Big Idea 3Big Idea 3

Ch. 12 – The Cell CycleCh. 12 – The Cell Cycle

Essential Knowledge 3.A.2 (a Essential Knowledge 3.A.2 (a & b)& b)

Review – Chromosome Review – Chromosome structurestructure

Before we begin the Before we begin the cell cycle, let’s review cell cycle, let’s review chromosomeschromosomes

A chromosome is a A chromosome is a tightly coiled piece of tightly coiled piece of DNADNA

DNA is a double helix of DNA is a double helix of chromatin wrapped chromatin wrapped around histone proteins around histone proteins

Parts:Parts: One side is a chromatidOne side is a chromatid The other side is an The other side is an

identical sister identical sister chromatidchromatid

Centromere (no genes Centromere (no genes located here)located here)

Chromosomes and numbersChromosomes and numbers Each of your somatic cells (body Each of your somatic cells (body

cells) have 46 chromosomescells) have 46 chromosomes Each parent gives 23 Each parent gives 23

chromosomes, making 23 pairs chromosomes, making 23 pairs (46 individual strands)(46 individual strands)

The chromosomes that make up The chromosomes that make up a pair (one from each parent) a pair (one from each parent) are called homologous are called homologous chromosomeschromosomes

They are the same length and They are the same length and have the same have the same centromerecentromere position (holding them together) position (holding them together) and they carry genes that and they carry genes that control the same inherited traitscontrol the same inherited traits

Ex – the gene for earlobe type Ex – the gene for earlobe type will be located at the same will be located at the same position on both homologous position on both homologous chromosomes); they would each chromosomes); they would each code for earlobe type, they may code for earlobe type, they may not code for the same TYPE of not code for the same TYPE of earlobeearlobe

Size and complexity of an Size and complexity of an organism has nothing to do with organism has nothing to do with how many chromosomes it has how many chromosomes it has

Haploid and diploidHaploid and diploid GametesGametes are sex cells (like an egg or are sex cells (like an egg or

sperm) that have half the number of sperm) that have half the number of chromosomes as our regular body chromosomes as our regular body cells– in humans each gamete has 23 cells– in humans each gamete has 23 chromosomes (instead of 46).chromosomes (instead of 46).

The symbol The symbol nn can be used to can be used to represent the number of represent the number of chromosomes in a gametechromosomes in a gamete

A cell with A cell with nn number number of of chromosomes is called a chromosomes is called a haploidhaploid cell cell (haploos means single in greek) – (haploos means single in greek) – they have one set of chromosomesthey have one set of chromosomes

When one haploid gamete combines When one haploid gamete combines with another it’s called with another it’s called fertilizationfertilization – – when that happens, the cell will now when that happens, the cell will now contain a total ofcontain a total of 2n 2n chromosomes (n chromosomes (n from the female and n from the male from the female and n from the male parent)parent)

A cell that has a A cell that has a 2n2n number number of of chromosomes is called a chromosomes is called a diploiddiploid cell – cell – they have 2 sets of chromosomesthey have 2 sets of chromosomes

Overview: The Cell TheoryOverview: The Cell Theory

There are 3 parts to the cell theory:There are 3 parts to the cell theory:– 1. A cell is the basic unit of life1. A cell is the basic unit of life– 2. All living things are made of one or 2. All living things are made of one or

more cellsmore cells– 3. Cells make more cells3. Cells make more cells

OverviewOverview Mitosis is generally Mitosis is generally

used to mean exact used to mean exact copying of cells copying of cells (technically it’s the (technically it’s the division of the nucleus)division of the nucleus)

Why is it important?Why is it important?– It’s what helped change It’s what helped change

you from a zygote to an you from a zygote to an embryo to a fetus and embryo to a fetus and finally to you (growth*).finally to you (growth*).

– It helps some organisms It helps some organisms reproduce (asexually)reproduce (asexually)

– Used when you form Used when you form scabs (repair)scabs (repair)

*you start life as a single *you start life as a single cell and end up with cell and end up with millions of cells with the millions of cells with the exact same DNA insideexact same DNA inside

The Cell CycleThe Cell Cycle This how we go from one This how we go from one

cell to make 2 cellscell to make 2 cells It’s basically like a It’s basically like a

photocopy machinephotocopy machine Cells duplicate their Cells duplicate their

genetic material before genetic material before they divide, ensuring that they divide, ensuring that each daughter cell receives each daughter cell receives an exact copy of the an exact copy of the genetic material(DNA)genetic material(DNA)

Three parts:Three parts:– InterphaseInterphase– MitosisMitosis– CytokinesisCytokinesis

The Cell Cycle cont. - The Cell Cycle cont. - InterphaseInterphase

Interphase is the first step Interphase is the first step (happens before mitosis (happens before mitosis starts)starts)– Consists of 3 phasesConsists of 3 phases– This is where the cell spends This is where the cell spends

most of its timemost of its time Begins with the Begins with the G1G1 phase phase

