as academic tutorial 5. stem cell division. so what are chromosomes? gy_1/animation/878

AS Academic Tutorial 5. Stem Cell Division

So what are chromosomes?

• http://advancedsciences.cambridge.org/ocr/biology_1/animation/878

G1

S

G2

mitosis

Cytokinesis:

new protein and organelles made

DNA replicates

Proteins needed for cell division made

Nucleus divides

cytoplasm divides

Let’s revise the cell cycle

growth

Stem Cell Cyclehttp://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.

Cell at interphase•Protein synthesis

•Organelle synthesis•DNA replication

So, before mitosis occurs…….

A single chromosome at the beginning of mitosis

Has two chromatids,as the DNA replicates during interphase before mitosis

centromere

Interphase – normal looking cells

Early prophase

DNA coils and condensesChromosomes take up stain

centrioles

nucleolus

3 happenings occurin prophase.

Centrioles move apart

Nucleolus fades

Chromosomes continue to condense

Nuclear membrane breaks down

prophase

Nucleolus disappears Chromosomes continue to condense

What were the 3happenings?

Prophase – wriggly worms!

metaphase

Nuclear membrane broken down

Chromosomes aligned on the equator

Each chromosome attached to spindle fibre by the centromere

Metaphase – spider’s legs exploding out of

middle!

Centromeres divide and chromatids pulled apart

Anaphase

Anaphase

anaphase

AnaphaseSister chromatids are pulled to opposite poles of the cell

Anaphase – fingers pulling apart

Telophase – two blobs in one cell

Cytokinesis

Mitosis Animations!

• 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

Let’s recognisethe phases!

Interphase

In a moment you will be preparing a root tip squash to look for stained cells like these.

early prophase

prophase

metaphase

Anaphase

Early telophase

Telophase

Cytokinesis in a plant cell

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 1. Use the whole page.2. Sharp pencil3. No shading4. No sketching5. 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.”