eukaryotic cell part I Flashcards
what are sphingolipids
a constituent of the plasma membrane which contain
1) sphingomyelins which contain a phosphocholine head group
2) glucosylcerebroside= a sphingolipid with a glucose
what are the cellular components of the cell responsible for
the coordinated and efficient function of the cell including providing shape and support, locomotion and reproduction
how can cellular components be classified
1) double membrane bound organelles
2) Single membrane bound organelles
3) cellular components without membrane
define organelle
membrane bound compartments or structures in a cell that perform a special function
the name means ‘little organ’
what are some double membrane bound organelles
1) nucleus
2) mitochondria
3) chloroplasts
what are some single membrane bound organelles
1) vacuole
2) lysosome
3) golgi apparatus
4) ER
5) peroxiomes
6) vesicles
what are some cellular compartments without a membrane
1) cell wall
2) ribosomes
3) cytoskeleton
what does the nucleus consist of
1) nuclear envelope
2) nucleoplasm
3) nuclear lamina
4) chromosomes and chromatin
5) nucleolus
what is the structure of the nuclear envelope
two membranes of phospholipid bilayers with idfferent proteins
the inner membrane defines the nucleus whilst the outer is continous with the RER
the nuclear pores is where the two membranes fuse
outline the nuclear pore
- ring like complexes composed of specific membrane proteins where material moves
- made up of multiple copies of different proteins called nucleoproteins which help cargo proteins through the pore
outline how larger proteins transverse through the nuclear pore
ribonucleoprotein and large proteins need the assistance of soluable transporter proteins
what is the nucleoplasm
suspends structures within the nucleus which are not membrane bound e.g. chromosomes
it is referred to as the karyoplasm or nuclear sap and contains many proteins
how does the nuceloplasm maintain the shape of the nucleus
protein fibres form a crisscross matrix within the nucleus
what is the nuclear lamina
- a protein mesh associated with the inner face of the inner membrane which provides mechanical support
- proteins called lamins form a 2D netowrk allong the inner surface of the membrane giving it its shape
what are chromosomes and chromatin
chromosomes conatin the genetic material where DNA is wrapped around histones into the nucleosomes
nucleosomes fold up to form chromatin fibre which is packed into chromosomes
what does chromatin divide into
1) euchromatin
2) heterochromatin
these represent two different degrees of DNA condensation (the least condensed sate appears loosley distributed in the nucleus)
what are the two forms of heterochromatin
1) constitutive= always remains heterochromatic
2) faculative= regions of euchromatin are converted to the heterochromatic state and silenced by deacetylation
what is the nucleolus
nucleus site of DNA replication and RNA transcription and processing
the sit ribosomal RNA synthesis and ribosome biogenesis
how are proteins transported in the nucleus
1) all proteins synthesised in the cytoplasm are imported into the nucleus by the nuclear pore complexes
2) these proteins contain nuclear localisation signals which direct their transport into the nucleus
what is the role of GTPase Ran in the transport of proteins
regulates interaction of transport receptors with cellular cargo proteins
what is the tole of Ran in the transport fo proteins
a monomeric G protein which acts as a molecular switch existing in two conformations
1) Ran+GDP
2)Ran+GTP
outline the process of nuclear import
1) importin binds to cargo protein
2) cargo complex diffuses through the nuclear pore
3) RanGTP interacts with importin causing conformational change which decreases affinity for cargo protein releasing it
4) importin RanFTP bind forming a complexand is exported back into the cytoplam
5) RanFTP is hydrolysed to RanGDP causing dissociation of importin
6) RanGDP is returned to nuceloplams by nuclear transport factor 2
7) guanin nucleotide exchange factor releases GDP and rebinding of GTP
outline the process of nuclear export
1) exportin 1 binds to the NES of the cargo protein to be transported with Ran-GTP
2) cargo complez diffuses thorugh NPC
3) GTPas activating protein converts RanGTP to Ran GDP
4) conformational change in Ran leads to dissociation of cargo complex
5) NES containing cargo protein relased into cytosol and exportin1 and RAnGDP go back to nucleus
6) GEF cuases felease and binding of GDP to GTP
what does NES and NLS stand for
NES= nuclear exporting signal
NLS= nuclear localisation siganl
what is needed for nuclear export
protiens need both NES and NLS signals
outline the process of nuclear export
1) exportin 1 binds to the NES of the cargo protein as well as the Ran-GTP forming a cargo complex
2) the cargo complex diffuses through the Nuclear pore complex
3) GTPase-activating protein converts Ran-GTP to GDP
4) this conformational change leads to dissociation of cargo complex
5) NES cargo protein is released into cystol and exportin and RanGDP are transported back to nucleus by NTF2
6) GEF cuases release of GDP and rebinding of GTP
what molecules hydrolyses Ran-GTP to GDP
GTPase-activating protein (GAP)
what causes the rebinding of Ran-GDP to GTP
guanine nucleotide exchange factor (GEF)
outline the process of the export of mRNA out the nucleus
1) mRNA remains associated with the specific heterogenic nuclear ribonucleoproteins in the messenger ribonuclear protein complex
2) an mRNA- exporter binds to the protein complex and diffuses through the nuclear pore
