Cell Biology Flashcards
What are the key differences between glycerophospholipids and sphingomyelin?
Glycerophospholipids contain a cis-double bond which allows the membrane to be more fluid at physiological temperature.
Sphingomyelin does not have this and results in a more viscous membrane
How does cholesterol modify lipid fluidity?
Cholesterol reduces membrane fluidity. It is also capable of “flip-flopping” from one leaflet to another, this facilitates membrane flexibility.
Rafts of cholesterol, sphingomyelin, and
glycolipids have low fluidity and serve as
clustering sites for membrane proteins
and receptors.
What attaches to cerebrosides and gangliosides and what does this do?
Oligosaccharides attach to cerebrosides (uncharged sugars) and gangliosides (charged sugars like sialic acid). These sugars play important roles in signal transduction
Integral membrane proteins are typically asymmetric, why is this?
Sialic acid residues of complex oligosaccharides are found only on the outer surface, while negatively charged phosphotidylserine phospholipids usually occur only on the inner face of the membrane.
In addition, the inside of the cell is a reducing environment so sulfhydryl groups do not form disulfide bonds like they do on the outside.
What is the function of the connection of nuclear envelope, ER, Golgi, plasma membrane, & endocytic vesicles?
The RNA which comes from the nucleus is translated into proteins by ribosomes lining the rough ER, the Golgi is a packaging center for these proteins, and endocytic vesicles transport proteins by vesicle trafficking: vesicle budding and targeted fusion.
The connection of these compartments also allows for the cytosol to be a reducing environment while the ER, golgi, endosomes, and lysosomes have oxidative environments.
The ER, Golgi, secretory vesicles, cell surface, and endosomes are linked together by _________. What does this facilitate?
The ER, Golgi, secretory vesicles, cell surface, and endosomes are linked together by microtubules. This facilitates vesicle transport in and out of cells (dynein moves vesicles in, towards the - end of MTs; Kinesin moves vesicles out of cells, toward the + end of MTs).
Nerve cells have exploited the same secretory and endocytic vesicle transport pathways.
What kind of environment is the cytosol? What about the ER-golgi system?
Cytosol is a reducing environment. ER-golgi system is an oxidating environment.
Nuclear pores contain the gating machinery to restrict passage
to molecules that bear the proper targeting signals. Where are these targeting signals?
The protein sequence itself will direct it to the appropriate organelle.
How can one differentiate active versus inactive gene transcription?
Active transcription occurs in Euchromatin, inactive transcription occurs in heterochromatin.
The TCA cycle and OXPHOS occur in the mitochondria, where do these processes occur?
Enzymes of the TCA cycle are located in the interior matrix. Oxidative-phosphorylation enzymes and ATP synthase are attached to the inner cristae. A gradient of protons between the inter-membrane space and matrix drives the production of ATP in ATP synythase particles.
What can result from mutations of mitochondrial genes?
The only genes that remain in mitochondria today are genes that produce components of the oxidative phosphorylation (OXPHOS), and thus mutations of these genes damage that system only. You should be aware that mutations, inherited or spontaneous, in mitochondrial DNA necessarily compromises oxidative phosphorylation and can lead to diseases in tissues (e.g., muscles, nerve cells) that require a lot of energy in the form of ATP.
What is the main function of peroxisomes?
Peroxisomes contain enzymes necessary for B-oxidation of long chain fatty acids. Inherited defects in peroxisomal enzymes cause diseases such as
adrenoleukodystrophy and Zellweger’s syndrome.
What is the function of chaperones? Proteasomes?
Chaperones are for protein folding, they protect proteins from the reducing environment of the cytosol and provide a hydrophobic environment for folding to occur. Proteasomes contain multiple proteases for protein degradation. Ubiquitin ligase enzymes in the cytosol attach ubiquitin-tags to proteins which are recognized by proteasomes.
What is the role of SRP (signal receptor particle)?
SRP binds to the start transfer sequences of RNA sequences of peptides destined for the ER. This stops translation until the ribosome binds to an SRP receptor on the ER. Once bound, the sequence is translated into a peptide released into the ER.
What is the role of start and stop transfer sequences on proteins?
What is a multi-pass integral membrane protein?
The start transfer sequence is bound to the membrane of the organelle for which the protein is destined. Once the stop transfer sequence is hit, the protein remains where it is. The start sequence is then clipped off, leaving one side of the protein inside the organelle and one side in the cytosol.
Some proteins may have muliple start and stop sequences, this results in multi-pass integral membrane proteins.
