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33 Cards in this Set
- Front
- Back
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List 6 functions of the cell membrane.
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Serve as physical boundary, enable cell-cell recognition, compartmentalize eukaryotic cells, attach to cytoskeleton and ECM, act as sites for receptor molecules, channels, and pumps; act as sites for biological reactions.
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Besides phospholipids, what lipids are in the cell membrane?
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Phospholipids are most dominant, but cholesterol and glycolipids are also present.
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How thick are PMs?
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5 nm. With associated proteins, it's 8 to 10 nm.
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Why does the ratio of protein in PMs vary with cell type?
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Function. A myelin membrane is 80% lipid. The inner mitochondrial membrane is 75% protein.
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Why are membrane proteins and lipids ampipathic?
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Because they have both hydrophilic and hydrophobic components. They need both.
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In freeze fracturing, what is used to coat the fractured surface?
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A thin layer of Carbon and a thin layer of heavy metal.
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These proteins associated with the PM regulate ion channels and cell signaling.
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Peripheral proteins.
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These PM proteins normally function as membrane receptors and transport proteins, and attach cells to each other and the ECM.
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Integral proteins.
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What kind of AA sequence indicates a transmembrane protein segment?
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A hydrophobic 20-30 AA chain.
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What can slow or stop the lateral movement of proteins in the PM?
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Contact with the cytoskeleton, contact with ECM, contact with proteins of an adjacent PM.
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Are carriers used in passive transport, active transport, or both?
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Both.
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Carriers in mitochondria import ____ and export ____.
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Pyruvate; ATP.
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What role do oligosaccharides on the PM play?
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They can be attached to membrane proteins and lipids to form glycoproteins and glycolipids. These are used in cell-cell recognition (immunology and embryonic development).
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These junctions for a "belt."
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Both occluding junctions and zonula adherens.
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What kind of protein do all cell junctions use?
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An integral protein.
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What proteins are involved in tight junctions? What kind of protein are they?
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Claudins and occludins; both integral, transmembrane proteins.
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What cytoskeletal element do tight junctions connect to?
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Actin.
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What cytoskeletal element do Adherens junctions and Desmosomes connect to?
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Adherens junctions--Actin
Desmosomes--IFs; usually keratin. |
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What protein enables the adherens junction of one cell to connect with the next cell's adhering junction?
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Cadherins. They span the 20-30nm gap between cells, extend through the PM, and are linked to actin.
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Where do you find desmosomes?
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Where there is much mechanical stress.
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What spans the gap between desmosomes of adjacent cells?
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Cadherins.
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What's epidermolysis bullosa simplex?
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A disease caused by mutations in the keratin gene. Epidermal cells easily fracture under pressure causing blisters.
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In adherens junctions, what binds the cadherins to the actin filaments?
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Another protein: a linker molecule called catenin.
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What do focal adhesions do?
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Basically like adherens junctions, but they connect the actin cytoskeleton to the ECM.
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What proteins do focal adhesions contain and what does it do?
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Integrin--it anchors the ECM to actin.
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What proteins do hemidesmosomes contain and what does it do?
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Integrin--it anchors the ECM to IFs.
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What cells are focal adhesions particularly important in?
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They occur in epithelium, but are really critical in cx tissue cells like fibroblasts where they aid in crawling locomotion.
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What can you say about the structure of integrins?
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They are heterodimers.
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How far apart are cells at the gap junction?
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2-4 nm
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What creates the gap?
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Proteins called connexons, made up of six subunits called connexins, extend from the PMs of each cell, creating an aqueous channel.
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What size molecules can pass though gap junctions?
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Up to 1.2 nm diameter; up to 1000 daltons.
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How would you disable a gap junction?
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Increase intracellular Ca. This method is used to isolate sick cells from healthy ones.
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What opens gap junctions?
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Low Ca inside the cell or high pH inside the cell.
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