Biology Chapter: Ribosomes and RER

Questions and Answers

What is the main function of the Golgi apparatus in cells?

To synthesize proteins exclusively

To generate energy through ATP synthesis

To replicate genetic material

To modify, sort, and package macromolecules (correct)

Which region of the Golgi apparatus is involved in receiving vesicles from the endoplasmic reticulum?

Medial-Golgi

Cis-Golgi network (correct)

Trans-Golgi network

Endo-Golgi

What type of modification is primarily performed by the Golgi apparatus on proteins from the rough endoplasmic reticulum?

Transcription

Phosphorylation (correct)

Dephosphorylation

Translation

What type of molecule does the Golgi apparatus help synthesize in the extracellular matrix?

Proteoglycans Signup and view all the answers

Which carbohydrate modification is specifically added by the Golgi apparatus to proteins destined for lysosomes?

Mannose-6-phosphate Signup and view all the answers

What substance does the Golgi import from the cytosol for protein modification?

Nucleotide sugars Signup and view all the answers

What is the primary role of sulfotransferases in the Golgi apparatus?

To sulfate certain molecules Signup and view all the answers

How does the Golgi apparatus contribute to the synthesis of glycosaminoglycans (GAGs)?

By polymerizing several GAGs onto core proteins Signup and view all the answers

What is a primary function of the smooth endoplasmic reticulum?

Synthesis of lipids and steroids Signup and view all the answers

Which enzyme found in the smooth endoplasmic reticulum is responsible for converting glucose-6-phosphate to glucose?

Glucose-6-phosphatase Signup and view all the answers

How does the sarcoplasmic reticulum primarily function in muscle cells?

It stores and releases calcium ions Signup and view all the answers

What structure within the endoplasmic reticulum facilitates the transport of proteins?

Transport vesicles Signup and view all the answers

What role does the signal sequence play in protein transport within the endoplasmic reticulum?

It serves as an address tag for protein destination Signup and view all the answers

In which type of cells is the sarcoplasmic reticulum primarily found?

Muscle cells Signup and view all the answers

What distinguishes the sarcoplasmic reticulum from other forms of smooth endoplasmic reticulum?

Its ability to store calcium Signup and view all the answers

How does the network structure of the smooth endoplasmic reticulum benefit its function?

It increases the surface area for enzyme action and storage Signup and view all the answers

What is the primary role of sulfation in proteoglycans?

To impact proteoglycan signaling and provide a negative charge Signup and view all the answers

What occurs when vesicles from the rough endoplasmic reticulum reach the Golgi apparatus?

They fuse with the Golgi membrane and release their contents Signup and view all the answers

In which cells is the Golgi apparatus particularly prominent?

Plasma B cells secreting antibodies Signup and view all the answers

What is the function of the trans-Golgi network (TGN)?

To sort and dispatch proteins to their destinations Signup and view all the answers

Which model proposes that the cisternae of the Golgi are built at the cis face and dismantled at the trans face?

Cisternal maturation model Signup and view all the answers

What evidence initially supported the cisternal maturation model?

Detection of collagen rods progressing through the Golgi Signup and view all the answers

Which statement best describes the transport mechanism in the Golgi apparatus?

May involve both vesicular transport and cisternal maturation Signup and view all the answers

What happens to molecules once they enter the lumen of the Golgi apparatus?

They are modified and sorted for transport Signup and view all the answers

What is the diameter of microtubules?

25 nm Signup and view all the answers

Which tubulin components are assembled to form microtubules?

Alpha tubulin and beta tubulin Signup and view all the answers

At which end do microtubules primarily grow?

Plus end Signup and view all the answers

What is the primary function of proteasomes?

To degrade unneeded or damaged proteins Signup and view all the answers

Which proteins are involved in microtubule movement toward the plus and minus ends?

Kinesins and dyneins Signup and view all the answers

What signals a protein for degradation by proteasomes?

Ubiquitin tagging Signup and view all the answers

What can be a result of protein degradation in proteasomes?

Creation of peptides and amino acids Signup and view all the answers

Which cellular structure's assembly is not directly related to microtubules?

Golgi apparatus Signup and view all the answers

What triggers the ribosome to bind to the rough endoplasmic reticulum (RER)?

A recognition particle binds to the hydrophobic amino acids. Signup and view all the answers

Which proteins are specifically responsible for targeting vesicles to the Golgi apparatus?

