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- At the 5’ end of the chain, the phosphate group of the first nucleotide in the chain sticks out. The phosphate group is attached to the 5' carbon of the sugar ring, which is why this is called the 5' end. At the other end, called the 3’ end, the hydroxyl of the last nucleotide added to the chain is exposed.
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Or in THE RING, the initial death shown in the opening scene motivates our intrepid protagonist reporter to look into what happened. The opening sequence can also immediately jump into paying off its main concept. Look at STAR WARS. What happens in the opening scene? Two ships shoot at each other; we see a star war.
- Overview
- Key points:
- Introduction
- Transcription overview
- RNA polymerase
- Transcription initiation
- Promoters in bacteria
- Promoters in humans
- Elongation
- Transcription termination
An in-depth looks at how transcription works. Initiation (promoters), elongation, and termination.
•Transcription is the process in which a gene's DNA sequence is copied (transcribed) to make an RNA molecule.
•RNA polymerase is the main transcription enzyme.
•Transcription begins when RNA polymerase binds to a promoter sequence near the beginning of a gene (directly or through helper proteins).
•RNA polymerase uses one of the DNA strands (the template strand) as a template to make a new, complementary RNA molecule.
•Transcription ends in a process called termination. Termination depends on sequences in the RNA, which signal that the transcript is finished.
•Transcription is the process in which a gene's DNA sequence is copied (transcribed) to make an RNA molecule.
•RNA polymerase is the main transcription enzyme.
•Transcription begins when RNA polymerase binds to a promoter sequence near the beginning of a gene (directly or through helper proteins).
•RNA polymerase uses one of the DNA strands (the template strand) as a template to make a new, complementary RNA molecule.
What makes death cap mushrooms deadly? These mushrooms get their lethal effects by producing one specific toxin, which attaches to a crucial enzyme in the human body: RNA polymerase.1
RNA polymerase is crucial because it carries out transcription, the process of copying DNA (deoxyribonucleic acid, the genetic material) into RNA (ribonucleic acid, a similar but more short-lived molecule).
Transcription is an essential step in using the information from genes in our DNA to make proteins. Proteins are the key molecules that give cells structure and keep them running. Blocking transcription with mushroom toxin causes liver failure and death, because no new RNAs—and thus, no new proteins—can be made.2
Transcription is essential to life, and understanding how it works is important to human health. Let's take a closer look at what happens during transcription.
Transcription is the first step of gene expression. During this process, the DNA sequence of a gene is copied into RNA.
Before transcription can take place, the DNA double helix must unwind near the gene that is getting transcribed. The region of opened-up DNA is called a transcription bubble.
Transcription uses one of the two exposed DNA strands as a template; this strand is called the template strand. The RNA product is complementary to the template strand and is almost identical to the other DNA strand, called the nontemplate (or coding) strand. However, there is one important difference: in the newly made RNA, all of the T nucleotides are replaced with U nucleotides.
The site on the DNA from which the first RNA nucleotide is transcribed is called the +1 site, or the initiation site. Nucleotides that come before the initiation site are given negative numbers and said to be upstream. Nucleotides that come after the initiation site are marked with positive numbers and said to be downstream.
If the gene that's transcribed encodes a protein (which many genes do), the RNA molecule will be read to make a protein in a process called translation.
[Are there steps between transcription and translation?]
RNA polymerases are enzymes that transcribe DNA into RNA. Using a DNA template, RNA polymerase builds a new RNA molecule through base pairing. For instance, if there is a G in the DNA template, RNA polymerase will add a C to the new, growing RNA strand.
RNA polymerase always builds a new RNA strand in the 5’ to 3’ direction. That is, it can only add RNA nucleotides (A, U, C, or G) to the 3' end of the strand.
[What do 5' and 3' mean?]
RNA polymerases are large enzymes with multiple subunits, even in simple organisms like bacteria. Humans and other eukaryotes have three different kinds of RNA polymerase: I, II, and III. Each one specializes in transcribing certain classes of genes. Plants have an additional two kinds of RNA polymerase, IV and V, which are involved in the synthesis of certain small RNAs.
To begin transcribing a gene, RNA polymerase binds to the DNA of the gene at a region called the promoter. Basically, the promoter tells the polymerase where to "sit down" on the DNA and begin transcribing.
Each gene (or, in bacteria, each group of genes transcribed together) has its own promoter. A promoter contains DNA sequences that let RNA polymerase or its helper proteins attach to the DNA. Once the transcription bubble has formed, the polymerase can start transcribing.
