Click here for the Eukaryotic Gene Expression student learning guide

1. Introduction

In the previous tutorials in this module, we’ve looked at how control of eukaryotic gene can involve

  1. modification of chromatin structure through acetylation and methylation (arrow number 1, above)
  2. control of transcription  (arrow number 2)

In what follows, we’ll look at regulatory methods that follow transcription.

2. Alternative Splicing of RNA

To splice is to “unite (two lengths of magnetic tape, photographic film, etc.) by overlapping and securing together two ends.”  Before the digital age, movies were shot on film. If you had a scene in your film that you didn’t want to use, you would cut that scene out, and then connect the remaining pieces. That’s splicing.

Splicing is a key move that happens when the initial RNA transcript (2) is processed into messenger RNA (3). Non-coding sequences called introns (f1 and f2) are cut out, and exons (expressed sequences) are spliced together. Subsequent modifications include addition of a 5′ G3P cap (at “g”) and a 3′ poly A tail (a segment consisting of repeated adenine ribonucleotides, represented by “j”). The start and stop codons are also shown (at “h” and “i,” respectively).

Alternative splicing relates to the fact that exons don’t have to be spliced together in the linear order in which they’re initially transcribed. The order can be changed, and exons can be dropped. Consider the image at right. In “B” you can see a primary RNA transcript that contains 6 exons. However, alternative splicing (indicated by the arrows at number 2) generates three unique mRNAs, which produce three unique proteins, each of which is lacking one or more exons. The result will be three proteins, with different three-dimensional conformations and different properties.

Alternative splicing explains why there are many more human messenger RNAs than there are genes. It’s estimated that about 80% of all human genes are alternatively spliced. Moreover, this might explain some features of human evolution. For example, while the human genome and chimpanzee genome are of equal size, there are significant differences in messenger RNA and protein that are can be attributed to alternative splicing that occurs in humans, and which doesn’t occur in chimpanzees (Principles of Life, Sinauer Associates, p222).

3. Regulation of translation by microRNAs (RNA interference)

Protein coding DNA accounts for only about 1.5% of the human genome. What’s the rest of the genome doing? A recent survey of the genome (the ENCODE project) revealed that “more than 80 percent of this non-gene component of the genome, which was once considered “junk DNA,” actually has a role in regulating the activity of particular genes (gene expression)” (see the Genetics home reference). Much of this regulation is thought to happen through non-coding RNAs.

The main type of non-coding RNA to know about is called a microRNA (miRNA). These miRNAs are about 22 nucleotides long. They originate from longer precursor RNAs that are cut apart by an enzyme. After being cut, each 22 nucleotide fragment forms a complex with a protein.

One of the main functions of miRNA is a process called RNA interference. Using complementary base pairing, the miRNA can bind with any cellular RNA (usually messenger RNA) with at least 7 complementary bases. Binding blocks mRNA translation into protein, and is sometimes followed by enzymatic degradation of the mRNA.

Adapted from “Plasticity Related MicroRNA…”, Ryan, Joilin, and Williams

The image at left illustrates microRNA activity. Letter “A” shows non-coding DNA. This is transcribed (“B”) into a pre-microRNA (“C”). Processing and export (“D”) converts this into a microRNA (“E”), which then associates with a protein called an RNA-induced silencing complex (“I”). If the miRNA partially matches its target messenger RNA (as shown at “H”) then translation is blocked (“J”). A complete match (“G”) results in RNA degradation (“K”). Obviously, both cases interrupt translation of proteins from mRNA, which is why the entire phenomenon is called RNA interference.

4. Checking Understanding: Alternative Splicing and RNA Interference

[qwiz qrecord_id=”sciencemusicvideosMeister1961-M24_alternative splicing and RNA interference”] [h]

Labeled Diagrams: Alternative Splicing and RNA Interference

[i]

[q labels = “top”]

 

[l]introns

[f*] Excellent!

[fx] No. Please try again.

[l]mRNA

[f*] Correct!

[fx] No. Please try again.

[l]poly-A tail

[f*] Great!

[fx] No, that’s not correct. Please try again.

