Gene Action ,Cell Division

8/8/2019 Gene Action ,Cell Division

1/32

THE NUCLEUSTHE NUCLEUSSite of DNA (InSite of DNA (Inchromosomes)chromosomes)

Enclosed by aEnclosed by amembranemembrane


2/32

DNA REPLICATIONDNA REPLICATIONThe double helixThe double helix

unzips unzipsNew bases pair upNew bases pair up

with the old oneswith the old onesThe moleculeThe moleculereplicates itself replicates itself Two identical copiesTwo identical copieseach with one oldeach with one oldstrand and one newstrand and one new


3/32

DNA ReplicationDNA Replication

DNA is the only molecule in the body capable of DNA is the only molecule in the body capable of replication.replication.DNA helicases break weak hydrogen bonds toDNA helicases break weak hydrogen bonds toproduce 2 free strands of DNA.produce 2 free strands of DNA.Bases of each of the freed DNA strands can bindBases of each of the freed DNA strands can bindto complementary bases.to complementary bases.Each copy is composed of one new strand andEach copy is composed of one new strand and

one strand from the original DNA molecule.one strand from the original DNA molecule.Preserves the sequence of bases in DNA.Preserves the sequence of bases in DNA.


4/32

DNA ReplicationDNA Replication


5/32

Cell DivisionCell Division

Process of cell reproductionProcess of cell reproductionNuclear & cytoplasmic (cytokinesis) divisionNuclear & cytoplasmic (cytokinesis) division

Nuclear divisionNuclear division- -meiosis & mitosismeiosis & mitosisMeiosisMeiosis--reproductive cell division (sperm &reproductive cell division (sperm &egg cells)egg cells)

MitosisMitosis--somatic cell divisionsomatic cell division


6/32

Cell Cy cleCell Cy cleInterphase (nonInterphase (non- -dividing cell phases):dividing cell phases):

GG11::Produces mRNA and proteins.Produces mRNA and proteins.

S:S:

If cell is going to divide, DNA replicated.If cell is going to divide, DNA replicated.GG22::Chromosome consists of 2 chromatids joinedChromosome consists of 2 chromatids joinedby centromere.by centromere.

Each chromatid contains a complete doubleEach chromatid contains a complete double- -helix DNA molecule. Each chromatid willhelix DNA molecule. Each chromatid willbecome a separate chromosome once mitoticbecome a separate chromosome once mitoticdivision completed.division completed.

Completes interphase.Completes interphase.


7/32

Cyclins promote different phases of the cellCyclins promote different phases of the cellcycle.cycle.

During GDuring G 11 phase an increase in cyclin Dphase an increase in cyclin Dproteins activates enzymes to move the cellproteins activates enzymes to move the cellquickly through the Gquickly through the G 11 phase.phase.

Overactivity of a gene that codes for cyclinOveractivity of a gene that codes for cyclinD might cause uncontrolled cell divisionD might cause uncontrolled cell division

(cancer).(cancer).


8/32

M itosis ( M Phase)M itosis ( M Phase)Prophase:Prophase:

Chromosomes become visible distinct structures.Chromosomes become visible distinct structures.Metaphase:Metaphase:

Chromosomes line up single file along equator.Chromosomes line up single file along equator. Action of spindle fibers attached to Action of spindle fibers attached tokinetochorekinetochore

Anaphase: Anaphase:Centromeres split apart.Centromeres split apart.

Spindle fibers shorten, pulling the 2Spindle fibers shorten, pulling the 2chromatids in each chromosome to oppositechromatids in each chromosome to oppositepoles.poles.

Telophase:Telophase:

Division of cytoplasm, producing 2 daughterDivision of cytoplasm, producing 2 daughtercells.cells.


9/32

M itosisM itosis


10/32

M itosisM itosis


11/32

Role of CentrosomeRole of Centrosome

All animal cells have centrosome, located near nucleus All animal cells have centrosome, located near nucleusin nonin non--dividing cell.dividing cell.

At center are 2 centrioles. At center are 2 centrioles.Each centriole composed of 9 bundles of Each centriole composed of 9 bundles of microtubules.microtubules.

