what is the difference between mitosis and meiosis? when will each occur?
TRANSCRIPT
What is the difference between mitosis and meiosis?
When will each occur?
The cell cycleObjectives Outcomes
3: Identify stages of the cell cycle.
5: Describe the stages of the cell cycle.
7: Explain the consequences of the cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The Cell Cycle, Mitosis, and Meiosis
New cells can only be made when existing cells divide. All cells have the ability to divide – but some cells lose this ability.
Intestinal epithelial lining - replaced every five days by cell divisionLiver cells - divide only to repair damage, and then stop dividingBone marrow cells - divide repeatedly to produce red and white blood cellsMeristem cells (tips of roots and shoots) – divide to produce new growthCambium cells (plants) – divide to form vascular tissue (xylem and phloem)
These are relatively unspecialised cells. Specialised cells often go through the cell cycle only once - the nerve cells, once formed cannot divide again.
In eukaryotic cells, there are two types of cell division – mitosis and meiosis. Mitosis is used to produce new cells for growth and repair. Meiosis is used in the formation of gametes only.
In prokaryotes (bacteria), cell division does not involve mitosis or meiosis – bacteria reproduce asexually, by a type of cell division termed by binary fission. Yeasts reproduce asexually by budding.
The cell cycle is the process that all body cells from multicellular organisms use to grow and divide. The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells.
The cell cycleThe cell cycle describes the sequence of cell growth and cell division.
It includes:Interphase
cell growth synthesis of organelles DNA copying and checking of genetic information
Mitosischromosomes divide
Cytokinesiscytoplasm divided between the daughter cells
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The cell cycleThe cell cycle describes the events during one complete cycle of division, they are represented in the chart:
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The cell cycle
Key terms: cell cycle, interphase, mitosis, cytokinesis.
MITOSIS (M)
Process by which a nucleus divides into two – each with an identical set of chromosomes – the nuclei are genetically identical
Four phases – prophase, metaphase, anaphase, and telophase
Followed by cytokinesis – division of the cell into two genetically identical daughter cells
INTERPHASE
Period of cell growth; cell prepares cell for cell division (mitosis); genetic material (DNA) is copied and checked for errors – prevents mutations being passed on
No apparent activity
New organelles and proteins are made
Divided into three phases (G1, S, and G2 phase)CELL
CYCLE
G1
S phase
G2
Mitosis (M)
Two daughter cells – genetically identical
The cell cycle can be divided into stages:
G1 (“growth phase” 1) - Cells prepare for DNA replicationS (“synthesis”) - DNA replication occursG2 (“growth phase” 2)- Short gap before mitosisM Mitosis (relatively short)
Affected by availability of nutrients
Between each stage the cell “checks” to see if it is OK to proceed to the next stage.
“Proof-reading” enzymes check the copied chromosomes for mistakes (mutations) – the cell may kill itself (undergo “suicide”) if harmful mutations are – a process known as apoptosis.
Bacterial cells complete the cycle every 20 minutes. Muscle cells never complete the cycle – “terminal differentiation”
Uncontrolled and repeated cell division by mitosis results in cancer (tumours)
Eukaryotic cells have a well- defined cell cycle of growth and division (mitosis). The length of the cycle varies (from minutes to hours, or , longer) ending with mitosis.
Each phase of the cycle involves specific activities, and varies in length from one organism to another.
The Cell Cycle
G1 + S + G2 = INTERPHASE No apparent observable activity
Cytokinesis – cell divides into twoDNA content = normal
G1 - First growth phase – longest phaseProtein synthesis – cell “grows”Most organelles producedVolume of cytoplasm increasesCell differentiation (switching on or off of genes)Length depends on internal and external factorsIf cell is not going to divide again it remains in this phaseDNA content = 20 (arbitary)
S - Replication phase DNA replication – this must occur if mitosis is to take placeThe cell enters this phase only if cell division is to followDNA content = double
G2 - Second growth phase - shortShort gap before mitosis (cell division)Cytoskeleton of cell breaks down and the protein microtubule components begin to reassemble into spindle fibres – required for cell divisionDNA content = 40
The Cell Cycle
The cell cycleTask
Create a poster outlining the cell cycle. Leave some space
for when we fully look at mitosis in the next lesson.
Outcomes
3: Identify stages of the cell cycle.
5: Describe the stages of the cell cycle.
7: Explain the consequences of the cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The cell cycleWhat happens when the cell
cycle is not controlled:
Cancer
Outcomes
3: Identify stages of the cell cycle.
5: Describe the stages of the cell cycle.
7: Explain the consequences of the cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The cell cycle
Key terms: cell cycle, interphase, mitosis, cytokinesis.