Chapter 3.1-3.2 Cell Membranes

Question 1

Cells are surrounded by a limiting barrier, the _____ (aka the ______ membrane) which covers the cell surface.

Answer 1

Cells are surrounded by a limiting barrier, the Plasma Membrane (aka the Cell membrane) which covers the cell surface.

Question 2

The interior of the cell is divided into two regions:

1) the ______, sperical or oval structure usually near the centre
2) the ______, the region outside of (1)

Answer 2

The interior of the cell is divided into two regions:

1) the nucleus, sperical or oval structure usually near the centre
2) the cytoplasm, the region outside of (1)

Question 3

The cytoplasm contains cell ______ and fluid surrounding them known as ______

Answer 3

The cytoplasm contains cell organelles and fluid surrounding them known as cytosol

Question 4

All of the fluid inside a cell (i.e. the cytosol + fluid inside all organelles incl the nucleus) is known as?

Answer 4

Intracellular fluid

Question 5

What is the largest intracellular fluid compartment?

Answer 5

The cytosol

Question 6

Membranes perform a variety of functions.

The most universal of which is:

• to act as a ______ _____ to the _____ of ______

In addition, they also have 2 more functions:

Answer 6

Membranes perform a variety of functions.

The most universal of which is:

• to act as a Selective B__arrier to the passage of molecules (semi-permeable)

In addition, they also have 2 more functions:

1. communication with other cells by detecting chemical signals from other cells
2. anchoring cell to adjacent cells and to the cellular matrix of CT proteins

Question 7

All membranes consist of a double layer of ______ molecules containing embedded ______

Answer 7

All membranes consist of a double layer ​of Lipid molecules containing embedded proteins

Question 8

What type of lipid is most commonly found in membranes?

Answer 8

Phospholipid

Question 9

Describe a phospholipid structure.

One end of the phospholipid has a _______ (head) region and the remainder which consists of ____ ____ ____ _____ _____, is _____. Thus, Phospholipids are _______

Answer 9

One end of the phospholipid has a charged (Polar) region and the remainder, which consists of two long fatty acid chains, is non-polar. Thus, phospholipids are amphipathic

Question 10

What compartments constitute the entire intracellular fluid?

Answer 10

The intracellular fluid compartment includes all of the water in the cytoplasm plus the water in the nucleus

Question 11

What two features of the phospholipid bilayer (plasma membrane) all cells to undergo moderate changes in shape without disrupting structural integrity?

Answer 11

1. Flexibility: chemical bonds don’t link the phospholipids to each other or the the membrane proteins = free to move = fluidity
2. Cells are filled with fluid

Question 12

The plasma membrane contains _______ (steroid), whereas intracellular membranes contain very little

Answer 12

The plasma membrane contains cholesterol, whereas intracellular membranes contain very little

Question 13

What feature of cholesterol makes it slightly amphipathic?

Answer 13

Cholesterol has a single polar hydroxyl group attached to its relatively rigid, nonpolar ring structure.

Question 14

Like phospholipids, cholesterol is inserted into the lipid bilayer with its _____ region toward the bilayer surface and its ______ rings in the interior in association with the fatty acid chains

Answer 14

Like phospholipids, cholesterol is inserted into the lipid bilayer with its polar region toward the bilayer surface and its non-polar rings in the interior in association with the fatty acid chains

Question 15

Table 3.1

What are four functions of the plasma membrane?

Answer 15

1. Regulate the passage of substances into and out of the cells and between cell organelles and cytosol
2. Detect chemical messengers arriving at the cell surface
3. Link adjacent cells together by membrane juntions
4. Anchor cells to the extracellular matrix

Question 16

The polar hydroxyl groups (of cholesterol) are joined to the polar regions of phospholipids through _______

Answer 16

The polar hydroxyl groups (of cholesterol) are joined to the polar regions of phospholipids through hydrogen bonds

Question 17

What effect does a highly ordered, tightly packed arrangement of cholesterol within the membrane have on membrane fluidity?

Answer 17

Would decrease membrane fluidity

Question 18

What are the two classes of membrane proteins?

Answer 18

1. Integral (intrinsic)
2. Peripheral (extrinsic)

Question 19

_______ membrane proteins are closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer

i.e. embedded within the membrane (partially or span entire membrane)

Answer 19

_______ membrane proteins are closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer

i.e. embedded within the membrane (partially or span entire membrane)

Question 20

Integral proteins that span the entire plasma membrane are called:

Answer 20

Transmembrane Proteins

Question 21

Like the phospholipids, the integral membrane proteins are ______: having ____ amino acid side chains in one region and _____ side chains clustered in a separate region

Answer 21

Like the phospholipids, the integral membrane proteins are amphipathic: having polar amino acid side chains in one region and nonpolar side chains clustered in a separate region

Question 22

The _______ chains of many transmembrane proteins cross the lipid bilayer several times

Answer 22

The polypeptide chains of many transmembrane proteins cross the lipid bilayer several times

Question 23

Functions of Integral proteins:

Some ________ proteins form channels through which ____ or _____ can cross the membrane.

Others are associated with the transmission of ______ across the membrane or the ______ of extracellular and intracellular ____ _____ to the plasma membrane

Answer 23

Functions of Integral proteins:

Some transmembrane proteins form channels through which ions or water can cross the membrane.

