Cell bio main terms

what is the difference between bacterial and eukaryotic cell membranes?

bacteria only have one plasma membrane, eukaryotes have a different membrane for each cell

What are the three classes of membrane lipids?

phosphoglycerides, sphingolipids, sterols

What are the four major head groups of phosphoglycerides

PC, PE, PS, PI, determines what type of phospholipid we use

what are the three components of phosphoglycerides?

glycerol backbone, tails, heads

sphingolipids

usually make up nerve cells, consist of fatty acid chains connected by an amide bond

sterols

membrane components that stiffen the membrane

what 3 parts of the cell do not have a single plasmamembrane

nucleus, mitochondiron, chloroplast, need to trap PMF

cholesterol

fills the gaps between phospholopid molecules, increases fluidity in cold temps

flippase

uses ATP to flip phospholipids into the cell

what are the two main phospholipids affected by flippase and turned out of the cell?

phosphatidylcholine and sphingomylin

what two molecules are affected by flippase and flipped into the cell

PS and PE

The presence of PS on the cell surface serves as a signal that directs the rapid removal of dead cells. How might this be engineered by the cell?

by activating scramblease and inactivating flippase

where does the synthesis of transmembrane proteins start?

on cytosolic ribosomes with the help of SRP

what type of fold crosses the membrane in a TMP?

alpha helices, with the hydrophobic side in the membrane

What are the hydrophobic amino acids?

any that are not polar

What are the steps of the FRAP procedure?

• Label molecules – Scientists attach a glowing tag (fluorescent dye) to molecules in a cell.

• Photobleach a spot – They use a strong laser to “bleach” (turn off the glow) in a small area.

• Watch recovery – Over time, unbleached glowing molecules move into that area.

  • Measure movement – The return of fluorescence shows how fast and freely molecules are moving.

selectins

transmembrane proteins that recognize sugar cells on neutrophils in the blood

what determines the lateral movement of lipids in the membrane?

temp, fatty acid tails, membrane composition

what side of the membrane would you find carbs?

outside because they aid in cell signaling

A researcher inhibits ATP production in a cell. Which membrane process will be most directly affected?

 

Flippase-mediated phosphatidylserine transport

A mutation causes constitutive (permanent) activation of scramblases in the plasma membrane. What is the most likely consequence?

 

Exposure of phosphatidylserine on the outer leaflet

Which organelle primarily relies on scramblases to maintain a symmetric lipid bilayer?

 

Endoplasmic reticulum

A drug selectively inhibits floppases. Which lipid distribution change is most likely?

 

Accumulation of phosphatidylcholine on the cytosolic leaflet

During apoptosis, which enzyme activity increases to signal phagocytic cells remove apoptotic bodies or cells?

Scramblase

A vesicle budding from the Golgi is enriched in specific lipid asymmetry. Which enzymes contributed MOST to this?

 

 

Flippases and floppases

Which process occurs WITHOUT energy input?

 

Scramblase activity

A scientist observes that a cell maintains high levels of phosphatidylserine on the cytosolic leaflet despite constant membrane turnover. Which mechanism explains this?

 

ATP-dependent inward transport by flippases

what is the difference between transporters and channels?

transporters move solutes via active transport

channels move ions via passive diffusion

what is the membrane permiable to from most to least?

small nonpolar molecules (O2), small uncharged polar molecules (H2O), large uncharged polar, ions

why is the membrane not permeable to ions?

keeps the concentration/ proton gradient

how do animal cells prevent osmotic swelling?

pumping out water Ions

passive transporters

move solutes along their natural electrochemical gradients

active transporters

pump against the proton gradient of a solute, usaly coupled with enerfgy source

SERCA

the main Ca2+ pump in muscle contraction (out into cytoplasm) and relaxation (in to serca)

what is the difference between a pump and a channel?

a pump undergoes a conformational change, channels dont

Na/K pump

3 Na out and 2K in, NA returns thorugh other channels

If a vesicle that is 1mM glucose adn 1mM NaCL was placed into distilled water, what would happen the fastest?

H2O would diffuse in

What makes something soluble in water?

polar, uneven charge distribution

ion channels

ion selective and gated based on size and charge

membrane potential

goverend by the permeablilty of a membrane to specific ions

look up membrane potential calculations

ok

what are teh different types of ion channels?

voltage gated, ligand gated, mechanically gated, light gated

voltage gated Na+ channel

at rest where the are positive amino acids, opens when there is depolarization of the channel

action potentials

use voltage gated ion channels to relay messages throughout the body

if the action potential (depolarization) was increasedm what would be the effect in nerve cells?

Na+ channel inactivation would be slowed

what happens when the Na+ channels of axons open?

