Notes 16-18 February
Notes 16-18 February BIO 151
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This 8 page Class Notes was uploaded by Chelsea Notetaker on Sunday February 21, 2016. The Class Notes belongs to BIO 151 at Central Michigan University taught by Professor Learman in Winter 2016. Since its upload, it has received 17 views. For similar materials see Human Biology in Biology at Central Michigan University.
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Date Created: 02/21/16
16 February 2016 Cell Origins > The perpetuation of life depends on accurate cellular replication > Eukaryotic Multicellular organisms depend on cell division for: development from fertilized cells, frowth, repair, reproduction > Prokaryotes and one-celled eukaryotes rely on division only for reproduction > Interphase – prepares the cell to divide -G1 – cell grows and performs normal functions > Synthesis – DNA replication, so there’s two of every chromosome (S Phase creates sister chromatids) - Chromatid – one piece/finger of a chromosome > G2 – cells grows in preparation for division, doubles everything in its cytoplasm > Division – separates all materials and divides, caused by actions of the cytoskeleton and associated motor proteins - Cytokinesis – separation of identical cells, the last step of division > Mitosis – creates exact copies of the same cell – for growth and development of the body, in somatic cells – maintenance/repair > Meiosis – reorganizes the genetic composition of the cells and reduces the number of chromosomes in the nucleus by half – for sexual reproduction, eggs and sperm, each one genetically unique > Mitosis starts with one 46-chromosome cell, copies all DNA, and separates once for two identical 46-chromosome cells > Cell division: chromosomes condense in center of the nucleus, nucleic membrane breaks down, mitotic spindle attaches to chromosomes. Spindle moves chromosomes to a line in the center, sister chromatids separate, nucleic membranes reform, cell divides. - Mitotic Spindle – chromosome movements are based on these movements of the cytoskeleton Class Activity Indicate how many chromosomes are in the cell at each time: Interphase G1: S Phase: G2: Mitosis during duplication: After Cytokinesis: > 46, 92, 92, 92, 46 > Mitosis is how humans grow and develop from a zygote to an adult - Zygote – fertilized egg cell > Humans have about 220 different kinds of cell, and all have the same DNA - Gene expression is what categorizes the cells, and the proteins that are made and used. The genes expressed in each cell determine its function > Acell with a specific job is a differentiated or specialized cell > Early in development cells have the potential to be any kind of body cell – these are called stem cells > As the embryo develops it becomes specialized – once it has specialized it cannot change or revert > For specialization some genes not needed by the cell are inactivated – only the genes needed for the cell to do its job are active. Even active genes are not active all the time. Class Activity Consider skin cells and nerve cells from the same adult. With each criterion, are the cells the same/identical or different? Size/Shape: Chromosomes Present: Genes Present: Genes Expressed: Proteins Present: > different, identical, identical, different, different >Development for humans begins after fertilization – sperm gamete (23 chromosomes) and egg gamete (23 chromosomes) have joined. The resulting zygote has 46 chromosomes, and is called a precursor cell that will eventually divide to produce all the other cells in an adult human. > Adult humans contain ~40-100 trillion cells > Stages of human development are only ‘successful’ if the environment is appropriate – hormones present/sensed and conditions > Conception to birth takes about 266 days > Postnatal/adulthood is reached in 20-25 years after fertilization > Prenatal – characterized by rapid mitosis and cell specialization > Pre-embryonic – fertilization to ~ 2 weeks > Embryonic – 3-8 weeks, early differentiation for organ systems > Fetal – 9 weeks to birth, more rapid growth 18 February > Immediately following fertilization the zygote undergoes rapid mitotic division, called cleavage, forming a solid sphere of cells: morula > ~ Day 4: blastocyst – sphere of cells with a cluster of cells inside, the cell mass, that will become the human body > ~ Day 6: blastocyst implants into mother’s uterus, forming the pre-embryo - 1/3 to ½ of zygotes don’t implant (because of a chromosomal abnormality, pH is incorrect, intrauterine environment isn’t correct) > Eggs come from the ovary, travel through the fallopian tube toward the uterus, where fetus occurs (must implant in uterus for full-term pregnancy) > ~2-12 weeks: placenta forms from extra-embryonic membrane, surrounding the embryo - Provides oxygen and nutrients, carries away CO2 and wastes - No direct mixing of maternal and fetal blood --- Some drugs, toxins and viruses can cross from mother’s blood to fetus’s > ~8-10 weeks: Embryo becomes fetus at 9 weeks; organ systems have almost fully formed > Pregnancy is organized into trimesters – becoming 40 weeks all told though development is typically only 38 weeks. The extra two weeks are counted prior to fertilization, to roughly when the egg was released. st > 1 Trimester – 0-12/14 weeks: lungs starting to form > 2 ndTrimester - ~13-24 weeks: if born at 24, baby might survive, though lungs are rudimentary > 3 Trimester - ~24-40 weeks: fetus has light sensitivity, taste buds, and fully formed lungs > Cell death is also important – Apoptosis – regulated by the cell, assists in development and maintenance. For example fingers start out webbed, and embryos start out with a tail. Potential Problems > Spontaneous abortion/miscarriage -Embryo suddenly stops development and is expelled -Usually because of chromosomal abnormalities -~30% of recognized pregnancies end this way (85% happening in the first trimester; after 20 weeks it is considered a stillbirth) > Implantation Position – should be high on the back of the uterus - Ectopic – implantation occurs in fallopian tubes - Placenta previa – implantation is too low in uterus (can cause hemorrhage, placenta blocks baby’s exit - Placental abruption – placenta detaches from uterus (can deprive baby of oxygen/nutrients and cause heavy bleeding in mother [who may not be aware of it]) > Birth defects – improper development, can be genetic or caused by exposure to environmental agent: - Tetragen – environmental, a mutagen - Alcohol – 2/1000 of birth defects caused here - Retinoids – cause excess vitamin A, used for acne (contains Accutane), is very hazardous * The critical period is 3-8 weeks after fertilization, when the embryo is most vulnerable Class Activity Some medications are considered unsafe for use during pregnancy, but some are considered safe after the first trimester. Why might this be? > Different things are developiong at different times. The critical period is in the first trimester. Also the medication may only affect heart development, but the heart starts development early. In the second trimester it isn’t as easy to damage. The organs are more sensitive in their early development. > Karyotype – image of chromosomes arranged by a computer into descending-size order > Autosome – non-sex chromosome > We inherit one version of each chromosome from each parent, forming homologous chromosome pairs > Human somatic cells have 46 chromosomes (formed by mitosis) > Gamete cells have 23 chromosomes (formed by meiosis) - Meiosis ‘reshuffles’ its chromosomes and creates a unique set of chromosomes every time it divides. >Meiosis: Interphase (Mom’s and Dad’s chromosomes duplicate), meiotic division (chromosomes scramble, then separate), cytokinesis, second meiotic division, second cytokinesis Class Activity Complete the following table: > *3 if you count the divisions of the first round of daughter cells, after the first division Functions of Mitosis: in somatic cells, development and maintenance. Functions of Meiosis: for genetic variety, to produce gametes **Remember we’ve got homework due on the 25 of February, this Thursday.