The Cell Cycle:Cell Growth, Cell

Division

Where it all began…

You started as a cell smaller than a period at the end of a sentence…

How did you get from there

to here?

And now look at you…

• Reproduction – asexual reproduction

• one-celled organisms

• Growth and Development– from fertilized egg to

multi-celled organism

• Repair and Replacement– replace cells that die

from normal wear & tear or from injury

Why do cells divide?

amoeba

Cell Cycle

Cell cycleM

Mitosis

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• cell doing its “everyday job”• cell grows• A few hours to indefinitely

– S = DNA Synthesis• copies chromosomes• 3-6 hours

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

proteins, membranes• 2-5 hours

G0

signal to

divide

Interphase• Longest phase of the

cell cycle– Consists of G1, S, G2

• Cell prepares for mitosis – replicates chromosome

• DNA & proteins

– produces proteins & organelles

green = key features

Organizing DNA• DNA is organized in

Nucleosomes– double helix DNA molecule

– wrapped around Histones• 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 package

DNA

chromatin

mitotic chromosome

double-strandedmitotic humanchromosomes

Mitotic Chromosome • Duplicated chromosome

– 2 chromatids

– narrow at centromere

– contain identical copies of original DNA

homologouschromosomes

homologouschromosomes

sister chromatidshomologous = “same information”single-stranded

double-stranded

Mitosis • Dividing cell’s DNA between

2 daughter nuclei– “dance of the chromosomes”

• 4 phases– Prophase– Metaphase– Anaphase– Telophase

Mitosis

Overview of mitosis

interphase prophase (pro-metaphase)

metaphase anaphase telophase

cytokinesis

I.P.M.A.T.

Prophase • Chromatin condenses

– Becomes chromosomes• chromatids

• Centrioles move to opposite poles of cell – animal cell

• Protein fibers cross cell to form mitotic spindle– microtubules

• actin, myosin

– coordinates movement of chromosomes

• Nucleolus disappears

green = key features

Transition to Metaphase • Prometaphase

– Special proteins attach to the centromeres • creating kinetochores

– microtubules attach at kinetochores • connect centromeres to

centrioles

– Nuclear envelope fragments

green = key features

Anaphase • Sister chromatids separate

– move to opposite poles

– pulled at centromeres

– pulled by motor proteins “walking”along microtubules

• actin, myosin• increased production of

ATP by mitochondria

• Poles move farther apart– polar microtubules lengthen

green = key features

Telophase• Chromosomes arrive at

opposite poles– Nuclear envelop starts to

reappear

– nucleoli form

– Chromosomes uncoil • no longer visible under light

microscope

• Spindle fibers disperse

• Cytokinesis– cell division

green = key features

Cytokinesis• Animals

– constriction belt of actin microfilaments around equator of cell

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

string

Mitosis in whitefish blastula

Cytokinesis in Plants• Plants

– Cell Plate• 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

onion root tip

G1/S checkpoint

• G1/S checkpoint is most critical

– primary decision point• “Go Ahead signal”

– if cell receives “GO” signal, it divides• internal signals: cell growth (size), cell nutrition • external signals: “growth factors”

– if cell does not receive signal, it exits cycle & switches to G0 phase

• non-dividing, working state

What about Stem cells?

• What are stem cells?

• How can they be used?

• What are concerns about using stem cells?

• What are the types of stem cells?

Multicellular organisms depend on interactions among different cell types.

• Tissues are groups of cells that perform a similar function.

• Organs are groups of tissues that perform a specific or related function.

• Organ systems are groups of organs that carry out similar functions.

CELL TISSUE ORGAN

vascular tissue

leaf

stem

lateralroots primary

root

SYSTEMS

roo

t sy

stem

sho

ot

syst

em

Specialized cells perform specific functions.

• Cells develop into their mature forms through the process of cell differentiation.

• Cells differ because different combinations of genes are expressed.

• A cell’s location in an embryo helps determine how it will differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

Stem cells can develop into different cell types.

• Stem cells have the ability to– divide and renew themselves– remain undifferentiated in form– develop into a variety of specialized cell types

• Stem cells are classified into three types.

– totipotent, or growing into any other cell type– pluripotent, or growing into any cell type but a

totipotent cell– multipotent, or growing into cells of a closely related

cell family

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

• Stem cells come from adults and embryos.

– Adult stem cells can be hard to isolate and grow.– The use of adult stem cells may prevent transplant

rejection.– The use of embryonic

stem cells raisesethical issues.

– Embryonic stem cellsare pluripotent andcan be grown indefinitelyin culture.

• The use of stem cells offers many current and potential benefits.

– Stem cells are used to treat leukemia and lymphoma.– Stem cells may cure disease or replace damaged

organs.– Stem cells & Blindness

– Stem cells may revolutionize the drug development process.