Unit 4 Notes
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This 6 page Class Notes was uploaded by Danielle Francy on Thursday April 7, 2016. The Class Notes belongs to Bio 190 at Towson University taught by Joseph Velenovsky in Fall 2015. Since its upload, it has received 27 views. For similar materials see Intro Biology for Health Professions in Biology at Towson University.
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Date Created: 04/07/16
Unit 4 Notes Cells must divide because: ● Growth ● Replacement of damaged cells ● Development embryo into an adult organism Cellular reproduction or Cellular division: ● Daughter cells ● Genetically identical ● No implied gender ● Parent cell duplicates chromosomes ● Each daughter cell receives a set Asexual Reproduction: ● No sperm or egg involved ● Not just singlecelled organisms ● Sea stars fragmented parts ● Plants growing from a clipping ● Parent and offspring identical in terms of genetic makeup ● One parent cell ● Is mitotic division ● Parent no longer exists after reproduction ● Minimal genetic variation ○ Mutation(primarily, but rare) Sexual Reproduction: ● Fertilization of an egg by a sperm ● Gametes= egg and sperm ● Testes and ovaries ● Meiosis ● Only half as many chromosomes as parent cell ● Diploid(2n) ● Haploid(n) ● Unique combination of genes ● Crossing over ● Not identical to parents or siblings ● Identical twins ● Two parents(multicellular organisms) ● Parents still exist after reproduction ● Requires: ○ Meiotic division ■ Each parent produces a gamete(half genetic info) ○ Fertilization(Gamete fusion) ■ Gametes fuse together to create a new individual with mixture of maternal and paternal genetic info Diploid vs Haploid: Diploid: ● Number of chromosomes in a body cell ● Characteristics of a species ● Always even number because chromosomes occur in pairs ● Both homologous chromosome members of each pair present in the cell Haploid: ● Number of chromosomes in a gamete ● One half the diploid number, but not just any half ● Only one member of each type/pair present ● When two haploid cells fuse, the diploid state is restored Homologous Chromosome Pairs: ● Each body/somatic cell contains two copies of each human chromosome/DNA molecule ● Are present in all stages of cell cycle ○ G1, G0, S, G2, MP, M,A,T,C ● Can be in chromatin (fully extended) or chromosomes (fully compacted) form depending on stage of cell cycle ● Can be replicated or unreplicated ● These two copies are: ○ A pair ○ “Homologous” because they have: ■ Same length ■ Same centromere position ■ Same sequence of genes, but… ■ Not necessarily same “variants” (alleles) for each gene because each member of the pair is from a different parent ● Same length, same centromere position, and same sequence of genes because they are the same chromosome ● Not same sequence of alleles because ○ One= maternal (a, b, c, d, e, F) ○ One= paternal (a, B, C, D, e, f) ● Never attached at centromere Sister Chromatids: ● Each= one side (one half) of a replicated chromosome ● Each contains one of the 2 daughter DNA molecules made during the S phase ● Are identical in both gene and allele sequence ● Always held together by the centromere ● When separated at anaphase, they become independent chromosomes Development: ● Zygote into an adult Renewal and Repair: ● Cells that die from normal bodily processes and accidental damage ● Replacement of damaged or lost cells Prokaryotes (bacteria and archaea): ● Single circular DNA molecule ● One chromosome when combined with associated proteins ● ***HU protein ● Histones ● Much smaller than eukaryotic chromosomes because there are no introns ● About twice the original size because there are two daughter cells ● Plasma membrane grows inward; more cell wall is made ● Separation ● Before true nucleus ● Evolutionary earlier ● DNA is circular; no limiting membrane; nucleoid Eukaryotes (eukarya): ● More complex and larger ● More genes ● 21,000 genes human ● 3,000 genes bacterium ● Nucleus, exception mitochondrial and chloroplastic ● Most of the time exist as chromatin ● Longthin fibers ● DNA and histones ● True nucleus; membrane enclosed ● Evolved from prokaryotes ● DNA is linear and paired; within the nucleus; true nucleus ● Larger ribosomes than prokaryotes Preparing to Divide: ● Chromatin coils up into chromosomes ● It