The Cytoskeleton and Membrane Transport

Question 1

Describe the structure and function of microfilaments

Answer 1

Structure:

Dimers of α- and β-tubulin polymerize to form microtubules, which are composed of 13 protofilaments assembled around a hollow core.

Function:

• Transport of vesicles, organelles and cell components
• Positioning membrane - enclosed organelles
• Miotic spindle
• Cilia and Flagella

Question 2

Describe the structure and function of intermediate filaments

Answer 2

Structure:

Intermediate filaments constitute flexible and stress-resistant networks in animal cells. They are composed of sequence-related fibrous proteins and represent the major determinant of cell and tissue plasticity.

Function:

A mechanical stress absorber and an integrating device for the entire cytoskeleton.

Question 3

What are the 3 components of the cytoskeleton?

Answer 3

Microtubules

Microfilaments

Intermediate filaments

Question 4

What is dynamic instability, give examples

Answer 4

The ability of microtubules to grow or shrink rapidly in response to a cells needs

Growing and shrinking depends upon:

• Tubulin concentration
• Microtubule associated proteins

Example: Microtubules during mitosis

Question 5

What is treadmilling and give examples

Answer 5

Treadmilling is a process that is seen in actin filaments and microtubules, among other cellular cytoskeletal filaments. A segment of the filament seems to “move” through a stratum or the cytosol when one end of the filament lengthens while the other end shortens.

Shortening of microtubules

Question 6

Explain the function of motor proteins

Answer 6

Involved in transport processes, cell motility, and the organization and maintenance of cytoskeletal structures.

Question 7

Give 5 roles of the cytoskeleton

Answer 7

Cell shape, structure and movement

Muscle Contraction

Motility -e.g. cilia and and flagella

Anchor organelles in place e.g. nucleus

Tensile Strength

Question 8

Role of Microtubule Organising Centres (MOC)

Answer 8

MOC control the location, number and orientation of microtubules

Centrosome is the major MOC in animals. Located close to nucleus and contains a pair of centrioles.

Provides dynamic instability

Question 9

Describe the structure and function of microtubules

Answer 9

Microtubules are microscopic, hollow tubes made of alpha and beta tubulin that are a part of the cell’s cytoskeleton.” Microtubules extend throughout the cell providing it with proper shape and keeping the organelles in place.

Microtubules determine the shape of a cell

Question 10

What is the chemical concentration gradient?

Answer 10

A chemical concentration gradient is a difference in the concentration of substances on either side of a membrane

Question 11

What is Electrical membrane potential?

Answer 11

Electrical membrane potential is a difference in electrical potential or voltage that exists across most cell membranes

Question 12

Are membranes hydrophobic or hydrophilic and why?

Answer 12

Hydrophobic - selectively permeable

Question 13

Give 5 ion examples that use an electrochemical gradient

Answer 13

Na+

K+

H+

Cl-

Ca2+

Question 14

Name the 2 types of membrane transport proteins

Answer 14

Channel Proteins

Transport/Carrier Proteins

Question 15

Explain what passive and active transport is

Answer 15

Passive - Along a concentration gradient (high to low). Does not require additional driving force or energy.

Active - Movement of a solute against its concentration gradient requires energy e.g. ATP

Question 16

How is facilitated diffusion carried out and what is used

Answer 16

Channel proteins provide corridors/channels for molecules to travel through the cell membrane

Aquaporins - allow the quick diffusion of water

Ion channels - These can be gated such as sodium channels open up to action potentials

Question 17

What is the name of the carrier protein that glucose uses for transport?

Answer 17

GLUT1 - found in almost all animal cell membranes that transport glucose across the bilayer

Question 18

How do carrier proteins transport molecules using facilitated diffusion?

Answer 18

Carrier proteins undergo subtle changes in shape which translocate a solute across the membrane

They are not opened simultaneously to either side of the membrane

Question 19

Explain what uniport transport is and give examples

Answer 19

Uniport - a single substance, that moves in a single direction
via facilitated diffusion

Examples: GLUT1, Mitochondrial uniporter regulator 1 (MCUR1).

Question 20

Explain how primary active transport is carried out and give an example of this

Answer 20

Requires energy, usually ATP, to pump a molecule against its concentration gradient.

In primary active transport, the proteins hydrolyse ATP to power the transport directly.

Proteins involved in primary active transport are often called pumps.

Example: Sodium potassium pump

Question 21

Explain how secondary active transport is carried out and give examples of this

Answer 21

Active transport of molecules utilising a carrier that uses a concentration gradient or electrochemical gradient as a source of energy.

Co-transport

Example: sodium-linked glucose transport & sodium-proton exchange

Question 22

Explain what Symport and Antiport is

Answer 22

Symport - two substances, move in the same direction

Antiport - two substances, moving in opposite directions

Question 23

Explain what the 2 types of glucose transport are called/ how they work

Answer 23

GLUT - Glucose transporter protein 1

SGLT - Sodium/glucose transporter

GLUT facilitates the passive diffusion of glucose across tissue barriers

SGLT - plays a key role in glucose absorption from the intestinal tract and renal tubes

Question 24

What are transport vesicles used for?

Answer 24

Vesicular transport is the active movement of substances across a cell membrane via a vesicle

Question 25

Name the 3 types of endocytosis

Answer 25

Pinocytosis

Phagocytosis

Receptor-mediated endocytosis

Question 26

Explain how exocytosis is carried out

Answer 26

The vesicle fuses with the membrane and releases contents to the extracellular fluid.

3 main functions:

1. Add components to the plasma membrane
2. Recycle receptors
3. Secrete specific substances out of the cell and into the extracellular fluid

Question 27

Explain how cell-to-cell transport works. Give an example of what tissue uses this and how

Answer 27

Gap junctionsare specialized connections that form a narrow pore between adjacent cells. These pores permit small molecules and ions to move from one cell to another.

Cardiac tissue - contains extensive gap junctions, to allow the rapid movement of ions between cells this helps the tissue beat in rhythm