L15 Flashcards
What are the main two types of cellular membrane?
Plasma membrane
Intracellular membranes of organelles
What is the plasma membrane?
Single bilateral membrane that encloses the cell and coordinates interactions with the surrounding environment
What do intracellular membrane define?
Various aqueous compartments within the cytoplasm
Main components in phospholipid bilayer?
Phospholipids, sphingolipids, glycolipids, membrane proteins (enzymes, transporters, signal receptors), sterols (cholesterol, ergosterol (fungi), phytosterol (plants)).
What is the direction of polar groups in phospholipid bilayers?
Facing outward, shield the hydrophobic fatty acid tails from water.
What can phospholipids properties be?
Zwitterionic at physiological pH. Negatively charged at basic pH. Negatively charged at physiological pH.
What are the types of phospholipids?
PE : phosphatidykethanolamine, PC : phosphatidylcholine, PS: phosphatidyl-serine, PI : phosphatidylinositol.
What are the types of sphingolipids?
SM : sphingomycelins, GlcCer : glucosylcerebroside.
What are the types of lipid flipping (under apoptosis)?
Scramblase : Xkr8 on
Flippass : ATP-driven off
Cellular components can be classified by their membrane bound status what can these be?
Double membrane bound organelles
Single membrane bound organelles
Cellular components without membrane
Define organelles
Membrane-bound compartments of structures in a cell that performs a specific function.
What are the double membrane bound organelles?
Nucleus, mitochondria, chloroplasts
What are the single membrane bound organelles?
Vacuole, lysosome, Golgi, ER, peroxisomes, vesicles
What are the cellular components which are not membranes?
Cell wall, cytoskeleton, ribosomes
What is the nucleus and what does it consist of?
Largest organelle in animal cells. Consists of nuclear envelope, nucleoplasm, nuclear lamina, chromosomes and chromatin, nucleolus.
What is the nuclear envelope?
Two membranes both phospholipid bilayers with different types of proteins
What are the two different types of proteins in the nuclear envelope?
Inner nuclear membrane which defines the nucleus. Outer nuclear membrane continuous with the rough ER.
What is the perinuclear space in the nuclear envelope?
Space between membranes which is continuous with the lumen of the rough endoplasmic reticulum.
In the nuclear envelope where do the two membranes fuse?
Nuclear pores
What is the nuclear pore?
Ring-like complexes composed of specific membrane proteins through which material moves between the nucleus and the cytosol.
What is the nuclear pore made of?
Multiple copies of different proteins called nucleoporins. They help cargo proteins traverse the nuclear pore.
What diffuses through the nuclear pore complex?
Ions, small metabolites, and globular proteins up to 60-100 kDa. Larger proteins and ribonucleoprotein complexes need the assistance of soluble transporter proteins.
What does the nuceloplasm do?
Suspends structures within the nucleus that are not membrane bound
Other names for the nucleoplasm?
Karyoplasm or the nuclear sap
What is the nucleoplasm?
Semi-solid, granular substance that contains many proteins.
What is the nucleoplasm responsible for?
Maintaining the shape and structure of the nucleus. Protein fibres form a crisscross matrix within the nucleus.
What is the nuclear lamina?
Protein mesh associates with the inner face of the inner nuclear membrane
What does the nuclear lamina do?
Provides mechanical support for the nucleus, regulates important cellular events.
What forms the nuclear lamina?
Fibrous proteins called lamins. Form a two dimensional network along the inner surface of the inner membrane giving it shape.
Where is genetic material in the nucleus packed?
Chromosomes, DNA is wrapped around histones into nucleosomes. Nucleosomes fold up to form a chromatin fiber which is packed into chromosomes.
What is chromatin?
DNA organised in nucleosomes that condense.
What are the two divisions of chromatin and what do they represent?
Euchromatin and heterochromatin, representing differing degrees of DNA condensation.
What is the least condensed state in interphase?
Chromatin, which is loosely distributed through the nucleus.
What are the two forms of heterochromatin?
Constitutive and facultative
What is constitutive heterochromatin?
Repetitive DNA, which always remains heterochromatic
What is facultative heterochromatin?
Regions of euchromatin converted into heterochromatic state and are silenced by histone deacetylation
What is the nucleolus the site of?
