Cell division, cell diversity & cell differentiation 2.6 Flashcards
What are the phases of the cell cycle?
- interphase
- mitosis
- cytokinesis
What is mitosis?
Type of nuclear division that maintains the chromosome number
What is the importance of mitosis?
- asexual reproduction
- growth
- tissue repair
What are the stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
What happens during prophase in mitosis?
- DNA supercoils and condenses becoming visible
- nuclear envelope breaks down
- spindle fibres form
What happens during metaphase in mitosis?
- Chromatids attach to the spindle fibres by their centromeres
- line up in the equator region
What happens during anaphase in mitosis?
- centromere of each pair of chromatids splits
- spindle fibres contract
- sister chromatids are pulled to opposite directions
What happens during telophase in mitosis?
- chromosomes reach the poles
- nuclear envelope forms
- chromosomes uncoil and decondense
What happens during cytokinesis in mitosis?
Plasma membrane folds inwards and rips the cytoplasm
What is cytokinesis?
Division of the cytoplasm of a cell following mitosis
What are the phases of interphase?
- G1
- S
- G2
What are the main checkpoints during the cell cycle?
- G1 checkpoint
- S checkpoint
- G2 checkpoint
- metaphase checkpoint
What happens at the G1 checkpoint?
- chromosomes checked for damage
- if damage is found the cell will not progress into S phase until damage is fixed
What happens at the S checkpoint?
- chromosomes checked to ensure they have been replicated correctly
- cell cycle stops if error found
What happens at the G2 checkpoint?
- additional check for DNA damage
- if damage found cycle is delayed until repairs are made
What happens at the M checkpoint?
Check to ensure spindle fibres are attached correctly to the chromosomes before anaphase
What are the purpose of the checkpoints?
- prevent uncontrolled division
- detect and repair damage to DNA
- ensure DNA is only duplicated once
What happens during the M phase of the cell cycle?
- cell stops growing
- cell undergoes nuclear division
What happens during the G0 phase of the cell cycle?
- It is a resting phase
- triggered in early G1 by checkpoint chemical
- cells may stay in this phase for a very long time (neurones)
- cells may undergo apoptosis, differentiation or senescence
What happens during the G1 phase of the cell cycle?
- cell growth & increases in size
- organelles duplicate
- trancription to create RNA
- protein synthesis
What happens during the S phase of the cell cycle?
- cell now has to commit to completing the cycle
- DNA replicates
- rapid due to DNA being exposed to random mutations
What happens during the G2 phase of the cell cycle?
- Cells grows
- proteins involved with mitosis are stimulated
- errors are detected and repaired
What is meiosis?
Type of nuclear division that results in the formation of cells containing half the number of chromosomes of the parent cell
How does meiosis produce genetic variation?
- crossover
- independent assortment of homologous pairs of chromosomes
- independent assortment of sister chromatids
What happens during prophase 1 in meiosis?
- DNA supercoils and becomes visible
- nuclear envelope breaks down
- spindle threads form
- homologous chromosomes join together to form a bivalent
- crossover occurs
What happens during metaphase 1 in meiosis?
- bivalents line up on the equator
- attached to spindles by the centromeres
- independent assortement of homologous chromosomes
- the way the chromosomes line up depends whcih pole they will be pulled to
What happens during anaphase 1 in meiosis?
- members of each pair of homologous chromosomes are pulled appart
- centromeres do not split
- spindle fibres contract
What happens during telophase 1 in meiosis?
- nuclear envelope forms around each set of chromosomes
- cell undergoes cytokinesis
What happens during prophase 2 in meiosis?
- nuclear envelope breaks down again
- chromosomes coil and condense
- spindle fibres form
What happens during metaphase 2 in meiosis?
- chromosomes line up at the equator
- spindle threads attached to the centromere
- independent assortment of sister chromatids
What happens during anaphase 2 in meiosis?
- centromeres divide
- chromatids of each chromosome are pulled appart to opposite poles
- chromatids are randomly segregated
What happens during telophase 2 in meiosis?
- Nuclear envelope forms around each of the 4 haploid cells
- cytokinesis
- chromatids uncoil and decondense
what is differentiation?
The process by which stem cells become specialised into different types of cells
What is a stem cell?
An unspecialised cell able to express all its genes and divide by mitosis
How are erythrocytes specialised?
- large SA:V
- flexible cytoskeleton so they can change shape
- contain no nucleus, mitochondria or ER
- biconcaved shape
How are neutrophils specialised?
- contain multilobed nucleus
- ingest pathogens by phagocytosis
- attracted to infection sites by chemotaxis
- contain lots of lysosomes
How are spermatozoa specialised?
- lots of mitochondria to provide ATP for undulipodium
- long and thin to move easily
- enzymes from the acrosome digest outer layer of the ovarum
How is squamous epithelial tissue specialised?
- squashed epithelial cells
- lign the alveoli
- thin
How is cilliated epithelial tissue specialised?
- contain no blood vessels
- short cell cycle
- protection, absorption, filtration and excretion
How is cartilage specialised?
- reduces friction and protective
- fibrous (vertabrae discs)
- elastic (outer ear)
- hyaline (trachea)
How is muscle tissue specialised?
- well vascularised
- elongated and contain myoligaments
- fibres
- skeletal, cardiac, smooth
How are palisade cells specialised?
- large vacuole - chloroplast are closer to the leaf surface
- many chloroplast
- little space between cells for air to circulate
How are root hair cells specialised?
- large SA
- carrier proteins in plasma membrane for active transport
- produces ATP for active transport
How are guard cells specialised?
- found in lower epidermis
- tips are more flexible
- rigid and thicker in the middle
How is epidermal tissue specialised?
- consists of flattened cells
- protective covering
- waxy surface
How is xylem specialised?
- dead hollow cells
- ligned with lignin so waterproof
- carry water up the plant
How is phloem specialised?
- consists of companion cells and sieve tubes
- companion cells retain orgnelles
- companion cells provide ATP for active transport
What does differentiation involve?
The expression of some genes and not others
What does totipotent mean?
- can turn into any cell including placenta
- 5 days after
What does pluripotent mean?
- can turn into any human specialised cell
- after 5 days
What does multipotent mean?
- already differentiated and can turn into groups of specialised cells
- after you have been born
What does potency mean?
The ability to differentiate
What are the uses of stem cells?
- bone marrow transplant
- testing for drug toxicity
- research parkinsons disease
