Final - Midterm 3

Question 1

based on cell activities readily visible in the light microscope, there are two major cell cycle phases:

Answer 1

M phase, interphase

Question 2

G0 phase

Answer 2

cells that have stopped dividing and are arrested in a stage preceding replication of cytoplasmic contents and organelles

Question 3

as animal cells enter mitosis, their microtubules disassemble and then reassemble forming the mitotic spindle with a focus at the:

Answer 3

centrosome

Question 4

what permits the interaction between the cytoplasmically-formed mitotic spindle and the chromosomes to occur

Answer 4

nuclear envelope breakdown

Question 5

the nuclear lamina is disassembled by:

Answer 5

the depolymerization of the lamin filaments

Question 6

the assembly and disassembly of intermediate filaments are controlled primarily by:

Answer 6

phosphorylation and dephosphorylation

Question 7

plectin:

Answer 7

composes the cross-bridges that hold intermediate filaments together

Question 8

if a cell contains an ATP analog that cannot be hydrolyzed, what will be the consequence to normal actin depolymerization:

Answer 8

there will be no depolymerization

Question 9

the Arp2/3 complex:

Answer 9

• nucleates new branches of actin off of existing filaments
• nucleates new branches of actin starting with the negative end of a monomer facing the complex

Question 10

what molecular motor is associated with actin filaments:

Answer 10

myosins

Question 11

what accounts for the decrease in the length of an entire muscle

Answer 11

the combined decrease in sarcomere length

Question 12

how does an actin thin filament manage to move continuously during a contraction cycle

Answer 12

all of the myosin heads beat out of synchrony with one another

Question 13

nebulin:

Answer 13

a protein that is thought to act like a ‘molecular ruler’ by regulating the number of actin monomers that are allowed to assemble into a thin filament

Question 14

titin:

Answer 14

blocks the myosin binding sites on actin thin filaments in a stimulated sarcomere

Question 15

ATP binding to myosin in a contraction cycle:

Answer 15

releases myosin from actin

Question 16

high affinity binding with the signalling molecule allows:

Answer 16

efficient recognition of extracellular signalling molecules by receptors on the responding cell’s surface

Question 17

where is the guanine nucleotide-binding site of the G protein located?

Answer 17

on the G alpha subunit

Question 18

what are the events of G protein activation:

Answer 18

1. binding of a hormone or neurotransmitter to a G-protein couples receptor
2. change in conformation of the cytoplasmic loops of the receptor
3. increase in the affinity of the receptor for a G protein on the cytoplasmic surface of the membrane
4. G protein binds to activated receptor forming a receptor G-protein complex
5. conformational shift in the alpha subunit of the G protein
6. release of GDP by the G protein
7. binding of GTP by the G protein

Question 19

in order to begin desensitization, the ____ domain of the activated G protein coupled receptor is phosphorylated by a specific enzyme called a _____

Answer 19

cytoplasmic, G protein coupled receptor kinase

Question 20

arrestins:

Answer 20

proteins that bind to GPCRs and compete for binding to those GCPRs with heterotrimeric G proteins

Question 21

how is signalling by an activated G alpha subunit terminated:

Answer 21

the bound GTP is hydrolyzed to GDP

Question 22

the role of A kinase anchoring protein is:

Answer 22

to confine PKA signalling to specific parts of the cell

Question 23

receptor mediated dimerization:

Answer 23

ligands act as allosteric regulators that turn on the ability of their receptors to form dimers

Question 24

once the kinase domain of receptor protein tyrosine kinase has been activated, what does the activated receptor protein tyrosine kinase do:

Answer 24

each receptor subunit phosphorylates its partner on tyrosine residues found in regions adjacent to the kinase domain

Question 25

what is usually responsible for terminating signal transduction by RTKs

Answer 25

receptor internalization

Question 26

SH3 domains on proteins recognize what on the protein they bind to:

Answer 26

a specific amino acid sequence

Question 27

what kind of enzyme activity does the Ras protein display

Answer 27

GTPase

Question 28

what holds Ras at the inner surface of the plasma membrane

Answer 28

attachment to a lipid group that is embedded in the inner leaflet of the bilayer

Question 29

how is Ras activity turned off

Answer 29

by hydrolysis of its bound GTP to GDP