The Cell Cycle

Genetic Information Genome: cell’s genetic

information DNA organized into

chromosomes• Diploid (2n): 2 sets of

chromosomes … somatic (body) cells

• Haploid (1n): 1 set of chromosomes… gametes (sex cells]

Sex Chromosomes – determine the sex of an organism

Autosomes- carry traits; not linked to sex

Chromosomes

Before cells divide, their DNA coils up tightly into chromosomes

Chromatin: DNA-protein complex that makes up chromosomes

Chromatids: replicated strands of a chromosome

Centromere: narrowing “waist” of sister chromatids

Functions of Cell Division

Unicellular reproduction Growth/Development Renewal/Repair

The Cell Cycle

Interphase (90% of

cycle) • G1 phase~ growth

• S phase~ synthesis

of DNA • G2 phase~

preparation for cell division

Mitotic phase• Mitosis~ nuclear

division • Cytokinesis~

cytoplasm division

Interphase

Growth 1 (G1)• Cell grows

Synthesis (S)• DNA replicates

Growth 2 (G2)• Cell grows and

prepares to divide

Mitotic Spindle

Spindle fibers (microtubules) originate from the centrosome• Some animal cells contain

centrioles Aster- short array of

microtubules that extend from centrosome

Kinetochore- protein structure on chromosomes that microtubules attach to

Mitosis

Prophase Prometaphase Metaphase Anaphase Telophase

Prophase

Chromosomes visible

Nucleoli disappear

Sister chromatids Mitotic spindle

forms Centrosomes

move to opposite ends of cell

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Prometaphase

Nuclear membrane fragments

Spindle interaction with chromosomes

Kinetochore develops

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Metaphase

Centrosomes at opposite poles

Centromeres are aligned

Kinetochores of sister chromatids attached to microtubules (spindle)

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Anaphase

Paired centromeres separate; sister chromatids liberated

Spindle fibers shorten at the kinetochore end

Chromosomes move to opposite poles

Each pole now has a complete set of chromosomes

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Telophase/Cytokinesis

Telophase• Daughter nuclei form• Nuclear envelopes

arise• Chromatin becomes

less coiled• Two new nuclei

complete mitosis Cytokinesis

• Cytoplasmic division

Plant and Animal Cytokinesis

Plant Mitosis

Bacteria Division

Prokaryotes divide by binary fission• Chromosome

duplicates• Cell grows• Membrane

pinches inward• Two identical

cells result

Evolution of Mitosis

The “missing links” between prokayrotic binary fission and eukaryotic mitosis

How do they know when to split?

Cell cycle has a control system

Cells pass through “checkpoints” • “Go-ahead” signal

cell continues to copy DNA and divide

• No signal cell leaves cell cycle and enters into G0 phase (no growth occurs)

Chemical Controls

Protein kinases activate or deactivate cells• “Stop” and “go”

signals To be active,

kinases must be attached to a cyclin (Cdks)• MPF (maturation –

promoting factor)~ triggers M-phase

Keeping Division in Check

Growth factors• Protein that

stimulates cells to divide

Density-dependent inhibition• Crowded cells stop

dividing Anchorage

dependence• Cells must attach

to a substrate to divide

Dividing Cells Gone Wild Transformation of single cell

• If not destroyed, will reproduce and form a mass of cells (tumor)

Benign or malignant• If cells don’t spread benign• Malignant tumors spread and/or damage major

organs Metastasis

• Spread of cells from original site • Through lymph and blood vessels