Lecture 2- Transport across the cytoplasmic membrane

Question 1

what is the function of a cytoplasmic membrane?

Answer 1

to control what passes into and out of a cell

Question 2

what kind of permeability is a cytoplasmic membrane?

Answer 2

selectively permeable (semi- permeable)
the cell plays an active role in determining its own selective permeability

Question 3

why cant we just wait for everything to diffuse into a cell?

Answer 3

the cell will die because it takes so long to diffuse things into a cell. it isnt just necessarily about size, things are just hard to diffuse across a cell membrane

Question 4

what normally uses passive diffusion?

Answer 4

water, oxygen, carbon dioxide

Question 5

does water only use passive diffusion?

Answer 5

no, there are also aquaporins used to move water across a cell membrane

Question 6

how is facilitated diffusion similar to passive diffusion? (3)

Answer 6

1. movement of molecules is not energy dependent
2. direction of movement is from high to low conc.
3. size of concentration gradient impacts rate of uptake

Question 7

how is facilitated diffusion different from passive diffusion? (3)

Answer 7

1. uses carrier molecules
2. smaller concentration gradient is required for significant uptake of molecules
3. effectively transports glycerol, sugars and amino acids

Question 8

not all bacteria are the same so what do the statements of facilitated diffusion have to do with that?

Answer 8

they are generalized statements!

Question 9

what are characteristics of carrier- mediated transport systems? (2)

Answer 9

show saturation effect
highly specific

Question 10

what does it mean to reach saturation in carrier- mediated transport systems?

Answer 10

take up all molecules it can
for example, it might be able to only take 4 molecules at once… therefore, if we give the carrier 20 molecules, it wont make the carrier protein move stuff into the cell any faster

Question 11

what is facilitated diffusion?

Answer 11

diffusion with a carrier that is driven by concentration gradients

Question 12

how much can a membrane transporter concentrate substance compared to the external environment?

Answer 12

1000 times (3x the magnitude)

Question 13

what are the 3 classes of membrane transporters that have been identified?

Answer 13

uniporters
antiporter
symporter

Question 14

what do uniporters do?

Answer 14

transport a substance from one side of a membrane to the other in one direction

Question 15

what do antiporters do?

Answer 15

transport one substance across the membrane in one direction and a second molecule in the opposite direction

Question 16

what do symporters do?

Answer 16

transport two molecules across the membrane in the same direction

Question 17

what do antiporters and symporters have in common?

Answer 17

they are both cotransporters

Question 18

transport requires energy, what are the two types of energy that are used?

Answer 18

ATP hydrolyzed to ADP
Proton motive force (PMF) coupled to transport (as a proton goes down conc. gradient, energy is generated to move a molecule against its conc. gradient)

Question 19

what are the two major mechanisms with carrier proteins?

Answer 19

active transport
group translocation

Question 20

what is active transport?

Answer 20

energy dependent pumping system in which the substance being transported combines with a membrane bound carrier which releases the substance into the cell UNCHANGED

Question 21

why might you need to use active transport?

Answer 21

concentration of substance inside the cell is higher than outside the cell
ex. sugars, amino acids, organic acids, inorganic ions

Question 22

what is an example of a transporter that uses active transport?

Answer 22

ABC type transporters

Question 23

what is group translocation?

Answer 23

molecule is transported and modified during transport

Question 24

what is an example of group translocation?

Answer 24

PTS system

Question 25

in lac permease of E. coli, how is lactose transported into E.coli?

Answer 25

simple transporter lac permease that is a symporter (transports lac permease and H+ into the cell simultaneously) is therefore energy driven

Question 26

what does ABC transport stand for?

Answer 26

ATP binding casette

Question 27

what are the most known large families that are apart of ABC transport?

Answer 27

B. subtilus E. coli

Question 28

what do ABC transporters do?

Answer 28

uptake organic compounds (sugars, amino acids), inorganic nutrients (sulfate, phosphate) and trace metals

Question 29

is ABC transport active or passive? is it specific or not?

Answer 29

active high specificity

Question 30

what is the difference between gram- negative bacteria and gram- positive bacteria in ABC transport?

Answer 30

gram- negatives: have periplasmic- binding proteins and ATP driven transport proteins gram positives: have substrate- binding lipoproteins and ATP driven transport proteins

Question 31

what are the 3 components to ABC transporters?

Answer 31

periplasmic binding protein integral membrane protein ABC protein that provides ATPase function

Question 32

how does a solute enter a gram negative bacteria? (6)

Answer 32

solute periplasmic space solute binds to solute binding protein binding protein + solute bind to the binding site on the integral membrane protein solute is released to integral membrane protein and protein goes down the permease channel ATP turns into ADP (because one phosphate was used to get solute into cell)

Question 33

what does the hydrolysis of ATP by ABC protein provide?

Answer 33

energy for translocation of solute

Question 34

what are the 3 major transport systems in prokaryotes?

Answer 34

simple transport ABC transporter group translocation

Question 35

what energy does simple transport use?

Answer 35

proton motive force

Question 36

what energy does ABC transport use?

Answer 36

ATP

Question 37

what energy does group translocation use?

Answer 37

phosphoenolpyruvate

Question 38

how is group translocation different from ABC transport?

Answer 38

substance is chemically altered during uptake across a membrane

Question 39

what does it mean when a substance is altered during translocation?

Answer 39

high concentration of the original substance does not build up in the cell, therefore this favors overall diffusion in the cell (transporting with the gradient)

Question 40

what transport system uses the PTS system?

Answer 40

group translocation

Question 41

what is the PTS system?

Answer 41

phospho relay that results in the phosphorylation and transport of a compound

Question 42

what is something unique that the PTS system does?

Answer 42

can help choose the best carbon source available ex. for E. coli there is an option to use glucose or lactose, the PTS system tells it to use all the glucose first because its a better carbon source

Question 43

what is the overall reaction of the phosphotransferase system?

Answer 43

PEP (into cell) + carbohydrate (out of cell) --> pyruvate (into cell) + carbohydrate--P (into cell)

Question 44

what are the 5 components of the PTS system? where are they located?

Answer 44

EI (enzyme I) in cytosol HPr (histidine protein) in cytosol IIA (enzyme IIA) in cytosol IIB (enzyme IIB) in cytosol or membrane IIC (enzyme IIC) membrane

Question 45

how does group translocation work with ex. phosphotransferase system in E. coli?

Answer 45

1. PEP donates P to a phosphorelay system 2. P is transferred through a series of carrier proteins (EI, HPr, IIA, IIB, IIC) and deposited onto the glucose as it is brought into the cell 3. sugar is phosphorylated during transport across the membrane