Exam 1 Study Guide (Cells & Organelles) pt 3

Question 1

What actual cell type most closely resembles the theoretical “typical” cell?

Answer 1

There are over 200 different types of cells, each specialized in its makeup to carry out its own particular function, so no one cell type represents a true “typical” cell.

Question 2

Describe the basic makeup of a typical cell membrane (Plasma membrane)

Answer 2

Fluid but relatively stable

A phospholipid bilayer with associated integral and peripheral proteins.

Question 3

What is the “catch phrase” for the plasma membrane (and cell membranes in general)?

Answer 3

Fluid mosaic model

A sea of fluid lipids contains a mosaic of many different proteins, including those that:

• float freely like icebergs in the lipid sea
• are constrained in their movement like a ship at anchor

Question 4

Describe the ability to view membranes of cells through the light microscope versus the ability to view membranes of cells using the electron microscope.

Answer 4

Too thin to see with light microscope, but can be observed with electron microscope

Question 5

As a general category, what type of substances are allowed by membrane lipids to move across membranes?

Answer 5

• Membrane allows passage of many lipid soluble substances

Question 6

As a general category, what type of substances are not allowed by membrane lipids to move across membranes?

Answer 6

• barrier to passage of charged or polar substances

“like dissolves like”. (Water is polar, oil is non-polar)

Question 7

Sequence the following constituents of the lipid bilayer from greatest proportion to least proportion within the membrane

Answer 7

Phospholipids (about 75% of the membrane)
Cholesterol (about 20 % of the membrane)
Glycolipids (about 5% of the membrane)

Question 8

Describe phospholipid molecules comprising cell membranes with regard to placement and orientation within the membrane

Answer 8

Bilayer occurs because lipids are amphipathic, having both polar and nonpolar parts

Question 9

Describe phospholipid molecules comprising cell membranes with regard to nature and polarity of different parts of the phospholipid

Answer 9

Phosphate-containing head is polar (hydrophilic)

Fatty acid tails are nonpolar (hydrophobic)

Question 10

How does the amphipathic nature of phospholipids relate to the bilayer structure of membranes and the parts of the bilayer that face the environment within the bilayer itself, as well as the environment away from the bilayer?

Answer 10

The polar head of the phospholipid is looking for other polar molecules to bond to i.e. H2O. Because both intracellular fluid and extracellular fluid are mostly composed of H2O the heads of the phospholipids naturally orient themselves toward the ECF and ICF. The hydrophobic tails are both nonpolar and naturally orient themselves toward one another also.

Question 11

Describe phospholipid molecules comprising cell membranes with regard to types of atoms that comprise the different parts of the phospholipid and their effect on polarity

Answer 11

The head of the lipid is mostly hydrogen and oxygen bonds resulting in a polar non-covalent bond. The tail of the lipid is mostly composed of a carbon tail this is covalently bonded and also non polar.

Question 12

What is the function of cholesterol in the membrane bilayer?

Answer 12

forms hydrogen bonds with heads of phospholipids and glycolipids, and fills the space between fatty acid tails

mediates membrane fluidity, makes lipid bilayer less fluid (and stronger) at normal body temperatures

increases membrane fluidity at lower temperatures

Question 13

What are the two categories of membrane proteins based on location relative to the overall structure of the membrane?

Answer 13

integral proteins and peripheral proteins

Integral proteins go throughout the ECF side and ICF side of the lipid bilayer.

Peripheral proteins are located on one side of the membrane. Attach to phospholipid heads or to integral proteins

Question 14

Compare the variability of lipids that are constituents of different types of cellular membranes with the variability of proteins that are constituents of different types of cellular membranes.

Answer 14

Membranes of different cell types and of different intracellular organelles exhibit a great variety of proteins, and are determiners of many of the membrane’s functions

In contrast with lipids in membranes of cells which vary only slightly

Question 15

Compare and contrast integral (membrane) protein(s), peripheral (membrane) protein(s), and transmembrane protein(s)

Answer 15

Integral proteins are amphipathic (like membrane lipids) and extend through or well into the bilayer

Most are transmembrane proteins (go all the way through the membrane bilayer)

• Form ion channels (channel proteins)
• Transporters (carriers)

Peripheral proteins are on one side of the membrane and attach to phospholipid heads or to integral proteins

Question 16

Compare the relative degree to which membrane cholesterol, membrane lipids, and the two types of membrane proteins are amphipathic.

Answer 16

Cholesterol is weakly amphipathic, having a small –OH group as its only polar part

Question 17

What is the composition of the glycocalyx?

Answer 17

proteins (to form glycoproteins)

lipids (to form glycolipids)

Question 18

What are the functions of the glycocalyx?

Answer 18

To protect cells from enzymatic action

For cell adhesion

For cell recognition

Question 19

How can the glycocalyx be used to identify the exterior plasma membrane surface?

Answer 19

Makes the outer membrane asymmetric, and provides a way to tell the outer surface from the inner surface.

Question 20

What features of the lipid bilayer of a plasma membrane cause it to be asymmetric?

Answer 20

Glycocalyx

Question 21

How do alterations of the glycocalyx enable cancer cells to avoid detection by the body’s immune system?

Answer 21

A cancer cell’s glycocalyx may change almost continuously, allowing it to keep ahead of immune system recognition systems and avoid destruction.

Question 22

The lipid bilayer is permeable to_____

Answer 22

nonpolar, uncharged molecules such as oxygen, carbon dioxide, and steroids

Question 23

The lipid bilayer is impermeable to______

Answer 23

ions and large uncharged polar molecules such as glucose

Question 24

The lipid bilayer is slightly permeable to_______

Answer 24

small uncharged polar molecules such as water and urea

Question 25

What are the three types of gradients that are important in living systems?

Answer 25

Concentration Gradients, in which the attribute is concentration of a chemical

Electrical Gradient, in which the attribute is electrical charges

Electrochemical Gradient, the combined influence of the above two