cell cycle identify the cell structures involved in cell division. identify and explain the events...

Cell CycleCell Cycle

Why Cells DivideWhy Cells Divide

Why do cells need to Why do cells need to divide?divide?

Cell Division - PurposeCell Division - Purpose

Provides a means of Provides a means of reproduction for organisms.reproduction for organisms.

Provides a means of growth Provides a means of growth in multicellular organisms.in multicellular organisms.

Provides a means of repair Provides a means of repair in multicellular organisms.in multicellular organisms.

ReproductionReproduction Unicellular organisms divide in Unicellular organisms divide in

order to form new organisms.order to form new organisms.

No Elizabeth, don’t go!

Apologies to Gary Larson and the FAR SIDE

ReproductionReproduction

Multicellular organisms divide Multicellular organisms divide to reproduce special cells to reproduce special cells (gametes) that will carry out (gametes) that will carry out the formation of a new the formation of a new organism.organism.

Growth Growth

Multicellular organisms are Multicellular organisms are made of millions to trillions made of millions to trillions of microscopic cells rather of microscopic cells rather than a few large cells. than a few large cells. Growth mainly occurs by Growth mainly occurs by increasing the number of increasing the number of cells.cells.

RepairRepair

Many microscopic cells as Many microscopic cells as opposed to only a few opposed to only a few large ones is also large ones is also advantageous in the case advantageous in the case of injury.of injury.

How soHow so??

Is there any advantage to Is there any advantage to possessing many small cells possessing many small cells as opposed to a few large as opposed to a few large cells?cells?

Examine the two cells below. The blue color represents the area of diffusion of glucose within the cell over equal periods of time. Do you see a potential problem that might suggest an answer to the question above?

nucleus

Surface Area to Volume Surface Area to Volume RatioRatio

1.1. Relative size of the surface Relative size of the surface area of the plasma membrane area of the plasma membrane and the volume of the cell and the volume of the cell reach a critical point.reach a critical point.

Analyze theAnalyze the

following cubic cell:following cubic cell:

LL WW HH

Day Day oneone

11 11 11

Day Day twotwo

22 22 22

Nuclear LimitationsNuclear Limitations

2.2. Limited capability of the Limited capability of the nucleus nucleus -- there is a finite amount -- there is a finite amount of genetic material of genetic material because the genome size because the genome size remains constant even as remains constant even as the cell grows.the cell grows.


What actually triggers or What actually triggers or cues the cell about the cues the cell about the need to divide?need to divide?

Most of it comes down to chemicals.


Two Two irreversible pointsirreversible points in cell in cell cyclecycle– replication of genetic materialreplication of genetic material– separation of sister chromatidsseparation of sister chromatids

REPLICATION (S phase) SEPARATION (anaphase)


CheckpointsCheckpoints – process is assessed & possibly haltedprocess is assessed & possibly halted

3 major checkpoints:3 major checkpoints:– GG11/S/S

can DNA synthesis begin?can DNA synthesis begin?– GG22/M/M

has DNA synthesis beenhas DNA synthesis been completed correctly?completed correctly? commitment to mitosiscommitment to mitosis

– spindle checkpointspindle checkpoint are all chromosomes attachedare all chromosomes attachedto spindle?to spindle? can sister chromatids separate can sister chromatids separate correctly?correctly?

Checkpoint control systemCheckpoint control system CheckpointsCheckpoints

– cell cycle controlled by cell cycle controlled by STOPSTOP & & GOGO chemical signalschemical signals at critical points at critical points

– signals indicate if key cellular signals indicate if key cellular processes have been processes have been completed correctlycompleted correctly


The “decision” to divide has The “decision” to divide has both external and internal both external and internal

chemical influences. chemical influences.


EXTERNALEXTERNAL– Cells can have direct contact Cells can have direct contact

with each other through cell with each other through cell junctions or surfaces.junctions or surfaces.