must coil because DNA must be compacted into a structure that is easily moved ● Histones ● Chromosomal structure and gene regulation ● The number of chromosomes varies widely among eukaryotes ● Humans46 ● Dogs78 ● Meaning, species specific ● Prokaryotic1 DNA Replication: ● Chromosomes duplicated when in chromatin form ● Condense and cellular division ● Sister chromatids ● Identical ● Joined at the centromere ● Once sister chromatids separate, they’re called chromosomes ● Identical to the chromosome that started the process ● One copy to each daughter cell ● Each daughter cell complete and identical set ● 46 single chromosomes in each daughter cell; human ● 23 pairs of chromosomes Cell Cycle: ● Cell division component of cell cycle ● Cell formation up until division into two daughter cells ● Cycle repeats ● Interphase(growing) ● Mitotic phase(actual cell division) ● Interphase is most of the cell cycle ● Metabolic activity is high ● Cell functioning greatly ● Intestinal cells release digestive enzymes and absorb nutrients ● Cytoplasm is produced ● Increased protein production ● Increases organelle production (cytoplasmic) ● Grows in size ● Chromosomes duplicate ● 90% of total cell cycle time Three Subphases: 1. G1 phase 2. S phase 3. G2 phase ● First gap ● Second gap ● Cell grows during all three ● Chromosomes duplicated during S phase ● Synthesis of DNA(S phase) DNA replication ● At the end of S phase, chromosomes are doubled ● 92 sister chromatids ● Growth duplication, growth M Phase ● 10% of time during cell cycle ● Mitosis and cytokinesis ● Nucleus and its contents (duplicated chromosomes) divide ● Two daughter nuclei ● Cytokinesis is divided in two ● Two genetically identical daughter cells ● Single nucleus ● Cytoplasm; organelles ● Plasma membrane ● Each daughter cell begins the cell cycle in the first gap ● Mitosis unique to eukaryotes ● Accurate ● Yeast; error late 1 in 100,000 cell divisions ● Development of human body ● Single cell ● Fusion of mother’s egg and father’s sperm ● Mitotic division results in embryonic growth ● About 10 trillion cells trace ancestry to first cell Interphase: ● Animal cell ● Cell growth ● Synthesize new molecules and organelles ● Late interphase (G2) doubled much of its contents ● Two centrosomes (microtubuleorganizing centers) found in cytoplasm ● Each centrosome one pair of centrioles (microtubules) ● Chromosomes are duplicated but are still in chromatin form (cannot tell individual chromosomes apart) Prophase: ● Changes in the nucleus and cytoplasm ● Formation of discrete chromosomes (folding and coiling) ● Two identical sister chromatids joined together at centromere ● Different from centrosome and centrioles ● Mitotic spindle begins to form (early mitotic spindle) ● Microtubules grow out of the centrosomes ● Centrosomes (2) move away from each other Prometaphase: ● Nuclear envelope breaks down ● Microtubules from centrosomes are present at the poles (ends) of the mitotic spindle ● Microtubules reach the chromosomes which at this point are higher condensed ● Within the centromere region, each sister chromatid has a kinetochore ● This protein structure attaches to a portion of the microtubules from the mitotic spindle(both poles) ● This attachment causes the chromosomes to begin an agitated motion ● Other microtubules (not attached to kinetochores) contact microtubules that have extended from the opposite pole ● ***Protein motors (enzymes called kinesins use ATP) associated with spindle microtubules move the chromosomes toward the center of the dividing cell ● Kinesins similar to myosin ● ***Dynein also involved; a separate motor protein complex ● Kinesins and Dynein work together Metaphase: ● Mitotic spindle fully formed and functional ● Poles are completely at opposite ends of the cell ● Chromosomes converge on the metaphase plate Definitions: Histones: Highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. Chromosome: Thread like structures located inside the nucleus of plant and animal cells. Chromatid: One half of two identical threadlike strands of a replicated chromosome Chromatin: A complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Kinesins: Move along microtubule filaments. Protein belonging to a class of motor proteins found in eukaryotic cells.
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