To get a better sense of how a promoter works, let's look an example from bacteria. A typical bacterial promoter contains two important DNA sequences, the - 10 and - 35 elements.
RNA polymerase recognizes and binds directly to these sequences. The sequences position the polymerase in the right spot to start transcribing a target gene, and they also make sure it's pointing in the right direction.
[How?]
Once the RNA polymerase has bound, it can open up the DNA and get to work. DNA opening occurs at the - 10 element, where the strands are easy to separate due to the many As and Ts (which bind to each other using just two hydrogen bonds, rather than the three hydrogen bonds of Gs and Cs).
In eukaryotes like humans, the main RNA polymerase in your cells does not attach directly to promoters like bacterial RNA polymerase. Instead, helper proteins called basal (general) transcription factors bind to the promoter first, helping the RNA polymerase in your cells get a foothold on the DNA.
Many eukaryotic promoters have a sequence called a TATA box. The TATA box plays a role much like that of the - 10 element in bacteria. It's recognized by one of the general transcription factors, allowing other transcription factors and eventually RNA polymerase to bind. It also contains lots of As and Ts, which make it easy to pull the strands of DNA apart.
Once RNA polymerase is in position at the promoter, the next step of transcription—elongation—can begin. Basically, elongation is the stage when the RNA strand gets longer, thanks to the addition of new nucleotides.
During elongation, RNA polymerase "walks" along one strand of DNA, known as the template strand, in the 3' to 5' direction. For each nucleotide in the template, RNA polymerase adds a matching (complementary) RNA nucleotide to the 3' end of the RNA strand.
[See the chemical reaction]
The RNA transcript is nearly identical to the non-template, or coding, strand of DNA. However, RNA strands have the base uracil (U) in place of thymine (T), as well as a slightly different sugar in the nucleotide. So, as we can see in the diagram above, each T of the coding strand is replaced with a U in the RNA transcript.
[See a diagram of the bases]
The picture below shows DNA being transcribed by many RNA polymerases at the same time, each with an RNA "tail" trailing behind it. The polymerases near the start of the gene have short RNA tails, which get longer and longer as the polymerase transcribes more of the gene.
RNA polymerase will keep transcribing until it gets signals to stop. The process of ending transcription is called termination, and it happens once the polymerase transcribes a sequence of DNA known as a terminator.
Initiation. RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene. Each gene (or group of co-transcribed genes, in bacteria) has its own promoter. Once bound, RNA polymerase separates the DNA strands, providing the single-stranded template needed for transcription. Elongation.
- No, you're not wrong. A tRNA contains hairpins as well, though the hairpins play different roles in the two cases. In transcription termination, th...
- Good question! Introns have multiple roles in biology including the regulation of gene expression. Other introns have functions after they are spli...
- Not really. Introns enable one gene to produce multiple polypeptide sequences, thereby creating a more efficient genome. This will make more sense...
- Really there isn't much difference — as far as I know the existence of the two terms is an accident of history — my advice would be to use gene. Ma...
- Yes, helicase was the enzyme that makes the DNA to unwinds its strands by breaking the Hydrogen bonds between the nucleotides.
- The RNA is actually synthesized using the antisense (complementary) strand as the template.
- This is briefly covered in the next article — short answer: yes, but transcription termination is still being actively studied and is not completel...
- Introns are actually noncoding DNA segments (in other words, they do not code for proteins), so splicing them out actually helps produce a function...
- No, transcription starts upstream of the AUG, so the mRNA contains a 5' untranslated region. Then ribosomes translate starting from the AUG in the...
- A hairpin loop is an unpaired loop of messenger RNA (mRNA) that is created when an mRNA strand folds and forms base pairs with another section of t...
Jan 26, 2024 · Key Elements of Film Form. This film opens with a tilt, as the camera pushes in at the same time, but it is made clear to the audience that as this sequence progresses this first part of the film is in reverse, this is indicated through the blood running back up into her nose rather than coming out.
Except for the very first shot in which the logo appears out of the clouds, every piece of the opening is present in this version, with even multiple chalkboard and couch gags filmed. Attached to the end of this sequence is the message "Come home to The Simpsons on Sky One."
Jan 19, 2024 · This scene repeats at the very end, after the series' title, showing that, even after the whole sequence, the race is still open.
A cold open (also called a teaser sequence) [1] is a narrative technique used in television and films. It is the practice of jumping directly into a story at the beginning of the show before the title sequence or opening credits are shown. In North American television, this is often done on the theory that involving the audience in the plot as ...
