Exam 1 - Cell Biology

What is the composition of F-actin filaments?

2 G-actin filaments wrapped around each other

A ______ is a membrane protein structure that allows ions to flow freely in or out through an opening of a particular size.

Channel

What is resting potential?

Difference of charges in the cell. Resting potential of a cell is negative compared to surroundings.

Phospholipids containing __________ are always found exclusively on the exterior side of a membrane.

Hydrophilic heads

What acts as an anchor for both ends of the microtubule?

MAPs Regulate MT assembly by stabilizing or destabilizing MTs

Co-transport of nutrients across the intestinal cell membranes is an active process that can move glucose against a concentration gradient. What is the energy requiring step for co-transport?

Na+ is using ATP to go into the cell

What is facilitated diffusion.

Passive transport; pumps and channels help molecules move down their gradients

Which of the following best describes the concept of dynamic stability as it applies to MTs?

Steady growth of MT, which abruptly collapses and shortens

What is the definition of critical concentration of purified tubulin dimers?

There is a certain concentration of dimers that need to be present before filaments can elongate Concentration of actin subunits needed to form filaments

Both types of motor proteins step from one tubulin to another, an 8 nm "step."

True

What is an antiporter?

Two different molecules moving in opposite directions (K+/Na+ ATPase)

Microtubules have a ____ arrangement in the main body of a flagellum.

9 + 2

What is the treadmilling of an actin filament?

Addition at the barbed end, dissociation at the pointed end with not net change

When is ATP hydrolyzed by actin?

After polymerization

To make a branch off an existing actin filament, cells use the protein ______.

Arp 2/3

What are the difference between channel and carrier?

Channel proteins carry molecules down their concentration gradient. Carrier proteins carry molecules against their concentration gradient, also undergo allosteric changes.

What are the differences between passive transport and simple diffusion?

Diffusion: Substance tends to move to high to low concentration until it becomes equal. Passive: does not require cell to expend energy, substance diffusing down gradient using no energy. Passive includes simple diffusion and facilitated diffusion.

According to the current model, what is the sequence of microtubule assembly?

Dimer, oligomer, protofilament, sheets of protofilaments, closing of MT, elongating MT

If the plasma membrane of an animal cell was made entirely permeable to Na+, the Na+/K+ pump would continue to pump ions and hydrolyse ATP, but not build a Na+ gradient.

False

Passive carriers transport sugars, active carriers transport ions.

False

The Na+/K+ ATPase pumps Na+ from the cell into the lumen of the intestine.

False

The permease (transporter) allows glucose and Na+ into the cell requires ATP.

False

The permease (transporter) pumps glucose from the cell into the blood requires ATP.

False

Passive carriers consume ATP energy when they transport ions, active carriers create ATP.

False (Active uses ATP, Passive creates ATP)

Passive carriers contain beta sheets in their transmembrane domains, active carriers contain alpha helices.

False (Passive: alpha helices, active: beta sheets)

Passive carriers are localized to the basolateral membrane of epithelial cells, active transporters are localized to the apical membrane.

False (active transporters can also be located in the basolateral membrane)

GLUTs are uniporters that use ATP hydrolysis for energy.

False (do not require ATP hydrolysis)

What are the common features of the motor proteins kinesin and dynein?

Generate force Walk along MT Kinesins walk towards the plus end Dyneins walk towards the minus end Head, tail, microtubule binding domain

What types of transport would increase at a linear rate (no saturation) proportional to the concentration gradient?

Ion channels, or just channels

Potassium ion (K+) channels are very selective for K+, although the ion sodium (Na+) has the same charge as K+ and is even smaller. What feature of the K+ ion channel explains this selectivity?

It uses all of its energy dehydrating K+ so it doesn't have enough energy for Na+. Each K+ has to shed all the H2O before diffusing through the membrane. Larger and requires more energy to be dehydrated.

What acts as a motor for driving chromosomes apart during mitosis?

Kinesins and dyneins

Describes the concept of "dynamic instability" as it applies to the microtubules.

MTs are constantly switching between phases of growing and shortening (even in the steady state)

The definition of _______ is a measure of ionic imbalance across the plasma membrane, caused by unequal concentrations of ions in the cytosol vs. the extracellular space; measured in millivolts.

Membrane potential

What serves as a site for microtubule and microfilament assembly?

Microtubule-organizing centers (MTOCs)

Concerning ion transport, how can passive carriers be distinguished from active transporters (pumps)?

Passive dissipates concentration gradients, while active builds concentration gradients

What is a motor protein?

Proteins or enzymes that move vesicles along MT and use ATP hydrolysis to move

In vitro and under steady state conditions, the critical concentration (Cc) of the barbed end of a filament is 0.1 um, and the Cc of the pointed end of this filament is 0.6 um. If the concentration of actin-ATP monomers is 0.3 um, what would happen to this actin filament?

