BS 161 Exam 2 Class 8

Properties of the plasma membrane

-Polar regions that interact with the outside and inside of the cell - Hydrophobic core region (of lipids) that creates the barrier -bilayer

Why do phospholipids spontaneously form a lipid bilayer?

- The fatty acid tails of the phospholipids interact through LDF's that are very weak but the water makes it stronger due to hydrophobic exclusion -Ultimately water is responsible for the formation of lipid bilayers

saturation of fatty acid tails impact on membrane fluidity

-Saturated fatty acid tails, which have no double bonds, are straight and tightly packed, reducing mobility, decreasing fluidity -Unsaturated fatty acid tails, have double bonds, more space, and increase fluidity

Describe the relationship between unsaturated fatty acid tails and cholesterol

-The cholesterol fits perfectly in between the phospholipids and can have LDF's between the two -The cholesterol filling in the gap allows it to stiffen the membrane. Decreasing the fluidity

Describe transporters

-Transporter allows for polar molecules to cross one side of the membrane to another -Pore has to be hydrophilic for polar molecule to go through

Functions of the plasma membrane

-a barrier to separate cell contents from the external environment -allows the cell to regulate molecules moving in or out of the cell -use for energy generation -help to maintain homeostasis by helping the cell to control its contents

How do cell membranes maintain homeostasis?

-controlling what substances may enter or leave cells -regulating membrane fluidity, letting the lipids to flow laterally the cell membrane

Why are membranes flexible?

-the lipids can move through the plane of the membrane(left and right/laterally), rotate on their axis and the tails can bend and flex.

Length of fatty acid tails impact on membrane fluidity

-the longer the fatty acid tails the mobility is is reduced because there's more surface to participate in LDF's

Presence of cholesterol impact of membrane fluidity

-· At temperatures found in cells cholesterol decreases fluidity, because the interaction of cholesterol with the phospholipid fatty acid tails reduces the mobility of the phospholipids. -· At low temperatures cholesterol increases fluidity, because it prevents phospholipids from packing tightly with other phospholipids.

Cholesterol lipid mass

30% of the lipid mass of membranes in animal cell membranes

percentage of lipids and proteins in structure of plasma membrane

50% lipids, 50% proteins

Temperature impact on membrane fluidity

High temperature: more fluid Low temperature: less fluid

Where is cholesterol foud?

In animal cell, not plant or bacterial cells

Explain why phospholipids form a lipid bilayer and triacyglycerols do not

Phospholipids form lipid bilayers because its amphipathic compared to triacylglycerol which is non polar

green

non polar and hydrophobic

Explain FRAP (Florescence Recovery After Photobleaching)

Step 1: cell where proteins are florescent 2: take a laser beam and focus on one portion of the cell which kills the fluorescence in a process called bleaching 3: the florescence goes away in that part of the cell and wait 4: found that the fluorescence came back over time. meaning protein molecules can move in the membrane because some in the non-bleached area moved to the bleached area

What does it mean for a membrane to be fluid?

When membranes are fluid it has the ability of membrane lipids to move in the plane the membrane

Why are membranes fluid?

extensive van der Waals forces between their fatty acid tails. These weak interactions are easily broken and re-formed

Define amphipathic

having both hydrophilic and hydrophobic parts.

How is the non polar barrier created for the lipid bilayer?

head of Phospholipids can interact with water and create a nonpolar barrier via fatty acid tails

(transporter) What amino acid side chains would you expect to find interacting with the extracellular fluid?

hydrophilic side chain

(transporter) What amino acid would you expect to find interacting facing the pore of the transporter?

hydrophilic side chain

What holds the membrane together?

hydrophobic effect/exclusion

(transporter) What amino acid side chains would you expect to find interacting with the fatty acid tails?

hydrophobic side chain

Describe the characteristics of an unsaturated fatty acid tail

that creates a kink preventing these phospholipids from compacting very close together

Why does the phospholipid rarely flip?

the head(which is polar) would have to force itself through the hydrophobic pore to get the other side. which is difficult because polar and non polar dont interact

importance of an aqueous environment to drive the formation of a lipid bilayer

the polar head groups(hydrophilic, has a phosphate/phospholipid)on the outside interact with water and the nonpolar tail groups(hydrophobic, fatty acid chains) come together on the inside away from water. This arrangement results from the tendency of polar molecules like water to exclude nonpolar molecules or nonpolar groups of molecules

What would happen if phospholipids were placed in a neutral pH solution?

they would spontaneously form a lipid bilayer

Are proteins amphipathic?

yes