cell cycle & karyotype (15)

why do cells divide

fertilization, embryogenesis, regeneration , growth and reproduction,

what are the four major events during cell division

1. cell division signals - external or internal

2. dna replication - doubling genetic information

3. dna segregation ( mitosis) - equal division of genetic information

4. cytokinesis - division of the cellular content

how does prokaryotes divide

binary fission

what is binary fission

• reproductive signals - availability of nutrients; physical parameters of the environment ( temperature,pH osmolarity)

• replication of DNA - cicular dsDNA chromosome; replication starts at ORI, moves bidirectionally and ends at TER site; cell grows in size

• segregation of DNA molecules - replication at the center center; ORI regions lead movement to opposite poles

• cytokinesis - begins immediately after chromosome replication ; FtsZ protein assembles into fibers & z-rings

what is the ori

the origin of replication

what is the ter 

the termination sequence

what is the replisomes

DNA polymerase and other proteins

what does it mean that DNA is replicated bidirectionally

The replication begins at ORI is copied in two opposite directions at the same time

what is the cytokinesis progress in prokaryotes

• the FTsZ assembled into a ring structure known as the z-ring 

• the z-ring contracts, pull the cell membrane inwards, creating a cleavage furrow  ( initiates formaiton of cell wall)

• furrow appears and cell wall grows inward, forming septum

eukaryotes cell division

• reproductive signals - unicellular ( similar to bacteria  - respond to environmental signals) ; multicellular - signals come for the external & internal environments ( organs & tissues)

• replication of DNA - many dsDNA ( linear) chromosomes; replication starts at multiple ORI sites

• segregation of DNA molecules - complex process for separation of sister chromatids; each new cell have the same amount of DNA

• cytokinesis - different mechanisms in plants (viscles from the golgi appartaus forms a cell plate) and animals ( cleavage furrow, z-ring)

cytokinesis in animals compared to plants

• animal cells use a contractile ring to pinch the membrane inward, forming a cleavage furrow ( contractile ring from actin and myosin filaments), membrane fully constricts which splits the cell

• plant cells builds a cell plante from vesicles that coalesce at the center and grow outward. ( phragmoplast and vesicles from Golgi appartaus), the plant expands outward and fueses with wall

what is interphase

• period of preparation for mitosis; consists of the G1, S, and G2 phases; occupies a larger protion of the cell cycle

• duration of interpahse differs

  • ex. early embryogensis every 30 min

  • adults - rapidly dividing cells every 24 hours

what is mitosis

• the period of active division of the nuclear matieral ( M phase), followed by cytokinesis

what is G0 phase

• cells do not prepare for division

• contiunes to perform their normal functions, often for long periods or permanently

• ex. neurons and cardiac muscle cells permanently in G0 after maturation

what happens during G1 phase

• first stage of interphase

• the cell increases in size and volume, expanding its cytoplasm

• organelles production - mitochronidra, ribosomes and other organelles are synthesized

• the cell produces proteins and enzymes need for DNA replication, metabolically active

• unreplicated chromosome ( a single chromatid)

what happens during s phase

• second stage of interphase

• replicates its entire DNA

• each chromosome is duplicated, forming two identical sister chromatids joined at the centromeres

• chromosomes appear as an x shape

what happens during g2 phase

• final stage of interphase

• preparation of mitosis

• cell growth continues, increase in size to accommodate division

• organelle duplication - replicated to ensure both daughter cells have what they need

• synthesis of spindle apparatus - produces proteins needed for mitosis like microtubles components for the spindle apparatus

what is M phase

• mitosis and cytokinesis

• equal division of genetic material & cytoplasmic content

how did scientists discovered cell-cycle regulatory molecules

• through cell fusion experiments and studies on frog oocytes showing cytoplasmic factors

• 1970s - experiments on fused cells

• limitations due to difficultly to control the experiment, didn’t explain where the regulatory molecules were located( nucleus vs. cytoplasm) , follow up experiments on African frog

where are the regulatory factors located ( M-phase promoting factor)

• the cytoplasm of M-phase cells contain a factor that drives immature occytes into M pahse to compelte their maturation

• cyclin proteins, a complex of cyclin and cdk that triggers entry into m phase

what is the role of cyclins and CDKs in regulation of the cell cycle

• Cyclins a regulatory proteins, and they bind to a CDK, which catalyzes the phosphorylation of other proteins to start mitosis

• Cyclins are only made at certain points in the cell cycle

what does MPF do

controls the passage from G2 to M phase

what type of regulation occur during cyclin binding

• allosteric activation - cyclin binding changes the shape of CDKs, exposing its active site

how is mpf activated and deactivated

• MPF has two phosphorylation sites at the cdk. Both sites are phosphorylated after cyclin binds to cdk

• in late g2, phosphatase removes the inhibitory phosphate, activating the mpf kinase activates via phosphorylation

• during late m-phase (anaphase) an enzyme complex starts attaching ubiuitin to cyclin, cyclins detaches and is degraded in proteasome - negative feedback inhibition

what is ubiquitin 

• small regulatory protein found in almost all eukaryotic cell

• main role is to tag other proteins for degradation, helping maintain cellular health ( ubiquitination)

what is the restriction point

• a checkpoint in late G, where the cell commits to DNA replication if conditions are favorable

• The cell evaluates external signals and internal conditions, if conditions are favorable, the cell activates g1/s cyclin-cdk complexes, pushing it into S phase

• if its unfavorable, the cell may pause for repairs, enter g0, and undergo apoptosis if damage is severe

what is g1 checkpoint

pass checkpoint if

• cell size is adequate

• nutrients are sufficient

• social signals are present

  • DNA is undamaged

what is the s checkpoint

• pass checkpoint if

• dna is completely replicated

  • dna is undamaged

what is g2 checkpoint

pass checkpoint if

• chromosomes have replicated successfully

• DNA is undamaged

  • activated MPF is present 

what is M-phase checkpoints

pass checkpoints if

• chromosomes have attached to spindle apparatus

• chromosomes have properly segregated and MPF is absent

what is a consequence of mutated p53 gene

• cell cycle will contiune even if there is a damge in the DNA

  • involved in 50% of the cancer

what are tumor suppressors

• regulatory proteins that halt cell cycle or initiate apoptosis

induction of cell cycle arrest due to detected DNA

• DNA damage detected during G1

• p53 activated by phosphorylation

• activated p53 binds to DNA and initiates transcription of p21 gene; p21 protein is made

• p21 protein binds to c1/s cyclin - cdk, inhibiting its ability to phosphorylate RB

• unphosphorylated RB binds with E2F1 and DP, inhibiting transcription of many cell cycle genes

• inducing cell cycle arrest

• when DNA is repaired, p21 breaks down allowing cell cycle to proceed

what is platelet derived growth factor

• at the site of a cut and bleed; stimulation of cell division to heal the wound

what is erythropoietin

• a glycoprotein secreted by kidneys; stimulate red blood cell production in bone marrow

what is interleukins

• secreted by white blood cells; primary function in activation and differentiation of immune cells during inflammatory and immune responses

what is a karyotype

• invdividuals’ complete set of chromosomes

• a complete set of 46 chromosomes: 22 authosomal pairs and 2 sex chromosomes

what is ploidy

the number of chromosome sets in a cell

• humans are diploid (2n = 46); the ploidy would be 2n.

what are growth factors

• proteins that stimulate division

what is trisomy 21

there is a extra chromosome in the 21 chromosome, causes down’s syndrome

what is xxy

kinefleter syndrome , where a invidual have a extra x chrosome, learning disability, infertile, more likely to get depression