(Stands for Gap, but think of it (Stands for Gap, but think of it as Grow, because that’s what as Grow, because that’s what happens) – Cell gets biggerhappens) – Cell gets bigger

SS phase (stands for synthesis) phase (stands for synthesis) is next – this is where DNA is is next – this is where DNA is copied (you double the copied (you double the amount of DNA)amount of DNA)

G2 G2 is the last phase of is the last phase of interphase – continues to interphase – continues to growgrow

Some cells never copy Some cells never copy themselves (like in your themselves (like in your central nervous system – central nervous system – nerves in your brain) so they nerves in your brain) so they stay in a phase called G0 stay in a phase called G0

LE 12-5LE 12-5

G1

G2

S(DNA synthesis)

INTERPHASE

Cytoki

nesis

MITOTIC(M) PHASE

Mitos

is

Mitosis is conventionally divided into four basic Mitosis is conventionally divided into four basic phases:phases:– ProphaseProphase– MetaphaseMetaphase– AnaphaseAnaphase– TelophaseTelophase– Remember: Remember: PMAT (or Please Make Another PMAT (or Please Make Another

Taco); Taco); Cytokinesis is well underway by late telophaseCytokinesis is well underway by late telophase

Phases of MitosisPhases of Mitosis it’s a smooth transition between it’s a smooth transition between

each phase (like a movie)each phase (like a movie) Prophase Prophase – first step of Mitosis– first step of Mitosis

– Chromatin (loose DNA) Chromatin (loose DNA) condenses and thickens into condenses and thickens into chromosomeschromosomes

– Nucleolus disappearsNucleolus disappears– Centrosomes begin to move to Centrosomes begin to move to

either side of the celleither side of the cell– Spindle fibers begin to formSpindle fibers begin to form– prometaphaseprometaphase – –

nuclear membrane nuclear membrane disappears, disappears,

chromosomes form two chromosomes form two kinetochoreskinetochores at the at the centromere - (kinetochores centromere - (kinetochores are like little pacmans that are like little pacmans that are inside the chromosomes are inside the chromosomes and spindles attach to them)and spindles attach to them)

Microtubules (which make Microtubules (which make up the spindle fibers) attach up the spindle fibers) attach to the chromosomesto the chromosomes

MetaphaseMetaphase

Meet in the MiddleMeet in the Middle All the All the

chromosomes line chromosomes line up along the center up along the center of the cellof the cell

Guided by the Guided by the spindle fibersspindle fibers

AnaphaseAnaphase

Move apart – Move apart – separate to the separate to the polespoles

All the sister All the sister chromatids chromatids separate separate simultaneously (we simultaneously (we don’t know how)don’t know how)

Spindle ApparatusSpindle Apparatus The mitotic spindle is an The mitotic spindle is an

apparatus of microtubules apparatus of microtubules (which make up spindle (which make up spindle fibers) that controls fibers) that controls chromosome movement chromosome movement during mitosisduring mitosis

In anaphase, sister In anaphase, sister chromatids separate and chromatids separate and move along the move along the kinetochore microtubules kinetochore microtubules toward opposite ends of toward opposite ends of the cellthe cell

LE 12-8bLE 12-8b

Chromosomemovement

Microtubule Motorprotein

Chromosome

Kinetochore

Tubulinsubunits

TelophaseTelophase The EndThe End New nuclear New nuclear

envelope formsenvelope forms Chromsomes relax Chromsomes relax

back into chromatin back into chromatin (DNA strands)(DNA strands)

Nucleoli reappearNucleoli reappear Each side has an Each side has an

identical copy of the identical copy of the DNADNA

*basically this is a *basically this is a rewind of what rewind of what happened in happened in ProphaseProphase

CytokinesisCytokinesis Happens Happens AFTER AFTER mitosis mitosis

is completeis complete In animal cells, In animal cells,

cytokinesis occurs by a cytokinesis occurs by a process known as process known as cleavage, forming a cleavage, forming a cleavage furrowcleavage furrow

Division of the cytoplasmDivision of the cytoplasm End with End with two identical two identical

daughter cellsdaughter cells Cells begin the process Cells begin the process

over again (starting with over again (starting with G1)G1)

PlantsPlants Plants go through Plants go through

the same process the same process with just a small with just a small differencedifference

They can’t just divide They can’t just divide in half because of in half because of their cell walltheir cell wall

They build a cell They build a cell plate that forms in plate that forms in the center of the cell, the center of the cell, which forms a new which forms a new cell wallcell wall

The cell cycle is regulated by The cell cycle is regulated by a molecular control systema molecular control system

The frequency of cell division varies with the The frequency of cell division varies with the type of celltype of cell

