Biology IB HL - 1.6 Cell Cycle Part 1

an ordered set of events which culminates in the division of a cell into two daughter cells

Interphase

M Phase

G1

S

G2

The stage in the development of a cell between two successive divisions

First intermediate gap stage in which the cell grows and prepares for DNA replication

Synthesis stage in which DNA is replicated

Second intermediate gap stage in which the cell finishes growing and prepares for cell division

The period of the cell cycle in which the cell and contents divide to create two genetically identical daughter cells

mitosis

cytokinsesis

Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two identical daughter cells

Interphase is an active period in the cell cycle when many METABOLIC reactions occur

D NA replication

O rganelle duplication

C ell growth

T ranscription/translation

O btain nutrients

Respiration (cellular)

DNA is copied during the S phase of interphase

Organelles must be duplicated for twin daughter cells

Cytoplasmic volume must increase prior to division

Key proteins and enzymes must be synthesised

Vital cellular materials must be present before division

ATP production is needed to drive the division process

DNA is usually loosely packed within the nucleus as unravelled chromatin

In this unravelled form, the DNA is accessible to transcriptional machinery and so genetic information can be translated

DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase

DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division (via supercoiling)

In this condensed form, the DNA is able to be easily segregated

DNA is inaccessible to transcriptional machinery

DNA is organised as chromosomes during the process of mitosis

a) prophase | b) telophase

As the DNA is replicated during the S phase of interphase, the chromosome will initially contain two identical DNA strands

These genetically identical strands are called sister chromatids

held together by a central region called the centromere

When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand

When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand

Mitosis is the process of nuclear division, whereby duplicated DNA molecules are arranged into two separate nuclei

Mitosis is preceded by interphase

divided into four distinct stages: prophase, metaphase, anaphase, telophase

The division of the cell in two (cytokinesis) occurs concurrently with the final stage of mitosis (telophase)

DNA is present as uncondensed chromatin (not visible under microscope)

DNA is contained within a clearly defined nucleus

Centrosomes and other organelles have been duplicated

Cell is enlarged in preparation for division

DNA supercoils and chromosomes condense (becoming visible under microscope)

Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)

Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres

The nuclear membrane breaks down and the nucleus dissolves

Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome

Microtubule depolymerisation causes spindle fibres to shorten in length and contract

This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)

Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate

Once the chromatids separate, they are each considered an individual chromosome in their own right