The cell cycle and cell division Flashcards
What are the processes occurring during interphase?
Replication of DNA and organelles
Self replication
Making new organelles
Synthesis of ribosomes, ATP and proteins
Extending the cell membrane
What is a chromosome?
A long string of DNA, packed tightly around proteins called histones.
What happens to chromosomes during interphase?
The DNA in a chromosome is replicated, forming two genetically identical strands called sister chromatids, joined at a point called the centromere.
Describe mitosis
One division resulting in two genetically identical daughter cells. Number of chromosomes stays the same. Maintains diploid number of chromosomes.
Describe meiosis
Two divisons resulting in four genetically varied daughter cells. Number of chromosomes is halved. Maintains the haploid number of chromosomes.
Where is mitosis typically observed?
In meristems.
Outline the steps of mitosis
Prophase: Chromosomes become visible, nuclear membrane break down, centrioles move to opposite poles of the cell.
Metaphase: Chromosomes arrange themselves at the equator of the spindle and attach to the spindle fibres at the centromere.
Anaphase: The centromeres split and the spindle fibres contract, pulling the chromatids to opposite parts of the cell.
Telophase: Spindle breaks down, nuclear membrane reforms.
Cells divide by cytokinesis.
How does cytokinesis occur in animal cells?
The cytoplasm splits and cell division occurs by the furrowing of the cell membrane.
How does cytokinesis occur in plant cells?
A plate forms across the equator of the cell and a new cell wall is laid down.
What is the role of mitosis?
Growth of cells
Repair of tissues
Replacement of dead and worn out cells
What is the drawback of mitosis?
Due to the lack of variation, there is an inability to adapt if the environment changes.
What is an oncogene?
A gene that causes cancer, which is the result of uncontrolled mitosis.
Describe how tumours can form
The cell cycle is controlled by genes which control the rate of cell division and ensure each stage is completed before moving on to the next one. Mutations can occur in these genes which may lead to unrestricted cell divisons and cancerous growth.
Where is meiosis typically observed?
In the anther of a plant.
Describe the steps of meiosis
Prophase 1: Chromosomes become visible and nuclear membrane breaks down. Homologous chromosomes form bivalents and join at chiasmata.
Metaphase 1: The spindle forms and bivalents line up randomly at the equator in homologous pairs- independent assortment.
Anaphase 1: Chromosomes separate due to the contraction of spindle fibres and move toward poles.
Telophase 1: Chromosomes reach new poles and new nuclear membranes form around two new nuclei, cell divides by cytokinesis.
Prophase 2: Chromosomes become visible, nuclear membrane break down, centrioles move to opposite poles of the cell.
Metaphase 2: Chromosomes arrange themselves at the equator of the spindle and attach to the spindle fibres at the centromere.
Anaphase 2: The centromeres split and the spindle fibres contract, pulling the chromatids to opposite parts of the cell.
Telophase 2: Spindle breaks down, nuclear membrane reforms.
Cells divide by cytokinesis.