– Certain chemicals can easily Certain chemicals can easily come in contact with come in contact with adjacent cells in this way.adjacent cells in this way.

Why Cells DivideWhy Cells Divide Cells can communicate with Cells can communicate with

each other by secreting each other by secreting chemical messengers into chemical messengers into the extracellular fluid.the extracellular fluid.

Paracrine signalingParacrine signaling – – target is near the signaling target is near the signaling source (ex. Adjacent cells)source (ex. Adjacent cells)

Hormonal signalingHormonal signaling – – signal travels through signal travels through bloodstream bloodstream from source to target (pituitary – from source to target (pituitary – ovaries)ovaries)

Synaptic signaling – chemicals travel across small “gap” Synaptic signaling – chemicals travel across small “gap” or synapse (neurotransmitters from neuron to neuron)or synapse (neurotransmitters from neuron to neuron)

Why Cells DivideWhy Cells Divide The signaling process The signaling process

consists of 3 stages:consists of 3 stages: EXTERNALEXTERNAL

1.1. ReceptionReception - - Chemical Chemical messengers interact with messengers interact with receptors,receptors, often those of the often those of the

plasma membraneplasma membrane..


INTERNALINTERNAL2.2. TransductionTransduction- - This begins a This begins a

chain of events in a chemical chain of events in a chemical pathway within the cell, such as pathway within the cell, such as a “phosphorylation cascade”a “phosphorylation cascade”– Phosphorylation cascading refers to the Phosphorylation cascading refers to the

transfer of phosphate groups from one transfer of phosphate groups from one protein molecule to the next, via a type protein molecule to the next, via a type of kinase enzyme, subsequently of kinase enzyme, subsequently activating the molecules in the pathway. activating the molecules in the pathway. (Think Domino effect)(Think Domino effect)


3.3. ResponseResponse - - cellular activity cellular activity – Could be:Could be:

Rearrangement of Rearrangement of cytoskeletoncytoskeleton

Opening/closing ion channelsOpening/closing ion channels Initiation of metabolic Initiation of metabolic

activity, such as cell division.activity, such as cell division.

Chemical Regulation of Chemical Regulation of the Cell Cyclethe Cell Cycle Once signaled, Kinase* proteins Once signaled, Kinase* proteins

give the go ahead signals at Ggive the go ahead signals at G11 and Gand G22 checkpoints. checkpoints.

– *Kinase proteins are a family of *Kinase proteins are a family of related proteins that activate related proteins that activate proteins which in turn activate proteins which in turn activate certain cell processes such as cell certain cell processes such as cell division.division.

These kinases (Cdks) These kinases (Cdks) themselves are not activated themselves are not activated until they are attached to until they are attached to cyclin cyclin (becoming MPFs)(becoming MPFs)

Cyclin concentrations Cyclin concentrations fluctuate within a cell, slowly fluctuate within a cell, slowly building up until cell division building up until cell division begins.begins.

The MPF’s (Cdk-cyclin) The MPF’s (Cdk-cyclin) cause nuclear membrane cause nuclear membrane destruction and stimulate destruction and stimulate other kinases, setting the other kinases, setting the chain of events in motion chain of events in motion known as mitosis.known as mitosis.

The Cell Cycle (Internet click here)(click on the words above to (click on the words above to go to website and ACQUIRE more information on go to website and ACQUIRE more information on the cell cycle.)the cell cycle.)

Consists of phases Consists of phases characterized by characterized by important events in the important events in the life of a celllife of a cell

The Cell Cycle (Internet click here)

(click on the words above to go to website and (click on the words above to go to website and ACQUIREACQUIRE more information on the cell cycle.) more information on the cell cycle.)

After MitosisAfter Mitosis

MPFs (partially made of cyclin) levels MPFs (partially made of cyclin) levels must drop to allow the cell to enter must drop to allow the cell to enter interphase again.interphase again.

Proteins such as ubiquitin*, regulate the Proteins such as ubiquitin*, regulate the cycle by causing the degradation of cycle by causing the degradation of cyclin and kinases.cyclin and kinases.

