Lecture 1

Question 1

cell’s DNA

Answer 1

• prokaryote single long DNA molecule
• eukaryote several DNA molecules
• humans body cells 46 chromosomes (23 x 2)
• human gamete 23 chromosomes
• not dividing, DNA is long thing chromatin fibre

Question 2

duplication

Answer 2

• two sister chromatids
• attached by adhesive proteins
• as condense, region connect shrinks to narrow area of centromere
• then chromatids pull apart to form chromosomes

Question 3

mitosis

Answer 3

• formation of daughter nuclei
• cytokinesis

Question 4

meiosis

Answer 4

• non identical daughter cell
• half of the chromosomes

Question 5

phases of mitosis

Answer 5

• mitotic (M) : alternated with interphase, mitosis and cytokinesis
• interphase (I) : cell grows, produces proteins and cytplasmic organelles, copies of chromosomes
• first gap interphase, synthesis interphase, second gap interphase (chromosomes only duplicate in S phase)
• interphase (I) :chromosomes duplicate not condensed, nuclear membrane bounds the nucleus
• prophase (P) : chromosomes tightly coiled, sister chromosomes join,
• prometaphase (P) :
• metaphase (M) :
• Anaphase (A) :
• Telphase (T) :

Question 6

Mitotic Phase (M)

Answer 6

• alternates with interphase
• includes mitosis and cytokinesis

Question 7

Interphase (I)

Answer 7

• 90% of cell cycle
• cell grows by producing proteins and cytoplasmic organelles
• copies chromosomes
• prepares for cell division
• G1 Phase (first gap); S phase (synthesis); G2 Phase (second gap) : cells grow by proteins and for eg. mitochondria and ER, chromosomes duplicated in S phase
• single centrosome replicates forming two centrosomes

Question 8

Late interphate

Answer 8

• chromosomes duplicated but not condensed
• nuclear membrane bounds nucleus
• controsome replicated (two centrosomes)
• each centrosomes has two centrioles (animals cells)

Question 9

Prophase (P)

Answer 9

• nucleoli disappear
• mitotic spindle forms (centrosomes and mictrotubules extend to form)
• radial arrays of shorter mictorubules for centrosomes called asters
• centrosomes move away from each other (propelled by lengthening microtubules)

Question 10

Prometaphase

Answer 10

• nuclear envelope fragments, microtubules for spindle interact with condensed centromere
• kinetochore microtubules for each pole
• nonkinetochore microtubules interact with opposited ends of spindle
• spindle fibers push sister chromatids until arranged at metaphase plate
• kinetochore (proteins and chromosomal DNA at centromere, joined sister chromatids facing opposite directions)

Question 11

Anaphase (A)

Answer 11

• centromeres divide (separating sister chromatids)
• pulled to each pole by spindle fibers
• each pole has equivalent collections of chromosomes

Question 12

Telophase (T)

Answer 12

• daughter nuclei begin to forms
• nuclear envelopes arise from fragements of parent cell’s nuclear envelope and portions of endomembrane system
• chromosome becomes less tightly coiled

Question 13

Cytokinesis

Answer 13

• division of cytoplasm (late telophase)
• formation of cleavage furrow (pinching cell in two)
• vesicles from Golgi apparatus produce cell plate in middle of cell (plants)

Question 14

Mitotic spindle

Answer 14

• distributes chromosomes to daughter cells
• composed of microtubules and proteins
• as spindle assembles, elements come for partial disassembly of cytoskeleton
• fibers elongates by more subunits of protein (tubulin)
• starts at centrosomes (nonmemranous organells organising cell’s microtubules)
• centrosome has pair of centrioles; not necessary for division (animals)

Question 15

Kinetochore/nonkinetochore

Answer 15

• motor proteins on kinetochore ‘walk’ attached chromosome along microtubule to pole
• excess microtubule sections depolymerise at kinetochore ends
• lengthen cell along axis
• interdigitate and overlap across metaphase plate
• suring anaphase overl reduced by motor proteins attached to microtubules walk using ATP
• as microtubules push apart, lengthen by adding new tubulin monomers at overlapping ends

Question 16

cytokinesis

Answer 16

• division of cytoplasm
• cleavage (cleavage furrow forms)
• contractile ring of actin microfilaments associated with molecules of motor protein mysoin (contraction causes pinch)
• [animals]
• during telophase vesicles form Golgi coalesce at metaphase plate (forming cell plate)
• plate enlarges until membranes fuse with plasma membrane at perimeter
• contents of vesilces for new cell wall

