General Bio week 9 notes
General Bio week 9 notes 1005
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This 6 page Class Notes was uploaded by Megan Wiggs on Monday October 17, 2016. The Class Notes belongs to 1005 at Virginia Polytechnic Institute and State University taught by MV lipscomb in Fall 2016. Since its upload, it has received 4 views. For similar materials see General Biology in Science at Virginia Polytechnic Institute and State University.
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Date Created: 10/17/16
How DNA is Arranged in the Cell - DNA is a working molecule - Must be replicated when cell is ready to divide - DNA is protected and packaged in very specific ways - The DNA must be packaged in a very ordered way to fit and function within a structure - Proteins and enzymes help maintain supercoiled structure of DNA 6.1 Genomic DNA A cells complete compliment of the DNA is called its genome Prokaryotes: - Genome is composed of a single, double stranded DNA molecule in the more of a loop or circle - Nucleoid contains genetic material - Some prokaryotes have smaller loops of DNA called plasmids that are not essential for normal growth Eukaryotes: - Genome comprises several double-stranded, linear DNA molecules bound with proteins to form chromosomes - Characteristic # of chromosomes in the nuclei of its cell - Human body: 46 - Somatic: 2 matched sets, called diploid 2n o Matched pair in a diploid are called homologous chromosomes Same length and have specific nucleotide segments called genes - Human cells that contain 1 set of 23 chromosomes are called gametes, or sex cells - Eggs and sperm are designated n, or haploid Genes are segments of DNA that code for a specific protein or RNA molecule - Traits are determined by genes - Genes are inherited from each parent, but also environment - Genes are expressed as characteristics and may have different variants called traits: caused by different DNA sequences diploid describes a cell, nucleus, or organism containing two sets of chromosomes (2n) gamete a haploid reproductive cell or sex cell (sperm or egg) gene the physical and functional unit of heredity; a sequence of DNA that codes for a specific peptide or RNA molecule genome the entire genetic complement (DNA) of an organism haploid describes a cell, nucleus, or organism containing one set of chromosomes (n) homologous chromosomes chromosomes of the same length with genes in the same location; diploid organisms have pairs of homologous chromosomes, and the members of each pair come from different parents locus the position of a gene on a chromosome 6.2 The Cell Cycle - An ordered series or events involving cell growth and cell division that produces 2 new daughter cells Interphase: the cell grows and the DNA is replicated - 3 stages of interphase are called G1 phase, S2, a d G2 - most time spent G1 Phase - 1 step of interphase - little change is visible - cell is quite active at the biochemical level - accumulating building blocks of chromosomal DNA & associated proteins & energy reserves to complete the task of replicating S phase - synthesis phase - replication results in 2 identical copies of each chromosome sister chromatids - centrosome is duplicated o 2 centrosomes will give rise to the mitotic spindle G2 Phase - second gap - cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation - may be additional cell growth - final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis Mitotic Phase: replicated DNA and cytoplasmic contents are separated & the cell divides st - mitosis is the 1 portion of the mitotic phase o composed into 5 stages, which accomplish nuclear division - cytokinesis is the 2 nd portion of the mitotic phase o physical separation of the cytoplasmic components of the 2 daughter cells Mitosis - prophase, prometaphase, metaphase, anaphase, & telophase—result in the division of the cell nucleus - Prophase: o nucleus disappears o centrosomes begin to move to opposite poles of the cell o sister chromatids begin to coil more tightly & become visible under a light microscope - Prometaphase o Formation of a connection between the chromosomes and cytoskeleton o Remnants of the nuclear envelope disappear o Chromosomes become more condensed & visually discrete o Mitotic spindle continues to develop o sister chromatid attaches to spindle microtubules at the centromere via a protein complex called the kinetochore. - Metaphase o Chromosomes are aligned in a plane called the metaphase plate, midway between the 2 poles of the cell o Sister chromatids are still tightly attached to each other o Chromosomes are maximally condensed - Anaphase o Sister chromatids at the equatorial plane are split apart at the centromere o Each chromatid, now called a chromosome, is pulled rapidly toward the centromere o Cells becomes visibly elongated - Telophase o events that set up the duplicated chromosomes for mitosis during the first three phases are reversed. o Chromosomes reach opposite ends and begin to unravel o Mitotic spindles are broken down into monomers that will be used to assemble cytoskeleton components for each daughter cell o Nuclear envelopes form around chromosomes Cytokinesis 2ndpart of mitotic phase which cell division is completed by physical separation of the cytoplasmic components into 2 new daughter cells Control of the cell cycle - length is highly variable even within the cells of an individual organism Regulation @ Internal Checkpoints - essential that daughter cells be exact duplicates of the parent cell - To prevent a compromised cell from continuing to divide internal control mechanisms that operate at three main cell cycle checkpoints which the cell cycle can be stopped until conditions are favorable o G1 Checkpoint determines whether all conditions are favorable for cell division to process Aka restriction point: cell irreversibly commits to the cell division process Check for damage to the DNA Cell that doesn’t meet all requirements will not be released into the S phase Grow o S phase Stop growing & Copy the DNA o G2 Bars the entry to the mitotic phase if certain conditions are not met Size and protein reserves are assessed Ensure all the chromosomes have been replicated & that the replicated DNA is not damaged Continue to grow o M Near the end of the metaphase stage of mitosis Aka spindle checkpoint b/c determines if all sister chromatids are correctly attached to the spindle
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