Cell Bio Hart Exam 3

diffusion is limited by...

Size, Ionic charge, and Polarity

membrane proteins

proteins that mediate transport of most molecules and all ions across membranes

simple diffusion

diffusion with no energy required, no transporter required, and occurs down the concentration gradient

facilitated diffusion

diffusion with no energy required, a transporter required, and occurs down the concentration gradient

includes channel proteins and uriporters

active transport and co-transport

diffusion with energy required, a transporter required, and usually occurring against the concentration gradient

includes symporters, anti porters, and ATP-powered pumps

multiple transmembrane a helices

structural property of most integral membrane transport proteins

GLUT1 Glucose Transporter

example of an integral membrane transport protein, involves conformational changes

Vmax (maximum velocity)

depends on the number of transporter proteins in the membrane

reach a maximum velocity

facilitated diffusion can be saturated (reach _______)

uniporters

GLUT1 and GLUT2 are _____

uniporter

are uniporters or passive diffusion faster?

Km

higher affinity = lower ___

GLUT1

which has a higher affinity for glucose? GLUT1 or GLUT2

Km

substrate at 1/2 Vmax

higher Vmax; Km remains constant

more transporters in facilitated diffusion means higher _____ while _____ remains constant

uniporters

carry one molecule at a time

mediated by conformational changes

specific for one species of molecule

concentration gradient

stored energy

GLUT1

transporter protein abundant in RBCs

higher glucose affinity

GLUT3

transporter protein in the brain/neurons

GLUT2

transporter protein in liver cells

takes up more glucose after eating, used for glycogen synthesis

lower affinity for glucose affinity

GLUT4

transporter protein in fat and muscle cells

imports glucose into cell via endocytosis in presence of insulin

GLUT5

transporter protein in intestinal epithelial cells

high specificity for fructose

liposomes

transport proteins can be purified and studied in artificial bilayer membranes called ______

osmotic pressure

_______ pressure causes water to move across membranes

aquaporin

water channels that increases cell permeability to water

channels

are channels or uniporters faster?

P-class Pumps

ATP-powered pump that pumps different ions (Ca2+, H+, Na+, K+)

energy from ATP hydrolysis drives transport against a concentration gradient

P-class Pump

ATP-powered pump with

2 alpha subunits that get phosphorylated during transport

2 beta subunits for regulation

only integral subunits

Asp is phosphorylated (weird)

V-class Pump

ATP-powered pump with

many integral and peripheral subunits

found in vacuolar and lysosomal membranes

and only pumps H+

F-class Pump

ATP-powered pump

found in mitochondria and chloroplasts

with many integral and peripheral subunits

and only pumps H+

usually uses H+ gradients to make ATP

V and F class pumps

which ATP-powered pumps are similar but not evolutionarily related? (convergent evolution)

ABC Superfamily (ATP Binding Cassette)

ATP-powered pump that

transports diverse molecules

with 4 domains - 2 transmembrane domains (channels)

and 2 cytosolic domains (ATP-binding domains)

ionic gradients and electric potential

____ gradients and _____ potential maintained across the plasma membrane by ATP-powered ion pumps

P-class Pump example

muscle Ca2+ ATPase pumps Ca2+ ions from the cytosol into the ER, allowing muscles to relax

involves pump phosphorylation and conformational changes

muscle Ca2+ ATPase

a type of P-pump with

-2 states- E1 (high affinity Ca2+ binding) and E2 (low affinity Ca2+ binding) based on AA side chain position

-multiple transmembrane a helices (4 bind Ca2+ during transport)

-excess cytoplasmic Ca2+ -> calmodulin binds Ca2+ -> activates Ca2+ pump to lower cytoplasmic Ca2+

P-class Na+/K+ ATPase

P-class pump that maintains the intracellular [Na+] and [K+] in animals cells

3 Na+ out, 2 K+ in per cycle

conformational changes, pump phosphorylation, distinct order of steps

H+ ATPase

V-class pump that pumps protons across mainly lysosomal and vacuolar membranes

V-class alone

do V-class pumps with or without an anion channel generate electric potential?

V-class plus anion channel

do V-class pumps with out without an ion channel have an acidic anterior but no electric potential?

