bio exam 2

What do bacteria cells lack in contrast to eukaryotic cells

Internal membrane

What is the plasma membrane involved in

Cell communication, import/ excel of molecules and cell growth motility

Describe plasma membrane in terms of thickness

Thin

What is the % breakdown of the membrane components

PM: 2% endoplasmic reticulum: 50% mitochondrial inner membrane 30%

Lipids are…

Fluid

Identify all parts

Peripheral protein; hydrophobic a helix; integral proteins; oligosaccharides; glycoproteins; cholesterol; glycolipid; phospholipid

Lipid-protein assemblies are held together by which type of bond?

Non covalent

What are the three major classes of lipids

Phosphoglycerides,shinglipids, cholesterol

amphiatic

Both hydrophobic and hydrophilic

sphingosine

an amino alcohol with long hydrocarbon chain

•sphingomyelin

if X is

phosphorylcholine; a phospholipid

•glycolipid

if X is carbohydrat

Plants don't have

Cholesterol

Cholesterol in membrane

Smaller than phospholid. •Makes membrane more fluid at low temp •vice/versa -20% of cell

What interactions are lipid bilayes based on

Hydrophobic

Asymmetry generated by

flippases and floppases

Cell surface is covered with

carbohydrates

•Carbohydrate content ——- - linked to both lipids & proteins

covalently

Integral proteins

Embedded in lipid bilayer

Lipid linked

Integral because lipid inside even though protein is outside

Integral membrane proteins

•amphipathic (like the lipids near them)

•AA in transmembrane domain forms hydrophobic

interactions with FA tails

•required detergents to solubilize (separate from

membrane)

Why does the lipid protein ratio vary

Based on function. Myelin sheat 79:18. Mitochondrial inner membrane 22:78

Structure of sphingolipids

Spingosine + fatty acid + X

X in a spingosine can be a _____ or _____

Phosphochlorine or carbohydrate

describe phospholipids

hydrophilic head, hydrophobic tail, based on glycerol. Most common types are PC, PE, and PS

cholesterol

interferes with phospholipid packing; makes membrane more fluid at lower temps and less fluid at higher temps

liposome

tiny, spherical artificial vesicle made of one or more phospholipid bilayers that enclose an aqueous (water-based) core

what does lipid composition do

• determines physical state of membrane

• influences activities of some membrane proteins

• may provide precursors or chemical messengers

asymmetry in the plasma membrane is generated by

flippases and floppases

what is the purpose of using detergents on integral proteins

extract proteins from the membrane and dissolve them in an aqueous solution by mimicking the lipid environment

describe what is happening here

• starting Components: An integral membrane protein spanning the lipid bilayer is mixed with detergent monomers (which have a hydrophobic tail and a hydrophilic head) that exist in equilibrium with detergent micelles.

  
  

  
  

• The Process: Detergent molecules disrupt the lipid bilayer and surround the hydrophobic regions of both the protein and the lipids.

  
  

  
  

• Final Products: The reaction yields a water-soluble protein–lipid–detergent complex alongside separate water-soluble lipid–detergent micelles, allowing the membrane protein to remain dissolved in an aqueous solution.

  
  

A transmembrane protein usually crosses the lipid bilayer as an

a helix

Glycophorin A

hydrophobic AA

hydropathy path

is a bioinformatic tool used in biochemistry to visualize and predict the hydrophobic and hydrophilic regions of a protein sequence.

Glycosylphosphatidylinositol (GPI)

complex sugar-fat molecule that acts like a cellular anchor.

