1.6 Cell division COPY Flashcards
(101 cards)
What are the three main stages the cell cycle is divided into?
1) Interphase
2) Mitosis
3) Cytokinesis
Diagram showing the three stages of the cell cycle
Interphase
- Interphase is the most active as well as the longest phase of the cell cycle.
- Cells will spend most of their life within this stage undergoing common cell processes such as metabolism, endocytosis, exocytosis, and using and obtaining nutrients.
- It involves many processes that occur both in the nucleus and cytoplasm.
- It encompasses three important phases of the cell cycle: G1 (Gap 1), S (synthesis), and G2 (Gap 2).
G1 location in the cell
-Takes place in the cytoplasm
G1 activities
- The cell grows and functions, normally undergoing everyday processes.
- Rapid protein synthesis takes place, allowing the cell to grow in size.
- Proteins required for DNA synthesis (the next phase) are made.
- Mitochondria and chloroplasts (in the case of plant cells) are replicated. This also continues in the S phase.
S location in the cell
Takes place in the nucleus
S activities
- The amount of DNA doubles as DNA replication takes place.
- The genetic material is duplicated but no chromosomes are formed yet.
G2 location in the cell
Takes place in the cytoplasm
G2 activities
- Protein synthesis occurs to produce the proteins needed for cell division, such as microtubule proteins that will make up a mitotic spindle.
- The cell is actively preparing for cell division.
Mitosis
- Mitosis is the division of the nucleus into two genetically identical daughter nuclei.
- It involves the separation of sister chromatids into individual chromosomes which are then distributed among the daughter nuclei.
Cytokinesis
- Once mitosis has been completed, with the formation of two nuclei with identical sets of chromosomes, the cell enters cytokinesis.
- In cytokinesis, the cytoplasm of a parental cell is divided between the two daughter cells.
What are cyclins?
Cyclins are a family of proteins that control the progression of cells through the cell cycle.
Function of cyclins in a cell
- Cyclins and CDKs regulate the cell cycle
- Cells cannot progress to the next stage of the cell cycle unless the specific cyclin reaches a certain concentration.
- Cyclins bind to enzymes called cyclin-dependent kinases (CDKs) and activate them.
- The activated CDKs then attach phosphate groups (phosphorylation) to other proteins in the cell.
- The attachment of phosphate triggers the other proteins to become active and carry out tasks; in this case, specific to the phases of the cell cycle.
- For example, Cyclin E, shown in purple in Figure 2, peaks just before the S phase and the peak leads to DNA replication.
- DNA replication must occur before mitosis can begin.
What must occur before mitosis can begin?
DNA replication
Explain how cyclins and CDKs regulate the cell cycle
- Depending on the presence and action of these proteins, the cell cycle can be fast or slow, and it may even stop altogether.
- Mutations in genes that code for cyclins can lead to problems regulating the cell cycle, which may lead to cancer.
What are CDKs?
Enzymes called cyclin-dependent kinases
Diagram showing the fluctuations of different cyclins during the cell cycle.
What is a difference between a cell in the G1 phase and a cell in the G2 phase of the cell cycle?
A cell in the G2 phase has more mitochondria than a cell in the G1 phase.
Which cyclin affects all four phases of the cell cycle?
D cyclin
What are the three important phases in interphase?
G1 (Gap 1), S (synthesis), and G2 (Gap 2).
The process of mitosis is the division of ___. This involves separating the ___ that was replicated in ___
The division of the nucleus
DNA
The S phase.
Describe mitosis in eukaryotic cells
- In eukaryotic cells, the separation of DNA is done through the formation of chromosomes.
- Eukaryotic chromosomes consist of DNA that is tightly wound around proteins called histones.
- Histones are basic (alkaline) proteins that form part of nucleosomes.
- Many nucleosomes are coiled together in a specific pattern to form a structure called a chromosome.
- During interphase, chromosomes are unpacked, so that protein synthesis and replication can take place. DNA is only visible during mitosis.
What are histones?
Histones are basic (alkaline) proteins that form part of nucleosomes.
Diagram of the relationship between chromosomes and supercoiling