Question 17

Mitosis evolved

Answer 17

• prokaryotes reproduce by binary fission
• most bacterial genes located on single bacterial chromosome (consists of circulare DNA molecule with proteins)
• chromosome highly folded and coiled in cell
• binary fission replicates beginning at one point on chromosome (origin of replication)
• as replicates, one origin moves to poles
• cell elongates
• once complete, plasma membrane grows inward (dividing parents cell into two daughter cells)
• movement similar to poleward movement of centromere regions of eukaryotic chromosomes
• bacterial lack visible mitotic spindles and microtubules
• some proteins in binary fission related to eukaryotic proteins, related to eukaryotic tubulin and actin
• as evolved, binary fission arose mitosis
• possible intermediate steps (dinoflagellates: replicated chromo. attached to nuc. envel. ; diatoms: spindle develops in nuc.)

Question 18

control system

Answer 18

• normal growth
• development
• maintenance

Question 19

cytoplasmic signals

Answer 19

• driven by specific chemical signals in cytoplasm
• experiment of cell fusion (different phases fused forming single cell with 2 nuclei; suggests chemicals present in S phase nucleus stimulated fused cell; Mphase with G1 induce 2nd cell to ender mitosis)
• cell control system
  cyclicallty operating molecules trigger, coordinate events in cell cycle

Question 20

Checkpoint

Answer 20

• stop/go signals
• transmitted withing cell by signal tansduction pathways
• built in for animals
• many come from cellular surceillance mechanisms
• indicate key cellular processes done correctly
• also signals from outside cell
• G1, G2, M major checkpoint phases
• G1; restriction point
• go = complete cycle, divide; stop = exit cycle, nondividing state (G0)
• liver cells called back to cell cycle by external cues for growth/injury factors
• specialised nerve/muscle cells never divide

Question 21

Factors

Answer 21

• rythmic fluctuations (protein kinases activate/deactivate other proteins by phosphorylating)
• kinases (present in constant amounts, require 2nd protein, cyclin; cyclin level fluctuate cyclically; cyclin dependent kinases, Cdks)
• cyclin levels sharp rise in Interphase, fall during mitosis
• MPF (maturation-promoting factor) triggers cell’s passage past G2 to M phase (promotes mitosis by phosphorlyrating variety of protein kinases; stimulated fragmentation of nuclear envelope by phosphorlyrating proteins of nuclear lamina; triggers breakdown of cyclin dropping levels during mitosis)

Question 22

internal/external cues

Answer 22

• M phase checkpoint ensures chromo. properly attached to spindle before anaphase (ensures daughters do not end up with missing chromosomes)
• signal to delay anaphase originates at kinetochores not attached to spindle microtubules (keeps anaphase-promoting complex, APC, inactive; kinetochores attached then APC activates then cyclin brakdown and inactivation of proteinsholding sister chromatids together)
• external factors: eg. lack of essential nutrients out of culture medium = no cell division

Question 23

Growth Factors

Answer 23

• proteins released by group of cells (stimulate division)
• platelet-derived growth factors (PDGF) by platelet blood cells bind tyrosine-kinase receprots of fibroblasts (type of connective tissue)
• triggers sognal-transduction pathways allowing for G1 checkpoint)

Question 24

PDGF

Answer 24

• fibroblasts in culture with only divide with meduim containing PDGF
• released in vicinity of injury (proliferation of fibroblasts to help heal wound)

Question 25

Density dependent inhibition

Answer 25

• divide until form single layer on inner surface of culture container
• gap created (cells with grow to fill gap)
• high densities, insufficient growth factors/nutrients cell growth limited

Question 26

anchorage dependence

Answer 26

• anchored to substratum (extracellular matrix of tissue)
• control mediated by pathways involving plasma membrane proteins + elements of cytoskeleton
• cancer cells exhibit neither density-dependent inhibition/ anchorage dependence

Question 27

cancer cells

Answer 27

• divide excessively and invide other tissues
• don’t stop dividing when growth factors depleted
• eithe rmanufactures GF / has abnormality in signalling pathway/ abnormal cell cycle control system
• infinite supply of nutrients = infinite division
• can be immortal
• evade destruction proliferate to form tumor
• benign tumor cells at originating site
• malignant tumor = invasive to impair functions of organs
• often detach and carried in blood/lymph system to other tissues (start metastasis)
• unusual number of chromosomes, may secrete signal molecules causing blood vessels to grow toward tumor
• treatment include high energy radiation/ chemotherapy toxic drugs
• target actively dividing cells
• interfere with specific cell cycle steps
• eg. Taxol prevents mitotic depolymerisation (prevents proceeding past metaphase)
• side effects affect normal cells