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Genetics Chapter 2: Chromosomes and Cellular reproduction

by: Adam Reinstein

Genetics Chapter 2: Chromosomes and Cellular reproduction PCB 3063

Marketplace > Florida Atlantic University > GENE - Genetics > PCB 3063 > Genetics Chapter 2 Chromosomes and Cellular reproduction
Adam Reinstein

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About this Document

These notes are made for Dr. David Binninger's Genetics class. The information came from in class notes, the textbook and from Dr.Binninger's powerpoints.
David M. Binninger
Class Notes
Genetics, Biology
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This 11 page Class Notes was uploaded by Adam Reinstein on Saturday September 3, 2016. The Class Notes belongs to PCB 3063 at Florida Atlantic University taught by David M. Binninger in Fall 2016. Since its upload, it has received 11 views. For similar materials see Genetics in GENE - Genetics at Florida Atlantic University.


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Date Created: 09/03/16
Genetics chapter 2    I. Prokaryotes and Eukaryotes A) Prokaryotes are unicellular organisms with a fairly simple cell  structure i. There are two fundamentally distinct types of prokaryotes: 1) Eubacteria­ true bacteria  2) Archaea­ “Ancient bacteria” that are evolutionarily closer to eukaryotes the eubacteria  B) Eukaryotic cells are compartmentalized by intracellular membranes  (aka have a nucleus) i. May be unicellular or multicellular II. Nucleus  A) The nucleus is a Eukaryotic organelle that separates a cell’s DNA  from the rest of the cell i. Transcription (RNA synthesis) in Eukaryotes is physically  separated from translation (protein synthesis) B) Prokaryotes do NOT have a nucleus  i. As a result of this, transcription and translation occur in the  same compartment C) These differences affect gene regulation  D) The structure of how DNA is contained in these cells dictates its  function III. Eukaryotic DNA A) Eukaryotic DNA uses a class of proteins called histones to form tightly packed chromosomes.  B) Chromatin­ a complex of Histones and DNA C) Histones help to keep the DNA tightly packed within the nucleus  Chromosomes D) Bacteria usually have a single circular chromosome E) Eukaryotes have multiple chromosomes that each have a single linear  DNA molecule F) replicating and distributing chromosomes to a new cell during cell  division is more complex in eukaryotes IV. Viruses A) Simple non­living structures composed of an outer protein coat and  DNA or RNA (but NOT both!) B) Viruses need a host cell to reproduce  i. This implies that viruses evolved after cells because they cant  reproduce without their host cell ii. The genes of viruses are more closely related to their host and  not to each other V. Cell Reproduction A) Three critical steps i. Accurate replication if the DNA ­9  1) Typical error rate is approximately 10  or 1 error per  billion nucleotides ii. A complete copy of the genome must be separated to different  regions of the cell iii. Cell must divide B) Prokaryotic Cell Reproduction  is rapid  i. Can possibly divide once every 20 mins, which can lead to 1  billion  VI. Plasmids A)   Common in bacteria; very rare in eukaryotes B)   Circular self­replicating DNA molecules C)   Small compared to the main chromosome D)  Contain bacterial genes i.  F­factor in E. coli is a plasmid required for conjugation  (genetic exchange) E)   Many plasmids carry genes for antibiotic resistance VII. Eukaryotic Cell Reproduction A) DNA is distributed among multiple chromosomes B)  Chromosomes are separated from the cytoplasm by the nuclear  envelope C)  Nucleus has an extensive crisscrossing network of protein fibers  called the nuclear matrix i. The nuclear matrix takes part in DNA replication, gene  expression, and modification of gene products D)  Eukaryotic Chromosomes i. Each species has a characteristic number of chromosomes per  cell ii.  Cannot predict the number of chromosomes based on  complexity of the organism iii.  All somatic cells have two sets of chromosomes: One maternal, the other paternal VIII. Ploidy  A) The number of sets of genetic info is the cells ploidy B) Haploid­ a single set of chromosomes C) Diploid­ two sets of chromosomes i. Two nearly identical chromosomes form a homologous pair ii. Each diploid cell has two copies of each gene.  iii. Different forms of the gene are called alleles D) Polyploid­ more than 2 sets of chromosomes IX. Chromosome Structure A) Each chromosome consists of a single DNA molecule that is  extensively coiled B)  During most of the cell cycle, the chromosomes are diffuse­ chromatin C)  Just before cell division, condense further to form the distinctive  characteristics of individual chromosomes X. Chromosomes have 3 essential parts to them: A) A centromere  i. This is an attachment site for the spindle microtubules ii.  Responsible for pulling chromosomes to the edges of the cell  during cell division iii.  Kinetochore forms on the centromere (specific DNA sequence) and is the attachment site of the spindle microtubules iv.  Lack of a centromere leads to chromosome loss which is usally fatal  v. The location of the centromere classifies chromosomes by 4 types 1) Submetacentric  2) Metacentric 3) Telocentric  4) Acrocentric  B) A pair of  telomeres i. Special structure on the end (terminus) of the chromosome ii.  