Cell CycleCell Cycle

The Cell Cycle DefinitionThe Cell Cycle Definition

a.a. The cell cycle is the regular The cell cycle is the regular sequence sequence of growth and divisionof growth and division that cells that cells undergo.undergo.

b.b. This occurs as one This occurs as one parent cellparent cell divides divides to form to form two identical daughter cells.two identical daughter cells.

Parent Cell Daughter Cells

“Parent” cell (or Plainsman in this case)

2 identical “daughter” cells

Cell Cycle StagesCell Cycle Stages

There are 3 main stages in the cell There are 3 main stages in the cell cycle:cycle:

1.1. InterphaseInterphase

2.2. MitosisMitosis

3.3. CytokinesisCytokinesis

STAGE 1: INTERPHASESTAGE 1: INTERPHASE

a.a. InterphaseInterphase is the is the firstfirst stage of the stage of the cell cell cycle.cycle.

b.b. It is the period It is the period BEFORE cell division BEFORE cell division occurs.occurs.

c.c. During interphase, the cell During interphase, the cell grows to its grows to its mature size,mature size, makes makes a copy of its DNAa copy of its DNA and and prepares to divide into 2 cells.prepares to divide into 2 cells.

STAGE 1: INTERPHASE STAGE 1: INTERPHASE (continued)(continued)

d. Interphase has three parts:d. Interphase has three parts:1.1. GrowthGrowth:: when the cell when the cell growsgrows to its to its mature size.mature size.2.2. DNA ReplicationDNA Replication:: in the nucleus, the cell makes a in the nucleus, the cell makes a

copy of its DNA.copy of its DNA.a. There will be a. There will be 2 identical sets of DNA2 identical sets of DNA at the end of at the end of

DNA replication.DNA replication.3.3. PreparationPreparation for division: when the for division: when the cell produces cell produces

structuresstructures that it will use to divide. that it will use to divide.

To sum interphase up, it’s when the cell is GROWING, To sum interphase up, it’s when the cell is GROWING, COPYING its DNA, and PREPARING to DIVIDE.COPYING its DNA, and PREPARING to DIVIDE.

STAGE 2: MITOSISSTAGE 2: MITOSIS

a.a. MitosisMitosis is the stage is the stage when the cell’s when the cell’s nucleus divides into nucleus divides into two nucleitwo nuclei (= plural of (= plural of nucleus). nucleus).

b.b. Each daughter cell Each daughter cell receives receives 1 copy of DNA1 copy of DNA from the parent cell. from the parent cell.

c.c. Condensed chromatin Condensed chromatin forms a forms a chromatid,chromatid, and two identical and two identical chromatidschromatids are called are called chromosome,chromosome, joined joined by a by a centromere.centromere.

Chromosome StructureChromosome Structure

STAGE 2: MITOSIS STAGE 2: MITOSIS (continued)(continued)

d. There are four phases of mitosis that can be d. There are four phases of mitosis that can be abbreviated as abbreviated as ““PMAT”:PMAT”:1.1. Prophase:Prophase: when 1) when 1) chromosomes form,chromosomes form, 2) 2)

spindle fibersspindle fibers form, and 3) the form, and 3) the nuclear nuclear membranemembrane (= nuclear envelope) breaks down. (= nuclear envelope) breaks down.

2.2. Metaphase:Metaphase: the the chromosomes line up in the chromosomes line up in the middlemiddle of the cell and of the cell and attach to aattach to a spindle fiberspindle fiber at the at the centromere.centromere.

3.3. Anaphase:Anaphase: centromeres centromeres splitsplit and the and the chromatidschromatids separateseparate while the cell becomes while the cell becomes stretched out.stretched out.

4.4. Telophase:Telophase: chromatidschromatids unravels back into unravels back into chromatin and a new chromatin and a new nuclear membrane forms.nuclear membrane forms.

STAGE 2: MITOSIS (continued)STAGE 2: MITOSIS (continued)

Prophase Metaphase Anaphase Telophase

1) 1) chromosomes chromosomes form form

2) spindle 2) spindle fibers form fibers form

3) the nuclear 3) the nuclear membrane membrane breaks down.breaks down.