COPII proteins Signup and view all the answers

What is the role of chaperonins in the rough endoplasmic reticulum?

To facilitate proper protein folding. Signup and view all the answers

What identifies lysosomal enzymes for transport in the RER?

A mannose-6-phosphate marker. Signup and view all the answers

Which of the following describes the process of N-linked glycosylation correctly?

It involves addition of a sugar backbone to the nitrogen of Asn. Signup and view all the answers

How are proteins shuttled between the rough endoplasmic reticulum (RER) and the Golgi apparatus?

Via membrane-bound vesicles. Signup and view all the answers

What is the initial process of glycosylation that occurs in the RER called?

N-linked glycosylation. Signup and view all the answers

What is the function of COPI proteins in the cellular transport system?

They return vesicles to the RER. Signup and view all the answers

Study Notes

Ribosomes and the Endoplasmic Reticulum (ER)

Ribosomes bind to the rough endoplasmic reticulum (RER) during the synthesis of proteins destined for the secretory pathway.
A signal recognition particle detects a signal sequence of hydrophobic amino acids, initiating ribosome attachment to the RER.
The ribosome passes the new protein through the ER membrane, with the initial signal sequence cleaved off in the ER lumen.
RER membrane is continuous with the nuclear envelope, allowing communication between them.
Vesicles with COPI and COPII proteins shuttle proteins between RER and Golgi apparatus; COPII directs vesicles to Golgi, while COPI retrieves them back to RER.
Membrane contact sites facilitate lipid and molecule transfer between the ER and other organelles.

Functions of the Rough Endoplasmic Reticulum (RER)

Key roles include production of lysosomal enzymes (marked by mannose-6-phosphate), regulated secretion of proteins, and synthesis of integral membrane proteins.
Proteins may undergo initial glycosylation processes (N-linked) during folding, aided by chaperonins, for proper function.
N-linked glycosylation involves the addition of a 14-sugar backbone to asparagine residues in properly folded proteins.

Smooth Endoplasmic Reticulum (SER)

Functions in lipid and steroid synthesis, carbohydrate metabolism, calcium regulation, drug detoxification, and receptor attachment.
Contains glucose-6-phosphatase for converting glucose-6-phosphate to glucose as part of gluconeogenesis.
SER is a network of tubules and vesicles that enhances surface area for enzyme action and storage.

Sarcoplasmic Reticulum (SR)

Specialized form of smooth ER found in muscle cells, designed for calcium ion storage and transport.
Plays a crucial role in excitation-contraction coupling by sequestering and releasing calcium ions during muscle stimulation.

Golgi Apparatus

Modifies, sorts, and packages macromolecules for secretion or internal use, akin to a post office.
Involved primarily in protein modification, especially those from the RER, but also in lipid transport and lysosome formation.
Post-translational modifications include glycosylation and phosphorylation, with specific tags like mannose-6-phosphate for lysosomal targeting.
Contains four functional regions: cis-Golgi network, medial-Golgi, endo-Golgi, and trans-Golgi network, each with distinct modifying enzymes.

Protein Transport through Golgi

Proteins enter the Golgi from the RER and are modified and sorted for transport to their final destinations.
Trans-Golgi network is crucial for sorting proteins into vesicles based on molecular markers.
The transport mechanism might involve vesicular transport or cisternal maturation, with both processes potentially working together.

Microtubules and Cytoskeleton

Microtubules are hollow cylinders made of tubulin dimers, essential for various cellular functions including shape, strength, and intracellular transport.
Microtubules grow at the plus end and shrink at the minus end, driven by GTP hydrolysis.
Motor proteins, kinesins (toward the plus end) and dyneins (toward the minus end), facilitate movement along microtubules, crucial for cilia and flagella function.

Proteasomes

Found in all eukaryotes and some bacteria, proteasomes degrade unneeded or damaged proteins through proteolysis.
Proteins are tagged for degradation by ubiquitin, a process catalyzed by ubiquitin ligases, enabling regulation of protein concentration and quality control.
The degradation process yields peptides used for synthesizing new proteins.

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Description

Explore the intricate relationship between ribosomes and the rough endoplasmic reticulum (RER) in protein synthesis. This quiz covers key functions of the RER, including its role in producing lysosomal enzymes and facilitating communication with the nuclear envelope. Test your knowledge on the essential processes involving ribosomes, vesicles, and membrane interactions.