BIOL 1020 Lipids & Membrane Dynamics

LECTURES 4-5

The one class of large biological molecules that does not form polymers

Lipids

Why are lipids hydrophobic?

Consist mostly of hydrocarbons (which are nonpolar)

3 biologically important lipids

Phospholipids, fats, steroids

Chemical structure of a glycerol

Three-carbon alcohol, hydroxyl attached to each carbon

Chemical structure of fatty acids

Carboxyl group linked to a long hydrocarbon chain

What links glycerol to (3) fatty acids to form a triaglyceride?

Ester linkages

Why do fats separate from water?

Water moles are hydrogen bonded to one another, but exclude the non-polar fats

What type of fatty acids DO NOT have double bonds?

Saturated fatty acids

________ fatty acids are liquid at room temperature.

“Unsaturated”

Define hydrogenation

The process of synthetically converting unsaturated fats to saturated fats by adding hydrogens

What does hydrogenation create with trans double bonds?

Unsaturated fats

Name of certain unsaturated fatty acids that are not synthesized in the human body, therefore must be supplied through diet.

Essential fatty acids

What type of cell do humans and other mammals store their fat in?

Adipose cells

What is the major/most abundant component of cell membranes?

Phospholipids

Define steroids (structure)

Lipids with a carbon skeleton (4 rings of carbon atoms)

Cholesterol is a component in ______ cell membranes

“Animal”

High levels of cholesterol in blood may lead to __________ disease

“Cardiovascular”

What are amphipathic molecules?

Molecules containing both hydrophobic and hydrophilic regions.

Membranes are held together by weak _______ interactions

“Hydrophobic”

Membranes rich in UNSATURATED / SATURATED fatty acids are more fluid than those rich in UNSATURATED / SATURATED fatty acids.

Unsaturated, saturated

At warm temperatures, how does the steroid cholesterol affect the membrane fluidity?

Restrains movement of phospholipids to prevent too much fluidity

Variations in lipids composition of cell membranes of many species are likely due to…

adaptations to specific environmental conditions

What large biological molecule determines most of the membrane’s specific functions

Proteins

Integral proteins that span the membrane are called?

Transmembrane proteins

What makes up the hydrophobic regions of an integral protein?

Stretches of nonpolar amino acids, often coiled into alpha helices

HIV cannot enter the cells of resistant individuals that lack what?

CCR5, a “co-receptor”

Carbohydrates are more commonly covalently bonded to?

Proteins (glycoproteins)

What structures determine how the plasma membrane has an asymmetrical distribution of components?

The endoplasmic reticulum (ER) and golgi apparatus. One builds the membrane, the other modifies it.

What type of molecules can dissolve in lipid bilayer, allowing for easy/rapid crossing of the plasma membranes?

Hydrophobic/non-polar molecules

Aquaporins

Channel proteins that facilitate passage of water across the plasma membrane

_________ proteins allow hydrophillic substances to pass across the membrane

“Transport”

Function of carrier proteins

Bind molecules and change shape to shuttle them across the membrane

What is diffusion?

Tendency for molecules to spread out evenly into available space

What is passive transport?

Diffusion of a substance across a biological membrane, with no energy expended to do so

T / F = Diffusion is not a spontaneous process

False, Diffusion IS a spontaneous process

What is osmosis?

Diffusion of water across a selectively permeable membrane

Water diffuses across a membrane from what region to what region until the solute concentration is equal on both sides

From the region of “lower solute concentration” to the region of “higher solute concentration”

What is tonicity?

The ability of a surrounding solution to modify H20 levels in cells

What is an isotonic solution?

Solute concentration is the same as inside the cell (no net water movement across the membrane)

What is a hypertonic solution?

Solute concentration is greater than that inside the cell (cell loses water)

What is a hypotonic solution?

Solute concentration is less than that inside the cell (cell gains water)

An animal cell generally fares best in an _______ environment

“Isotonic”

Hypertonic/hypotonic environments create osmotic problems for organisms that lack ___ ____.

“Cell walls”

What is osmoregulation?

The control of solute concentrations and water balance

What happens to a plant cell in a hypotonic environment?

Water enters, the cell swells, it becomes turgid (firm).

What happens to a plant cell in an isotonic environment?

No net water movement, cell is flaccid (limp)

What happens to a plant cell in a hypertonic environment?

Cell loses water, membrane pulls away from cell wall, plant wilts as a result of this process known as plasmolysis (typically lethal)

What is facilitated diffusion?

Passive transport where transport proteins (channel or carrier proteins) help a solute move down its concentration gradient, requiring no energy (NOTE: Some can move solutes against their concentration gradients)

What are ion channels?

Channel proteins (a type of transport protein) that facilitates the diffusion of ions

What are gated channels?

Some ion channels, which open or close in response to a stimulus

How do carrier proteins transport molecules?

Molecule binds on one side, protein changes shape (conformation), molecule is released on the other side of the membrane

What triggers conformation in carrier proteins?

Binding and release of molecules

What is active transport?

A process that requires energy (usually ATP) to transport solutes against the concentration gradient, performed by specific proteins embedded in membranes.

What is the sodium-potassium pump an example of?

Active transport system

What does active transport allow cells to do?

Maintain concentration gradients that differ from their surroundings

What is membrane potential?

The voltage difference across a membrane

How is voltage created?

Differences in the distribution of charged ions across a membrane

What drives the diffusion of ions?

Electrochemical gradient

What two forces make up the electrochemical gradient?

1. A chemical force (ion’s concentration gradient)

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

What is meant by membrane potential?

The stored energy from a difference in charges across the membrane

What is an electrogenic pump?

A transport protein that generates voltage across a membrane

What is the major electrogenic pump of animal cells?

Sodium-potassium pump

What is a proton pump? How does it function?

An electrogenic pump in plants, fungi, and bacteria that pumps protons out (like H+), creating a charge difference to store energy for cellular work

What is cotransport?

Occurs when active transport of a solute indirectly drives transport of other solutes

Define a semipermeable membrane

A membrane that allows some substances to pass through, while blocking others.

What structure controls the beating of cilia and flagella?

Microtubules