17: Lipids
- Page ID
- 175611
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The lipids are a large and diverse group of naturally occurring organic compounds that are related by their solubility in nonpolar organic solvents (e.g., ether, chloroform, acetone and benzene) and general insolubility in water. There is great structural variety among the lipids, as will be demonstrated in the following sections.
- 17.1: Prelude to Lipids
- This page outlines the FDA's 2003 mandate requiring trans fatty acids to be listed on food labels due to health risks, effective January 1, 2006. It explains that trans fats, formed by turning liquid oils into solid fats, can elevate bad cholesterol levels. The chapter also covers the roles of fatty acids and lipids in energy provision and biological functions like energy storage and cell membrane structure.
- 17.2: Fatty Acids
- This page discusses fatty acids as carboxylic acids essential for lipid structure, classified into saturated and unsaturated types. It highlights the necessity of essential fatty acids like linoleic and α-linolenic, which must be acquired through diet. The page also covers the role of prostaglandins, derived from arachidonic acid, in physiology, and notes that waxes, esters of long-chain fatty acids, serve protective functions for plants and animals.
- 17.3: Fats and Oils
- This page discusses triglycerides, comprising three fatty acids and glycerol, differing in melting points and sources: saturated fats are animal-based and unsaturated oils are plant-based. It highlights the health concerns over saturated and trans fats from margarine and hydrogenated oils. Consumers are encouraged to use polyunsaturated oils and reduce fat intake.
- 17.4: Membranes and Membrane Lipids
- This page discusses the structure and function of cell membranes, emphasizing their lipid and protein composition. Membrane lipids, primarily phospholipids and sphingolipids, create a bilayer that provides fluidity and facilitates various cellular functions. Integral and peripheral proteins allow the transport of ions and molecules, while lipid diversity aids in cell recognition and communication.
- 17.6: Membrane Structure and Composition
- Since most cells live in an aqueous environment and the contents of the cell are also mostly aqueous, it stands to reason that a membrane that separates one side from the other must be hydrophobic to form an effective barrier against accidental leakage of materials or water. Cellular membranes were partially defined as being composed primarily of phospholipids: molecules consisting of a phosphorylated polar head group attached to a glycerol backbone that has two long hydrocarbon tails.
- 17.7: Components and Structure
- Among the most sophisticated functions of the plasma membrane is the ability to transmit signals by means of complex, integral proteins known as receptors. These proteins act both as receivers of extracellular inputs and as activators of intracellular processes. These membrane receptors provide extracellular attachment sites for effectors like hormones and growth factors, and they activate intracellular response cascades when their effectors are bound.
- 17.8: Membrane Proteins
- This page discusses the classification of membrane proteins into integral and peripheral types. Integral proteins span the membrane, acting as channels, pumps, receptors, and enzymes, while peripheral proteins are surface-bound, aiding in signaling and structure. Channel proteins, which can be open or closed, facilitate selective ion movement and include various types like ligand-gated and voltage-gated channels. The regulation of ion flow is vital for cellular functions.
- 17.11: Endocytosis and Exocytosis
- Endocytosis is a mechanism for internalizing large extracellular molecules (e.g., proteins), insoluble particles, or even microorganisms. The three main types of exocytosis are phagocytosis, pinocytosis and receptor-mediated endocytosis. Pinocytosis is non-specific. Phagocytosis targets large structures (e.g., bacteria, food particles…) and is not particularly specific. As its name suggests, receptor-mediated endocytosis is specific for substances recognized by a cell-surface receptor.
- 17.12: Diffusion
- Diffusion can be described as the random movement of particles through space, usually due to a concentration gradient. Diffusion is a spontaneous process and is a result of the random thermal motions between two particles.
- 17.13: Steroids
- This page discusses the importance of steroids, particularly cholesterol, in mammals, highlighting their roles in cell membranes and hormone synthesis while noting the health risks associated with high cholesterol levels. It also covers the production of bile acids and salts from cholesterol in the liver and their role in digestion.
- 17.E: Exercises
- This page discusses the melting points of fatty acids, highlighting stearic acid as the highest, followed by elaidic and oleic acids. It also notes that palmitelaidic acid has a lower melting point due to its shorter carbon chain. Additionally, it examines various oils in margarine, the roles of lecithin and cerebrosides, the diffusion of compounds through cell membranes, and the significance of steroid hormones and prostaglandins, particularly the LDL to HDL ratio.
- 17.S: Lipids (Summary)
- This page covers lipids, highlighting their solubility, biological roles, and various types including fatty acids and triglycerides. It discusses key reactions such as saponification and hydrogenation, as well as the dual properties of phospholipids in cell membranes and the crucial role of cholesterol in animals. The chapter emphasizes the significance of lipids in energy storage and cell structure, alongside their interactions within biological systems.