Nucleus Flashcards
Genes in nucleus code for…
Proteins
How dos information from gene get out of nucleus
RNA
What translates information from genes into proteins
Ribosomes
Ribosome structure
- complexes made of ribosomal RNA’s and proteins
Can be found in two locations:
- Bound ribosomes attached to rER
- Free ribosomes in the cytoplasm
Ribosome function
- carry out translation
- gets information from nucleus and turns it into protein
- amount of organelles represents its function (the more protein synthesis a cell needs to do, the more ribosomes it has)
The nuclues
- most prominent organelle (5- 10 micrometers in diameter)
- one nucleus per cell (in most cases)
- contains most of the cells genes (some additional genes are found in the mitochondria and chloroplasts)
- serves as repository of inherited genetic information
CELLS CONTROL CETRE
Structure of the nucleus
- surrounded by NUCLEAR ENVELOPE
- has channels calls NUCLEAR PORES
- contains tightly packaged DNA
- has prominent area called the nucleolus
The nuclear envelope
Composed of two membranes
- outer and inner membranes with perinuclear space inbetween
Each membrane is a phospholipid bilayer
Outer membrane continuous with ER
Nuclear lamina
- inner surface of nuclear envelope is lines by the nuclear lamina
- which is composed of intermediate filaments
- maintain shape of nucleus
- helps organise the packing of the DNA within the nucleus
Nuclear Pores
- channels made of protiens (nucleoporins) that form the nuclear pore complex
- spans nuclear envelope (both membranes and inside and outside of nucleus)
- about 1000 per cell
- controls moment of molecules out of or not the nuclues (necleo-cytoplasmic exchange)
Bigger then gap junction - bigger then protein carries
How things (and what things) travel form nucleus to cytoplasm
- mRNA, tRNA and ribosomal subunits move from nucleus to cytoplasm
- mRNA (messenger RNA) carries information from a gene
- tRNA (transfer RNA) and ribosomal subunits are needed to build protiens
How things (and what things) move from cytoplasm to nucleus
- active transport - requires energy
- control signals, building materials and energy move from cytoplasm to nucleus
- when to turn a gene on or off
- the building blocks for RNA
- energy for chemical synthesis
The nucleolus
- a prominent nuclear structure within non-dividing cells
- non membrane bound specialised region within the nucleus
- responsible for making ribosomal RNA and ribosomal subunits
- transported out of the nuclear and assembled as ribosomes in cytoplasm - maybe two or more nucleoli per cell depending on species and stage of cell cycle
Structure of DNA within the nucleus
- DNA is a nucleotide polymer
- each human cell contains about 2.5m of human DNA
- 250,000 times the diameter of the nucleus
- therefore DNA must be very well packed
- but must also be accessible
DNA organisation within the nucleus
- the DNA double helix is about 2nm in diameter
- the helix interacts with specific proteins called histones (H2-H4)
- this interaction forms a 10nm diameter fibre
- each bead is called a nucleosome
- further interactions between the DNA and other histone (H1) cause the 10nm fibre to coils to form the 30nm fibre
- the 30nm fibre then loops to form 300nm fibre
- during cell decision the 300nm fibres coil to form metaphase chromosomes
