Cell Division Flashcards
what is the cell cycle
- highly ordered sequence of events that take place in a cell
- formation of 2 genetically identical daughter cells
what is interphase
- DNA is replicated
- protein synthesis
- mitochondria and chloroplast grow and divide
- not a resting phase
what are the stages of interphase
G1- first growth phase
- proteins are synthesised - RNA, enzymes
S- Synthesis phase
- DNA is replicated in the nucleus
G2 - second growth phase
- cell continues to increase in size
- duplicated DNA is checked for errors
what is the G0 phase
- resting phase
- cell leaves the cycle temporarily or permanently
- for differentiation - can no longer divide
- error or damage in DNA
what are checkpoints
- control mechanisms of the cell cycle
- monitor and verify whether the processes at each phase of the cell cycle are correct before progessing
what is the G1 checkpoint
- end of G1 phase and before S phase
- if correct it triggers DNA replication or incorrect enters resting phase
Checks for
- cell size, nutrients, growth factors, DNA damage
what is the G2 checkpoint
- end of G2 phase and before mitotic phase
- if correct it can begin mitosis if not it enters the resting phase
Checks for
- cell size, DNA replication, DNA damage
what is the spindle assembly checkpoint
- metaphase checkpoint
- mitosis cannot proceed until the checkpoint has been passed
checks for
- chromosomes attached to spindle
what is mitosis
- ensures that daughter cells produced are identical
- growth, repair, replacement of tissues
- asexual reproduction
- prophase, metaphase, anaphase , telophase
what are chromosomes
- each DNA molecule (chromosomes) is converted into two identical DNA molecules (chromatids)
- two chromatids are joined at the centromere
what happens in prophase
- chromosomes condense and are visible when stained
- chromosomes consist of two sister chromatids identical joined at the centromere
- protein microtubules form spindle fibres
- centrosomes move towards opposite poles and spindle fibres attach
- nuclear envelope is broken down
what happens in metaphase
- spindle fibres continue to extend
- chromosomes line up at the metaphase plate of the spindle
- spindle fibres reach the chromosomes and attach to the centromeres
- each sister chromatid is attached to a spindle fibre originating from opposite poles
what happens in anaphase
- centromere holding together the sister chromatids separate and divide into two
- spindle fibres shorten
- chromosomes are pulled to opposite poles by spindle fibres
what happens in telophase
- chromosomes arrive at apposite poles and condense
- nuclear membranes begins to reform around each set of chromosomes
- spindle fibres break down
- chromosomes uncoil and nucleolus is formed
what is cytokinesis
- division of the cell into separate cells
how does cytokinesis occur in animal cells
- cleavage furrow forms around the middle of the cell
- cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming two cells
how does cytokinesis occur in plant cells
- vesicles in Golgi apparatus assemble on the metaphase plate
- vesicles fuse with each other and the membrane divides into two
- new sections of cell wall form along new sections of membrane
what is meiosis
- production of haploid cells
- sexual reproduction
- two divisions
what happens in meiosis 1
- pair of homologous chromosomes are separated into two cells
- haploid cells
what happens in meiosis 2
- pairs of chromatids in each daughter cell are separated forming 2 or more cells
- produces 4 haploid daughter cells
what happens in prophase 1
- chromosomes condense, nuclear envelope breaks, spindle fibre formation
- homologous chromosomes pair and form bivalents
- crossing over
what happens in metaphase 1
- homologous pairs line up along the metaphase plate
- independent assortment
what happens in anaphase 1
- homologous chromosomes pulled to opposite poles and the centromere doesn’t divide
- chromatids break and re join
what happens in telophase 1
- chromosomes condense, spindle fibres break down, chromosomes uncoil
- undergoes cytokinesis
what happens in prophase 2
- chromosomes condense and become visible, nuclear envelope breaks down, spindle fibre formation
what happens in metaphase 2
- individual chromosomes assemble along the metaphase plate
- independent assortment
what happens in anaphase 2
- chromatids of individual chromosomes are pulled to opposite poles after division of the centromere
what happens in telophase 2
- chromatids assemble at the poles
what happens in cytokinesis in meiosis
- 4 genetically different haploid daughter cells
what is crossing over
- non sister chromatids exchange alleles
- meiosis 1 homologous chromosomes pair up and are close in proximity
- non-sister chromatids cross and entangle
- crossing points called chiasmata
- entanglement places stress on DNA molecules
- section of chromatid from one chromosome may break and re join with another
what is independent assortment
- production of different combinations of alleles in daughter cells increasing genetic variation
what are specialised cells
- cells in multicellular organisms that are differentiated to carry out specific functions
what is the structure of erythrocytes
- flattened biconcave shape to increase surface area to volume ratio
- no nuclei to maximise space for haemoglobin
- flexible and can squeeze through narrow capillaries
what is the structure of palisade cells
- chloroplasts for photosynthesis
- closely packed together to form a layer
- thin walls to increase carbon dioxide diffusion rate
- large vacuole to maintain pressure
what are tissues and the types
- collection of differentiated cells that have a specialised function
- nervous tissue - adapted to support transmission of electrical impulses
- epithelial tissue - cover internal and external body surfaces
- muscle tissue - contract
- connective tissue - holds tissues togetherorg
what are organs and organ systems
- collection of tissues adapted to form a particular function
- digestive system
- cardiovascular systemw
what are stem cells
- undifferentiated cells that undergo several cell divisions
- found in the bone marrow
what is potency and the types
- cell’s ability to differentiate into different cell types
totipotent - differentiate into any cell type
pluripotent - form all tissue types but not all organisms
multipotent - only form a range of cells within certain types of tissue
how are erythrocytes replaced
- multipotent cell divides to form proerythrocytes
- cell undergoes changed and can form an erythrocyte
- haemoglobin builds up in the cytoplasm
- nucleus is ejected
- cell forms a mature erythrocyte
what are the sources of animal stem cells
embryonic and adult
what are the sources of plant stem cells
meristems
how are stem cells used in medicine
heart disease - muscle tissue is damaged
Alzheimer’s - brain cells are destroyed
burns - stem cells grown on biodegradable meshes to produce new skin
what are the ethical obligations in stem cells
- religious and moral objections - life begins at contraception = murder
- lack of consensus as to when the embryo has rights
