Nucleus Flashcards
What is the structure of ribosomes?
They are complexes made of ribosomal RNA’s and proteins. Found in two places:
Free ribosomes are in cytoplasm
Bound ribosomes are attached to rough ER
What is the function of ribosomes?
To carry out translation.
The more protein synthesis a cell needs to do, the more ribosomes it has
What is the nucleus?
The most prominent organelle, contains most of the cells genes, serves as a repository of inherited genetic information, the cells control centre
What is the structure of the nucleus?
Surrounded by a nuclear envelope, has channels (to move things in and out) called nuclear pores, contains tightly packaged DNA, has a prominent area called the nucleolus.
What is the structure of the nuclear envelope?
It is composed of two membranes (inner and outer with perinuclear space in-between), each membrane is a phospholipid bilayer, the outer membrane is continuous with the ER.
What is the nuclear lamina?
The lining on the inner surface of the nuclear envelope. It is composed of intermediate filaments. It maintains the shape of the nucleus and helps organise the packing of DNA within the nucleus.
What are nuclear pores?
Channels made of proteins (nucleoporins) that form the Nuclear Porin Complex, they span the nuclear envelope, and control the movement into or out of the nucleus (nucleo-cytoplasmic exchange)
What moves through the nuclear pores from the nucleus to the cytoplasm?
mRNA (carries info from a gene), tRNA and ribosomal subunits (that are used to build proteins)
What moves through the nuclear pores from the cytoplasm to the nucleus?
Control signals (when to turn a gene on and off), building materials (the building ‘blocks’ of RNA) and energy (for chemical synthesis).
What is the nucleolus?
A prominent nuclear structure within NON-DIVIDING cells (darker area in the nucleus). It is not bound by a membrane. Can be two or more in the nucleus.
What is the function of the nucleolus?
Responsible for making ribosomal RNA and ribosomal subunits (which are then transported out of the nucleus and assembled as ribosomes in the cytoplasm).
How is DNA packed in the nucleus?
The DNA double helix wraps around histones (proteins) to form a bead called a nucleosome (this is a 10nm fibre)
The string of nucleosomes starts to coil and becomes a 30nm fibre.
Then the fibre loops to form a 300nm fibre (which is packed enough to fit in the nucleus).
During cell division the 300nm fibre coils to form metaphase chromosomes.
Euchromatin vs Heterochromatin
Euchromatin: less dense and contains genes being used by that cell.
Heterochromatin: more dense, contains genes NOT being used by the cell.
When the environment/needs of the cell changes they can switch depending on what is needed.
Why is euchromatin less tightly packed?
To allow access for transcriptional machinery to be able to access specific DNA regions to begin transcription.
