2.2-All cells arise from other cells Flashcards
Cycle of division with the intermediate growth periods.
1. Interphase
2. Mitosis or meiosis (nuclear division)
3. Cytokineses (cytoplasmic division)
Explain what the cell cyle does not occur in some cells.
After differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have the ability to divide.
What is the difference between the cell cycle and mitosis?
Cell cycle includes growth period between divisions; mitosis is the only 10% of the cycle and refers only to nuclear division.
Outline what happens during interphase.
G1: cell synthesis proteins for replication e.g. tubulin for spundle fibres and cell size doubles.
S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere.
G2: organelles divide.
State the purpose of mitosis.
Produces 2 genetically identical daughter cells for:
1. Growth
2. Cell replacement/ tissue repair
3. Asexual reproduction
Name the stages of mitosis.
- Propase
- Metaphase
- Anaphase
- Telophase
Outline what happens during prophase.
- Chromosomes condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere).
- Centrioles move to opposite poles of cell (animal cells) & mitotic spindle fibres form.
- Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm.
Outline what happens during metaphase.
Sister chromatids line up at the cell equator, attached to the mitotic spindle by their centromeres.
Outline what happens during anaphase.
Requires energy from ATP hydrolysis.
1. Spindle fibres contract = centromeres divide.
2. Sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of cell (looks like āVā shapes facing each other).
3. Spindle fibres break down.
Outline what happens during telophase.
- Chromosomes decondense, becoming invisible again.
- New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome.
Explain the procedure for a root tip squash experiment.
- Prepaer a temporary mount of root tissue.
- Focus an optical microscope on the slide. Count total number of cells in a stage of mitosis.
- Calculate mitotic index (proportion of cells undergoing mitosis).
Explain how to prepare a temporary root tip mount.
- Place root in hydrochloric acid to halt cell division & hydrolyse middle lamella.
- Stain root tip with a dye that binds to chromosomes.
- Macerate tissue in water using mounted needle.
- Use mounted needle to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles.
Name 2 dyes that bind ti chromosomes.
- Toluidine blue (blue)
- Acetic orcein (purple-red)
Why is only the root tip used when calculating mitotic index?
- Meristematic cells at root tip are actively undergoing mitosis.
- Cells further from root tip are elongationg rather than dividing.
What are tomour supressor genes?
Genes that code for proteins to trigger apoptosis (programmed death of damageed cells).
What are proto-oncogenes?
Genes that code for proteins to stimulate cell cycle to progress from one stage to the next.
How can mutation to tumour suppressor genes & proto-oncongenes cause cancer?
- Tumour suppressor: no production of a protein needed to slow the cell cycle.
- Proto-oncongenes: form permanently-activated oncongenes.
- Disruption to cell cycle -> uncontrolled cell division -> tumour.
Syggest how cancer treatments control the rate of cell division.
Disrupt the cell cycle:
- Prevent DNA replication
- Disrupt spindle formation = inhibit metaphase/anaphase
- Can also damage healthy cells
How do prokaryotic cells replicate?
**Binary Fission: **
1. DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm.
2. Cell elongates, separating the 2 DNA loops.
3. Cell membrane contracts & septum forms.
4. Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids.
Estimate the exponential growth of bacteria within 8 hours. Assume binary fission occurs once every 20 minutes & there is 1 bacterium at the start.
8x60 = 480 minutes
480/20 = 24 divisions
2^24
Why are viruses classified as non-living?
They are acellular; no cytoplasm, no metabolism & cannot self-replicate.
Outline how viruses replicate.
- Attachment proteins attach to receptors on host cell membrane.
- Enveloped viruses fuse with cell membrane or move in via endocytosis & release DNA/RNA into cytoplasm or viruses inject DNA/RNA.
- Host cell uses viral genetic information to synthesise new viral proteins/nucleic acid.
- Components of new viral particle assemble.
How do new viral particles leave the host cell?
a) Bud off and use cell membrane to form envelope.
b) Cause lysis of host cell.
Why is it so difficult to develop effective treatments against viruses?
They replicate inside living cells so it is difficult to kill them without killing host cells.
