Download The Cell Cycle and Cell division - Learning Central

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See
http://www.sci.sdsu.edu/multimedia/mitosis/
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"DNA is, ..so precious and so fragile that we now
know that the cell has evolved a whole variety of
repair mechanisms to protect its DNA from
assaults by radiation, chemicals and other
hazards. This is exactly the sort of thing that the
process of evolution by natural selection would
lead us to expect." Francis Crick in What Mad
Pursuit.
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Gene: unit of heredity, residing at a specific point
on a chromosome; a length of DNA that specifies
a product
Chromosome: condensed, linear DNA and
protein, containing genes and intervening
sequences
DNA: the genetic material in all living organisms;,
located in the nucleus onchromosomes in
eukaryotes
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 Somatic
cell division
◦ Define somatic cell.
 Controlled
by:
◦ Genes (indirectly)
◦ Hormones (directly)
◦ Environment (directly)
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UNCONTROLLED
MITOSIS!
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The Cell Cycle, Cell division and Cell Work
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food
water
oxygen
Cell renewal
Supporting life/
life quality
environment
Communication
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 Growth
 Development
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Repair of the organism
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Detection and repair of genetic damage
 Prevention
of uncontrolled cell division
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State 2 key factors that control frequency of cell division
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Describe the different phases of the cell cycle
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Discuss the primary importance of Interphase in respect
of nursing interventions
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State the 4 phases of mitosis
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List the changes that occur in each phase of mitosis
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State the differences between natural and pathological
cell death
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•How
does a one-celled embryo grow into a multicellular organism?
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When do cells need to be made in adults?
ex. skin cells in humans are continuously being sloughed
off and replaced
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as many as 100 billion (1011) cells are lost daily
In abnormal situations, cells may divide “out of control”
= cancer
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©Cardiff University/Genetics/CSAN
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The cell cycle is cyclically events that has set of reaction
sequences that both trigger and coordinate key events in
the cell cycle
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The system (e.g. in animal cells) is driven by a built-in clock
that can be adjusted by external stimuli (chemical messages)
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Checkpoint - a critical control point with ‘stop’ and ‘go-ahead’
signals that regulate the cell cycle
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Three Major checkpoints are found in the G1, G2, and M
phases of the cell cycle
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◦ The G1 checkpoint ensures that the cell is large enough to
divide, and that enough nutrients are available to support the
resulting daughter cells.
◦ If a cell receives a go-ahead signal at the G1 checkpoint, it
will usually continue with the cell cycle
◦ If the cell does not receive the go-ahead signal, it will exit the
cell cycle and switch to a non-dividing state called G0.
◦ Most cells in the human body are in the G0 phase
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For Example - Platelet-Derived Growth Factors –
(PDGF ) required for the division of fibroblasts which are
essential in wound healing
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When injury occurs, platelets (blood cells important in
blood clotting) release PDGF
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Fibroblasts are a connective tissue cells
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The binding of PDGF leads to a proliferation of
fibroblasts and a healing of the wound
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When a cell population reaches a certain density, the
amount of required growth factors and nutrients available
becomes insufficient to allow continued cell growth
E.g. Cells grown in culture will rapidly divide until a single
layer of cells is spread over the area of the petri dish,
after which they will stop dividing
If cells are removed, those bordering the open space will
begin dividing again and continue to do so until the gap
is filled
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These are the cells which no longer respond to
cell-cycle controls –
Cancer cells do not respond normally to the body's
control mechanism.
◦ They divide excessively and invade other tissues
◦ If left unchecked, they can kill the organism
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Cancer cells do not exhibit contact inhibition
◦ If cultured, they continue to grow on top of each other
when the total area of the petri dish has been covered
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May produce required external growth factor themselves or
possess abnormal signal which falsely convey growth signals
thereby bypassing normal growth checks
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Cancer cells exhibit irregular growth sequences
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If growth of cancer cells does cease, it does so at random
points of the cell cycle
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Cancer cells can go on dividing indefinitely if they are given a
continual supply of nutrients
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Normal mammalian cells growing in culture only divide 20-50
times before they stop dividing
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The length of this period varies in different cell types
Certain cells divide very frequently
Examples
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 Blood
forming cells divide rapidly
 Epithelial
cells divide frequently though
much slower than RBC producing cells
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These tend to remain within Interphase until
death
Nerve cells ?