[l]pre-mRNA

[f*] Good!

[fx] No. Please try again.

[q labels = “top”]

 

[l]Alternative splicing

[f*] Great!

[fx] No. Please try again.

[l]pre-mRNA

[f*] Great!

[fx] No, that’s not correct. Please try again.

[l]transcription

[f*] Excellent!

[fx] No, that’s not correct. Please try again.

[l]translation

[f*] Great!

[fx] No. Please try again.

[q labels = “top”]

 

[l]miRNA

[f*] Excellent!

[fx] No. Please try again.

[l]mRNA degradation

[f*] Great!

[fx] No, that’s not correct. Please try again.

[l]DNA

[f*] Good!

[fx] No, that’s not correct. Please try again.

[l]precursor miRNA

[f*] Good!

[fx] No. Please try again.

[l]Blocked translation

[f*] Good!

[fx] No. Please try again.

[q multiple_choice=”true”] Which of the statements below most closely matches what’s being depicted in the following diagram?

[c] Every DNA gene has one corresponding protein product.

[f] No. Look at “D,” “E,” and “F,” above. Three proteins coming from one gene.

[c*] Multiple proteins can be produced from one gene.

[f] Exactly. By shuffling or deleting exons, alternative splicing allows multiple proteins to be created from one coding DNA.

[c] Prokaryotes have more flexibility in how genes are expressed than do eukaryotes

[f] No. That’s probably not true (just consider the alternative splicing shown above), and, it’s definitely not depicted in the image above.

[/qwiz]

5. Regulation of Translation by Proteins

In the previous sections, we saw how microRNAs can regulate translation. What follows are some additional processes by which translation can to be regulated. We’ll look at this in the context of regulation of cellular iron concentration.

The first example involves the production of a protein called ferritin. Ferritin is involved with controlling the amount of iron in cells. This is important because while iron is an essential nutrient, the accumulation of too many free iron ions (Fe2+) can be toxic. Ferritin protein binds iron, storing it in a non-toxic form (from which the iron can be released when the cell needs it).

Ferritin mRNA contains a regulatory sequence that’s called an iron-response element (or “IRE,” shown at “1” in diagrams “A” and “B” above). When iron levels are low (diagram “A”), the IRE is bound by a regulatory protein called an IRE-binding protein, shown at “2.” When bound by this protein, the IRE blocks the start codon (“3”), preventing translation.

When iron levels are high (diagram “B”), iron binds with the IRE binding protein, causing a conformational change that keeps prevents the IRE-binding protein from binding with the iron response element (at “1”). Number “6” shows the IRE bound with iron. When iron binds with the IRE-binding protein, the iron response element sequence in the mRNA changes conformation. As a result, ribosomes can bind with the mRNA and translate it, producing the ferritin protein (“7”). Note: number 4 in diagrams A and B above indicates the stop codon.

Note that this results in negative feedback: as ferritin is produced, more free iron will be captured, lowering the iron concentration.

The mechanism described above involves control of translation by regulating the ability of ribosomes to bind with mRNA. Another mechanism of translational control involves mRNA degradation. The example of this that we’ll examine below also involves regulation of iron metabolism, and it also involves an iron response element in mRNA. Note the overlap, and try to keep these two mechanisms separate as you study the example below.

The transferrin receptor protein is a membrane receptor that binds with transferrin, a glycoprotein that binds with iron in biological fluids. When transferrin binds with the transferrin receptor protein, it induces receptor-mediated endocytosis, creating a vesicle that brings the transferrin (and iron) into the cell.

Production of the transferrin receptor protein is also controlled by an IRE-binding protein.

Diagram “A” shows what happens when iron levels are low. An IRE (iron response element) binding protein (shown at “6”) binds with the iron response element (“5”), a regulatory sequence in the untranslated region of the transferrin receptor protein mRNA. You can tell that the sequence is in the untranslated region because it’s on the 3′ end of the mRNA, after the stop codon (at “4”). The IRE/IRE-binding protein complex blocks degradative enzymes in the cytoplasm that would break down the mRNA. As a result, the mRNA is preserved, and ribosomes (1) can bind with the mRNA and translate the transferrin receptor protein (at “2”). This allows the cell to take in additional iron.

