Membrane Structure & Function

Question 1

what is the plasma membrane?

Answer 1

the plasma membrane surrounds the cell providing a boundary between the cells internal environment and the outside world.

Question 2

what is the structure of the plasma membrane?

Answer 2

phospholipid bilayer

Question 3

what does the phospholipid bilayer contain?

Answer 3

hydrophobic tails and hydrophilic head.

Question 4

what is a phospholipid?

Answer 4

2 fatty acid tails, glycerol, a phosphate group

Question 5

in animal cell membranes, the steroid…?

Answer 5

cholesterol is also found. it is located between the phospholipids in the bilayer.

Question 6

what does the plasma membrane consist of?

Answer 6

phospholipids, cholesterol, and protein, carbohydrates

Question 7

what are the two different types of membrane proteins?

Answer 7

integral and peripheral proteins.
integral: 80%
peripheral: 20%

Question 8

what are integral proteins?

Answer 8

proteins that are embedded in the lipid bilayer by their hydrophobic regions.
they may have a hydrophilic region extending on one or both sides of the membrane called transmembrane proteins.

Question 9

what are peripheral proteins?

Answer 9

• these proteins dont penetrate the lipid bilayer
• they are loosely associated with the inner OR outer side of the plasma membrane

Question 10

how are membrane proteins held in place?

Answer 10

by attaching to the fibers of the extracellular matrix or by attaching to the cytoskeleton

Question 11

functions of membrane proteins?

Answer 11

• transport: moving substances across the cell membrane
• enzymatic activity: membrane proteins act as enzymes that speed up chemical reactions.
• signal transduction/receptor molecules: membrane proteins serve as receptors that detect signals. when a signal binds to the receptor, it triggers a response inside a cell, helping it react to changes in its environment.
• cell-cell recognition: specifically glycoproteins: protein that has a carbohydrate group attached, they help distinguish between self and foreign. important for immune response and embryonic development.
• intercellular joining: membrane proteins can help cells stick together. some form gap junctions that are channels that allow materials to pass directly from one cell to another.
• attachment to the cytoskeleton and ecm: membrane proteins anchor the cell to its cytoskeleton. helps maintain the cells shape and provides structural support.

Question 12

most membranes contain?

Answer 12

small but significant amounts of carbohydrates.

Question 13

carbs in membranes?

Answer 13

• usually branched chains that have 15 sugar units.
• most of the carbohydrates are in the form of glycoproteins: protein with a carbohydrate attached to it.
• some are in the form of glycolipids: lipid with carbohydrate attached to it.
  MAINLY GLYCOPROTEINS

Question 14

the carbohydrates protrude to the?

Answer 14

external side of the membrane: the function is playing a role in cell to cell recognition, especially glycoproteins.

Question 15

the type of blood type you are depends on?

Answer 15

the type of carbohydrate you have sticking out of the surface of the red blood cells.
4 blood types: ab,a,b,o

Question 16

the carbohydrates found differ between?

Answer 16

cell types, between species, and differ between members of the same species

Question 17

what is the fluid mosaic model?

Answer 17

most accepted current model that is used to describe the structure of a membrane.
- mosaic refers to the different types of proteins present within the phospholipids. ex: rbc have 50+ different types of proteins in its plasma membrane.
- fluid refers to the membrane being fluid. the phospholipids and the proteins can move freely about the membrane, move laterally, flip from one side to another, but proteins move but they dont move too much because they are large.

Question 18

membrane fluidity is important for cell functionality and is affected by?

Answer 18

• temperature
• the type of lipids that the membrane is composed of

Question 19

the fluidity of the membrane increases with?

Answer 19

increasing temperature

Question 20

the fluidity of the membrane decreases with?

Answer 20

decreasing temperature

Question 21

membranes with longer chain fatty acids are?

Answer 21

less fluid than those with shorter chains.

Question 22

membranes with short chain fatty acids are?

Answer 22

more fluid than those with longer chains.

Question 23

membranes that contain more unsaturated fatty acids are?

Answer 23

more fluid.

Question 24

cholesterol is found?

Answer 24

between the phospholipids in either layer.

Question 25

cholesterol acts as?

Answer 25

a temperature buffer

Question 26

at high temperatures, cholesterol makes the membrane?

Answer 26

less fluid because it restrains the movement of phospholipids.

Question 27

at low temperatures, cholesterol makes the membrane?

Answer 27

more fluid. it interacts with the hydrocarbon chains so that they do not fit as tightly together.

Question 28

most organisms that experience temperature fluctuations can?

