Lecture 10 - nucleus Flashcards
What is the nucleus?
The nucleus is a large organelle that contains cell information (RNA and DNA).
What is the function of the nucleus?
To serve as a repository of inherited genetic information
Act as the cell’s control centre
Maintaining integrity of DNA so it doesn’t get damaged
What is an example of a cell that doesn’t have a nuclei?
Red blood cells
What surrounds the nucleus?
The nuclear envelope
What is the nuclear envelope?
The nuclear envelope is composed of two membranes that surround the nucleus (inner and outer layer). The outer membrane continues with the membrane of the endoplasmic reticulum.
What is the nuclear pore complex?
Then you can have a complex dots the surface of the nuclear envelope and has the role of regulating transport across the membrane.
What is the function of the nuclear pore complex?
To control the movement of molecules out of or into the nucleus
What goes out of the nucleus?
mRNA, tRNA and ribosomal subunits.
What is mRNA?
mRNA (messenger RNA) carries information from a gene
What is needed to build proteins?
tRNA (transfer RNA) and ribosomal subunits are needed to build proteins.
What goes into the nucleus? And why is it important.
Control signals, building materials and energy.
These are important for the nucleus because:
It tells the nucleus when to turn a gene on or off
The building “blocks” for RNA
Energy for chemical synthesis
What is the nuclear lamina?
A sheet of tissue of filaments that line the inner surface of the nuclear envelope that is made of intermediate filaments.
What do we call lamina intermediate filaments
Lamins
What is the function of the nuclear lamina?
Maintain shape of nucleus (gives the nucleus its circular shape)
Help organise the packing of DNA within the nucleus. There are territories that certain chromosomes can be found and these spaces are separated by the lamina.
What happens if the nuclear lamina is defective?
Cells cannot produce a normal nuclear lamina so their nuclei are unable to retain a spherical shape. This limits the ability of affected cells to divide and makes it difficult for things to travel in and out through pores. This results in abnormal features and premature aging
How do defects in the nuclear lamina occur?
Due to certain genetic disorders resulting in a mutated form of lamin protein
What is the nucleolus (nucleoli)?
It’s a prominent nuclear structure within non-dividing cells (inside nucleus)
What is the function of the nucleolus?
To make ribosomal RNA which combines with proteins to produce ribosomes.
What is the diameter of DNA double helix?
2nm
How does the DNA pack itself to fit inside the nucleus?
In order to pack DNA in cells it needs to be coiled. Proteins called histones cluster together around DNA to create bead like structures (10nm). Another histone H-1 interacts with the string of beads that cause them to coil up, increasing diameter but saving space while doing so (30nm). This then gets folded again (super coiling) which packs it all even tighter so it can fit in the nucleus (300nm).
What happens to the 300nm fibre during cell division?
It coils to form metaphase chromosomes.
What does DNA have to look like to be displayed as a karyotype?
When they are metaphase chromosomes. This only happens for cell during cell division so it doesn’t look like this most the time
What is euchromatin?
DNA the cell is using.
What is heterochromatin?
DNA the cell is not using
Compare euchromatin to heterochromatin
Euchromatin: less dense, contains genes being used by the cell.
Heterochromatin: more dense, contains genes not being used by cell
Describe the relationship between euchromatin and heterochromatin
They have a dynamic relation with the amount of euchromatin and heterochromatin depending on what genes need to be used.
Describe the location of chromosomes within the nucleus
Generally pairs are not located together in the nucleus but during interphase the location of the chromosomes is not random.