When iron levels are high, the cell no longer “wants” to take in additional iron (because, as stated above, high levels of iron can be toxic). Iron binds with the IRE binding protein, causing it to change shape in a way where it no longer binds to the IRE sequence (“5”) in the mRNA. This allows degradative enzymes to digest the mRNA (indicated by the broken-down RNA at “8”). Again, note the negative feedback. High iron concentration keeps the mRNA for the transferrin receptor from being maintained in the cell. With the mRNA destroyed, little transferrin receptor will be produced, and little iron-containing transferrin will be brought into the cell, lowering the cellular iron level.

6. Protein Processing and Breakdown

A final opportunity for regulation of eukaryotic gene expression involves the modification and/or destruction of proteins. Think back for a moment to the cell cycle, which is controlled by the accumulation and then destruction of cyclin. How is this destruction accomplished?

One method is to target a protein for destruction by tagging it with ubiquitin, a protein that is made up of 76 amino acids. Ubiquitin is present in cells throughout the eukaryotic domain (hence, it’s ubiquitous), and it’s structure is highly conserved in eukaryotic cells.

In the image to the right, a protein is shown at “1.” A team of ubiquitin activating enzymes (not shown) attaches a short chain of ubiquitins to the  protein (at “2”). Once tagged with ubiquitin (“3”), the protein is recognized by a proteasome (“4”), a protein complex that breaks proteins down to short peptides (at “6”), which can then be recycled into individual amino acids that can be used in later instances of protein synthesis.

7. Eukaryotic Gene Regulation: Cumulative Quiz

That’s as far as we’re going to go (for now) in terms of explaining eukaryotic gene regulation. The following quiz will test your mastery on the material immediately above, and also include questions relevant to the entire module.

[qwiz random = “true” style=” width: 650px !important; ” qrecord_id=”sciencemusicvideosMeister1961-M24_Eukaryotic Gene Regulation, cumulative quiz”] [h]

Eukaryotic Gene regulation: Cumulative Quiz

[i]

[q] In the diagram below, the iron response element is at

[textentry single_char=”true”]

[c*] 1

[f] Excellent. The iron response element is a regulatory sequence in the mRNA, indicated by number “1.”

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. The iron response element is a regulatory sequence. Look for something that’s part of the DNA.

[q] In the diagram below, the start codon is at

[textentry single_char=”true”]

[c*] 3

[f] Nice. Number “3” is the start codon.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint. Look at diagram B. Where’s the point immediately after which the ribosome starts producing proteins.

[q] In the diagram below, which is the system’s key regulatory protein, shown in its active form (where it prevents translation)?

[textentry single_char=”true”]

[c*] 2

[f] Excellent. Number 2 shows the iron-response element binding protein. When bound to the IRE, this protein shuts down translation.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. When bound to the IRE, this protein shuts down translation.

[q multiple_choice=”true”] The diagram below is about gene regulation through control of

[c] acetylation and methylation

[f] No. Acetylation and methylation are ways that cells control DNA packaging. At the point, we have mRNA and ribosomes. Choose a later moment in gene regulation.

[c] alternative splicing

[f] Sorry, that’s not correct.

[c] transcription

[f] No. At the point, we have mRNA and ribosomes. Transcription has already happened.

[c*] translation

[f] Fabulous. At this point, there’s mRNA and ribosomes. This is about translational control

[q] In the diagram below, the regulatory sequence in the mRNA is at which number?

[textentry single_char=”true”]

[c*] 5

[f] Nice work! Number “5” is the regulator sequence in the mRNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Look for a part of the mRNA that seems to be exerting some regulatory control over mRNA degradation.

[q] In the diagram below, regulation is about preventing or allowing enzymes that break down mRNA. These enzymes are indicated by which number?

[textentry single_char=”true”]

[c*] 7

[f] Awesome. Number “7” indicates an enzyme that breaks down mRNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Look for a something which seems to be breaking down mRNA in “B,” but blocked from doing so in diagram “A.”

