IB Biology2 Cells

2.5 Cell Division

Jason de Nys

All syllabus statements ©IBO 2007All images CC or public domain or link to original material.

http://commons.wikimedia.org/wiki/File:Scotchquaileggs.jpg

2.5.1 Outline the stages of the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis

http://commons.wikimedia.org/wiki/File:First_gap_cell_lifecycle.svg

Interphase is the longest portion of a cell’s life and has three subdivisions:First Gap

G1

http://commons.wikimedia.org/wiki/File:Synthesis_cell_lifecycle.svg

SSynthesis

http://commons.wikimedia.org/wiki/File:Second_gap_cell_lifecycle.svg

G2

Second Gap

Mitosis: The cell divides it’s chromosomes into 2 identical sets4 Main stages

Detail in 2.5.4

http:

//co

mm

ons.w

ikim

edia

.org

/wik

i/Fi

le:P

roph

ase_

proc

ario

tic_m

itosi

s.sv

ghtt

p://

com

mon

s.wik

imed

ia.o

rg/w

iki/

File

:Met

apha

se_p

roca

riotic

_mito

sis.

svg

http:

//co

mm

ons.w

ikim

edia

.org

/wik

i/Fi

le:A

naph

ase_

proc

ario

tic_m

itosi

s.sv

ghtt

p://

com

mon

s.wik

imed

ia.o

rg/w

iki/

File

:Tel

opha

se_p

roca

riotic

_mito

sis.

svg

Cytokinesis

http://commons.wikimedia.org/wiki/File:Cytokinesis_eukaryotic_mitosis.svg

Stage EventsGap 1 (G1) • Protein Synthesis

• Organelles produced• Cytoplasm increases in size

Synthesis (S) DNA is duplicatedGap 2 (G2) • Organelles produced

• Cytoplasm increases in sizeMitosis The cell divides it’s chromosomes into two

identical sets4 Stages• Prophase• Metaphase• Anaphase• Telophase

Cytokinesis The parent cell divides into two daughter cells

2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.

In cancerous cells, control of mitosis has been lost and they divide… and divide… and divide.

This leads to tumours (cancer tissue) that displaces healthy tissue and interferes with proper function.

Cancer can arise from any cells capable of mitosis

http://commons.wikimedia.org/wiki/File:Brenner_tumour_intermed_mag.jpg

Background: A Brenner tumour in an ovary. These are usually

benign, but can be malignant

2.5.3 State that interphase is an active period in the life of the cell when many metabolic reactions occur, including protein synthesis, DNA replication, and an increase in the number of mitochondria and chloroplasts.

State: give a specific name, value or other brief answer without explanation or calculation

The name ‘interphase’ implies a period of time between stages and that nothing much is going on. This is not the case!

This is when the cell is going about it’s day-to-day ‘business’ i.e. carrying out it’s programmed functions and growing.

Imagine if cells did not have a growth phase. What would happen to the size of daughter cells with progressive rounds of mitosis?

Think: What else would have to stop when the chromatin is tightly coiled and condensed into chromosomes for mitosis?

http://commons.wikimedia.org/wiki/File:Chromosome.svg

That’s right, transcription can’t be done when the DNA is tightly coiled.

So Interphase is when all of the cell’s genetic instructions are processed.

http://commons.wikimedia.org/wiki/File:Chromosome.svg

It depends on the tissue that the cell is in and what the function of the cell is supposed to be, but the cell can stay at G1 indefinitely

This is often referred to as G0, or resting phase. Nerve and heart muscle cells, once differentiated, never go past G1. They just keep on keeping on, doing their jobs until they are damaged or until the death of the organism.

Extension:

http://www.flickr.com/photos/seyyed_mostafa_zamani/4266283238/

2.5.4 Describe the events that occur in the four stages of mitosis

^C

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

Prophase

Metaphase

Anaphase

Telophase

First 3D video of mitosis. Source forgotten, let me know if you know!

Pea

MAT

http://www.flickr.com/photos/cmatsuoka/3732303102/http://www.flickr.com/photos/zaser/2524931166/

People

Meet

And

Talkhttp://www.flickr.com/photos/chuckp/252924532/

2.5.5 Explain how mitosis produces two genetically identical nuclei

Think back to slide 3… What happens during the

synthesis part of interphase?

http://commons.wikimedia.org/wiki/File:Synthesis_cell_lifecycle.svg

SSynthesis

http://www.flickr.com/photos/wellcomeimages/5987498303/http://www.flickr.com/photos/thejcb/4117622551/

∴ Both nuclei are identical

So, the chromosomes in the nucleus have been exactly copied See: Replication Core 3.4, AHL 7.2

During Prophase the Chromatin condenses into the familiar X shaped chromosome, which is actually two identical chromatids joined at the centromere.

And then when the chromosomes split in half during anaphase, the identical chromatids are dragged to opposite ends of the cell

Cytokinesis cuts the cell in half, with one set of duplicate DNA in one daughter cell and the other identical set in the other daughter cell

∴ Both nuclei are identical

2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis

Any time new cells are required, mitosis is required:

• Growth: An 18 year old has many more cells than an 18 month old!

• Embryonic development: You start as a zygote, one cell!• Tissue repair: Burnt, bashed, cut or eaten; dead or lost

cells need to be replaced.• Asexual reproduction: In eukaryotes only

remember: what do prokaryotes do?

http://www.flickr.com/search/?l=cc&mt=all&adv=1&w=all&q=mitosis&m=text

Make your own Play Doh™ or Plasticine™ mitosis model

to further your understanding

make your own playdough!

Further information:

Animation by John Kyrk

Three of the best sites for IB-specific Biology information. The top link takes you to the PPT by Stephen Taylor