What is the major thing happening to a cell during G1?

Answer 1

G1, or gap 1, is the first stage of interphase. The other stages of interphase are: S (synthesis), G2 and then finally M (mitosis). There is also a G0 stage where the cell is not preparing for division. For example nerve cells are continuously in this stage as they do not divide.

G1 is like the cell cycle control stage. If the cell is not ready to divide, it does not pass this stage. During this stage the cell is checking that it is ready to start DNA replication in the S stage. There are many check points in G1 that are regulated by cyclins and cyclin dependant kinases (cdk's). CDK's are protein complexes. Kinases are enzymes that can activate or inactivate other proteins by phosphorylation. The things that could halt G1, and thus a protein inhibiting the complex, include cell damage and DNA damage. The cycle then halts until the cell has repaired the damage. If the damage is irreparable, proteins will then signal the start of apoptosis (programmed cell death). Tumour supressors such as p21 and p53, and RB (retino blastoma) also play a role in the cycle. To pass into S stage the cell must pass the restriction point. After this point the cell has commited to dividing.

It is when these checkpoints and cycles go wrong that cancer can persist, hence th name tumour suppressor. When cells divide uncontrollably, and divide when damaged, cancer can arise.

A significant amount of cancers have defected tumour supressor proteins.

Answer 2

It's being divided into two identical daughter cells.

Answer 3

The cell is growing and, most importantly, checking to see that replication is possible during the next phase which is synthesis. Checks and repairs to the genetic material happen during G1.

Answer 4

Growth