Exam 3 Cell Bio

Question 1

Six Plasma Membrane Transport Systems

Answer 1

Na+/K+ Pump
Na+ Leak Channel
K+ Leak Channel
Voltage Gated Na+
Voltage Gated K+
Voltage Gated Cl2+

Question 2

Na+/K+ Pump Facts

Answer 2

Active
Na+ in
K+ out
ATP Driven

Question 3

Na+ Leak Channel Facts

Answer 3

Passive
Na+ in
Electrochemical gradient
Ungated

Question 4

K+ Leak Channel Facts

Answer 4

Passive
K+ out
Electrochemical gradient
Ungated

Question 5

Voltage Gated Na+ Facts

Answer 5

Passive
Na+ in
Open at -40 mV to +40 mV
Gated

Question 6

Voltage Gated K+ Facts

Answer 6

Passive
K+ out
Open at +40 mV to -70 mV
Gated

Question 7

Voltage Gated Cl2+ Facts

Answer 7

Passive
Cl2+ in
Electric signal

Question 8

How does an ion fit through an ion channel?

Answer 8

An ion is coated in water molecules that act as a water shell.

The water shells are released in the vestibule of the channel protein and ions enter the selectivity filter through the membrane.

Outside of the membrane, ions are surrounded once more by water shells.

Question 9

How does a membrane maintain its membrane potential?

Answer 9

When (+) and (-) charges are evenly spread in and out of the cell, the membrane potential is 0.

Positive charges can line up against one side of the membrane and negative charges can line up against the other side of the membrane.

This creates the membrane potential.

Question 10

Three stimuli that influence ion channels opening

Answer 10

1. Mechanically gated
2. Ligand-gated (intra or extracellular)
3. Voltage-gated

Question 11

Voltage-gated Na+ channel conformation steps

Answer 11

1. Depolarization: -40 mV: Na+ gate opens allowing ions to leave
2. Propagation: Ions continue transferring increasing mV.
3. Resting: Cell hits +40 mV and is inactivated.
4. Repolarization: Cell slowly decreases to -70 mV due to K+ entering the cell, the channel is reactivated/closed at -60 mV.
5. Depolarization eventually occurs again.

Question 12

How do action potentials affect neurons?

Answer 12

1. Ca2+ channels are closed in the presynaptic cell.
2. Electric signal is received in the form of an action potential.
3. This signal opens the Ca2+ channels.
4. This triggers neurotransmitters (chemical signals) to be released.
5. Neurotransmitters cross the axon.
6. They are received by neurotransmitter-gated ion channels or receptors in the postsynaptic cell.
7. They are then converted back to electric signals.

Question 13

Endosome purpose

Answer 13

Sorting of endocytosed material

Question 14

Peroxisomes

Answer 14

Oxidative breakdown of toxic molecules

Question 15

Rough ER Purpose

Answer 15

Ribosomes are freely moving and embedded into the membrane for protein creation.

Question 16

Smooth ER Purpose

Answer 16

Lipid synthesis and function

Question 17

Golgi Apparatus

Answer 17

Receives proteins and lipids for modification, sorting and packaging for secretion or delivery to other organelles

Question 18

How do proteins know where they should be transported?

Answer 18

Their mRNA encoded a signal sequence that is specific to where they need to be moved in the cell

Question 19

Signal recognition particle

Answer 19

A particle in the ER that binds to a growing polypeptide and moves it to bind to an SRP receptor in the ER membrane.

SRP is then released for reuse.

Once in the membrane, the ER signal sequence is no longer required and cleaved off by signal peptidase.

Question 20

Hydrophobic Signal Sequences

Answer 20

A sequence in a polypeptide.

SRP binds to a signal sequence generated by a ribosome and mRNA.

The short polypeptide enters a transmembrane protein translocator then the ribosome moves the polypeptide along in making it.

Once the translocator comes to the hydrophobic stop-transfer sequence, the protein translocator is removed and the polypeptide remains in the membrane where it is.

The signal sequence is cleaved off with signal peptidase

A polypeptide may be locked twice into a membrane with a start-transfer and stop-transfer signals. Or it may enter the ER membrane fully

Question 21

Exocytosis

Answer 21

Vesicular transport out of the cell

Question 22

Endocytosis

Answer 22

Vesicular transport into the cell

Question 23

receptor-mediated endocytosis

Answer 23

Clathrin-coated vesicles are surrounded by coats made of two multimeric proteins, clathrin and adaptor protein, to bring macromolecules to a cell

provides the driving force to induce a flat membrane to form a spherical vesicle

Question 24

triskelion

Answer 24

basic unit of clathrin lattices (triplet patterns emanating from a center)

