Membrane Transport

Question 1

Compare between intercellular and intracellular

Answer 1

Exchange within the cell itself, i.e. the intracellular environment
Exchange between the surrounding intercellular medium

Question 2

Types of macrotransfer

Answer 2

Exocytosis
Movement out of the cell
Endocytosis
Movement into the cell

Question 3

Exocytosis is

Answer 3

Process of releasing large biomolecules through the plasma membrane

Question 4

Define Ca2+-dependent Exocytosis (regulated)

Answer 4

Requires the presence of Ca2+ for the vesicle to be released
Important process in:
Neuronal communication
Converts electrical information into chemical information (at the synapse).
Hormone release
Insulin from β-cells (as shown before – secretory/zymogen granules)

Question 5

Explain vesicle trafficking by using the terms tethering, docking, and fusion

Answer 5

Tethering: Tethering interactions are likely to be involved in concentrating synaptic vesicles at the synapse

Tethering [by tethering proteins] involves links over distances of more than about half the diameter of a vesicle from a given membrane surface (>25 nm)

Docking: The holding of two membranes within a bilayer’s distance of one another (<5-10 nm).

Tethering and docking of a transport vesicle at the target membrane precedes the formation of a tight core SNARE complex

Fusion: Driven by SNARE proteins

Process of merging the vesicle membrane with the target one

Results in release of large biomolecules into the extracellular space (or in case of neurons in the synaptic cleft).

Question 6

A process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane.

Answer 6

Endocytosis

Question 7

Endocytosis is for cells that have an

Answer 7

Uptake of polar or large molecules
Cannot pass through the hydrophobic plasma membrane.

Question 8

Phagocytosis is

Answer 8

The plasma membrane extends to surround the material to be engulfed.

Plasma membrane receptors may bind to antibodies on the surface of the foreign body.

An intracellular vacuole or heterophagosome is then formed.

The ingested material is on the inside of a plasma membrane-bound vesicle.

Question 9

What is the vacuole in phagocytosis fused with?

Answer 9

The vacuole now moves into the cell and fuses with a primary lysosome.

Digestion proceeds in the newly formed secondary lysosome.

This process is most commonly seen in phagocytic cells like monocytes, neutrophils and macrophages.

Question 10

Pinocytosis involves…

Answer 10

Involves materials of molecular or macromolecular dimensions in the surrounding medium.
Most cells exhibit pinocytotic activity though the extent varies.

Question 11

Receptor mediated pinocytosis is when molecules bind to…

Answer 11

receptors on the plasma membrane and are selectively adsorbed.

Question 12

Clathrins are…

Answer 12

Clathrin coated pits may be formed where receptors concentrate

Clathrin attaches to the intracellular portion of the receptor with the aid of adaptor proteins as endocytosis occurs

Question 12

What does it mean when we say that exocytosis must balance endocytosis?

Answer 12

A large macrophage can engulf/endocytose 25% of its own volume of fluid each hour by the process of pinocytosis.

This removes 3% of its plasma membrane each minute (100% of its plasma membrane per hour).

The total surface area and volume of the cell remains unchanged.

This means that exocytosis must balance endocytosis with respect to the amount of membrane involved.

Question 13

____________ is the transfer of small molecules and ions across cell membranes, both internal and external.

Answer 13

Microtransfer

Question 14

True or False: Passive transport doesn’t require energy and examples include primary and secondary transports

Answer 14

False, although passive transport does not require energy, examples of passive transport are simple and facilitated diffusion.

Question 15

What is active transport?

Answer 15

Requires energy
Primary and secondary active transport

Question 16

Describe Brownian motion

Answer 16

First observed indirectly by the Scottish botanist Robert Brown.
Under the light microscope, pollen grains in water are seen to be moving here and there (random movement) in water. So called Brownian Motion applies to particles 2m and does not require energy consumption
It is due to collisions with the water molecules which we can’t see.

Question 17

Describe diffusion

Answer 17

The tendency for all molecules in liquids and gases to move in all directions until they are evenly distributed in the available space.
- Dependent on movement of molecules, due to their kinetic energy, from regions of high concentration to low concentration
- Occurs whenever such a concentration gradient exists
- Movement ceases when the equilibrium constant reaches 0.

Question 18

Simple diffusion is through the…

Answer 18

lipid bilayer

Question 19

Facilitated diffusion is through…

Answer 19

a channel protein or carrier protein.

Question 20

In simple diffusion, we can see…

Answer 20

This requires the membrane to be freely permeable to the molecules and ions at the time in question

Water and small non-polar molecules (O2, CO2) pass freely through the plasma membrane by diffusion.

Molecules diffuse across the membrane by passive transport

Question 21

____________ enter some animal cells by a process of facilitated (or mediated) diffusion.

Answer 21

Glucose and other molecules (e.g. amino acids, nucleotides)

Question 22

Two types of protein facilitate the diffusion, and each one uses a different mechanisms:

Answer 22

Channel proteins (e.g. K+ ion channels)

Carrier proteins (e.g. sugars, amino acids and nucleotides) are specific permeases which are highly selective often transporting only one type of molecule. The mechanism involves a conformational changes to transfer the bound solute

No energy is required for transport; essentially this is a passive transport mechanism

Question 23

True or False: Macromolecules and charged ions (H+, Na+, K+, Cl-) DO NOT pass freely through cell membranes.

Answer 23

True, these molecules require the use of selective pores or channels (so called ‘membrane transport proteins’) to cross/transfer from one side of the membrane to the other.

Question 24

_____________ act as selective carriers translocating substances from one surface to another.

Answer 24

Integral transmembrane proteins

Question 25

If the process is working ________ a concentration gradient, it is energy-dependent and requires Adenosine Triphosphate (ATP) molecules.

Answer 25

against

Question 26

Explain primary active transports

Answer 26

Typically move molecules against their electrochemical gradient.
Uses energy in the form of ATP
Primary active transporters areATPaseproteins.
Primary active transporters are also referred to aspumps.

Question 27

List some examples of substances transported by primary active transport

Answer 27

Na+, K+, Ca2+ and H+

Question 28

Examples of pumps:

Answer 28

Na+/K+-ATPase, Ca2+-ATPase,
H+/K+-ATPase, H+-ATPase pumps, Reverse of ATP synthase

Question 28

The sodium-potassium pump transports:

Answer 28

3 Na+ ions from inside to out
2 K+ from outside to in
1 ATP hydrolysed

Question 29

Secondary active transport, movement of a solute against its gradient (e.g. glucose) does not use ATP directly. Instead…

Answer 29

energy is used in primary transport to set up the concentration gradient of the driving ion (e.g. sodium) to provide energy for secondary transport.

Question 30

What is a Cotransport/ symport?

Answer 30

driving ion and the driven molecule (or ion) move in the same direction

Question 31

What is an exchange/ antiport?

Answer 31

driving ion and the driven molecule (or ion) move in opposite directions

Question 32

In a Sodium-Dependent Co-transport Carrier System…

Answer 32

A Na+ ion associates with one of two exposed active sites on a transmembrane protein.
*This causes a conformational change in the second site which binds a glucose molecule.
*The carrier now transfers the Na+ and glucose to the cytosol face.
*The Na+ ion is released into the cytoplasm.
The glucose molecule is now released from the second site.