Cell division and diversity

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Khads <3

Cards (93)

What are body cells called?
Somatic - diploid
What are homologous chromosomes?
+ somatic cells have inherited one chromosome from each parent - makes them diploid
+ match chromosomes in length, centromere position and type of genes found at each locus/ position
What are karyographs?
+ make chromosomes visible and give them contrast by staining them - reveals banding patterns
+ pair chromosomes according to size and banding pattern, arranged and photographed as karyograph
+ Each chromosome pair is numbered
+ Humans have 22 pairs of autosomes and 1 sex chromosomes
+ cells replicated at different rates
+ some cells NEVER replicate e.g. nerve cells
What are the reasons for G0 (cell arrest)?
+ Differentiation - once a cell has become specialised for a particular function it is no longer able to divide
+ DNA damage - DNA no longer viable. can no longer divide and the cell enters permanent cell arrest (G0) and the majority of cells only divide a limited no. times and become senescent
+ Aging - as you age, the number of cells in the G0 phase increases. Growing number of senescent cells linked with age-related diseases
How do lymphocytes go into G0?
+ can be stimulated back into cell cycle from G0
+ in immune response + begin dividing again (memory lymphocytes)
What is semi-conservative DNA replication?
+ new double strand consists of one strand from original molecules
+ other strand newly synthesised
+ possible due to completely base pairing
How can the change in the quantity of DNA during the cell cycle be shown?
+ on a graph which shows the change in the amount of DNA
+ starts at G1 where the x-axis = time and the y-axis = DNA amount
How does the quantity of DNA in the cell change during mitosis?
+ S- phase has cell DNA replication so DNA amount increases
+ mitosis occurs after DNA replication so already has maximum amount of DNA
+ during cytokinesis the cytoplasm halves and two new daughter cells are formed and each has the original DNA
How does DNA condense and uncondense during the cell cycle?
+ G1/G0: DNA uncondenses/ unwound into chromatin and not visible.
+ S: uncondensed DNA is semi-conservatively replicated
+ G2 phase: DNA uncondenses and error checked
+ M phase DNA condenses into visible chromosomes which are split into chromatids during mitosis and DNA unwinds
What are cyclins?
+ cell cycle regulator proetins
+ four basic types: G1 cyclins, G1/S cyclins, S cyclins and M cyclins
+ signalling molecules involved in cell communication
+ expressed at specific stages in cell cycle (genes switched on for protein synthesis)
+ broken down by other enzymes when not needed to progress onto next phase of cell cycle
What is CDK?
+ enzymes cyclin-dependent kinases are inactive until the correct cylcin binds to it
+ makes it a functional enzyme and allows it to modify the target proteins
+ activated by binding to cyclin and this causes the enzymes/ proteins to by phophorylated
What are benign tumours?
+ growths of abnormal cells that are contained in one area
+ usually within a membrane and does not invade other cells
+ can be operated on and removed e.g. verucas
What are malignant tumours?
+ tumour cells invade neighbouring tissues and spread to different parts of the body in the blood to form secondary tumours
+ tumour breaks out of its original tissue and develops its own system of blood vessels
+ travel through the blood stream to other parts of the body
How can CDK by used to treat cancer?
+ if overexpression of cyclin gene results from mutation, excessive amounts of cyclin disrupts the regulation of the cell cycle
+ this can lead to uncontrolled cell division, tumour formation and cancer
What can chemotherapy do to CDK activity?
+ can use chemicals that target and inhibit CDK activity
+ reduce or stop cell division and hence cancer formation, especially at G1 checkpoint
What happens during prophase?
+ condense into chromosomes and become visible by supercoiling (shorten and thicken)
+ nuclear envelope disintegrates
+ centrioles go to opposite poles of the cell
+ spindle fibres start to form
What happens during metaphase?
+ chromosomes line up in metaphase plate equator
+ chromosomes lined up by spindle fibres
+ longer phase and lasts around 20 minutes
+ spindle fibres attach to centromeres
+ checkpoint: spindle fibre attachment to centromere double-checked
What happens during anaphase?
+ chromosomes pulled apart by spindle fibres to form separate chromosomes at poles of cells
+ shorten and pull a set of chromosomes/ one sister chromatid apart to opposite poles of the cell
What happens during telophase?
+ chromatids reach opposite pole and are now called chromosomes
