Cell Cycle and MitosisCell Cycle and Mitosis

AP BiologyUnit 3

Cell Cycle

• Cell Cycle = the entire cycle of a cell from one division to the next– Interphase (G1, S, G2) =

between cell divisions– M Phase (Mitosis and

Cytokinesis) = cell division

– Continuous process of replication alignment separation (of DNA)

Interphase

• Most of the time, a cell is in Interphase

• G1 (Gap1)– Cell grows, copies organelles– Protein synthesis and all normal activities of

cell (like cellular respiration) are carried out

Interphase

• S (Synthesis)– DNA is copied – Protein synthesis, cellular respiration occur – Cell continues to grow, copy organelles

• G2 (Gap2)– Cell growth continues – Protein synthesis and cellular respiration occur– Cell prepares to divide

M Phase• Mitosis = division of the nucleus

• Cytokinesis = division of the rest of cytoplasm and its contents

• Results in 2 identical daughter cells

• Important for growth, repair, asexual reproduction

Duplicating Chromosomes

• Before cell division can occur, all of the DNA must be copied in S phase

• After duplication, you have 2 sister chromatids per chromosome

Sister Chromatids

• Sister Chromatids = identical copies of a chromosome

• Centromere = where sister chromatids are attached to one another

Chromosome BEFORE duplication

Chromosome AFTER duplication

Chromosome after mitosis

Question…

• Why do chromosomes duplicate?– To have a copy of DNA for each new daughter

cell

Haploid vs. Diploid

• Diploid (2n)– 2 copies of each chromosome – All somatic cells are diploid (non-gametes)

• Haploid (n)– 1 copy of each chromosome– Sperm and egg are haploid

Mitosis vs. Meiosis

• Mitosis – Results in 2

identical diploid daughter cells from the original diploid cell

• Meiosis– Results in 4

nonidentical haploid cells from one original diploid cell

Phases of Mitosis• Prophase

• Prometaphase

• Metaphase

• Anaphase

• Telophase

“P P M A T”

Phases of Mitosis• Prophase (P)

– Chromosomes begin to condense into chromatids

– Mitotic spindle forming

• Prometaphase– Chromosomes

condensed & attached to spindle fibers, nuclear envelope in fragments

Phases of Mitosis

• Metaphase (M)– Chromosomes line up

in the middle of the cell

• Anaphase (A)– The spindle fibers pull

the sister chromatids apart

• Telophase (T)– Nuclear Envelope

reforms

Overview: Phases of Mitosis

Cytokinesis

• Cytokinesis differs between Animal and Plant cells

• Animal Cells – forms a cleavage furrow– Cells narrow and pinch off

from each other

• Plant Cells- forms a cell plate

Cleavage Furrow

Cell Plate

Control of the Cell Cycle

• Checkpoints– determine if the cell is able to continue to the

next phase– Regulated by external and internal signals

(trigger signal transduction pathways) – ability proceed usually depends on whether

certain processes have been completed• Ex. Cell cannot start G2 until DNA has been

replicated

Control of Cell Cycle

• Ex. PDGF – Platelet Derived Growth Factor – Released by platelet cells in response to an

injury– Allows fibroblast cells in the damaged area to

pass the G1 checkpoint divide – Cell division helps to repair the damaged area

Control of Cell Cycle: G0

• G0

– A nondividing state that cells go into if they don’t get the signal to proceed in the cell cycle

– Most cells in the human body are in this state

– Cells can also be triggered to come out of G0 and re-enter the cell cycle by external signals

Control of Cell Cycle

• Cyclins and Cyclin-dependent kinases (Cdks)– Regulatory proteins that

determine if the cell can pass checkpoints

– Cyclins vary in concentration throughout the cell cycle

– presence of specific cyclin/Cdks bound together (MPF) determines if cell can continue through cell cycle

Binary Fission

• Bacteria don’t go through mitosis

• Why not?– No nucleus, just free floating

DNA

• Steps of Binary Fission– Cell grows in size– Copy DNA– Split cell into 2 new cells

Cancer

• Cancer is uncontrolled cell growth

• Cancer cells do not respond to checkpoint signals keep on dividing

• Cancer cells no longer perform their normal functions, steal nutrients from other cells, crowd out other cells.