The cell cycle appears to be driven by The cell cycle appears to be driven by specific chemical signals present in the specific chemical signals present in the cytoplasmcytoplasm

Control of the Cell CycleControl of the Cell Cycle

• For many cells, the GFor many cells, the G11 checkpoint seems to be checkpoint seems to be the most important onethe most important one

• If a cell receives a go-If a cell receives a go-ahead signal at the Gahead signal at the G11 checkpoint, it will usually checkpoint, it will usually complete the S, Gcomplete the S, G22, and , and Mitosis phases and divideMitosis phases and divide

• If the cell does not receive If the cell does not receive the go-ahead signal, it will the go-ahead signal, it will exit the cycle, switching exit the cycle, switching into a nondividing state into a nondividing state called the Gcalled the G00 phase phase

M G2

G1 S

The Cell Cycle Clock: Cyclins and The Cell Cycle Clock: Cyclins and Cyclin-Dependent KinasesCyclin-Dependent Kinases

How does the cell know when to divide?How does the cell know when to divide?– Two types of regulatory proteins are involved in Two types of regulatory proteins are involved in

cell cycle control: cyclins and cyclin-dependent cell cycle control: cyclins and cyclin-dependent kinases (Cdks)kinases (Cdks)

– The activity of cyclins and Cdks fluctuates The activity of cyclins and Cdks fluctuates during the cell cycleduring the cell cycle

There are proteins inside of the cell, and as they There are proteins inside of the cell, and as they build up throughout the life of the cell you eventually build up throughout the life of the cell you eventually get a critical number that tells the cell to advance to get a critical number that tells the cell to advance to the next stage of divisionthe next stage of division

CalledCalled cyclins cyclins (the number of these fluctuates (the number of these fluctuates depending on where you are in the cell cycle – so depending on where you are in the cell cycle – so depending on how many you have, it will tell the cell depending on how many you have, it will tell the cell to move on to the next phase)to move on to the next phase)

CDKs CDKs are a cyclin-dependent are a cyclin-dependent kinasekinase ( (a chemical that a chemical that can speed up actions in the cellcan speed up actions in the cell))

A typical cell in your body would have many CDKs; A typical cell in your body would have many CDKs; cyclin builds up over time, and begin to fit into the cyclin builds up over time, and begin to fit into the CDKs, which activates a “CDK cyclin complex” CDKs, which activates a “CDK cyclin complex” (you (you don’t need to know specific complex names for don’t need to know specific complex names for the test), the test), which creates a protein that can do stuff which creates a protein that can do stuff like:like:

– MPFMPF – mitosis promoting factor- is a specific – mitosis promoting factor- is a specific type of CDK that break up the nucleus to begin type of CDK that break up the nucleus to begin cell divisioncell division

– Work on microtubules to help build the spindle Work on microtubules to help build the spindle apparatusapparatus

Cancer and other stuffCancer and other stuff Cancer is basically cells reproducing out Cancer is basically cells reproducing out

of controlof control– Occasionally you get a mutation that Occasionally you get a mutation that

suppresses the cancer suppressing suppresses the cancer suppressing genegene

– They can move to other parts of They can move to other parts of your body and activate other cells to your body and activate other cells to become cancerousbecome cancerous

– A group of cells growing out of A group of cells growing out of control is called a tumorcontrol is called a tumor

If abnormal cells remain at the original If abnormal cells remain at the original site, the lump is called a benign tumorsite, the lump is called a benign tumor

Malignant tumors invade surrounding Malignant tumors invade surrounding tissues and can metastasize, exporting tissues and can metastasize, exporting cancer cells to other parts of the body, cancer cells to other parts of the body, where they may form secondary tumorswhere they may form secondary tumors

Apoptosis Apoptosis – programmed cell death (the – programmed cell death (the cells shrink and shrivel in a controlled cells shrink and shrivel in a controlled process)process)– Happens in your hands and feet as Happens in your hands and feet as

they begin to develop, or when a they begin to develop, or when a leaf falls from a treeleaf falls from a tree

Necrosis Necrosis – cell death due to injury or – cell death due to injury or illness of the tissueillness of the tissue

Binary FissionBinary Fission Prokaryotes (bacteria and archaea) reproduce by Prokaryotes (bacteria and archaea) reproduce by

a type of cell division called binary fissiona type of cell division called binary fission In binary fission, the chromosome replicates In binary fission, the chromosome replicates

(beginning at the origin of replication), and the (beginning at the origin of replication), and the two daughter chromosomes actively move aparttwo daughter chromosomes actively move apart

Since prokaryotes evolved before eukaryotes, Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fissionmitosis probably evolved from binary fission

Certain protists exhibit types of cell division that Certain protists exhibit types of cell division that seem intermediate between binary fission and seem intermediate between binary fission and mitosismitosis