Lecture 23 Flashcards
Nuclear lamina
- supports nuclear envelope
- think filamentous protein meshwork next to nucleoplasmic leaflet of INM
Where are tRNA and rRNA transcribed?
from DNA found in nucleolous
What is the nucleolus**
- largest structure inside the nucleus of eukaryotic cells
What are biosynthesis of ribosomes?
- synthesis of ribosomal rRNAs
- rRNA processing
- assembly of subunits- rRNA and ribosomal proteins
- 40s and 60s subunits are exported to cytoplasm where they are assembled as 80s ribosomes
How many pores per nucleus?
3000-4000 pores
Nucelar import
- regulated movement of proteins into nucleus requires a Nuclear Localization Signal (NLS)
INtermediate filaments
- composed of keratins in cytoplasm (outside lines)
- composed of lamins in nucleus (middle)
What are nucleoporins (NUPs)?
large family of diff proteins
Ribosomes components**
Small ribosomes: read RNA
Large ribosomes: join amino acids to form a polypeptide chain
- these have 1 or more ribosomal RNA molecules and ribosomal protein variety
What is a lamina?
found in animal cells only
- plants have nuclear lamina but NOT made of lamina protein
- bound to inner membrane of nuclear envelope by integral membrane proteins
- provides structural support for nuclear envelope
- attachment sites for chromatin
Nucleocytoplasmic Trafficking
Nuclear import/export is critical for cellular function
- nucleotides for transcription
- structural proteins
- DNA packaging proteins
- proteins for DNA replication, repair and transcription
- proteins for RNA processing (splicing) and export
- proteins for ribosomes synthesis and export
What is the inner nuclear membrane (INM)?**
has integral proteins and connects to nuclear lamina
Nuclear pore complex
involved in the arrangement of diff types of proteins
- composed of nucleoporins (NUPs)
- octagonal symmetry
- projects into cytoplasm and nucleoplasm
- SUPRAMOLECULAR complex: very big
Nucleus Functions
- storage, replication and repair of genetic material
- expression of genetic material
- transcription: mRNA, tRNA, rRNA
- RNA splicing - ribosome biosynthesis
- noncoding RNAs don’t encode proteins, include tRNA and rRNA
Where are Nuclear Pores found?
inner and outer membrane fuses
What are Nuclear Localization Signal (NLS)?
several positively charged amino acids w/in protein sequence
Nuclear envelope importance**
- separate nuclear content from the cytoplasm
- separates transcription and translation
- selective barrier, allows limited movement of molecules between nucleus and cytoplasm
Nucleus Structure
- 2 parallel phospholipid bilayers, 10-15 nm separation
How do NLS target proteins to nucleus
- proteins w/ NLS (cargo) interact w/ important protein in cytoplasm
- cargo/importin complex interacts w/ FG-NUPs at NPC and enters nucleoplasm
- Ran-GTP interacts w/ importin; cargo dissociates and stays in the nucleoplasm
- Ran-GTP/ importing complex exists nucleus through NPC
- GTP hydrolyzed to GDP
- importin release in cytoplasm to find new cargo
Nuclear Pore
- gateways between cytoplasm and nucleus
What is the outer nuclear membrane (ONM)**
- binds ribosomes
- is continuous w/ rough ER
What is a promoter region?
- control of transcription RNA splicing before nuclear export of mRNAs
What is heterochromatin?**
around nuclear membrane
- non essential genes are in here
What is homochromatin?**
essential genes more spread out