This brings about the end of mitosis and This brings about the end of mitosis and the reforming of the nuclear membrane.the reforming of the nuclear membrane.

Thus the new cells continue to Thus the new cells continue to interphase.interphase.

**Ubiquitin – common across most eukaryotic species; hence Ubiquitin – common across most eukaryotic species; hence ubiquitous.ubiquitous.

Other Division Halting Other Division Halting ProcessesProcessesDensity-dependent inhibitionDensity-dependent inhibition – –

when the cell density when the cell density reaches a certain maximum, reaches a certain maximum, many cells stop dividing. many cells stop dividing.

Anchorage dependenceAnchorage dependence – – contact with a substratum contact with a substratum may influence if a cell stops may influence if a cell stops dividing.dividing.

External signalsExternal signals Growth factorsGrowth factors

– coordination between cellscoordination between cells– protein signals released by protein signals released by

body cells that stimulate other body cells that stimulate other cells to dividecells to divide

density-dependent inhibitiondensity-dependent inhibition – crowded cells stop dividingcrowded cells stop dividing– each cell binds a bit of growth each cell binds a bit of growth

factorfactor not enough activator left to not enough activator left to

trigger division in any one celltrigger division in any one cell Degradation of protein growth Degradation of protein growth

factors also possiblefactors also possible anchorage dependenceanchorage dependence

– to divide cells must be attached to divide cells must be attached to a substrateto a substrate ““touch sensor” receptorstouch sensor” receptors

Example of a Growth Example of a Growth FactorFactor

Platelet Derived Growth Factor (PDGF)Platelet Derived Growth Factor (PDGF)– made by platelets in blood clotsmade by platelets in blood clots– binding of PDGF to cell receptors stimulates binding of PDGF to cell receptors stimulates

cell division in connective tissuecell division in connective tissue heal woundsheal wounds

Other Division Halting Other Division Halting ProcessesProcesses

Necrosis and Apoptosis Necrosis and Apoptosis Necrosis – death due to insult/injuryNecrosis – death due to insult/injury Apoptosis – programmed cell deathApoptosis – programmed cell death What benefits would there be for an What benefits would there be for an

organism to destroy its own cells?organism to destroy its own cells?http://virtuallaboratory.colorado.edu/Biofundamentals/lectureNotes/Topic5-4_CellDeath.htm

CancerCancer Transformation – Alterations in genes Transformation – Alterations in genes

implicated with cell cycle begin the implicated with cell cycle begin the conversion of a normal cell to conversion of a normal cell to cancerous cell.cancerous cell.

OncogenesOncogenes Tumor Supressor genesTumor Supressor genes

– Tumor – mass of abnormal cellsTumor – mass of abnormal cells Benign – tumor remains at siteBenign – tumor remains at site Malignant – Becomes invasive enough to Malignant – Becomes invasive enough to

interfere with organ functioninterfere with organ function Metastasis – cancer cells spread to other sitesMetastasis – cancer cells spread to other sites

Development of Development of CancerCancer Cancer develops only after a cell Cancer develops only after a cell experiences ~6 key mutations (“hits”)experiences ~6 key mutations (“hits”)– unlimited growthunlimited growth

turn turn onon growth promoter genes growth promoter genes

– ignore checkpointsignore checkpoints turn turn offoff tumor suppressor genes (p53) tumor suppressor genes (p53)

– escape apoptosisescape apoptosis turn turn offoff suicide genes suicide genes

– immortality = unlimited divisionsimmortality = unlimited divisions turn turn onon chromosome maintenance genes chromosome maintenance genes

– promotes blood vessel growthpromotes blood vessel growth turn turn onon blood vessel growth genes blood vessel growth genes

– overcome anchor & density dependenceovercome anchor & density dependence turn turn offoff touch-sensor gene touch-sensor gene

DNA damage is causedby heat, radiation, or chemicals.

p53 allows cellswith repairedDNA to divide.

