Biology Chapter 10 Primer Questions

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Questions and Answers

Describe four different ways that Eubacteria and Eukaryotes differ in their mechanisms of protein synthesis.

Eubacteria: Transcribed mRNA often codes for multiple proteins; Eukaryote: mRNA translates into a single protein. 2. Eubacteria: Transcription and translation occur next to each other; Eukaryote: Transcription and translation occur in different parts of the cell. 3. Eubacteria: Control transcription by protein repressors; Eukaryote: Use operators and activators. 4. Eubacteria: No splicing, no protein cap, no poly A-tail; Eukaryote: 'mRNA processing'.

Distinguish the control of transcription between Eubacteria and Eukaryota.

Eukaryotes use activators to activate transcription and transcription factors to influence the promoter region, while Eubacteria use repressors that bind to DNA to turn off transcription without transcription factors.

Describe RNA processing using the following words: nucleus, exon, intron, primary RNA transcript, mature RNA transcript, 5' cap, 3' poly-A tail, spliceosome, small nuclear RNA.

Use the CGRP/Calcitonin gene to describe how alternatively spliced exons can create new gene products.

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Describe how eukaryotes package their gene products.

mRNA docks to ribosome at the rough endoplasmic reticulum, gets translated into proteins, which are then packaged into transport vesicles and sent to the Golgi apparatus, entering through the cis face and exiting via the trans face. Signup and view all the answers

After packaging in the Golgi apparatus, what are the two main fates of protein products?

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Where in the cell do transcription and translation occur in prokaryotes? In eukaryotes?

In prokaryotes, transcription and translation both occur in the cytoplasm. In eukaryotes, transcription occurs in the nucleus and translation occurs in the ribosomes of the rough endoplasmic reticulum. Signup and view all the answers

What is a transcription factor, and what does it do?

A small molecule or protein used in eukaryotic transcription control that binds to activators and speeds up initiation of transcription. Signup and view all the answers

What are exons and introns? What is their fate?

Exons are remaining segments of the gene that produce the mature mRNA transcript, while introns are sections that are removed and recycled. Both are destined for export out of the nucleus. Signup and view all the answers

What is a lysosome, and why doesn't it consume itself?

Lysosomes are vesicles that fuse with structures to break them down; they activate proton pumps to create an acidic environment that allows digestive enzymes to function without damaging the lysosome itself. Signup and view all the answers

What is a repressor in Bacteria and what does it do?

A repressor is a protein that stops transcription. Signup and view all the answers

Use the example of the lac operon to explain how transcription is regulated in Bacteria.

The lac operon metabolizes lactose; if lactose is present, it activates transcription. In absence of lactose, a repressor binds to the operator to stop transcription. Signup and view all the answers

Study Notes

Differences Between Eubacteria and Eukaryotes in Protein Synthesis

Eubacteria produce polycistronic mRNA, coding for multiple proteins; eukaryotic mRNA is monocistronic, coding for a single protein.
Transcription and translation in eubacteria occur simultaneously in the cytoplasm; in eukaryotes, they are separated—transcription takes place in the nucleus, and translation occurs in the cytoplasm.
Eukaryotes use activators and transcription factors to control transcription, regulating gene expression to a finer degree; eubacteria rely on repressors that bind to operators to inhibit transcription.
Eubacteria lack mRNA processing features such as splicing and added caps/tails, while eukaryotic mRNA undergoes extensive processing before translation.

Control of Transcription

Eukaryotic transcription is activated by activators binding to enhancers, working at a distance from RNA polymerase's initiation site.
Eukaryotes use transcription factors to facilitate the binding of RNA polymerase, thus providing graded control of gene expression.
Eubacteria control transcription via repressors binding to DNA operators, with no involvement of transcription factors.

RNA Processing

In the nucleus, the primary RNA transcript undergoes processing where introns (non-coding regions) are removed and exons (coding regions) are spliced together.
A 5' cap is added for stability and initiation of translation, while a 3' poly-A tail aids in export from the nucleus and protects against degradation.
The spliceosome, composed of small nuclear RNAs (snRNA) and proteins, facilitates the splicing process, ensuring only mature RNA transcripts exit the nucleus.

Alternative Splicing: CGRP/Calcitonin Gene

The primary RNA transcript from the CGRP/Calcitonin gene can be alternatively spliced to generate different proteins.
Two gene products, Calcitonin and CGRP, are formed in different tissues: Calcitonin in the thyroid and CGRP in the hypothalamus, showcasing functional diversity.

Packaging of Gene Products in Eukaryotes

Ribosomes translate mRNA into proteins, which are directed to the rough endoplasmic reticulum (ER) for proper folding and modification.
Proteins packaged into transport vesicles are sent to the Golgi apparatus, entering at the cis face and exiting at the trans face to further refine and sort them for their cellular destinations.

Fates of Protein Products After Golgi Packaging

Proteins may be directed to lysosomes for degradation, where they undergo digestion by enzymes in an acidic environment.
Alternatively, proteins can be released via exocytosis, merging with the cell membrane to expel substances outside the cell.

Location of Transcription and Translation in Cells

In prokaryotes, both transcription and translation occur in the cytoplasm, enabling rapid protein synthesis.
In eukaryotes, transcription happens in the nucleus, and translation occurs at ribosomes on the rough ER.

Function of Transcription Factors

Transcription factors are proteins that bind to specific DNA sequences, enhancing the efficiency of transcription initiation by promoting RNA polymerase binding.

Exons and Introns

Exons are the segments retained in mRNA, coding for the final protein product; introns are non-coding segments excised during RNA splicing.
Introns are recycled for nucleotides, while exons are exported from the nucleus as part of the mature mRNA ready for translation.

Lysosomes and Their Function

Lysosomes are vesicles containing digestive enzymes that break down cellular waste and foreign material.
They prevent self-digestion by maintaining an acidic internal environment activated by a proton pump, enabling enzymes to function without damaging the lysosomal membrane.

Role of the Repressor in Bacteria

Repressors are regulatory proteins in bacteria that bind to specific DNA sites, blocking transcription and preventing mRNA synthesis.

Regulation of Transcription: The Lac Operon

The lac operon in bacteria facilitates lactose metabolism; it is activated only when lactose is present.
In absence of lactose, a repressor binds to the operator, halting transcription; lactose binds the repressor, negating its function and allowing transcription to proceed.

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Test your understanding of the differences in protein synthesis mechanisms between Eubacteria and Eukaryotes in this flashcard quiz. Explore various aspects of transcription and translation processes, and how they differ across these two domains of life.