ABC Superfamily

ATP-protein pump that binds and hydrolyzes 2 ATPs to drive conformational changes in each cycle

some are flippases

energy across a membrane

selective movements of ions creates a transmembrane electric potential difference

no movement = no electric potential

electrochemical gradient

ionic charge gradient + concentration gradient

K+ resting potential (-70mV)

membrane potential in animal cells depends largely on _________ resting potential

open K+ channels

K+ flows out the cell until the electric potential pushing it back in equals the ionic gradient pushing it out

K+ channels are homotetramers

only K+ can pass through K+ channels

only K+ can fit in K+ channels

hydration shells are lost in the channel, carbonyl oxygens take over shielding

Na+ is too small to be properly shielded in the channel

Na+ influx is used as an energy source, like ATP

Na+ entry into mammalian cells has a negative delta G due to a combination of the concentration gradient and membrane potential

symporters

co-transport can move ions and small molecules against concentration gradients and in the same direction

conformational changes involved

2 Na+/Leucine Symporter

Na+ loses its hydration shell during transport, fitting perfectly into its channel

co-transported Leu COO- has ionic interactions with Na+

antiporters

co-transport can move ions and small molecules against concentration gradients and in different directions

help regulate cell pH

plant vacuole function

what organelle utilizes

ion channels

antiporters

and V-class ATPase H+ pumps

transepithelial transport

Movement of substances through, rather than between, adjacent epithelial cells connected by tight junctions, such as absorption of nutrients in the small intestine.

tight junctions

Membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

apical membranes

Cell membranes in contact with intestinal lumen

basolateral membranes

cell membrane in contact with the blood

rehydration therapy

transport in the intestinal epithelium

apical membrane: 2 Na+/glucose symporter

basolateral membrane: K+/Na+ exchange P-class pump

parietal cells using a P-class pump

transepithelial transport in the stomach that causes acidification of the stomach lumen by_____ cells using a _____ pump

osteoclast cells using a V-class pump

transepithelial transport in ________ cells using a _____ pump for bone repair and maintenance

secretory pathway (bound) and soluble (free) ribosomes

how does the cell sort proteins to their correct locations?

targeting proteins to the ER via the secretory pathway

-nascent protein enters the ER co-translationally

-proteins destined for secretion will be inserted into the ER lumen

-proteins destined to reside in a membrane remain embedded in the ER membrane

Rough ER

organelle that is a series of flattened membrane sacs with surface ribosomes

the lumen of the ER

secretary proteins synthesized on surface ribosomes of the ER pass into ________

signal sequence on their amino terminal end

secretary proteins initially have a _______ sequence on their _________ end which is necessary for ER targeting

co-translational transport

ER membrane must be present during protein synthesis in order for protein to translocate

hepatocytes (liver cells)

cells which secrete albumin and transferrin in a constitutive manner

pancreatic acinar cells

cells which secrete digestive enzymes in a regulated manner

secretory pathway

1. co-translational import of proteins into or across the ER membrane

2. transport vesicles either fuse with the cis-golgi or form the cis-golgi reticulum

3. retrograde movement of vesicles back to the ER

4. cisternal migration (progression)

cisternal migration

part of the secretory pathway where

1. a cis-golgi stack physically moves to the medial position, then to the trans position

2. retrograde vesicles constantly move membrane back to keep Golgi-resident proteins localized

3. secretory proteins move outward to the trans-golgi reticulum

4. proteins are sorted by constitutive secretion pathway or stored secretory vesicles

constitutive (continuous secretion pathway)

one of 2 ends to cisternal migration where secretory vesicles fuse immediately with the plasma membrane

stored secretory vesicles

one of 2 ends to cisternal migration where there is regulated release of proteins by signal transduction (release of Ca2+ into the cytosol facilitates fusion of the secretory vesicle with the plasma membrane)

temperature sensitive sec mutations

mutations in yeast that affect secretion in different temperature conditions

cytosol

where does synthesis of secretory proteins begin?