-Vertex
-Clathrin light chain
-Clathrin heavy chain
-Terminal globular domain

Question 25

Clathrin-coated vesicles transport process

Answer 25

1. A cargo receptor in the plasma membrane receives an external cargo molecule 2. Internal receptor binds to adaptin 3. More cargo molecules and adaptin are bound 4. Clathrin bind to adaptin and the membrane begins distorting inward 5. Dynamin begins cutting off part of the membrane to contain the cargo molecules in a vesicle. 6. Eventually, the vesicle moves to transport the cargo and clathrin-adaptin is released

Question 26

LDL meaning

Answer 26

Low-density lipoproteins Hydrophilic on the outside and hydrophobic on the inside Type of cholesterol

Question 27

LDL process

Answer 27

1. LDL binds to LDL receptors 2. Receptor changes confirmation 3. Adaptin binds to receptor 4. Clathrin binds to adaptin and triskelion formation distorts membrane 5. Dynamin pinches off plasma membrane to a clathrin-coated vesicle 6. Uncoating ATPase removes clathrin-coat 7. The naked vesicle binds to endosome 8. The pH of endosomes are about 6.5 and breaks hydrogen bonds 9. Receptor breaks free of cargo as it enters endosomes due to lower pH 10. Endosome sorts and send to the lysosome 11. pH continues breaking down lipoproteins with hydrolytic enzymes that break down peptide bonds 12. Proteins are broken down to amino acids 13. The lipids are then available for free use as cholesterol 14. It will then travel as other lipoproteins to other parts of the body

Question 28

Transcytosis

Answer 28

the transfer of molecules to a new part of the membrane

Question 29

Explain how membrane potential is governed by the permeability of a membrane to specific ions.

Answer 29

The more permeable the membrane is to a particular ion, the more that ion will contribute to the overall electrical charge across the membrane

Question 30

Understand how transmitter-gated ion channels in the postsynaptic membrane convert the chemical signal back into an electrical signal.

Answer 30

when a neurotransmitter binds to them, allowing specific ions to flow across the cell membrane, which in turn changes the membrane potential and generates a localized electrical signal in the postsynaptic neuron

Question 31

Explain how signal sequences direct proteins to the correct compartment

Answer 31

They are directed by ribosomes who have "read" the signal sequence unique to the next location of the protein

Question 32

Full mRNA to rough ER peptide process

Answer 32

--mRNA transcription in cytoplasm on ribosome --Signal sequence transcribed and ribosome stops transcribing --Signal recognition particle (SRP) binds to signal sequence and molecule moves to rough ER --SRP binds to SRP receptor in rough ER membrane --Signal sequence growing peptide chain moved to protein translocator --SRP and receptor displaced for reuse --Ribosome continues transcription

Question 33

Understand how proteins are modified in the ER and Golgi apparatus and further sorted in the Golgi.

Answer 33

--Protein built in rough ER and dedicated for new organelles are glycosylated in the ER lumen --A sugar/mannose is added to arginine in a signal sequence --The mannose on the protein binds to a receptor in the ER membrane --A vesicle buds and the vesicle is directed to the cis-Golgi --Phosphate is added to the mannose of the protein to create mannose-6-phosphate in the protein --The protein is transferred through the medial Golgi to the trans-Golgi --The protein binds to the mannose-6-receptor and a vesicle buds

Question 34

Illustrate how lysosomal proteins get to the lysosome.

Answer 34

--The vesicle transports a protein+mannose+phosphate from the rough ER to the endosome --The vesicle fuses with the endosome and due to the lower pH of 6.5, the phosphate group is broken off of the protein --The phosphate is returned to the Golgi via a new vesicle --The protein with mannose binds to a new receptor that brings it to a lysosome with a pH of 4.5 --This lower pH and hydrolytic enzymes break down the bond between the sugar and protein, along with any peptide bonds in the protein

Question 35

Explain the process of vesicle docking including the role of tethers and SNAREs.

Answer 35

--A Rab protein on a vesicle acts as a docking station --The Rab protein uses energy (ATP) to bind to two tethering SNARES --Conformational changes of the t-SNARE occur to bring the vesicle closer to the plasma membrane --T-snares of the target membrane bind to v-snares to create coiled coils (alpha helices structures binding together) --The vesicle is pulled so close to the plasma membrane that cytoplasm is pushed out of the way and the plasma membranes fuse --Cargo particles are released into the cell --Vesicle cell membrane components are merged into the target cell --ATP unsnares t- and v-SNARES for reuse --v-SNARES are returned to the originating plasma membrane via vesicles

Question 36

Exocytosis - Secretory

Answer 36

--Vesicles store concentrated secretory proteins --As the action potential signal is received, the vesicle can bind to receptors in the plasma membrane --The vesicle is able to release the secretory proteins into the extracellular space

Question 37

Exocytosis - Unregulated

Answer 37

--Vesicles are constantly moving to a plasma membrane and releasing cargo proteins from their cargo