Ch. 4 A Tour of the Cell

Taylor - Campbell Biology: Concepts & Connections 10th Edition

Taylor, Simon, Dickey, Hogan10th EditionCampbell Biology: Concepts & ConnectionsISBN: 9780136538783Not the one you use?Change textbook

Taylor, Simon, Dickey, Hogan 10th Edition

Ch. 4 A Tour of the Cell

Problem 16

Chapter 4, Problem 16

Describe the pathway of the protein hormone insulin from its gene to its export from a cell of your pancreas.

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Identify the insulin gene on the DNA within the nucleus of a pancreatic cell. This gene contains the instructions necessary to produce the insulin protein.

Transcription of the insulin gene occurs, where an mRNA (messenger RNA) copy of the gene is made. This mRNA will carry the genetic code from the DNA out of the nucleus to a ribosome in the cytoplasm.

Translation takes place at the ribosome, where the mRNA is read and used to assemble the amino acids into the primary structure of the insulin protein. This process involves tRNA (transfer RNA) which brings the appropriate amino acids to the ribosome based on the sequence of the mRNA.

The newly synthesized insulin protein undergoes post-translational modifications in the rough endoplasmic reticulum (ER) where it is folded into its functional three-dimensional structure and any necessary chemical modifications are made.

The insulin is then packaged into vesicles in the Golgi apparatus, where it is further processed and sorted for export. The vesicles transport the insulin to the cell membrane, where they fuse with the membrane and release the insulin into the bloodstream.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein. In the case of insulin, the gene encoding this hormone is transcribed into messenger RNA (mRNA) in the nucleus of pancreatic cells. This mRNA then undergoes processing and is transported to the cytoplasm, where it serves as a template for protein synthesis.

Protein Synthesis

Protein synthesis involves two main processes: transcription and translation. After mRNA is produced, ribosomes in the cytoplasm translate the mRNA sequence into a polypeptide chain, which folds into the functional insulin protein. This process is crucial for producing insulin, which regulates glucose levels in the blood.

Protein Secretion

Protein secretion is the process by which proteins are transported out of a cell. For insulin, once synthesized and properly folded in the endoplasmic reticulum, it is packaged into vesicles that travel to the Golgi apparatus for further processing. Finally, insulin is secreted from the pancreatic beta cells into the bloodstream in response to elevated blood glucose levels.

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Protein Secretion

Related Practice

Textbook Question

Is this statement true or false?

'Animal cells have mitochondria; plant cells have chloroplasts.'

Explain your answer, and describe the functions of these organelles.

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Textbook Question

Describe the structure of the plasma membrane of an animal cell. What would be found directly inside and outside the membrane?

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Textbook Question

Imagine a spherical cell with a radius of 10 μm. What is the cell's surface area in μm²?

Its volume, in μm³? (Note: For a sphere of radius r, surface area = 4πr² and volume = 4/3πr³.). Remember that the value of π is 3.14.)

What is the ratio of surface area to volume for this cell? Now do the same calculations for a second cell, this one with a radius of 20 μm. Compare the surface-to-volume ratios of the two cells.

How is this comparison significant to the functioning of cells?

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Textbook Question

How might the phrase 'ingested but not digested' be used in a description of the endosymbiotic theory?

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Textbook Question

Cilia are found on cells in almost every organ of the human body, and the malfunction of cilia is involved in several human disorders. During embryological development, for example, cilia generate a leftward flow of fluid that initiates the left-right organization of the body organs. Some individuals with primary ciliary dyskinesia exhibit a condition (situs inversus) in which internal organs such as the heart are on the wrong side of the body. Explain why this reversed arrangement may be a symptom of PCD.

Microtubules often produce movement through their interaction with motor proteins. But in some cases, microtubules move cell components when the length of the microtubule changes. Through a series of experiments, researchers determined that microtubules grow and shorten as tubulin proteins are added or removed from their ends. Other experiments showed that microtubules make up the spindle apparatus that 'pulls' chromosomes toward opposite ends (poles) of a dividing cell. The figures below describe a clever experiment done in 1987 to determine whether a spindle microtubule shortens (depolymerizes) at the end holding a chromosome or at the pole end of a dividing cell. Experimenters labeled the microtubules of a dividing cell from a pig kidney with a yellow fluorescent dye. As shown on the left half of the diagram below, they then marked a region halfway along the microtubules by using a laser to eliminate the fluorescence from that region. They did not mark the other side of the spindle (right side of the figure).

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