Cell Processes Lecture 22

Question 1

Non Mediated Transport

Answer 1

• doesn’t directly use transporter protein
• diffusion through bilayer
• important for absorption of nutrients and excretion of waste
• non-polar hydrophobic molecules

Question 2

Mediated Transport

Answer 2

moves material with the help of a transporter protein

Question 3

Active Transport

Answer 3

uses ATP to drive substances against the concentration gradient

Question 4

Passive Transport

Answer 4

moves substances down their concentration gradient with only their kinetic energy

Question 5

Vesicular Transport

Answer 5

moves materials across membrane in small vesicles either by exo or endocytosis

Question 6

Ion Channels

Answer 6

Water filled pores that span the hydrophobic core of the lipid bilayer and allow passage of ions across the cell membrane (ion do not bind to channel pore)

Question 7

Ion Selectivity

Answer 7

Specific amino acids lining the pore determine the sensitivity of the channels to ions and by being selective they can harness the energy stored in different ion gradients

Question 8

Gated Channels - opening/closing of gate is controlled by

Answer 8

• Voltage
• Ligand binding
• Cell Volume
• pH
• phosphorylation

Question 9

What does the diffusion of ions generate

Answer 9

a measurable current of 10^-12 amps

Question 10

How can the current fluctuations be measured

Answer 10

Patch Clamp method

Question 11

What do the current fluctuations represent

Answer 11

• opening and closing of single ion channels

- conformational changes in channel structure that are associated with channel gating

Question 12

Carriers - Transport can be

Answer 12

passive or active

Question 13

In carriers the substrate ……. so a …….. is undergone meaning transport rates are …….. than carriers

Answer 13

directly interacts with the transport proteins; conformational change; slower

Question 14

Carriers exhibit:

Answer 14

• Specificity
• Inhibition
• Competition
• Saturation

Question 15

Saturation

Answer 15

Glucose transport occurs until all binding sites are saturated

Question 16

Steps to facilitated diffusion of glucose

Answer 16

1) Glucose binds to transport protein
2) Transport Protein changes and glucose moves across the membrane
3) Kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate

Question 17

What does the conversion of glucose do

Answer 17

maintains a concentration gradient for glucose entry

Question 18

Active Transport

Answer 18

an energy requiring process that moves molecules and ions against their concentration gradient

Question 19

Primary Active Transport

Answer 19

• energy directly derived from ATP hydrolysis

- typical cell uses 30 of its energy on primary active transport

Question 20

Secondary Active Transport

Answer 20

• energy stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient

Question 21

Na/K ATPase: _ Na+ ions are ______ from the cell as _ K+ are ______ ____ the cell therefore the pump generates a ___ _______ and is ______. This process is known as the _____ _____ _____

Answer 21

3; removed; 2; brought into; net current; electrogenic; pump leak hypothesis

Question 22

The difference of Na+ concentration (low) and K+ concentration (high) is important for

Answer 22

• maintaining resting membrane potential
• electrical excitability
• concentration of muscle
• maintenance of steady state cell volume
• uptake of nutrients via secondary active transporters
• maintenance of intracellular pH by secondary active transporters

Question 23

How do the secondary active transporters work

Answer 23

They use energy stored in the ion gradients created by active transporters to move substances across their own concentration gradient thus indirectly use the energy obtained by the hydrolysis of ATP

Question 24

Examples of secondary active transporter

Answer 24

• Na+ antiporter or exchangers (Na+ in Ca2+ or H+ out)

- Na+ symporters or cotransporters (GLucose or amino acids rush in together with Na+ ions)

Question 25

Endocytosis

Answer 25

bringing large particles into the cell

Question 26

Phagocytosis

Answer 26

• Cell eating by macrophages and WBCs as pseudopods extend from the phagosome and the phagosome fuses with a lysosome which degrades the particle

Question 27

Pinocytosis

Answer 27

Cell drinking (no receptor proteins involved) and no pseudopods form so it is non selective drinking of extracellular fluid

Question 28

Receptor mediated endocytosis

Answer 28

1) Desired substance binds to receptor protein in pit region of cell membrane
2) Binding causes membrane to fold inward forming a vesicle
3 -4) Vesicle becomes uncoated and combine with endosome
5) Receptor proteins separate from ligands and return to surface
6-7) Ligands are digested by lysosomal enzymes or transported across cell

Question 29

Exocytosis

Answer 29

Substances are exported from the cells by fusion of the vesicle with the cell membrane