1.6 Cell division Flashcards
What is the cell cycle?
An ordered set of events which culminates the division of a cell into two daughter cells
What are the two main phases of the cell cycle?
Interphase and M phase
What is interphase?
The stage in the development of a cell between two successive divisions
What are the three stages of interphase?
G1
S
G2
What is G1 phase?
First intermediate gap stage where the cell grows and prepares for DNA replication
What is S phase?
Synthesis stage where DNA is replicated
What is G2 phase?
Second intermediate gap stage where the cell finishes growing and prepares for cell division
What is M phase?
The period of the cell cycle where the cell and contents divide into two genetically identical daughter cells?
What is mitosis?
Nuclear division where DNA is separated into two identical nuclei
What is cytokinesis?
Cytoplasmic division where cellular contents are segregated and the cell splits into two
What are the stages of M phase?
Mitosis and cytokinesis
When in the cell cycle do many metabolic reactions occur?
Interphase
What processes need to occur for interphase to prepare the cell for successful division? (doctor)
DNA replication
Organelle duplication
Cell growth
Transcription/Translation
Obtain nutrients
Respiration
What is DNA replication in interphase?
DNA is copied during the S phase of interphase
What is organelle duplication in interphase?
Organelles must be duplicated for twin daughter cells
What is cell growth in interphase?
Cytoplasmic volume must increase prior to division
What is transcription/translation in interphase?
Key proteins and enzymes must be synthesised
What is obtain nutrients in interphase?
Vital cellular materials must be present before the division
What is respiration in interphase?
ATP production is needed to drive the division process
How is DNA usually packed within the nucleus?
Loosely as unravelled chromatin
What is DNA accessible to as chromatin?
To transcriptional machinery
What does the fact that DNA is accessible to transcriptional machinery mean?
Genetic information can be translated
When and where is DNA organised as chromatin?
In all non-dividing cells and throughout interphase
How is DNA packaged prior to division?
Into a tightly wound and condensed chromosome
How is DNA packaged into a chromosome?
Supercoiling
As a chromosome, what is DNA inaccessible to?
Transcriptional machinery
As chromosome, what is DNA able to do easily?
Be easily segregated
When is DNA organised as chromosomes?
During mitosis
When is chromosome visible?
During mitosis
What is a chromosome?
A condensed form of DNA
Why will the chromosome initially contain two identical DNA strands?
As DNA is replicated during S phase of interphase
What are genetically identical DNA strands called?
Sister chromatids
What holds sister chromatids together?
The centromere
What happens when chromatids separate during mitosis?
They become independent chromosomes each made of a single DNA strand
What are the four stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
Where is DNA contained in interphase?
In a clearly defined nucleus
What have been duplicated in interphase?
Centrosomes and other organelles have been duplicated
Why is the cell enlarged in interphase?
In preparation for division
What does DNA and chromosomes do in prophase?
DNA supercoils and chromosomes condense
What are the five structures to comment about in prophase?
DNA
Chromosomes
Centrosomes
Nuclear membrane
Nucleus
What do paired centrosomes do in prophase?
Move to opposite poles of the cell and form microtubule spindle fibres
What are chromosomes comprised of?
Genetically identical sister chromatids
What does the nuclear membrane do in prophase?
Breaks down
What does the nucleus do in prophase?
Dissolves
What do microtubule spindle fibres from the centrosomes do?
Connect to the centromere of each chromosome
What does microtubule depolymerisation cause?
Spindle fibres to shorten in length and contract
When does microtubule depolymerisation happen?
Metaphase
What happens in metaphase when the spindle fibres shorten and contract?
The chromosomes align in the centre of the cell
What three things do you need to comment on in metaphase?
Spindle fibres connecting
spindle fibres contracting
Chromosomes aligning
What continues in anaphase?
The contraction of spindle fibres
What does the continued contraction of spindle fibre in anaphase cause?
Genetically identical sister chromatids to separate
What happens once when the chromatids separate in anaphase?
They are considered their own individual chromosome
What do the genetically identical chromosomes do in anaphase?
Move to opposite poles of the cell
What three things do you need to comment on in anaphase?
Separation of chromatids
Individual chromosomes
Opposite poles of cell
In telophase, what happens when the two chromosomes arrive at the poles?
Spindle fibres dissolve
What do the chromosomes do in telophase?
Decondense
What does the nuclear membrane do in telophase?
Reform around each chromosome set
When does cytokinesis occur?
Concurrently with telophase
What does cytokinesis end up doing?
Splitting the cell into two
What four things do you need to comment on in telophase?
