UNIT 1.6 Flashcards
Outline the events of Interphase
G1 – First intermediate gap stage in which the cell grows and prepares for DNA replication
S – Synthesis stage in which DNA is replicated
G2 – Second intermediate gap stage in which the cell finishes growing and prepares for cell division
Outline the events of metaphase
Mitosis – Nuclear division, whereby DNA (as condensed chromosomes) is separated into two identical nuclei
Cytokinesis – Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two
Give a detailed description of the events of interphase
NA replication – DNA is copied during the S phase of interphase
Organelle duplication – Organelles must be duplicated for twin daughter cells
Cell growth – Cytoplasmic volume must increase prior to division
Transcription / translation – Key proteins and enzymes must be synthesised
Obtain nutrients – Vital cellular materials must be present before division
Respiration (cellular) – ATP production is needed to drive the division process
Mnemonic: DOCTOR
Give a comparison between Chromatin & Chromosomes
Chromatin:
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
Chromosome:
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 however is inaccessible to transcriptional machinery
DNA is organised as chromosomes during the process of mitosis (condense in prophase, decondense in telophase)
Give a comparison between a Chromatid and a Chromosome
A chromosome is the condensed form of DNA which is visible during mitosis (via microscopy)
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 and are 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
Outline the events of Prophase (Mitosis)
Prophase:
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
Outline the events of Metaphase (Mitosis)
Metaphase:
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)
Outline the events of Anaphase (Mitosis)
Anaphase:
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
The genetically identical chromosomes move to the opposite poles of the cell
Outline the events of Telophase (Mitosis)
Telophase:
Once the two chromosome sets arrive at the poles, spindle fibres dissolve
Chromosomes decondense (no longer visible under light microscope)
Nuclear membranes reform around each chromosome set
Cytokinesis occurs concurrently, splitting the cell into two
Outline Cytokinesis in animal cells
After anaphase, microtubule filaments form a concentric ring around the centre of the cell
The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre
When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed
Because this separation occurs from the outside and moves towards the centre, it is described as centripetal
Outline Cytokinesis in plant cells
After anaphase, carbohydrate-rich vesicles form in a row at the centre of the cell (equatorial plane)
The vesicles fuse together and an early cell plate begins to form within the middle of the cell
The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
Because this separation originates in the centre and moves laterally, it is described as centrifugal
What is Mitotic Index and what is one use of it ?
The mitotic index is the ratio between the number of cells in mitosis and the total number of cells
It can be determined by analysing micrographs and counting the relative number of mitotic cells versus non-dividing cells
-Can be used as a prognostic tool for cancer to predict how cells will react to chemotherapy.
What are cyclins ?
Cyclins are a family of regulatory proteins that control the progression of the cell cycle
Cyclins activate cyclin dependent kinases (CDKs), which control cell cycle processes through phosphorylation
When a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation
The phosphorylated target protein will trigger some specific event within the cell cycle (e.g. centrosome duplication, etc.)
After the event has occurred, the cyclin is degraded and the CDK is rendered inactive again
How are cyclin concentrations moderated ?
Different cyclins specifically bind to, and activate, different classes of cyclin dependent kinases
Cyclin levels will peak when their target protein is required for function and remain at lower levels at all other times
What is a Mutagen?
A mutagen is an agent that changes the genetic material of an organism (either acts on the DNA or the replicative machinery(Can be physical,Chemical or Biological)