Nucleus site of DNA replication, and RNA transcription and processing.
Where is the nucleolus?
Inside the nucleus
What is nucleolus the site of?
Ribosomal RNA synthesis and ribosome biogenesis.
Reminder! What occurs in protein translation?
The ribosome moves along the mRNA, tRNAs arrive delivering their amino acid. The ribosome produces a polypeptide chain
What happens in ribosome biogenesis?
mRNA, tRNA, rRNA are made in the nucleus. Ribosomal proteins are made in the cytoplasm, but assembled in the nucleus.
What happens in nuclear transport?
All proteins in the nucleus are synthesised in the cytoplasm and imported into the nucleus through nuclear pore complexes. Such proteins contain nuclear-localisation signal (NLS) that directs their selective transport into the nucleus. NLS are bound by importins.
What is the nuclear localisation signal?
One or more short sequences of positively charged lysines or arginines exposed on the protein surface.
What does Ran do in nuclear transport?
Regulates interactions of transport receptors with cellular cargo proteins
What is Ran? What are its two conformations?
A monomeric G protein that acts as a molecular switch it exists in two conformations. Ran + GTP and Ran + GDP.
What effect does high affinity binding of the GTP bound form to import receptors?
Promotes cargo release, whilst binding to export receptors stabilises their interaction with cargo.
What happens in nuclear import? steps 1-4
Importin binds the cargo protein, cargo complex diffuses through the nuclear pore. Ran-GTP interacts with importin causing a conformational change that decreases affinity for the cargo protein releasing the cargo protein. Importin Ran-GTP complex is exported back in the cytoplasm.
What happens in nuclear import? steps 5-7
Ran-GTP is hydrolysed to Ran-GDP with the help of GTPase-activating protein. Ran-GDP is returned to the nucleoplasm by nuclear transport factor 2. Guanine nucleotide-exchange factor causes release of GDP and rebinding of GTP.
What is needed in nuclear export?
Proteins with a nuclear exporting signal are required to export macromolecules from the nucleus to the cytoplasm.
What is a nuclear exporting signal (NES)?
A short target peptide contain four hydrophobic residues on the protein
What do proteins that are getting imported and exported have?
NLS and NES
What happens in nuclear export? Steps 1-4
Exportin 1 binds to the NES of the cargo protein to be transported with Ran-GTP. Cargo complex diffuses through an NPC. GTPase activating protein converts Ran-GTP to Ran-GDP. Conformational change in Ran leads to dissociation of the cargo complex.
What happens in nuclear import? Steps 5-7
NES containing cargo protein is released into the cytosol. Exportin 1 and Ran-GDP are transported back into the nucleus. Ran-GDP is transported by NTF2. Guanine nucleotide exchange factor causes release of GDP and rebinding of GTP.
What happens once an mRNA is completed?
It is exported out of the nucleus into the cytoplasm before it can be translated into the encoded protein
What happens in the nuclear export of mRNAs?
mRNA remains associated with specific heterogenic nuclear ribonucleoproteins in a messenger ribonuclear protein complex. An mRNA exporter binds to mRNPs. The mRNP-mRNA exporter complex diffuses through the nuclear pore.
What are mitochondria?
One of the biggest organelles in the cell.
What does the mitochondria’s outer membrane contain?
Porins making the membrane permeable to molecules
What does the mitochondria’s inner membrane contain?
20% lipid and 80% protein. It is less permeable.
What takes place in the inner membrane?
Proton motive force, electron transfer chain
What does the inner membrane of mitochondria contain?
A large number of infoldings called cristae which increase surface area.
What do cristae do?
Increase SA enhancing ability to generate ATP.
What do F0F1 complexes do in the cristae?
Synthesise ATP
What does the mitochondrial matrix contain?
Mitochondrial DNA, ribosomes, granules.
What occurs in the mitochondrial matrix?
Glycolysis and Beta oxidation
What after vacuoles are the largest plant and green algae cells?
Chloroplast
What do chloroplast contain? And what are they?
Extensive internal system of interconnected membrane-limited sacs called thylakoids. Thylakoids are flattened to form disks and stacks (grana). Thylakoid membranes contain photosynthetic pigments and ATP synthases