Step 1

DNA damage iscaused by heat,radiation, or chemicals.

Step 1 Step 2

Damaged cells continue to divide.If other damage accumulates, thecell can turn cancerous.

Step 3p53 triggers the destruction of cells damaged beyond repair.

ABNORMAL p53

NORMAL p53

abnormalp53 protein

cancercell

Step 3The p53 protein fails to stopcell division and repair DNA.Cell divides without repair todamaged DNA.

Cell division stops, and p53 triggers enzymes to repair damaged region.

Step 2

DNA repair enzymep53

proteinp53

protein

p53 — master regulator genep53 — master regulator gene

Explain the purpose of meioisis. Compare and contrast the processes of mitosis and meiosis.

Distinguish between male and female gametogenesis in humans. Define tetrad, homologous chromosome, synapsis. Describe the process of crossing-over. Identify the composition of a eukaryotic chromosome. Explain the results of a duplication, deletion, inversion and translocation of chromosomes. Define nondisjunction and provide examples of several genetic disorders resulting from nondisjunction.

Genomes and Genomes and ChromosomesChromosomes

A Closer Look at Reproduction A Closer Look at Reproduction

Genomes and Genomes and ChromosomesChromosomes

An organism is determined An organism is determined by its organism’s genetic by its organism’s genetic material or material or genomegenome. .

In order to maintain life, In order to maintain life, any new cells created must any new cells created must possess the same exact possess the same exact genome. genome.

Genome and Genome and ChromosomesChromosomes

The mitotic portion of the The mitotic portion of the cell cycle ensures that the cell cycle ensures that the genome is transferred genome is transferred correctly to the new cells correctly to the new cells created. created.

Genes and ChromosomesGenes and ChromosomesChromosomes are the condensed version of the DNA-protein complex called chromatin.

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Genes and ChromosomesGenes and Chromosomes

Once the Once the chromatin is chromatin is replicated replicated during the S during the S phase of the phase of the cell cycle a cell cell cycle a cell is ready to is ready to divide.divide.

Kinetochore

Mitosis vs. MeiosisMitosis vs. Meiosis

Mitosis Meiosis

Both

Mitosis vs. MeiosisMitosis vs. Meiosis

MitosisMitosis BothBoth MeiosisMeiosis

Chromosome Chromosome ReplicationReplication

Cell Cell division – division – end cell end cell ##Chromosome Chromosome

ResultResult

During S phase

Once -two

Twice –four

Same as original:

Diploid

Half of the

original- haploid

MeiosisMeiosis

For what purposes would For what purposes would “HALF” the chromosome “HALF” the chromosome material be appropriate?material be appropriate?

For the union of two cells (gametes) – sexual reproduction.

Meiosis IMeiosis I

Homologous ChromosomesHomologous Chromosomes pair up forming a “tetrad” in pair up forming a “tetrad” in a process called a process called synapsissynapsis..

At certain points the At certain points the chromatids of the homologs chromatids of the homologs may crisscross, forming a may crisscross, forming a chiasmatachiasmata..

Meiosis IMeiosis I

As the cell transists from As the cell transists from metaphase to anaphase it metaphase to anaphase it is the homologs which are is the homologs which are separated rather than the separated rather than the chromatids.chromatids.

Meiosis IMeiosis I

Cytokinesis occurs, resulting Cytokinesis occurs, resulting in two haploid cells.in two haploid cells.

Depending on the type of Depending on the type of gamete, meiosis II may gamete, meiosis II may proceed directly or be proceed directly or be carried out at a later date.carried out at a later date.

Meiosis IIMeiosis II

Proceeds much like the Proceeds much like the process of mitosis, process of mitosis, however, the end results however, the end results differ due to Meiosis I.differ due to Meiosis I.

4 haploid cells are created.

MeiosisMeiosis

Humans –Humans ––Spermatogenesis – 4 viable Spermatogenesis – 4 viable haploid sperm produced.haploid sperm produced.

