Cell Bio Cell Cycle, Apoptosis

Question 1

M - mitosis

Answer 1

nuclear & cell division (cytokinesis) - relatively short in time compared to interphase

Question 2

G1: gap 1

Answer 2

Hours to days or more (some are so long that they may not go back into cycle)

Question 3

G0: quiescent

Answer 3

apparently non-dividing cells - long term temporary or permanent (extended G1)

Question 4

S: synthesis of DNA

Answer 4

remember, most cells will wind up with shortened telomeres (need nutrients, growth factors, etc.)

Question 5

G2: gap 2

Answer 5

completion of G1 replication and replicated genome ready to undergo mitosis

Question 6

interphase

Answer 6

• metabolically active with euchromatin & heterochromatin observed
• G1 –> G2 (no mitosis)

Question 7

gap

Answer 7

• named because of the apparent gap in activity under the microscope
• seems like this but actually replicating and actively metabolizing (intracellular)
• G1, G0, and G2 are still metabolically, and biochemically active, etc.
• G1 variation on a theme (become longer or shorter)
• permanent G0 (cells with extended G1 phase) - post-mitotic and will not reenter the cell cycle

Question 8

cell replication

Answer 8

central to wound healing, normal cell replacement, tumor growth (via cell cycle)

Question 9

Step 1 of M phase

Answer 9

prophase (chromosome condense) - daughter chromosomes attached and mitotic spindle formation

Question 10

step 2 of M phase

Answer 10

prometaphase (nuclear membrane breakdown) - dissolution begins

Question 11

step 3 of M phase

Answer 11

. metaphase (chromosomes align) - daughter chromosomes align at metaphase plate (equator of spherical cell) and attach to MT structure (depolymerization of MT to drive separation)

Question 12

step 4 of M phase

Answer 12

anaphase (chromosome separate) - pull at poles

Question 13

step 5 of M phase

Answer 13

telophase (nuclear membrane reforms) - cleavage furrow forms with microfilaments

*complete chromosome separation –> reformation of nuclear membrane –> 2 daughter cells

Question 14

cytoskeletal proteins in M Phase Sub-Steps

Answer 14

• intermediate filament depolymerization (phosphorylation) throughout cell and repolymerization (dephosphorization) in daughter cells
• nuclear lamins under nuclear membrane need to depolymerize (IF)
• microtubule depolymerization to pull spindles
• microfilament polymerization for cleavage furrow to separate cells (contractile ring)

Question 15

permanently stopped cells

Answer 15

*post-mitotic

• “terminally differentiated” - maturation/specialization over
• upper layers of epidermis, many neuronal cells, skeletal muscle, RBC
• RBCs as characteristic terminally differentiated because they do not have a nucleus

*never enter the cell cycle

Question 16

indefinitely stopped cells

Answer 16

• quiescent = G0 Gzero extended but can be stimulated again
• liver cells (liver damage/tissue loss would stimulate)
• some WBC (right stimulus would start cell cycle again in lab conditions)
• some can be triggered to divide with the right signal

Question 17

(t/f) WBCs can start cell cycle in normal conditions

Answer 17

false; need to right stimulus mostly via lab conditions (most WBC are in G0)

Question 18

routinely stop & go cells

Answer 18

• certain epidermal (lower level mitosis but never upper layers) - every 28 days
• gut lining epithelial cells (highly active and continual replacement)
• bone marrow (blood cell progenitors)

Question 19

myeloid stem cell

Answer 19

• the ability to enter the cell cycle always
• myeloblasts have shorter-term ability to enter the cell cycle
• RBCs and platelets (no DNA/nucleus) do not go into the cell cycle
• granulocytes are mostly post-mitotic

Question 20

cell cycle control

Answer 20

*some of the signals (dozens of + and - signals)

• external signals –> internal signals –> consequences

Question 21

external positive signal (just one of many examples)

Answer 21

• EGF - epidermal growth factor (protein promotes skin cell replication)
• outside cell –> inside response
• many non-skin tissues produce & respond to EGF (stimulate cycling of cells)
• kidney, salivary gland, prostate, thyroid, bone marrow, lung, breast, uterus, & colon
• large precursor protein processed to small active peptide
• increased production in many cancer cells

*breast cancer treatment targeting balance (over-stimulation of EGF)

Question 22

EGF receptor

Answer 22

*transmits a signal across the membrane

• transmembrane glycoprotein with 3 sub-regions
• one projects from the cell surface & binds EGF (extracellular)
• one span across lipid bilayer
• one projects into cytoplasm & has kinase activity (cytoplasmic portion activation) - attaches -PO4 groups to tyrosine in itself & other proteins
• kinase domain hyperactive from mutations present in cancers (excess cell growth)
• enzymatic activity built-in

Question 23

external positive signals ex. EGF to internal consequences

Answer 23

• ligand binding & dimer formation (2 receptors) - EGF binds extracellularly
• activation of receptor kinase & self-phosphorylation at cytoplasmic tail (self and trans)
• cytoplasmic proteins associated w/ receptor are phosphorylated
• intracellular kinase activated & phosphorylate other cytoplasmic proteins (signal cascade)
• move to nucleus & cause transcription of genes encoding cell cycle promoting proteins cyclins & Cdk’s once phosphorylated
• multiple proteins activated due to increase levels of cyclin/Cdk activity