[q] In the diagram below, which number shows a proteasome?

[textentry single_char=”true”]

[c*] 4

[f] Excellent. Number 4 shows a proteasome.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Proteasomes are large molecular complexes that break down proteins. If “1” is a protein, then what could be breaking it down?

[q] In the diagram below, which number shows protein that’s been tagged with ubiquitin for destruction?


[textentry single_char=”true”]

[c*] 3

[f] Nice job! Number 3 shows a protein that’s been tagged with ubiquitin.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. Number “1” is the protein, and “2” is ubiquitin.

[q] In the diagram below, small peptides that can be recycled into amino acids are shown at

[textentry single_char=”true”]

[c*] 6

[f] Good work! “6” shows the peptides left over after the larger protein has been broken down by the proteasome.

[c] Enter word

[f] M

[c] *

[f] No. Here’s a hint. Number “1” is the protein, and “2” is ubiquitin.

[q multiple_choice=”true”] Number 2 in the diagram below illustrates which concept related to eukaryotic gene regulation.

[c] acetylation and methylation

[f] No. Acetylation and methylation are ways that cells control DNA packaging. Step 2 is about what happens to precursor RNA as it’s made into messenger RNA.

[c*] alternative splicing

[f] Excellent! Number 2 shows how through alternative splicing, a single gene can be transformed into three protein products.

[c] transcription

[f] No. While transcription is definitely being shown above (step 1), the question is about step 2, where one pre-mRNA results in three different mRNAs, and 3 different proteins. What’s that called?

[c] translation.

[f] No. Translation is definitely happening (in step 3), but the question is about step 2, where one pre-mRNA results in three different mRNAs, and 3 different proteins. What’s that process called?

[q] In the diagram below, which letter indicates a precursor microRNA?

[textentry single_char=”true”]

[c*] C

[f] Correct! Letter “c” shows a precursor microRNA. Subsequent processing will result in an miRNA.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Look for something that’s a product of transcription, and which will need subsequent processing to become the microRNA shown at “E.”

[q] In the diagram below, which letter shows a microRNA associated protein?

[textentry single_char=”true”]

[c*] I

[f] Nice job!. Letter “I” shows a microRNA associated protein, also known as an

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Look for a protein that hooks onto a single stranded microRNA, and which (when with the miRNA) can either block translation (J) or degrade mRNA (K).

[q] In one form of RNA interference, a complete match between a microRNA and a corresponding messenger RNA sequence sets the stage for subsequent enzymatic breakdown of the mRNA. In the diagram below, where do you see that breakdown happening?

[textentry single_char=”true”]

[c*] K

[f] Good work! Letter “K” shows messenger RNA being broken down subsequent to binding with microRNA.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Look for a part of the image that shows mRNA being broken down into its component RNA nucleotides.

[q multiple_choice=”true”] The diagram below shows regulation of gene expression through

[c*] RNA interference

[f] Great job. The image above shows RNA interference

[c] alternative splicing

[f] No. While it’s possible the alternative splicing could have produce the mRNA in this diagram,  the key point involves molecule “E” interfering with a process that involves ribosomes (at “F”). What type of molecule  is “E,” and what process are ribosomes involved with?

[c] transcription

[f] No. While transcription is definitely being shown above (step B), the regulatory process comes later in the diagram. Here’s a hint: what type of molecule  is “E,” and what process are ribosomes (shown at “F”) involved with?

[q] In the diagram below, which number is a DNA bending protein?

[textentry single_char=”true”]

[c*] 1

[f] Nice job! “1” is a DNA bending protein.

[c] Enter word

[f] No.

[c] *

[f] No. Which part of the diagram seems to be associated with a bend in the DNA?

[q] In the diagram below, which number an enhancer?

[textentry single_char=”true”]

[c*] 2

[f] Nice job! “2” is an enhancer.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Here’s a hint. The enhancer is part of the DNA, and it’s composed of 3 distal control elements.

[q] In the diagram below, which number is pointing to one or more distal control elements?

[textentry single_char=”true”]

[c*] 3

[f] Nice job! “3” is pointing to distal control elements, which together make up the enhancer.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. The distal control elements are sequences within DNA, and they make up the enhancer.

