The nucleus Flashcards
How big is the nucleus?
5-10 micrometres
What does the nucleus serve as?
Repository of inherited genetic information.
What organelle is continuous with the nucleus?
The endoplasmic reticulum
What is the structure of the nucleus?
It is surrounded by the nuclear envelope. Composed of a double membrane, each of which are a phospholipid bilayer with a gap in-between.
What is a nuclear pore?
Pores in the nucleus which control the movement of molecules our of or into the organelle. They are visible on the surface of the nucleus having a flower-like structure.
What travels out of the nucleus through nuclear pores?
- mRNA (messenger RNA which carries information from a gene)
- tRNA (transfer RNA)
- Ribosomal units needed to build proteins
What travels into the nucleus through the nuclear pores?
- Control signals (tells the nucleus when to turn and gene on or off)
- Building block (for RNA)
- Energy for chemical synthesis
What is the nucleus being controlled by?
Control signals.
What lines the inner surface of the nuclear envelope?
The nuclear lamina which is composed of intermediate filaments
What is the purpose of the nuclear lamina? What would happen if it wasn’t there?
It is there to maintain the shape of the nucleus and helps organise the packing of DNA within the nucleus. If the nuclear lamina is defective, the nuclei will be unable to maintain there spherical shape and this could limit the cells ability to divide. This results in abnormal feature e.g. premature aging.
What is the nucleolus?
A prominent nuclear structure within two non-dividing cells which is responsible for making ribosomal RNA which combines with proteins to form ribosomes. Can have two or more per cell.
How much DNA does a human cell contain?
2.5 metres.
Why does DNA need to be very well packed?
As there is around 250,000 times the diameter of the nucleus of DNA, which will need to be packed very well to fit in the nucleus. It needs to also be easily accessible so that the right parts can be found when needed.
How is the DNA packed to form is nucleosome?
Each DNA double helix is about 2 nanometres in diameter. The helix interacts with specific proteins called histones (H2 - H4). DNA twists around them which allows DNA to be organised, allowing accessibility. This interaction forms the 10nm diameter fibre. Each of these beads is called a nucleosome.
How does the DNA get packed further, after forming the nucleosome?
Further interactions between DNA and histone (H1) cause the 10nm fibre to coil to form a 30nm fibre. This 30nm fibre then loops to form a 300nm fibre.