Depolarization, action potential, reversal of polarity

ABC (ATP Binding Cassette) transporters

ligand gated channels that allow Cl- and HCO3- ions out of the cell

What is an example of mechanically gated channels?

basilar membrane in the ear, moved by sound vibrations

How do transporters and channels select which solutes to move across the membrane?

channels: discriminate based on size and charge

transporters: bind solutes with high specificty like enzymes

how did nuclear and ER membrane evolve

invagination of the plasma membrane

what are the three mechanisms for protein sorting?

pores, across membranes, vesicles, all require E

which mechanism do proteins remain folded in transport?

pores, vesicles

what transport mechanism requires proteins to be unfolded?

transport across membranes

what directs proteins to the correct compartment?

Signal sequences

Nuclear protein sorting

proteins enter through nuclear pores and contain a nuclear localization signal

where do the nuclear import receptors return to after they import cargo?

cytosol for recycling

Ran-GTP

binds to importins and releases cargo brought into the nucleus

Ran-GDP

causes dissociation of ran from import receptor for reuse

Ran GAP

Switched Ran GTP to GDP causing dissociation from receptor, keeps in cytoplasm

Ran GEF

Switches Ran GDP to GTP, binding to receptor and keeps it in nucleus

what would be a result of no Ran GEF?

Failure of cargo proteins to be released from import into the nucleus, accumulation of transport molecules

protein sorting in mitochondria and chloroplasts

requires unfolding and a signal sequence, slides along the outer membrane until it aligns with inner membrane translocator

what is the order of import for a protein in mitochondria and chloroplasts?

OM receptor, OM translocator, IM translocator, Matrix

what type of proteins need to be imported into the mitochondrial matrix?

TCA enzymes, most things the mitochondrial ribosomes cant make

where must proteins go when they are being synthesized?

the ER

what are the 3 parts of an ER signal sequence?

hydrophillic positive N region, hydrophobic middle (5-15aa), c-region with cleavage site

what happens if the ER stop transfer sequence is in the middle of the protein?

it becomes a transmembrane protein

what happens if the ER signal sequence is removed?

the protein remains in the cytosol

what happens if the stop transfer sequence of a protein is removed?

it will go all the way through the translocator into the lumen

dynamin dependent uptake

requires dynamin to pinch off membrane when destination is reached

dynamin independent uptake

have other mechanisms that dont require pinching off the membrane

adaptins

capture correct cargo that is coming into the cell

clathrin

coat cargo assigned to them by adaptins

Clathrin coated vesicles

clathrin plays no part in choosing specific molecules for transport, adaptins deterimine this

what is an example of receptor mediated endocytosis?

import of cholesterols

how does the endocytosis of cholesterol occur?

adaptin binds to LDL receptor tail, recruits clathrin to form vesicle, fuses with endosome, LDL released by lysosome

SNAREs

aid in fusing vesicles to their target membranes

Rab proteins/ tethering proteins

work together to deterime the destination of a vesicle and direct it to its target

Proteins destined for the ER are typically directed by:

 

An N-terminal signal sequence

How do most proteins enter the ER?

 

Co-translational translocation

Which component recognizes the ER signal sequence?

SPRs

Which molecule provides directionality (moving things in one direction) in nuclear transport?

 

Ran GTPase

Proteins entering mitochondria must:

unfold

Which transport requires proteins to remain folded?

nuclear

A newly synthesized protein in the ER fails to receive proper N-linked glycosylation. What is the most likely outcome?

The protein misfolds and is retained in the ER

A patient lacks the enzyme required to add fucose to the H antigen precursor. What blood type phenotype results?

bonbay

A slightly misfolded protein is synthesized in the ER. What determines whether it exits the ER?

 

Recognition by ER quality control mechanisms

Cisternal maturation

 

Golgi cisternae themselves move and mature over time

what is an example of regulated exocytosis?

insulin release

If the LDL receptor cannot release LDL in the endosome, what is the likely consequence?

 

LDL and receptor remain bound, disrupting recycling

Which is NOT a possible fate of receptors after endocytosis?

immediate secretion outside of the cell

What happens if the lysosomal H⁺ pump is nonfunctional?

 

Lysosomal pH increases, reducing enzyme activity

What is the fate of macromolecules (proteins) in the endocytic (endocytosis) pathway after they have been internalized and reach the early/sorting endosome?

they are degraded in the lysosomes, or diverge into a different plasma membrane through transcytosis, or return to the same plasma membrane where they originally resided.

what is the difference between A and O blood?

A has NAG

what method replaced radioative molecule tagging?

Green flourecent protein because it is safer

constitutive scretory pathways

happens all the time, supplies plasma membrane with lipids and proteins