–Oogenesis – 1 viable haploid Oogenesis – 1 viable haploid egg and 3 non-functional egg and 3 non-functional polar bodies produced.polar bodies produced.

http://legacy.owensboro.kctcs.edu/gcaplan/anat2/notes/gametogenesis.jpg

What is the advantage of producing one LARGE egg as opposed to 4 smaller ones?

MeiosisMeiosis

Plants – produce spores Plants – produce spores which then mitotically which then mitotically divide to form divide to form gametophyte. This gametophyte. This produces gametes which produces gametes which then fuse to form then fuse to form sporophyte.sporophyte.

Genetic VariationGenetic Variation

Does not exist in cells Does not exist in cells produced by mitosis, unless produced by mitosis, unless some mutation arises.some mutation arises.

Sexual reproduction Sexual reproduction provides a recombination of provides a recombination of genetic material in 3 ways.genetic material in 3 ways.


Independent assortment of Independent assortment of homologues.homologues.


Random joining of gametes.Random joining of gametes.Getting here is

only HALF the race

Boys!


Crossing over, Crossing over,

as demonstrated in lab activity,as demonstrated in lab activity,

involves the exchange of genetic involves the exchange of genetic material between nonsister material between nonsister chromatids, during prophase I chromatids, during prophase I


Deletion and duplication –Deletion and duplication –

see lab activitysee lab activity Inversion–Inversion–

see lab activitysee lab activity

CHROMOSOMES, CHROMOSOMES, KARYOTYPES, KARYOTYPES, AND SEXUAL LIFE AND SEXUAL LIFE CYCLESCYCLES

KARYOTYPEKARYOTYPE

“CARTOONIZED” Ideogram of chromosome after staining. The short arm of the chromosome is referred to as “p” and the long arm as “q”.

KARYOTYPEKARYOTYPE

ORDERED DISPLAY OF AN ORDERED DISPLAY OF AN INDIVIDUAL’S CHROMOSOMES.INDIVIDUAL’S CHROMOSOMES.

PREPARED BY TREATING CELLS PREPARED BY TREATING CELLS WITH DRUG TO STIMULATE WITH DRUG TO STIMULATE MITOSIS AND THEN ADDING MITOSIS AND THEN ADDING ANOTHER TO STOP IT AT ANOTHER TO STOP IT AT METAPHASE.METAPHASE.

KARYOTYPEKARYOTYPE

CAN BE USED TO CAN BE USED TO DIAGNOSE CERTAIN DIAGNOSE CERTAIN GENETIC DISORDERS GENETIC DISORDERS (SUCH AS (SUCH AS ANEUPLOIDYANEUPLOIDY CAUSED BY CAUSED BY NONDISJUNCTION).NONDISJUNCTION).

KARYOTYPESKARYOTYPES

COLOR ENHANCED BY COMPUTER

KARYOTYPESKARYOTYPES•BANDING CREATED BY THE USE OF DYES.

•USED TO IDENTIFY SPECIFIC CHROMOSOMES.

CHROMOSOME LENGTH, SHAPE, AND POSITION OF CENTROMERE USED FOR IDENTIFICATION.

KARYOTYPESKARYOTYPESWhat can you determine about this individual?

KARYOTYPESKARYOTYPESWhat about this individual?

KARYOTYPESKARYOTYPESLASTLY, WHAT ABOUT THIS INDIVIDUAL?

Sexual Life CyclesSexual Life Cycles

Many organisms, other than Many organisms, other than animals, sexually reproduce. animals, sexually reproduce.

Sexual reproduction is a way to Sexual reproduction is a way to increase variety within a population.increase variety within a population.

This can then lead to evolution of This can then lead to evolution of the populations themselves.the populations themselves.

The sexual life cycle itself, has been The sexual life cycle itself, has been subject to evolutionary changes.subject to evolutionary changes.

cell cycle identify the cell structures involved in cell division. identify and explain the events...

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