Cell Biology Exam 4: Chapter 14 pt.1

Cellular Reproduction: Mitosis

how do cells reproduce

by the process of cell division

what does mitosis lead to & what is it the basis for

cells that are genetically identical to their parent and serves as the basis for producing new cells

what does meiosis lead to & what is it the basis for

production of cells with half of the genetic content of the parent and is basis for producing new sexually reproducing organisms

2 stages of the cell cycle

• M phase

• Interphase

M phase: what does it include

• mitosis

• cytokinesis

Interphase: what does it include

• G1 phase (growth)

• S phase (synthesis)

• G2 phase (growth)

Interphase: G1 phase

cell grows and carries out normal metabolism & organelles duplicate

Interphase: S phase

• DNA replication & chromosome duplication

• only time chromosomes are duplicated

Interphase: G2

• cell grows & prepares for mitosis

• cell growth & copying of chromosomes in preparation for cell division

cell grows during _____ 3 phases but chromosomes are duplicated only during the ___ phase

all 3 (G1,S,G2),

cells in vivo: what cells lack the ability to divide & why

• nerve cells, muscle cells, or red blood cells

• they are highly specialized, once these cells have differentiated they remain in that state until they die

cells in vivo: cells that do not normally divide can be _____ to begin DNA synthesis (how & what types of cells)

• the cells can be induced to begin DNA synthesis and divide when given an appropriate stimulus

• liver cells & lymphocytes

in vivo: cells that normally possess a relatively high level of mitotic activity

hematopoietic stem cells

what kind of division do stem cells have

• asymmetric in which the daughter cells have different dates

• ex.) some can become lymphocytes or liver cells etc

Mitosis & Cytokinesis: prophase

• chromosomal material condenses to form compact mitotic chromosomes, chromosomes are seen to be composed of two chromatids attached together at the centromere

• cytoskeleton is disassembled, and mitotic spindle is assembled

• golgi complex and ER fragment, nuclear envelope disperses

Mitosis & Cytokinesis: prometaphase

• chromo

Mitosis & Cytokinesis: metaphase

chromosomes are aligned along metaphase plate, attached by chromosomal microtubules to both plates

Mitosis & Cytokinesis: anaphase

• centromeres split and chromatids separate

• chromosomes move to opposite spindle poles

• spindle poles move farther apart

Mitosis & Cytokinesis: telophase

• chromosomes cluster at opposite spindle poles

• chromosomes become dispersed

• nuclear envelope assembles around chromosome clusters

• golgi complexes and ER reforms

• daughter cells formed by cytokinesis

prophase: what is prepared for segregation & what is assembled

• duplicated chromosomes are prepared for segregation

• mitotic machinery is assembled

prophase: 2 ways that form the mitotic chromosome

• chromosome compaction occurs during prophase

• condensin protein is also responsible for compaction

prophase: condensin

• protein responsible for compaction

• helps compaction of intramolecular DNA

centromeres: where do they occur & what do they serve as

they occur at primary constriction (center) on chromosomes and serve as the binding site for proteins

kinetochores: where are they located & what occurs here

• they are on the outer surface of centromeres

• they are the sites where chromosomes attach to the microtubules of the mitotic spindle

what is the centrosome

a microtubule-organizing structure

what is the mitotic spindle made of

microtubules

centrosome cycle

centrioles are duplicated, progresses along with the cell cycle

what happens to the centrosomes during prophase

the centrosomes move apart from one another as they organize the bundles of microtubules that form the mitotic spindle

prometaphase: nuclear envelope

the nuclear envelope 1st breaks down, freeing the sister chromatids from the nucleus, which is necessary for separating the nuclear material into two cells

prometaphase: protein formation (what is it called & where does it form)

development of protein formation called a kinetochore around the centromere, the central point joining the sister chromatids

centromere

central point joining the sister chromatids

metaphase: what occurs to the chromosomes

the chromosomes are aligned at the spindle equator on the metaphase plate

microtubules in a mitotic spindle are highly organized: 3 types of microtubules

• astral microtubules

• chromosomal microtubules

• polar microtubules

astral microtubules

radiate from the centrosome to the region outside the body of the spindle

chromosomal microtubules

move chromosomes to the poles

polar microtubules

maintain the integrity of the spindle

when does anaphase begin

when sister chromatids split and move apart

anaphase: what happens to the chromosomes

chromosomes are split in synchrony

anaphase: where do chromosomes move to & what happens to microtubules

as chromosomes move towards a pole, microtubules attached to kinetochores are shortened

anaphase A

movement of chromosomes toward the poles

anaphase B

when the two spindle poles move in opposite directions due to elongation of microtubules

what forces are required for chromosome movements at anaphase

ATP-driven microtubule motor proteins (dynein & kinesin)

