Nucleus Flashcards
What are ribosomes made of, and where are ribosomes found
Complexes made of ribosomal RNA and proteins
Found in two locations - bound ribosomes are attached to rough ER and free ribosomes are found in the cytoplasm
What is the function of ribosomes
To carry out translation
What dictates the number of ribosomes within a cell
The protein synthesis demand of the cell
Outline the structure of the nucleus
Surrounded by nuclear envolope
Has channels called Nuclear pores
Contains tightly packaged DNA
Has prominent area called Nucleolus
What are the features of the nuclear envelope
Composed of two phospholipid bilayers membranes (inner, outer, with perinuclear space in between)
Outer membrane is continuous with endoplasmic reticulum
What is the nuclear lamina
The lining of the inner surface of the nuclear envelope
What is the composition and function of the nuclear lamina
Composed of intermediate filaments
Maintains nucleus shape
Helps organise packing of DNA within nucleus
What are nuclear pores
Channels made of proteins (nucleoporins) that form the nuclear pore complex
They span the nuclear envelope
Approx 1000 per cell
Controls movement of materials into and out of nucleus (nucleo-cytoplasmic exchange)
What molecules move from nucleus to cytoplasm
mRNA, tRNA, and ribosomal subunits move from nucleus to cytoplasm
What molecules move from cytoplasm to nucleus
Control signals, building materials, and energy
I.e. when to turn gene on/off, RNAA building blocks, energy for chemical synthesis
What is the nucleolus
A prominent, non membrane bound nuclear structure within non dividing cells located in the nucleus
Responsible for making ribosomal RNA and ribosomal subunits
May be two or more depending on species and stage of cell life
Outline the DNA organisation within the nucleus
2nm wide DNA double helix interacts with histone (H2-H4) proteins to form a 10nm fibre. Each bead is called a nucleosome
Further interactions between DNA and another histone (H1), causing 10nm fibre to coil to form 30nm fibre
30nm fibre then loops to form 300nm fibre
What happens to the 300nm fibre during cell division
It coils to form metaphase chromosomes
What is the difference between Euchromatin and Heterochromatin
Euchromatin - less dense, contains genes being used by that cell
Heterochromatin - More dense, contains genes not being used by the cell
What is the relationship between Euchromatin and Heterochromatin
Dynamic relationship - depends on what DNA is required
