Lecture 1 - 5 Flashcards
What is post translational modification?
- covalent addition/ cleavage of proteins after protein biosynthesis = occurs on the amino-acid chain or at a terminal
How do cells become pluripotent stem cells?
modify transcription factors within the cells and cause fully formed cells to revert/reprogram into pluripotent stem cells
What are the key types of post-translational modifications of proteins?
- phosphorylation
- glycosylation
- acetylation
- methylation
What does cleavage refer to?
in terms of adding nucleases and restriction enzymes where the DNA is cut
How is insulin produced in terms of cleavage?
- protein being produced by ribosome and fed through membrane into interstitial space.
- produces one large primary structure with parts that need to be cut away
- post translational modification is produced
- protein exported into golgi vessels to be cleaved
- unwanted peptide parts are removed
- produce a smaller protein product which can act as insulin
What is the function of adding new functional groups to proteins?
enable cell signaling and the cell to react specifically and rapidly to events
What is phosphorylation?
the addition of a phosphate group to the protein, which changes its activity
What are protein kinases?
enzymes that catalyze the transfer of a phosphate group from a high-energy donor molecule to a specific substrate-phosphorylation
How do protein kinases transfer a phosphate group to a protein?
Take ATP and remove the phosphate from it and knock the hydrogen off of the hydroxyl group and add a phosphate to it
What is phosphatases?
enzyme that catalyse the removal of a phosphate group from a substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group
What is the regulation of glycogen breakdown by phosphorylation?
- pathway initiated by epinephrine binding to its receptor and cAMP binding to cAMP-dependent protein kinase.
- signal transmitted to its intracellular target by the sequential action of protein kinases
What is glycosylation?
when a carbohydrate is covalently bound to a functional group on a protein via a glycosidic bond
what is the function of glycosylation?
- help correct folding of protein
- increase protein stability
- immune response
What are the 5 types of glycosylation?
- N-linked = glycan bind to amino group of asparagine
- O-linked = monosaccharides bind to hydroxyl group serine or threonine
- Glypiation = glycan core links a phospholipid and a protein
- C-linked = mannose binds to the indole ring of trytophan
- Phosphoglycosylation = glycan binds to serine via phosphodiester bond
What are the two types of acetylation?
- N-terminal
- Lysine acetylation
What is the role of N-terminal acetyltransferases (NATs)?
NATS transfer an acetyl group from acetyl-coenzyme A (AC-CoA) to the alpha amino group o f the first amino acid residue of the protein
What is an example of antagonistic acetylation and what is their function?
Histones
- located in cytoplasm or nucleus, function in gene expression regulation
What is methylation?
transfer of methyl group on to a lysine (2x or 3x) and arginine (1x or 2x)
What can lysine methylation lead to?
can lead to activation or suppression of gene expression
What is the function of Arginine methylation?
- regulation of RNA processing
- gene transcription
- DNA damage repair
- protein translocation
- signal transuction
What is the function of lysine methylation?
- histone function regulation
- epigenetic regulation of transcription
- lysine methyltransferase
What activates p53?
activated by various genotoxic stresses by regulation apoptosis, DNA repair, senescence
What are the main classes of ion channels in the plasma membrane?
- transporters
- linkers
- receptors
- enzymes
What is the function of ion channels?
transport ions across the plasma membrane and regulate membrane potential
What is membrane potential (Vm)?
the difference in electrical potential between interior and the exterior of a cell
What are the three main types of passive transport?
- simple diffusion
- osmosis
- facilitated diffusion
What are the two main types of active transport?
- primary direct active transport
- secondary indirect active transport
What is ion movement governed by?
- potential across membrane
- concentration gradient for that ion
What are the three type of ion channel gating?
- voltage gated = changes in voltage open and close the channel
- ligand gated = ligands regulate opening and closing
- tension gated = mechanical stress/stimulation open and close the channel
How does patch-clamp electrophysiology work?
- use suction to isolate a section of the plasma membrane
- can use different ions and drugs to see how they affect the function of the channel
- can monitor changes of electrical current
What is the difference between diffusion and flux?
diffusion = movement of molecules moving down a concentration gradient
flux = ions moving across a plasma membrane by diffusion/movement of ions
What are the excitable cells resting membrane potential?
Neuron cell = -70mv
Skeletal muscle cell = -90mv
Isle of langerhans = -70mv
How is the resting membrane potential maintained?
non-gated (leak) potassium channels are open causing potassium to have the highest permeability at rest
How can we measure membrane potential?
use a glass microelectrode and insert into the cell’s plasma membrane to measure the difference in voltage between the electrode in the cell and the electrode in the solution.
What is the formula for the Nernst equation?
Eion = (61 / valence of ion)log [ion]outside/[ion]inside
What are the terms for the different postassium imbalances?
large amount of potassium = hyperkalaemia
small amount of potassium = hypokalaemia
What are the different ways we can investigate ion channel structures?
- X-ray crystallography
- Cyro-EM
What is the structure of an ion channel?
- composed of alpha subunits
- 4 domains
- voltage sensing domain (outside) and pore-forming domain (inside)
How can we predict where the voltage sensor is on an ion channel?
voltage sensor is where there are 6 runs of Argenine
How can we remove the selectivity filter for sodium?
Within the pore-forming region there is a residue for lysine (K), if the lysine is substituted in the 1237 location for a glutamic acid (E) you can remove the selectivity for sodium.
What residues are responsible for ion channel gating?
2 glutamate and 2 aspartate residues = 4 highly negative amino acids
What are the 3 types of germ layers that peuripotent stem cells can differentiate into?
- Endoderm
- Mesoderm
- Ectoderm
