2.2 - Cell Replication

What are the stages of Binary Fission?

• Circular DNA molecule (chromosome) replicates and attaches to separate sides of the cell

• Cell grows to twice its original size

• Cytoplasm divides

• The daughter cell synthesises a new cell wall

Prokaryotes are able to multiply rapidly because of their small size, and high SA:V ratio, allowing them to absorb nutrients faster. Replication is exponential.

What are the 3 main stages of Mitosis?

Interphase: Replication of parent DNA cell

Mitosis: Organise the chromosomes and divides into two separate groups

Cytokinesis: Membrane splits and creates two new cells

What are the 4 main stages of Interphase?

G1 (growth)

G0 (resting)

S (synthesis)

G2 (growth)(preparation for prophase)

What happens in G1 (growth)?

G1 (growth): Cellular content (not chromosomes) are duplicated, cell grows in size, prepares the DNA for cell division, longest phase of interphase.

What happens in G0?

G0 (resting): Stage can also be known as 'cell cycle arrest', some cells get stuck here and some skip to continue on. The stage is a checkpoint: Is the cell big enough? Is the environment suitable enough? If not, repeat the phase until checkpoints are met. P53 is a protein from the DNA that checks out the gene to ensure that it can move to the next stage.

What happens in S (synthesis)?

S (synthesis): Each of the 46 chromosomes are duplicated by the cell. The long chromosome strand will 'unzip' itself and connect with another strand to form two new daughter strands (leading and lagging). Chromatid duplication and centromere holds the two chromatids together, multiple chromatids are known as chromatin.

What happens in G2?

G2: The cell 'double checks' the duplicated chromosomes for error, making any necessary repairs. Cell volume increases, sometimes cell death can occur as it is not right for replication, shortest phase. Another checkpoint: Has the DNA been copied well? Is the volume ok? Environment still good?

What happens in Prophase?

• DNA coils to form distinct chromosomes

• Nuclear membrane disappears (allows chromosomes to be free in the cell)

• Spindle fibers form from centrioles

• Drift to either side of the cell

• Cant observe distinct chromosomes yet

What happens in Metaphase?

• Fully condensed chromosomes (2 chromatids each) align at centromere in the equator

What happens in Anaphase?

• Spindle fibers shorten

• Chromatids are drawn to the poles of the cell

• Pull apart the sister chromatids

• Centromere connections are cut (broken)

What happens in Telophase?

• Chromosomes reach the poles

• Nuclear membrane forms around the chromatids

• Chromosomes unwind to become thread-like again

• Nucleus forms

What happens in Cytokinesis?

• Divide cytoplasm

• New membrane forms in animal cells (cell wall if plant)

Animal Cell:

Microfilaments assemble around middle of the cell

ATP used to squeeze in half

Plant Cell:

Cell wall cant be squeezed together

Golgi body sends vesicles with cell-wall-building-material to center

Cell wall fills in gaps, cleaves the cell into two

What are the similarities of binary fission and mitosis

• Used by both prokaryotic and eukaryotic cells

• Allows for genetic diversity

• Creates two identical daughter cells

What are the differences of binary fission and mitosis?

Binary Fission:

• DNA is replicated

• Simple process

Mitosis:

• Chromosomes are replicated

• Used for growth and repair of cells

• Forms two membrane bound nuclei