Fatty acid anchor

• internal PM face
• covalently linked to FA
• kinases, etc.

how does cholesterol affect the membrane

cholesterol disrupts close packing of fatty acids & interferes with their
mobility
• abolish sharp transition temperatures & creates condition of
intermediate fluidity
• it tends to increase durability & decrease permeability of membrane

Maintaining membrane fluidity

internal temp. of most organisms (not
birds/mammals) changes with outside temp.
• organisms respond by altering membrane lipid
composition
1. Desaturase enzymes single --> double bonds
2. Phospholipases and acyltransferases
reshuffle fatty acid chains to create lipids
with two unsaturated chains

Phospholipases

Phospholipases are a diverse group of enzymes that break down phospholipids into fatty acids and other lipophilic substances by hydrolyzing specific ester bonds

Acyltransferase

An Acyltransferase is a type of transferase enzyme that catalyzes the transfer of an acyl group (derived from a carboxylic acid or acyl-CoA donor) to an acceptor molecule

desaturase

enzyme that introduces carbon-carbon double bonds into fatty acid chains, converting saturated fatty acids into monounsaturated or polyunsaturated fatty acids.

Asymmetry of membrane lipids – membrane sidedness

Phospholipid content
varies between the inner
and outer leaflets of the
membrane
•e.g., phosphatidylserine
(PS) inner leaflet
•glycolipids outer leaflet

Scramblases

transmembrane proteins that move phospholipids bidirectionally between the two leaflets of a cell membrane

Newly-synthesized lipids are added to the

ER cytosolic membrane

Flippases

in Golgi and PM move specific phospholipids (e.g., PS) to cytosolic leaflet

Floppases

move specific phospholipids (e.g., PC) to outer leaflet

Sphingomyelin

a type of sphingolipid and phospholipid found in animal cell membranes

Lipid rafts

specialized, dynamic microdomains within cell membranes enriched in cholesterol and sphingolipids that act as organizing platforms for cell signaling and membrane transport

Phosphatidylcholine (PC)

a major class of phospholipids containing choline

Flippases/scramblases

can help lipids switch leaflets

how often does transfers diffusion happen

every 28 hrs

how often does lateral shift happen

millionth of a second

in the example of human and mouse cell, how long did it take for the cells to fuse in a mosaic format

transition temp of 59 F

Fluorescence Recovery After Photobleaching (FRAP)

• Measures the mobility and diffusion rates of fluorescently tagged molecules (like proteins or lipids) within living cells.

• The Process:

  1. Baseline: Measure initial fluorescence intensity.

  2. Bleach: Zap a specific region with a high-intensity laser to permanently destroy fluorescence.

  3. Recover: Track unbleached molecules diffusing back into the dark area.

  4. Plateau: Record final intensity once recovery stops.

• Why Recovery Level Is < 100%:

  • Immobile Fraction: Some molecules are physically anchored and cannot move.

FRAP: what does the rate of the recovery tell you

the rate of diffusion

FRAP; what does the recovery rate tell you

direct measure of % of labeled molecules free to move

What are the results from FRAP

1. proteins move more slowly in PM than in artificial
   lipids

2. large fraction (30-70%) not free to diffuse
   FRAP

describe the movement of this protein

freely

Describe the movement of this protein

confined in membrane by other proteins

Describe the movement of this protein

stuck to cyto

apical plasma membrane

regulation of nutrient and water intake

regulated secretion

protection

lateral plasma membrane

cell contact and adhesion

cell communication

Basal membrane

cell-substratum contact

ion gradient generation

•cell cortex of RBC

contains portions such as spectrin that strengthen the plasma membrane of RBC

•spectrin mutations

individuals anemic; cells break in capillaries. not stable

What would you see if you FRAP-ed spectrin?

the recovery would be fast

Cell Membrane vs. Lipid Bilayer

• Lipid Bilayer: The structural foundation of the membrane. It is a simple, two-layered sheet made strictly of phospholipids (hydrophilic heads facing out, hydrophobic tails facing in).

• Cell Membrane: The entire functional organelle surrounding the cell. It includes the lipid bilayer plusall embedded proteins, glycoproteins, glycolipids, and cholesterol (the Fluid Mosaic Model).

