Key Area 5

(b) The cell cycle

The cell cycle regulates the growth and replacement of genetically identical cells throughout the life of the organism.

This is a continual process but it can be divided up into distinct stages. The whole cycle can be divided up into two parts:

Interphase - consisting of G1, S and G2.
The mitotic phase - involving mitosis and cytokinesis.

Task 74

It was period 4 on a Wednesday, ahead of another post-lockdown triple period in AH Biology. Stevie was up to his old tricks and had farted in the class.

"Aw, right, Miss, get him telt - that is pure boggin and it's gieing me the boke. Stevie, open they windows and get yerself oot!".

"Right, right, calm down - windows are open and the fart particles will diffuse down the VERY steep concentration gradient out the window soon. Now, in your notes, to distract yourself, sketch a diagram of the cell cycle to show interphase and the mitotic phase. You may find your face masks have another benefit at this precise time..."

Time for you to complete Task 74 too. Suggested answers are here.

How the cell cycle works - Animation

Interphase

Inerphase is divided into 3 sub-phases:

G1 - a growth phase where proteins and organelles are synthesised.
S phase - during which the DNA is replicated
G2 phase - a further growth phase.

Interactive Cell Cycle

Mitotic Phase

At the end of G2, cells enter the mitotic phase (M). The M phase is divided into 2 stages:

Mitosis - where the nucleus and its contents divide. The chromosomal material is separated by the spindle microtubules. Mitosis consists of 4 stages called prophase, metaphase, anaphase and telophase. Spindle fibres are crucial throughout this process: they control the omvement of chromosomes on the metaphase plate; they separate sister chromatids; they help form new daughter nuclei.
Cytokinesis - the cytoplasm is separated into two daughter cells.

Task 75

Dr McRobbie was feeling concise today. She quickly said "describe the three stages of interphase".

You should concisely complete this task too. Suggested answers are available here.

A quick memory aid for the 4 mitosis stages:

Prophase

During prophase, DNA condenses into chromosomes, each consisting of two sister chromatids. Nuclear membranes break down. Spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region.

Metaphase

Chromosomes are aligned at the metaphase plate (equator of the spindle).

Anaphase

As spindle microtubules, shorten by depolymerisation, sister chromatids are separated, and the chromsomes are pulled to opposite poles.

Telophase

The chromosomes decondense and nuclear membranes are formed around them.

This image shows the 4 distinct stages of mitosis, as observed by electron microscopy. The genetic material can be seen as darker regions. During metaphase, the chromosomes can be seen aligning along the equator, starting to be pulled apart during anaphase and distinct separation during telophase.

Ultimately, this process resulted in the formation of 2 genetically identical diploid daughter cells. But it is tightly regulated and does not continue unless the cell and its contents are classed as ready for division. In the next section, we find out how this controlled is managed in the cell.

Task 76

During prophase, spindle fibres extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region. Carry out some research and draw a labelled diagram to show all structures mentioned in this description.

Time to review with Hank Green in Crash Course Biology.

Click here for a Quizlet on Topic 1, Key Area 5b

Now go to SCHOLAR "5.2 The Cell Cycle" for consolidation and to complete the interactive Mitosis activity