Chapter 12

Question 1

Where is the plasma membrane found and what does it have ?

Answer 1

The plasma membrane is found at the boundary of the cell and it has selective permeability

Question 2

What is the structure for all biological membranes

Answer 2

The structure is a phospholipid bilayer

Question 3

Explain the structure of the phospholipid

Answer 3

The head is hydrophilic facing the outside
The tail is hydrophobic being able to reach the membrane

Question 4

In the animal membrane what type of steroid is found?

Answer 4

The steroid cholesterol is found and is located in between the phospholipids in the bilayer

Question 5

What does the plasma membrane consists of ?

Answer 5

proteins, carbs, cholesterol ,phospholipid

Question 6

What are the two types of membrane proteins

Answer 6

Integral proteins and peripherical proteins

Question 7

What are integral proteins ?

Answer 7

The proteins are embedded in the lipid bilayer by their hydrophobic regions

They may have a hydrophilic region extending on oner or both sides of the membrane -(Transmembrane proteins)

Question 8

What are the peripheral proteins ?

Answer 8

Do not penetrate in the lipid bilayer

Associated loosely with the inner or outer side of the plasma membrane

Question 9

How are the membrane proteins held in place?

Answer 9

The membrane may be held in place by attaching fibres to the ECM

OR

May be held in place by attaching to the cytoskeleton

Question 10

What are the functions of the membrane proteins ?

Answer 10

Transport
Enzymatic activity
Signal transduction
Cell to cell recognition
Intercellular joining ( proteins involved in forming gap junctions)
Attachment to the cytoskeleton and the ECM( helps gives cells shape and structural support )

Question 11

What are the membrane carbs ?

Answer 11

Most membranes contain small significant amounts of carbs
Usually branched chains that have less than 15 sugar units

Question 12

What form are the membrane carbs found in ?

Answer 12

Most of them are found as Glycoproteins (proteins attached to a carb )
Some are found in the form of glycolipids(a lipid with a carb attached to it)

Question 13

Where are carbs found in the membrane

Answer 13

They are found in the external side of the membrane and function in cell to cell recognition

Question 14

What is an example of glycoproteins ?

Answer 14

Human blood types( different types of glycoproteins found on the surface)
They have an RH factor either positive or negative
Play a role in cell to cell recognition > need blood type to match for recognition

Question 15

How do carbs found in the membrane differ?

Answer 15

They differs in terms of cell types , between species and differ in between members of the same species

Question 16

What is the fluid mosaic model?

Answer 16

The most accepted current model that is sued to describe the structure of a membrane
Proposed by Jonathan singer and Garth nicolson in 1972

Question 17

What does mosaic mean

Answer 17

Refers to the different types of proteins present within the phospholipid bilayer

Examples are RBC have around 50 different of proteins in it’s plasma membrane

Question 18

What does fluid mean

Answer 18

The membrane is fluid
The phospholipids and proteins can move freely around the membrane

Question 19

Why is maintaining fluidity important?

Answer 19

Allows membrane proteins to move freely in order to carry out the functions

Allows cells to change shape which is important during cell division and movement

Allows materials like lipids and proteins to diffuse

Allows membrane to self heal

Is Able to adjust to temp which is vital for cellular functions

Question 20

What is membrane fluidity affected by ?

Answer 20

Affected by temp and the types of lipids that make up the membrane

Question 21

How does temp affect fluidity ?

Answer 21

Fluidity increases with increasing temp
Decreases with decreases temp

Question 22

How does lipid composition affect the membrane fluidity ?

Answer 22

Dependant on the type of lipid that makes up the membrane

Question 23

How does fatty acid composition affect the fluidity of a membrane ?

Answer 23

The length of the fatty acid side chain- membrane that have longer fatty acids chains are less fluid with those with shorter chains

Membranes that contain unsaturated fatty acids are more fluid - this is because the unsaturated fatty acids contain one or more double bonds which Create kinks preventing the molecules from packing tightly together

Presence of sterols= found in between the phospholipids in either layers

Question 24

How does cholesterol influence fluidity ?

