Nucleus - L10 Flashcards
What are ribosomes made of ?
Ribosomal RNA and proteins
Two types of ribosomes?
Found attatched to the rough ER
Free ribosomes floating in cytosol
What determines the no. of ribosomes made?
More protein synthesis means that more ribosomes are required
How big is the nucleus?
5 - 10 µm
Does the nucleus have all the genes?
No, it has most. Other genes are found in the mito and chloroplast
What are the two things that the nucleus does?
Houses the inheritable DNA and has some control over the cell’s processes
What does the nuclear envelope do?
Acts as a barrier to protect the genes inside from damage
Nuclear pores fucntion
Allows stuff to pass through
Where is the nuclear envelope connected to?
It’s continuous with the ER
The perinuclear space is continuous with the lumen
How many membranes is the nuclear envelope?
2 made of phospho bilayers
Inner layer of the nuclear envelope lined by what?
Nuclear lamina made of a meshwork of intermediate filaments
What does the nuclear lamina do?
The intermediate filaments are strong and rigid so it helps to maintain the structure and shape of the nucleus + in packing the DNA
What is a nuclear pore made of?
Multiple proteins called nucleoporins
- It spands both the membranes
Term for what moves in and out of the cell through nuclear pores?
Nucleocytoplasmic exchange
What moves out of the nucleus via pore?
mRNA, tRNA and ribosomal subunits
What moves inside the nucleus via pores?
Chemical signals to turn a gene on or off, building mats for ribosomes and energy for chemical synthesis
What is a nucleolus?
A prominent structure when the cell is not dividing
Is the nucleolus membrane bound?
No
What does the nucleolus do?
Makes the ribosomal RNA and it’s subunits –> transported to cytosol to make the ribosomes
What determines how many nucleoli are present?
Stage of the cell cycle, cell type and its species
Where are nucleoli found (frog egg reference)
Found in the viable cells to make proteins for the cell
What is DNA?
A nucleotide polymer
Why is effective packaging of DNA important?
Around 2.5m in each cell, all stretched around the sun 6 times, hence must be packaged and organised well to fit in cell but also accessible.
How big is the DNA double helix?
2nm
What does the DNA wrap around to form a 10nm diameter form?
Wraps around proteins called histones (H2 - H4)
What is an optimum?
8 histones interacting
How many times does the DNA wrap around the histone?
1.67 times to form beads called nucleosomes
How does DNA go from 10nm - 30nm?
It coils around an H1 histone
30 - 300nm?
Coils in a flower shape, found in non-dividing cells.
It supercoils to form metaphase chromosomes during cell division
How is DNA screened for defects?
Using a Karyotype
During which cell stage are the chromosomes not random?
Interphase
Are chromosome pairs usually together when no cell division is occuring?
No
What is Euchromatin?
Less dense areas of chromatin meaning that the cell is currently using the genes i.e it is “active” and more easily accessible
What is Heterochromatin?
More dense area, genes are currently not being used
What kind of relationship between Heterochromatin and Euchromatin?
Dynamic
