Topic 3 15/4/09 14:12. Zygotes

Transcription

1 Tpic 3 15/4/09 14:12 Zygtes

2 Ova Structure Fllice cells utside Zna Pellucida inside them Releases hrmnes, attracting sperm and triggering lyssme reactin Acrsme swells and fuses with vum Penetrating Z.P Z.P thickens t prevent ther sperm entering Sperm Ovum Acrsme N acrsme Tail N tail Mitchndria Mitchndria N lipids Lipid stres ATP stre N ATP stre Haplid nucleus Haplid nucleus Sperm

3 Lyssme Digestive enzyme triggered by Z.P hrmnes Causes jelly-like vum cating t thicken, denying entry t ther sperm Newly fertilised egg = ZYGOTE Mitsis Prduces 2 ( t ) diplid cells Interphase Organelles & DNA replicate N Interphase in zygte Appearance

4 Nndescript, n bvius chrmsmes Dark patches = nucleli cntaining ribsmes DNA is unravelled fr replicatin Prphase Chrmatids thicken Spindle frms, centriles acting as anchrs Centrmeres jin chrmatids Nuclear Envelpe disintegrates Metaphase Centrmeres attach at equatr Anaphase Centrmeres split Spindle shrtens Spindle breaks dwn when chrmatids reach ples Telphase Reverse prphase Chrmatids lengthen Nuclear envelp refrms Cytplasmic Divisin Prtein filaments & micrfibrils cndense cell at neck, pinching cytplasm apart In plants, ribsmes build a new cell plate between the tw cells Mitsis Ensures genetic stability Every cell has the same DNA in a bdy Grwth and repair Asexual reprductin Binary fissin in bacteria meisis Prduces 4 haplid cells Prmtes genetic variatin thrugh randm assrtment Stem Cells Ttiptent <8 cells in embry

5 Pluriptent <50 cells in embry, BLASTOCYST Multiptent E.g Bne marrw; can frm multiple nerve cells Uses Tissue Typing 20 tissue lines wuld prvide fr 90% f the pp Immunsuppressants Suppress immune system Therapeutic clning Diplid nucleus frm adult int embry Therefre frming a blastcyst which matches the patient Ethics Fr Against T alleviate human suffering Pandra s bx; slippery slpe Ovums frm IVF wasted Other cells viable Culd imprve understanding Embry = persn Embrynic cells mst versatile Odd side effects? Save children with cngenital Pressure t supervulate diseases Prmter regin The lcatin fr RNA plymerase t bind n a gene If blcked r absent, expressin wn t take place. FOP Caused by misprductin f BMP-4 hrmne which stimulates bne grwth in mnctyes. If a repressr is missing, bne grws everywhere. Hmebx genes Master genes which cntrl differentiatin f rgans and rchestrate develpment Melanin stuff

6 Tyrsinase synthesizes melanin When stimulated by Melanctye Stimulating Hrmne (MSH) MSH receptrs increases in UV light Melanin prduced in melanctyes, then put melansmes, which gather arund nucleus t prtect it Cancer Inherited Cmes frm lack f repairing genes fr DNA Breast cancer Lking fr specific, hereditary mutatins Preventative surgery may be pssible Mutagens Asbests Tar UV light Viral Viral infectins can trigger cancer, pssibly due t transfer f ncgenes Free radicals Cause mutatin by xidising stuff Cmbated by free radicals Humane Genme prject genes 50%= Junk DNA Shws evlutin Uses Identificatin f new genes and identifying threats Identifying new drug targets Persnalised drugs Understanding basic bilgy better Shwing and understanding evlutinary prgress Issues Insurance Wh shuld use them; better nt t knw? Obligatry? Shuld it determine eligibility fr treatment?

7 Egenics Screening Can cmbat diseases such as Duchenne muscular dystrphy Which is sex linked Germ line therapy Inserting desired genes int germ cells i.e. zygtes Prtein Trafficking 1. DNA mrna, mrna mves ut 2. mrna attaches t ribsme 3. Prteins made n rbsmes, enter RER 4. Prtein assumes end shape and is packaged as it mves thrugh ribsmes 5. Vesicle is pinched ff 6. Enters Glgi apparatus 7. Prteins mdified t fulfull final functin 8. Final vesicles are pinched ff, cntaining final prtein 9. Exit cell by excytsis Acetabularia 2 strains, different hats Nucleus and stem separated, hybiridzed Stem in the shrt term determines hat If hat chpped ff, new, regrwn hat matches nucleus Clning Dangerus; versized babies Develp diseases such as arthritis quickly Gene Expressin Attaching a methyl (-CH 3 ) grup t a gene deactivates it Gene expressin requires RNA plymerase & suitable transcriptin factrs t attach t the prmter regin n the DNA. Transcriptin factrs Sme always present

8 Sme specially synthesized Sme nly activated by hrmnes (grwth factrs etc) Expressin can be prevented by prtein repressr mlecule Which prevents transcriptin factr binding by blcking the prmtr regin. E.G. in B-Galactsidase in E.Cli, lactse inhibits the repressr mlecule, allwing the transcriptin f lactse digesting enzyme (B-Galactsidase) Signalling Direct Signal prtein passes int nucleus, acts as transctiptin factr Indrect Signal prtein binds t receptr, causing messenger mlecule t be released in cell, which acts as transcriptin factr Nature Vs. Nurture Height Nat + Nur Taller men mre attractive/ reprductive Mre prtein in diets, less inbreeding, better medicine, less child labur, better heating & husing All lead t increasing height Cancer When cell multiplicatin > apptsis DNA damaged thrugh mutagens (UV light, asbests, tar) r incrrect gamete frmatin Oncgenes Cde fr stimulating prteins in the cell cycle, perpetuating it T many = Cancer Tumur Suppressant Genes TSG) Prduce cycle stpping prteins. If inhibited, cancer

9 At checkpints in the cell-cyle (perpetuated by clin & cyclin dependent kinases) Chemicals are released t cntinue the cycle The build up f CDK catalyses phsphrylatin f ther prteins, making them active Cancer Natural Inherited Chemical: tar in brnchi causes Abut 5% is inherited mutatin in epithelial cells Physical: UV light, mles Lack f DNA repairing prteins, r Tumurs dd ratis f nc/tsg Diet: Free radicals Mutatins accumulate in the sperm f lder men Metastasis The spread f cancer