Golgi Apparatus

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Which type of endoplasmic reticulum is studded with ribosomes, giving it a 'rough' appearance?

Rough ER

What is the function of the smooth endoplasmic reticulum (SER)?

Lipid biosynthesis

What is the main function of the endoplasmic reticulum (ER)?

Transport of synthesized proteins

What are microsomes?

Closed vesicles in the ER

What are the two basic types of endoplasmic reticulum?

Rough ER and smooth ER

What is the function of the rough endoplasmic reticulum (RER)?

Protein synthesis

Which type of ER lacks bound ribosomes and is involved in lipid synthesis and detoxification reactions?

Smooth ER

Which function is NOT associated with smooth ER?

Protein synthesis

Which organelle plays a major role in the contraction process of muscle cells?

Sarcoplasmic reticulum

Which type of ER is involved in protein synthesis and can be detected by staining with basic dyes?

Granular ER

Which function is associated with smooth ER in liver cells?

Detoxification of drugs and toxic chemicals

Which organelle is responsible for the synthesis of fatty acids and phospholipids?

Smooth ER

Which organelle is responsible for the degradation of abnormally folded or unfolded proteins in the cytosol?

Lysosome

During protein translocation, which proteins pass completely into the ER lumen?

Soluble proteins

Which type of protein insertion occurs when a polypeptide contains multiple start-transfer and stop-transfer signals?

Multipass transmembrane protein insertion

What is required for the posttranslational translocation of proteins into the ER?

ATP

What organelle selectively transports ER resident proteins back to the ER?

Golgi apparatus

What is the self-protective mechanism against ER stress called?

Unfolded protein response

Which organelle is particularly well developed in protein secreting cells in the exocrine pancreas?

Endoplasmic reticulum

Which organelle is responsible for the synthesis and transport of proteins within the cell?

Endoplasmic reticulum

What is the function of the signal sequence or signal peptide in protein synthesis?

It enables the cellular transport machinery to correctly position the protein inside or outside the cell

Which Nobel Prize was awarded for the discovery of the signal hypothesis?

Nobel Prize in Physiology or Medicine

What is the role of protein targeting in the cell?

To ensure correct sorting of proteins

Which two types of proteins are translocated co-translationally?

Proteins that are secreted from the cell and lysosomal enzymes

Which of the following is true about the signal peptide in the process of protein transport into the ER lumen?

The signal peptide attaches to the SRP receptor on the ER membrane.

What is the role of the ribosome receptor in protein transport into the ER lumen?

To anchor the ribosome to the ER membrane.

What is the function of the translocon proteins in the ER membrane?

To open a channel in the ER membrane for polypeptide transport.

What is the role of signal peptidase in protein transport into the ER lumen?

To cleave the signal peptide from the polypeptide chain.

Which modification occurs in the ER for newly synthesized proteins?

Addition and processing of carbohydrates.

What is the role of protein disulfide isomerase in the ER lumen?

To catalyze the rearrangement of disulfide bonds.

Which of the following is NOT a function of cell membranes?

Synthesizing ATP

What is the main structural component of cell membranes?

Lipids

Which organelles maintain the characteristic differences between their contents and the cytosol?

Endoplasmic reticulum and mitochondria

What can ion gradients across membranes be used for?

All of the above

What do protein sensors in the plasma membrane do?

Transfer information across the membrane

What is the basic fluid structure of the cell membrane?

Lipid bilayer

What is the main function of the lipid bilayer in the cell membrane?

Acting as a barrier to the passage of most water-soluble molecules

What is the main role of specialized membrane proteins in establishing ion gradients?

Driving the transport of selected solutes

How do most molecules move in the cell membrane?

Along the surface of the membrane

What is the thickness of the lipid bilayer in the cell membrane?

5 nm

Which type of lipid molecule constitutes about 50% of the mass of most animal cell membranes?

Phospholipids

What is the main function of membrane proteins in the plasma membrane?

