Topic 1.6: Cell Division Flashcards
Cell Cycle
The cell cycle is an ordered set of events that culminates in cell division
Main Phases of the Cell Cycle
a) Interphase
b) M phase
Interphase
An active phase of the cell cycle where many metabolic reactions occur
a) G1
b) S
c) G2
G1
Cell grows and prepares for DNA replication
S
Synthesis stage in which DNA is replicated
G2
Cell finishes growing and prepares for cell division
M Phase
The period of a cell cycle in which the cell and contents divide
a) Mitosis
b) Cytokinesis
Mitosis
Nuclear division, whereby DNA is separated into two identical nuclei
Cytokinesis
Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two
Key events in Interphase for division (Doctor)
a) DNA replication (S)
b) Organelle duplication (G2)
c) Cell growth
d) Transcription / Translation
e) Obtain nutrients
f) Respiration
How and when do chromosomes condense?
By supercoiling during mitosis
Chromatin
a) DNA loosely packed
b) Accessible to transcription and translation
Chromosome
a) DNA tightly packed
b) Inaccessible to transcription
c) Organized into chromosomes
Sister chromatids
Genetically identical strands of DNA joined at a centromere
Phases of Mitosis
a) Prophase
b) Metaphase
c) Anaphase
d) Telophase
Prophase
a) DNA supercoils and condenses (forms visible chromosomes)
b) Nuclear membrane dissolves
c) Centrosomes move to poles and begin to produce spindle fibres
Metaphase
a) Centrosome spindle fibres attach to the centromere of each chromosome
b) Spindle fibres contract and move the chromosomes towards the cell centre
c) Chromosomes form a line along the equator of the cell
Anaphase
a) Spindle fibres continue to contract
b) Sister chromatids separate and move to opposite sides of the cell
c) Sister chromatids are now regarded as two separate chromosomes
Telophase
a) Chromosomes decondense (DNA forms chromatin)
b) Nuclear membranes form around the two identical chromosome sets
c) Cytokinesis occurs concurrently
Cytokinesis
a) Cytoplasmic division occurs to divide the cell into two daughter cells
b) Each daughter cell contains one copy of each identical sister chromatid
c) Daughter cells are genetically identical
Interphase
a) DNA is uncondensed (chromatin)
b) DNA is replicated (S phase) to form genetically identical sister chromatids
c) Cell grows in size and organelles are duplicated (G1 and G2)
Cytokinesis in Animals
Microtubules form a concentric ring and contract towards the centre (centripetal)
Cytokinesis in Plants
Vesicles form at the cell centre and fuse outwards to form a cell plate (centrifugal)
Mitotic index
Measure of the proliferation status of a cell population (i.e. number of dividing cells)
Function of the Mitotic Index
a) The mitotic index will be elevated during growth and repair processes
b) Acts as a prognostic tool for cancer
Cyclins
Proteins that control the progression of the cell cycle
Cyclins process
a) Cyclins bind to cyclin dependent kinases (CDKs)
b) The activated complex phosphorylates proteins involved in specific cell cycle events (e.g. centrosome duplication)
b) After the event has occurred, the cyclin is degraded and the cyclin dependent kinase is rendered inactive
Cyclin Expression Patterns
a) Cyclin concentrations need to be tightly regulated to ensure the cell cycle progresses in a proper sequence
b) Cyclin levels will peak when their target protein is required for function and remain at lower levels after
Tumours
Abnormal cell growths resulting
Cancer
Diseases caused by uncontrolled cell division
Types of tumour cells
a) Benign (Remain in their original location)
b) Malignant (Invade neighbouring tissue)
Metastasis
Spread of cancer from an original site to a new body location (forming a secondary tumor)
Mutagen
Agent that changes the genetic material of cells
Examples of mutagens
a) Radiation (X-rays / UV)
b) Reactive oxygen species and metals
c) Viruses / Bacteria
Carcinogens
Mutagens that lead to the formation of cancer
Oncogene
Gene that has the potential to cause cancer
Proto-oncogenes (Gas)
Stimulate cell growth and proliferation
Tumour suppressor (Brakes)
Repress cell cycle progression
Correlation between smoking and incidence of cancers
a) There is a strong positive correlation between the frequency of smoking and the incidence of cancer
b) Cigarette smoke contains >60 known carcinogens
Mechanisms of Cell Death
a) Necrosis (uncontrolled ‘cell homicide’)
b) Apoptosis (programmed ‘cell suicide’)
Necrosis (uncontrolled ‘cell homicide’)
a) The cell loses functional control due to injury, toxins, etc.
b) There is a destabilization of the membranes, leading to swelling
c) The cell bursts and releases its contents (causing inflammation)
Apoptosis (programmed ‘cell suicide’)
a) It is a controlled event triggered by mitochondrial proteins
b) Cell contents are packaged in membranous protrusions
c) The cell fragments into apoptotic bodies which are recycled
Cell Cycle Checkpoints
a) G1 checkpoint
b) G2 checkpoint
c) Metaphase checkpoint
G1 checkpoint
a) Monitors potential growth conditions (nutrients, etc.)
b) Assesses level of DNA damage (from UV, etc.)
G2 checkpoint
a) Monitors state of pre-mitotic cell (suitable size, etc.)
b) Identifies and repairs any DNA replication errors
Metaphase checkpoint
Ensures proper alignment (prevents aneuploidy)
