First half of chapter 5: Membrane Transport

Describe the plasma membrane structure

Structure– FluidMosaic Model

i. Lipids (bilayer)

ii. Carbohydrates (for recognition, adhesion, fluidity)

iii. Proteins (recognition, adhesion, TRANSPORT)

1. Integral

2. peripheral

Describe plasma membrane function

Selective permeability

How does the plasma membrane structure support its function

Through transport proteins:

1. channels (examples: aquaporins, ion channels)

2. Carriers (confirmational changes)

How does the plasma membrane preform its function through passive transport

Diffusion:

Osmosis(for water)

Facilitated diffusion (channels and carrier proteins)

What are the 4 types of osmosis

tonicity, isotonic, hypertonic, hypotonic

How does the plasma membrane preform its function through active transport

Ion pumps(sodium potassium, proton)

Co-transport (harness concentration of one thing to move something else)

Bulk transport(vesicles): exocytosis, endocytosis

What does it mean that the plasma membrane is a fluid mosiac model

its movable and maintains integrity

What can affect fluidity of the plasma membrane

temperature, lipid concentration (how packed together they are can make more or less fluid)

Variations in lipid composition of cell membranes of many

species appear to be adaptations to….

specific environmental conditions

Ability to change the lipid compositions in response to

temperature changes has evolved in organisms that live…

where temperatures vary

How do cells recognize each other

by binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane

Membrane carbohydrates may be covalently bonded to…

lipds (glycolipids) and proteins (glycoproteins)

Carbohydrates on the external side of the plasma

membrane vary among…

species, individuals, and even

cell types in an individual

What do integral proteins do

penetrate the hydrophobic interior of the lipid bilayer

Integral membranes span the _______ and are called ____________ proteins

membrane, transmembrane

What do the hydrophobic regions of integral proteins consist of?

one or more stretches of nonpolar amino acids, often

coiled into α helices

Where are peripheral proteins

loosely bound to the surface of the membrane

What are the six major functions of membrane proteins

Transport

Enzymatic activity

Signal transduction

Cell-cell recognition

Intercellular joining

Attachment to the cytoskeleton and extracellular matrix (EC

M)

What molecules can dissolve in the lipid bilayer of the membrane and cross it easily

Hydrophobic (nonpolar)

What molecules have a harder time crossing the membrane

polar molecules, water, sugar, ions

Transport proteins allow for what

passage of hydrophilic substances across the membrane

What are channel proteins

Transport proteins with a hydrophilic channel that certain molecules or ions can

use as a tunnel

What are aquaporins

Channel protein that facilitate the passage of water

What do carrier proteins do

Transport proteins that bind to molecules and change shape to shuttle them across the membrane (think of a revolving door)

What is a transport protein specific to?

The substance it moves

Diffusion is the tendency for molecules to

spread out evenly into the available space

Although each molecule moves randomly, diffusion of a population of molecules may be…

directional

At dynamic equilibrium, how many molecules cross the membrane?

as many molecules cross the membrane in one direction as in the other

Substances diffuse down their ___________ __________, from where it is more concentrated to where it is less concentrated

concentration gradient

Substances are affected and unaffected by which concentration gradients

Substances move down their own concentration gradient,

unaffected by concentration gradients of other

substances

The diffusion of a substance across a biological

membrane is passive transport because…

no energy is

expended by the cell to make it happen

What is osmosis

the diffusion of free water across a selectively permeable membrane

How does water diffuse across a membrane

from the region of lower solute concentration to the region of higher solute

concentration until the solute concentration is equal on both sides

What are characteristics of molecules that can easily go through the plasma membrane

small and nonpolar

What are characteristics of molecules that cannot easily go through the plasma membrane

large and/or polar

What does it mean if an animal cell is hypotonic

solute is less concentrated outside so H2O moves in, causing cell to lyse

What does it mean if an animal cell is isotonic

Solute is the same in and out, considered normal for animal cells

What does it mean if an animal cell is hypertonic

solute more on outside, h2o leaves cell, shriveling it up

What is tonicity

ability of surrounding solution to cause gain or lose water in the cell

What does it mean if a plant cell is hypotonic

h2o moves in causing cell to be turgid/firm, this is the normal state

What does it mean if a plant cell is isotonic

solute is the same inside and out causing flaccidity of the cell, this is ok but not ideal

What does it mean if a plant cell is plasmolyzed

h2o is coming out,the inside of the cell shrivels up. This is not good

In facilitated difussion what speeds up the passive movement of specific molecules across the plasma membrane

transport proteins

what do channel proteins provide

corridors that allow a specific molecule or ion to cross the membrane

what do channel proteins include

aquaporins, for facilitated diffusion of water

Ion channels, that open or close in response to a stimulus (gated channels)

How does active transport move substances

across membranes against their concentration gradients

What does active transport allow for

allows cells to maintain concentration gradients that differ from their surroundings

What does active transport require

energy, usually in the form of ATP

How does the sodium potassium pump work (6 steps)

What is membrane potential

the voltage across a membrane (difference in electric)

What is voltage created by

differences in the distribution of anions and cations across a membrane

What drives the diffusion of ions across a membrane

two combined forces, collectively called the electrochemical gradient

What are the two combined forces that make up the electrochemical gradient

a chemical force (the ion’s concentration gradient)

An electrical force (the effect of the membrane potential on the ion’s movement)

When does cotransport occur

when a transport protein can couple the “downhill” diffusion of a solute to the “uphill” transport of a second solute against its electrochemical gradien

What do plant cells use to drive active transport of nutrients into the cell

the gradient of hydrogen ions generated by proton pumps

How do large molecules, sush as polysaccharides and proteins cross the membrane

in bulk by means of vesicles

What does bulk transport require

energy

What are the 5 types of bulk transport

Exocytosis

Endocytosis

Phagocytosis (“cellular eating”)

Pinocytosis (“cellular drinking”)

Receptor-mediated endocytosis

What do human cells use receptor-mediated endocytosis to do

to take in cholesterol for membrane synthesis and the synthesis of other steroids

cholesterol travels in particles called

low-density lipoproteins (LDLs)

n the inherited disease familial hypercholesterolemia,what is defective or missing?

LDL receptors

In hypercholesterolemia, cholesterol accumulated in the blood, contributing to what

atherosclerosis