Muscle cells?
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This is the longest period of the complete cell cycle
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May appears to the eye to be a resting stage between cell
divisions
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It is in fact a period of diverse activities
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Interphase activities are indispensible in making the next
mitosis possible
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During this period, it also carries out metabolic
activities
example–
burning glucose for energy
◦ It performs specialised functions
example –
preparing molecules, to secrete
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Is the "resting" or non-mitotic portion of the cell
cycle
 It is comprised of G1, S, and G2 stages of the cell
cycle.
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◦ Chromatin condenses the nuclear envelope
begins to disperse.
◦ Production of mRNA and tRNA –
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During which:
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DNA replicates or makes copies the DNA strings.
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DNA is Deoxyribonucleic Acid
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The Centriole divide
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Performs specialised functions –
◦ Creates more cellular material, for example
◦ Proteins are actively produced.
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Carries out metabolic activities
◦ e.g. creating energy, producing waste products
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Replication of DNA must occur◦ mistakes occur and are corrected,
Mistakes are corrected by enzymes that chop out
the defective bit, using the undamaged strand as
a template, it assembles correct codes.
If not corrected, successive generations will
appear as mutations.
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The Cell Cycle includes:
1. MITOSIS (a period of active division called the M
phase);
- the nucleus divides into 2 nuclei.
2. INTERPHASE (a period of non-division) which is
divided into three parts.
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G1 (gap1
18 or more hours)
-
Cells increase in size.
Some cells miss this stage
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there is of DNA protein
synthesis assembly of new
molecules & reproduction
of mRNA & tRNA
S (DNA synthesis 6 + hours) DNA (chromosome)
replication,
there is also continued
duplication of some
organelles.
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G2 (gap 2 (2-5hours
premitotic) ) –
- preparation for Mitosis.
- Chromatin condenses & the
nuclear envelope begins to
disperse.
- There is also production of
mRNA and tRNA
- similar to G1 & some cells miss
this stage
G0 (stop phase (indefinite) )
arrest of cell division
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 P-Prophase
 M-Metaphase
 A-
Anaphase
 T- Telophase
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 A-
Anaphase
 P-Prophase
 T- Telophase
 M-Metaphase
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Prophase
Metaphase
•Centrosomes migrate
•Spindle fibers form
•Chromatin condenses
•microtubules
attach to chromosomes
•Chromosomes move to
midline/metaphase plate
Telophase
Anaphase
•Links break
•Daughter chr.
move to poles
Cytokinesis
•Chr. reach poles and
decondense
•Nuclear envelope reforms
•Spindle fibers disappear
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When do somatic cells divide? ie. Why do cells divide?
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What is this cell division called?
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MITOSIS (2n to 2n)
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What happens if chromosomes are not duplicated
correctly?
ex. Cri-du-Chat syndrome
Small part of chromosome 5 is lost: results in heart
problems, mental retardation, and other problems
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Chromosomes appear
Chromatids.
– condensed-
(2 identical chromatids were formed
during S phase)
These attach to centromere.
2 Centrioles (tiny microtubular
organelles )
duplicate, move and stop on
opposite sides of the cell.
Chromatids
tighter,
disappears,
envelope disintegrates.
coil
nucleolus
nuclear
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Chromatids
◦ align in the middle of the cell-
 pulled by spindle fibres
They line up along spindle fibres
Nuclear Membrane now disappears
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 Chromatids
◦ pulled by spindle fibres
◦ to opposite ends of the cell.
