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