as poor diet, lack of exercise, sun overexposure, and smoking can increase the chance of getting cancer. 30
Here s a schematic of the two genetic pathways 31
Cancer treatments Include: Selective surgical tumor removal. Chemotherapy and radiation, which target ALL rapidly dividing cells both cancerous and healthy. The death of healthy cells cause side effects. New more targeted drugs home in on receptors for growth factors. Early detection key to successful treatment. 32
Cell death/apoptosis Two main functions: Eliminates excess cells to carve out functional structures like fingers and toes. Weeds out cells that might harm the organism. Apoptosis must be overcome for mitosis to occur. For example, many critters lose the webbing between their toes, others don t. 33
Killer enzymes dismantle the cells destined for death Caspases apoptosis specific enzymes. Triggered when death receptor protein receives signal. Cuts apart cell s proteins and destroys cell. 34
And now the sad story; 1030B Count 40 35 30 25 20 Count 15 10 5 0 0-10% <10-20% <20-30% <30-40% <40-50% <50-60% <60-70% <70-80% <80-90% <90-100% 35
And it continues; 1030D Count 50 45 40 35 30 25 Count 20 15 10 5 0 0-10% <10-20% <20-30% <30-40% <40-50% <50-60% <60-70% <70-80% <80-90% <90-100% 36
Here s some of the concepts that most of you blew: Acids add H + (ph < 7); Bases add HO - (ph > 7). Ionic bonds are formed between ions of opposite charge and are quite strong, as long as no water, e.g. table salt. RNA has the nitrogenous bases A, C, G, and U (not T). Endosymbiosis supported by mitochondrial and chloroplast genomes being similar to bacterial genomes. The endoplasmic reticulum has nothing to do with mrna production; it uses mrna in ribosomes to make proteins. Enzymes lower a reaction s activation energy. In competitive inhibition a substance blocks the active site by competing for it; in noncompetitive inhibition a substance binds to some other site that shuts it down. Oxidation is the loss of electrons, reduction the gain. Glucose + O2 respiration CO2 + H2O + ATP The Krebs Cycle begins with Acetyl-CoA. 37
And they just keep coming. The electron transport chain occurs in mitochondria in Eukaryotes, in the cell membrane in prokaryotes. The electron carriers of respiration are NADH and FADH2, which are used by the proton pump proteins of the electron transport chain in the inner mitochondrial membrane to establish a chemiosmotic proton gradient. Oxygen is the final electron acceptor of the electron transport chain. Fermentation only uses glycolysis. Photosynthesis has two components the light reactions, and the carbon (or light-independent) reactions. Photosystem I and II are part of the light reactions of photosynthesis; II ATP and I NADPH. They are located in the chloroplast thylakoid membranes. Leaves are green because photopigments reflect green wavelengths of light, not absorb it! Sunlight + H20 light reactions + ATP carbon reactions glucose! O2 is the waste product of the light reactions; CO2 is input for the carbon reactions the carbon is fixed into glucose. 38