Lecture 4: Biomolecules II - lipids + membranes

What is the overarching concept regarding lipids in biological systems?

Lipids are not water soluble and create barriers in biological systems.

What are the key characteristics of lipids?

- not polymers

- NP/hydrophobic = cannot make H-bonds with water

- Degree of saturation impacts fluidity + permeability

what are lipids mostly built by?

mostly built by NP covalent bonds between hydrogen and carbon

what is amphipathic?

- molecule has both P and NP regions

- can make H-bonds with the polar side of molecule but not the other end

What is the structure of phospholipids?

Phospholipids consist of a hydrophilic polar head group and two hydrophobic fatty acid tails.

How do phospholipids arrange themselves in a membrane?

Phospholipids spontaneously form a bilayer due to interactions between their hydrophilic heads and hydrophobic tails with water.

What determines the stability of lipids?

The degree of saturation and length of the fatty acid chains determine the stability of lipids.

What are the differences between saturated and unsaturated fatty acids?

- Saturated fatty acids have single bonds between carbons

- Unsaturated fatty acids have one or more double bonds. (arranged in cis or trans)

what does saturation mean?

how many H-bonds are being made in fatty acids

Saturated lipids (butter)

- cannot add anymore hydrogens to the carbons, all covalently bonded already

- can be a little bit stable

- solid at room temp

Saturated lipids with long hydrocarbon tails (wax)

- have longer chains which can mean greater capacity for more van der waals interactions

- can be more stable than butter

unsaturated lipids (oil)

- due to these kinks, we want to be able to tightly pack van der waals

- relativly short chained

what are lipid bilayers?

phospholipids are amphipathic molecules that spontaneously arranged because of how different regions of phospholipids interact with water

what are the components of phospholipids?

- fatty acid tail (hydrophobic/NP)

-phosphate head (hydrophilic/P)

why do phospholipids spontaneously form into a bilayer?

because of how the head and tail regions interact with water

what happens when you increase the # of phospholipid molecules in an aqueous solution?

the arrange in a bilayer

What determines stability?

degree of saturation

what is homeoviscous adaptation?

cells can adapt to changing temperatures by adjusting the composition of lipids to maintain optimal membrane fluidity

What does adding cholesterol do to the membrane?

in lipid bilayer, keeps them more stable at high temperatures and more fluid at low temps

What types of molecules can freely cross a lipid bilayer?

Gases (O2, CO2,N2), hydrophobic molecules, and very small polar molecules can move across freely.

What is selective permeability in the context of plasma membranes?

means that some substances can pass through the membrane while others cannot.

what does concentration gradient mean?

a difference in the amount of that substance

What is facilitated diffusion?

Facilitated diffusion is the movement of molecules from high to low concentration through a protein tunnel, which is a form of passive transport.

What role do aquaporins play in cellular transport?

Aquaporins are channel proteins that facilitate osmosis by increasing the permeability of the membrane to water.

What is the function of carrier proteins in membrane transport?

Carrier proteins change shape when they bind to molecules, allowing them to cross the bilayer.

What are the four critical functions of plasma membranes?

- Plasma membranes recognize signals and responds

- regulate entry and exit of substances

- act as barriers

- attach to other structures

What is active transport?

Active transport moves molecules against their concentration gradient

what are the 2 requirements for active transport?

1. input of energy - low to high concentration is passive

2. carrier protein to move it across membrane (protein pump)

What is the difference between integral and peripheral membrane proteins?

- Integral membrane proteins span the membrane

- peripheral proteins are attached to the surface of the membrane.

What types of molecules cannot freely pass through the lipid bilayer?

Ions and larger polar molecules cannot freely move across the lipid bilayer.

What is the role of proteins in plasma membranes?

Proteins in plasma membranes serve as signal receptors, transporters, channels, pores, and anchors.

What is passive transport?

Passive transport is the movement of molecules from high to low concentration without the need for energy.

What determines the direction of water movement in osmosis?

Water movement in osmosis is determined by solute concentration gradients.

What is the significance of the fluid mosaic model of plasma membranes?

the model describes plasma membranes as structures where components can move laterally and change according to cellular needs.

What is the role of fatty acid length and saturation in permeability?

Fatty acid length and degree of saturation determine the permeability of membranes, with longer and saturated chains being less permeable.

What is the function of channel proteins in facilitated diffusion?

Channel proteins allow specific molecules to pass through the membrane by changing shape to open and close.

What is the relationship between concentration gradients and passive transport?

Passive transport relies on concentration gradients, with molecules moving from areas of high concentration to low concentration.