Cell Growth and Cell Growth and ReproductionReproduction

Limitations on Cell SizeLimitations on Cell SizeDiffusionDiffusion Larger the cell, the longer it takes to get Larger the cell, the longer it takes to get

nutrients from outside the cell through nutrients from outside the cell through diffusion.diffusion.

DNADNA Larger cells need more DNA to support the Larger cells need more DNA to support the

functions of the cell (i.e. protein synthesis).functions of the cell (i.e. protein synthesis).

Limitations on Cell SizeLimitations on Cell SizeSurface Area to Volume RatioSurface Area to Volume Ratio Volume increases at a higher rate than Volume increases at a higher rate than

surface area.surface area. As cell increases in volume, more nutrients As cell increases in volume, more nutrients

are needed and more wastes are created.are needed and more wastes are created. Surface area of the cell is not sufficient for the Surface area of the cell is not sufficient for the

diffusion of nutrients and wastes.diffusion of nutrients and wastes.

Cell DivisionCell Division

Occurs before the cell becomes too large Occurs before the cell becomes too large to be efficient.to be efficient.

Results in two cells which are identical to Results in two cells which are identical to the original parent cell.the original parent cell.

Chromosomes, Chromatin, and Chromosomes, Chromatin, and Sister ChromatidsSister Chromatids

ChromatinChromatin Long strands of DNA wrapped around Long strands of DNA wrapped around

proteins called histones.proteins called histones.Each groups of histones is called a nucleosome.Each groups of histones is called a nucleosome.

Exist between times of division.Exist between times of division.

Chromosomes, Chromatin, and Chromosomes, Chromatin, and Sister ChromatidsSister Chromatids

ChromosomesChromosomes Before a cell can divide, chromatin must be Before a cell can divide, chromatin must be

reorganized into tight coils called reorganized into tight coils called chromosomes.chromosomes.

Appear before cell division and disappear Appear before cell division and disappear soon after cell division is complete.soon after cell division is complete.

Chromosomes, Chromatin, and Chromosomes, Chromatin, and Sister ChromatidsSister Chromatids

Sister ChromatidsSister Chromatids Accurate transmission of chromosomes Accurate transmission of chromosomes

during cell division is critical, so before during cell division is critical, so before division chromosomes copy themselves.division chromosomes copy themselves.

When copied, chromosomes form two sister When copied, chromosomes form two sister chromatids that are exact copies of each chromatids that are exact copies of each other.other.

The two sister chromatids are held together The two sister chromatids are held together by a centromere.by a centromere.

Chromosomes, Chromatin, and Chromosomes, Chromatin, and Sister ChromatidsSister Chromatids

Cell CycleCell Cycle

Sequence of growth and division in a cell.Sequence of growth and division in a cell.

Divided into two parts:Divided into two parts: InterphaseInterphase MitosisMitosis

InterphaseInterphaseGrowth period in which a cell spends Growth period in which a cell spends most of its life.most of its life.

InterphaseInterphase3 distinct divisions:3 distinct divisions:

1.1. Cell grows and protein production is high.Cell grows and protein production is high.

2.2. Cell copies its chromosomes and DNA Cell copies its chromosomes and DNA synthesis occurs.synthesis occurs.

3.3. Short period of growth during which Short period of growth during which mitochondria and other organelles are mitochondria and other organelles are manufactured and cell parts needed for cell manufactured and cell parts needed for cell division are assembled.division are assembled.

MitosisMitosisPeriod of nuclear division.Period of nuclear division.

During mitosis, two daughter cells are During mitosis, two daughter cells are formed.formed. Each daughter cell contains a complete set of Each daughter cell contains a complete set of

chromosomes.chromosomes.

Following mitosis, the cytoplasm divides, Following mitosis, the cytoplasm divides, separating the two daughter cells.separating the two daughter cells.

4 Phases of Mitosis4 Phases of Mitosis

1.1. ProphaseProphase

2.2. MetaphaseMetaphase

3.3. AnaphaseAnaphase

4.4. TelophaseTelophase

ProphaseProphase

Longest phase of mitosis.Longest phase of mitosis.

