Topic 4.1: Cell Membranes and Transport

Question 1

Why is the term fluid used in description of the cell surface membrane?

Answer 1

both the phospholipids and proteins can move around

Question 2

Why is the term mosaic used in the description of the cell surface membrane?

Answer 2

because when viewing the surface of the membrane, the scattered proteins produce a mosaic-like pattern

Question 3

features of the fluid-mosaic model

Answer 3

phospholipids arranged in a bilayer, proteins, cholesterol

Question 4

How are phospholipids arranged in a bilayer?

Answer 4

• the hydrophilic/polar heads face outwards to interact with the aqueous-environment inside and outside of the cell
• the hydrophobic/nonpolar tails face inwards toward each other

Question 5

peripheral proteins

Answer 5

completely hydrophilic, sit on the surface of the phospholipid bilayer

Question 6

integral proteins

Answer 6

hydrophobic and hydrophilic regions, embedded in the phospholipid bilayer

Question 7

transmembrane proteins

Answer 7

span the whole membrane

Question 8

What do phospholipids form?

Answer 8

a bilayer, the basic structure of a membrane

Question 9

Why is the cell surface membrane semi-permeable?

Answer 9

the hydrophobic tails on the interior of the bilayer make it different for polar molecules/ions to cross

Question 10

How do phospholipids affect the fluidity of the membrane?

Answer 10

the more unsaturated tails —–> the more fluid

the longer the tails —-> the less fluid

Question 11

role of cholesterol in a cell surface membrane

Answer 11

help stabilize the membrane by regulating its fluidity

Question 12

What happens to phospholipids when it’s hot?

Answer 12

they move apart

Question 13

What happens to the cell surface membrane when it’s cold?

Answer 13

phospholipids move together

Question 14

What is the role of cholesterol when the conditions are hot?

Answer 14

the cholesterol hold the phospholipids together to prevent them from moving apart

Question 15

What is the role of cholesterol when the conditions are cold?

Answer 15

cholesterol keeps the phospholipids spaced apart so they do not move too close together causing the bilayer to become rigid

Question 16

glycoproteins and glycolipids

Answer 16

proteins and phospholipids with short carbohydrate chains attached to them

Question 17

What roles do the carbohydrate chains give glycoproteins and glycolipids?

Answer 17

1. they act as receptors
2. they act as cell markers
3. help stabilized membrane structure by forming hydrogen bonds with water

Question 18

function of a receptor

Answer 18

to bind with small molecules that arrive at a cell’s surface

Question 19

function of cell markers/antigens

Answer 19

allows for cells to recognize each other (cell-cell recognition is important)

Question 20

why is cell-cell recognition important

Answer 20

• growth and development
• immune responses, where surface antigens allow WBC’s to distinguish between “self” and “non-self”

Question 21

transport proteins

Answer 21

help ions and polar molecules to move in and out of cells

Question 22

channel transport porteins

Answer 22

provide hydrophilic channels that allow ions to diffuse through, most are “gated” to control when ions are exchanged

Question 23

carrier transport proteins

Answer 23

have binding sites for specific molecules and can change shape to “carry” a molecule that binds to this site across the membrane

Question 24

enzymes

Answer 24

catalyze chemical reactions associated with cellular functions that occur at a cell surface

Question 25

two methods of cell signaling

Answer 25

chemical and electrical

Question 26

cell signaling

Answer 26

any method by which one cell sends a message to another cell

Question 27

chemical signaling

Answer 27

chemical signals (e.g. hormones) transmitting messages between cells

Question 28

electrical signaling

Answer 28

nerves transmitting messages between cells

Question 29

What is cell signaling important for?

Answer 29

coordinating the activities of cells

Question 30

Stages of CHEMICAL signaling

Answer 30

1. secrete the chemical signal by exocytosis 2. ligands diffuse through the tissue fluid OR through the bloodstream to reach the target cells 3. binding of a ligand to a receptor that triggers a series of events inside the target cells that ends in the desired response

Question 31

target cells

Answer 31

cells that have complementary-shaped receptors to the ligand

Question 32

3 steps of a cell signaling pathway

Answer 32

1. RECEPTION 2. TRANSDUCTION 3. RESPONSE

Question 33

what is the reception step of a cell signaling pathway

Answer 33

the ligand binds to a complementary receptor (glycoprotein or glycolipid) in the cell surface membrane of a target cell

Question 34

what is the transduction step of a cell signaling pathway

Answer 34

the message is transmitted to the correct location inside the cell through a series of chemical reactions

Question 35

what is the response step for a cell signaling pathway

Answer 35

the desired cellular response is activated

Question 36

Main purpose of the transduction step of a cell signaling pathway

Answer 36

to amplify the response

Question 37

how is the response amplified during the transduction step of a cell signaling pathway?

Answer 37

one ligand binds to a receptor in the cell surface membrane and leads to the production of many second messenger molecules. these second messenger molecules activate the series of chemical reactions needed to cause the cellular response