| Mitosis overview | - Cell division produces two daughter cells
- Have same number of chromosomes as the parent cell
- Exact copy of DNA from parent |
| Importance of mitosis | - Growth and repair
- Differentiation |
| Stages of mitosis | - Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase and cytokinesis |
| Interphase | - DNA unravels + replicates
- Doubles genetic content
- Organelles replicated
- ATP content increases |
| Prophase | - Chromosomes condense
- Tiny bundles of proteins, centrioles, move to opposite ends of cell
- Form a network of protein fibres across- spindle
- The nuclear envelope breaks down and chromosomes are free in cytoplasm |
| Metaphase | - Chromosomes (each with 2 chromatids) line up along the middle of cell
- Become attached to the spindle by their centromere |
| Anaphase | - Centromeres divide
- Separating each pair of chromatids to opposite ends of the spindle
- Chromatids appear v-shaped |
| Telophase | - Chromatids uncoil, becomes long + thin again
- They are chromosomes again
- Nuclear envelope forms around each group of chromosomes
- There are now two nuclei |
| Cytokinesis | - Division of cytoplasm
- Forms 2 daughter cells that are genetically identical |
| Chromatin | - DNA joined to histones |
| How prokaryotic cells replicate | - Binary fission |
| Binary fission process (simple explanation) | - DNA replicates
- Division of the cytoplasm
- Forms cell wall |
| Binary fission process | - Circular DNA + plasmids replicate
- Cell gets bigger
- DNA loops move to opposite ends of cell
- Cytoplasm divides
- Forms 2 daughter cells
- Each having one copy of circular DNA but different number of copies of plasmids |
| How viruses use host cells to replicate themselves | - Attachment proteins binds to complementary receptor proteins on host cells
- Some viruses can only bind to one type of cell
- Inject their DNA or RNA into host cell
- Host cell organelles replicate viral particles |
| Investigating mitosis | - Cut tip from growing root
- Prepare boiling tube with 1M HCL
- Put in water bath at 60*c
- Transfer root tip into tube, leave for 5 minutes
- Rinse root with cold water
- Dry it
- Cut 2mm from very tip
- Place root on microscope slide
- Use mounted needle to break top open
- Add few drops of stain
- Place cover slip, squash it down
- Look at mitosis under optical microscope |
| How to calculate density of substance from microscopic image | - No. per mm2
- Estimate field of view using a ruler
- Calculate area of field of view using pie/r/2
- Count no. of stomata
- No. of stomata/area
- Repeat it and calculate a mean |
| How to calculate calibration with eyepiece graticule and micrometer | What each eye piece is worth:
- Count stage divisions (epg 10)
- Calculate the actual size of the stage divisions (each is 10 micrometers)
- So, 10 x 10 = 100 micrometers
- Work out the size of 1 epd (total size/no. of epd)
- So each epd = 1 micrometer |
| Using an optical microscope | - Clip slide that has been prepared on the stage
- Select lowest-powered objective lens
- Use coarse adjustment knob to bring shape up to just below the objective lens
- Look down eyepiece, move coarse + fine adjustment knob to focus it
- To increase magnification, swap to a higher-powered objective lens and focus |
| Mitotic Index | - The proportion of cells undergoing mitosis |
| Mitotic Index calculation | Mitotic index = number of cells with visible chromosomes/total number of cells observed |
| Graticule and micrometer | - Used to calculate cell size |
| Using a graticule and micrometer | - Line up eyepiece graticule and the stage micrometer (like a ruler)
- Each division on the stage micrometer is 0.1 mm long
- At this magnification, 1 division on the stage micrometer = 4.5 divisions on the eyepiece graticule
- To work out size of 1 division on the eye piece graticule, divide 0.1 by 4.5 (=0.022 mm) |
| Example of calculation using a graticule and micrometer | - If you look at a cell under the microscope at this magnification and its 4 eyepiece divisions long
the calculation is 4 x 0.022 = 0.088 mm |
| Artefacts | - Things that get in the way of observations
- e.g. dust, air bubble and fingerprints
- Usually made during preparation of slides |
