Cell Cycle and Cellular Reproduction

Mader-Chapter 9… and some extra stuff

Essential knowledge 3.A.2: In eukaryotes, heritable information is passedto the next generation via processes that include the cell cycle and mitosisor meiosis plus fertilization.a. The cell cycle is a complex set of stages that is highly regulated withcheckpoints, which determine the ultimate fate of the cell.Evidence of student learning is a demonstrated understanding of eachof the following:1. Interphase consists of three phases: growth, synthesis of DNA,preparation for mitosis.2. The cell cycle is directed by internal controls or checkpoints.Internal and external signals provide stop-and-go signs at thecheckpoints.To foster student understanding of this concept, instructors canchoose an illustrative example such as:• Mitosis-promoting factor (MPF)• Action of platelet-derived growth factor (PDGF)• Cancer results from disruptions in cell cycle control3. Cyclins and cyclin-dependent kinases control the cell cycle.

✘✘ Knowledge of any one cyclin-CdK pair or growth factor is beyondthe scope of the course and the AP Exam.

4. Mitosis alternates with interphase in the cell cycle.5. When a cell specializes, it often enters into a stage where itno longer divides, but it can reenter the cell cycle when givenappropriate cues. Nondividing cells may exit the cell cycle; orhold at a particular stage in the cell cycle.b. Mitosis passes a complete genome from the parent cell to daughtercells.Evidence of student learning is a demonstrated understanding of eachof the following:1. Mitosis occurs after DNA replication.2. Mitosis followed by cytokinesis produces two geneticallyidentical daughter cells.3. Mitosis plays a role in growth, repair, and asexual reproduction4. Mitosis is a continuous process with observable structuralfeatures along the mitotic process. Evidence of student learningis demonstrated by knowing the order of the processes(replication, alignment, separation).

✘✘Memorization of the names of the phases of mitosis is beyond thescope of the course and the AP Exam.

Where it all began…You started as a cell smaller than a period at the end of a sentence…

• Going from egg to baby…. the original fertilized egg has to divide…

and divide…and divide…

and divide…

Getting from there to here…

• For reproduction – asexual reproduction

• one-celled organisms

• For growth– from fertilized egg to

multi-celled organism • For repair & renewal

– replace cells that die from normal wear & tear or from injury

Why do cells divide?

amoeba

Size vs. Surface Area

A cell that is actively metabolizing must stay small by continuously dividing so that it can efficiently move metabolites into and out of the cell

Also, remember that there is only one copy of

DNA!

The Life Cycle of the Cell

Do all mammalian cells, through the adult stages of life, continuously move through the cell cycle?

Cell Cycle MMitosis

G1Gap 1

G0Resting

G2Gap 2

SSynthesis

• Cell has a “life cycle”

cell is formed from a mitotic division

cell grows & maturesto divide again

cell grows & matures to never divide again

G1, S, G2, M G1G0

epithelial cells,blood cells,stem cells

liver cells

brain / nerve cellsmuscle cells

Interphase• 90% of cell life cycle

– cell doing its “everyday job”• produce RNA, synthesize proteins/enzymes

– prepares for duplication if triggered

I’m working here!

Time to divide& multiply!

Interphase• Divided into 3 phases:

– G1 = 1st Gap (Growth)• cell doing its “everyday job”• cell grows

– S = DNA Synthesis• copies chromosomes

– G2 = 2nd Gap (Growth)• prepares for division • cell grows (more)• produces organelles,

proteins, membranes

G0

signal to

divide

Interphase• Nucleus well-defined

– DNA loosely packed in long chromatin fibers

• Prepares for mitosis – replicates chromosome

• DNA & proteins– produces proteins &

organelles

green = key features

• Synthesis phase of Interphase– dividing cell replicates DNA– must separate DNA copies correctly to 2

daughter cells• human cell duplicates ~3 meters DNA • each daughter cell gets complete

identical copy• error rate = ~1 per 100 million bases

– 3 billion base pairs in mammalian genome– ~30 errors per cell cycle

» mutations (to somatic (body) cells)

S phase: Copying / Replicating DNA

Organizing DNA• DNA is organized in

chromosomes– double helix DNA molecule– wrapped around histone

proteins• like thread on spools

– DNA-protein complex =chromatin• organized into long thin fiber

– condensed further during mitosis

DNA

histones

chromatin

duplicated mitotic chromosome

ACTGGTCAGGCAATGTC

double stranded chromosome

Copying DNA & packaging it…• After DNA duplication, chromatin condenses

– coiling & folding to make a smaller packageDNA

chromatin

mitotic chromosome

double-strandedmitotic humanchromosomes

Mitotic Chromosome Duplicated chromosome

2 sister chromatids narrow at centromeres contain identical

copies of original DNAhomologouschromosomes

homologouschromosomes

sister chromatids homologous = “same information”

single-strandeddouble-stranded

Mitosis • Dividing cell’s DNA between

2 daughter nuclei– “dance of the chromosomes”

• 4 phases– prophase– metaphase– anaphase– telophase

Overview of mitosis

interphase prophase (pro-metaphase)

metaphase anaphase telophase

cytokinesis

I.P.M.A.T.

Cytokinesis• Animals

– constriction belt of actin microfilaments around equator of cell

• cleavage furrow forms• splits cell in two• like tightening a draw string

Cytokinesis in Animals

(play Cells Alive movies here)(play Thinkwell movies here)

Mitosis in whitefish blastula

Cytokinesis in Plants• Plants

– cell plate forms• vesicles line up at

equator– derived from Golgi

• vesicles fuse to form 2 cell membranes

– new cell wall laid down between membranes

• new cell wall fuses with existing cell wall

Cytokinesis in plant cell

Mitosis in plant cell

onion root tip

Getting the right stuff • What is passed on to daughter cells?

– exact copy of genetic material = DNA• mitosis

– organelles, cytoplasm, cell membrane, enzymes

• cytokinesis

chromosomes (stained orange)in kangaroo rat epithelial cellnotice cytoskeleton fibers

Cell Cycle Checkpoints… Control of the Cell Cycle

• Regulated by internal and external signals

• Check points are built in stop points that must be overridden by go-ahead signals

• G1 Checkpoint- If cell receives go-ahead, cell usually continues through cycle. Keep in mind, most cells of a human remain in the G0 phase

• G2 Checkpoint- production of MPF pushes cell into mitosis

• M Checkpoint- Before anaphase occurs, all chromosomes must be attached to spindle fibers

Control of the Cell Cycle• Protein kinases (enzymes

that activate other proteins by phosphorylation), Cdks in this case, remain at a constant level

• Cyclins build up• The two combine to form

MPF, maturation promoting factor, which pushes the cell into the M phase

Stop and Go-Internal and External Signals

• Nutrient factors in medium• Growth factors- local regulators,

proteins, that initiate the cell communication that results in cyclins being produced. Cell communication from nearby cells is termed paracrine signaling

• Density dependent inhibition• Anchorage dependence

Cancer- the loss of cell cycle control• Do not heed normal cell signals• Normal cell undergoes “transformation” through one or more

gene mutations• Loss of density dependent inhibition and anchorage

dependence• Benign tumors stay in local tissue but malignant tumors can

spread to other tissue