Biology
DNA & genes
Inside every one of your cells sits a coiled thread holding the complete blueprint for you.
What you need first
You have learned that traits are inherited through genes. But where are these genes actually kept? They sit in a long called DNA, and that molecule lies in the , the control centre of your cells. DNA is the store for the blueprint of every living thing, and a gene is simply a section on this long thread.
The double helix
DNA looks like a twisted rope ladder. This shape is called a double helix. Two long strands wind around each other, and between them lie the rungs of the ladder. Each rung is made of two smaller parts that fit together exactly like two puzzle pieces.
Click a rung to change the left base.
Rule: A pairs with T, G pairs with C.
A T G → T A CFour bases and one rule
The rungs are made of four building blocks called bases: A, T, G, and C. They do not pair up at random but follow a fixed pairing rule. A always fits with T, and G always fits with C. If one strand has an A, then across from it there is guaranteed to be a T. That is why one strand is enough to complete the other.
The blueprint in every cell
It is not the bases themselves that carry the information, but their order. The base sequence is the blueprint, much like letters that form words. This DNA is present in full in almost every body cell. In a human body cell it is spread across 46 chromosomes, that is 46 neatly packed bundles of DNA inside a single cell nucleus.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What is the twisted shape of DNA called?
Which base pairs with A according to the pairing rule?
How many different bases are there in DNA?
According to the pairing rule, G always fits with … .
Across how many chromosomes is the DNA in a human body cell spread?
Match each term from the text with the right description.
Where this leads