Long, stringy chromatin coils up into Long, stringy chromatin coils up into visible chromosomes.visible chromosomes.

Nucleus disappears as the nuclear Nucleus disappears as the nuclear envelope and nucleolus disintegrate.envelope and nucleolus disintegrate.

ProphaseProphase

In animal cells, the centrioles migrate to In animal cells, the centrioles migrate to opposite sides of the cell and the spindle opposite sides of the cell and the spindle forms between them.forms between them.

In plant cells the spindle forms without In plant cells the spindle forms without centrioles.centrioles.

ProphaseProphase

CentriolesCentrioles

Small dark, cylindrical structures made of Small dark, cylindrical structures made of microtubules.microtubules.

Located just outside the nucleus.Located just outside the nucleus.

Play a role in chromotid separation.Play a role in chromotid separation.

SpindleSpindle

Football shaped, cage like structure Football shaped, cage like structure consisting of thin fibers made of consisting of thin fibers made of microtubules.microtubules.

Plays a vital role in separation of sister Plays a vital role in separation of sister chromatids.chromatids.

MetaphaseMetaphase

ShortShort

Doubled chromosomes become attached Doubled chromosomes become attached to the spindle fibers by their centromeres.to the spindle fibers by their centromeres.

Chromosomes are pulled by the spindle Chromosomes are pulled by the spindle fibers and begin to line up on the mid-line fibers and begin to line up on the mid-line of the spindle.of the spindle.

MetaphaseMetaphase

Each sister chromatid is attached to its Each sister chromatid is attached to its own spindle fiber. Each of these spindle own spindle fiber. Each of these spindle fibers extend to opposite poles to ensure fibers extend to opposite poles to ensure that each new cell receives and identical that each new cell receives and identical and complete set of chromosomes. and complete set of chromosomes.

MetaphaseMetaphase

AnaphaseAnaphase

Beginning is marked by the separation of Beginning is marked by the separation of sister chromatids.sister chromatids.

The centromeres split apart and chromatid The centromeres split apart and chromatid pairs from each chromosome separate pairs from each chromosome separate from each other.from each other.

Chromatids are pulled apart by the Chromatids are pulled apart by the shortening of microtubules in the spindle shortening of microtubules in the spindle fibersfibers

AnaphaseAnaphase

TelophaseTelophase

Begins as chromatids reach the opposite Begins as chromatids reach the opposite poles of the cell.poles of the cell.

Many of the changes that occurred during Many of the changes that occurred during prophase are reversed as the new cells prophase are reversed as the new cells prepare to exist independently.prepare to exist independently.

TelophaseTelophaseTightly wound chromosomes begin to Tightly wound chromosomes begin to unwind.unwind.

Spindle begins to break down.Spindle begins to break down.

Nucleolus reappears.Nucleolus reappears.

New nuclear envelope forms around each New nuclear envelope forms around each set of chromosomes.set of chromosomes.

New double membrane begins to form New double membrane begins to form between the two nuclei.between the two nuclei.

TelophaseTelophase

CytokinesisCytokinesis

Division of the cytoplasm following Division of the cytoplasm following telophase.telophase.

Animals:Animals: Towards the end of telophase, the plasma Towards the end of telophase, the plasma

membrane pinches in along the equator and membrane pinches in along the equator and the two cells begin to separate.the two cells begin to separate.

CytokinesisCytokinesis

Plants:Plants: A structure called a cell plate is laid down A structure called a cell plate is laid down

across the equator of the cell.across the equator of the cell. A cell membrane forms around each cell and A cell membrane forms around each cell and

new cell walls form on each new side of the new cell walls form on each new side of the cell plate until separation is complete.cell plate until separation is complete.

CytokinesisCytokinesis

Results of MitosisResults of Mitosis

Unicellular organisms produce two new Unicellular organisms produce two new single-celled organisms.single-celled organisms.

Multicellular organisms produce groups of Multicellular organisms produce groups of cells that work together as tissues to cells that work together as tissues to perform specific functions.perform specific functions. Tissues further organize to form organs.Tissues further organize to form organs. Multiple organs form an organ system.Multiple organs form an organ system.