3.1 in the Beginning

8/16/2019 3.1 in the Beginning

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3.1 In the beginning:

Prokaryotic cell: Bacteria and cyanobacteria (photosynthetic bacteria) They have no nuclei or other membrane-bound cell organelles. Diameter0.5 and 5

Eukaryotic cells: contain membrane bound organelles- nuclei,

Mitochondria. arger than a pro!aryotic cell.Diameter "0 or more.

Mitochondria: #nner o$ its " membrane is$olded, $orm %nger li!e pro&ections called cristae.ater stages o$ aerobic respiration.Nucleus: 'ontains chromosomes and anucleolus. D in chromosomes genes that control synthesis o$ proteins.

Nucleolus: Dense body *ithin the nucleus *here ribosome+s are made.RER: ystem o$ interconnected membrane-bound attened sacs.ibosome are attached to the outer sur$ace. /roteins made by theseribosome+s are transported to the to other parts o$ the cell.Ribosomes: Made o$ 1 protein, these small organelles are $ound $reein the cytoplasm or attached to . They are the site o$ protein synthesis.

'ell sur$ace membrane2 /hospholipids bilayer containing proteins andother molecules $orming a partially permeable membrane.


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SER: i!e . Does not have any attached ribosome+s. are ma!elipids are steroids. .g. reproductive hormones.Golgi aaratus: stac!s o$ attened, membrane bound sacs $ormed by$usion o$ vesicles $rom . Modi%es proteins and pac!ages them invesicles $or transport.

!ysosomes2 pherical sacs containing digestive en3ymes and bound by asingle membrane. #nvolved in the brea!do*n o$ un*anted structures*ithin the cell, and in destruction o$ *hole cells *hen old cells are to bereplaced or during development. The acrosome is a specialised lysosome."entrioles: very animal cell has 4 pair o$ centrioles. ollo* cylindersmade o$ a ring o$ nine protein microtubules. #nvolved in the $ormation o$spindle during nuclear division.

Gametes:Mammalian Gametes2 e6 cells.

7emale2 8vum(egg)

• #ncapable o$ independentmovement.

• 9a$ted along oviduct touterus by ciliated cells liningand muscular contractions o$ the tube.

• 'ytoplasm o$ the ovumcontains proteins and lipid

$ood $or a developingembryo.

• urrounding cell is &elly-li!ecoating called :8/;'#D.

• 0.4mm.

Male2 perm.

• Much smaller than ovum and is motile.

• nable to s*im, sperm cell has a

agellum po*ered by energy released bythe mitochondria.

• perm are attracted to the ovum bychemicals released $rom it.

• To penetrate the ovum the acrosome inthe head o$ the sperm releasesdigestive en3ymes, *hich brea! do*n the3ona pullucida o$ the ovum.

• crosome is a type o$ lysosome.

• ead 5

Plant gametes:


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Male part 2 tamen.

• Made o$ anther attached to the stal!!no*n as a %lament.

• #nside anther , cells divide to produce

pollen grains *hich contain male

gamete nuclei.7emale part2 7emale ovary

• 4 or more ovules develop *hich containthe $emale gametes, the ova (singularovum)

chromosomes. "" homologous pairs. 4 pair o$ se6

chromosomes.

7undemantal di?erence bet*een se6 cells are other cells is the no. o$

chromosomes they contain.

o* do gametes $orm2 " types o$ cell divison in living organisms. M#T8#

D M#8#.

Mitosis produces ne* body cells as organism gro*s and develops. This

retains the $ull no. o$ chromsosomes called the D#/8#D 8. ("n).

Meiosis produces gametes *ith only @ no. o$ chromos omes called/8#D 8 (n).

Indeendent

assortment: ine up

during meiosis 4 is a

source o$ variation.

This process is

random. "rossing

o#er: 'rossing over

produceschromosomes that

contain ne*

combinations o$ alleles

$rom both parent.

