L11_12_Chp8_9_notes - Chapter 8 How Cells Reproduce...

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Chapter 8 How Cells Reproduce Understanding Cell Division What instructions are necessary for inheritance? How are those instructions duplicated for distribution into daughter cells? By what mechanisms are instructions parceled out to daughter cells? Reproduction Parents produce a new generation of cells or multicelled individuals like themselves Parents must provide daughter cells with hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation Division Mechanisms Eukaryotic organisms ---Mitosis --Meiosis Prokaryotic organisms--Prokaryotic fission Roles of Mitosis Multicelled organisms; some protistans, fungi, plants, animals To promote growth, Cell replacement, Asexual reproduction Meiosis Functions only in sexual reproduction Precedes the formation of gametes (sperm and eggs) or spores Chromosome A DNA molecule & attached proteins Duplicated in preparation for mitosis Sister Chromatids Each chromosome and its copy stay attached to each other as sister chromatids until late in the nuclear division process; attach at the centromere Nucleosome A nucleosome consists of part of a DNA molecule looped twice around a core of histone proteins Organization of Chromosomes Cell Cycle Cycle starts when a new cell forms During cycle, cell increases in mass and duplicates its chromosomes Cycle ends when the new cell divides Interphase Usually longest part of the cycle Cell increases in mass Number of cytoplasmic components doubles DNA is duplicated Stages of Interphase Control of the Cycle Once S begins, the cycle automatically runs through G2 and mitosis The cycle has a built-in molecular brake in G1 Cancer involves a loss of control over the cycle, malfunction of the “brakes” Stopping the Cycle Some cells normally stop in interphase Neurons in human brain Arrested cells do not divide Adverse conditions can stop cycle Nutrient-deprived amoebas get stuck in interphase Chromosome Number Sum total of chromosomes in a cell -For Somatic cells, Chromosome number is diploid (2 n ) Two of each type of chromosome
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-For Gametes, Chromosome number is haploid ( n ) One of each chromosome type Human Chromosome Number Diploid chromosome number ( n ) = 46 Two sets of 23 chromosomes each One set from father One set from mother Mitosis produces cells with 46 chromosomes – two of each type Lots of DNA
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This note was uploaded on 03/20/2008 for the course BI SC 001 taught by Professor Schlegel during the Spring '99 term at Pennsylvania State University, University Park.

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L11_12_Chp8_9_notes - Chapter 8 How Cells Reproduce...

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