[q] In the diagram below, which number is pointing to one or more activators?

[textentry single_char=”true”]

[c*] 4

[f] Awesome! “4 is pointing to two activators.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. The activators bind with distal control elements, which are sequences within the DNA.

[q] In the diagram below, if “8” represents mediator proteins, then which number indicates a general transcription factor?

[textentry single_char=”true”]

[c*] 5

[f] Way to go! If “8” represents mediator proteins, then  “5” would have to be a general transcription factor.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint. The general transcription factor binds near the promoter, making it possible for RNA polymerase to bind the promoter and transcribe the gene. If RNA polymerase is “7” and “8” represents mediator proteins, then which number could represent a general transcription factor?

[q] In the diagram below, the promoter is at

[textentry single_char=”true”]

[c*] 6

[f] Way to go!  “6” represents the promoter.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. The promoter is just upstream of the gene, and it’s where RNA polymerase binds.

[q] In the diagram below, if “5” represents a general transcription factor, then what number would represent mediator proteins?

[textentry single_char=”true”]

[c*] 8

[f] Way to go! If “5” represents a general transcription factor then  “8” would have to be the mediator proteins.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint. The general transcription factor binds near the promoter, making it possible for RNA polymerase to bind the promoter and transcribe the gene. If RNA polymerase is “7” and “8” represents mediator proteins, then which number could represent a general transcription factor?

[q] In the diagram below, RNA polymerase is represented by number

[textentry single_char=”true”]

[c*] 7

[f] Excellent.  “7” represents RNA polymerase.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint. RNA polymerase binds with the promoter, just upstream of the gene.

[q] In the diagram below, the TATA box is at


[textentry single_char=”true”]x

[c*] 2

[f] Excellent. The A-T rich region at the start of the promoter is known as the TATA box.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. The TATA box is rich in adenine and thymine base pairs.

[q] In the diagram below, the template DNA is at

[textentry single_char=”true”]x

[c*] 4

[f] Nice job. “4” is the template DNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. The template DNA is the strand of DNA that’s transcribed into RNA. If 8 is RNA, then what has to be the template strand of DNA?

[q] In the diagram below, a general transcription factor is shown at


[textentry single_char=”true”]x

[c*] 5

[f] Way to go. “5” is a general transcription factor.

[c] 7

[f] No, but you’re on the right track. “7” is a transcription factor, but it’s binding fairly late in the process. Find a transcription factor that shown binding before RNA polymerase arrives.

[c] *

[f] No. Find something that binds to the DNA before RNA polymerase (and makes that binding possible). 

[q] In the diagram below, which letter indicates distal control elements?


[textentry single_char=”true”]

[c*] a

[f] Excellent. Distal control elements are at “a.”

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint. When you see “distal,” think “distant.”

[q] In the diagram below, which letter indicates intron DNA?

[textentry single_char=”true”]

[c*] e

[f] Nice job. The intron DNA (at “e”) is DNA that gets cut out of the pre-RNA before it gets made into mRNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. The intron DNA is DNA that gets cut out of the pre-RNA before it gets made into mRNA. “F” represents two RNA segments that have been cut out…so just work up from there and you’ll have the answer. 

[q] In the diagram below, pre-mRNA (still with introns) is represented by number


[textentry single_char=”true”]

[c*] 2

[f] Awesome. “2” is pre-mRNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Spliced out RNA introns can be seen at “f.” Look for RNA that still contains introns.  

[q] In the diagram below, messenger RNA is represented by number

[textentry single_char=”true”]

[c*] 3

[f] Good work. “3” is messenger RNA.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. RNA introns can be seen in number  “2.” Look for RNA in which the introns have been spliced out.

[q multiple_choice=”true”] Which statement below best captures the significance of the process being illustrated?

[c] If promoters share common control elements, than one signal can activate multiple genes.

[f] No. This isn’t about activation of multiple genes. It’s about how a cell that contains multiple genes knows which one to activate.

[c] Through alternative splicing, one gene can produce multiple proteins.

