2.2 All Cells Arise From Other Cells Flashcards
Cell cycle and it’s stages
Cycle of division with intermediate growth periods
Interphase
Nuclear division
Cytokinesis
Why doesn’t cell cycle occur in some cells
Cell differentiation is when cells no longer have the ability to divide
Diff. between cell cycle and mitosis
Cell cycle includes growth period between divisions
Mitosis is 10% of cycle and only refers to nuclear division
What happens during interphase
G1: Cell synthesises proteins for replication
S: DNA synthesis, consists of 2 chromatids joined by centromere
G2: Organelles divide
State purpose of mitosis
2 genetically identical daughter cells for:
Growth
Tissue repair
Asexual reproduxtipn
Stages of mitosis
Prophase, Metaphase, Anaphase, Telophase
What happens at Prophase
Chromosomes condense and become visible
Centrioles separate and move to opposite poles of cells
Spindle fibres are produced from centrioles which create a spindle apparatus from poles of cell
Spindle fibres attach to centromere and chromatids on chromosome in later stages
Plants have a spindle apparatus but lacks…
Centrioles
What happens at Metaphase
Chromosomes align at equator of cell
Spindle fibres releases from poles now attach to centromere and chromatid
What happens at Anaphase
Spindle fibres retract and pulls centromere and chromatids towards opposite poles
Centromere divides into 2 and individual chromatids are pulled to each opposite pole
Separate chromatids = chromosomes
What energy is used for Anaphase
ATP which is provided by respiration in mitochondria
What happens at Telophase
Chromosomes are now at each pole of cell and become larger and thinner again
Spindle fibres disintegrates and Nucleus starts to reforms
What happens at Cytokinesis
Cytoplasm splits into 2 to create 2 new genetically identical cells
Explain root tip experiment
Place root in dilute HCl to halt cell division and hydrolyse middle lamella
Stain root tip with Toluidene Blue so that it binds to chromosomes
Macerate tissue in water with mounted needle
Use mounted needle at 45 to press down coverslip and obtain a single layer of cells. Avoid air bubbles
Focus an optical microscope on the slide. Count total number of cells in field of view and number of cells in a stage of mitosis
Calculate mitotic index (proportion of cells undergoing mitosis)
Name 2 dyes that bind to chromosomes
Toluidene 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 away from root tip are elongating rather than dividing
What are tumour suppressor genes
Genes that code for proteins to trigger apoptosis/ slows cell cycle
What’s apoptosis
Programmed death of damaged 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 and proto oncogenes cause cancer
Tumour suppressor: no production of a protein needed to slow cell cycle
Proto oncogenes: form permanently activated oncogenes
Disruption to cell cycle
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Uncontrolled cell division
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Tumour
How does cancer treatment control rate of cell division
Disrupt cell cycle:
Prevent DNA replication
Disrupt spindle formation = inhibit Metaphase/Anaphase
Explain binary fission
DNA loop replicates and stay attached at the cell membrane
Plasmids replicate in the cytoplasm
Cell membrane starts to get longer and eventually it retracts and a septum forms in the middle.
The cell has now divided into 2 with the same DNA but a variable number of plasmids
Why are viruses classified as non living
Acellular: no cytoplasm, no metabolism and cannot self replicate
Explain virus replication
Virus attaches to host cell membrane by attachment proteins
Injects nucleic acids via cell membrane
Cell replicates nucleic acids and produces virus particles