Transport specific molecules across the membrane

What percentage of proteins encoded in an animal's genome are estimated to be membrane proteins?

30%

Which type of lipid molecule contains a three-carbon glycerol backbone and various fatty acid tails?

Phosphoglycerides

What is the role of cholesterol in eukaryotic plasma membranes?

Provide structural support

Which type of lipid molecule has sugars attached and is found exclusively in the monolayer facing away from the cytosol?

Glycolipids

What is the most common sphingolipid in cell membranes, consisting of a fatty acid tail and a phosphocholine group?

Sphingomyelin

Which lipid molecule constitutes more than half the mass of lipid in most mammalian cell membranes?

Phospholipids

What is the basic structure that provides the foundation for all cell membranes?

Lipid bilayer

Which type of lipid molecule contains a hydrophilic or polar end and a hydrophobic or nonpolar end?

Phospholipids

Which structure do phospholipid molecules spontaneously form in aqueous environments?

Double-layered sheets

Which part of the phospholipid molecules are shielded from water in the bilayer structure?

Hydrophobic tails

What is the function of lipid asymmetry in the lipid bilayer?

To bind cytosolic proteins

What is the role of the enzyme protein kinase C (PKC) in the lipid bilayer?

To require negatively charged phospholipids for its activity

How is the translocation of phosphatidylserine thought to occur in apoptotic cells?

By activating a scramblase

What is the term used to describe the two-dimensional fluidity of lipid molecules within a lipid bilayer?

Lipid fluidity

What is the term used to describe synthetic lipid bilayers in the form of spherical vesicles?

Liposomes

What is the term used to describe synthetic lipid bilayers formed across a hole in a partition between two aqueous compartments or on a solid support?

Planar bilayers

What is the term used to describe the process of transferring phospholipids between the inner and outer monolayers of the lipid bilayer?

Phospholipid translocation

What is the term used to describe the nonspecific transfer of phospholipids in both directions between the two monolayers of the lipid bilayer?

Scramblase activation

What is the major lipid component of most animal cell membranes?

Phospholipids

Which lipid molecule has a three-carbon glycerol backbone and various fatty acid tails?

Phospholipids

What is the most common sphingolipid in cell membranes, consisting of a fatty acid tail and a phosphocholine group?

Sphingomyelin

Which type of lipid molecule contains a hydrophilic or polar end and a hydrophobic or nonpolar end?

Phospholipids

What is the role of cholesterol in eukaryotic plasma membranes?

Provides structural support

What is the function of glycolipids in eukaryotic plasma membranes?

Cell-cell recognition

What is the function of the smooth endoplasmic reticulum (SER)?

Lipid synthesis

What is the function of the rough endoplasmic reticulum (RER)?

Protein synthesis

What is the main function of the endoplasmic reticulum (ER)?

Protein synthesis

What is the basic structure that provides the foundation for all cell membranes?

Lipid bilayer

Which type of lipid molecule constitutes the majority of the mass of most animal cell membranes?

Phospholipids

What is the term used to describe the nonspecific transfer of phospholipids in both directions between the two monolayers of the lipid bilayer?

Scrambling

What is the function of the enzyme protein kinase C (PKC) in the plasma membrane?

Activating cytosolic proteins

What is the role of cholesterol in eukaryotic plasma membranes?

To regulate fluidity and permeability

What is the term used to describe synthetic lipid bilayers in the form of spherical vesicles?

Liposomes

What is the main function of lipid asymmetry in the lipid bilayer?

To convert extracellular signals into intracellular ones

How do phospholipid molecules spontaneously aggregate in aqueous environments?

By sandwiching hydrophobic tails between hydrophilic head groups

What is the thickness of the lipid bilayer in the cell membrane?

2 nanometers

What is the term used to describe the two-dimensional fluidity of lipid molecules within a lipid bilayer?

Fluidity

What is the function of the translocator protein in the translocation of phosphatidylserine in apoptotic cells?

To transport phospholipids from the outer monolayer to the inner monolayer

Which of the following is NOT a function of cell membranes?

Synthesizing ATP and driving the transport of solutes

Which organelles maintain the characteristic differences between their contents and the cytosol?

Nucleus, endoplasmic reticulum, and Golgi apparatus

What is the main role of specialized membrane proteins in establishing ion gradients?

Driving the transport of solutes

How do most molecules move in the cell membrane?

In the plane of the membrane

What is the basic structure that provides the foundation for all cell membranes?

Lipid bilayer

What is the role of cholesterol in eukaryotic plasma membranes?

Regulating membrane fluidity

What is the function of the rough endoplasmic reticulum (RER)?

Synthesizing proteins

What is the main function of membrane proteins in the plasma membrane?

Acting as sensors of external signals

What is the thickness of the lipid bilayer in the cell membrane?

5 nm

Which type of lipid molecule constitutes about 50% of the mass of most animal cell membranes?

Phospholipids

Study Notes

Endoplasmic Reticulum (ER)

  • The type of ER studded with ribosomes is called Rough Endoplasmic Reticulum (RER), giving it a 'rough' appearance.
  • The function of Smooth Endoplasmic Reticulum (SER) is lipid synthesis and detoxification reactions.
  • The main function of ER is protein synthesis and transport.
  • Microsomes are fragments of ER.
  • The two basic types of endoplasmic reticulum are RER and SER.

Rough Endoplasmic Reticulum (RER)

  • RER is involved in protein synthesis and can be detected by staining with basic dyes.
  • RER has bound ribosomes.

Smooth Endoplasmic Reticulum (SER)

  • SER lacks bound ribosomes and is involved in lipid synthesis and detoxification reactions.
  • SER is not associated with protein synthesis.

Cell Membranes

  • The main structural component of cell membranes is phospholipids.
  • Cell membranes maintain the characteristic differences between their contents and the cytosol.
  • Ion gradients across membranes can be used for energy.
  • Protein sensors in the plasma membrane detect changes in the environment.
  • The basic fluid structure of the cell membrane is a lipid bilayer.
  • The main function of the lipid bilayer is to separate the cell from its environment.
  • Most molecules move in the cell membrane via lateral diffusion.
  • The thickness of the lipid bilayer is 3-4 nm.

Lipid Molecules

  • Phospholipid molecules have a hydrophilic or polar end and a hydrophobic or nonpolar end.
  • Phospholipid molecules spontaneously form a bilayer structure in aqueous environments.
  • Phospholipid molecules are shielded from water in the bilayer structure.
  • Lipid asymmetry in the lipid bilayer has vital functions.
  • Cholesterol is present in eukaryotic plasma membranes and helps maintain fluidity.
  • Sphingolipids have a three-carbon glycerol backbone and various fatty acid tails.
  • Phosphatidylserine is a type of phospholipid.

Protein Synthesis and Transport

  • During protein translocation, proteins pass completely into the ER lumen.
  • The signal sequence or signal peptide is required for protein synthesis.
  • The function of the ribosome receptor is protein targeting.
  • Translocon proteins in the ER membrane help in protein transport.
  • Signal peptidase is involved in protein transport into the ER lumen.
  • Protein disulfide isomerase is involved in the ER lumen.

Organelles

  • The organelle responsible for protein synthesis and transport is the ER.
  • The organelle responsible for the synthesis of fatty acids and phospholipids is the ER.
  • The organelle responsible for the degradation of abnormally folded or unfolded proteins in the cytosol is the ER.

Quiz: Understanding the Golgi Apparatus in Cell Functions Test your knowledge on the Golgi apparatus (GER) and its importance in various cell types! This quiz covers protein secretion in exocrine pancreas cells, collagen and elastin production in connective tissue cells, antibody production in fibroblasts, neurotransmitter production in plasma cells, lysosomal enzyme-containing phagocytic cells, and more. Challenge yourself and enhance your understanding of the Golgi apparatus in cell functions.

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