Module 2 Section 6: Cell Division and Cellular Organisation Flashcards
When does the cell cycle start and end
Starts when a cell has been produced by cells division
Ends with the cell dividing to produce two identical cells
What does the cell cycle consist of
Cell cycle consists of:
A period of cell growth and DNA replication - interphase
A period of cell division - M phase
M phase involves mitosis ( nuclear division ) and cytokinesis ( cytoplasmic division )
What is the interphase divided into
Interphase ( cell growth ) is subdivided into three separate growth stages
These are called G1, S and G2
How is the cell cycle regulated
Regulated by checkpoints
Checkpoints occur at key points during cycle to make sure its okay for the process to continue
What happens in G1 phase
Growth Phase 1:
Cell grows in size
Proteins synthesised
Organelles replicate ( mitochondria, ribosomes etc )
What happens in the S phase
Synthesis phase:
Replication of each chromosome in nucleus
Now called sister chromatids ( joined at centromere )
What happens in the G2 phase
Growth 2 phase:
Cell grows in size
Duplicated DNA checked for errors
Energy stores ( ATP ) are increased
What does the G1 checkpoint check for
Checks:
Cell is the correct size
Nutrients/ chemicals are present
Growth factors present
Any damage to DNA
Before entering S phase
What does G2 checkpoint check for
Checks:
Cell is correct size
DNA has been replicated without damage
If this is correct, cell can enter mitosis
What does the spindle assembly checkpoint ( metaphase checkpoint ) check for
Checks for:
Chromosome attachment to the spindle
Full stages of cell cycle
Gap phase 1
G1 checkpoint
Synthesis
Gap phase 2
G2 checkpoint
M phase
Spindle assembly checkpoint ( metaphase checkpoint )
What is the cell cycle needed for
Growth of tissue/ organism ( not of cells )
Replacement of worn out/ damaged cells
Repair of body tissues ( e.g. bone, muscle )
Asexual reproduction/ cloning
What are the stages that mitosis is separated into
Mitosis is one continuous process
Can be described as a series of division stages:
Prophase
Metaphase
Anaphase
Telophase
What happens during the interphase
Cell carries out normal functions
Prepares to divide
DNA unravelled and replicated, to double amount of chromosomes
Organelles replicated to make spares
ATP content is increased
What happens during prophase
Chromosomes condense, getting shorter and fatter
Centrioles move towards opposite ends of the cell
Form spindle fibres across cell
Nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What happens during the metaphase
Chromosomes ( as two sister chromatids ) line up along the middle of cell
Their centromere is attached to the spindle fibres
Metaphase checkpoint occurs here
What happens during the anaphase
Centromeres divide
This separates each pair of sister chromatids
Spindles contract, pulling chromatids to opposite ends of the cell, centromere first
What happens during the telophase
Chromatids reach opposite poles on spindle fibres
They uncoil and become long and thin
Called chromosomes again
A nuclear envelope forms around each group of chromosomes so there are two nuclei
What happens in cytokinesis
Cytoplasm divides
In animal cells, a cleavage furrow forms to divide the cell membrane
There are now two daughter cells that are genetically identical to original cell and to eachother
Cytokinesis usually begins in anaphase and ends in telophase
Separate process to mitosis
What are multicellular organisms made of
Made up of different cell types that are specialised for their functions
E.g. liver cells, muscle cells, white blood cells
Where do specialised cells come from
These all originated came from stem cells
What are stem cells
Stem cells are unspecialised cells
They can develop into different types of cell
All multicellular organisms have some form of stem cells
Where are stem cells found in humans
Stem cells usually found in early embryos and in a few places in adults
What can stem cells in early embryos do
They can develop into any type of human cell
They are pluripotent
What can adult stem cells do
Stem cells in adults can only develop into a limited range of cells
They can also divide to produce more undifferentiated stem cells, so they can renew themselves
They are multi potent
How do stem cells become specialised cells
Stem cells divide to become new cells, which then become specialised
This process where cells become specialised for their job is called differentiation
What are stem cells used for in animals
Used to replaced damaged cells
E.g. to make new skin or blood cells
What are stem cells used for in plants
Plants are always growing
So stem cells are needed to make new shoots and roots throughout their lives
Stem cells in plants differentiate into various plant tissues including xylem and phloem
How do cells in bone marrow differentiate into blood cells
Bone are living organs, containing nerves and blood vessels
The main bones of the body have marrow in the centres
Here, adult stem cells divide and differentiate to replace worn out blood cells
These can be erythrocytes (red blood cells) and neutrophils (white blood cells that help fight infection)
How do cells in the meristem differentiate into xylem and phloem
In plants, stem cells are found in the meristems (parts of the plant where growth can taken place)
In the root and stem, stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes
Meristems can be used for repair of damaged tissue
What can scientists use stem cells for
Stem cells can develop into different specialised cell types, so scientists think they can be used to replace tissues in a range of diseases e.g. Alzheimer’s and Parkinson’s
How cans stem cells be used to treat Alzheimer’s disease
With Alzheimer’s, nerve cells in the brain die in increasing numbers
This results in severe memory loss
Researchers hope stem cells can be used to regrow healthy nerve cells in people with Alzheimer’s
How can stem cells be used to treat Parkinson’s
Parkinson’s disease causes tremors that patients can’t control
The disease causes a loss of a particular type of nerve cell in the brain
These cells release dopamine which is used to control movement
Transplanted stem cells may help regenerate the dopamine-producing cells