Cell division and stem cells Flashcards
what happens in interphase? (not names of the phases in it)
- cell spends most of its time here
- cell is not dividing
- DNA replication
- protein synthesis
- chloroplasts grow and divide
G1 - interphase
1st growth phase
- proteins making up organelles are synthesised
- cell increases in size
S phase - interphase
synthesis - DNA replicated
G2 - interphase
2nd growth phase
- cell increases in size
- energy stores increase
- DNA checked for errors
mitotic phase of cell cycle
- mitosis - nucleus divides
- cytokinesis - cytoplasm divides and 2 cells produced
what is G0?
- stage where cell moves out of cell cycle
- permanent or temporary
reasons for g0
- differentiation - cell becomes specialised to carry out a particular function - unable to divide
- DNA has become damaged - enters permanent cell arrest - most cells do this as they can only divide a set no. of times
G1 checkpoint
- after mitosis, at end of G1 phase before S
- checks for cell size, DNA damage, growth factors, nutrients
- if it passes checks, it is triggered for DNA replication
G2 checkpoint
- end of G2 phase before mitosis
- checks for DNA damage and replication, cell size
- checks if DNA replicated without error
- if it passes checks it moves into mitosis
spindle assembly checkpoint/ metaphase checkpoint
- during mitosis when all chromosomes should be attached to spindles
- checks all chromosomes attached to spindles and aligned
- mitosis won’t happen if checkpoint not passed
mitosis definition
- process of nuclear division before a cell physically divides in 2
- DNA is copied into each of 2 daughter cells
why is mitosis needed?
- growth
- repair
- asexual reproduction
prophase - mitosis
- chromatin fibres coil up and condense to form visible chromosomes
- centriole divides and moves to opposite poles
- nucleolus disappears
- nuclear envelope disintegrates
- spindle fibres attach to centromeres and begin moving chromosomes to centre
metaphase- mitosis
- each centriole is at a pole
- centrioles produce spindle fibres
- spindle fibres attach to centromere of chromosomes
- chromosomes pulled to equator
anaphase- mitosis
- spindle fibres contract
- centromere divides and chromatids pulled to opposite poles of cell by centromere
- each half recieves 1 chromatid from each chromosome
telophase- mitosis
- chromatids (now called chromosomes) reach poles of spindle and begin to uncoil and become less distinct
- nucleolus reformed
- nuclear envelope starts to reform at each pole
cytokinesis in animal cells
- the cell divides by starting with constriction from edges of cell - a cleavage furrow forms
- cell-surface membrane pulled inwards by cytoskeleton to fuse around the middle
cytokinesis in plant cells
- vesicles from golgi apparatus assemble along equator and fuse with each other and the cell membrane
- cell is divided in 2
- cell wall is laid down
how many chromosomes does a human body cell contain
46 chromosomes
23 pairs of homologous chromosomes
are gametes haploid or diploid?
haploid - one copy of each chromosome
homologous chromosome
- 2 chromosomes with different alleles for the same gene in the same location on the chromosome
- 1 from each parent
how is a zygote formed?
2 haploid cells fuse
prophase I meiosis
- chromosomes condense
- nuclear envelope disintegrates
- spindle fibres begin to form
- homologous chromosomes pair up forming bivalents
- crossing over occurs - chromatids entangle
crossing over
- during prophase I of meiosis
- chromatids exchange alleles so they have new combinations of alleles
metaphase I meiosis
- spindle fibres attach to centromere
- homologous chromosomes line up on equator
- independent assortment - maternal and paternal chromosomes randomly put on either side of equator - results in genetic variation
anaphase I meiosis
- homologous chromosomes pulled by spindle fibres to poles - not pulled apart
- causes variation
telophase I meiosis
- nuclear envelopes reform
- chromosomes uncoil
- cells undergo cytokinesis
- cells now haploid
prophase II meiosis
beginning of second division
- chromosomes recondense
- nuclear envelope breaks down again
- spindle fibres reform
metaphase II meiosis
- chromosomes lined on equator by spindle fibres
- independent assortment again
- more genetic variation
ananphase II meisosis
- chromatids split apart by sindle fibres
- chromatids move to poles of cells
telophase II meiosis
- chromatids uncoil
- nuclear envelopes reform
- cytokinesis
- 4 haploid daughter cells
tissues definition and examples
collection of differentiated similar cells with specialist function
- animal tissues - nervous, epithelial, muscle, connective
- plant tissues - epidermis, vascular
organ definition and examples
collection of tissues adapted to carry out particular function eg. heart, lungs, leaf
organ system
multicellular organisms have interconnected organ systems
- each system has a number of organs to carry out functions
eg. digestive system, cardiovascular
specialised cell
differentiated cells that carry out a particular function
stem cells
- undifferentiated cells originated from mitosis or meiosis
- not adapted to particular function
- unspecialised and have ability to differentiate and become any cell type
totipotent
- stem cells that can differentiate into any type of cell
- eventually produce whole organism
- eg. fertilised egg
pluripotent
- form all tissue types but not whole organisms
- present in early embryos
- origin of all different tissue types
multipotent
- can only form a range of cells within certain tissue type
- eg. haematopetic stem cells in bone marrow - form types of blood cell
how have stem cells in bone marrow adapted to erythrocytes function?
- only few organelles - more room for haemoglobin
- life span of 120 days - replaced constantly - stemm cell colonies in bone marrow produce 3 billion erythrocytes per kg of body mass per day
how have stem cells in bone marrow adapted to neutrophils function?
- live for about 6 hours - colonies of stem cells in bone marrow produce 1.6 billion per kg per hour
embryonic stem cells
- present at early stages of embyonic development - totipotent - after 7 days a blastocyst (mass of cells) forms and they are pluripotent until birth
adult stem cells
- bone marrow - multipotent
- umbilical cord of newborn babies
sources of plant stem cells
(pluripotent)
- meristems - found wherever growth is occurring eg. tip of roots and shoots
- between phloem and xylem - vascular cambium (can only differentiate into cells present in xylem and phloem)
uses of stem cells
- heart disease - muscle tissue damaged as result of heart attack
- type 1 diabetes - insulin producing cells destroyed by body
- Parkinson’s - shaking and rigidity caused by death of dopamine-producing cells in brain