Spindle fibres dissolve
chromosome condenses
Cytokinesis splits cell
Nuclear membrane reforms
When is cytokinesis different?
In animal and plant cells
After anaphase, in animal cells, what forms a ring around the centre of the cell?
Microtubule filaments
What do the microfilaments constrict to form?
A cleavage furrow
How does a cleavage furrow deepen?
From the periphery to the centre
What happens when the cleavage furrow meets in the centre?
The cell becomes completely pinched off and two cells are formed
Why is the cell separation described as centripetal?
Because it occurs from the outside to the centre
In anaphase in plant cells, what forms in a row at the centre of the cell?
Carbohydrate-rich vesicles
In plant cells what do the vesicles do?
Fuse together
In plant cells, what begins to form within the middle of the cell?
An early cell plate
What does the cell plate do in plant cells?
Extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
Why is plant cell separation described as centrifugal?
As the separation begins in the centre and move separately
What is the mitotic index?
A measure of the proportion of dividing cells
When may the mitotic index be elevated?
During processes that promote division like normal growth or cellular repair
What is mitotic an important prognostic for predicting>
The response of cancer cells to chemotherapy
When identifying mitotic cells, what will cells undergoing mitosis lack?
Clearly defined nucleus
When identifying mitotic cells, what do cells undergoing mitosis possess?
Visibly condensed chromosomes
When identifying mitotic cells, what will prophase look like?
Chromosomes condensed by still confined to a nuclear region
When identifying mitotic cells, what will metaphase look like?
Chromosomes aligned along the equator of the cell
When identifying mitotic cells, what will anaphase look like?
Two distinct clusters of chromosomes at poles of the cell
When identifying mitotic cells, what will telophase look like?
Two nuclear regions present within a single cell
What is the mitotic index the ratio between?
The number of cells in mitosis and the total number of cells
How can the mitotic index be determines?
Analysing micrographs and counting the relative number of mitotic cells versus non dividing cells
What are cyclins?
A family of regulatory proteins that control the progression of the cell cycle
What do cyclins activate?
Cyclin dependent kinases (CDKs)
What do CDKs control?
Cell cycle processes through phosphorylation
What happens when a cyclin and CDK form a complex?
The complex will bind to a target protein and modify it via phosphorylation
What will the phosphorylated target protein trigger?
Some specific event within the cell cycle
What happens after the target protein induced event has occured?
The cyclin is degraded and the CDK is rendered inactive again
Why do cyclin concentrations need to be tightly regulated?
To ensure the cell cycle progresses in a proper sequence
What do different cyclins specifically bind to and activate?
Different classes of cyclin dependent kinases
When will cyclin levels peak?
When their target protein is required for function
Describe cyclin levels when their target protein is not required?
It will remain low
What are tumours?
Abnormal cell growths resulting from uncontrolled cell division
Where can tumours occur?
In any tissue or organ
What are diseases caused by the growth of tumours collectively known as?
Cancers
What is a mutagen?
An agent that changes the genetic material of an organism
Where will a mutagen act?
On the DNA or on the replicative machinery
What are the three ways mutagens may be in origin?
Physical
Chemical
Biological
What are three examples of physical mutagens?
Sources of radiation
Ultraviolet light
Radioactive decay
What are chemical mutagens?
DNA interacting substances including reactive oxygen species and metals
What are biological mutagens?
Viruses, certain bacteria and mobile genetic elements
What are mutagens that lead to the formation of cancer further classified as?
Carcinogens
What is an oncogene?
A gene that has the potential to cause cancer
What are two basic classes of genes which cause mutations which cause cancers?
Proto-oncogenes and tumour suppressor genes
What do proto-oncogenes do?
Code for proteins that stimulate the cell cycle and promote cell growth and proliferation
What do tumour suppressor genes do?
Code for proteins that repress cell cycle progression and promote apoptosis
What happens when a proto-oncogene is mutated or subjected to increased expression?
It becomes a cancer causing oncogene
How are tumour suppressor sometimes referred to as?
Anti-oncogenes
What is it when cancer is benign?
When tumour cells remain in their original location
What is it when a cancer is malignant?
It spreads and invade neighbouring tissue
What is metastisis?
The spread of cancer from one location to another, forming a secondary tumour
What are secondary tumours made up of?
The same type of cell as the primary tumour
What is there a strong link between smoking and?
The incidence of cancers
What does cigarette smoke contain?
Over 4,000 chemical compounds
How many chemical compounds are known to be carcinogenic?
60
What is there a strong positive correlation between the frequency of smoking and?
The development of cancer
What cancers are attributed to tobacco use?
Lung
Mouth
Stomach
Liver
Pancreas
Bowel