+ nuclear envelope forms around each of the two new groups of chromosomes and spindle fibres are broken down by enzymes
+ chromosomes start to uncoil
What are the phases of budding?
+ growth of bud, bud emergence, DNA replication, nuclear migration, chromosomes segregation and nuclear division, cytokinesis
A) scar
B) buds
What happens during growth and bud emergence? 
+ cell grows and commits to division under the correct conditions
+ spindle pole body duplication
+ spindles push towards point in parent cell to make a bud emerge
+ bud forms on outer surface of parent cell
+ swelling produces a daughter cell and DNA replicates
What is nuclear migration?
+ DNA migrates towards bud, spanning both cells
+ replicated nucleus migrates into the bud and divides
What happens during spindle formation/ mitosis in yeast cells?
+ set of chromosomes are pulled to bud
+ parent cell and nucleus divides
+ cell wall is formed between the parent and the bud
What happens during chromosome segregation in yeast cells?
+ nuclear division
+ bud breaks away to become a new daughter cell, leaving behind a scar
What is the difference between pluripotent and totipotent stem cells?
+ pluripotent can give rise to various types of cells
+ totipotent stem cells are capable of giving rise to any cell type or a complete embryo
What is cytokinesis?
+ Begins during telophase
+ The cytoplasm divides (cytokinesis) and now there are two daughter cells that are genetically identical to the original cell each other.
What is parthenogenesis?
+ observed in reptiles and birds
+ Before eggs form, the female cells gain twice the usual number
of chromosomes during meiosis
+ This results in a standard pair of chromosomes derived from two sets of pairs
+ So the eggs get a full chromosome count and genetic variety and breadth (known as heterozygosity) rivalling that of a sexually reproducing lizard
How does cytokinesis occur in animal cells?
A cleavage furrow forms as cytoskeleton pulls the membrane inwards, until it fuses around the middle, forming two cells
How does cytokinesis occur in plant cells?
+ vesicles from the Golgi (carrying cell wall building materials)
+ line up in the middle, fusing first with each other to form the cell plate and then to the cell membrane, dividing the cell in two
+ cell wall then develops along the membrane
What are totipotent stem cells?
+ most potent stem cell
+ can divide and produce any type of body cell
+ translates only part of DNA during development to result in cell specialisation
+ occurs only for a limited time in early mammalian embryos - up to 16 days after fertilisation
What are pluripotent stem cells?
+ found in embryos and can differentiate into any cell but the placenta cell
+ become almost any type of cell
+ used in research to treat human disorders
+ cannot specialise to form a placenta
What are the issues and potential applications of using stem cells?
+ could be used to regrow damaged human cells
+ sometimes does not work
+ stem cells may divide to form tumours
What are multipotent stem cells?
+ divide to form a limited number of different cell types
+ found in mature mammals
What is meiosis 1?
+ first divison which is a reduction division
+ pairs of homologous chromosomes are separated into two haploid cells
+ each intermediate cell only contains one full set of genes (haploid)
What is meiosis II?
+ second division similar to mitosis
+ pairs of chromatids present in each daughter cell is separated
+ form two more cells
+ four haploid daughter cells produced in total
What occurs during meiosis prophase 1?
+ chromosomes condense
+ homologous chromosomes pair up to form bivalents and there is a crossing over of genetic material
+ nuclear envelope disintegrates
+ nucleolus disappears and spindle formation begins
Why does crossing over occur?
chromosomes are large DNA molecules so become entangled when moved through the cytoplasm
What occurs during metaphase 1 in meiosis?
+ homologous pairs of chromosomes line up along the equator in bivalents
+ arrangements/ orientation of bivalents on the equator is random (independent assortment)
+ maternal or paternal chromosomes can end up facing either pole
+ can result in many different combinations of alleles facing poles
+ results in genetic variation
What occurs during anaphase 1?
+ bivalent chromosomes separated so chiasmata broken apart (form chromosomes)
+ completed reductive division of meiosis splitting the homologous pair
+ recombinant sister chromatids (chromosomes) at each pole not genetically identical
+ independent segregation
What happens during telophase 1 in meiosis?
+ chromosomes assemble at each pole and nuclear membrane reforms
+ chromosomes uncoil and cell undergoes cytokinesis