Chapter Six

Question 1

describe the structure of phospholipids and how they can vary in the bilayer.

Answer 1

basic model is polar hydrophilic phosphate heads on the outside and the inside of the cell, with non polar fatty acid tails on the inside of the bilayer.
Things that may vary:
1. the fatty acid chain length
2. the degree of saturation
3. the phosphate groups

membranes are dynamic, constantly forming, transforming, fusing, and breaking down

Question 2

describe the fluid mosaic model and how does fluidity vary?

Answer 2

it is the general structure of biological membranes which contain the basic lipid bilayer (lake) and a variety of proteins which float.

fluidity depends on a few things

1. lipid concentration, cholesterol and saturated, long fatty acid chains pack tightly and make it less fluid
2. fluidity decreases as the temp drops, some organisms even change composition of lipids from saturated to unsaturated when temp drops

Question 3

what are transmembrane proteins?

Answer 3

proteins that extend all the way through phospholipid bilayer, and contain one or more transmembrane domains

Question 4

what are transmembrane domains?

Answer 4

an inner or outer side of the bilayer, that have specific functions

Question 5

what integral proteins?

Answer 5

are proteins that are amphipathic and can be in any part of the bilayer

Question 6

what are peripheral proteins?

Answer 6

proteins that lack hydrophobic regions, so they cannot penetrate the bilayer

Question 7

What are glycolipids?

Answer 7

sugars + lipid

Question 8

What are glycoproteins?

Answer 8

sugar + proteins

Question 9

How do cells arrange themselves in groups?

Answer 9

cell recognition -none cell specifically recognizes and bind to another of a specific type

cell adhesion - connection between cells is strengthened
(homotypic or heterotypic)

Question 10

what is a cell junction?

Answer 10

specialized structures that hold cells together

Question 11

what are the three types of cell junctions?

Answer 11

1. tight junctions - prevent substances from moving through spaces between cells, ensures directional movement (bladder)
2. Desmosomes - “spot welds” materials can move around in the ECM and it provides mechanical stability (skin)
3. Gap junctions - allows communication, channel proteins, muscles/nerve

Question 12

What is the ECM?

Answer 12

it is a heterogeneous mix of materials surrounding cells (membranes also adhere to the matrix)

Question 13

What is a protein that binds to the ECM and binds to other materials in the ECM

Answer 13

Integrin is a transmembrane protein that binds to the matrix outside epithelial cells and to actin filaments inside the cell.

Question 14

What is selective permeability?

Answer 14

when a something, specifically the membrane, allows certain substances but not others

Question 15

explain simple diffusion.

Answer 15

a type of diffusion that goes with the concentration gradient

the driving force is the energy that comes from the concentration gradient

it does not require a membrane protein or an energy input

Question 16

explain passive transport.

Answer 16

passive transport eg. facilitated diffusion

-passive movement of polar molecules through a membrane involving a specific protein

it goes with the concentration gradient and its driving force is the energy that comes from the concentration gradient

it requires membrane proteins, (channel or carrier) and it requires no energy input

Question 17

explain active transport.

Answer 17

active transport goes against the concentration gradient

the driving force is ATP hydrolysis, and it requires a transport protein, and it does require an energy input

Question 18

What affects rate of diffusion?

Answer 18

1. Size and mass of molecule or ion
2. Temperature
3. Density of solution
4. Concentration gradient (70% to 0%) is faster than (20% to 10%)
5. Volume (area and distance)

Question 19

What is osmosis?

Answer 19

the diffusion (process of random movement toward equilibrium) of water

when water from a low solute concentration moves to an area of high solute concentration to balance \

Question 20

Isotonic solution?

Answer 20

equal solute concentrations between two solutions

water flows in and out at the same rate

plants require this, and if a plant is isotonic it has good turgor pressure

Question 21

hypotonic?

Answer 21

when the solution we are referring to has a low solute concentration, and higher water concentration

cells burst in hypotonic solutions relative to the cells solute concentration

Question 22

hypertonic?

Answer 22

when a solution has a high solute concentration

Question 23

what is turgor pressure?

Answer 23

when plants with rigid cell walls build up internal pressure from water entering that give the cell structure

and prevents more water from entering

Question 24

What are the kinds of proteins involved in active transport?

Answer 24

1. Uniporter (uni = one) - moves one substance in one direction
2. Symporter (sym = same) - moves two substances in one direction
3. Antiporter - moves two substances in opposite directions

Question 25

What is primary active transport?

Answer 25

process of moving two substances against their concentration gradient which requires direct hydrolysis of a high energy molecule

uses a integral glycoprotein (antiporter)

Question 26

what is secondary active transport?

Answer 26

when the energy from the concentration gradient established from primary active transport is used to transport other molecules such as glucose against their gradient

a symporter protein (two things SAME direction) couples the movement of glucose against the concentration gradient with the passive movement of Na+

Question 27

what is endocytosis?

Answer 27

when macromolecules like proteins, polysaccharides and nucleic acids are to large to cross the membrane

the cell membrane folds inward around the macromolecule and forms a vesicle

Question 28

Phagocytosis?

Answer 28

when molecules or entire cells are engulfed

some protists feed this way, and some white blood cells engulf foreign substances

when this happens a “food vacuole” or a phagosome forms, and it fuses with a lysosome

Question 29

Pinocytosis?

Answer 29

when a vesicle forms to bring in small dissolved substances or fluids into a cell

much smaller vesicles than in phagocytosis

Question 30

receptor-mediated endocytosis?

Answer 30

when highly specific macromolecules bind to receptor proteins and create a coated vesicle

example is LDL (cholesterol) cells have specific protein receptors for it

Question 31

Exocytosis?

Answer 31

when materials in vesicles are expelled from the cell

eg. indigestible materials, digestive enzymes, neurotransmitters