[f] No. This isn’t about one gene, but two. What determines which gene gets expressed?

[c*] The combination of activators in a cell’s nucleus determines which genes that cell will express.

[f] Excellent. The process illustrated above is combinatorial control of gene expression.

[q multiple_choice=”true”] Which statement below best captures the significance of the process being illustrated?

[c*] If promoters share common control elements, than one signal can activate multiple genes.

[f] Excellent. What’s shown above is how all three genes share a common control element (indicated by “c.”) This allows one transcription factor (“b”) to turn on all three genes.

[c] Through alternative splicing, one gene can produce multiple proteins.

[f] No. This is about three genes producing three proteins at the same time. What could bring that about?

[c] The combination of activators in a cell’s nucleus determines which genes that cell will express.

[f] No. While that’s true, it’s not what’s being illustrated above. Here you have one activator activating three genes. How could that come about.

[q multiple_choice=”true”] Which statement below best captures the significance of the process being illustrated?

[c] Binding of signals at the membrane can set off a signal transduction cascade, resulting in quick changes throughout the cell.

[f] No. The signal (“f” is entering the cell’s cytoplasm, and not binding at the membrane. Next time, find a better description of what’s happening.

[c] Through alternative splicing, one gene can produce multiple proteins.

[f] No. This shows one gene expressing one protein product. Next time, find a better description of what’s happening.

[c*] Hormones can enter cells, bind with receptors, and become transcription factors.

[f] Fabulous. This illustration is showing how steroid hormones like estrogen work. They enter cells, bind with receptors, and then act as transcription factors.

 

[q] In the diagram below, a proteasome would be active at number

[textentry single_char=”true”]

[c*] 8

[f] Nice. Proteasomes break down proteins.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint: Proteasomes break down proteins.

[q] In the diagram below, alternative RNA splicing would occur at number

[textentry single_char=”true”]

[c*] 3

[f] Excellent. “3” shows where a pre-RNA transcript is processed to create mRNA.

[c] Enter word

[f] No.

[c] *

[f] No. Here’s a hint: There are two representations of RNA in the cell’s nucleus. Look there, and one of the arrows will be your answer.

[q] In the diagram below, heterochromatin is indicated by letter

[textentry single_char=”true”]

[c*] a

[f] Excellent. Letter “a” shows densely packed chromatin, also known as heterochromatin.

[c] Enter word

[f] No, that’s not correct.

[c] *

[f] No. Here’s a hint: Find where the DNA is tightly packed and therefore unavailable for transcription.

[q] In the diagram below, “1” is  described as[hangman].

[c] heterochromatin

[f] Good!

[q] In the diagram below, “3” s structure composed of eight[hangman] proteins. The entire structure is called a [hangman]

.

[c] histone

[f] Good!

[c] nucleosome

[f] Great!

[q] The key difference between the DNA at “1” and “2” is that the DNA at “1” is inaccessible to RNA[hangman], and therefore not[hangman]

 .

[c] polymerase

[f] Correct!

[c] transcribed

[f] Excellent!

[q] The illustration below is designed to depict female [hangman]. Microscopic examination of the cells of this person’s (or any female’s) nuclei would reveal that one of her X chromosomes had been transformed into a  [hangman] body, a tight piece of [hangman] that is not expressed. Because X chromosomes are inactivated [hangman], there are patches of cells throughout the body that express the alleles in one of the X chromosomes, but not the other.

[c] mosaicism

[f] Correct!

[c] Barr

[f] Great!

[c] heterochromatin

[f] Good!

[c] randomly

[f] Correct!

[q] In the diagram below,  letter “E” (along with “G” and “H” shows [hangman] . The heavy blue line underneath the ribosome (at “F”) is [hangman]. One way to describe what’s being shown below is RNA[hangman]

.

[c] miRNA

[c] mRNA

[c] interference

[q] In the diagram below, number “8” is pointing to an[hangman] group. As a result of “8,” the gene indicated by number “7” is available for[hangman].

[c] acetyl

[c] transcription

[x][restart]

[/qwiz]

Links

This tutorial ends this module on eukaryotic gene expression.

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