(Unit 2) Chapter 7: Membrane Structure and Function

Question 1

Define:

Selective permeability

Answer 1

Allows some substances to cross it more easily than others

Question 2

Define:

Amphipathic

Answer 2

Has both a hydrophilic region and a hydrophobic region

Question 3

What is the most abundant lipids in most membranes?

Answer 3

Phospholipids

Question 4

What is a “fluid mosaic model”?

Answer 4

The membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a double layer (bilayer) of phospholipids

Question 5

When were membranes first seen with the electron microscope?

Answer 5

1950s

Question 6

By the 1960s, the ______-________ ________ had become widely accepted as the structure not only of the plasma membrane, but also of all the cell’s internal membranes

Answer 6

Davson-Danielli sandwich

Question 7

True or False:

The flip-flop movement of phospholipids occur very rapidly, while the lateral movement of phospholipids is quite rare

Answer 7

False, the lateral movement of phospholipids is very rapid (10^7 times/second) while the flip-flop movement is quite rare (once per month)

Question 8

Why do unsaturated hydrocarbon tails make the membrane more fluid than saturated hydrocarbon tails?

Answer 8

The kinks in the unsaturated hydrocarbon tails prevent them from packing closely together, thus making it more fluid

Question 9

What are the two major populations of membrane proteins?

Answer 9

Integral proteins

Peripheral proteins

Question 10

Define:

Integral proteins

Answer 10

Penetrate the hydrophobic core of the lipid bilayer; many are transmembrane (span the membrane) while others only penetrate partway through

Question 11

Define:

Peripheral proteins

Answer 11

Not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane

Question 12

What are the major functions performed by proteins of the plasma membrane? (6)

Answer 12

Transport
Enzymatic activity
Signal transduction
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 13

Describe the Transport function of the proteins of the plasma membrane:

Answer 13

Proteins that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute; some may hydrolyze ATP and change shape to actively pump something across

Question 14

Describe the Enzymatic activity function of the proteins of the plasma membrane:

Answer 14

Proteins may be an enzyme with its active site exposed to substances in the adjacent solution; Several enzymes in an membrane may be organized together as a team on a metabolic pathway

Question 15

Describe the Signal transduction function of the proteins of the plasma membrane:

Answer 15

Some proteins are receptors with a binding site for a specific chemical messenger; binding may cause a change of shape of the protein which relays the message inside the cell (e.x. binding to cytoplasmic protein)

Question 16

Describe the Cell-cell recognition function of the proteins of the plasma membrane:

Answer 16

Some glycoproteins serve as identification tags to be recognized by membrane proteins of other cells

Question 17

Describe the Intercellular joining function of the proteins of the plasma membrane:

Answer 17

Membrane proteins of adjacent cells may hook together in various kinds of junctions (gap junctions, tight junctions etc.)

Question 18

Describe the Attachment to the cytoskeleton and extracellular matrix (ECM) function of the proteins of the plasma membrane:

Answer 18

Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins (helps maintain cell shape and stabilizes the location of certain membrane proteins)

Question 19

True or False:

Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes

Answer 19

True

Question 20

What do names that start with “glyco-“ refer to?

Answer 20

Refers to the presence of carbohydrate

Question 21

Membrane carbohydrates are usually _____, branched chains of fewer than __ _____ units

Answer 21

Short

15 sugar

Question 22

What are membrane carbohydrates covalently bonded to lipids called?

Answer 22

Glycolipids

Question 23

What are membrane carbohydrates covalently bonded to proteins called?

Answer 23

Glycoproteins

Question 24

In the synthesis of membrane components and their orientation on the resulting membrane:
Where does the process start? What happens?

Answer 24

In the endoplasmic reticulum

The synthesis of membrane proteins and lipids; carbohydrates are added to proteins (making glycoproteins)

Question 25

In the synthesis of membrane components and their orientation on the resulting membrane:
Where does the second step occur? What happens?

Answer 25

In the Golgi apparatus

Glycoproteins undergo further carbohydrate modification, lipids acquire carbohydrates (becoming glycolipids)

Question 26

True or False:

After the proteins acquire carbohydrates, they cannot be modified

Answer 26

False, after carbohydrates are added to proteins in the endoplasmic reticulum, the carbohydrate portions can then be modified

Question 27

In the synthesis of membrane components and their orientation on the resulting membrane:
What happens in the third step?

Answer 27

The transmembrane proteins, membrane glycolipids, and secretory proteins are transported in vesicles to the plasma membrane

Question 28

In the synthesis of membrane components and their orientation on the resulting membrane:
What are transported in the third step? Where are they transported to? (4)

Answer 28

Transmembrane proteins
Membrane glycolipids
Secretory proteins
Transported to plasma membrane

Question 29

In the synthesis of membrane components and their orientation on the resulting membrane:
In the final step, what happens? (2)

Answer 29

Vesicles fuse with the membrane, releasing secretory proteins from the cell
Vesicle fusion positions the carbohydrates of membrane glycoproteins and glycolipids on the outside of the plasma membrane

Question 30

The asymmetrical arrangement of ________, ______, and their associated _____________ in the plasma membrane is determined as the membrane is being build by the __ and _____ _________

Answer 30

Proteins
Lipids
Carbohydrates
ER
Golgi apparatus

Question 31

True or False:

The carbohydrates on the extracellular side of the plasma membrane vary from species to species

Answer 31

True, they very among individuals of the same species, and even from one cell type to another in a single individual

Question 32

What is one traditional example in humans of extracellular carbohydrate variation?

Answer 32

The four human blood types (A, B, O, AB) reflect variation in the carbohydrates on the surface of red blood cells

Question 33

True of False:

Cell membranes are not permeable to specific ions and a variety of polar molecules

Answer 33

False, cell membranes are permeable to specific ions and a variety of polar molecules

Question 34

What can cross the lipid bilayer of the membrane easily? Why?

Answer 34

Nonpolar molecules (hydrocarbons, carbon dioxide, oxygen etc.)
They are hydrophobic and can cross without the aid of membrane proteins

Question 35

Why are ions and polar molecules impeded when passing through the membrane?

Answer 35

The hydrophobic core of the membrane impedes the direct passage, along with gatekeeper proteins