AP Biology : Understanding Types of Cellular Communication
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Example Question #424 : Cellular Biology
During routine analysis of the cell, a researcher identifies a lysosome on his slide. Which of the following signal sequences must be added to peptides to ensure their proper delivery to the lysosome?
Galactosidase
KDEL
Mannose-6-phosphate
None, the Golgi apparatus knows when specific enzymes must go to the lysosome
Caspase
Mannose-6-phosphate
Mannose-6-phosphate is a special signal peptide that must be added to proteins destined for the lysosome in the Golgi apparatus. This ensures proper delivery to the lysosome so that it may carry out its digestive functions. KDEL is a target peptide sequence that prevents the protein from being secreted from the endoplasmic reticulum. If it is a functional KDEL motif, it will be retrieved by the Golgi apparatus via retrograde transport to the endoplasmic reticulum lumen. Galactosidase is a glycolipid enzyme, which if not present gives a lysosomal storage disease known as Fabry’s disease. Caspases are proteins that are involved in signaling apoptosis.
Example Question #425 : Cellular Biology
Which of the following molecules acts as a signal sequence on apoptotic cells that attracts phagocytic cells to clean up the dead cell?
Cytochrome C
Phosphatidylserine
Low intracellular calcium concentration
Double-stranded DNA
Microfilaments
Phosphatidylserine
Phosphatidylserine is a phospholipid membrane component of the cell actively held facing the cytosolic side of the cell by an enzyme called flippase. This is an important distinction from all other phospholipids because all others are free to flip back and forth from both sides of the membrane. However, when a cell is undergoing the process of apoptosis, phosphatidylserine is no longer forced to stay on the cytosolic side; when it flips and is shown on the outer surface of the cell, it acts as a signal for the phagocytic cells to engulf and destroy the cell.
Example Question #426 : Cellular Biology
Which of the following is able to transfer a phosphate group and activate a protein?
Protein kinase
Phosphodiesterase
G protein
Adenylyl cyclase
Phosphotase
Protein kinase
A protein kinase phosphorylates proteins and activates them by adding a phosphate group. Phosphodiesterase breaks phosphodiester bonds. Phosphotases remove phosphate groups and dephosphorylate a protein. G proteins are usually bound to a receptor and can begin a cascade of reactions when activated. Adenylyl cyclase converts ATP to cAMP.
Example Question #427 : Cellular Biology
What is the main purpose of glycoproteins on the cell surface?
They are involved in maintaining cellular membrane fluidity
They are involved in cell-to-cell recognition
They are involved in ATP synthesis and the electron transport chain
They are involved in steroid hormone binding
They are involved in cell-to-cell recognition
Glycoproteins are attached to the cell membrane's lipid bilayer. They serve a unique role at the cellular level to help with cell to cell recognition. Glycoproteins serve as unique "markers" allowing nearby cells to know they have reached their destination. Cholesterol is embedded in the cell membrane to maintain fluidity.
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