Chapter 12 – The Cell Cycle

AP Biology

In 1855 Rudolf Virchow stated “where a cell exists, there must have been a preexisting cell, just as animal arises from animal and plant arises from plant.”

“Omnis cellula e cellula” means every cell from a cell.

How does an organism such as Amoeba produce offspring compared

to a human? • Amoeba - one cell divides to create an

entire organism.• Human - cells divide to repair, maintain,

or become part of a multicellular organism ; gametes (half the chromosomes) are made for reproduction

What might be a disadvantage to the progeny of an Amoeba compared to the offspring of humans?

• Offspring of humans have more variation• because gametes are continuously mixing

chromosomes from different organisms while in Amoebas the organisms itself is copied and divided to make more which leads to less variation which is bad if the environment changes and the population is not suited for the change.

Vocab

1) genome – all genetic information in a cell (organism)2) chromosomes - packages of DNA molecules (46 in humans)3) somatic cells - all body cells except reproductive cells4) gametes - reproductive cells with half the # of chromosomes5) chromatin - DNA-protein complex

6) sister chromatids - identical copies of chromosomes7) centromere - the “waist” where sisters are connected8) Mitosis - division of the nucleus (P,PM,M,A,T) which produces

genetically equivalent cells9) cytokinesis - division of the cytoplasm10) Meiosis - division that produces gametes

Stages of the Cell Cycle

Interphase• G1 - phase

– Cell is performing normal cell functions while growing

• S - phase– DNA replicates

(copies)

• G2 - phase– Organelles double in

number to prepare for division

Prophase

• Spindle fibers (ropes) form• Centrioles (make spindles)

move to opposite poles• Chromosomes become

visible• Nuclear membrane and

nucleolus breaks apart

Metaphase

• Chromosomes line up along the equator (middle of the cell)

Anaphase

• Chromatids (copies of chromosomes) separate and move to opposite poles

Telophase• Nuclear membrane

forms around each group of chromosomes and the nucleolus reappears

• Chromosomes unwind and seem to disappear

• Spindle fibers degrade• Cytokinesis begins

(pinches in)

Cytokinesis

• The process by which the cytoplasm divides and one cell becomes two individual cells.

Purpose of Mitosis - Cell Division

• Growth• Repair

During cell divison, parent cells must be able to:

• Make a copy of all information (DNA)

• Transfer one copy of this information (DNA) to each daughter cell so they get the same instructions

• Provide each daughter cell with enough cellular machinery (organelles) in order to function

Things to think about:1) Why is it important that DNA copies are

distributed equally to the daughter cells?

2) Why is it important that each daughter cell receive all of the cellular organelles? (These include mitochondria, chloroplasts, Golgi apparatus, and endoplasmic reticulum.) Describe which processes might be affected if a daughter cell did not receive one of these organelles.

3) Cells need nutrients as building blocks for new biomolecules. Other than nutrients, what product(s) of metabolism is provided for the cell? At what points during the stages of cell division are these products required?

4) What difficulties might arise for an organism if muscle cells or nerve cells are damaged?

Mitosis

Mitosis

Cytokinesis• Division of the cytoplasm

Mitosis Animation

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

More Vocab

1) mitotic spindle - fibers made of microtubules; attach to chromosomes

2) centrosome - non-membranous organelle; assembly of spindle microtubules starts

3) kinetochore - structure of protein and chromosomal DNA at the centromere; “walks” the chromosome down the microtubule

4) metaphase plate - the plane midway between the two poles where the chromomomes line-up during metaphase

What is the function of kinetochore and non-kinetochore microtubules?

• kinetechore - “walk” the chromosomes to one pole

• non-kinetechore - elongating the whole cell during anaphase

Animal vs. Plant

• Animal– cleavage; – cleavage furrow appears, deepens until cell is spit

in two

• Plant– cell plate; – vesicles from Golgi apparatus move to middle of

cell

Binary Fission – “division in half”

What brings about the separation of the two daughter cells?

Still a mystery …

Evolution of Mitosis

Regulation of the Cell Cycle

The cell cycle is driven by specific chemical signals in the cytoplasm.

1970’s – Experimentation:

• Two cells in different phases of the cell cycle are fused together. If one is in S while another in G1, the G1 immediately enters S.

• Likewise, if one is undergoing Mitosis the second nucleus also enters Mitosis.

More Vocab• Cell Cycle Control System:

– A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle.

• Checkpoint:– Point where stop and go-ahead signals regulate the cycle.

• 2 main regulatory molecules:– Protein kinases– Cyclins

• Cdks: • proteins that drive the cell cycle and rise and fall

depending on the concentration of cyclin.

• MPF: • “maturation or M-phase promoting factor”• cyclin-Cdk complex• Triggers cells passage past the G2 checkpoint and into M-

phase

Figure 12.14 – Campbell 6th Edition

Role of Cdk, cyclin, and MPF:

• Cdk:– Binds to cyclin to form MPF

• Cyclin:– Binds to Cdk to form MPF

• MPF: Cdk + cyclin– Promotes mitosis by phosphorylating proteins– Breakdown of its own cyclin

• Which is conserved? Why?Cdk: It’s an enzyme so it’s reusable!

Kinetechore Involvement:

• Kinetechores not yet attached to microtubules trigger a signal that delays the onset of anaphase by keeping the Anaphase Promoting Complex (APC) in an inactive state.

• After all kinetochores are attached the “wait” signal ceases and APC becomes active.

• Cyclin is broken down and proteins holding sister chromatids together are inactivated.

More Vocab:

• Growth Factor:– Protein released by certain body cells that

stimulate other cells to divide.

• PDGF:– Stimulates the division of fibroblast cells; helps

heal wounds.

• Density dependent inhibition:– Crowded cells stop dividing.

• Anchorage dependence:– Cells must be attached to substratum in order to

divide.

Cancer

• Failure to exhibit density dependent inhibition

• Failure to exhibit anchorage dependent inhibition

• Cell cycle control system is abnormal• Manufactures its own growth factors or

abnormal signal pathway

Last of the Vocab:

• Transformation:– Process that converts normal cells to cancer cells

• Tumor:– Mass of abnormal cells within otherwise normal

tissue• Benign Tumor:

– Remain at original site– Can be removed

• Malignant Tumor:– Abnormal cells move to different regions, impair

function of one or more organs; CANCER

• Metastasis:– Spread of cancer cells to locations distant from the

original site

Breast Cancer