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What is the primary way DNA initially associates with histones?
What is the primary way DNA initially associates with histones?
What is the function of the histones in the nucleosome?
What is the function of the histones in the nucleosome?
Approximately how many base pairs of DNA are wrapped around the core of eight histones in a nucleosome?
Approximately how many base pairs of DNA are wrapped around the core of eight histones in a nucleosome?
What is the term for the structural unit of DNA and histones?
What is the term for the structural unit of DNA and histones?
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How many histones are present in the core of a nucleosome?
How many histones are present in the core of a nucleosome?
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Carrier proteins facilitate transport of substances across the membrane against their concentration gradient.
Carrier proteins facilitate transport of substances across the membrane against their concentration gradient.
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Membrane pumps consume ATP to move ions and solutes down a concentration gradient.
Membrane pumps consume ATP to move ions and solutes down a concentration gradient.
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Gap junctions allow for the exchange of ions and large molecules between adjacent cells.
Gap junctions allow for the exchange of ions and large molecules between adjacent cells.
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Transmembrane proteins form channels that selectively allow the passage of all ions.
Transmembrane proteins form channels that selectively allow the passage of all ions.
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Cells can respond to physical stimuli through the use of receptors.
Cells can respond to physical stimuli through the use of receptors.
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Channels are used for active transport, consuming ATP.
Channels are used for active transport, consuming ATP.
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Signal reception and transduction occur through the use of transmembrane proteins and receptors.
Signal reception and transduction occur through the use of transmembrane proteins and receptors.
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Membrane proteins are only involved in cell signaling and not in membrane transport.
Membrane proteins are only involved in cell signaling and not in membrane transport.
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Transmembrane proteins are not involved in forming channels that allow the passage of ions and small molecules.
Transmembrane proteins are not involved in forming channels that allow the passage of ions and small molecules.
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Phospholipids are most stable when organized into a single layer.
Phospholipids are most stable when organized into a single layer.
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Cholesterol molecules are embedded within the lipid bilayer, increasing the fluidity of all membrane components.
Cholesterol molecules are embedded within the lipid bilayer, increasing the fluidity of all membrane components.
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Integral proteins are bound to one of the two membrane surfaces, particularly on the extracellular side.
Integral proteins are bound to one of the two membrane surfaces, particularly on the extracellular side.
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The plasma membrane is impermeable to small molecules.
The plasma membrane is impermeable to small molecules.
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Transmembrane proteins are only involved in signal reception, not in membrane transport.
Transmembrane proteins are only involved in signal reception, not in membrane transport.
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Lipophilic molecules diffuse through membranes very slowly.
Lipophilic molecules diffuse through membranes very slowly.
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The plasma membrane is not involved in exchanging materials between the cell and its environment.
The plasma membrane is not involved in exchanging materials between the cell and its environment.
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Channel-linked receptors promote the transfer of molecules or ions across the membrane before ligand binding.
Channel-linked receptors promote the transfer of molecules or ions across the membrane before ligand binding.
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G-protein–coupled receptors bind to ATP upon ligand binding.
G-protein–coupled receptors bind to ATP upon ligand binding.
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Receptors for hydrophilic signaling molecules are usually peripheral proteins in the cytoplasm of target cells.
Receptors for hydrophilic signaling molecules are usually peripheral proteins in the cytoplasm of target cells.
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Enzymatic receptors exhibit catalytic activity without ligand binding.
Enzymatic receptors exhibit catalytic activity without ligand binding.
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Target cells for a specific ligand contain multiple sets of cell surface and cytoplasmic receptor proteins.
Target cells for a specific ligand contain multiple sets of cell surface and cytoplasmic receptor proteins.
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Cells bearing receptors for a specific ligand are referred to as signaling cells for that molecule.
Cells bearing receptors for a specific ligand are referred to as signaling cells for that molecule.
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Study Notes
DNA-Histone Association
- The initial process involves DNA associating with small basic proteins called histones.
- The structural unit formed by the association of DNA and histones is called the nucleosome.
- A nucleosome has a core consisting of eight histones.
- Around 150 base pairs (bp) of DNA are wrapped around the core of histones in a nucleosome.
The Plasma Membrane Structure
- The plasma membrane ranges from 7.5 to 10 nm in thickness and is only visible through an electron microscope.
- Membrane phospholipids are amphipathic, consisting of nonpolar (hydrophobic) long-chain fatty acids linked to a charged polar (hydrophilic) head that bears a phosphate group.
- Phospholipids are most stable when organized into a double layer (bilayer) with the hydrophobic fatty acid chains located in a middle region away from water and the hydrophilic polar head groups contacting water.
- Molecules of cholesterol, a sterol lipid, insert at varying densities among the closely-packed phospholipid fatty acids, restricting their movements and modulating the fluidity of all membrane components.
Transmembrane Proteins and Membrane Transport
- Proteins are major constituents of membranes (~50% by weight in the plasma membrane).
- Integral proteins are incorporated directly within the lipid bilayer, whereas peripheral proteins are bound to one of the two membrane surfaces, particularly on the cytoplasmic side.
- Channels are multipass proteins forming transmembrane pores through which ions or small molecules pass selectively.
- Cells open and close specific channels for Na+, K+, Ca2+, and other ions in response to various physiological stimuli.
- Carriers are transmembrane proteins that bind small molecules and translocate them across the membrane via conformational changes.
- Membrane pumps are enzymes engaged in active transport, utilizing energy from the hydrolysis of adenosine triphosphate (ATP) to move ions and other solutes across membranes, against often steep concentration gradients.
Signal Reception and Transduction
- Cells in a multicellular organism communicate with one another to regulate tissue and organ development, control growth and division, and coordinate their functions.
- Adjacent cells form communicating gap junctions that couple the cells and allow exchange of ions and small molecules.
- Cells use different types of receptors to detect and respond to various extracellular molecules and physical stimuli.
- Membrane proteins perform several specific recognition and signaling functions, playing a key role in the interactions of the cell with its environment.
- Each cell type in the body contains a distinctive set of cell surface and cytoplasmic receptor proteins that enable it to respond to a complementary set of signaling molecules in a specific, programmed way.
- Receptors for hydrophilic signaling molecules, including polypeptide hormones and neurotransmitters, are usually transmembrane proteins in the plasmalemma of target cells.
- Three important functional classes of receptors are: • Channel-linked receptors that open associated channels upon ligand binding to promote transfer of molecules or ions across the membrane. • Enzymatic receptors, in which ligand binding induces catalytic activity in associated peripheral proteins. • G-protein–coupled receptors that, upon ligand binding, stimulate associated G-proteins which then bind the guanine nucleotide GTP and are released to activate other cytoplasmic proteins.
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Description
Learn about the structure of DNA and how it associates with histones to form nucleosomes, the basic units of chromatin. Understand how DNA wraps around histones to form chromatin.
