Making More Cells - Cell Proliferation

Question 1

Number of Cells

Answer 1

3 x 10^13 x 2m (number of cells multiplied by total length of DNA length per cell) = 6 x 10^13m
For comparison, the distance to the Sun from Earth is approximately 150 million kilometres
So the DNA content of a person adds up to approximately 400 times the distance of the Sun.

Question 2

Length of DNA

Answer 2

Joined end to end, each nucleated cell contains approximately 2m of DNA

Question 3

Aneuploidy

Answer 3

Aneuploidy: An aneuploids an individual organism whose chromosome differs from the wild type by part of a chromosome set. Generally, the aneuploid chromosome set differs from wild type by only one or a small number of chromosomes. Aneuploids can have a chromosome number either greater or smaller than that of the wild type.

Question 4

Polyploidy

Answer 4

Polyploidy: Polyploid cells and organisms containing more than two paired (homologous) sets of chromosomes.

Question 5

Are aneuploidy and polyploidy lethal?

Answer 5

DNA must be replicated only once per cell cycle/cell division
Aneuploidy and polyploidy are generally lethal so the cell must replicate the whole genome, but only do so once per cell division/cycle, how is this accomplished?

Question 6

Initiation of spermatogenesis

Answer 6

The initiation of spermatogenesis is during puberty is probably regulated by the synthesis of Bone Morphogenic Protein (BMP8B) by the spermatogenic sperm cells (spermatogonia)

Question 7

Oogenesis

Answer 7

• 1-2 months before the birth of a female baby, most of her 7 million oogonia die, and the remaining surviving oogonia enter meiosis I and become primary oocyte.
  
  • The primary oocytes arrest at the prophase I stage of the first meiotic division until the start of menstrual cycle
    The secondary oocytes arrest at the metaphase stage of the second meiotic division until the fertilisation takes place.

Question 8

G0 cells

Answer 8

At G0, cells can be stimulated to enter the cell cycle (G0 cells are outside the cell cycle).

Question 9

How are cells stimulated to enter the cell cycle?

Answer 9

Cells can be stimulated to enter through these growth factors, for example binding to the cell surface receptors

Question 10

Example of common growth factor

Answer 10

One example is the epidermal growth factor (EGF). Binding to the EGFR (epidermal growth factor receptor) signals proliferation to the cell, and the cell will enter the G1 phase and the cell cycle.

Question 11

G1 cell checkpoint

Answer 11

There is a checkpoint at the end of G1 to determine whether or not the cell is ready to undergo DNA replication which is probably the most critical step. If that goes wrong, there are lethal consequences.

Question 12

S phase and M phase Checkpoint

Answer 12

There is an S phase checkpoint to ensure DNA replication has occurred correctly and then there’s also M phase or mitotic checkpoint which determines if the cell is ready to enter the mitosis.

Question 13

Function of checkpoints in cell cycle

Answer 13

Checkpoints can halt the cell cycle and promote cell death in some circumstances (apoptosis) to protect the organism from DNA damage or replication failure.

Question 14

Defects in checkpoints

Answer 14

Defects in checkpoints lead to polyploidy and aneuploidy.

Question 15

Cyclins

Answer 15

Cyclins don’t have detectable enzyme activity.
Cyclins bind to and activate specific kinases: Cyclin dependent kinases.
Cyclins activate cyclin dependent kinases (CDKs) to regulate checkpoints.

Question 16

Example of CDK complex regulation

Answer 16

Cyclin -CDK complexes regulate pRB (Rb) and pRB controls the G1/S checkpoint.