Bio Test 4a Flashcards
the M phase is made up of?
- mitosis: divides DNA
- cytokenesis: divides cellular content and cytoplasm
M phase
to accurately separate and distribute chromosomes
sister chromatids
duplicated chromosomes
centrosome
- microtubule organizing center
- is composed of Y-tubulin rings
- contains pair of centrioles which is also composed of microtubules
Y-tubulin
where microtubules begin to grow from
What are the five stages of mitosis?
prophase prometaphase metaphase anaphase telophase
prophase
- condensation of chromosomes, condensins coils up single DNA molecule
- duplication and separation of centrosome
- assembly of microtubules
- breakdown of nuclear envelope
prometaphase
- attachment of chromosomes to microtubules at kinetochore sites
- mitotic spindles is complex cytoskeletal machine which is composed of microtubules to separate replicated chromosomes
- three kinds of microtubules: aster, kinetochore, and interpolar
- chromosomes begin active movement
metaphase
chromosomes aligned at mitotic spindle equator
anaphase
separation of sister chromatids by shortening interpolar microtubules and move apart of centrosomes
telophase
- daughter chromosomes arrive at poles
- reassemble of nuclear envelope
- assembly of contractile ring for cytokenesis
cytokenesis
- cytoplasmic division
- different cytoskeletal structure is responsible for cytokenesis called contractile ring which consists of myosin and actin filaments
structure of microtubules
- tubulin hetero-dimers to 13 protofilaments to hollow tube
- polarity: beta-tubulin is the positive end growing faster
major functions of microtubules
- anchoring membrane-enclosed organelles
- guiding intracellular transport
- cell division
- movement of cilia and flagella
guiding intracellular transport
- mediated by motor proteins (kinesin and dynein)
- conduct directional movement
- kinesins move towards positive end; dyneins to the negative end
Major functions of actin filaments
- special cell structure
- cell shape (contractile bundles)
- cell migration
- cell division (contractile ring)
- intracellular transport
- muscle contraction
characteristics of cell migration
- lamellipodium
- filopodium
- intracellular changes
lamellipodium
sheet-like structure at the leading edge of crawling cells
filopodium
thread-like structure at the leading edge of crawling cells
intracellular changes in cell migration
- protrusion: forming filopodia and lamellipodia
- focal adhesion: using integrins proteins
- attachment and traction
- contraction at the back
drugs that interfere with microtubule assembly have been used to treat what disease?
cancer
name the two subunits of microtubules….
- beta-tubulin (positive end)
- alpha-tubulin (minus end)
taxol
binds and stabilizes microtubules
colchicine
binds subunits and prevents polymerization
phalloidin
binds and stabilizes filaments
cytochalasin
caps filament plus end
names for chromosomes
- homologous chromosomes
- sister chromatids
- daughter chromosomes
Meiosis
important for sexual reproduction, creates gametes which reduces the number of chromosomes in half (adults are diploid and gametes are haploid)
germ-line cells
only cells that can undergo meiosis to produce gametes
what are the unique features of meiosis?
- synapsis
- homologous recombination
- reduction division
- create genetic variations by crossing over and independent assortment
synapsis
homologous chromosomes pair along their length
homologous recombination
genetic exchange between homologous chromosomes
reduction division
two successive divisions
Stages of Meiosis
- Meiotic division I
- Meiotic division II
Meiotic division I
- pairing of homologous chromosomes
- homologous chromosomes cross over to form chiasma
- genetic recombination occurs
- separate homologous chromosomes
- sister chromatids are no longer identical due to crossing over
chiasma
site at which crossing over occurs
Meiotic division II
separate sister chromatids
genetic variations in meiosis
- crossovers during meiotic prophase I
- independent assortment of maternal and paternal homologous during metaphase I and anaphase I
- fertilization
nondisjunction
improper separation of DNA during meiosis
- aneuploidy
- could happen during meiotic I and II
- resulting in trisomy or monosomy
- trisomy 21
aneuploidy
abnormal number of chromosomes in cells
trisomy 21
down syndrome gene that is affected
transposons
transposable DNA elements
- same repetitive sequence on the ends
- bacterial transposons usually carry antibiotic resistant gene
- transposons in humans
What technique is used for transposition in bacteria?
- nonreplicative (cut and paste)
- replicative
transposons in humans
- two types: transposon (DNA to DNA) and retroteansposon (DNA to RNA to DNA)
- make up 50% of human genome
- Alu and L-1 elements are retrotransposons
- viruses behave like transposons
Alu
enes up in introns or non-coding regions
Prophase I in meiosis
homologous chromosomes become closely associated in synapsis, exchange segments via crossing over, and then separate
Metaphase I in meiosis
- terminal chiasmata holds homologous pair together
- spindle microtubules attach kinetochore proteins on outside of centrosome
- joined pairs of homologues line up in middle
Anaphase I in meiosis
- spindle fivers begin to shorten and pull whole centromeres toward poles
- each pole receives member of homologous pair
Telophase I in meiosis
- chromosome are segregated into two clusters; on at each pole
- nuclear membrane re-forms
Prophase II in meiosis
nuclear envelope breaks down
Metaphase II in meiosis
sister chromatids line up in middle
Anaphase II in meiosis
sister chromatids move to opposite poles
Telophase II in meiosis
nuclear envelope re-forms
