Department of Kinesiology and Applied Physiology WCR Chapter 3: Cells Overview Plasma membrane: structure Plasma membrane: transport Resting membrane potential.
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Department of Kinesiology and Applied Physiology WCR
Department of Kinesiology and Applied Physiology 2
Do exercise scientists need to think about cells?Exercise in a Pill
•“AMPK and PPARδ Agonists Are Exercise Mimetics”•AICAR activates intracellular pathways that are also activated by exercise. Mice taking AICAR look like mice on exercise. Mice on AICAR plus exercise are supermice.
Narkar et al., Cell 2008.
Fibroblasts
Erythrocytes
Epithelial cells
(d) Cell that fights disease
Nerve cell
Fat cell
Sperm
(a) Cells that connect body parts, form linings, or transport gases
(c) Cell that storesnutrients
(b) Cells that move organs and body parts
(e) Cell that gathers information and control body functions
(f) Cell of reproduction
SkeletalMusclecell
Smoothmuscle cells
Macrophage
Figure 3.1
Generalized Cell
• All cells have some common structures and functions
• Human cells have three basic parts:– Plasma membrane—flexible outer boundary– Cytoplasm—intracellular fluid containing
A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane.
A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell.
Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together.
(c) Attachment to the cytoskeleton and extracellular matrix (ECM)
A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here.
Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions.
Lipid-insoluble solutes (such as sugars or amino acids)
(b) Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein
The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell.
As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradientinto the cell. (ECF = extracellular fluid)
(a) Endocytosis:PhagocytosisThe cell engulfs a large particle by forming pro-jecting pseudopods (“false feet”) around it and en-closing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein-coated but has receptors capable of binding to microorganisms or solid particles.
(b) Endocytosis:PinocytosisThe cell “gulps” drops of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated.
(c) Receptor-mediatedendocytosisExtracellular substances bind to specific receptor proteins in regions of coated pits, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles.