BSCI170 Choi Midterm 2

fluid mosaic model of the cell membrane (what is it and 2 main parts)

the structure and organization of the plasma/cell membrane

phospholipid bilayer and membrane proteins + carbohydrates

fluid part of the fluid mosaic model

phospholipid bilayer, cholesterol

mosaic part of the fluid mosaic model

membrane proteins, carbohydrates, things embedded w/in or associated w/ the lipid bilayer

how many proteins per phospholipid

1 per 25, but does vary depending on function

why are membrane proteins important

proteins or glycoproteins displayed on the cell surface can act as ID tags

Phospholipid bilayer (what is it made of and why is it important

made of phospholipids with hydrophilic and polar heads and hydrophobic and non polar tails. important because the cell membrane builds itself

integral proteins (what is it + function)

deeply embedded (partially or fully) tunnels that move materials

what do integral proteins rely on to cross the membrane? why are they important?

alpha helices and beta pleated sheets. beta pleated sheets allow for “tunnels” and these protein folding structures ensure the protein stays stable and comfy in the fatty core

peripheral proteins (what is it + function)

surface anchors that are noncovalently attached to charged heads or other proteins

they anchor the cells internal skeleton and help with signals

carbohydrates (what is it + function)

glycoproteins and glycolipids (attaching to proteins or lipids) to act as ID tags and play a role in communication and adhesion

glycoproteins

carbohydrates attached to the surface of proteins

glycolipids

carbohydrates attached to the surface of lipids

proteoglycan

proteins with many carbohydrate chains

anchored proteins

proteins covalently attached to fatty acids or other lipid groups with a lipid tail used to keep the protein tucked into the membrane

anchored vs non-anchored proteins

no movement vs movement

lateral movement vs flip-flop movement in phospholipid bilayers

lateral: side to side, happens frequently

flip-flop: sifts between inner and outer layer, rarely happens.

what influences membrane fluidity

the nature of fatty acid tails

what influences membrane permeability

size and chemical nature of the molecule

saturated (viscous)

only single bonds between carbons making it less permeable

unsaturated (fluid)

carbon double bond so the phospholipids can’t pack together tightly, making it more permeable

6 major functions of membrane proteins

1. transport mechanisms (moving molecules)

2. enzymatic activity

3. signal transduction

4. intercellular joining

5. cell-cell recognition

6. attachment to cytoskeleton

transport mechanisms (moving molecules)

by energy and by direction

transport by energy

passive and active transport

transport by direction

uniport, symport, and antiport

uniport

one molecule transported at once

symport

2 different molecules transported in the same direction

antiport

2 different molecules transported in opposite directions

enzymatic activity

enzymes break down or build proteins

individual enzymatic activity

transport process that involves a single enzyme or transporter protein

linked groups enzymatic activity

transport process involving multiple enzymes or transporter proteins

signal transduction

cells receive and respond to signals from environment, “hearing” what’s happening in the body

receptor signal transduction

a protein on the outside catches a specific signal (like a hormone)

relay signal transduction

protein changes shape and passes message into the cell

response signal transduction

cell acts on the message (the cell grows, moves, makes a new cell, etc.)

intercellular joining

a physical connection between cells that can be temporary (to pass a message) or permanent (to lock together). it can facilitate communication and can provide physical support and tissue formation

cell-cell recognition

cells identify and interact with other cells using unique ID tags to see if the substance belongs to it. the immune system scans these ID tags to defend the body

what does attachment to cytoskeleton do

anchoring for strength and shape

internal support

proteins hook onto the cytoskeleton to maintain shape

external support

proteins also grab the extracellular matrix (sticky mesh outside the cells)

vesicle transport

moving big loads via vesicles (endo/exocytosis)

do hydrophobic nonpolar molecules get into the cell membrane?

yes, with a fast pass

do small, uncharged polar molecules get into the cell membrane?

yes, with a slow pass

do ions and large uncharged polar molecules get into the cell membrane?

no pass, they hit a wall and may need a door to get in.

Cell junctions

Specialized regions of the cell membrane that act as the door connecting two buildings

tight junctions (what and examples)

create a firm, watertight seal between 2 adjacent animal cells that helps with waterproofing

examples:

• used to keep urine contained in the bladder

• keep water in and bacteria out of the skin

• ensures nutrients go through cells and not around them in the gut

desmosomes

form a strong spot weld between cells, provides intense mechanical strength

ex: the heart uses these because its constantly moving and squished

gap junction

a direct channel between 2 adjacent animal cells that allows ions and nutrients to pass between cells

direction of passive transport

high to low concentration

direction of active transport

low to high concentration

types of passive transport

simple diffusion, facilitated diffusion, osmosis

passive transport

move ions and molecules across the cell membrane without energy, instead using concentration gradient from a high to low concentration

simple diffusion

passive diffusion through small nonpolar molecules (co2, o2, small lipids) that continues until equilibrium is reached

spontaneous process

a process that keeps happening until everything is fully balanced

What factors determine rate of diffusion in simple diffusion? what is that influence?

1. diameter of molecule - smaller mol = faster diffusion

2. temperature of the solution - high temp = faster diffusion

3. electric charge of diffusing materials - charged = slower diffusion

4. concentration gradient - steeper gradients = faster diffusion

5. travel distance - farther = slower diffusion

6. solvent density - thicker = slower diffusion

when diffusing two solutes what concentration is focused on?

it’s only dependent on its OWN concentration

dynamic equilibrium

molecules never stop moving, even when balanced they move just with no net change

Glomerular filtration

Diffusion in kidneys, an example of simple diffusion where small molecules pass through easily and large molecules are kept inside

facilitated diffusion

using specialized transport proteins to help let polar and charged molecules through

channel proteins

open tunnels for quick passage into the membrane, move tens of millions of molecules a second.

only specific ions or polar molecules fit in the tunnel. no energy needed.

carrier proteins

revolving doors that bind and carry specific molecules

ligands

protein that swallows a molecule to help bring it through the bilayer

voltage gated channels

open /close in response to a change in voltage (difference in charges) across the membrane. it allows for near instant movement of ions.

aquaporin channels

channel proteins that allow water to diffuse across the cell membrane at a very high rate

carrier proteins

integral protein that undergoes conformational change (shape shift) that allow for transport

hypertonic

environment around the cell has a higher solute concentration than the cell, the cell loses h2o and shrivels

osmosis

passive movement of h2o across a semipermeable membrane from high h2o concentration (low solute) to low h2o concentration (high solute) using no energy

hypotonic

environment around the cell has a lower solute concentration than the cell, the cell gains h2o and expands, may explode

isotonic

environment around the cell has the same solute concentration as the cell, no net h2o movement across cell membrane

osmosis in plants

unlike animal cells, plant cells have a rigid cell wall that prevents them from bursting

turgor pressure

water fills the vacuole, pushing the membrane against the wall to keep the plant upright

is the cytoplasm hypertonic or hypotonic to the cellular environment in plants

its always slightly hypertonic!

active transport

moves uphill against the concentration gradient and requires energy and uses membrane proteins

primary (direct) active transport

the direct bruning of ATP to pump molecules that creates a charge difference across the membrane

steps of primary active transport

1. 3 sodium and one atp bind to the protein pump from inside the cell

2. atp undergoes hydrolysis and releases adp and phosphorylates an amino acid in the pump protein, changing the shape of the pump

3. shape change causes sodium to be release out of the cell. 2 potassium ions enter the pump

4. 2 potassium ions bind to the pump

5. dephosphorylation causes pump to release inorganic phosphate leading to 2 potassium ions being released inside the cell and the pump returning to its original form

secondary (indirect) active transport

movement of two molecules across the membrane by hitching a ride from an existing gradient built by primary transport

substance 1 in secondary transport

moves down its concentration gradient (high to low), releasing energy and providing power

substance 2 in secondary transport

moves up its concentration gradient (low to high), harnessing the energy from substance 1 and hitching a free ride

sodium glucose co transport

an example of secondary transport where sodium ions are the power source and glucose is the hitchhiker. the cell successfully pulls in fuel by using the sodium gradient it already built

bulk transport

moving entire cells, fluid droplets, or large proteins by wrapping them in membrane vesicles

one way proteins in active transport

they are selective and unidirectional protein carriers, meaning that each protein only moves a specific molecule and only moves it one way.

cellular balance

a precise control that keeps the cells internal environment stable

electrochemical gradient

movement of ions. the cell spends energy to build a graident (primary transport) an then harvests that gradient to stay alive (secondary transport)

chemical gradient

difference in the amount of a substance

electrical gradient

difference in the charge of a substance (positive vs negative)

is the cell interior negative or positive? why?

mostly negative due to trapped proteins

endocytosis

the process of active transport of molecules into the cells by the action of engulfing it along with its membrane

phagocytosis

“cell eating”
engulfment of large particles or even whole cells into the cell through the formation of a large vesicle called a phagosome

pinocytosis

“cell drinking”

the intake of small dissolved molecules or fluids from the extracellular environment into the cell through the formation of smaller vesicles

receptor mediated endocytosis

binding of specific extra cellular molecules to receptor proteins on the cell membrane which triggers the formation of a vesicle that carries the targeted molecule into the cell. very selective

where does receptor mediated endocytosis occur

clathrin coated pits

5 step process of receptor mediated endocytosis

1. ligand binding

2. lateral movement

3. coated pit formation

4. membrane invagination

5. vesicle formation

ligand binding in receptor mediated endocytosis

ligands bind to specific receptors on the cell surface

lateral movement in receptor mediated endocytosis

the receptor-ligand complexes move laterally in the membrane, reaching a region called a “coated pit”

coated pit formation in receptor mediated endocytosis

coated pits are areas of the membrane with a special coat made of proteins

membrane invagination in receptor mediated endocytosis

starting to engulf the receptor-ligand complexes

vesicle formation in receptor mediated endocytosis

invaginated membrane pinches off from the cell surface, creating a vesicle

exocytosis

cells moving molecules from inside the cell to outside the cell

used for secretion, waste removal, chemical messaging, and rebuilding the cell membrane

what are vesicles formed by

golgi apparatus, endosomes, and pre-synaptic neurons

constitutive exocytosis

the regular secretion of molecules

regulated exocytosis

moving materials from inside the cel to outside the cell, relying on extracellular signals