Microtubules grow out of pericentriolarMicrotubules grow out of pericentriolar

material.material.


12/32

Centrosome replicates itself during interphaseCentrosome replicates itself during interphase

(if cell is going to divide).(if cell is going to divide).Identical centrosomes move away from eachIdentical centrosomes move away from eachother during prophase.other during prophase.Take up opposite poles by metaphase.Take up opposite poles by metaphase.

Microtubules from both centrosomes formMicrotubules from both centrosomes formspindle fibers.spindle fibers.

Spindle fibers pull chromosomes toSpindle fibers pull chromosomes to

opposite poles during anaphase.opposite poles during anaphase.


13/32

M eiosis (Reduction Division)M eiosis (Reduction Division)

Cell division occurring in ovaries and testes toCell division occurring in ovaries and testes toproduce gametes (ova and sperm cells).produce gametes (ova and sperm cells).

Has 2 divisional sequences:Has 2 divisional sequences:F irst division:F irst division:Homologous chromosomes line up side by sideHomologous chromosomes line up side by sidealong equator of cell.along equator of cell.

Spindle fibers pull 1 member of theSpindle fibers pull 1 member of thehomologous pair to each pole.homologous pair to each pole.Each of the daughter cells contains 23Each of the daughter cells contains 23different chromosomes, consisting of 2different chromosomes, consisting of 2chromatids.chromatids.


14/32

M eiosis (Reduction Division)M eiosis (Reduction Division) ))

Second division:Second division:

Each daughter cell divides, withEach daughter cell divides, with

duplicate chromatids going to each newduplicate chromatids going to each newdaughter cell.daughter cell.

Testes: produce 4 sperm cells.Testes: produce 4 sperm cells.

Ovaries: produce one mature egg,Ovaries: produce one mature egg,polar bodies die.polar bodies die.


15/32


16/32


17/32


18/32

Cell DeathCell Death

Pathologically:Pathologically:Cells deprived of blood supply swell, theCells deprived of blood supply swell, themembrane ruptures, and the cell burstsmembrane ruptures, and the cell bursts(necrosis).(necrosis).

Apoptosis: Apoptosis:Cells shrink, membranes become bubbled, nucleiCells shrink, membranes become bubbled, nucleicondense.condense.


19/32

Capsases ( executioner enzymes ):Capsases ( executioner enzymes ):Mitochondria membranes become permeableMitochondria membranes become permeableto proteins and other products.to proteins and other products.

Programmed cell death:Programmed cell death:Physiological process responsible forPhysiological process responsible forremodeling of tissues during embryonicremodeling of tissues during embryonicdevelopment and tissue turnover in the adult.development and tissue turnover in the adult.


20/32

cytokinesiscytokinesis

Begins during late anaphase & terminates at Begins during late anaphase & terminates at same time as telophasesame time as telophase

Cleavage furrow formationCleavage furrow formation- -extend aroundextend aroundcell s equatorcell s equatorF urrow progresses inwardF urrow progresses inward

Resembles constricting ringResembles constricting ringCuts completely through the cellCuts completely through the cellF orms 2 separate portions of cytoplasmF orms 2 separate portions of cytoplasm


21/32

RNARNA protein S ynthesisprotein S ynthesis

One gene codes for one polypeptide chain.One gene codes for one polypeptide chain.Each gene is several thousand nucleotideEach gene is several thousand nucleotidepairs long (DNA).pairs long (DNA).

Each gene contains the code for theEach gene contains the code for theproduction of a particular type of mRNA.production of a particular type of mRNA.

For the genetic code to be translated into

For the genetic code to be translated intosynthesis of a particular protein, the DNAsynthesis of a particular protein, the DNA

code is copied onto a strand of RNAcode is copied onto a strand of RNA(genetic transcription).(genetic transcription).


