40 Questions
What is the primary function of membranes in a cell?
Executing transport, enzyme activity, and cell communication
Which type of lipid molecule is most abundant in membranes?
Phospholipids
What is the estimated frequency of lateral movement in the plasma membrane?
100000000 times per second
What is the primary reason for the fluidity of membranes?
Non-covalent bonds between lipid molecules
What is the characteristic of the plasma membrane in terms of its composition?
Asymmetrical
What is the estimated number of different types of lipids found in membranes?
500-1000
What is the primary function of clathrin-positive compartments and vesicles in the cell?
Endocytosis
What is the thickness of most membranes in the cell?
5-10 nm
What is the characteristic of the movement of lipids in the membrane?
Rapid lateral movement and slow flip-flop movement
What is the composition of the membrane in terms of lipids and proteins?
Approximately 50 lipid molecules per protein
Which type of molecules can dissolve in the lipid bilayer and pass through the membrane rapidly?
Hydrophobic molecules
What is the primary function of the Na+/K+ pump in animal cells?
To control the osmolarity of the cell
What is the role of clathrin molecules in the cell?
To assemble at the membrane and cause it to bend inwards
What is the function of post-translational modifications of proteins?
To target proteins to specific compartments in the cell
What is the primary function of motor proteins in the cell?
To transport vesicles and organelles around the cell
What is the function of the nuclear pore complex?
To import and export macromolecules between the nucleus and cytoplasm
What is the role of myosin motor proteins in muscle contraction?
To walk along actin filaments and drag other filaments along
What is the function of chromatophores in cephalopods?
To change the colour of the organism
What is the primary function of the Golgi body in protein synthesis?
To package proteins for secretion
What is the function of ubiquitination in protein degradation?
To mark proteins for degradation in the proteasome
What is the primary mechanism by which cells regulate their intracellular osmolarity?
Actively pumping out inorganic ions from the cell
What is the role of glycosylation in protein targeting?
Targeting proteins to the plasma membrane
What is the primary function of the nuclear envelope?
To regulate protein import and export
What is the primary function of myosin motor proteins in cells?
To transport vesicles along actin filaments
What is the primary mechanism of protein transport through the nuclear pore complex?
Recognition of nuclear localisation signals
What is the primary function of the Na+/K+ pump in animal cells?
To maintain a stable concentration of inorganic ions
What is the primary mechanism of vesicle transport in cells?
Vesicular transport
What is the primary function of the Golgi body in protein synthesis?
To package and modify proteins for transport
What is the primary mechanism of osmosis in cells?
Water moving into the cell
What is the primary function of phosphorylation in protein targeting?
Regulating protein-protein interactions
What is the primary function of membranes in terms of cell communication?
Cell recognition and signaling
What is the characteristic of membrane-bound ribosomes in terms of protein synthesis?
Synthesizing proteins for secretion
What is the key difference between bacterial membranes and animal cell membranes?
Bacterial membranes have a different composition than animal cell membranes
What is the primary function of phospholipids in membranes?
To form the lipid bilayer structure
What is the result of the asymmetrical structure of the plasma membrane?
Selectively permeable membrane
What is the role of non-covalent bonds in maintaining membrane fluidity?
To regulate the movement of lipids in the membrane
What is the characteristic of the movement of lipids in the plasma membrane?
Lateral movement occurs rapidly, while flip-flop movement occurs slowly
What is the function of enveloped viruses in terms of membrane composition?
To derive their membrane composition from the host cell
What is the result of the variation in head groups, hydrocarbon chain lengths, and saturation states of phospholipids?
Increased diversity of membrane lipids
What is the characteristic of the composition of membranes in terms of lipids and proteins?
Lipids are much smaller than proteins
Study Notes
Cell Membranes and Compartments
- Cell membranes are sheet-like structures, 2 molecules thick, forming closed boundaries, typically 5-10 nm thick.
- Membranes are composed of lipids and proteins, with approximately 50 lipid molecules per protein in a plasma membrane.
- Phospholipids are the most abundant membrane lipids, with 500-1000 different types identified, varying in head groups, hydrocarbon chain lengths, and saturation states.
Membrane Structure and Function
- The plasma membrane is asymmetrical, with lateral movement occurring around 100 million times per second and flip-flop movement less than once per month.
- Membrane fluidity depends on non-covalent bonds, membrane composition, and temperature.
- The plasma membrane regulates molecular traffic, allowing hydrophobic molecules like hydrocarbons to dissolve in the lipid bilayer and pass through rapidly.
Cellular Compartmentalization
- Cells are compartmentalized, with separate regions for different functions, and busy with various activities.
- The amino acid sequence of a protein contains instructions for its cellular location.
- Post-translational modifications like glycosylation, phosphorylation, and ubiquitination affect protein location and function.
Protein Transport
- There are three main ways to transport proteins: gated transport (nuclear pore), transmembrane transport (mitochondria), and vesicular transport (motor proteins).
- The nuclear envelope consists of two concentric membranes with nuclear pores, importing proteins and exporting mRNA.
Motor Proteins and Vesicle Transport
- Three types of motor proteins (myosin, kinesin, and dynein) transport vesicles along actin microfilaments and microtubules, requiring ATP energy.
- Motor proteins also play a role in muscle contraction and cell movement.
- In some organisms, motor proteins transport pigment molecules along microtubules to change color and adapt to environmental conditions.
Test your knowledge of cell membranes, organelles, and their functions. Learn about the different types of membranes, organelles, and their roles in cellular processes.
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