molecular exam 4, 1

most biological membranes are ___

inside the cell, not just on the plasma membrane on the outside of the cell

compartmentalization

how eukaryotes use internal membranes to divide the cells into organelles

each with distinct environments, molecules and functions

eukaryotes are highly

compartmentalized

____ dominate cell surface area

intracellular membrane systems

membranes= __ specialization

biochemical

membranes form a

trafficking network

components of a phospholipid

a hydrophilic head

2 hydrophobic fatty acid tails

hydrophilic head contains

a polar group

a phosphate group

a glycerol backbone

this all interacts with water

hydrophobic tails contain

long hydrocarbon chains

function of hydrophobic tails

to make the membranes selectively permeable

amphipathic

molecules that have hydrophobic and hydrophilic regions

hydrophobic interior forms a __ for

barrier for ions, prevents polar molecules and water soluble substances from crossing freely

traits of hydrophobic interior

oily

non polar

hydrophobic interior allows for

gradients

signaling

compartmentalization

phospholipids __ due to their

self-assemble due to their dual nature

the biological membrane is composed of

phospholipids

proteins

cholesterol

carbs

the biological membrane behaves like a

2 dimensional fluid

phospholipids and proteins move

laterally

phospholipids and proteins movement essential for

signaling

membrane repair

protein redistribution

the molecules that are embedded in the membrane are

transmembrane proteins

lipid-anchored proteins

peripheral proteins

cytoskeleton attachments

=mosaic

the cytoskeleton is linked to

proteins

cytoskeleton functions

helps to maintain cell shape

helps control protein distribution

helps direct membrane movement (endocytosis and exocytosis)

membrane= identity platform, meaning proteins determine

signaling

transport

cell types specificity

membranes are dynamic meaning there is

constant movement that gives resilience

plasma membrane defines the

cell and separates the cytosol from the extracellular environment

fluidity

non-covalent interactions between phospholipids

proteins in membranes

integral membrane proteins

lipid anchored proteins

peripheral membrane proteins

integral membrane proteins

transmembrane proteins

span the entire bilayer

often form dimers

integral membrane proteins used for

transport

receptors

adhesion

integral membrane touch

hydrophobic interior and polar surfaces

integral membrane proteins have 1 or more

alpha helical or beta sheet transmembrane motif

lipid anchor proteins are __ attached to a

covalently attached to a lipid

lipid anchor proteins mediate

signaling and anchor proteins locally

peripheral membrane proteins are __ bound to

non covalently bound to polar heads or other proteins

peripheral membrane proteins sit on the

surface

peripheral membrane proteins often connect to the

cytoskeleton

cadherins in an adherins junctions

cell to cell adhesion structure found in tissues, especially in epithelial sheets

cadherins

transmembrane proteins that glue cells together

catenins

link cadherins to the cytoskeleton

a-catenin connects to

actin filaments

cadherin adhesion is physically linked to the__ and maintains

internal scaffolding of the cell

maintains tissue structure and communicates mechanical signals

if a protein has an ER signal, it enters the

secretory pathway

secretory pathway is for proteins that

get secreted out of the cell

end up in membranes

become lysosomal proteins

protein location is dictated by

signal sequences (short amino acid codes that tell the cell where the protein belongs

proteins are synthesized in the

cytosol

golgi=

sorting and modification hub

tracks where proteins should go

vesicular transport is

bidirectional

some secretion is __ and some is

automatic and some is controlled

lysosomes receive materials from 2 major pathways

the golgi and endocytosis

a donar compartment holds __ that that has proteins that need to be

cargo that has proteins that need to be transported

membrane bound organelles send material to other organelles using

vesicles that bud from one compartment and fuse with another

budding

a small piece of membrane bulges outward and pinches off, forming a vesicle

the vescile that budded off contains

cargo

membrane proteins for transport

identity tags

budding requires __ proteins

coat

motor proteins move the vesicle on

microtubules

transport between organelles is the main mechanism of

intracellular transport

vesicle transport occurs in 2 coordinated steps

budding (vesicle formation)

fusion (delivery to target membrane)

what does the cell use to make vesicle transport accurate

coat proteins

GTPases

SNAREs

coat protein functions

shape the membrane

select cargo

concentrate the vesicle contents

3 types of coat proteins

COPI

COPII

Clathrin

COPI path

golgi and c-golgi → ER

golgi recycling

COPII path

ER → c-golgi

clathrin path

plasma membrane -> endosome or trans-golgi→ endosome

endocytosis

2 types of SNARE proteins

v-snares (on vesicle)

t-snares (on target membrane)

vesicles must __ before fusion

uncoat

what starts vesicle formation

sar1 and ARF

gtp hydrolysis provides energy for

vesicles to pinch off

cell rescues proteins that belong in the ER but sometimes get swept forward into the golgo with

a retrieval signal called KDEL (C terminal sequence)

mutations in KDEL=

proteins get secreted

what does KDEL do at low and high pHs

low: binds proteins

high: releases proteins

golgi cisternase (stacks) mature as they move forward from

cis → medial → trans

golgi enzymes themselves move __ in vesicles

backwards

proteins that are meant to stay in cis, medial or trans compartments have

retention signals

what is the TGN

trans-golgi network

final sorting station of the golgi

the TGN sends proteins in 3 directions

constitutive secretion

regulated secretion

lysosome/endosome pathway

constitutive secretion

vesicles leave and fuse with plasma membrane

no special signal required

“always on” secretion

regulated secretioon

vesicles wait in storage until a signal triggers release

released in bursts

“held until told to go” signal

lysosome/endosome pathway

proteins destined for lysosomes or late endosomes

these carry sorting signals and are packaged into clathrin vesicles

retrograde transport

movement of materials back towards the center of the cell

why endosomes matter

they sort cargo

they decide whether proteins are recycled back to membrane or sent to lysosome to be degraded