Unit 1: Introduction to Cell and Molecular Structures/Function

Question 1

At the beginning of transcription, one of two things can happen to the protein that is going to be formed depending on what type of protein it is. What is the process that MEMBRANE-BOUND PROTEINS, such as receptor and ion channels, undergo?

Answer 1

Translocation, in which the type that we specifically talk about for the scope of this class is COTRANSLATIONAL-TRANSLOCATION.

Question 2

What differentiates co-tranlational translocation from the alternative process by which proteins are traditionally synthesized? Specifically, describe a STRUCTURAL difference that occurs during TRANSCRIPTION.

Answer 2

The additional of a amino-acid signal sequence is added on for soon-to-be proteins undergoing COTRANSLATIONAL-TRANSLOCATION

Question 3

Describe the function of SRP’s in terms of CO-TRANSLATIONAL TRANSLOCATION

Answer 3

SRP’s, or SIGNAL RECOGNITION PARTICLES, are charged with identifying ribosomes that have specific amino-acid sequences attributed to this process. SRP’s mediate the process of co-translational translocation

Question 4

Where does the polypeptide chain go in COTRANSLATIONAL TRANSLOCATION?

Answer 4

Through the mediation of SRP’s, the polypeptide chain is fed through the interior of the ER LUMEN due to its corresponding ribosome docking on the membrane-bound translocon, allowing the ribosome to open up so that the chain can feed directly through.

Question 5

Describe the differences between the function of the GOLGI APPARATUS and the ER

Answer 5

While the ER was moreso concerned with forming secondary and tertiary structures of proteins, the GOLGI is involved with storing, packaging, and modifying proteins as need be as they pass through the different components of the golgi (cis - medial - trains) and are examined for any sign of misfolding (lysosomes or taken back a step) or need for modification.

Question 6

What is the purpose of CLARATHIN and DYNAMIN in terms of VESICULAR TRANSPORTATION

Answer 6

Typically, proteins are transported through vesicles. Vesicles are coated with specialized proteins that designate and signal the direction the vesicles needs to go. Clarathin + API is one such combination that signals that a vesicle needs to go from the TRANS-GOLGI to an ENDOSOME! In order for the vesicle to bud off from the membrane and be closed off to roam the cytosol, DYNAMIN is in charge.

Question 7

What type of signaling pattern is evident at a CHEMICAL SYNAPSE? ELECTRICAL SYNAPSE?

Answer 7

Chemical - Paracrine (signaling with nearby cells)
Electrical - Juxtacrine (direct physical signaling between cells)

Question 7

Describe the ORDER OF SIZING for the following: MICROTUBULES, MICROFILAMENTS, NEUROFILAMENTS

Answer 7

In order for largest in diameter to smallest, it would be MICROTUBULES, NEUROFILAMENTS, and MICROFILAMENTS

Question 8

T/F: All cytoskeletal structures are POLAR in nature

Answer 8

FALSE! Of the three, NEUROFILAMENTS are stable and NON-POLAR unlike the other cytoskeletal structures.

Question 9

T/F: Axonal transport mechanisms are all passive in nature.

Answer 9

FALSE! Axonal transport is an active process.

Question 10

What is the DIFFERENCE between SLOW and FAST AXONAL TRANSPORT?

Answer 10

While both SLOW and FAST axonal transport are active processes, FAST involves membraneous organelles that travel in RETROGRADE (towards AXON) and ANTEROGRADE (towards SOMA) fashion at a much faster rate than SLOW axonal transport, which is for moving cystolic and cytoskeletal proteins in an ANTEROGRADE FASHION ONLY

M - myosins
K - kinesins
A - anterograde
—–
R - retrograde
D - dyenins

Question 11

What is LOCAL PROTEIN SYNTHESIS?

Answer 11

Recall that dendrites have RIBOSOMES, and thus can engage in PROTEIN SYNTHESIS when mRNA is taken through to the site where the protein will be needed for the MICROTUBULES and MICROFILAMENTS

Question 12

Which TYPE of GLIAL CELLS are found in the CNS?

Answer 12

Astrocytes, Oligodendrocytes, Microglia, Ependymal Cells, Radial Glia

Question 13

Which TYPE of GLIAL CELLS are found in the PNS?

