10 - The Cell Cycle

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important role of cell division

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transmit new information

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what forms when cell undergoes reproduction or cell division

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two daughter cells genetically identical to each other and parent cell

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before parents splits into two

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duplicates chromosomes (contains cells genetic information in form of DNA)

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define asexual reproduction

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creation of genetically identical offspring by single parent without participation of sperm and egg

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the offsprings of asexual reproduction are called?

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clones (genetically identical individuals)

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principle of inheritance in asexual reproduction

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lone parent and each offspring have identical genes

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Define sexual reproduction

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requires fusion of gametes, egg and sperm

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production of gametes require type of division that only occurs in

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gonads

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how many chromosomes can a gamete produce

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half as many as parent cell (unique combination of genes)

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cell division enables sexually reproducing organisms to

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develop from a single cell into an adult organism

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after organisms fully grow, cell division continues to

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renew and repair cells that die from normal or accidental wear

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function of cell division in amoeba and body

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reproduction, repair and renew

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prokaryotes reproduce through

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binary fission

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in typical prokaryotes

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genes are carried on one circular DNA molecular

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Summarize division of prokaryotes

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duplication, separation, elongation, division

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why is binary fission classified as asexual reproduction

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does not require fusion of gametes

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Eukaryotic cells usually

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Have more genes that prokaryotic cells

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genes in humans and eukaryotes are found in

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nucleus

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grouped into multiple

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chromosomes

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Eukaryotic chromosomes consists of

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one long DNA molecule ( genes + protein attached)

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DNA + protein

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chromosomes (condensed) / chromatin (diffused)

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chromosomes of eukaryotes condense and divide after

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being duplicated

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when does a chromosome consists of two identical chromatids

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growing interphase

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cell division is key component in

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cell cycle

Front 25

two main stages of cell cycle

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growing stage (interphase)

actual cell division (mitotic phase)

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sub stages of interphase

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G1 (first gap), S (DNA synthesis), G2 (second gap)

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most of cell cycle is spent in interphase compromising

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90% total to for cell cycle

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high metabolic activity in interphase

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performs normal functions, grows in size, duplicates chromosomes

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where cell typically divides

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mitotic phase (M phase)

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accounts

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10 % of total time

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Two overlapping stages

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mitosis (nuclear divide), cytokinesis (cytoplasm divide)

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mitosis is unique to

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eukaryotes

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solution to

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allocating identical copy of whole set of chromosomes to two daughter cells

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mitotic cell division ensures

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body receives 46 chromosomes from original cell

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chemical prevents DNA synthesis, cells are trapped

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G1

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parts of cell

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plasma membrane, nuclear envelope, chromatin, centrosomes

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In prophase, chromatin at tightly coiled forming

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discrete chromosomes

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Each duplicated chromosome appear as

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two identical chromatids joined together

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in cytoplasm, mitotic spindle begins to form as microtubules that

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rapidly grows out from centrosome that moves away

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In prometaphase, nuclear envelope

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break into fragments

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Microtubule extend in nuclear region

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reaching chromosomes

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Some of the spindle attach to

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kinetochore

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othe microtubules contact with

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other microtubules from it end

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proteins associated with chromosomes move chromosomes

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towards the centre

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In metaphase, mitotic spindle

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fully formed and poles at opposite ends

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centrosomes of all chromosomes

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line up

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kinetochore of two sister chromatids

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attached to microtubules from opposite ends

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In anaphase, two centromere of each chromosome are

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apart, separating sister chromatids

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motor proteins of kinetochore wlak sister chromatids toward

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opposite poles

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spindle not attached to chromosomes

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lengthen

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In telophase,

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cell elongation continues

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daughter nuclei appear at poles of cells as nuclear envelope

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forms around chromosomes

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by end of telophase, chromatin fibers uncoil, mitotic spindle

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disappears

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In cytokinesis, occurs simultaneously with

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telophase

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in animal cells, forms

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cleavage furrow

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But in plant cell, forms

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cell plate

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rate of cell division is affected by

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environmental factors

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timing of cell division must be carefully controlled to

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develop normal and maintain tissues

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Physical factors

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anchorage dependence, density dependent inhibition,

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Anchorage dependence

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cells anchor to dish surface to divide

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Density dependent inhibition

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when cells form a complete layer, they stop dividing

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If cells are scrape away,

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remaining cells divide and refill until contact with each other

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Cancer cells

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tumor cells divide uncontrollably even if they filled a layer

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Chemical factors

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nutrients and growth factors

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Most cells in living animals are

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anchored and fixed

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Do not divide unless signalled, growth factors

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Serve as main signals

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cell cycle control system

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triggers and coordinates

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checkpoint

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stop and go signals regulate cycle

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Default of checkpoints

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halt unless override with go signals

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What are the three checkpoints

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G1, G2, M

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intracellular signals

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cellular processes have been completed and proceed past point

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messages form outside cell,

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environmental condition and presence of growth factors

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Most imporant checkpoint is

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G1

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If signal never arrives

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cells switches to permanently non dividing state called Go phase

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Which checkpoints exists as duplicated chromosomes

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G2, M

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Cancer begins when normal cel converted to

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cancer cell

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They have

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altered proteins and destroyed immune systems

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A mass of abnormally growing cells is called

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tumor

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benign tumor

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abnormal cell remains on site

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malignant tumor

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spread into other tissues

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Cancer is when tumor is

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malignant

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Cancer cells

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proceed past checkpoints, synthesis growth factors, stop dividing at random points, immortal

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Mammalian cells typically divide about

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20 to 50 times before stop

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Ways to treat cancer

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Remove surgically, high energy radiation, chemotherapy (tazol (freezes), vinstablin (prevents from forming) mitotic spindle