the cell cycle 4A and 4B

Question 1

why do cells replicate?

Answer 1

to produce new cells in an organism for the purposes of
Growth and development
Maintenance and repair
Reproduction

Question 2

binary fission

Answer 2

process by which prokaryotic organisms (eg bacteria) divide and reproduce

Cell replication in prokaryotes (eg. Bacteria)
Produces two identical copies of the cell
A form of asexual reproduction ( one parent cell)

Question 3

step 1 of binary fission

Answer 3

The circular main chromosome is uncoiled and the DNA is replicated. Plasmids also replicate.

Question 4

step 2 of binary fission

Answer 4

The cell elongates (grows longer) as it prepares to separate into two new cells.

Question 5

step 3 binary fission

Answer 5

The duplicated circular main chromosomes migrate to opposite ends.

Question 6

step 4 binary fission

Answer 6

Cell undergoes CYTOKINESIS by pinching inwards and creating a SEPTUM (dividing new wall). Cell wall and membrane forms producing 2 identical daughter cells

Question 7

what are plasmids and how do they replicate?

Answer 7

Plasmids are small circular loops of DNA that are separate from the main bacterial chromosome (nucleoid). They replicate independently so they could be unevenly separated into the two new cells.

Question 8

what are the 3 steps of the eukaryotic cell cycle?

Answer 8

Interphase (cell growth & chromosome replication)
Mitosis ( separation of chromosomes)
Cytokinesis (division of the cytoplasm)

Question 9

Interphase

Answer 9

First and longest stage of the cell cycle.
Made up of three phases :
- G1 phase:
Cell synthesizes more proteins to grow in size
Replication of organelles

  - S phase:  Cell replicates its DNA so that each chromosome is made up of two sister chromatids held together by a centromere.

  - G2 phase: Final stage of interphase Cell continues to grow and prepare for mitosis Synthesizes more proteins

Gap 0 (G0) phase: Cells that no longer divide rest in this phase.

Question 10

mitosis

Answer 10

Second stage of the eukaryotic cell cycle.
It involves the separation of the replicated chromosomes into two new cells.

Made up of four stages :
- prophase
- metaphase
- anaphase
- telophase

Question 11

prophase

Answer 11

• Chromatin (loose DNA ) in the nucleus condenses into
  chromosomes so that they are visible.
  
  • Centrioles migrate to oppose ends of the cell and spindle
  • fibres begin to form.
    Nuclear membrane and nucleolus disappear.
    Chromosomes are made up of two sister chromatids.

Question 12

metaphase

Answer 12

The spindle fibres are fully formed.
Centromere of each chromosome attaches to a spindle fibre.
The chromosomes line up across the equator of the cell.

Question 13

anaphase

Answer 13

The spindle fibres contract/shorten
Centromere splits pulling the sister chromatids to opposite ends of the cell.

Question 14

telophase

Answer 14

Chromosomes collect together at the poles of the cell.
Nuclear membrane reforms, producing two identical DAUGHTER CELLS.
Spindle fibres disintegrate.
Chromosomes uncoil and can no longer be seen.

Question 15

cytokinesis

Answer 15

After mitosis, the cytoplasm and the organelles are evenly distributed into the two daughter cells.

Question 16

cytokinesis in animal cells

Answer 16

a cleavage furrow develops and pinches the plasma
membrane into two cells.

Question 17

cytokinesis in plant cells

Answer 17

a cell plate ( later becomes a cell wall) forms at the
equator to separate the two new cells.

Question 18

chromatid

Answer 18

Chromatids are the identical halves of a duplicated chromosome, joined at the centromere.

Question 19

centromere

Answer 19

links a pair of sister chromatids together. during mitosis spindle fibres attach to the centromere

Question 20

spindle fibres

Answer 20

play a crucial role in mitosis by separating the chromosomes into the two daughter cells….. edit

Question 21

how is the cell cycle regulated?

Answer 21

There are 3 checkpoints in the cell cycle where the cell is checked for errors

If errors are found, the cell is either repaired or undergoes apoptosis ( programmed cell death).

Question 22

Where are the 3 checkpoints and what happens at each checkpoint?

Answer 22

G1/S
Check to see if cell has grown to the right size
Checked to see if the cell has synthesized protein for DNA replication
Checks if there are enough nutrients and oxygen

G2/M
Ensures that DNA has replicated correctly.
Checks if the cell has enough resources for mitosis.

Metaphase
The cell checks the formation of the spindle fibres
Checks that the chromosomes are attached and aligned before anaphase.