Question

During transcription, what happens to the RNA polymerase if a repressor protein attaches to the operator?
A).It begins transcription.
B).It begins translation.
C). It cannot attach to enzyme 1.
D). It cannot attach to the promoter

Answer 1

The operator is the portion of DNA, at the beginning of a gene, where a transcription factor or repressor binds. If the transcription factor cannot bind, the RNA Pol cannot attach to begin transcription.

I hope this helps!

Answer 2

So it would be a then

Answer 3

You know that DNA has the information for heredity in all living things. But sometimes that DNA is not copied correctly. When there's an error in the DNA, it leads to something called a mutation. There are two kinds of mutations we're going to study, point mutations and frameshift mutations. In this segment, we're going to go over changes or mutations in DNA. DNA is like a sentence made up of three letter words. If the sentence is altered, then the meaning of the sentence is permanently changed. The example they have on the screen here is the pot was hot. If you change some of these letters around, you get just a bunch of letters that don't mean the originally intended sentence. So the DNA is read in segments of three bases. Each three sequential bases are a codon. A mutation is a permanent change in the DNA sequence of a gene. Remember that genes code for all the traits in every single organism. So if the DNA sequence is changed, then the gene is permanently changed. It may or may not change the protein that is coded for by that gene. A point mutation is the kind of mutation that causes a change in just a single base pair in the DNA. The example they give here shows you very clearly what the originally intended sequence of amino acids, or protein, was supposed to be-- isoleucine, serine, leucine, cysteine. That was what the DNA originally intended for the protein to look like. If a mutation occurs, which it did here-- the T was mutated for some reason to an A-- you end up with a different amino acid in this position where the serine is supposed to be. All right? So that the ultimate protein is isoleucine, threonine, leucine, cysteine-- not what was originality intended. So that's the problem that occurs with a mutation or change in the DNA. A substitution is a kind of point mutation where you have the replacement of one base with another in the DNA sequence. That results in a point mutation. Here they're showing you the C is mutated to the G. So you have a different sequence of bases, different sequence of codons, in that strand of DNA. And what they're showing you here, if you have a sentence of three letter words here-- the cat ate the rat-- and the r gets changed to an h, you have a sentence that has a totally different meaning. It's kind of like having a telephone number. And if you dial one number incorrectly in a telephone number, you aren't going to reach the person who you originally intended to call. So-- three different kinds of effects that a point mutation can have. A missense mutation is one that occurs when you have an actual change in the amino acid. So the amino acid is altered from what it was originally intended to be. Here you've got GAA. It gets mutated to GTA. So that calls for a different amino acid-- the VAL instead of the GLU. So you've got an altered chain, then, of amino acids. A nonsense mutation occurs when the original DNA that calls for, in this case, the cysteine, gets mutated. The TGC here gets mutated to TGA, and you end up with a stop code. So that protein is shortened. The sequence of amino acids gets chopped off. And you've got a much shorter protein than was originally intended, and it can't do the job that it's originally intended to do. The next kind of mutation is actually called a Silent mutation, because there's no change in the amino acid. Even though you do have a change here in the sequence of the bases-- instead of GAA, which was the original intention, you have GAG--but you still have the same amino acid called for. And that's because multiple codons can code for the same amino acid. So that's the information, then, on point mutations. What are the causes and effects of DNA mutations? All right? What we've learned so far is that there is a type of DNA mutation called a point mutation. And that's caused when you have a substitution of one base pair, it's not the one that was originally intended. There are three different types-- a missense, nonsense, or a silent point mutation. There's another kind of mutation, and it's usually more devastating than the point mutations. It's called a frame shift mutation. And it occurs when there's either an insertion or deletion of a base. We're going to learn how those things occur, and what their effects are in the next segment. This next segment deals with another kind of DNA mutation called a Frameshift mutation. That's a mutation where a single base is added or deleted from DNA. And since a sequence of DNA can be thousands of bases long, one change where you've either added or taken away one base is going to change the entire reading frame of that sequence of DNA, because the DNA can only be read in sequences of 3. So, if you add a base or if you take a base away, you have changed that reading frame from what it was originally intended to be-- like this, GGT to GAG. Look at the letters here, THE CAT ATE THE RAT. If you change those letters-- If you add a letter or take a letter away-- you've change that sequence. So, in this next slide, we're going to deal with the specific kinds of Frameshift mutations. An insertion Is a change in the DNA sequence caused by the addition of