Cell Structure and Function Exam 3 Questions
and Verified Answers
How did compartmentalization arise? Correct Answer: Plasma membrane grew around and engulfed an
object
Generation of nucleus and ER
Generation of mitochondria
Compartmentalization meant that proteins must be targeted to specific locations in the cell
Sorting signals are amino acid sequences within proteins that direct protein localization and transport
Protein sorting signals Correct Answer: Can be from 2-60 amino acids
Signal sequences are sorting signals found at N-terminus
Signal peptidases clip signal sequences off after localization has occurred
How is signal sequences determined Correct Answer: 1. Molecular Bio Approach
Take bits of transported protein and fuse/clone amino acid sequence to a reporter protein and check
distribution (GFP)
2. Biochemical Approach
Direct purification of signal sequence
3. Genetic Approach
Break (mutate) specific parts of protein to identify sequence for localization
Protein transport may involve Correct Answer: 1. Gated transport - controlled opening of pore
complexes (nucleus exclusive)
2. Transloator based transport - transmembrane protein translocators transfer protein from one side of
membrane to other, protein must be unfolded to pass thru
, 3. Vesicular transport - often small spherical membrane packages that ferry proteins from one
compartment to another
Endoplasmic Reticulum (ER) Correct Answer: An extensive membranous network in eukaryotic cells,
continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-
free (smooth) regions
ER is 50% of all membrane in cell (lots of surface area)
Dynamic
ER and nuclear envelope are contiguous
Two forms:
1. Smooth - shorter tubules
2. Rough - longer flat stacks (bc of ribosomes, it looks rough)
Function of ER Correct Answer: Entry point into membrane trafficking pathway
Protein quality control
Protein modifications
Stores intracellular Ca++
Lipid biosynthesis
Detoxification
Smooth - functions in Ca++ storage, production of lipids, and detoxifying enzymes (varies greatly in size
in diff cell types, will expand when needed)
Rough - Cytoplasmic entry point for proteins into vesicular trafficking system, transport of proteins into
ER is co-translational (uses energy of protein translation into ER), protein modifications
Signal recognition particle (SRP) Correct Answer: Made of six proteins and one RNA
Possesses a critical GTPase protein
and Verified Answers
How did compartmentalization arise? Correct Answer: Plasma membrane grew around and engulfed an
object
Generation of nucleus and ER
Generation of mitochondria
Compartmentalization meant that proteins must be targeted to specific locations in the cell
Sorting signals are amino acid sequences within proteins that direct protein localization and transport
Protein sorting signals Correct Answer: Can be from 2-60 amino acids
Signal sequences are sorting signals found at N-terminus
Signal peptidases clip signal sequences off after localization has occurred
How is signal sequences determined Correct Answer: 1. Molecular Bio Approach
Take bits of transported protein and fuse/clone amino acid sequence to a reporter protein and check
distribution (GFP)
2. Biochemical Approach
Direct purification of signal sequence
3. Genetic Approach
Break (mutate) specific parts of protein to identify sequence for localization
Protein transport may involve Correct Answer: 1. Gated transport - controlled opening of pore
complexes (nucleus exclusive)
2. Transloator based transport - transmembrane protein translocators transfer protein from one side of
membrane to other, protein must be unfolded to pass thru
, 3. Vesicular transport - often small spherical membrane packages that ferry proteins from one
compartment to another
Endoplasmic Reticulum (ER) Correct Answer: An extensive membranous network in eukaryotic cells,
continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-
free (smooth) regions
ER is 50% of all membrane in cell (lots of surface area)
Dynamic
ER and nuclear envelope are contiguous
Two forms:
1. Smooth - shorter tubules
2. Rough - longer flat stacks (bc of ribosomes, it looks rough)
Function of ER Correct Answer: Entry point into membrane trafficking pathway
Protein quality control
Protein modifications
Stores intracellular Ca++
Lipid biosynthesis
Detoxification
Smooth - functions in Ca++ storage, production of lipids, and detoxifying enzymes (varies greatly in size
in diff cell types, will expand when needed)
Rough - Cytoplasmic entry point for proteins into vesicular trafficking system, transport of proteins into
ER is co-translational (uses energy of protein translation into ER), protein modifications
Signal recognition particle (SRP) Correct Answer: Made of six proteins and one RNA
Possesses a critical GTPase protein