◦ And renamed Chromosomes
 Result:
twice as many Chromosomes
as in the parent cell
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Chromosomes extend
they become visible
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nuclear membranes reform
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Nucleoli reappear
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Spindles disappear
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◦ around each group of newly divided chromosomes
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The cell membrane pinches inward
like a belt tightening between two poles
until
2 daughter cells are formed
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All cellular activity is controlled by genes
This is influenced by
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Genetic Inheritance
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The Environment
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Insufficient O2 & nutrition slows
◦ cellular respiration
◦ cell renewal processes
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Mitosis stop at G1 or G2 phase
This phase is called is called G0
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Occurs in 2 ways:
◦ Necrosis occurs when pathological changes kill a cell
◦ Apoptosis occurs as a normal physiological response
 Also called programmed cell death
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3-53
Dividing cells will
divide until they run
out of space =
contact inhibition.
Example = Wound
healing
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Reductive cells division
No Duplication of
Genetic material
The process results in 23 single chromosomes
instead of pairs of chromosomes
Genetic material
halved
The chromosomes are cross over & randomly
sorted & this gives rise to genetic diversity in
normal situations
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Biological flow of
information
(central dogma)
DNA
RNA
Protein
Trait
Reading DNA
& making
Protein
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Briefly explain base paring
Briefly explain triplet coding for amino acids
Name 2 amino acids
Define transcription & translation of DNA
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Reading the DNA code within the nucleus= Transcription
BASE PARING
PURINES
PYRIMIDINES
Adenine pairs with
Thymine
Guanine pairs with
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Cytosine
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Allows molecules to act as templates for replication of
amino acids
It allows for transmission of a genetic code
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PURINES
PYRIMIDINES
 Adenine pairs with
Thymine
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Guanine pairs with
& Uracil
Cytosine
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Adenine(A) Thymine(T) Cytosine(C) Guanine(G)
letters A T C G ” = DNA code
Copying the code in the nucleus.
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G is read as C
A is read as T
But ribosome's
change T to ‘U’
(uracil)
In the Cytoplasm
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You do not have to
remember these
codes- the concept is
important though
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Translation occurs in the cytoplasm where the
Ribosomes are located.
Ribosomes bind to messenger RNA and read
triplet codes for amino acids in the correct
sequence to form a polypeptide chain;
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There are 50.000 different protein containing
compounds in the body
forming a part of enzymes, hormones or structural
proteins
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PROTEINS
◦ DETERMINE THE FUNCTION OF THE CELL
GENES CONTROL CELL DIVISION
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DNA -repeatedly refreshed
◦ Genetic information is renewed in its original format: If
this does not occur - then chaos can occur within the
cellular environment.
Viruses
for example can alter protein synthesis,
this is the basis for viral disease.
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Tight coiling
Only uncoiling specific sections for protein synthesis.
e.g. from viruses and prions –
?how do they affect the DNA strand?
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http://www.youtube.com/watch_popup?v=fKyljuk
BE70
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gene - basic unit of heredity; codes for a specific trait
locus - the specific location of a gene on a chromosome (locus - plural loci)
genome - the total hereditary endowment of DNA of a cell or organism
somatic cell - all body cells except reproductive cells
gamete - reproductive cells (i.e. sperm & eggs)
chromosome - elongate cellular structure composed of DNA and protein - they are the vehicles which
carry DNA in cells
diploid (2n) - cellular condition where each chromosome type is represented by two homologous
chromosomes
haploid (n) - cellular condition where each chromosome type is represented by only one chromosome
homologous chromosome - chromosome of the same size and shape which carry the same type of
genes
chromatid - one of two duplicated chromosomes connected at the centromere
centromere - region of chromosome where microtubules attach during mitosis and meiosis
Allele - alternate forms of the same gene
Homozygous - having two identical alleles for a given gene
Heterozygous - having two different alleles for a given gene
Genotype - genetic makeup of an organism
Phenotype - the expressed traits of an organism
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