AS Academic Tutorial 5. Stem Cell Division

So what are chromosomes? http://advancedsciences.cambridge.org/ocr/biology_1/animation/878

Let’s revise the cell cycle Cytokinesis: cytoplasm divides Nucleus divides growth new protein and organelles made mitosis G1 Proteins needed for cell division made G2 S DNA replicates

Stem Cell Cycle http://www.cellsalive.com/cell_cycle.htm

True or False? The longest stage in the lifecycle of a stem cell is mitosis. Mitosis is the division of a nucleus. Replication of the DNA to produce identical sister chromatids occurs in the G2 phase. The products of the cell cycle are genetically identical cells. If there are 10 units of DNA in the original cell in G1, there are 20 in each of the new cells after cytokinesis.

So, before mitosis occurs……. Cell at interphase Protein synthesis Organelle synthesis DNA replication

A single chromosome at the beginning of mitosis Has two chromatids, as the DNA replicates during interphase before mitosis centromere

Interphase – normal looking cells

3 happenings occur in prophase. Early prophase centrioles nucleolus DNA coils and condenses Chromosomes take up stain

prophase Centrioles move apart Nuclear membrane breaks down Nucleolus fades Chromosomes continue to condense

Nucleolus disappears Chromosomes continue to condense What were the 3 happenings?

Prophase – wriggly worms!

Nuclear membrane broken down metaphase Chromosomes aligned on the equator Nuclear membrane broken down Each chromosome attached to spindle fibre by the centromere

Metaphase – spider’s legs exploding out of middle!

Anaphase Centromeres divide and chromatids pulled apart

Anaphase

anaphase

Anaphase Sister chromatids are pulled to opposite poles of the cell

Anaphase – fingers pulling apart

Telophase – two blobs in one cell

Cytokinesis

Mitosis Animations! http://www.cellsalive.com/mitosis.htm http://uk.youtube.com/watch?v=nPG6480RQo0&feature=related Musical introduction! http://uk.youtube.com/watch?v=ELVwj5JDfg8&feature=related http://www.youtube.com/watch?feature=iv&src_vid=nPG6480RQo0&v=VGV3fv-uZYI&annotation_id=annotation_706798 3D good http://www.youtube.com/watch?v=cvlpmmvB_m4&feature=endscreen&NR=1 Very clear - good http://www.cellsalive.com/mitosis.htm

In a moment you will be preparing a root tip squash to look for stained cells like these. Let’s recognise the phases! Interphase

early prophase

prophase

metaphase

Anaphase

Early telophase

Telophase

Cytokinesis in a plant cell

Labels with arrow heads. So now to the practical – see instructions in booklet page 4……Draw any 2 cells you find showing different mitotic phases, or 2 cells from the prepared slides. Biological Drawings Use the whole page. Sharp pencil No shading No sketching Labels with arrow heads.

When you have finished…….. Tidy all your equipment carefully away. Start answering the quizzes in the booklet pages 1 – 3 and 5, and then go on to the exam questions pages 8 - 13. They start easy and become challenging! Page 8 should read “ Fig 5.1 shows drawings of nuclei, A to D, from 2 different plant species. Two of them show prophase of mitosis.”