Genes and Inheritance [1]: DNA (A Level Biology)

Uploaded by freeeschool on 02.09.2012

A Level Biology: Genes and Inheritance 1 - DNA
Hi! Welcome to my first video on this topic of Genes and how they affect you. This first
video will be looking at the structure of DNA and how it is organized within your cells.
The first thing to establish is what makes you unique or what makes you “you”. The
two things that determine an individual’s characteristics are the environment and their
genes. Through genes you received from your parents and therefore, they are inherited.
The environment is essentially all of the stimuli that you receive from outside. It
could be things like your exposure to light; it can be the amount of food that you are
exposed to and your experiences in general.
Your genes are basically your blueprint. They enable you to make things called proteins.
Proteins are the building blocks for life. They’re the structure that you are made
of and they are the chemicals that control the reactions in your body. Your genes, I
said before, are set of instructions for making these proteins.
The smallest sub-unit of genetic material is called DNA. This diagram here represents
the DNA found within your cells. If we take one of the sections here or pieces of DNA
here, there are 3 billion of those in virtually every cell within the human body. These are
what are known as bases. These bases come in four different varieties: Adenine, thymine,
guanine and cytosine.
You notice that they always pair together in a very, very specific way. One in which
they always go together is the adenine always binds to the thymine and the cytosine always
binds to the guanine and you can see that represented here with these different-colored
bases. For instance here, the guanine in green and the cytosine is in red and you notice
that those two always bind together. The thymine in yellow and the adenine in blue; they always
bind together.
In a DNA, you do not only have the bases in the middle, but you also have two other sections
that are represented by this gray strip here. That’s a phosphate group and a ribose sugar
joined together.
The three major parts of a DNA are ribose sugar, phosphate group and the bases that
you have here.
You may have heard of DNA being referred to as a double helix. All that simply means is
that it has two strands that are connected together that twist around one another; a
bit like a coiled spring and hence, the name double helix.
This diagram here has nine nucleotide bases joined up. The next major sub-unit of genetic
material is called a gene. A gene is something which codes for a particular characteristic;
be that eye color or hair color. A gene usually consists of tens of thousands of nucleotide
bases and pieces of DNA joined together.
So you start to get an idea of just how small the piece of DNA actually is.
In summary, your DNA which is the smallest sub-unit of genetic material is referred as
deoxyribonucleic acid or DNA for short. It is made up of nucleotide bases and which therefore
are adenine, thymine, cytosine and guanine, ribose sugar and phosphate group and the bases
always pair up in a particular way so the adenine always binds to the thymine and the
cytosine always binds with the guanine and they form a structure called a double helix
which basically looks like a coiled spring wrapped around.
A gene, which codes for a particular characteristic; this could be something like an eye color
or hair color and a gene is made of lots of pieces of DNA and in some cases, up to tens
of thousands of pieces of DNA.
[end of audio – 04:23] A Level Biology: Genes and Inheritance 1 - DNA