The Cytoskeleton and Membrane Transport Flashcards
Describe the structure and function of microfilaments
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
Describe the structure and function of intermediate filaments
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.
What are the 3 components of the cytoskeleton?
Microtubules
Microfilaments
Intermediate filaments
What is dynamic instability, give examples
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
What is treadmilling and give examples
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
Explain the function of motor proteins
Involved in transport processes, cell motility, and the organization and maintenance of cytoskeletal structures.
Give 5 roles of the cytoskeleton
Cell shape, structure and movement
Muscle Contraction
Motility -e.g. cilia and and flagella
Anchor organelles in place e.g. nucleus
Tensile Strength
Role of Microtubule Organising Centres (MOC)
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
Describe the structure and function of microtubules
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
What is the chemical concentration gradient?
A chemical concentration gradient is a difference in the concentration of substances on either side of a membrane
What is Electrical membrane potential?
Electrical membrane potential is a difference in electrical potential or voltage that exists across most cell membranes
Are membranes hydrophobic or hydrophilic and why?
Hydrophobic - selectively permeable
Give 5 ion examples that use an electrochemical gradient
Na+
K+
H+
Cl-
Ca2+
Name the 2 types of membrane transport proteins
Channel Proteins
Transport/Carrier Proteins
Explain what passive and active transport is
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
How is facilitated diffusion carried out and what is used
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
What is the name of the carrier protein that glucose uses for transport?
GLUT1 - found in almost all animal cell membranes that transport glucose across the bilayer
How do carrier proteins transport molecules using facilitated diffusion?
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
Explain what uniport transport is and give examples
Uniport - a single substance, that moves in a single direction
via facilitated diffusion
Examples: GLUT1, Mitochondrial uniporter regulator 1 (MCUR1).
Explain how primary active transport is carried out and give an example of this
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
Explain how secondary active transport is carried out and give examples of this
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
Explain what Symport and Antiport is
Symport - two substances, move in the same direction
Antiport - two substances, moving in opposite directions
Explain what the 2 types of glucose transport are called/ how they work
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
What are transport vesicles used for?
Vesicular transport is the active movement of substances across a cell membrane via a vesicle
Name the 3 types of endocytosis
Pinocytosis
Phagocytosis
Receptor-mediated endocytosis
Explain how exocytosis is carried out
The vesicle fuses with the membrane and releases contents to the extracellular fluid.
3 main functions:
- Add components to the plasma membrane
- Recycle receptors
- Secrete specific substances out of the cell and into the extracellular fluid
Explain how cell-to-cell transport works. Give an example of what tissue uses this and how
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