  • Analogy: The lipid bilayer is the bread of a sandwich; the cell membrane is the entire sandwich with all the meats, cheeses, and toppings included.

what are some non polar hydrophobic molecules that can pass though the semipermeable membrane

O2, CO2, N2, and benzene

what are some small uncharged molecules that can pass though the semipermeable membrane

H2O, glycerol, and ethanol

what are some larger uncharged polar molecules that cannot pass through

amino acids, glucose, and nucleotides

what are some ions that cannot freely pass through the semipermeable membrane

H+, Na+, HCO3-, K+, Ca2+, Cl-, and Mg2+

In which direction do flippases move phospholipids?

hey move specific phospholipids from the outer leaflet to the inner leaflet (flipping "in").

What do floppases do, and how do they differ from flippases?

Floppases move phospholipids in the opposite direction—from the inner leaflet to the outer leaflet (flopping "out"). Like flippases, they also require ATP and maintain membrane asymmetry.

Why are scramblases described as non-specific and bidirectional?

They transport phospholipids randomly back and forth between both leaflets at the same time, without favoring any specific type of lipid.

What is the ultimate biological purpose of flippases versus scramblases?

• Flippases: Maintain membrane asymmetry, keeping the cell membrane organized and healthy.

• Scramblases: Destroy membrane asymmetry, often to signal processes like blood clotting or cell death (apoptosis).

what is the concentration intracelluar and extracellular of Na+

5-15:145

what is the concentration intracelluar and extracellular of K+

140;5

what is the concentration intracelluar and extracellular of Ca2+

10^-4 and 1-2

What role do the nucleotide, sugar, and amino acid transporters play on the plasma membrane?

They are specialized carrier proteins that import essential building blocks (nucleotides, sugars, and amino acids) from the outside into the cell

What is the function of the Na+/K+Na+/K+ pump located on the plasma membrane?

It actively pumps sodium (Na+Na+) out of the cell and potassium (K+K+) into the cell, which is crucial for maintaining electrochemical gradients and cellular balance.

What specific ion pump is found on the lysosome membrane, and what is its purpose?

A H+H+ (proton) pump. Its purpose is to transport hydrogen ions into the lysosome to maintain the acidic interior required for digestive enzymes to function.

What is the function of the pyruvate transporter associated with the mitochondrion?

It transports pyruvate across the mitochondrial membranes so it can enter the mitochondrial matrix for cellular respiration

How do ATP and ADP interact with the inner mitochondrial membrane carrier shown in the diagram?

The carrier exports newly synthesized ATP out of the mitochondrion into the cytosol while importing ADP back into the matrix

Facilitated diffusion

passive transport where polar molecules and ions move across a cell membrane from an area of high concentration to low concentration with the help of transmembrane transport proteins

Does facilitated diffusion require ATP

no

channels

open or close; move faster than transporters,

transporters

undergo a series of conformational changes (alternate access)

influx

into cell

eflux

out of cell

Diffusion

moving from high concentration to low concentration

Diffusion leads to an increase in

entropy

explain the components of the electrochemical gradient

chemical - concentration difference

electric - ions attracted to opposite charges

what are the conditions for diffusion through membrane

must be concentration difference

must be membrane permeable

directly through lipid

molecule size (smaller is faster)

partition coefficient

measure of polarity; ratio of solubility in nonpolar solvent/water

Potassium channel has a ______ for ion specificity

selectivity filter

how do voltage gated ion channels open

change in voltage difference

how do ligand gated channels open

opens due to ligand binding; usually not the transported species

how does a stress (mechanically) gated ion channel open up

due to mechanical stimulation

What is the patch clamp method, and what is its primary use in cell biology/neuroscience?

used to study ionic currents passing through individual or multiple ion channels in cells. A tiny glass micropipette creates a tight seal ("patch") with the cell membrane, allowing researchers to record electrical currents (movement of ions) with high resolution.

What event triggers the opening of voltage-gated Ca2+ channels in the presynaptic nerve terminal?

action potential at nerve terminal