cell bio chapter 11

What does a cell’s plasma membrane do?

it enables the internal molecular composition of a cell to differ from that of the
cell’s environment

What do eukaryotic cells have that prokaryotic cells do not?

internal membranes

What is the function of a eukaryotic cell’s internal membrane?

it keeps molecules inside one intracellular component from mixing with other molecules

What do the receptor proteins in the plasma membrane act as?

sensors that enable the cell to receive information about
changes in its environment and respond to them

Why is the flexibility of the plasma membrane important for the cell?

it allows for cell growth and movement

What kind of protein molecules allow a cell to selectively import/export specific substances?

channels and pumps

What is the first function of the plasma membrane?

to receive information

What is the second function of the plasma membrane?

importing and exporting molecules

What is the third function of the plasma membrane?

the allow for movement and expansion

How many membranes are the nucleus and mitochondria enclosed by?

2 membranes

What makes the structure of a lipid molecule amphipathic?

it has a hydrophilic head and hydrophobic tail

How thick is the lipid bilayer?

5 nm

What is phosphatidylcholine (PC)?

the most common phospholipid in cell membranes and made up of 5 parts

What is the role of choline in PC?

it is the hydrophilic head

What is the role of phosphate in PC?

it links choline to glycerol

What is the role of glycerol in PC?

it links phosphate to 2 hydrocarbon chains

What are the 2 hydrocarbon chains in PC derived from?

fatty acids

What is the difference between saturated and unsaturated fatty acids?

saturated fatty acids are made up of only single bonds while unsaturated fatty acids have at least one double bond

What are the 3 major types of membrane lipids?

phospholipids, glycolipids, sterols

Why are phospholipid bilayers self-sealing?

Exposed hydrophobic tails are unfavorable in water, so the bilayer closes

What is a liposome?

an artificial, self-sealing phospholipid bilayer that forms a spherical compartment

What makes the liposome structure stable?

the sealed compartment shields the hydrophobic tails from water which is energetically favorable

What kind of tails increase the fluidity of the cell membrane?

Unsaturated fatty acid tails and short tails

What influences the fluidity of the bilayer?

temperature and phospholipid composition (tail types)

What is lateral diffusion?

Side-to-side movement of membrane lipids/proteins

What is rotation?

A lipid spinning around its own axis

What is flexion?

Bending/movement of a lipid’s fatty acid tails

What is a flip-flop?

when a membrane lipid moves from one layer of the bilayer to the other

What are flip-flops so rare?

because the hydrophilic head would have to pass through the hydrophobic interior

Where in the ER membrane are newly synthesized phospholipids added?

the cytosolic side of the ER membrane

What is the function of scramblases?

to transfer phospholipids to the opposite monolayer so the entire bilayer expands

What is the function of flippases?

maintain plasma membrane asymmetry by moving specific phospholipids between monolayers

How does cholesterol stiffen membranes?

It fits between phospholipid tails which restricts their movement and makes the bilayer more rigid

How does cholesterol act as a temperature buffer?

It decreases membrane fluidity at high temperatures and prevents excessive rigidity at low temperatures

How does cholesterol affect hydrocarbon chains?

it prevents them from coming together and crystalizing

What makes phospholipids and glycolipids asymmetrically distributed in the bilayer?

glycolipids are only in the outside layer while phospholipids are in both

How is membrane orientation maintained during transport?

Vesicles build from and fuse with membranes which preserves the orientation

Where do glycolipids acquire their sugar groups?

In the Golgi apparatus, where the enzymes that add the sugars are located

Why are sugar chains important for cell to cell interactions?

They allow cells to recognize, bind to, and communicate with one another

What does a transporter/channel do?

allows specific substances to cross the cell membrane

What do anchor proteins do?

Attach membrane proteins to structures inside or outside the cell, helping hold them in place

What is a transmembrane protein?

A protein that spans the entire membrane bilayer

What are two examples of transmembrane proteins?

α helices and β barrels

What is a monolayer-associated protein?

A protein associated with only one side of the membrane

What is an example of a monolayer associated protein?

amphipathic α helices

What is a lipid-linked protein?

A protein attached to the membrane through a covalently attached lipid

What is a protein-attached protein?

A membrane protein attached to another membrane protein rather than directly to the lipid bilayer

What is a transmembrane hydrophilic pore?

A water-friendly channel through the bilayer formed by multiple α-helices

What is a bacterial porin?

A membrane protein that forms a water-filled channel using a 16-stranded β-sheet arranged as a β-barrel

What are 2 commonly used detergents?

SDS and Triton X-100

What does a detergent do to a lipid bilayer?

It separates membrane lipids and proteins and keeps them in water-soluble complexes called micelles

What strengthens and supports the cell membrane?

a meshwork of fibrous proteins called the cell cortex

What is spectrin?

a long, thin protein that forms the cell cortex in human RBCs

How do spectrin dimers form cell cortex?

by binding with attachment proteins and transmembrane proteins

How can the lateral movement of membrane proteins be restricted?

By tethering them to the cortex, ECM, other cells, or by diffusion barriers

How do diffusion barriers block lateral movement?

by creating a tight junction proteins can’t move through, this creates polarity

What does the gut epithelial cell illustrate?

That proteins are restricted to moving within certain domains by junctions

Why is it important that the eukaryotic cell surface is coated with sugars?

sugars form a protective coating and play an important role in cell-cell recognition and adhesion

How do cell-surface carbohydrates help neutrophils?

They allow neutrophils to be recognized and adhere to blood vessel walls at infection sites