Lipids and Membranes 2 Flashcards
Which factor decreases the melting temperature of a unsaturated fat? Why?
More cis bonds (type of double bond) = lower melting temperature. Thus, unsaturated fats require lower temperature to be in liquid form than saturated fats.
As the kinks in the unsaturated fat molecule caused by cis double bonds makes it harder for Van der Waals forces to pack the molecule together (to become a solid).
What is the function of the cell membrane?
To separate the interior of the cell from the outside environment.
Which molecules do not easily cross cell membranes?
Ions and larger polar molecules (e.g. amino acids, glucose and nucleotides).
What are the many proteins that reside within cell membranes responsible for?
1) The generation and regulation of potential and chemical gradients.
2) Signal transduction between interior and exterior of the cell.
3) Transfer of nutrients and metabolites.
How do nerve cells communicate through cell membranes?
By releasing small neurotransmitter molecules which are stored in membrane-bound vesicles in the nerve cell into the narrow cleft between cells. The signal is received by receptor molecules on the neighbouring cell membrane.
What types of molecules are transported across cell membranes via passive diffusion/osmosis?
Small gas molecules (e.g. carbon dioxide and oxygen) and some small fat soluble (non-polar) molecules.
How do transmembrane protein channels and transporters carry nutrients in and waste out of cells?
By being passive channels (e.g. aquaporin) that just open or close to let water in or out, or specific and selective to transport particular proteins, or pump proteins or certain ions.
What is endocytosis?
The absorption of species into the cell membrane by engulfing them in a pit in the membrane which is then pinched off and transported inside the cell membrane in a vesicle.
What is exocytosis?
The process where an internal vesicle fuses with the outer cell membrane, releasing its contents to the outside.
What is the function of the cytoskeleton? How is it relevant to the cell membrane?
To provide the physical strength of the cell. The cell membrane contains the anchor points from which the cytoskeleton is connected.
What are the properties and function of the cytoskeleton’s intermediate filaments?
Flexible and able to withstand high tensile forces. They form a dense network that provides mechanical resistance against large deformations and connects the cell nucleus to the cell periphery.
What is the function of the cytoskeleton’s actin cortex?
It is attached to the membrane by anchor proteins and provides strength and stiffness to the cell wall.
What are the properties and function of the cytoskeleton’s microtubules?
Highly rigid tubelike fibres that exert pushing and pulling forces on the cell membrane. Crucial for separating chromosomes during cell division.
What is the function of kinesin motors?
To pull vesicles along microtubules.
What is the endoplasmic reticulum (ER)?
A region of the cell which reads genetic code from adjacent nuclei and uses it to synthesise the proteins and lipids required by the cell.
