Gene Expression | NCEA Level 2 Biology Strategy Video | StudyTime NZ

– Kia ora guys and welcome to StudyTime’s Level 2 Strategy Video
for gene expression. I’m McKenzie. – And I’m Hattie. So this standard is all about basically how your genes get from being in your DNA to coding for what you actually look like and all the expressions of that, as well as the ways
that that can go wrong. So today we’ll be running you through some common questions that come up and some key ideas behind the whole paper. – So let’s get into it. – Probably the most common, but also the most inefficient study method that we see students using for this paper is to try to learn every single thing individually, like it’s
separate information. The key here is that this paper’s really about one big process. Everything comes back to the idea that one gene on your DNA
codes for one protein, which causes all your physical traits, and if that gene changes,
that protein changes. So, when you’re studying,
try not to break down everything into little concepts. Instead try to look at the bigger picture, so you can study by doing things like drawing out flow charts. Watching videos can also be a good idea or trying to explain
how some new information fits into all the information
you’ve learned previously. – As Hattie mentioned
before, this standard centers around one big
idea, but this can be broken down into three different sections. So, we start with DNA replication, and this occurs in our nucleus, as we’ve always known it to happen. Secondly, we have transcription and this also happens in the
nucleus and it creates our RNA. Thirdly, we have our translation. And this happens on the ribosomes, which is an organelle within the cell. So, it’s important when
you’re understanding this overall process that you understand the role of enzymes throughout this. And while you don’t need to know names, you need to understand that they are really catalyzing the whole thing. Secondly, being confident
with your understanding of different organelles, their names, and their different
functions is really important in understanding what exactly is going on at each step of the process. – Another common concept
for the question to address is the differences between DNA
and RNA and why they exist. The key differences between DNA and RNA, that DNA is a very long
molecule because it contains the entire genetic code for a chromosome, whereas RNA is a short molecule because it will only be
about one gene at a time. You’ll also want to know
that DNA is double stranded, whereas RNA is single stranded, and that there’s slightly
different base pairing rules, because on RNA you have the
base U instead of the base T. When you want to think
about how those differences actually came about or what they’re for, the main difference that
you’re gonna be focusing on is that double strandedness. So, DNA needs to be kept exactly the same because each cell needs
to have exactly the same DNA in it for the body to function. So to do that, it needs to be able to sort of self-correct
if there are any mistakes. Being double stranded makes
the molecule more stable, and it also means that there’s a way to correct for mistakes by
using the base pairing rule. RNA doesn’t have to
have this sort of thing because RNA is a very
short-lived molecule, so it only needs to exist
long enough to be copied off. You also need to know that
DNA is a long molecule because it needs to carry
the entire genetic code, whereas RNA needs to be short enough just so it can make that one
protein off that one gene. The advantage of using RNA instead of just copying a protein directly off the DNA is also often asked
about, and that’s about the fact that there
could be multiple pieces of RNA for the same gene floating around the cell at any given time, so lots of proteins could be being made, whereas there’s gonna only
have one copy on the DNA. RNA can also exist the nucleus
and go to the ribosomes. There are no ribosomes in the nucleus, so that’s another advantage of having RNA. And then finally, you want to talk about how tRNA has its own structure, because tRNA only exists to match up amino acids with the
mRNA to make a protein. So if you see a question that asks you about the structure of DNA, RNA, a good thing to do is to draw a diagram and explain the key differences, but also to link back to this key idea of DNA staying in the nucleus
and RNA exiting the nucleus. – So another key area of this standard surrounds the idea of mutations, and we can break this into two
different types of mutations, the first one being point mutations, and this includes insertion,
substitution or deletion, and secondly is block mutations, and these involve things like
inversion and repetition. For this standard we’d recommend probably focusing on point mutations mostly. For mutations in general,
you need to understand how exactly they work,
what exactly is happening, and how they can potentially
result in a frame shift. You also want to understand how the changing of the base pairing sequences can result in a different
amino acid forming, however not necessarily all the time, because if you refer to your
table of amino acid production and the triplets that can code for it, you can see that there
are some double ups, and so there are some
mutations that can happen which will still produce
the same amino acid. So, questions will often ask you to discuss a type of disease
as a form of mutation. And a really good example
of this is cystic fibrosis. Now, there are heaps
of different mutations that can result in this,
but if you are discussing it in terms of something like substitution, your form of cystic
fibrosis is going to be less severe than other types of mutations, which can have far greater effects on the overall protein
that’s being created. – A concept from this paper that students often find particularly hard to understand is metabolic pathways. Now the real definition of these is that it’s a path of
enzyme-catalyzed reactions where the product from one reaction acts as the substrate for the next. This is just a fancy way of saying that you have this one initial substrate, and bit by bit by several enzymes it gets turned into the final product so you can actually
express a particular gene. What this means is that there are several different mutations that can
lead to the same end result because there’s so many enzymes involved in a metabolic pathway
and each one of them is necessary for the entire chain to work. If any one of the breaks,
if there’s a mutation in the gene that codes
for any of those enzymes, the entire pathway will stop working and basically the products will just pile up before their broken enzyme so you’ll never get the end product. This is actually kind of how scientists figured out that one gene
codes for one protein by seeing that these different mutations, although they led to the same result, would lead to a buildup
of different products. A particularly tricky
question that they can ask you about metabolic pathways is why two parents could have the
same metabolic disorder, but have offspring that
don’t have the disorder. Now this is definitely an
excellence portion of a question. The key idea here is
that if the two parents have mutations with different enzymes within that pathway, all
they need to do is pass on at least one functioning
allele for the other bits. As long as the offspring
has a functioning allele for each step in the metabolic pathway, even if they also have inherited some nonfunctional ones from their parents, the entire pathway will
function in the offspring and the offspring can
not have that disorder. – So our last tip is about
the environment’s impact on phenotypes that an organism has. So, it isn’t just about the genotype that an organism has that
expresses the phenotype directly. But also other environmental
factors that can change it. So, a really common question is about taking two cuttings of a plant, IE they have the same genetic code, they’re genetically identical, and they’re grown at different altitudes. Now what this results in is the plants growing in slightly different ways to accommodate for this
change in environment. Now, this doesn’t change
the genetic coding at all, but simply the phenotype
that is expressed. Now, for animals, a way
that we can think of it as well, is something as
common as tanning and freckles. So, what these are different ways that the phenotype is
expressed, despite the genotype. So guys, this has been StudyTime’s Level 2 Strategy Video
for gene expression. One last thing to remember is that, like we’ve been saying
throughout this video, it’s all about this one big process of how DNA creates proteins and how this translates into our
phenotypes that we see. – As always, we’d recommend checking out a few years of past
exams, just to get a feel for what NZ curator likes to ask you. Also checking out the
StudyTime walk through guides, which are available for free online or to purchase in print
with next day delivery. So, good luck! (inspirational music)


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