cells Flashcards
(21 cards)
Why do cells divide?
To produce new cells for:
- Growth and development
- Maintenance and repair
- Reproduction
Cells replicate to replace damaged or dead cells, support organism growth, and reproduce in both prokaryotic and eukaryotic organisms.
What is binary fission?
A method of cell replication in prokaryotes that produces two identical copies of the cell.
Binary fission is a form of asexual reproduction involving one parent cell.
What are plasmids?
Small circular loops of DNA in bacteria that replicate independently of the main chromosome.
Plasmids can be present in multiple copies within a bacterial cell.
What occurs during the process of binary fission?
The following steps:
- Circular main chromosome uncoils and replicates
- Cell elongates
- Duplicated chromosomes migrate to opposite ends
- Cytokinesis occurs by forming a septum
- Two genetically identical cells are formed
Plasmids may be unevenly distributed to the daughter cells.
How does cell growth occur in bacteria?
Cells replicate exponentially, doubling the number after each cycle of replication, approximately every 20 minutes.
Under optimal conditions, bacterial populations can grow rapidly, but environmental factors eventually limit this growth.
What are the three stages of the eukaryotic cell cycle?
The stages are:
- Interphase
- Mitosis
- Cytokinesis
Each stage has specific functions crucial for cell division.
What is interphase?
The first and longest stage of the cell cycle, consisting of three phases: G1, S, and G2.
Interphase is where the cell grows and prepares for mitosis.
What happens during the G1 phase of interphase?
Cell synthesizes proteins and replicates organelles to grow in size.
G1 is the first phase of interphase.
What is the G0 phase?
A resting phase where cells that no longer divide remain. Some may re-enter the cell cycle, while others are terminally differentiated.
Examples of terminally differentiated cells include nerve and some muscle cells.
What occurs during the S phase of interphase?
Cell replicates its DNA, resulting in each chromosome consisting of two sister chromatids.
In humans, somatic cells have a diploid number of 46 chromosomes.
What happens during the G2 phase of interphase?
The cell continues to grow and prepares for mitosis by synthesizing more proteins.
G2 is the final phase before mitosis.
What are the four stages of mitosis?
The stages are:
- Prophase
- Metaphase
- Anaphase
- Telophase
Each stage has distinct processes for chromosome separation.
What occurs during prophase?
Chromatin condenses into visible chromosomes, centrioles migrate, and the nuclear membrane disappears.
Chromosomes are composed of two sister chromatids at this stage.
What happens during metaphase?
Spindle fibers attach to centromeres, and chromosomes line up across the equator of the cell.
This alignment is crucial for proper chromosome separation.
What occurs during anaphase?
Spindle fibers contract, centromeres split, pulling sister chromatids to opposite ends of the cell.
This ensures that each daughter cell will receive an identical set of chromosomes.
What happens during telophase?
Chromosomes reach the poles, the nuclear membrane reforms, and chromosomes uncoil.
Two identical daughter cells are formed at the end of this stage.
What is cytokinesis?
The division of the cytoplasm and organelles into two daughter cells.
In animals, a cleavage furrow forms; in plants, a cell plate develops.
What are the three checkpoints in the cell cycle?
The checkpoints are:
- G1/S
- G2/M
- Metaphase
These checkpoints ensure that the cell is ready for the next phase and checks for errors.
What happens at the G1/S checkpoint?
Checks if the cell has grown to the right size and synthesized proteins for DNA replication, and ensures there are enough nutrients and oxygen.
This is the first checkpoint in the cell cycle.
What occurs at the G2/M checkpoint?
Ensures that DNA has replicated correctly and checks for sufficient resources for mitosis.
This checkpoint is crucial for preventing errors during cell division.
What is checked at the metaphase checkpoint?
Checks the formation of spindle fibers and ensures that chromosomes are properly attached and aligned before anaphase.
This checkpoint is vital for accurate chromosome separation.
