Lesson 1: Membrane and ER Flashcards
What is the main function of the plasma membrane?
The plasma membrane separates the cell’s interior from the external environment and regulates molecule import, export, movement, and communication.
What is the basic structure of the plasma membrane?
A phospholipid bilayer with embedded proteins, cholesterol, and glycolipids/glycoproteins.
Name the four key properties of the plasma membrane.
- Maintains structural integrity
- Movement and expansion
- Import and export of molecules
- Receives and transmits information
What components make up the plasma membrane?
Phospholipids (30-40%), proteins (40-50%), cholesterol, and glycolipids/glycoproteins.
What is the role of phospholipids in the membrane?
They form the bilayer, with a hydrophilic head and hydrophobic tails, creating a selective barrier.
What are the two types of phospholipids in the membrane?
Phosphoglycerides (based on glycerol)
sphingolipids (based on sphingosine). - interact more with other phospholipids and the outside environment -> more hydrophilic interactions
What is the role of cholesterol in the plasma membrane?
Cholesterol is a steroid molecule
binds between hydrophobic and hydrophilic part of phospholipid
decreases membrane deformability and permeability while preventing fatty acid crystallization.
What is the glycocalyx, and what is its function?
A glycoprotein and glycolipid layer outside the cell that acts as a protective barrier and aids in cell recognition.
How is membrane fluidity regulated?
By factors such as temperature, fatty acid chain length, protein content, cholesterol, and unsaturation of fatty acids.
What is the asymmetry of the plasma membrane?
Different lipids and proteins are distributed unevenly between the inner and outer layers of the bilayer.
What are the two types of membrane proteins?
Integral (transmembrane) proteins and peripheral (extrinsic) proteins.
Name four functions of membrane proteins.
Transport, cell signaling, adhesion, and enzymatic activity.
How do integral proteins differ from peripheral proteins?
Integral proteins span the membrane, while peripheral proteins are attached to the membrane’s surface.
What is the role of glycoproteins in the plasma membrane?
They participate in cell-cell recognition and adhesion.
What are lipid rafts, and why are they important?
Microdomains rich in cholesterol and sphingolipids, organizing receptors for signal transduction.
Groups of multiple receptors
signal transfer to intracellular environment
What are the three main types of transport across the membrane?
Passive transport, active transport, and vesicular transport.
What is simple diffusion, and what molecules use it?
Movement of small, non-polar molecules (e.g., O₂, CO₂) across the membrane without energy. Very small molecules
How does facilitated diffusion differ from simple diffusion?
It uses protein channels or carriers to move molecules like glucose and ions across the membrane. NO NRG
Required in some special epithelium like the kidneys to regulate H2O diffusion
What is active transport, and what does it require?
Movement of molecules against the concentration gradient using ATP
important for depolarization of cell membrane in neurons to generate electric impulses
What is the main function of the RER?
Protein synthesis and folding.
What is the primary function of the SER?
Lipid synthesis
steroid production (gonads and adrenal gland)
detoxification
ion storage
biogenesis of cell membranes
glycogen metabolism (catabolism of hepatic glycogen)
What type of cells have abundant RER?
Cells with high protein production, like plasma cells and pancreatic cells.
What is a unique function of SER in muscle cells?
It functions as the sarcoplasmic reticulum, regulating calcium storage and release.
How does the ER contribute to protein modification?
Proteins undergo glycosylation (50%), disulfide bond formation, and folding in the RER.
What enzyme in the SER is important for detoxification?
Enzymes that add hydroxyl groups to toxins to make them water-soluble and favoring their elimination.
How does the SER participate in glycogen metabolism?
It contains enzymes like glucose-6-phosphatase, aiding in glycogen breakdown in hepatocytes.
What are ribosomes, and what is their function?
Ribosomes are RNA-protein complexes that synthesize proteins.
the two subunits of ribosomes associate only when protein synthesis occurs
What are the two types of ribosomes?
Free ribosomes (cytosolic proteins) and bound ribosomes (membrane or secretory proteins).
What is the difference between eukaryotic and prokaryotic ribosomes?
Eukaryotic ribosomes are 80S, while prokaryotic ribosomes are 70S.
What is the role of the signal recognition particle (SRP) in protein synthesis?
SRP binds to the signal peptide on an amino acids then directs ribosomes to the ER where it binds to a receptor for translocation of proteins into the lumen through a translocation channel.
After translocation signaling sequence is cute and the protein becomes completely internalized.
What happens to proteins after synthesis in the RER?
They are folded, modified (e.g., glycosylated), and sent to the Golgi apparatus.
What is the clinical significance of ABC transporters?
They pump out drugs/chemoagents, contributing to multidrug resistance in cancer cells.
How does the plasma membrane contribute to disease resistance?
Altered transport proteins (e.g., MDR1) can expel chemotherapeutic agents, reducing efficacy.
What happens to phosphatidylserine during apoptosis?
It flips from the cytosolic side to the extracellular side, signaling programmed cell death.
What is the function of the plasma membrane’s selectivity?
It ensures controlled exchange of molecules, maintaining the cell’s internal environment.
Why is the plasma membrane described as a fluid mosaic model?
Lipids and proteins move laterally, creating a dynamic, fluid structure with a mosaic pattern.
What is the glycocalyx’s role in immunity?
It acts as a molecular filter and participates in cell-cell adhesion and recognition.
The plasma membrane is:
Selective, fluid, asymmetric, and discontinuous.
What constitutes phospholipids?
Phospholipids have a polar hydrophilic head and two
hydrocarbon hydrophobic tails
The head is constituted by:
- glycerol linked to a phosphate group
- the phosphate group binds choline, serine or ethanolamine
The tails are fatty acids chains which can have different length
What increases fluidity of the cell membrane?
- increase in temperature
- increase in unsaturated fatty acids
What decreases fluidity of the cell membrane?
- increased length of fatty acid chains
- increase in proteins
- increase in cholesterol
What are glycolipids?
Glycolipids are lipids with a carbohydrate attached by a covalent
bond
* Asymmetry: located only in the extracellular side of the
membrane bilayer -> due to lipids glycosylation occurring in the
lumen of the Golgi apparatus which mimics the extracellular side
of the cell
* Function: protection and cell recognition
What is the endoplasmic reticulum?
Network of interconnected,
membrane-enclosed, tubules and
sacs (cisternae)
Extends from nuclear membrane
throughout the cytoplasm
50% of all cell membranes
Variable shape
Extension depending on the
metabolic needs of the cell
Where does glycosylation of proteins take place?
starts in the ER and is completed in the Golgi apparatus
What are some additional functions of the RER?
acquisition of protein steric conformations (secondary
and tertiary structure)
assembling of polypeptides with quaternary structures
beginning of protein glycosylation, that will be completed in the Golgi apparatus
hydroxylation of lysine and proline residues
How are cell membrane proteins synthesised?
lipids are synthesized by enzymes located in SER
newly synthesized molecules are inserted in the lipid bilayer on
the cytoplasmic side
enzymes named “flippase” catalyze the flip-flop movement to
bring the newly synthesized molecules on the opposite side of
the bilayer
