topic 2A: cell division Flashcards
- interphase
-the DNA REPLICATES semi conservatively (s phase)
-leading to 2 CHROMATIDS (identical copies) joined at a CENTROMETRE
-the number of ORGANELLES and volume of CYTOPLASM increases, protein synthesis at G1 and G2 phase
- mitosis
the NUCLEUS DIVIDES to produce 2 nuclei with IDENTICAL copies of DNA produced by the parent cell
- cytokinesis
-the CYTOPLASM and CELL MEMBRANE divides to form 2 new genetically identical daughter cells
describe the behaviour of chromosomes during stage 1 PROPHASE of mitosis and the role of spindle fibres attached to centrometres in the separation of chromatids
STAGE 1
-chromosomes condense becoming shorter and thicker so visible and apear as 2 sister chromatids joined by a centromere
-the nuclear envelope breaks down
-the CENTRIOLES (tiny bundles of protein) move to opposite poles forming SPINDLE (protein fibres) NETWORK
-(spindle fibres start to ATTACH to chromosomes by their CENTROMERES)
stage 2 METAPHASE
-Spindle fibres ATTACH to chromosomes by their CENTROMETRES
-Chromosomes align along EQUATOR
stage 3 ANAPHASE
-spindle fibres shorten and contract
-CENTROMERE DIVIDES
-pulling chromatids (from each pair) to opposite POLES of cell
stage 4 TELOPHASE
-chromosomes uncoil, becoming longer and thinner
-nuclear envelopes reforms, so there are now 2 nuclei
-spindle fibres and centrioles break down
explain the importance of mitosis in the life of an organism
Parent cell divides to produce 2 genetically identical daughter cells for:
-GROWTH of multicellular organisms by increasing cell number
-REPLACING cells to repair damaged tissues
-ASEXUAL reproduction
Describe how tumours and cancers form
-a mutation in the DNA / genes thats controlling mitosis can lead to uncontrolled cell division
-a tumour formed if this results in mass of abnormal cells, invades surrounding tissue
-MALIGNANT tumour: cancerous, can spread (metastasis)
-BENIGN tumour: non-cancerous
Suggest how cancer treatments control rate of cell division
-some disrupt SPINDLE FIBRE ACTIVITY AND FORMATION:
-so chromosomes can’t attach to spindle by their CENTROMERE
-so chromatids can’t be SEPARATED to opposite poles (no ANAPHASE)
-so prevents / slows MITOSIS
-some prevent DNA REPLICATION during interphase:
-so can’t make 2 COPIES of each chromosome (CHROMATIDS)
-so prevents and slows MITOSIS
-these are MORE EFFECTIVE against cancer cells due to uncontrolled cell division, but also disrupts the cell cycle of rapidly dividing healthy cells
Describe how prokaryotic cells replicate
binary fission in prokaryotic cells involve:
1. REPLICATION of circular DNA
2. REPLICATION of PLASMIDS
3. DIVISION of CYTOPLASM to produce 2 daughter cells, each with a SINGLE copy of circular DNA and a VARIABLE number of copies of plasmids
Describe how viruses replicate
virus are NON LIVING and DO NOT UNDERGO CELL DIVISION:
- ATTACHMENT PROTEINS attach to complementary RECEPTORS on host cell
- Inject viral NUCLEIC ACID (DNA/RNA) into host cell
- Infected HOST CELL REPLICATES virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released
Describe how to prepare squashes of cells from plant root tips
- cut a THIN slice of ROOT TIP (5mm from end) using scalpel and mount onto a slide
- Soak root tip in HYDROCHLORIC ACID then rinse
- STAIN for DNA (eg. with toluidine blue)
- LOWER COVERSLIP using a mounted needle at 45 degrees without trapping air bubbles
- SQUASH by firmly pressing down on glass slip but do not push sideways
Explain why root tips are used. (1)
Where dividing cells are found and MITOSIS occurs
Explain why a stain is used. (1)
-to DISTINGUISH CHROMOSOMES
-chromosomes not visible without stain
Explain why the cover slip needs to be
squashed / pressed down. (1)
-(Spreads out cells) to create a SINGLE LAYER OF CELLS
-So LIGHT PASSES through to make chromosomes visible
Explain why the cover slip should not be
pushed sideways. (1)
-avoid rolling cells together and BREAKING CHROMOSOMES
Give two reasons why the roots should
be soaked in acid. (2)
-SEPERATE cells and cell walls
-to allow S TAINto diffuse into cells
-to allow cells to be more easily SQUASHED
-to STOP MITOSIS
Describe how to set-up and use an optical microscope
- Clip slide onto STAGE and turn on LIGHT
- Select LOWEST POWER OBJECTIVE LENS (usually x 4)
- a. Use COARSE FOCUSING dial to MOVE STAGE close to lens
b. Turn COARSE FOCUSING dial to move stage away from lens until image comes into focus - Adjust FINE FOCUSING dial to get clear image
- Swap to HIGHER POWER OBJECTIVE LENS, then REFOCUS
What are the rules of scientific drawing?
-look SIMILAR to specimen and image - draw parts to the same SCALE and relative size
-NO SKETCHING - only CLEAR, CONTINUOUS lines
-NO SHADING and hatching
-include a MAGNIFICATION SUPPLY (eg. x 400)
-LABEL with straight, UNCROSSED LINES
Explain how the stages of mitosis (prophase, metaphase, anaphase and telophase) can be identified
In INTERPHASE (not mitosis), chromosomes aren’t visible but nuclei are. In mitosis, chromosomes are visible.
STAGE 1 PROPHASE: Chromosomes are VISIBLE and DISTINCT because CONDENSING, But RANDOMLY ARRANGED because no spindle activity / not attached to SPINDLE FUBRE
STAGE 2 METAPHASE: Chromosomes lined up on EQUATOR because attaching to spindle
STAGE 3 ANAPHASE: Chromatids (in two groups) at POLES of spindle
-Chromatids V SHAPED because being PULLED APART at their centromeres by spindle fibres
STAGE 4 TELOPHASE: Chromosomes in TWO SETS, one at each pole
What is a mitotic index (MI)?
-PROPORTION of cells undergoing mitosis (with VISIBLE CHROMOSOMES )
-MITOTIC INDEX = number of cells undergoing MITOSIS / TOTAL number of cells in sample
Explain how to determine a reliable MI from observed squashes
-Count cells in MITOSIS in field of view
-Count only WHOLE CELLS / only cells on top and right edges → STANDARISE counting
-Divide this by TOTAL number of cells in FIELD OF VIEW
-REPEAT with MANY / AT LEAST 5 FIELDS OF VIEW selected RANDOMLY → creates a more REPRESENTATIVE sample
-Calculate a reliable MEAN
Suggest how to calculate the time cells are in a certain phase of mitosis
- Identify PROPORTION of cells in named phase at any one time
-Number of cells in that phase / total number of cells observed - MULTIPLY by LENGTH OF CELL CYCLE
