dna - Chromosome and chromatid numbers during cell cycle phases - Biology Stack Exchange
What is the relationship between chromatin fibre, chromosomes, DNA and . A chromosome generally has telomeres and centromeres, defining the tips of the. The microtubules act as a guide for chromosome movement. Explain the relationship between the terms "chromosome" and "chromatid". A chromosome is a. The term DNA, chromosome, and chromatin are three terms which have very bases from adjacent strands are one of the primary ways in which the double.
That guy looks something like that. They separate from each other, and then once they've separated from each other, what could happen? Let me delete some of that stuff over here. Delete that stuff right there.
So you have this double helix. They were all connected. Now, they separate from each other. Now once they separate, what can each of these do? They can now become the template for each other. If this guy is sitting by himself, now all of a sudden, a thymine base might come and join right here, so these nucleotides will start lining up. So you'll have a thymine and a cytosine, and then an adenine, adenine, guanine, guanine, and it'll keep happening.
And then on this other part, this other green strand that was formerly attached to this blue strand, the same thing will happen. You have an adenine, a guanine, thymine, thymine, cytosine, cytosine. So what just happened? By separating and then just attracting their complementary bases, we just duplicated this molecule, right?
We'll do the microbiology of it in the future, but this is just to get the idea. This is how the DNA makes copies of itself. And especially when we talk about mitosis and meiosis, I might say, oh, this is the stage where the replication has occurred. Now, the other thing that you'll hear a lot, and I talked about this in the DNA video, is transcription.
In the DNA video, I didn't focus much on how does DNA duplicate itself, but one of the beautiful things about this double helix design is it really is that easy to duplicate itself. You just split the two strips, the two helices, and then they essentially become a template for the other one, and then you have a duplicate. Now, transcription is what needs to occur for this DNA eventually to turn into proteins, but transcription is the intermediate step.Differences on chromatid and chromosome
And then that mRNA leaves the nucleus of the cell and goes out to the ribosomes, and I'll talk about that in a second. So we can do the same thing.
So this guy, once again during transcription, will also split apart. So that was one split there and then the other split is right there. And actually, maybe it makes more sense just to do one-half of it, so let me delete that. Let's say that we're just going to transcribe the green side right here. Let me erase all this stuff right-- nope, wrong color. Let me erase this stuff right here. Now, what happens is instead of having deoxyribonucleic acid nucleotides pair up with this DNA strand, you have ribonucleic acid, or RNA pair up with this.
And I'll do RNA in magneta. So the RNA will pair up with it. And so thymine on the DNA side will pair up with adenine. Guanine, now, when we talk about RNA, instead of thymine, we have uracil, uracil, cytosine, cytosine, and it just keeps going. That mRNA separates, and it leaves the nucleus. It leaves the nucleus, and then you have translation.
The transfer RNA were kind of the trucks that drove up the amino acids to the mRNA, and this all occurs inside these parts of the cell called the ribosome.
But the translation is essentially going from the mRNA to the proteins, and we saw how that happened. You have this guy-- let me make a copy here. Let me actually copy the whole thing.
This guy separates, leaves the nucleus, and then you had those little tRNA trucks that essentially drive up. So maybe I have some tRNA.
Let's see, adenine, adenine, guanine, and guanine. A codon has three base pairs, and attached to it, it has some amino acid. And then you have some other piece of tRNA. Let's say it's a uracil, cytosine, adenine.
And attached to that, it has a different amino acid. Then the amino acids attach to each other, and then they form this long chain of amino acids, which is a protein, and the proteins form these weird and complicated shapes. So just to kind of make sure you understand, so if we start with DNA, and we're essentially making copies of DNA, this is replication. You are transcribing the information from one form to another: Now, when the mRNA leaves the nucleus of the cell, and I've talked-- well, let me just draw a cell just to hit the point home, if this is a whole cell, and we'll do the structure of a cell in the future.
If that's the whole cell, the nucleus is the center. That's where all the DNA is sitting in there, and all of the replication and the transcription occurs in here, but then the mRNA leaves the cell, and then inside the ribosomes, which we'll talk about more in the future, you have translation occur and the proteins get formed. So mRNA to protein is translation.
You're translating from the genetic code, so to speak, to the protein code.
Chromosome and Chromatid Numbers during Mitosis and Meiosis | DAT Bootcamp
To first clarify this topic, it is first essential to understand some basic definitions. Throughout most of the cell cycle, DNA is packaged in the form of chromatin.
However, during mitosis and meiosis, chromatin exists in an additional level of organization known as a chromosome.
Chromosomes are an even denser packaging of chromatin that are visible with a light microscope, particularly during metaphase. Chromosomes can exist in duplicated or unduplicated states. At the beginning of mitosis, for example, a chromosome consists of two sister chromatids — chromatids are the term used to describe the chromosome in its duplicated state.
First, during the S phase of interphase, the genetic material of a cell is duplicated. A human has 46 chromosomes a set of 23 you inherit from your mother, and a set of 23 from your father. After the genetic material is duplicated and condenses during prophase of mitosis, there are still only 46 chromosomes — however, they exist in a structure that looks like an X shape: For clarity, one sister chromatid is shown in green, and the other blue. These chromatids are genetically identical.
However, they are still attached at the centromere and are not yet considered separate chromosomes.
Thus, the above picture represents one chromosome, but two chromatids. During prophase and metaphase of mitosis, each chromosome exists in the above state. For humans, this means that during prophase and metaphase of mitosis, a human will have 46 chromosomes, but 92 chromatids again, remember that there are 92 chromatids because the original 46 chromosomes were duplicated during S phase of interphase. In other organisms, however, the centrosomes do not duplicate at all between meiosis I and II.
Instead, the two centrioles that make up a single centrosome separate, and each acts as a separate spindle pole during meiosis II.
The two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles. In metaphase II, the chromosomes line up individually along the metaphase plate.
In anaphase II, the sister chromatids separate and are pulled towards opposite poles of the cell. In telophase II, nuclear membranes form around each set of chromosomes, and the chromosomes decondense. Cytokinesis splits the chromosome sets into new cells, forming the final products of meiosis: In humans, the products of meiosis are sperm or egg cells. In some cases, meiosis does produce four functional gametes: However, when meiosis takes place during oogenesis, egg cell production, in human females, only one functional egg cell is made.
At the end of meiosis I, only one of the two daughter cells continues down the egg cell pathway, while the other becomes a non-egg cell called a polar body. Similarly, of the two products of meiosis II, one will become a functional egg cell, while the other will become a second polar body. The polar bodies are not normally fertilized by sperm cells, and they typically undergo programmed cell death, or apoptosis, within 24 hours of being produced 2 2.
How meiosis "mixes and matches" genes The gametes produced in meiosis are all haploid, but they're not genetically identical. For example, take a look the meiosis II diagram above, which shows the products of meiosis for a cell with 2.