The barbed end will grow by adding monomers while the pointed end will shrink by losing monomers

Explain the mechanism of a voltage-gated channel.

The voltage gated Ca+ channel opens, neurotransmitter released, received into transmitter

Actin exists in cells in two major forms called G actin and F actin.

True

After insulin signaling, GLUT4 is transported to the membrane of various cells to increase glucose transport in tissues (But not if you have Type II Diabetes).

True

By changing the proteins within its membrane, our cells can be made to function very differently.

True

GLUT1 transports glucose across the blood brain barrier.

True

GLUT2 initially transports glucose into the pancreas after eating, allowing insulin to be released into the bloodstream.

True

GTP cap in a microtubule is found only on the plus end of the microtubule.

True

GTP cap in a microtubule is spontaneously lost over time by hydrolysis of GTP to GDP in the tubulin subunits.

True

GTP cap in a microtubule promotes the elongation of the microtubule in which it is found.

True

K+ ions have a smaller hydration shell than Na+ ions, allowing the passage of hydrated K+, but not Na+, through the selectivity filter of the K+ channel.

True

Passive carriers dissipate concentration gradients, activate transporters build concentration gradients.

True

The K+ channel is gated closed to Na+ and only opens when it "senses" K+.

True

The Na+/K+ ATPase pumps Na+ from the cell into the blood, maintaining low Na+ levels in the cell.

True

The actin cytoskeleton generates cell movement in the following way: Directed polymerization of actin filaments against the plasma membrane and the interaction of actin filaments and the motor protein myosin.

True

The action of the Na+/K+ ATPase pumps maintains an excess of Na+ ions outside the cells and an excess of K+ ions inside the cell. The K+ ion channels are unidirectional and only allow the transport of ions out of the cell.

True

The central cavity of the K+ channel can only accommodate hydrated K+ but not hydrated Na+.

True

The microtubule-organizing center (MTOC) nucleates microtubule assembly.

True

Do motor proteins undergo conformational changes when the motor travels?

Yes

Co-transport of nutrients across the intestinal cell membranes is an active process that can move glucose against a concentration gradient. The energy requiring step for co-transport is: a. The Na+/K+ ATPase that pumps from the cell into the blood, maintaining low Na+ levels in the cell b. The permease (transporter) that allows glucose and Na+ into the cell requires ATP c. The permease (transporter) that pumps glucose from the cell into the blood requires ATP d. The Na+/K+ ATPase that pumps Na+ from the cell into the lumen of the intestine

a. The Na+/K+ ATPase that pumps from the cell into the blood, maintaining low Na+ levels in the cell

The binding of _______ forms bundles of parallel actin filaments.

crosslinking proteins

In a typical animal cell, which of the following types of transport would increase at a linear rate (no saturation) proportional to the concentration gradient? Roughly draw Na+, Ca2+, Cl-, and K+ distributions inside and outside cell. a. Movement of amino acids into a cell b. Movement of Na+ out of a cell c. Movement of glucose into a cell d. Movement of Na+ into a cell e. Movement of K+ into a cell

d. Movement of Na+ into a cell

Concerning ion transport, how can passive carriers be distinguished from active transporters (pumps)? a. passive carriers are localized to the basolateral membrane of epithelial cells, active transporters are localized to the apical membrane b. Passive carriers consume ATP energy when they transport ions, active carriers create ATP c. Passive carriers contain beta sheets in the transmembrane domains, active carriers contain alpha helicies d. Passive carriers dissipate concentration gradients, active transporters build concentration gradients e. Passive carriers transport sugars, active carriers transport ions

d. Passive carriers dissipate concentration gradients, active transporters build concentration gradients

Membrane proteins called ____ channels open to allow ions to flow in and out of the cell when the concentration of ions nearby is changed.

ion

Under normal physiological conditions during elongation, the barbed end of an actin filament is called ____ , is capped by _____ and structurally different than the _____ end.

plus gelsolin minus

The force generating powerstroke of myosin along an actin filament occurs when myosin ______________.

releases Pi but is still bound to ADP

Cells can continue to import glucose molecules even when the cytoplasmic concentration is very high. This would be an example of _______ type of transport.

secondary active

The Na+/K+ transporter is a well-studied example of _______ type of transport.

secondary active (antiporter)

Tubulin dimers may assemble at the plus end and disassemble at the minus end simultaneously in a process known as _____.

treadmilling.

Specific amino acids that line the selectivity filter of the K+ channel can dehydrate K+ and allow passage of that ion but cannot coordinate the dehydration of Na+. True or False

true