1.6 Cell Cycle Flashcards
What is the cell cycle?
an ordered set of events which culminates in the division of a cell into two daughter cells
What are the 2 phases of the cell cycle?
Interphase
M Phase
What are the 3 sub-stages of interphase?
G1
S
G2
What is interphase?
The stage in the development of a cell between two successive divisions
What occurs at G1?
First intermediate gap stage in which the cell grows and prepares for DNA replication
What occurs at S?
Synthesis stage in which DNA is replicated
What occurs in G2?
Second intermediate gap stage in which the cell finishes growing and prepares for cell division
What is M phase?
The period of the cell cycle in which the cell and contents divide to create two genetically identical daughter cells
What two substages does M phase have?
mitosis
cytokinsesis
What is cytokinesis?
Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two identical daughter cells
What type of reactions occur during interphase?
Interphase is an active period in the cell cycle when many METABOLIC reactions occur
What events have to occur during interphase for successful cell division?
D NA replication O rganelle duplication C ell growth T ranscription/translation O btain nutrients Respiration (cellular)
Why does interphase need DNA replication?
DNA is copied during the S phase of interphase
Why does interphase need organelle duplication?
Organelles must be duplicated for twin daughter cells
Why does interphase need cell growth?
Cytoplasmic volume must increase prior to division
Why does interphase need transcription/translation?
Key proteins and enzymes must be synthesised
Why does interphase need the cell to obtain nutrients?
Vital cellular materials must be present before division
Why does interphase need respiration?
ATP production is needed to drive the division process
How is DNA found in the nucleus?
DNA is usually loosely packed within the nucleus as unravelled chromatin
Why is DNA found in the form of unravelled chromatin in the nucleus?
In this unravelled form, the DNA is accessible to transcriptional machinery and so genetic information can be translated
In what cells is DNA organised as chromatin?
DNA is organised as chromatin in all non-dividing cells and throughout the process of interphase
What form is DNA found in prior to division? What process is used?
DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division (via supercoiling)
Why is DNA put into its condensed form (chromosome) before division?
In this condensed form, the DNA is able to be easily segregated
Why is DNA being in the form of a chromosome not ideal?
DNA is inaccessible to transcriptional machinery
When is DNA organised as chromosomes?
DNA is organised as chromosomes during the process of mitosis
In what phase does DNA:
a) condense
b) decondense
a) prophase
b) telophase
What will chromosomes contain during the S phase of interphase?
As the DNA is replicated during the S phase of interphase, the chromosome will initially contain two identical DNA strands
What are genetically identical strands of DNA called?
These genetically identical strands are called sister chromatids
What holds sister chromatids together?
held together by a central region called the centromere
What happens to the chromatids after mitosis?
When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand
What is mitosis?
Mitosis is the process of nuclear division, whereby duplicated DNA molecules are arranged into two separate nuclei
What is mitosis preceded by?
Mitosis is preceded by interphase
What four stages is mitosis divided into?
divided into four distinct stages: prophase, metaphase, anaphase, telophase
When does cytokinesis occur?
The division of the cell in two (cytokinesis) occurs concurrently with the final stage of mitosis (telophase)
- In what form is DNA present in, in interphase?
DNA is present as uncondensed chromatin (not visible under microscope)
- Where is DNA found during interphase?
DNA is contained within a clearly defined nucleus
- What happens to organelles during interphase/ in preparation for interphase?
Centrosomes and other organelles have been duplicated
- How does the cell look like in interphase?
Cell is enlarged in preparation for division
- What does DNA look like during prophase?
DNA supercoils and chromosomes condense (becoming visible under microscope)
- What are chromosomes composed of?
Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
- What role do centrosomes play in prophase?
Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
- What happens to the nuclear membrane during prophase?
The nuclear membrane breaks down and the nucleus dissolves
- What role do microtubule spindle fibres play in metaphase?
Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
- What does microtubule depolymerisation help happen in metaphase?
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)
- What happens to chromatids in anaphase?
Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
- What are chromatids considered to be once separated in anaphase?
Once the chromatids separate, they are each considered an individual chromosome in their own right
- What do the chromatids do in anaphase?
The genetically identical chromosomes move to the opposite poles of the cell
- What happens to the spindle fibres in telophase?
Once the two chromosome sets arrive at the poles, spindle fibres dissolve
- What happens to chromosomes during telophase?
Chromosomes decondense (no longer visible under light microscope)
- What happens to the nuclear membrane during telophase?
Nuclear membranes reform around each chromosome set
- What is the final step to splitting the cell?
Cytokinesis occurs concurrently, splitting the cell into two
Is cytokinesis the same in plant and animal cells?