Required for chromosome stability iii.  May play a role in controlling cell division and possibly aging and cancer C) Origins of Replication  i. These are the sites where DNA synthesis begins  ii. Each chromosome must be duplicated prior to cell division iii.  After DNA Replication there are two identical copies—Called sister chromatids—held together at the centromere iv.  Each chromatid contains a single DNA molecule XI. Cell Cycle and Mitosis A) Process that passes an exact copy of the genetic information from a parent cell to two new daughter cells B) Checkpoints occur at critical transition steps along the cell cycle XII. Interphase A) Majority of the cell cycle when growth, differentiation and  preparation for cell division occurs B) Three sub­phases of interphase G , S, 1 2 i. G =1 ell growth and synthesis of proteins needed for cell  division are made, this lasts several hours ii.  G1/S checkpoint is critical, the cell waits in G  1ntil it has all  the enzymes needed for DNA Replication  iii.  Cell may exit the cell cycle (G0) if conditions are not favorable iv.  If cell continues past G1/S checkpoint, it is committed to cell  division C) G P0 se This is a non­dividing phase that can arise if the  environment is unsuitable, the cell can remain here for long periods of time or in some cases indefinitely  D) S Phase i. DNA Synthesis ii.  Each chromosome is duplicated iii.  Before S phase, each chromosome is one chromatid iv. After S phase, each chromosome is composed of two  chromatids v.  Blocking DNA synthesis (due to drugs or a mutation) stops  further advancement in the cell cycle E) G P2 se  i. Additional events occur in preparation for cell division ii.  Critical G2/M checkpoint must be passed before entering  mitosis (M phase), this check point ensures that the cell’s DNA  is completely replicated and undamaged  XIII. Six Stages of Mitosis A) Prophase i. Chromatin begins to condense ii. Chromosome structure becomes visible with the light  microscope iii. Mitotic spindle develops from a pair of centrosomes in animal  cells iv. Some plants do not have centrosomes or centrioles v. Centriole is a specialized organelle within the centrosome B) Prometaphase i. Nuclear membrane disintegrates ii.  Spindle microtubules enter the nuclear region iii.  Microtubules attach to the kinetochore of one of the sister  chromatids iv.  Microtubules from the opposite side of the cell attach to the  kinetochore of the other sister chromatid C) Metaphase i. Chromosomes align in a single line called the metaphase plate ii.  Spindle­assembly checkpoint establishes that each  chromosome has spindle fibers attached from opposite poles of  the cell D) Anaphase i. Anaphase begins as the chromosomes start moving toward  opposite poles of the cell ii.  The centromere splits and the two sister chromatids become  separate chromosomes E) Telophase i. Chromosomes reach the spindle poles ii.  Nuclear membrane reforms around the chromosomes iii.  Chromosomes decondense iv.  Cytoplasm divides – cytokinesis F) Chromosome movement i. Microtubules are composed of subunits of tubulin  ii.  Microtubules have polarity iii.  Special proteins function as molecular motors to disassemble  tubulin subunits G) Changes in chromosome number and DNA during the cell cycle XIV. Summary of Mitosis A) Produces two genetically identical copies of a cell B)  Each cell has the complete set of chromosomes C)  Each cell has about half the cytoplasm and organelles D) Mitosis produces two cells with the same number of chromosomes E)  Cytoplasmic content is divided unevenly therefore the two cells   NOT exactly the same (in cytoplasmic content, otherwise genetically   identical) XV. Meiosis A) Specialized form of cell division B) Meiosis reshuffles the parental genes among their progeny C) Driving force in evolution D) Meiosis produces cells with 50% of the normal number of  chromosomes (haploid product) E) Fertilization restores the normal chromosome number F) Unlike Mitosis, meiosis has two nuclear divisions, not just one. i. Separated into meiosis I and meiosis II G) Meiosis produces four cells with half of the normal chromosome  number H) Meiosis produces cells with genetic variability I) DNA replication (S phase) occurs before cell division J) During prophase I, synapsis occurs  i. synapsis­ 2 pairs (4 chromatids) of homologous chromosomes  form a bivalent or tetrad. (see image below) K) Crossing over occurs on the tetrad  i. Genetic Recombination/crossing over: when homologous  chromosomes exchange genetic info (see image below) ii. This is the main source of genetic variation  L) Anaphase I is similar to anaphase in mitosis, except we are pulling  apart the tetrad, NOT the sister chromatids M)Meiosis II is functionally equivalent to mitosis N) Centromeres divide and each cell receives one of the two sister  chromatid O) Genetic Diversity arises from 2 sources: i. Crossing over ii. Random distribution of maternal and paternal chromosomes:  During metaphase the way in which the chromosomes align in  the center is random and can shuffle alleles on different  chromosomes.  synapsis


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