Cell cycle Flashcards
Cell cycle stages
Interphase (most of time)
Mitotic phase
What happens in interphase?
DNA is replicated: DNA is decondensed in the form of chromatin
Organelles replicated
Nucleoli visible
ATP content increased so more energy stores in the cell
Cells get larger
DNA condensing
DNA in cell is in form chromatin = appears as dark
Where they aren’t visible
But then condenses to be thick and visible and short in prophase so are viewed as chromosomes
What is chromatin visible as after condensing?
A chromosome
What is formed after DNA replication?
2 sister chromatids joined together by centromeres
Ready to be split apart in mitosis
Stages of mitotic phase in order?
Prophase
Metaphase
Anaphase
Telophase
What happens in prophase?
Chromatin condenses to be viewed as chromosomes
Centrioles formed at opposite ends of cell forming network of protein (spindle fibres)
Nuclear membrane breaks down so chromosomes lie free in cytoplasm
Chromosomes are visible and in the form of 2 sister chromatids: joined at centromere attached to spindle fibre
What happens in metaphase?
The chromosomes (consisting of 2 sister chromatids) line up in equator of cell, attached to spindle fibres at centromere
What happens in anaphase?
The centromeres divide which pulls sister chromatids apart to opposite poles as the spindle fibre shortens
This process requires ATP
Separated chromatids appear v shaped and are now counted as 1 chromosome
What happens in the first stage of telophase?
The spindle fibre apparatus breaks down As half the chromatids reach opposite side of the poles still with a centromere they decondense = long and thin now chromosomes
Nuclear membrane and nucleolus reappear = 2 nuclei around the 2 groups of chromosomes
What happens in cytokinesis?
Central cell surface membrane breaks down so cells divided into 2 genetically identical daughter cells
What does mitosis specifically refer to?
Division of the nucleus
What does cytokinesis refer to?
Division of the cell
What kind of process is mitosis?
Controlled
How are cancers and tumours formed?
By uncontrolled cell division
What do cancer treatments focus on?
Controlling rate of cell division
How do cancer treatments control rate of cell division?
Inhibit DNA replication such as inhibiting DNA polymerase/hydrolyse enzymes or nucleotide synthesis
Damage DNA so cell kills itself
How do prokaryote cells divide?
Binary fission
How does binary fission occur?
Replication of circular DNA loop and plasmids
Division of cytoplasm = 2 identical cells
How to count number of chromosomes in a cell?
Count number of centromeres
Mitotic index
Number of cells in mitosis/ total number of cells in the field of view
How to find the mean mitotic index of a sample?
Count the number of cells in mitosis in a field of view and divide by the total number of cells in the same field of view
Repeat for a large number of field of views on the same magnification and calculate the mean
What does random sampling of field of views ensure?
Avoids any bias so we can accurately represent the whole tissue in the samples
How can we make sure counts of the cells are accurate?
Repeat counting
Have a standardised way of counting eg by only including full cells and ignoring half cells
What varies the mitotic index in an experiment using the same plant?
The plant was grown in different conditions such as different temperature or light intensity so some plants were undergoing mitosis at a faster rate
The field of view taken was not properly representative of the whole plant
