We spent the last few lectures talking about the structure of DNA, how DNA is copied, how that allows genetic information to be passed from one generation to the next. We learned about how the information in DNA is used to build proteins in your cells, and we learned about genetic variability, how over time changes accumulate in DNA, what causes those changes, and how bacteria in particular have this ability to share DNA with other bacteria. Today we want to talk a little bit about how gene expression, the ability for cells to take information in DNA and turn it into proteins, how that's controlled. And in bacteria, that's controlled by a structure in the DNA called an operon. And so what this is showing you here, and you can refer back to this picture as well in the lecture slides if it's helpful, but just to give you some context, here's our whole bacteria.
Here's some DNA or chromosomal DNA. And the operon is a little piece of that chromosomal DNA that contains genes for proteins that the cell needs. And in addition to those genes, it's also going to contain some regulatory sequences.
So these are sequences that allow the cell to control whether or not these genes are turned on, whether or not they're expressed, or whether they're turned off and not expressed. And then we know that genes come together to form... Our genes are copied to make the transcripts, the RNA, and then those transcripts can get translated into proteins. And in bacterial operons, oftentimes we have related proteins clustered together. So all three of these proteins would actually be part of the same pathway in a cell.
And that doesn't work the same way in eukaryotic cells, but this is very common in bacterial cells for them to be nicely organized like this. Now I want to spend a moment talking about a quality called genotype and phenotype. So genotype we've mentioned in the past. We said that's all of the DNA that your cells contain.
So it's all the genes you got from mom, all the genes you got from dad. It's the complete sequence of your DNA. Phenotype is a more subtle trait.
It's basically what you look like, but it's not just your physical outer appearance, it's the proteins that you make. So for example, someone with sickle cell anemia would make both a normal sickle cell, make a normal hemoglobin, and then the sickle cell version of hemoglobin. But it's easy to focus on things that are really easy to look at.
And so what we can see is the outside of a person. So here's two individuals with really different phenotypes. One individual is very tall, one individual is much shorter. And then, of course, they have differences in hair color and hair patterns in terms of one person has a head full and the other has some male pattern baldness, etc.
So what's the difference between these two individuals? They're both humans and they actually have 99.9% of the same DNA. Well, the reality is they have some genes, right, that are different.
And so where their genes are unique, we say that's their genotype. And how those genes get expressed is their phenotype. So, for example, the basketball player has a tall phenotype and the actor has a shorter phenotype.
So when we're talking about phenotype, we're asking how those genes are expressed, how they allow an organism, whether it's a human or a bacteria, to look a certain way or be able to do certain things. For example, you know, the ability for some bacteria to ferment sugars while other bacteria cannot. That would be phenotypes. Now one of the things that's interesting about phenotypes is they're controlled by not just the DNA, not just the sequence of DNA you inherit from mom and dad, they're also controlled by the environment.
So the environment can have, not always, but it can have a major effect on a person's phenotype. So let's look at an example of that. This is one of those really horrible experiments that we would never do. It would be unethical.
It's kind of a nice illustration of this because if we look at the Korean Peninsula in terms of evolutionary status, the individuals that live on the Korean Peninsula have very similar DNA. All humans have very similar DNA, but that particular group has been living in that same group, and there is no significant difference, for example, between the typical genes you would find in someone from North Korea versus South Korea. the Korean peninsula artificially broke up about 70 years ago I think and What happened was that the two Koreas ended up on really different paths. So South Korea had a path of more westernization and capitalism and things like that.
And we have North Korea that has a really different political system. And because of those differences in their political systems, they also ended up with really differences in the availability of nutrition. So if you look back 70 years ago, and it may be a little further than this, this now because I've been using this graph for a few years as well.
So maybe we're maybe thinking 80 years ago. If you look back, you notice that all the individuals in that age group are about the same height on average. That would mean that their genes that they have for height, which we're expecting to be really similar between North Koreans and South Koreans because again, they are genetically not particularly diverse and all humans aren't particularly diverse because we haven't been evolving very long, but That particular group has been isolated on the Korean Peninsula for a very short period of time together. So it's a very genetically homogeneous group from a genotype point of view. If you look at what happens now after the Koreas split, so as people get younger, this is a longer and longer amount of time since the two Koreas became artificially separated.
And what you see is that in South Korea, the height increased, right? But in North Korea, the height has stayed about the same. So what's the difference between these two height differences?
It shouldn't be genes because these two groups of people have not had a chance to evolve completely different heights. And that would be a really dramatic difference. And the reason is nutrition.
That in South Korea, because again of their political system, there's been a greater availability for people to get all the calories and the micronutrients and the vitamins, etc. that they need to fully develop into. the potential height that their genotype would have provided. So what we're saying here is the people in North Korea have the same genes.
They could have been as tall as the people in South Korea, but they didn't really get enough to eat, or they didn't get the right kinds of food. And we know that in North Korea that nutrition has been a tremendous problem for people in that country. So again, it's a horrible experiment.
You'd never take two groups of people and then make sure one group had subpar nutrition for... 70 years, but it's been done unfortunately, and so we can go back and look epidemiologically at this data. And I don't want to pick too much on North Korea, but the reality is that all over the world we see children who are stunted in their growth because they don't have enough nutrition.
So this is just an example here in 2015. These are children in sub-Saharan Africa. These are children in South Asia, East Asia, Europe. Central Asia, Latin America, and the Middle East, and North Africa. And then you see there's hardly any in North America at this point, although we certainly have poverty and nutrition problems in the United States in many places.
All right, so this is just an example of how your genotype is not the only thing that controls, in this case, the phenotype is something you can see how tall you are. It's also the environment that you live in, in this case, the nutrition that you get. So genotype is part of your phenotype, but it's not necessarily all of your phenotype, particularly in these types of traits that are really affected by the environment. So now what we're going to do is we're going to talk about how gene expression affects phenotypes. We've talked a little bit about the environment, but we're going to focus now for the rest of the lecture on how genes themselves, how their expression is controlled, and how that also can affect phenotype that you see.