Question

(a) Endoplasmic reticulum _______ (b) Smooth endoplasmic reticulum ________ (c) Rough endoplasmic reticulum ______ (d) Golgi complex _______ (e) Transport vesicles ______ (f) Secretory granules _____ (g) Endosome _____ (h) Lysosome ____ (i) Mitochondrion ____ (j) Chloroplast ______ (k) Nucleus _____ (l) Plasma membrane ____ 1\. Location of most of the cell's DNA 2\. Site of fuel oxidation 3\. Separates the inside of the cell from the outside 4\. Carries important biochemicals into the cell 5\. Membrane with ribosomes attached 6\. Site of photosynthesis 7\. Contains digestive enzymes 8\. Destined for fusion with the plasma membrane 9\. Common form of cytoplasmic membrane 10\. Site of carbohydrate addition to proteins 11\. Facilitate communication between the rough endoplasmic reticulum and the Golgi complex 12\. Processes exogenous chemicals An exit strategy. Trace the pathway of the formation of a secretory protein from its gene to its exocytosis from the cell.

Short answer

Mitochondrion: 2, Chloroplast: 6, Nucleus: 1, Endoplasmic reticulum: 9, Smooth ER: 12, Rough ER: 5.

Step-by-step solution

Match (a) Endoplasmic reticulum

The endoplasmic reticulum (ER) comes in two forms: smooth and rough. The smooth ER processes exogenous chemicals, and the rough ER has ribosomes attached. Therefore, the endoplasmic reticulum as a whole is a common form of cytoplasmic membrane. This corresponds to option 9.

Match (b) Smooth endoplasmic reticulum

The smooth endoplasmic reticulum is involved in processing exogenous chemicals, such as drugs and toxins. This function matches option 12 (Processes exogenous chemicals).

Match (c) Rough endoplasmic reticulum

The rough endoplasmic reticulum is characterized by the presence of ribosomes on its surface, making it a membrane with ribosomes attached. This aligns with option 5.

Match (d) Golgi complex

The Golgi complex is responsible for adding carbohydrates to proteins, which assists in protein modification and sorting. This function corresponds to option 10 (Site of carbohydrate addition to proteins).

Match (e) Transport vesicles

Transport vesicles facilitate the movement of molecules between the rough endoplasmic reticulum and the Golgi complex. This is described by option 11 (Facilitate communication between the rough endoplasmic reticulum and the Golgi complex).

Match (f) Secretory granules

Secretory granules are cellular structures that carry substances destined for exocytosis, thus destined for fusion with the plasma membrane. This matches option 8 (Destined for fusion with the plasma membrane).

Match (g) Endosome

Endosomes are involved in transporting substances from the cell surface into the cell, which aligns with option 4 (Carries important biochemicals into the cell).

Match (h) Lysosome

Lysosomes contain digestive enzymes used for breaking down cellular waste and debris. This function matches option 7 (Contains digestive enzymes).

Match (i) Mitochondrion

Mitochondria are the sites of ATP production through fuel oxidation, which is their primary function. This aligns with option 2 (Site of fuel oxidation).

Match (j) Chloroplast

Chloroplasts are involved in photosynthesis, converting light energy into chemical energy in the form of glucose. This corresponds to option 6 (Site of photosynthesis).

Match (k) Nucleus

The nucleus is the location where most of the cell's DNA is housed and replicated. This is described by option 1 (Location of most of the cell's DNA).

Match (l) Plasma membrane

The plasma membrane provides a barrier between the interior of the cell and its external environment. This corresponds to option 3 (Separates the inside of the cell from the outside).

Trace the Pathway of a Secretory Protein

The pathway of a secretory protein involves several steps: 1. The gene encoding the protein is transcribed into mRNA in the nucleus. 2. The mRNA is translated into a protein by ribosomes on the rough endoplasmic reticulum, where initial processing occurs. 3. The protein is transported to the Golgi complex in transport vesicles for further modification, such as the addition of carbohydrates. 4. After processing, the protein is packaged into secretory granules. 5. Finally, the secretory granules fuse with the plasma membrane in a process known as exocytosis, releasing the protein outside the cell.

Key concepts

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is an essential cellular organelle comprising two types: smooth and rough ER. The rough ER is studded with ribosomes and plays a vital role in the synthesis of proteins. During protein synthesis, the ribosomes on the rough ER translate mRNA into proteins, which will eventually be transported to their destinations within or outside of the cell.
The smooth ER, in contrast, lacks ribosomes but serves to process exogenous substances such as drugs and toxins. It is involved in lipid metabolism and acts as a storage organelle, closely associating with the rough ER to ensure a smooth flow of synthesized proteins. Thus, the ER is fundamental in managing biochemical pathways and maintaining cellular homeostasis.

Protein Synthesis

Protein synthesis is a multi-step process beginning in the cell nucleus, where DNA is transcribed into mRNA. The mRNA then exits the nucleus and travels to the ribosomes located on the rough endoplasmic reticulum (ER). Here, it undergoes translation, which is the conversion of mRNA into a polypeptide chain.

• Initiation: mRNA binds to ribosomal units associated with the rough ER.
• Elongation: tRNA brings amino acids that are added to the growing peptide chain.
• Termination: A stop codon signals the end of protein synthesis, allowing the completed protein to be released.

After initial synthesis, these proteins undergo folding and potential modification, often involving the addition of carbohydrates, a task carried out by the Golgi complex. Proteins then continue on their respective pathways, depending on their cellular roles.

Cellular Transport

Cellular transport encompasses various processes that move substances within a cell or from the cell's interior to its exterior and vice versa. Essential components of this process include transport vesicles, which ferry proteins between the endoplasmic reticulum and the Golgi complex. This flow is crucial for proteins to be modified correctly before reaching their final destinations. In addition to these, secretory vesicles play a pivotal role in exocytosis by transporting proteins to the plasma membrane for release outside the cell. Similarly, endosomes transport molecules from the plasma membrane into the cell and assist in sorting and directing them to appropriate destinations. Such intricate movements ensure the efficient function of cellular operations and the maintenance of overall cellular health.

Exocytosis

Exocytosis is the process by which cells expel substances to the external environment. It is a vital function for the secretion of proteins, such as hormones and enzymes, which are integral to intercellular communication and metabolism.
During exocytosis, secretory granules filled with proteins approach the plasma membrane. Here, the membrane of the granule fuses with the plasma membrane, allowing the contents to be released outside the cell.

• Vesicle Trafficking: Transport vesicles carry proteins from the Golgi complex to the cell surface.
• Docking: Vesicles are positioned near the plasma membrane readying for fusion.
• Fusion: Vesicle membranes merge with the plasma membrane, opening to discharge their cargo.

Exocytosis plays a crucial role in maintaining cellular equilibrium and enabling cells to respond rapidly to environmental stimuli.