Others are associated with the transmission of chemical signals across the membrane or the anchoring of extracellular and intracellular protein filaments to the plasma membrane

Question 24

Peripheral Membrane Proteins are NOT ______, and do not associate with the ____ regions of the lipids in the membrane

Answer 24

Peripheral Membrane Proteins are NOT amphipathic, and do not associate with the nonpolar regions of the lipids in the interior of the membrane

Question 25

Peripheral membrane proteins are located at the membrane _\_\_\_\_\__ where they are bound to the _____ regions of the _______ and also (in some cases) to the \_\_\_\_\_\_

Answer 25

Peripheral membrane proteins are located at the membrane _surface_ where they are bound to the _polar_ regions of the _integral membrane proteins_ and also (in some cases) to the _charged polar regions of the membrane phospholipids_

Question 26

Most of the peripheral proteins are on the ____ surface of the plasma membrane

Answer 26

Most of the peripheral proteins are on the _cytosolic_ surface of the plasma membrane

Question 27

What are some examples of peripheral membrane functions: (3)

Answer 27

1. some are **enzymes** that mediate metabolism 2. Others involved in **local transport** of small molecules along or between the membrane 3. Associated with cytoskeletal elements that influence **cell shape and motility**

Question 28

The extracellular surface of the plasma membrane contains small amounts of ______ covalently linked to some of the membrane lipids and proteins

Answer 28

The extracellular surface of the plasma membrane contains small amounts of _carbohydrate_ covalently linked to some of the membrane lipids and proteins

Question 29

Carbohydrates on the extracellular surface of the plasma membrane consist of short, branched chains of _______ that extend from the cell surface into the extracellular fluid where they form a layer known as the \_\_\_\_\_\_\_

Answer 29

Carbohydrates on the extracellular surface of the plasma membrane consist of short, branched chains of _monosaccharides_ that extend from the cell surface into the extracellular fluid where they form a layer known as the **_glycocalyx_**

Question 30

Surface carbohydrates enable:

Answer 30

Cells to identify and interac with each other

Question 31

What are Lipid Rafts

Answer 31

Cholesterol-rich regions of decreased membrane fluidity that are believed to serve as organizing centers for the generation of complex intracellular signals

Question 32

The way that cells become organized into tissues and organs depends, in part, on the ability of ______ (transmembrane protein) to bind to specific proteins in the extracellular matrix and link them to the membrane proteins on adjacent cells

Answer 32

The way that cells become organized into tissues and organs depends, in part, on the ability of _integrins_ (transmembrane protein) to bind to specific proteins in the extracellular matrix and link them to the membrane proteins on adjacent cells

Question 33

What are three types of junctions?

Answer 33

1. Desmosome 2. Gap Junction 3. Tight Junction

Question 34

\_\_\_\_\_\_ consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm

Answer 34

_Desmosomes_ consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm

Question 35

Desmosomes are characterized by accumulations of protein known as ______ along the cytoplasmic surface of the plasma membrane

Answer 35

Desmosomes are characterized by accumulations of protein known as "_dense plaques"_ along the cytoplasmic surface of the plasma membrane

Question 36

Dense plaques (of desmosomes) serve as anchoring points for \_\_\_\_\_

Answer 36

Dense plaques (of desmosomes) serve as anchoring points for _cadherins_

Question 37

What are cadherins?

Answer 37

Proteins that are extend from the cell into the extracellular space where they link up and bind with cadherins from an adjacent cell

Question 38

What does the presence of numerous desmosomes between cells provide?

Answer 38

Structural integrity of tissues. Common in areas subject to considerable stretching (eg the skin)

Question 39

Other proteins in desmasomes, such as ______ filaments, anchor the cytoplasmic surface of desmosomes to interior structures of the cell

Answer 39

Other proteins in desmasomes, such as _keratin_ filaments, anchor the cytoplasmic surface of desmosomes to interior structures of the cell

Question 40

A ________ forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them

Answer 40

A _Tight Junction_ forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them

Question 41

Most epithilial cells are joined by tight junctions near their _____ surfaces

Answer 41

Most epithilial cells are joined by tight junctions near their _apical_ surfaces

Question 42

Tight junctions are found in epithelial tissue specialized for_**\_\_\_\_\_**_ (kidney, intestine) and functionally, for nearly _______ junctions

Answer 42

Tight junctions are found in epithelial tissue specialized for _molecular transport_ (kidney, intestine) and functionally, for nearly _impermeable_ junctions

Question 43

What is important about the movement of organic nutrients near tight junctions?

Answer 43

Prevent any molecules from moving through the interstitial space between cells - all molecules must go through the cells rather than between them = control types/amounts of substances absorbed

Question 44

The ________ consists of protein channels linking the cytosols of adjacent cells

Answer 44

The _gap junction_ consists of protein channels linking the cytosols of adjacent cells

Question 45

In the region of the gap junction, two opposing plasma membrances come within 2-4nm of each other which allows specific proteins called _______ from the two membranes to join forming small transmembrane channels linking the two cells

Answer 45

In the region of the gap junction, two opposing plasma membrances come within 2-4nm of each other which allows specific proteins called _connexins_ from the two membranes to join forming small channels linking the two cells

Question 46

A variety of cell types possess gap junctions: name two

Answer 46

1. Heart muscle = transmision of electrical activity between cells - depolarization 2. Bone cells

Question 47

Gap junctions ______ and ______ couple cells

Answer 47

Gap junctions _electrically_ and _metabolically_ couple cells

Question 48

What type of substances could move through gap junctions of cells?

Answer 48

Small water-soluble molecules and ions