Answer 13

Schwann and Satellite Cells

Question 14

Describe the DIFFERENCE in GATE COUNT for PORES, ION CHANNELS, and CARRIERS

Answer 14

Pores, or ion channels that are always open, have 0 GATES
Ion channels have 1 GATE
Carriers have 2 GATES

Question 15

Describe the DIFFERENCES and SIMILARITIES between ANTIPORTERS and SYMPORTERS

Answer 15

Antiporters are carriers/ion channels that allow for ions to travel in different directions, while symporters are carriers/ion channels that allow ions to travel in the same direction. Antiporters and symporters are typically both affiliated with active transport

An example of an ANTIPORTER is the sodium potassium pump in which 2K+ pumped IN, 3 Na+ pumped OUT (against concentration gradient, powered by ATP through PRIMARY ACTIVE TRANSPORT)

An example of a SYMPORTER is the sodium glucose co-transporter in which the movement of SODIUM DOWN CONCENTRATION GRADIENT powers movement of GLUCOSE inside and AGAINST its CONCENTRATION GRADIENT (powered by the electrochemical difference of sodium across the membrane, SECONDARY ACTIVE TRANSPORT)

Question 16

How are ion channels SELECTIVE?

Answer 16

The primary mechanism of ion channel selectivity is the SELECTIVITY FILTER, which is a narrow passage in the channel that strips the water molecules from ions for them to pass through the narrow passage with amino acid residuals (if the weak electrostatic bonds they form with these residues is energetically favorable, then the ions will be propelled forward. The diameter of this narrow path also prevents ions from crossing through this area due to how torturous the path.

Question 17

Describe the difference between OHMIC and RECTIFYING (NON-OHMIC) channels

Answer 17

Recognize that the properties of Ohm’s Law (I = VR) designate a linear relationship in which as current increases, the voltage across the membrane increase, and the resistance decreases - an OHMIC CHANNEL will show this perfectly linear relationship of conductance, and can be seen in ion channels like voltage-gated sodium channels**

RECTIFYING channels do not perfectly abide by Ohm’s Law, as the conductance is EXPONENTIATED. At certain currents, the conductance increases much higher than would be expected in a perfectly linear relationship. An example is the inward-rectifying potassium channels. NOTE: these channels are NOT the same as leaky channels! They are still mediated by voltage and current, but they have greater conductance and thus less resistance at certain changes in potential.

Question 18

T/F: All aspects of ion channels are involved in PASSIVE transport through the means of faciliated diffusion.

Answer 18

FALSE!
While the passage of ions through ion channels is PASSIVE in nature as facilitated diffusion on its own is not a form of active transport, the conformational changes that allow ion channels to open and close their GATING mechanisms is inherently ACTIVE in nature (requires energy!)

Question 19

What are some POPULAR forms of CHANNEL GATE MODULATION?

Answer 19

This modulation can be in the form of REVERSIBLE (dissassociate easily) and IRREVERSIBLE (involves covalent bonding, much more diffiucult) antagonists that can bind COMPETITIVELY (active site, prevent endogenous ligand from binding entirely) or NON-COMPETITIVELY (allosteric site, seperate from where the endogenous ligand would bind) in an effort to modulate the receptor activity.

Question 20

Describe the differences between HETERO-OLIGOMERS, HOMO-OLIGOMERS, and AUXILLARY SUBUNITS

Answer 20

When categorizing ion channels, we can look towards the structural components of these channels to identify commonalities. Hetero-oligomers are subunits that do not all match one another, Homo-olgomers are subunits that do match one another (some further differentiation in these group is the differences in motifs or presence of repeating motifs), and the addition of auxillary subunits can act as sources of further modulation that are unique to specific ion channels.

Question 21

Describe the difference between a SUBUNIT, TRANSMEMBRANE DOMAIN and a MOTIF

Answer 21

Subunits are the first division of an ion channel, and they can be described in a collective with as hetero-oligomers, homo-oligomers, or auxillary (modulating). Transmembrane domains exist within the subunit of an ion channel, and they can thrive on their own as membrane-bound proteins (tertiary structures**). MOTIFS are secondary-protein structures typically in the form of alpha helices and beta sheets that bind to transmembrane domains and extend into extracellular and cytoplasmic, and as such, cannnot exist apart from the domains. The variations in these structures help with defining structural differences that can be found in families of these ion channels for classification.

Question 22

Describe the major difference between GAP JUNCTIONS and SELECTIVE ION CHANNELS

Answer 22

Gap junctions have a LARGE PORE and are relatively NONSELECTIVE in what they allow through (ions can generally pass, fluorescent dyes, etc). while SELECTIVITY FILTERS make ion channels much more selective when needed!