one or more extra base pairs. That's a type of Frameshift mutation. Here you've got THE CAT ATE THE RAT. Here you've got ACT TGC, which is the original intention. If you add an extra T in here, you have no logical meaning after the first two words-- everything else doesn't make any sense. So that's what happens with this DNA because it can only be read in sequences of 3. Now you've got an A in here, where it should be a T. So you've got ATG instead of TGC. So that would be a mutation that would cause all of the bases from this point on-- from this point right here on-- to be different from what they were originally intended to be. Deletion is a change in the DNA sequence caused by the elimination of one or more base pairs, resulting in a Frameshift mutation. Here we've got THE CAT ATE THE RAT and we took the C out, so that you've got now this A in here where there should be a C. So, you've got-- in the DNA, AGC, CTT. Now you've got ACC instead of ACG. So the entire reading frame is shifted, changed, and doesn't make any sense. Those are the two kinds of Frameshift mutation; insertion and deletion. What are the causes and effects of DNA mutations? The causes are either point mutations, which means that one base has been substituted for another, or a frameshift mutation, which means that one base has either been inserted into the DNA strand, or it's been deleted from the DNA strand. In any of these cases, you have a change in the amino acid sequence, and so a change in the ultimate protein that's produced. Sometimes the change can be very minor. Sometimes it's very devastating. What we're going to look at next is what these mutations actually look like in humans and in other organisms. DNA mutations occur because a base has either been added, or eliminated, or changed in a DNA molecule. Once that happens that changes the codon in the DNA, and that can have the effect of changing the protein that is supposed to be coded for by that DNA. Mutations can be passed on from generation to generation, or they can arise spontaneously and just be newly created. Contrary to what a lot of people think, mutations are actually quite rare. And also contrary to socially accepted ideas, mutations are not always harmful. If they occur in the 97% of DNA that doesn't code for anything that we know of, then that's not going to have an effect on the organism. You may have heard the term mutant in relation to a TV show or a movie. Those are basically pretty much media created mutants, media created terms. The actual term mutant is referring to a change in DNA. If you have blue eyes, you actually have a mutation. It arose spontaneously about 10,000 years ago and it's kind of a socially accepted fact or socially accepted thought that if you have blue eyes, your parents had blue eyes. Really, if you have blue eyes, your parents could have had brown eyes or green eyes or some other combination of eye color. All you inherited from them was the mutation for blue eyes and that's why you have the blue eyes. Somatic mutations are mutations that occur in body cells, they occur after fertilization, and they are not passed on to offspring. Most forms of cancer are mutations that occur in body cells after fertilization. If you have skin cancer because you've been out in the sun too much, you aren't going to give that skin cancer to your children. Germline mutations occur in the gametes. Those are the reproductive cells, either the egg cells or the sperm cells. They certainly can be passed on to offspring. And they also can be passed on either by passing on just one gene or by passing on two genes. Cystic fibrosis is an example of a condition where the person who has it has inherited a mutated gene from each parent. So he has or she has two mutated genes. It's a very serious condition where the mucus in your lungs builds up to points where it becomes very difficult to breathe, your respiratory system becomes damaged. It's a life-threatening condition. The effects of DNA mutations on the phenotype of an organism can range from there being no change-- and the only way you would know that would be if you actually ran a DNA test and could see that there was no change in the DNA-- a small change-- where the eye color of this cat here-- there's a blue eye and a green eye-- this makes the cat look different but it doesn't affect the way that the cat sees, it doesn't affect its vision. Also, there could be a severe change because of a mutation-- it can be a severe physical or mental change. In this case, this very young child has a condition called Progeria, where they show the effects of aging, but they aren't aged, they're very young. Some mutations can occur from a mutagen, which is an agent that simply causes a mutation in the DNA. Most people are aware that radiation can cause a change in DNA. So that's why when you get x-rays, they put a lead shield over you or a lead apron over you so that the radiation can't harm your cells. If you are exposed to too much sun, repeated exposure to the sun and sunburns or even repeated exposure to ultraviolet rays in a tanning bed, you can get skin cancer from that. The chemicals in cigarettes, of which there are 4,000, 50 of those chemicals are known mutagens. You can get sick from that, either from the direct cigarette smoking or indirectly from second-hand smoke. Now, little exposures to these things aren't really going to cause any serious harm, health harm. Little exposure over very long periods of time can cause harm or a very large dose of any of this at once can cause serious harm to your cells. These are just some of the examples of what can happen from DNA mutations.