Chapter 4A & B Cell Cycles Flashcards
What are the purposes of cell replication in an organism?
Cell replication occurs for growth and development, maintenance and repair, and reproduction.
Maintenance and Repair
Cells are constantly dying or get damaged.
Cell replication allows these cells to be replaced
Growth & Development
For a multicellular organism to grow and develop, cells need to replicate (we grow by making more cells not by cells getting larger).
Humans start life as a single cell (zygote) that replicates into an embryo, foetus and then a baby.
Reproduction
Prokaryotic and eukaryotic cells replicate to reproduce (producing more cells ).
What are plasmids in bacteria?
Plasmids are small circular loops of DNA separate from the main bacterial chromosome (nucleoid).
What is binary fission in prokaryotes (e.g., bacteria)?
Binary fission is a form of asexual reproduction in prokaryotes where one parent cell divides to produce two identical copies of the cell.
What happens during the first stage of binary fission in bacteria?
The circular main chromosome is uncoiled and replicated, and plasmids also replicate.
How does the cell prepare for binary fission?
The cell elongates (grows longer) as it prepares to separate into two new cells.
What happens to the duplicated chromosomes during binary fission?
The duplicated circular main chromosomes migrate to opposite ends of the cell. (they may also be attached to cell membrane and get pulled apart)
What is cytokinesis in binary fission?
Cytokinesis occurs when the cell pinches inwards, forming a septum (a dividing new wall).
How are plasmids involved in binary fission?
Plasmids replicate independently of the main circular chromosome and may be unevenly separated into the two new cells.
What happens at the final stage of binary fission?
A new cell wall and membrane are formed down the center of the cell, resulting in two new genetically identical cells.
What is exponential cell replication?
Exponential cell replication means the number of cells doubles after each cycle of replication.
How long does each cycle of cell replication take?
Each cycle of cell replication takes approximately 20 minutes.
What is interphase in the cell cycle?
Interphase is the first and longest stage of the cell cycle, made up of three phases:
G1 phase (cell growth)
S phase (DNA replication)
G2 phase (preparation for mitosis)
What are the three stages of the eukaryotic cell cycle?
he three stages of the eukaryotic cell cycle are:
Interphase (cell growth & chromosome replication)
Mitosis (separation of chromosomes)
Cytokinesis (division of the cytoplasm)
Can cells exit the cell cycle?
Yes, cells can exit the cell cycle from the G1 phase and enter the G0 (resting phase).
What happens during the Gap 1 (G1) phase of the cell cycle?
During the G1 phase, the cell synthesises more proteins to grow in size and replicates organelles.
What is the Gap 0 (G0) phase in the cell cycle?
The G0 phase is where cells that no longer divide rest. Some cells are quiescent (dormant/resting) but may re-enter the cell cycle, while others are terminally differentiated and remain in G0 permanently (e.g., nerve cells, some muscle cells).
What happens during the Synthesis (S) phase of the cell cycle?
During the S phase, the cell replicates its DNA so that each chromosome consists of two sister chromatids held together by a centromere. In humans, somatic (body) cells have 46 chromosomes (23 pairs), known as the diploid number (2n).
What happens during the Gap 2 (G2) phase of the cell cycle?
The G2 phase is the final stage of interphase, where the cell continues to grow, prepares for mitosis, and synthesizes more proteins.
What is mitosis in the eukaryotic cell cycle?
Mitosis is the second stage of the eukaryotic cell cycle and involves the separation of the replicated chromosomes into two new cells.
What happens during prophase of mitosis?
Chromatin (loose DNA) condenses into visible chromosomes.
Centrioles migrate to opposite ends of the cell, and spindle fibres begin to form.
The nuclear membrane and nucleolus disappear.
Chromosomes are made up of two sister chromatids.
What are the four stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
