In the cells that make up your body, about 2 metres (6 feet) of DNA – strings of genes – are coiled up and packaged into a typically roundish nucleus. This nucleus is only about one hundred-thousandth of a metre wide. I’ve said before that the DNA packed into the nucleus “appears to be a tangled mess”. But looks can be deceptive.
In this great little video Carl Zimmer challenges the idea that DNA in the nucleus is arranged randomly. Job Dekker and his group are finding that the nucleus is actually very organised. Zimmer conjures up an image of tiny robots in the cell folding the DNA very precisely.Science Happens! Episode 5: Everything you thought you knew about the shape of DNA is wrong]
Some genes control other genes. Dekker’s research suggests that the way DNA folds helps this process – by bringing controlling genes close to the genes they regulate. One cause of cancer could be bad folding that interferes with this control mechanism.
Dekker’s group is trying to work out which genes lie next to each other and how DNA is folded. The answer will be extremely complex. Dekker thinks that one day this knowledge will make it possible to fix badly folded DNA in cancer cells.
Earlier I showed you how you could use food dye to investigate how water moves through celery.
Did you do it?! If you did, good on you! What did you find?
This is what I saw.
The first photo (on the left) shows the celery leaves after an hour in the food colouring and water. The other two photos were taken after a whole day. If you look closely you can also see a line of blue going up the stem.
The leaf got bluer the longer it sat in the blue water.
Why? Remember how water travels up tubes through the plant to the leaves? The blue dye is carried in the water, but it can’t get out of the leaf so it stops there. The longer you wait the more dye has stopped in the leaves, and that makes them go bluer.
When did you notice the leaves start to go blue? It happened quite quickly. The water travels quickly up the plant.
If more and more water goes into the leaves why aren’t they getting wetter? Or perhaps bigger?
The leaf only keeps as much water as it needs. The water that’s drawn up into the leaves escapes through tiny holes in the leaves. More water moves up through the stem to take its place.
Why can’t you see this water escaping? The water that escapes out of the leaves has evaporated – that means it has turned into a gas. Water gas is called water vapour and it’s invisible.
This is what I saw when I cut across the stalk. I cut the stems every 3 cm.