The Mitotic cell cycle Flashcards
telomere
protective sequences of nucleotides found at ends of chromosomes, shortening every time a cell divides.
telomerase
enzyme allowing replenishment of telomeres
chromosome structure
double structure, made of two identical chromatids (each containing one dna molecule), centromere holds the two chromatids together, telomeres are at ends
chromatin
mixture of proteins and dna
histones
proteins which dna wraps around to prevent tangling
packaging proteins
why do histones react easily with dna?
they are basic and so react with acidic dna
nucleosome
a cylindrical shape made up of 8 histones with which dna wraps itself around (5/3 turns). dna inbetween is held in place by histone molecules. can be coiled and supercoiled.
2 forms of chromatin
euchromatin and heterochromatin
euchromatin
loosely coiled chromatin (seen between divisions)
heterochromatin
tightly coiled chromatin (seen at nuclear division)
mostly inactive genes.
stains more densely
when is chromatin most condensed
metaphase so is easier to separate into 2 new cells
mitosis
cell division producing 2 genetically identical daughter nuclei, each containing same number of chromosomes as parent
cell cycle stages
interphase
nuclear division
cell division
interphase
cell grows and performs normal function, synthesising proteins and other substances.
2 types of nuclear division
mitosis
meiosis
cell cycle
regular sequence of events that takes place between one cell division and the next
what happens in the s phase
(s=synthesis of dna)
dna replication, forming 2 sister chromatids joined by a centromere
what happens in the G1 phase
(interphase)
cellular contents, except chromosomes, duplicated
cell makes RNA, enzymes and other proteins needed for growth
what happens in the G2 phase
cell checks the duplicated chromosomes to make repair, continues with function and prepares for division
mitosis acronym
IPMAT
cytokinesis
when the cytoplasm is constricted between 2 nuclei
and in plant cell, cell wall is laid down equator
mitosis importance
allows for growth of multicellular organisms from unicellular zygotes
replacement and repair of damaged tissue
asexual reproduction
immune response (clonal proliferation of white blood cells)
how many daughter cells are produced in meiosis
haploid/diploid?
4
haploid
differences between meiosis and mitosis
meiosis has 4 haploid daughter and mitosis 2 diploid
meiosis has 2 divisions while mitosis has 1
mitosis genetically identical daughters while meiosis has genetically different daughter cells
how are genes on a chromosome structured
start sequence
exon (coding region)
intron (noncoding region)
stop sequence
exon
coding region of dna
intron
non-coding region of dna
reproduction via mitosis
simple eukaryotic organisms reproduce mitotically via budding in which daughter cell buds off of parent cell
method of reproduction for prokaryotes
binary fission
proportion of cell’s time in interphase
90%
stages of interphase
G1
S
G2
m phase
mitosis and cytokinesis
apoptosis
programmed cell destruction
repeated sequence of telomerase in humans
how many times is it repeated
TTAGGG
repeated 2500 times
interphase
replicates dna
centrosome, composed of 2 centrioles is also replicated
early prophase
nuclear membrane breaks down
dna condenses into chromosomes
centrioles move to opposite poles of cell
late proteins
chromosomes appear w centromeres
spindle fibres form (microtubules and proteins)
metaphase
spindle fibres attach to chromosomes or span the cell
chromosomes line up along equator of cell
anaphase
spindle fibres shorten, pulling to opposite poles of cell
late anaphase
other spindle fibres lengthen, causing cell to elongate
telophase
2 new nuclei form, cleavage forms between 2 new cells
origin of spindle fibres
centrosome
cytokinesis in plants
cell plate is formed via vesicles derived from the Golgi joining to form cell wall
cytokinesis in animals
ring of microtubules gather in center of cell and form a cleavage furrow which inverts to separate
Cells in meristem
Totipotnet and undifferentiated
Mitosis in plants
Occur in meristem
Divide, elongate and specialise
Root cap
Protects the growing tip of root behind, undergoing cell division to replace lost cells
mitotic index
ratio of cells in mitosis to the number of cells counted
Number of cells in mitosis/number of cells counted
stem cells
undifferentiated cells found in multicellular organisms characterised by properties of self-renewal and potency
how do stem cells specialise
develop from a multipotent cell which divides to produce a daughter stem cell and precursor cell (lymphoid/myeloid)
3 types of stem cell
totipotent
pluripotent
multipotent
totipotent stem cells
can differentiate into all cells in an organism
pluripotent
give rise to any cells of the body, except extra-embryonic cells
multipotent
adult stem cells giving rise to limited number of cell types, related to tissue of origin.
self-renewal
the ability to divide many times while maintaining unspecialised state
potency
the ability to differentiate into specialised cells
skin regions
epidermis
dermis
epidermis
layered barrier
dermis
supports and nourishes the epidermis
keratinocytes
skin cells w life cycle of 4 weeks, formed by division of stem cells at basal layer, differentiating to form layers of the epidermis.
keratinised layer
flattened layer of dead cells covered w waterproof keratin
granuled layer
layers of cells containing granules of keratin
prickle cell layer
polyhedral cell layer tightly bound so appear spiky
checkpoint
a critical regulatory point in the cell cycle
G1 checkpoint
cell size must be large enough
availability of sufficient nutrients
signals from other cells received
if not, will enter an arrested phase (G0)
G2 checkpoint
cell size
chromosomes replicated
proteins synthesised
metaphase checkpoint
all chromosomes attached to mitotic spindle at correct tension
cyclin b degraded, sister chromatids separate
moves on to anaphase
3 checkpoints
g1
g2
metaphase
whats entry into the cell phase controlled by?
cyclin B, reaching concentration peak at g2-m phase boundary
apoptosis
programmed cell death
formation of cancer cells
mutations caused by mutagens caused cells controlling cell growth and replication to turn into oncogenes. can be ruled out by checkpoints however tend to evade checkpoints and divide rapidly
carcinogens
mutagens that cause cancer
benign tumors
harmless
formation matched by cell death
malignant tumours
primary tumour, encouraging capillary formation, providing w more nutrients
metastasis
new capillary route for malignant cells to break away from primary tumour to other body parts
