21 Cell Cycle I- Cell Bio

What are the four phases of the cell cycle?

G1 (cell growth and monitoring), S phase (DNA replication), G2 phase (cell growth and monitoring), M phase (mitosis and cytokinesis)

What stage is longer, M phase or iterphase?

Interphase

What do cohesins do?

protein complex ring that holds together sister chromatids (assembly during S phase, requires ATP)

What do condensins do?

protein complexes also form rings, but around individual chromatids, promoting chromosome condensation

What are mitotic spindles made of and what do they do?

made of microtubules, separates the duplicated chromosomes

What are contractile rings made of and what do they do?

made of actin and myosin filaments, divides the cell in two

T or F: In the contractile ring during cytokinesis, myosin forms bipolar filaments that can pull on actin filaments

True

What happens in prophase?

duplicated chromosomes (sister chromatids) condense

mitotic spindles start to form outside the nucleus

centromeres move apart

nuclear envelope still intact

What happens in prometaphase?

nuclear envelope breaks down

spindle microtubules attach to kinetochores of chromosomes

What happens in metaphase?

sister chromatids align at spindle equator and attach to opposite poles of spindle

What happens in anaphase?

sister chromatids separate pulling toward each spindle

spindles move outward

kinetochore microtubule shortened

What happens in telophase?

daughter chromosomes arrive at spindle poles

decondense

new nuclear envelope reassembles

What happens in cytokinesis

contractile ring divides cytoplasm

2 daughter cells created

reformation of the interphase array of microtubules nucleated by the centrosome

Figures below represent different stages of mitosis in animal cells. Which represents prometaphase?

D

What happens to the cohesin (links/holds the sister chromatids) proteins during mitosis?

they are removed

T or F: Spindle poles act as microtubule-organizing centers during cell division.

True

What is the centrosome in animal cells?

pair of centrioles (cylindrical organelle composed of tubulin) that is the MTOC

What is the centrosome of the cell duplicated?

In S phase (triggered by G1/S Cdk and S-Cdk)

What does each mitotic spindle have at each pole?

an aster (help anchor centrosomes at the poles)

What are the three types of microtubules involved in mitotic spindles?

Kinetochore MTs- connect centrosome to sister chromatid

Non-kinetochore (interpolar) MTs (aka spindle poles)- pushes apart centrosomes with motor proteins and microtubule-associated proteins

Astral MTs- from poles to cell cortex help position

T or F: Among the three types of microtubules in the mitotic spindle, only the non-kinetochore microtubules overlap in the center of the cell during mitosis.

True

Which way does motor protein kinesins move?

plus end

Which way does motor protein dynein move?

minus end

What motor protein is an exception?

kinesin-14, moves towards minus end

What type of microtubules in mitotic spindle use motor proteins?

non-kinetochore microtubules

What helps break down the nuclear envelope in prometaphase?

M-Cdk (cell cycle kinase signal)

How are sister chromatids attached to the microtubules?

kinetochore protein at the centromere portion

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statement is T or F: The centromere nucleates a radial array of microtubules called an aster.

False, centrosome (MTOC) does, centromere is structure on the sister chromatids

Are chromosomes involved in forming spindles?

Yes, can stabilize/organize microtubules into functional mitotic spindles in plant cells with no centrosomes

How do chromosomes stay at the metaphase plate during metaphase?

continuous growth and shrinkage of microtubules are required align chromosomes and maintain the stability of the metaphase spindle

What does separase do?

degrades cohesion linkages and separates sister chromatids in anaphase

What does securin do?

binds to separase, inhibiting it, removed by activated anaphase-promoting complex

What happens if kinetochore is not attached to the centromere?

There is a stop signal and the anaphase-promoting complex is not activated

What happens in anaphase a?

sister chromatids move toward the spindle poles, driven by the shortening of the kinetochore microtubules, pulls individual chromatids towards the polls

What happens in anaphase b?

spindle poles moved further apart/ pushed apart by elongation/ growth of the spindle at plus ends by sliding of antiparallel interpolar microtubules with motor proteins

T or F: Myosin motor proteins are involved in chromosome segregation during anaphase.

False, kinesin and dynein involved

When does the nuclear envelope reform?

telophase

What mediates cytokinesis?

contractile ring made of actin and myosin filaments

How do plant cells divide differently?

divide from inside out with a cell wall formed inside

What assembles the dividing cell wall in plants between the two sets of segregated chromosomes?

phragmolast

What is used in cell wall matrix assembly in plant cells?

polysaccharides and glycoproteins brought by vesicles

How are the mitochondria and chloroplast divided in cytokinesis?

partitioned randomly

What happens to the ER and golgi apparatus in cytokinesis?

Er is cleaved in two

Golgi undergoes fragmentation and associates with spindle microtubules via motor proteins

Which of the following are important for formation of the contractile ring during cytokinesis?

Microfilaments/ actin filaments (made of actin and myosin)