Answer 24

Cholesterol acts as a temp buffer - experts different effects at different temperatures

At high temps makes the membrane less fluid (restrains the movement of phospholipids )

At low temps makes the membrne more fluid
(Interacts with the hydrocarbon chains so that they don’t fit as tight together when the temperature is low )

Question 25

What is the role of cholesterol

Answer 25

Helps keep the membrane fluid with the temperature changes

Question 26

How can organisms regulate membrane fluidity ?

Answer 26

By changing the lipid composition of the membrane Called homeoviscous adaption takes place in bacteria , yeasts , plants and ectotherms

Question 27

Examples of homeviscous adaptions

Answer 27

Fish in an outdoor pond in the cold will increase unsaturated fatty acids And archea in hot springs will have more unsaturated fatty acids

Question 28

What is membrane asymmetry

Answer 28

Membranes contain diff kinds of lipids and proteins which are randomly disturbuted in between the two monolayers Each membrane has a distinct side that has a unique composition of proteins and lipids

Question 29

What side of the membrane will the glycoprotein be found ?

Answer 29

On the extra cellular side , carb chains facing outward interacting with the external environment

Question 30

How are materials transported across a membrane ?

Answer 30

Solutes are carried across through three different mechanisms 1) simple diffusion 2)facilitated diffusion 3) active transport

Question 31

What are the difference in between active and passive ?

Answer 31

Passive = simple , no energy , movement is with the concentration gradient, transport proteins are used for facilitated diffusion Active transport = energy is required , movement id against the concentration gradient and transport proteins are always involved

Question 32

What is the function of active transport

Answer 32

Allows cells to uptake essential nutrients from the environment when they are lower outside the cell then inside the cell Allows secretory or waste products to be removed from the cell when the concentration is higher outside the cell Allows a constant , non equilibrium concentration of certain ions inside the celll

Question 33

What is the sodium potassium pump?

Answer 33

Sodium is pumped out of the cell and potassium is pumped into the cell Both are pumped against their concentration gradient A transport protien called the sodium potassium pump located in the plasma membrane move here ion

Question 34

How many Na + are pumped for every K+ ions?

Answer 34

Every 3 for every 2 Results in difference in charge between the outside and the inside of the cell Cytoplasm is negative in charge compared to the extracellular fluid

Question 35

What is membrane potential?

Answer 35

Voltage across the plasma membrane

Question 36

What is an electrogenic pump?

Answer 36

Pumps that generate voltage Sodium potassium is major electrogenic pump in animal cells

Question 37

What is the electrogenic pump in plants , bacteria and fungi

Answer 37

Proton pump Helps the store energy that can be used for future cellular work Transport materials across the membrane( transport sucrose into sieve tube cells)

Question 38

What is co transport

Answer 38

Occurs when a pump transporting a specific solute across the membrane is responsible for indirectly pumping another solute across the membrane against the concentration gradient

Question 39

How can water and small molecules move across the membrane

Answer 39

They can move via diffusion other transport processes that move molecules include facilitated diffusion and active transport

Question 40

How do large molecules enter and exit the cell

Answer 40

Large proteins and polysaccharides Generally cross the membrane by a mechanism involving vesicles

Question 41

What is exocytosis?

Answer 41

Large molecules exit via exocytosis I)A vesicle that contains proteins buds from the golgi II) the vesicle travels along a microtubule to the plasma membrane III) the outside of the vesicle binds to the inside of the plasma membrane IV) the two membranes fuse , releasing (secreting) the proteins outside of the cell Example = pancreatic cell secreting insulin

Question 42

What is endocytosis ?

Answer 42

The cells take in the molecules by forming new vesicles from the plasma membrane

Question 43

What are is phagocytosis

Answer 43

1)phagocytosis (cellular eating)= folds the plasma membrane called pseudopods surround a particle Basically a phagocytic vacuole is formed and the vacuole fuses with a lysosome and the material is digested (defences by certain white blood cells)

Question 44

What is pinocytosis ?

Answer 44

pinocytosis (cellular drinking )= results from the inward folding of the plasma membrane to form a pocket. Fuses to make a vesicle and then fuses with lysosome to breakdown internalized materials

Question 45

What is receptor mediated endocytosis ?

Answer 45

On the plasma membrane are receptors for certain substances When the receptor binds to its Ligand, the complex moves to a special region on the plasma membrane called a coated pit It forms a vesicle and then the vesicle fuses with a lysosome