chapter 8 cell reproductionocw.nctu.edu.tw/course/biology/modrenbiologyi_lecturenotes/ch08.pdf ·...

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Copyright 2005—Brooks/Cole—Thomson Learning

Tobin and Dusheck: Asking About Life, 3E Chapter 8

Chapter 8

Cell Reproduction



First Human cell line

•In 1951, firsthuman cell lineHeLa was culturedin the lab.

•HeLa cells weregenerated fromthe cervical tumortissue of HenriettaLacks.

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Key Questions•How is cell division critical to the

lives of single-celled andmulticelled organisms?

•How do eukaryote cells divideduring mitosis and cytokinesis?

•How does the DNA fit into thenucleus without becoming tangled?

•How do cells regulate the cell cycle?



How Do Cells Divide?•Mitosis — simple division of a

cell into 2 new cells•Provides for growth•Creates replacements for cells•In single celled organisms,

produces new individuals•Cell copies DNA before it divides

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Early Info AboutChromosomes

•WaltherFlemming— detaileddescription ofchromosomalmovementduring mitosis

•Did not knowrole of nucleusnorchromosomes



Discovering the Function ofChromosomes

•At first, scientists assumed thatthe chromosomes in a cell were allalike

•19th century biologists did notrealize that chromosomes carryhereditary information

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Discovering the Function ofChromosomes

•Wilhelm Roux noticed the complexway the X-shaped chromosomes splitduring mitosis

August Weismann(1889) suggested thenucleus containedthe hereditarymaterial; he called it“germ plasm”



Cell reproduction

•The replication of DNA•The equal distribution of DNA to

the two daughter cells•The division of the rest of cell

material into tow daughter cells

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How Do ProkaryoticCells Divide?

•Divide by binary fission•Have only 1 chromosome,

no nuclear membrane

•Duplicatechromosome

•Then, cellpinches into 2cells



Karyotype

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Sock Karyotyping



How Do Eukaryotic Cells Divide?

•More complicated process•Have a nucleus with pairs of

homologous chromosomes — pairsof matching chromosomes

•Cell cycle — Everything thathappens to a cell from the time itfirst forms until it divides

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Cell Cycle•Several phases–M, mitosis

phase, includesboth mitosisand cytokinesis

–Interphase•G1 (gap or growth phase) cell doubles all

its materials•S (synthesis) DNA replicates•G2 (gap) assembles molecular machinery



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Mitosis Overview

•Continuous Process•Has 4 phases:–Prophase–Metaphase–Anaphase–Telophase

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Prophase

•Replicated chromosomescondensed and become visible

•Chromosomes appear as 2chromatids

•Microtubule spindles appear;centrioles appear

•Nuclear membrane disappears



Metaphase

•Longest stage of mitosis•Chromosomes line up between the

2 poles of the spindle•Form a disc called the metaphase

plate

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Anaphase•Chromatids separate•Microtubules attached to the

centromeres shorten•Separated chromosomes move

away from the metaphase plate



Telophase•Mitotic apparatus breaks down•Chromosomes unwind•Nucleus reappears with

membranes covering the 2 newsets of chromosomes

•Each chromosome consists of only1 chromatid-like structure

•Cytokinesis occurs

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Fitting DNA Into a Cell•Proteins called histones pack the

DNA into small, tight bundlescalled nucleosomes

•Strings of nucleosomes fold andloop to form chromosomes that fitinto the cell

•No one knows exactly how thisoccurs

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Cytokinesis

•In plant cells, telophaseincludes the building ofnew cell membranes andcell walls

•In animal cells,actin filamentsform acontractile ringthat pinches thecytoplasm in 2

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New Cell Wall



Mitosis Mindbenders•A human cell has 46

chromosomes in its cells. Afterthe S phase of the cell cycle,how many chromosomes will thecell contain?•How many homologous pairs of

chromosomes will the cell haveat prophase?

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When Do CellsStop Dividing?•Cell senescence —

cell has a limitednumber of divisions

•Growth RegulatingProteins

•ContactInhibition–Stop dividing

when touchinganother cell



When Is It Time to Divide?•Divide only when cell has doubled

its mass•Various events regulate a cell’s

passage through the cell cycle,including the completion of DNAsynthesis and fluctuations incyclins (proteins whoseconcentrations change during thecell cycle)

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Key Concepts•Cell division involves 3 processes:

replication of DNA, its equaldistribution to each daughter cell,and division of cytoplasm

•Microtubules and other componentsprovide for chromosomal distribution

•Similar molecular mechanisms areused to regulate the cell cycle in alleukaryotic cells

chapter 8 cell reproductionocw.nctu.edu.tw/course/biology/modrenbiologyi_lecturenotes/ch08.pdf ·...

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