During meiosis 4

homologous pair. t

points they ma!e

contact called chiasmata, the chromatids brea! and region. The non-sister

chromatids e6change corresponding sections o$ D. This is calledcrossing over.


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$ertilisation in %o&ering lants:

• Ta!es place in the embryo sac *ithin the ovule.

• /ollen germinates on the style tube gro*s do*n through the styleto*ards the ovary, *ith its gro*th controlled by the tube nucleus.

• /ollen grain contains " nuclei, the tube nucleus and the generativenucleus.

•


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• 7ormation o$ ne* cellular proteins occursthrpughout interphase.

• D synthesis occurs during theS phase. The S phase separates the%rst gap or G1 $rom the second gap

G' phase.• The lengths o$ interphase di?ers

depending on the role o$ the cell.

• The and


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• part $rom usual mutation both strands are identicalcopies.

• They are " chromosomes &oined at 4 region calledcentromere.

• Microtubules $rom the cytoplasm $orm aAD structure called sindle.

• The centrioles move around the nuclear envelope and

position themselves at opposite sides o$ the cell.ME/-P,-SE:

• The brea!do*n o$ the envelope signals the end o$prophase and the start o$ metaphase..

• The chromosomes+ centromeres attachthe spindle %bres at the euator.

• 9hen this has been completed the cell has reachedthe end o$ metaphase.

-N-P,-SE:• #n the ne6t stage o$ mitosis, anaphase, the centromeres

split.

• The spindle %bres shorten, pulling the t*ohalves o$ each centromere in oppositedirections.

• 4 chromatid o$ each chromosome is

pulled to each o$ the poles.

• naphase ends *hen the separated chromatidsreach poles and the spindle brea!s do*n.

/E!+P,-SE:• This last stage o$ mitotic division is

telophase.

• This is e?ectively the reverse o$ prophase.

• The chromosomes unravel and the

nuclear envelope re$orms, so that the " set o$the genetic in$ormation become enclosed in the separate nuclei.

"ytolasmic di#ison:

$ter nuclear division the %nal reorgansisation into " ne* cells

occurs, called cytoplasmic division.#n animal cell, the cell sur$ace membrane constricts around thecentre o$ the cell.

ring o$ protein %laments bound to the inside o$ the cell sur$acemembrane is though to contract until the cell isdivided into " ne* cells.

0hy is mitosis imortantnsures genetic consistency. This is achieved by2

• D replication prior to nuclear division

• The arrangement o$ the chromosomes on the spindle

and the separation o? chromatids to the poles.


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Early embryonic de#eloment 2 stem cells:$ter human 3ygote has undergone three complete cell cycles, it consists o$ Cidentical cells. ache cell is said to be totiotent as it can develop in to acomplete human being.

By 5 days a$ter conception, a hollo* ball o$ cells called the blastocyst has$ormed. The outer blastocyst cell layer goes on to $orm the lacenta. The innercell mass, o$ 50 or so cells go on to $orm the tissues o$ the developing embryo.

They are !no*n as the luriotent embryonic stem cells. ach o$ these cellscan potentially give rise to most cell types, though they cannot give rise to all"4> di?erent cells types that ma!e up the human body.

"ell become more dierentiated:s the embryo develops into a multicellular body, the cells $rom *hich it is madebecome increasingly dierentiated. Most lose capacity to develop into a *iderange o$ cells. #nstead they become increasing specialised, $unctioning as a redblood cell, one o$ the cell types in bone, a plat 6ylem vessel. These cells are

!no*n as multiotent.

Potential use o( human stem cells in medicine:

• They may 4 day produce universal human donor cells *hich *ould provide

ne* cell, tissues or organs $or treatment and repair by transplantation.

• Their potential to develop into any cell type o?ers the greatest e6ibility$or development, unli!e adult stem cells *hich are committed todeveloping only into certain cell types.

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3.1 in the Beginning