Week 9 - Nucleus and Nucleolus Flashcards
What is a histone?
A protein that binds to DNA to form eukaryotic chromosomes
What is a nucelosome?
A protein - DNA complex containing 8 histone proteins (it is the most basic level of chromosome packing)
What is a Chromatin?
Repeating nucleosome structure, like beads on a necklace, also bound to none-histone proteins
What are chromosomes?
Defined region of chromatin that carries information relating to specific set of genes ( 1/3 DNA, 2/3 protein)
What are sister chromatids?
identical copies of the same chromosome, metaphase of mitosis
What is the process called when you go from DNA to MRNA?
Transcription - occurs in the nucleus, requires specific enzymes, called RNA polymerase
What is the process called when you go from mRNA to proteins?
Translation - occurs on the ribosomes in the cytosol, specific amino acids are matxhed to the mRNA sequence to form a polypeptide
What is the nucleus and its characteristics?
The nucleus is the biggest single organelle within eukaryotic cells, containing the genetic material (DNA), packages as a chromatin, and is the site of RNA synthesis ( transcription) , also contains an area termed the nucleolus
What is the nuclear envelope?
A double membrane that surrounds the nucleus. Its outer membrane is continuous with the endoplasmic reticulum of the cell. It controls the entry and exits of materials in and out of the nucleus and contains the reactions taking place within it.
What are nuclear pores?
Allow the passage of large molecules in and out of the cell
What is the structure of the nuclear pore complex?
- large quaternary protein structure
- aqueous channel that connects the nuceloplasm to the cytosol
- very ordered 8 fold symmetry
- made up of nucleophorins
What is the nucleoplasm?
The jelly-like material that makes up the bulk of the nucleus
What is the definition of genetic material?
Consists of protein-bound, linear DNA (deoxyribonucleic acid)
What is the nucleolus?
A small region within the cytoplasm which maufactures ribosomal RNA and assembles the ribosomes (process called ribosomal biogenesis). The nucleolus is NOT surrounded by a membrane.
What is the nuclear lamina?
A network of laminate intermeidate filaments which form a cage-like structure around the genetic material (protection)
What protein sizes can freely diffuse through the NPC?
< 5000 DA
proteins up to 60 KDa but takes longer
What size proteins cannot diffuse through NPC?
> 60 KDa CANNOT diffuse
require a specialised mechanism and ENERGY
What is GTP?
Guanosine Triphosphate
What are Nuclear Import Receptors?
- They recognise specific Nuclear Locialisation Signals
- Bind to FG repeats on nucleoporins in the cytosolic domain of NPC
- Proteins move through the NPC binding to FG repeats
Explain GTP binding protein
Protein that binds GTP and also acts as a GTPase (hydrolyses GTP to GDP)
Explain GAP
GTPase activating protein. Binds to GTP binding protein and induces GTP hydrolysis
Explain GEF
Guanine nucleotide exchange factor. Binds to GTP-binding protein and causes it to release GDP
What are the 2 types of Chromatin?
1 - Heterochromatin = transcriptionally inactive
2 - Euchromatin = transcriptionally active
What are ribosomes the site of?
Protein synthesis - mRNA translation
What does the unit S stand for?
Svedberg unit - non linear, influenced by mass, density and shape
It is how quickly an organelle sinks to the bottom of a tube if centrifuged
What subunits make up a ribosome?
- large subunit - 60S (5S + 5.8S + 28S rRNA + 49 proteins)
- small subunit - 40S (18S rRNA + 33 proteins)
- all together = 80S as it is non-linear
What are the characteristics of rRNA genes?
- 4 rRNA’s are encoded by more then 200 rRNA genes split across 6 chromosomes
- rRNA genes are clustered together on a DNA sequence called TANDEM REPEATS (this speeds up transcription - as it is more efficient)
What are 18S, 5.8S and 28S rRNA’s transcribed by?
RNA polymeriase 1 in the nucleolus
What is 5S rRNA transcribed by?
RNA polymerase 3 in the nucleoplasm and then transported to the nucleolus
What do snoRNP’s do?
- Small nucleolar ribonucleoproteins are small nucleolar RNAs complexed with proteins
- complexed with structural proteins and enzymes which modify the 90S ‘pre-ribosome’
- recognise specific areas of rRNA that require modification
What are the 3 modifications snoRNPs are responsible for?
1 - Methylation
2 - Isomerisation
3 - Cleavage - 45S pre-ribosomal RNA modification
What are the Cleavage enzymes called and their function?
1 - Exoribonucleases - remove externally transcribed spacers
2 - Endoribonucease - removed internally transcribed spacers