Answer 28

regulate their membrane fluidity by changing the lipid composition of their membrane, called HOMEOVISCOUS ADAPTATION.

Question 29

fish in an outdoor pond, when cold, there are more unsaturated or saturated fatty acids?

Answer 29

unsaturated fatty acids

Question 30

archaea in a hot spring, when hot, there are more unsaturated or saturated fatty acids?

Answer 30

saturated fatty acids

Question 31

membrane asymmetry?

Answer 31

membranes contain different kinds of lipids and proteins. - they are randomly distributed between the two monolayers. - each membrane has a distinct side that has a unique composition.

Question 32

extracellular face vs cytoplasmic face?

Answer 32

extracellular face: outside cytoplasmic face: inside

Question 33

membranes are selectively?

Answer 33

permeable

Question 34

solutes are carried across membranes via?

Answer 34

3 different mechanisms: simple diffusion, facilitated diffusion, and active transport

Question 35

passive process?

Answer 35

simple diffusion and facilitated diffusion - no energy is required to move solutes across. - movement is with the concentration gradient: high to low. - for facilitated diffusion, transport proteins are required: channel or carrier proteins.

Question 36

what kind of transport proteins are required for facilitated diffusion?

Answer 36

channel or carrier proteins

Question 37

active process?

Answer 37

active transport: - energy is required - movement is against the concentration gradient: low to high - transport proteins are always involved in this process: carrier proteins

Question 38

function of active transport?

Answer 38

1. allows the cell to uptake essential nutrients from the environment when they are lower outside the cell than inside the cell. 2. it allows secretory or waste products to be removed from the cell even when the concentration is higher outside the cell. 3. it allows a constant nonequilibrium concentration of certain ions inside the cell.

Question 39

in an animal cell there are more potassium ions inside the cell than outside the cell. more sodium ions outside the cell than inside the cell? how is this maintained?

Answer 39

- sodium is pumped out of the cell and potassium is pumped into the cell. - both are pumped against their concentration gradient. - a transport protein called sodium potassium pump located in the plasma membrane of animal cells moves these ions.

Question 40

more about the sodium potassium pump?

Answer 40

3 sodium out for every 2 potassium in. this results in a difference of charge between the outside and inside of the cell. the cytoplasm is negative in charge compared to the extracellular fluid.

Question 41

cells have voltages across their plasma membrane, this voltage is referred to as?

Answer 41

membrane potential.

Question 42

pumps that generate a voltage are called?

Answer 42

electrogenic pumps.

Question 43

whats the major electrogenic pumps in animal cells?

Answer 43

sodium potassium pump.

Question 44

whats the major electrogenic pumps in plant cells?

Answer 44

proton pump.

Question 45

why are these pumps useful?

Answer 45

by generating these voltages across membranes, these pumps help the cell to store energy that can be used for future cellular work. ex: transport of materials across the membrane

Question 46

in plants, the proton pump is used to?

Answer 46

transport sucrose into a sieve tube cell.

Question 47

what is cotransport?

Answer 47

cotransport occurs when a pump transporting a specific solute across the membrane is responsible for indirectly pumping another solute across the membrane against its concentration gradient.

Question 48

molecules such as water and small solutes can move across the membrane via?

Answer 48

diffusion

Question 49

how do large proteins and polysaccharides enter and exit the cell?

Answer 49

large molecules generally cross the membrane by a mechanism involving vesicles.

Question 50

large molecules exit via?

Answer 50

exocytosis: example is pancreatic cell secreting insulin.

Question 51

large molecules enter via?

Answer 51

endocytosis: the cell takes in molecules by forming new vesicles from the plasma membrane.

Question 52

3 types of endocytosis are?

Answer 52

phagocytosis, pinocytosis, and receptor mediated endocytosis.

Question 53

what is phagocytosis?

Answer 53

- cellular eating - folds of the plasma membrane called pseudopods surround a particle. - a phagocytic vacuole is formed - the vacuole fuses with a lysosome and the material is digested ex: used as a means of acquiring food, and defence by certain white blood cells.

Question 54

what is pinocytosis?

Answer 54

- pinocytosis are cellular drinking - results from the inward folding of the plasma membrane to form a pocket. - it fuses to form a vesicle - the vesicle fuses with a lysosome for breakdown of the internalized materials.

Question 55

what is receptor mediated endocytosis?

Answer 55

- on the plasma membrane there are receptors for certain substances. - when the receptor binds to the ligand, the complex moves to a special region on the plasma membrane called a coated pit. - forms a vesicle - the vesicle fuses with a lysosome.