3.2.2 All Cells Arise From Other Cells Flashcards
State what the cell cycle is and outline its stages.
Cycle of division with intermediate growth periods.
1. Interphase
2. Mitosis or Meiosis
3. Cytokinesis
Explain why the cell cycle does not occur in some cells.
After differentiation, some types of cell in multicellular organisms 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 only 10% of the cycle and refers only to nuclear division.
Outline why happens during interohase.
G1: cell synthesises proteins for replication (e.g. tubulin for spindle 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:
- growth
- cell replacement/tissue repair
- asexual reproduction
Name the stages of mitosis.
- Prophase
- 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) and 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.
- Spindle fibres contract = centromeres divide.
- Sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles of cell.
- 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.
- Prepare a temporary mount of root tissue.
- Focus an optical microscope on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis.
- Calculate mitotic index (proportion of cells undergoing mitosis).
Outline how to prepare a temporary mount of root tissue.
- Place root in hydrochloric acid to halt cell division and hydrolyse middle lamella.
- Stain root tip with a dye that binds to chromosomes.
- Macerate tissue in water using mounted needle.
- Use mounted needle at 45° to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles.
Name 2 dyes that bind to chromosomes
- Toluidine blue (blue)
- Acetic orcein (purple-red)
Why is only the root tip used when calculating a mitotic index?
- Meristematic cells at root tip are actively undergoing mitosis
- Cells further from root tip are elongating rather than dividing
What are tumour suppressor genes?
Genes that code for proteins to trigger apoptosis or slow cell cycle (e.g. p53 acts between G1 and S in interphase so damaged DNA cannot replicate).
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 and proto-oncogenes cause cancer?
- Tumour suppressor: no production of a protein needed to slow the cell cycle.
- Proto-oncogenes; form permanently-activated oncogenes.
-Disruption to cell cycle -> uncontrolled cell division -> tumour
Suggest how cancer treatments control the rate of cell division.
Disrupt the cell cycle:
- prevent DNA replication
- disrupt spindle formation = inhibit metaphase/anaphase
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 and 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 and there is 1 bacterium at the start.
8 x 60 = 480
480/20 = 24
2²⁴
Why are viruses classified as non-living?
They are acellular: no cytoplasm, no metabolism and cannot self-replicate.
Outline how viruses replicate.
- Attachment proteins attach to receptors on host cells membrane.
- Enveloped viruses fuse with cell membrane or move in via endocytosis and 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?
Replicate inside living cells = difficult to kill them with killing host cells.