____ and ___ are found at kinetochores of chromosomes

dynein & kinesis

what does depolymerization of microtubules generate

sufficient force to move the chromosomes

anaphase: in yeast, a protein is pushed by the force of depolymerization to do what

help move the chromosome toward the spindle pole

movement of chromosomes during anaphase in animal cells: where does the force required for DNA movement come from

the release of strain energy from when a microtubule depolymerizes

spindle checkpoint

operates as the metaphase/anaphase transition to check for misaligned chromosomes

spindle checkpoint: what do unattached kinetochores contain

a protein complex that sends a “wait” signal to prevent entry into anaphase → must have attachment for anaphase to pull the chromosomes apart

spindle checkpoint: if a cell were not able to postpone chromosome segregation

it would greatly elevate the risk of the daughter cells receiving an abnormal number of chromosomes (aneuploidy)

telophase: what stage of mitosis is it & what happens to the daughter cells

• final stage of mitosis

• the daughter cells return to interphase

telophase: mitotic spindle

disassembles

telophase: nuclear envelopes

nuclear enveloped of the two nuceli are reassembled

telophase: chromosomes

becomes dispersed

telophase: cytoplasm

is partitioned into two cells in a process called cytokinesis

telophase: why do chromosomes become dispersed

so genes involved an be expressed

cytokinesis

• division of the cytoplasm into two distinct daughter cells

• cytoplasm partitioned into two cells

what is mitotic movement powered by

microtubule motors (dynein and kinesin-related proteins)

where are the molecular motors located

at the spindle poles and kinetochores

what are the 3 features of the motor proteins

• keep the poles apart

• bring chromosomes to the metaphase plate and keep them there

• elongate the spindle during anaphase B

cytokinesis in animal cells: where does it start

starts with the indentation of the cell surface

cytokinesis in animal cells: what does the contractile ring theory suggest

that a thin band of actin and myosin filaments generates the force to cleave the cell

cytokinesis in animal cells: what is the site of filament assembly (the plane of cytokinesis) determined by

a signal coming from the spindle poles

cytokinesis in plant cells: cell plate

formation of the cell plate → precursor to a new cell wall

cytokinesis in animal cells: cells build a cell _____ and cell ___ in the cell center

membrane, wall

cytokinesis in animal cells: phragmoplast & material for the cell wall

• the cell plate begins with the appearance of the phragmoplast, which then proceeds laterally

• material for the cell wall is brough to the phragmoplast by golgi vesicles

mitosis mneumonic

• Intelligent → Interphase

• Parents → Prophase

• Pay → Prometaphase

• More → Metaphase

• Attention → Anaphase

• To - Telophase

• Children → Cytokinesis

is interphase a part of mitosis

no, but since the cells spends most of its life in the interphase stage, it is usually considered and discussed together with the other stages

cell cycle control system

• sequential events

• similar to clock

• involves 2 types of proteins

cell cycle control system: 2 types of proteins

• cyclins

• cyclin-dependent kinases (Cdks)

cell cycle control system: when do protein kinases like cdk become activated

just before the start of the s phase

checkpoints

• cycle stops until a go-ahead signal is received

• G1 to S

• G2 to M

what was the first cyclin-cdk complex discovered

MPF (maturation promoting factor)

what does kinase activity depend on

presence of cyclin subunit

what must happen for cells to pass through a point of commitment

Cdks must be transiently activated by specific cyclins

why is the cyclin concentration & MPF activity low during the G₁, S, and G₂ phase but high during the M phase

• you don’t want the cell to divide during G₁, S, and G₂

• cyclin & MPF activity are highest during promotion of cell division (M phase)

what does activated cdk do

phosphorylates proteins for specific for the particular transition

what happens to cyclin after mitosis & what must occur for the cell cycle to proceed again

• it gets degraded after mitosis

• must accumulate before cell cycle can proceed again