NO
- What is the first event during cytokinesis for animal cells that occurs after anaphase?
cytokinesis in animal cells
After anaphase, microtubule filaments form a concentric ring around the centre of the cell
- What is the role of microfilaments in cytokinesis? What do they form?
cytokinesis in animal cells
The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre
3.What is the role of the cleavage furrow?
cytokinesis in animal cells
When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed
- What is the separation of the two cells described as?
cytokinesis in animal cells
Because this separation occurs from the outside and moves towards the centre, it is described as centripetal
- What is the first event of cytokinesis in plant cells?
cytokinesis in plant cells
After anaphase, carbohydrate-rich vesicles form in a row at the centre of the cell (equatorial plane)
- What do the vesicles do? What is formed?
cytokinesis in plant cells
The vesicles fuse together and an early cell plate begins to form within the middle of the cell
- What happens to the cell plate? What does it help do?
cytokinesis in plant cells
The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
- What is the separation described as?
cytokinesis in plant cells
Because this separation originates in the centre and moves laterally, it is described as centrifugal
What is the mitotic index?
The mitotic index is a measure of the proliferation status of a cell population (i.e. the proportion of dividing cells)
When might the mitotic index be higher?
The mitotic index may be elevated during processes that promote division, such as normal growth or cellular repair
Why might the mitosis index be important?
It also functions as an important prognostic tool for predicting the response of cancer cells to chemotherapy
What do cells that are undergoing mitosis look like?
Cells undergoing mitosis will lack a clearly defined nucleus and possess visibly condensed chromosomes
How do you calculate the mitotic index?
number of cells in mitosis / total number of cells
What are cyclins?
Cyclins are a family of regulatory proteins
What is the role of cyclins?
control the progression of the cell cycle
What do cyclins activate?
Cyclins activate cyclin dependent kinases (CDKs)
What is the role of CDKs?
control cell cycle processes through phosphorylation
- What happens between a cyclin and CDK?
When a cyclin and CDK form a complex, the complex will bind to a target protein and modify it via phosphorylation
- What happens to the target protein?
The phosphorylated target protein will trigger some specific event within the cell cycle (e.g. centrosome duplication, etc.)
- What happens after the cyclin has completed its role?
After the event has occurred, the cyclin is degraded and the CDK is rendered inactive again
Why do cyclin concentrations need to be tightly regulated?
Cyclin concentrations need to be tightly regulated in order to ensure the cell cycle progresses in a proper sequence
Are cyclins specific?
YES
Different cyclins specifically bind to, and activate, different classes of cyclin-dependent kinases
When will cyclin levels peak?
Cyclin levels will peak when their target protein is required for function and remain at lower levels at all other times
What are tumours?
Tumours are abnormal cell growths resulting from uncontrolled cell division and can occur in any tissue or organ
What are cancers?
Diseases caused by the growth of tumours are collectively known as cancers
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)
What 3 types of mutagens can there be?
physical, chemical and biological
What are examples of physical mutagens?
Sources of radiation including X-rays (ionising), ultraviolet (UV) light and radioactive decay
What are examples of chemical mutagens?
DNA interacting substances including reactive oxygen species (ROS) and metals (e.g. arsenic)
What are examples of biological mutagens?
Viruses, certain bacteria and mobile genetic elements (transposons)
What are mutagens called when they lead to the formation of cancer?
Mutagens that lead to the formation of cancer are further classified as carcinogens
What is an oncogene?
An oncogene is a gene that has the potential to cause cancer
What are most cancers caused by? give name of 2 factors
Most cancers are caused by mutations to two basic classes of genes – proto-oncogenes and tumour suppressor genes
What do proto-oncogenes code for?
code for proteins that stimulate the cell cycle and promote cell growth and proliferation
What do tumour suppressor genes code for?
code for proteins that repress cell cycle progression and promote apoptosis
What has to happen to a proto-oncogene in order for it to cause cancer, what is it then called?
When a proto-oncogene is mutated or subjected to increased expression it becomes a cancer-causing oncogene
What can tumour suppressor genes also be called and why?
Tumour suppressor genes are sometimes referred to as anti-oncogenes, as their normal function prevents cancer
What is metastasis?
Metastasis is the spread of cancer from one location (primary tumour) to another, forming a secondary tumour
What does it mean if tumour cells are benign?
when tumour cells remain in their original location
What does it mean if tumour cells are malignant?
when tumour cells spread and invade neighbouring tissue (malignant)
What type of cells are secondary tumours made out of?
Secondary tumours are made up of the same type of cell as the primary tumour – this affects the type of treatment required
E.g. If breast cancer spread to the liver, the patient has secondary breast cancer of the liver (treat with breast cancer drugs)
What happens to the chromatids after mitosis?
When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand
