Cellular Structure, Proteins, Metabolic Pathways and Movement Across Cell Membranes

Question 1

What distinguishes eukaryotic cells from prokaryotic cells?

Answer 1

Eukaryotic cells are characterized by the presence of membrane-bound organelles and serve as the building blocks for both unicellular and multicellular organisms. In contrast, prokaryotic cells lack membrane-bound organelles and are exclusively found in unicellular organisms.

Question 2

Can you explain the distinction between cytoplasm and cytosol?

Answer 2

Cytoplasm is the cellular region outside the nucleus that houses various organelles and the fluid surrounding these organelles, known as cytosol.

Question 3

What is a nucleus in an organelle?

Answer 3

The nucleus is the control center of the cell, responsible for transmitting and expressing genetic information. It houses the cell’s DNA, which carries the instructions for making proteins and coordinating cellular activities.

Question 4

What are ribosomes in an organelle?

Answer 4

Ribosomes are the cellular workhorses for protein synthesis. Composed of RNA and protein, they read the genetic code from the nucleus and assemble amino acids into proteins.

Question 5

What is the Endoplasmic Reticulum (ER) in an organelle?

Answer 5

The ER consists of both rough and smooth regions. The rough ER, studded with ribosomes, plays a vital role in protein packaging and modification. In contrast, the smooth ER lacks ribosomes and is involved in lipid synthesis, calcium storage, and release.

Question 6

What is the Golgi apparatus in an organelle?

Answer 6

The Golgi apparatus functions as a protein packaging and processing center. It receives proteins from the ER, modifies them, and packages them into vesicles for transport to their final destinations.

Question 7

What are endosomes in an organelle?

Answer 7

These intracellular vesicles act as transport shuttles, moving molecules between the Golgi apparatus, plasma membrane, and lysosomes. They play a crucial role in intracellular trafficking.

Question 8

What are mitochondria in an organelle?

Answer 8

Mitochondria are often referred to as the cell’s powerhouses. They utilize oxygen in a chemical process to produce ATP (adenosine triphosphate), the cell’s primary energy currency. This process involves the breakdown of glucose and fatty acids.

Question 9

What are lysosomes in an organelle?

Answer 9

Lysosomes are digestive organelles filled with enzymes. They play a vital role in breaking down and recycling cellular waste, as well as digesting particulate matter that enters the cell.

Question 10

What are peroxisomes in an organelle?

Answer 10

Peroxisomes are involved in the breakdown of fatty acids and detoxification of harmful substances, particularly hydrogen peroxide. They contribute to cellular health and maintenance.

Question 11

What are cytoskeleton filaments in an organelle?

Answer 11

The cytoskeleton provides structural support to the cell and is composed of three main types of filaments: actin filaments, intermediate filaments, and microtubules. These filaments are responsible for cell shape and movement.

Question 12

What are the functions of the plasma membrane, and what components can be identified

Answer 12

It regulates the passage of substances into and out of the cell and between cell organelles and the cytosol.
It detects chemical messengers at the cell surface.
It establishes connections between adjacent cells.
It anchors cells to the extracellular matrix.

Question 13

Describe the three different membrane junction types

Answer 13

Desmosomes: These are intercellular regions found between adjacent cells, characterized by a 20-nanometer gap between plasma membranes. They rely on cadherin proteins to bind between cells, providing the structural integrity of tissue.
Tight Junctions: Tight junctions result from the fusion of plasma membranes between cells, creating a seamless barrier without extracellular space. This provides a physical barrier and help control the selective passage of substances.
Gap Junctions: Gap junctions consist of protein channels connecting neighboring cells’ cytosols, formed by connexin proteins. These channels are small and only permit the passage of small molecules and ions, such as Na+ and K+, enabling intercellular communication.

Question 14

Based on your knowledge of tight junctions, what is the unction does they serve in the epithelium of the intestine?

Answer 14

Tight junctions act as a barrier, hindering the free passage of most substances across the epithelium. In the context of the intestine, this barrier retains food within the intestinal space until it undergoes complete digestion into usable components. Subsequently, the digested products are selectively absorbed through the epithelial layer in a controlled fashion.

Question 15

What is transcription and translation?

Answer 15

Transcription is the process of copying genetic information from DNA to mRNA in the nucleus. Translation is the synthesis of proteins from mRNA in the cytoplasm.

Question 16

What is a codon?

Answer 16

A three-base sequence in RNA that specifices one specific amino acid.

Question 17

How does pre-mRNA differ from mRNA?

Answer 17

The primary RNA transcript, known as pre-mRNA, contains the full sequence of nucleotides, including both exons (coding regions) and introns (non-coding regions). Before entering the cytoplasm, a process called splicing takes place. During splicing, the spliceosome removes the intron-derived segments, resulting in the formation of mature mRNA. The key distinction is that pre-mRNA includes introns, while mature mRNA does not.

Question 18

How is protein synthesis regulated?

Answer 18

Protein synthesis is primarily regulated by transcription factors, which function as gene switches. They can either activate or repress the initiation of transcription at the promoter region. Cell signaling pathways influence transcription factors, affecting their binding to the promoter.
Apart from transcription, regulation occurs during the initiation of protein assembly on ribosomes and mRNA degradation in the cytoplasm. These processes collectively govern protein synthesis.

Question 19

What are the consequences of a DNA mutation on a cell?

Answer 19

While many mutations are harmless, some can result in the development of diseases, including cancer, by altering cell functions while still allowing cell growth and replication. However, mutations can also lead to cell death.

Question 20

What is protein degradation?

Answer 20

Protein degradation involves the targeting of proteins for breakdown by a small peptide called ubiquitin. Ubiquitin binds to the protein, guiding it to the proteasome. Inside the proteasome, the protein is unfolded and broken down into smaller peptides, allowing for the recycling of its amino acids.

Question 21

Given that Protein X and Y both have crucial roles in regulating blood pressure and can bind to the same ligand, with Protein Y increasing blood pressure and Protein X lowering it when bound to the ligand, and knowing that Protein Y has a higher affinity for the ligand than X, what would be the expected outcome if the ligand were administered to an individual with normal blood pressure?

Answer 21

When the ligand is administered to a person with normal blood pressure, we would anticipate an increase in blood pressure. This is because Protein Y has a higher percentage of saturation with the ligand compared to Protein X. However, it’s important to note that Protein X also binds to the ligand to some extent, so it would partially counteract the effects of Protein Y. Another possibility is that if the ligand is administered at a very high dose, both proteins could become fully saturated.

Question 22

What factors can increase enzyme-mediated reactions?

Answer 22

Enzyme-mediated reactions can be enhanced by increasing temperature, substrate concentration, enzyme concentration, and enzyme activity.

Question 23

What causes the rate of enzyme-mediated reactions to reach a maximum at high substrate concentrations, and does the enzyme’s affinity for its substrate influence the maximum reaction rate?

Answer 23

The rate of enzyme-mediated reactions depends on substrate concentration; a higher substrate concentration leads to a faster product formation rate. However, at very high substrate concentrations, all enzymes become occupied by substrates, limiting further rate increases. If more enzymes were available, the rate could increase but would still reach a new maximum.
The enzyme’s affinity for its substrate mainly affects the rate of product formation at lower substrate concentrations and doesn’t impact the maximum reaction rate at high substrate concentrations.

Question 24

Where are the enzymes of the Krebs cycle, oxidative phosphorylation, and glycolysis located, and what are the different processes?

Answer 24

The enzymes involved in these processes are located as follows:
- Krebs Cycle: This mitochondrial pathway occurs in the matrix of mitochondria. It utilizes breakdown products of organic macromolecules to yield CO2, ATP, and H+.
- Glycolysis: Glycolysis takes place in the cytosol. It is a reaction that breaks down glucose into pyruvate (or lactate under anaerobic conditions), NADH, H+, water, and ATP.
- Oxidative Phosphorylation: Enzymes for oxidative phosphorylation are found in the inner mitochondrial membranes. This process involves the formation of ATP by utilizing the energy released when O2 combines with H+ to form water.

Question 25

Consider a nonpolar molecule that crosses a plasma membrane and enters a cell. What factors might increase its rate of diffusion? What happens to the rate of diffusion into the cell if a molecule is metabolized as soon as it enters the cell?

Answer 25

The rate of diffusion is influenced by several factors:
* Concentration Gradient: The greater the difference in concentration between the two sides of the membrane, the faster the molecule will diffuse.
* Surface Area: A larger surface area of the membrane allows for more molecules to pass through, increasing the rate of diffusion.
* Permeability Coefficient: A higher permeability coefficient indicates easier passage through the membrane.
If a molecule is metabolized immediately upon entering the cell, the rate of diffusion will continue until all the molecules have crossed the membrane. This is because metabolism does not affect the initial concentration gradient driving the diffusion process.

Question 26

Why is mediated transport necessary for the movement of molecules like glucose into or out of a cell? Additionally, why does active transport become essential when moving ions against their concentration gradient?

Answer 26

Mediated transport is required for molecules such as glucose because they are polar and cannot pass through the nonpolar lipid bilayer of the plasma membrane via simple diffusion.
Ions, which are also polar, face a similar challenge. They can only move across the membrane through facilitated diffusion channels when there is a concentration gradient. However, when ions need to be transported against their concentration gradient, active transport mechanisms come into play. This involves the hydrolysis of ATP to actively pump the ions across the membrane, overcoming the concentration gradient barrier.

Question 27

Can you explain endocytosis and provide details about its three primary forms?

Answer 27

Endocytosis is a cellular process where the plasma membrane forms pockets that eventually close to create vesicles containing extracellular material.
* Pinocytosis: The cell engulfs extracellular fluid and dissolved substances.
* Phagocytosis: The cell engulfs larger particles, often bacteria or other substantial substances.
* Receptor-mediated endocytosis: This process involves the formation of clathrin-coated pits, which pinch off membrane regions containing receptor-ligand complexes. It’s a highly specific mechanism for capturing particular molecules.