Chapter 10: Eukaryotic Cell Biology

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

Vesicles full of digestive enzymes. Its structure ensures it can only function in an acidic environment.

11) Use the CGRP/Calcitonin gene to describe how alternatively spliced exons can create new gene products. Use the following words: primary RNA transcript, exon, intron, CGRP, Calcitonin, thyroid, hypothalamus.

After transcription, a primary RNA transcript is obtained with necessary codes for both the CGRP and the Calcitonin. Depending on which protein-hormone is needed, different sequences of introns and exons will exist. In the hypothalamus, CGRP will be spliced in the thyroid gland, Calcitonin will be alternatively spliced.

8) Be able to distinguish the control of transcription between bacteria and the Eukaryota. Be able to describe the two different mechanisms. Use the words promotor, repressors, activators, enhancers, transcription factors, proximity to transcription initiation site, RNA polymerase.

Bacteria- Proteins called repressors bind to sections of DNA called operators right next to the transcription initiation site to turn off transcription. Eukaryota- Also use operators to suppress transcription. In addition, proteins called activators can exert their influence far from the transcription initiation site of the RNA polymerase. Activators start transcription by binding to sections of DNA called enhancers. Then transcription factors will bind to the promoter and the DNA bends so the activator can come into contact with the transcription factor.

7) Describe four different ways that Eubacteria and Eukaryotes differ in their mechanisms of protein synthesis (includes both transcription and translation).

Eubacteria: codes for several proteins at one time, transcription and translation occur right next to each other, have repressors that bind to operators to turn off transcription, leave mRNA alone Eukaryote: each mRNA is translated into one single protein, transcription takes place in nucleus while translation takes place in cytoplasm, have operators to turn off transcription, have activators that bind to enhancers activating transcription, mRNA is ready to leave nucleus

5) What are exons and introns? What is their fate?

Exons: leftover segments of mRNA that bind together producing mature the mature mRNA transcript Introns: entire sections of mRNA which are thrown away/ recycled for their nucleotides

13) After packaging in the Golgi apparatus, what are the two main fates of protein products as described in the Primer? Use the words lysosome, exocytosis, phagocytosis, vesicle fusion, proton pump, acidic environment, digestive enzymes.

One fate is when lysosomes fuse with a phagocytosed food vesicle which activates the proton pump to pump H+ into the lysosome, creating an acidic environment. Digestive enzymes can only function in an acidic environment, the other fate is exocytosis via the secretory vesicle.

3) Describe the mechanism(s) prokaryotes use to control which genes are transcribed. Ditto for eukaryotes.

Prokaryotes: proteins called repressors bind to sections of DNA called operators turning off transcription Eukaryotes: proteins called activators bind to sections of DNA called enhancers initiating transcription

1) How many proteins does an mRNA code for in prokaryotes? In eukaryotes?

Prokaryotes: several separate proteins Eukaryotes: single protein

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

Prokaryotes: transcription and translation in cytoplasm Eukaryotes: transcription in nucleus, translation in ribosome/cytoplasm

10) Describe RNA processing (pretty big question) in Eukaryotes. Use the following words: nucleus, exon, intron, primary RNA transcript, mature RNA transcript, 5' cap (function), 3' poly-A tail (function), spliceosome (function), small nuclear RNA (snRNA, function).

RNA processing in Eukaryotes occurs in the nucleus. Primary RNA transcript is processed to produce a mature RNA transcript. Spliceosomes are made up small nuclear RNA (snRNA) and protein. Their primary function is to cut out stretches of pre-mRNA called introns. The leftover regions that are joined together and want to be expressed are called exons. A "cap" is added to the 5' end and a poly-A tail is added to the 3' end of pre-mRNAs. The cap and tail serve as recognition signals for translation and protect the message from degradation by ribonucleases.

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

Small proteins and molecules that bind to activators speeding up initiation of transcription

9) From lecture, be able to step through the process of transcription of the Lac operon in bacteria. Using the appropriate terms from the question above, as well as lactose.

The lac operon requires lactose to be transcribed. When lactose is not present, a repressor binds to the lac operon, inhibiting RNA from doing its job of preventing mRNA from being transcribed. When lactose is present, it binds to the repressor, thus changing its shape and inhibiting it from binding to the lac operon. RNA polymerase is now able to bind to the promoter to move along the lac operon to transcribe a strand of mRNA.

12) Describe the steps by which eukaryotes package their gene products, both for proteins that will remain in the cytoplasm, and those destined for other locations. Use the words, cytoplasm, ribosome, rough endoplasmic reticulum, smooth endoplasmic reticulum, transport vesicle, golgi apparatus, cis face, trans face.

mRNA for cytoplasmic proteins in synthesized by ribosomes in the cytoplasm. mRNA for other proteins is synthesized by ribosomes attached to the RER. Protein is threated into the RER lumen as it is made. When protein is complete, it gets packaged into a vesicle. The vesicle buds off from RER and travels to the golgi. The vesicle buds off from RER and travels to the Golgi. The vesicle fuses with the cis golgi and its contents enters the cis golgi proteins travels through golgi from cis to trans inside the golgi, proteins receive "markers," "zipcode" etc. to target it for its from final destination. From the trans golgi, the protein is again packaged in vesicle and is transported to its final destination.