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
Euchromatin
Less dense, contains genes being used by that cell
Heterochromatin
- more dense, contains genes not being used by that cell
Relationship between euchromatin and heterchromomatin
Dynamic Relationship
How does transcriptional machinery access specific DNA regions to begin transcription
Euchromatin is less tightly packed so allows access