22/32

RNA TRANSCRIPTIONRNA TRANSCRIPTION

Messenger RNAMessenger RNA copies from copies from

DNADNAmm--RNA cariesRNA cariesthe message tothe message tothe rough ERthe rough ER


23/32

G enetic TranscriptionG enetic TranscriptionRNARNA--polymerase breaks weak hydrogenpolymerase breaks weak hydrogen

bonds between paired bases of DNA.bonds between paired bases of DNA.Regulatory molecules act as transcriptionRegulatory molecules act as transcriptionfactors by binding to promoter region of factors by binding to promoter region of gene, activating the gene.gene, activating the gene.

Double stranded DNA separates at regionDouble stranded DNA separates at regionto be translated.to be translated.

One freed strand of DNA serves as guide.One freed strand of DNA serves as guide.

F reed bases pair with complementaryF reed bases pair with complementaryRNA nucleotide bases.RNA nucleotide bases.RNA detaches.RNA detaches.


24/32

Types of RNATypes of RNA

4 types of RNA produced within nucleus by4 types of RNA produced within nucleus bytranscription.transcription.

Precursor mRNA prePrecursor mRNA pre--mRNA):mRNA): Altered in nucleus to form mRNA. Altered in nucleus to form mRNA.

Messenger RNA (mRNA):Messenger RNA (mRNA):Contains the code for synthesis of specificContains the code for synthesis of specificproteins.proteins.

Transfer RNA (tRNA):Transfer RNA (tRNA):Decodes genetic message contained inDecodes genetic message contained inmRNA.mRNA.

Ribosomal RNA (rRNA):Ribosomal RNA (rRNA):

F orms part of the ribosome structure.F orms part of the ribosome structure.


25/32

PrePre--mRNAmRNAContains excessContains excessbases within thebases within theprepre--mRNA.mRNA.Introns:Introns:

Regions of nonRegions of non- -coding DNA withincoding DNA withina gene.a gene.

Exons:Exons:Coding regions.Coding regions.

Introns are removedIntrons are removedand the ends of and the ends of exons spliced byexons spliced bysnRNPs to producesnRNPs to producemRNA.mRNA.


26/32

Protein S ynthesisProtein S ynthesis

Each mRNA passes through ribosomes formingEach mRNA passes through ribosomes forminga polyribosome.a polyribosome.

Association of mRNA with ribosomes is needed Association of mRNA with ribosomes is neededfor genetic translation.for genetic translation.Translation:Translation:

Production of specific protein according toProduction of specific protein according tocode contained in mRNA base sequence.code contained in mRNA base sequence.


27/32



28/32


Each mRNA contains hundreds of nucleotidesEach mRNA contains hundreds of nucleotidesarranged in sequence determined by thearranged in sequence determined by the

complementary base pairing with DNA.complementary base pairing with DNA.Codon:Codon:

Each 3 bases (triplet) is a code word for aEach 3 bases (triplet) is a code word for aspecific amino acid.specific amino acid.


29/32



30/32

Transfer RNATransfer RNA

Translation of the codonsTranslation of the codonsaccomplished by tRNAaccomplished by tRNAand enzymes.and enzymes.

tRNA bends on itself,tRNA bends on itself,

making an anticodon (3making an anticodon (3nucleotides that arenucleotides that arecomplementary tocomplementary tocodon of mRNA).codon of mRNA).

Synthetase enzymes joinSynthetase enzymes joinspecific amino acids tospecific amino acids tothe ends of tRNA within athe ends of tRNA within agiven codon.given codon.


31/32

F ormation of a Pol ypeptideF ormation of a Pol ypeptide

Anticodons of tRNA binds to mRNA codons. Anticodons of tRNA binds to mRNA codons.Each tRNA carries a specific amino acid.Each tRNA carries a specific amino acid.

tRNA bring amino acids close together.tRNA bring amino acids close together. Amino acid detaches from tRNA. Amino acid detaches from tRNA.

Enzymatically this amino acid isEnzymatically this amino acid istransferred to the amino acid on thetransferred to the amino acid on thenext tRNA.next tRNA.

Polypeptide chain grows.Polypeptide chain grows.Interactions between amino acids cause chainInteractions between amino acids cause chainto twist and fold forming secondary andto twist and fold forming secondary andtertiary structure.tertiary structure.


32/32

Translation of mRNA

Documents

Gene Action ,Cell Division