Chapter 11: Membrane structure

What does the cell membrane of an organism do?

It separates a cell from its surroundings, enabling the molecular composition of a cell to differ from its environment

• with eukaryotes having internal membranes as well that separate the inside of an organelle from the cytosol

What does the cell membrane prevent?

Molecules on one side from freely mixing with those on the other side

How is the plasma membrane involved in cell communication?

they contain receptor proteins that are able to receive signals from the external environment

How is the plasma membrane involved in import and export of molecules?

They contain channels and transporters that enable the import and export of small molecules

How is the plasma membrane involved in cell growth and motility?

The lipid bilayer is flexible, allowing for a cell to grow, change shape, and move

What do internal membranes have the ability to do?

They can form many different compartments in a eukaryotic cell such as membrane enclosed organelles, with the nucleus and mitochondria being enclosed by two membranes

What connects the hydrophilic head of a phospholipid to its hydrophobic tail?

A glycerol molecule that connects the hydrophilic head to the carboxyl group present in the hydrophobic tails

When do kinks occur in a phospholipids hydrophobic tail?

When there is a double bond between two carbon atoms

What is the most common phospholipid?

Phosphatidylcholine

What are fat molecules?

Molecules that are entirely hydrophobic with the most common one being triacyclglycerols, which is a molecule that stores energy and consists of a glycerol attached to 3 hydrocarbon tails

What are amphipathic phospholipids able to form in water?

Bilayers with its head facing towards the water and its tails being buried in the middle and not exposed to the water

what are phospholipids bilayers able to do spontaneously?

They can spontaneously close in on themselves to form a sealed compartment

Why is a phospholipids closed structure stable and energetically favorable?

As its able to protect its hydrophobic tails from being exposed to water, which would be energetically unfavorable

Why can the membrane behave as a two-dimensional fluid?

Due to each individual lipid molecule in the bilayer being able to move within their own monolayer

how does cholesterol affect a cell membrane?

By filling in the gaps present between each phospholipid, stiffening the membrane and making the hydrophobic tails more rigid and condensed

How are newly synthesized phospholipids added to the cytosolic side of the lipid bilayer?

When enzymes on the cytosolic side of the ER makes new phospholipids from fatty acids, they are inserted into the cytosolic monolayer. Causing scramblases to randomly redistribute the phospholipids between both layers, allowing the membrane to grow evenly as a bilayer.

How are certain phospholipids confined to one side of the membrane?

When membranes leave the ER and incorporate into the Golgi apparatus, it encounters flippases, a type of transporter, that selectively removes lipids from the noncytosolic monolayer and flips them to the cytosolic side. Helping establish and maintain asymmetrical distribution of the phospholipid characteristics within the membrane

Why is the bending or curving of the membrane bilayer important?

Its essential for processes such as the budding of membrane vesicles

What do membranes retain during the transfer of molecules between cell compartments?

They are able to retain the orientation of both the cytosolic side and non cytosolic side

How are Phospholipids and glycolipids distributed?

They are distributed asymmetrically in the lipid bilayer of a cell

What are the 4 different classes of proteins?

• Transporter and channel proteins

• anchor protein

  • which binds to other proteins internally and externally, preserving them

• Receptor proteins

• Enzymes

What are integral proteins?

A type of membrane protein that are permanently embedded within the cell membrane with there being 3 kinds

• Transmembrane proteins

• Monolayer associated proteins 

• Lipid-linked proteins

What are transmembrane proteins?

They are proteins that extend across the bilayer as either a single a-helix, multiple a-helixes, or as a rolled up B-sheet. With some having parts of their mass exposed on both sides or on one side of the membrane

What are monolayer associated proteins?

They are proteins that are anchored to the cytosolic side of the lipid bilayer by an amphipathic a-helix

What are lipid-linked proteins?

They are proteins that are attached to either side of the bilayer by a covalently attached lipid molecule

What are peripheral proteins?

They are a type of membrane protein that are attached to the membrane by weak non-covalent interactions with other membrane proteins