ER signal sequence

sequence at the end secretory proteins, the first 16-30 basic AA residues at the amino terminus, that directs the ribosome to the ER and transport of nascent proteins across the ER membrane

SRP (signal recognition particle)

hydrophobic residues of the signal sequence bind the __________

SRP (signal recognition particle)

cytosolic complex partially assembled in the nucleolus that binds the hydrophobic signal sequence and the large ribosomal subunit (LSU) to direct them to the ER membrane

SRP

protein and RNA complex made of 6 proteins plus a single RNA of 300 nucleotides

Alu DNA elements are derived from this RNA

translocon

SRP binds the signal sequence and the ribosome LSU and stops further translation until it interacts with the ______ using GTP hydrolysis

SRP receptor

receptor in the ER membrane consisting of an a/B dimer

translocon

a set of transmembrane proteins that form a channel through the ER membrane where nascent chain continues to be synthesized, driven by GTP hydrolysis

covalent cross-linking

indeitification of translocon proteins by ______________ (method)

switch proteins; dissociation

P54 of SRP and the a subunit of the SRP receptor are _____ proteins, so GTP hydrolysis triggers _____ of SRP from the ribosome and its receptor

translocation:

-GTP binds SRP and its receptor, stabilizing the interactions and positioning the ribosome directly over the translocon

-the signal sequence is transferred from SRP to the translocon, inducing a conformational change, letting the peptide chain into the ER lumen

-hydrolysis of GTP occurs on SRP and its receptor, triggering dissociation of SRP from the ribosome and its receptor

-SRP returns to the cytosol to be recycled while translation continues in the ER lumen

translocation:

-___ binds SRP and its receptor, stabilizing the interactions and positioning the ribosome directly over the translocon

-the _______ _________ is transferred from SRP to the translocon, inducing a conformational change, letting the peptide chain into the ___________

-_________ of GTP occurs on SRP and its receptor, triggering dissociation of SRP from the ribosome and its receptor

-SRP returns to the cytosol to be recycled while translation continues in the ER lumen

rER; secretory protein

membrane proteins that reside in the plasma, ER, Golgi, and lysosome membranes are synthesized in the ______ and follow the same pathway as a _______ ________

orientation

___________ of the membrane protein within the membrane is determined while it is synthesized in the rER

type I membrane protein

-N-terminus in ER lumen, C-terminus in cytosol

-only to have signal sequence on N-terminus

type II membrane protein

-N-terminus in the cytosol, C-terminus in the ER lumen

-single internal signal-anchor (SA) sequence that is not cleaved

type III membrane protein

-N-terminus in ER lumen, C-terminus in cytosol

-single internal SA sequence that is not cleaved

-basic AA on carboxy side

Tail anchored membrane protein

-N-terminus in cytosol, C-terminus in ER lumen

-targets post-translationally to the ER

-v-SNARE, t-SNARE

Type IV membrane protein

-Contains two or more transmembrane domains

-N-terminus in ER lumen, C-terminus in cytosol

-GPCRs, voltage gated Ca2+ channels, glucose transporters, ABC pumps, Sec 61

GPI-linked membrane protein

N-terminus in ER lumen, no C-terminus

topogenic sequences

sequences that determine protein orientation within the membrane

stop-transfer anchor (STA)

sequence that serves as a membrane anchor, comes trans-membrane a helix

ex: insulin receptor (type I IMP)

signal-anchor (SA) sequence

-determine protein orientation

-act as signal sequence and membrane anchor

basic AAs

flanking sequence that carries the most ______ AAs remains on the cytoplasmic side

post-translationally

C-terminal tail-anchored proteins are _______________ inserted

Get3 ATPase (NOT SRP!)

what recognizes the topogenic signal of C-terminal tail-anchored proteins?

Get1/Get2, use ATP

where are C-terminal tail-anchored proteins transferred to for membrane insertion instead of the translocon? what do they use for energy?

multiple topogenic sequences

multipass transmembrane proteins have multiple ___________ sequences

common for ion channels

SRP only interacts with first SA

Type IV IMPs

GPI (glycosylphosphatidyl inositol)

instead of an a helix, some proteins are anchored to membranes by ____

cytosolic portion

some cells use GPI as anchors instead of a helices because it gets ride of the _______________ that may interact with the cytoskeleton