ChromosomeChromosomes line up in s line up in the center of the center of the cell and the cell and attach to a attach to a spindle fiber spindle fiber at the at the centromere.centromere.

Centromeres Centromeres split and the split and the chromatids chromatids separate while separate while the cell the cell becomes becomes stretched out.stretched out.

ChromsosomChromsosomes unravels es unravels back into back into chromatin chromatin and a new and a new nuclear nuclear membrane membrane forms.forms.

STAGE 3: CYTOKINESISSTAGE 3: CYTOKINESIS

a.a. CytokinesisCytokinesis starts at the end of mitosis and is starts at the end of mitosis and is when when the parent cell dividesthe parent cell divides, passing out the organelles , passing out the organelles into the two new cells.into the two new cells.

b.b. In an In an animalanimal cell, the cell, the cell membranecell membrane formsforms around around the center of the two new cells and thethe center of the two new cells and the cytoplasm is cytoplasm is divided evenly.divided evenly.

c.c. In a In a plantplant cell, the cell membrane forms before the cell, the cell membrane forms before the cell wall. A cell wall. A cell platecell plate is created between the two is created between the two new cells which gradually new cells which gradually becomes the cell wall.becomes the cell wall.

d.d. Once Once cytokinesiscytokinesis is complete, the is complete, the new cells enternew cells enter interphaseinterphase again and the cell again and the cell cycle cycle repeatsrepeats..

NOW THERE ARE 2 NEW CELLS!!! NOW THERE ARE 2 NEW CELLS!!!

CYTOKINESIS IN A PLANT CYTOKINESIS IN A PLANT CELLCELL

Length of the cell cycleLength of the cell cycle

a.a. The The length of the cell cycle varieslength of the cell cycle varies for for all types of cells.all types of cells.1. Cell division DOES NOT occur in all of your 1. Cell division DOES NOT occur in all of your

brain cells… what do you think that brain cells… what do you think that means?means?

b.b. InterphaseInterphase is ALWAYS the is ALWAYS the longestlongest stage of the cell cycle…NO MATTER stage of the cell cycle…NO MATTER WHAT KIND OF CELL IT IS!!!!!!!!!!WHAT KIND OF CELL IT IS!!!!!!!!!!

DNA ReplicationDNA ReplicationThis occurs in InterphaseThis occurs in Interphase

a.a. DNADNA replication is important replication is important because it makes sure that because it makes sure that each each daughter cell will have all of the daughter cell will have all of the genetic information it needs.genetic information it needs.

b.b. James WATSONJames WATSON and and Francis Francis CRICKCRICK were the two scientists that were the two scientists that figured out the figured out the structure of DNA.structure of DNA.

c.c. The shape of DNA is called a The shape of DNA is called a double double helixhelix because it looks like a because it looks like a twisted twisted ladderladder or or spiral staircase.spiral staircase.

d.d. The two sides of the DNA ladder are The two sides of the DNA ladder are made of made of deoxyribosedeoxyribose (a type of (a type of sugar) and alternates with sugar) and alternates with phosphates.phosphates.

IT’S PRETTY!

DNA StructureDNA Structure

e. The e. The rungsrungs of the ladder are made of the ladder are made of a of a pair pair of molecules, called of molecules, called nitrogen basesnitrogen bases, and there are , and there are four types:four types:1.1. ADENINE:ADENINE: only pairs with thymine.only pairs with thymine.2.2. THYMINE:THYMINE: only pairs with adenine. only pairs with adenine.3.3. CYTOSINE:CYTOSINE: only pairs with guanine. only pairs with guanine.4.4. GUANINE:GUANINE: only pairs with cytosine. only pairs with cytosine.ALWAYS REMEMBER: ALWAYS REMEMBER: A-TA-T and and C-GC-G

because it’s how they pair!because it’s how they pair!

DNA ReplicationDNA Replication

f. During DNA replication, the f. During DNA replication, the two sides two sides unwind and unwind and separate.separate.

g. In the nucleus, other free-g. In the nucleus, other free-floating floating nitrogen basesnitrogen bases will will attach to the separated attach to the separated strands of strands of DNA.DNA. These will These will form an form an identical strand of identical strand of DNADNA as the original as the original separated strand.separated strand.