Chapter 1Chapter 1

Biology 102Biology 102

Gene expression (cont.)/Gene expression (cont.)/

Begin Cellular reproductionBegin Cellular reproduction

Chapter 1Chapter 1

Lecture outlineLecture outline

Gene expression and regulation (cont.)Gene expression and regulation (cont.)MutationsMutationsRegulation of gene expressionRegulation of gene expression

Cellular reproductionCellular reproductionTypes of cellular reproductionTypes of cellular reproductionMitosis vs. meiosisMitosis vs. meiosisOverview of mitosis/cell cycleOverview of mitosis/cell cycleSteps of mitosisSteps of mitosis

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MutationsMutations

Mutations and protein synthesisMutations and protein synthesisSource of mutationsSource of mutations

Exposure to mutagensExposure to mutagensErrors in replication and transcriptionErrors in replication and transcription

Results of mutationResults of mutation: Changes in DNA can : Changes in DNA can result in changes in the proteins for which result in changes in the proteins for which they codethey code

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Examples of MutationsExamples of Mutations

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Effects of mutationsEffects of mutations

Some are insignificantSome are insignificantMore than one codon for most amino acidsMore than one codon for most amino acidsThird nucleotide position is often not importantThird nucleotide position is often not important

G-U-G-U-nn = valine = valineU-C-U-C-nn = serine = serineC-G-C-G-nn = arginine = arginine

Some are HarmfulSome are HarmfulFrameshift, missense or nonsenseFrameshift, missense or nonsense

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Effects of mutationsEffects of mutations

Mutations can be beneficial!Mutations can be beneficial!Altered proteins may be more effective than Altered proteins may be more effective than

originalsoriginalsMutations are Mutations are thethe source of genetic variation source of genetic variationSignificance to ability to evolveSignificance to ability to evolve

X-men!X-men!

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Gene expression

Individual cells express only a small Individual cells express only a small fraction of their genesfraction of their genes

Gene expression is influenced by Gene expression is influenced by developmental stage and environmentdevelopmental stage and environment

How is gene expression regulated? How is gene expression regulated?

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Regulation of gene expression (cont.)Regulation of gene expression (cont.)

Types of regulationTypes of regulation Frequency of transcriptionFrequency of transcription

Turned on or off at promotor Turned on or off at promotor regionregion

Rate/amount of mRNA Rate/amount of mRNA translatedtranslated

Some mRNA stable, others Some mRNA stable, others break downbreak down

Activation/inactivation of Activation/inactivation of proteinsproteins

Lifespan of the proteinLifespan of the protein

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Types of cell reproductionTypes of cell reproduction

BinaryFission BinaryFission (bacteria)(bacteria)

DNA replicated

Membrane added

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False-Color EM of Dividing BacteriumFalse-Color EM of Dividing Bacterium

Division planeDivision plane

Cell wallCell wall

CytoplasmCytoplasm

NuclearNuclearmaterialmaterial

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Asexual reproduction by mitosisAsexual reproduction by mitosis

New individualsNew individuals

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Asexual Reproduction by MitosisAsexual Reproduction by Mitosis

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Mitotic Mitotic

cell cell divisiondivision

Mitotic Mitotic cell cell division & division &

differ-differ-entiationentiation

Functions of Mitosis in animalsFunctions of Mitosis in animals

TissuesTissues

OrgansOrgansFertilized eggFertilized egg(zygote)(zygote) Multicell stageMulticell stage

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Mitosis, Meiosis, and the Sexual CycleMitosis, Meiosis, and the Sexual Cycle

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telophase

metaphase

anaphase

cell

divi

sion

GG00: : nondividingnondividing

interphaseinterphase

Focus on MitosisFocus on Mitosis

S: Synthesis S: Synthesis of DNA; of DNA; chromosomes chromosomes duplicatedduplicated

GG11: Growth: Growth

GG22: Growth: Growth

prophase

cytokinesis

Mito

sis

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InterphaseInterphase DNA exists as

chromatin: The chromosomes (blue) are in the thin, extended state Wrapped around protein DNA is 2 meters long! Replicated while in this

form The microtubules (red)

extend outward from the nucleus to all parts of the cell.

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ProphaseProphase DNA condenses into DNA condenses into

distinct chromosomesdistinct chromosomes Additional windingAdditional winding Relationship of genes and Relationship of genes and

chromosomeschromosomes Diploid: Homologous pairs of Diploid: Homologous pairs of

chromosomeschromosomes Sister chromatids held Sister chromatids held

together by centromere at this together by centromere at this stagestage

Don’t confuse diploid with Don’t confuse diploid with sister chromatids!sister chromatids!

Mitotic spindle forms from Mitotic spindle forms from microtubulesmicrotubules Chromosomes attachedChromosomes attached

Nuclear membrane Nuclear membrane disappearsdisappears

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MetaphaseMetaphase Chromosomes are Chromosomes are

lined up in midlinelined up in midline The chromosomes have

moved along the spindle microtubules

Homologous chromosomes aligned “head to toe”

At end of metaphase, centromeres release sister chromatids

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AnaphaseAnaphase

Sister chromatids have separated, and one set of chromosomes moves along the spindle microtubule to each pole of the cell.

Cell still diploid, but chromosomes now are only single chromatids Cell is always diploid

throughout this process!

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TelophaseTelophase The chromosomes have

gathered into two clusters, one at the site of each future nucleus.

Chromosomes begin to decondense back to chromatin

Nuclear membrane forms

Followed by cytokinesis Cytoskeleton “pinches” cell

into two parts Plants form new cell wall

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Cytokinesis of a Ciliated CellCytokinesis of a Ciliated Cell

Cleavage FurrowCleavage Furrow

Daughter CellsDaughter Cells

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Cytokinesis in PlantsCytokinesis in Plants

Vesicles fuse to form cell wall

and membranesComplete

separation of daughter cells

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Mitosis: ReviewMitosis: Review

Kinetochores align at cell’s

equator

Nucleolus disappears;

Nuclear envelope breaks down

Microtubules attach to

kinetochores

Chromosomes condense and

shorten

Centrioles begin to move apart;Spindle forms

Duplicated chromosomes

remain elongated

Centrioles have also been duplicated

LateLateInterphaseInterphase

EarlyEarlyProphaseProphase

LateLateProphaseProphase MetaphaseMetaphase

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Mitosis: Review (cont.)Mitosis: Review (cont.)Free spindle fibers push poles apart

Chromatids become

independent chromosomes

One set of chromosomes;

Begin unwinding

Nuclear envelope re-

forms

Cytoplasm divided along

equator

Each daughter gets 1 nucleus &

half of cytoplasm

Spindle disappears; Nucleolus reappears

AnaphaseAnaphase TelophaseTelophase CytokinesisCytokinesisNextNext

InterphaseInterphase

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How do cells “know” when to How do cells “know” when to stop dividing?stop dividing?

Cell senescenceCell senescence Cells are programmed to stop dividing.Cells are programmed to stop dividing. Cells of older people programmed to stop dividing Cells of older people programmed to stop dividing

earlier (50x for newborn cells, 30x for aged person's earlier (50x for newborn cells, 30x for aged person's cells)cells)

Growth controlGrowth control Cell division inhibited by contact with other "like" cells.Cell division inhibited by contact with other "like" cells.

Ex: wound closure.Ex: wound closure. Cancer cells do not exhibit growth control. Something has Cancer cells do not exhibit growth control. Something has

gone haywire. They keep growing.gone haywire. They keep growing.