Chapter 5 Summary
Chapter 5.1
- Each cellular membrane (including organelle membranes) is a fluid mosaic made up of many different lipids, proteins and carbohydrates.
- Phospholipids are the most common lipid in cellular membranes, and they form a lipid bilayer. Sphingolipids and sterols are other types of lipids in cellular membranes.
- Membrane proteins can be classified as integral, peripheral or lipid-anchored, depending on how they interact with phospholipid bilayers.
- Carbohydrates are typically found on the exterior surface of the plasma membrane. They attach to lipids or proteins, forming glycolipids and glycoproteins, respectively.
- Membrane fluidity is affected by temperature, the structure of phospholipids, and the presence of cholesterol.
Chapter 5.2
- Membranes are selectively permeable, meaning they allow some substances to pass through them while blocking others.
- The permeability of a membrane to a solute depends on the properties of the solute and the properties of the membrane itself.
- Two types of transport proteins facilitate diffusion across membranes: channel proteins and carrier proteins.
- A solute gradient occurs when a solute is more concentrated in one area than another.
- Gradients across membranes can exist in the form of concentration gradients (neutral solutes) or electrochemical gradients (charged solutes).
Chapter 5.3
- In passive transport, substances diffuse down a concentration gradient or electrochemical gradient, which does not require the cell to expend any energy.
- Solutes pass directly through the phospholipid bilayer of a membrane during simple diffusion.
- Solutes cross a membrane via channel or carrier proteins during facilitated diffusion.
- Osmosis, the diffusion of free water molecules across a membrane, can occur via simple or facilitated diffusion.
- When the osmolarity is different on either side of a cellular membrane, water will move via osmosis to the side of the membrane with higher osmolarity.
- Tonicity describes the impact of an extracellular solution’s osmolarity on a cell’s osmosis and (consequently) volume.
Chapter 5.4
- In active transport, solutes move up (against) a concentration gradient or electrochemical gradient, which requires energy input from the cell.
- Primary active transport directly uses ATP hydrolysis as its energy source.
- There are four main types of carrier proteins in primary active transport: P-type, V-type, F-type, and ABC-type ATPases. Some of these are uniporters, while others are antiporters.
- Secondary active transport utilizes the energy from primary transport (in the form of an electrochemical gradient) to move another solute against its concentration gradient.
- Carrier proteins in secondary active transport are either antiporters or symporters.
Chapter 5.5
- Vesicular transport is the processes whereby substances are moved into and out of cells enclosed within membrane-bounded vesicles.
- Exocytosis transports materials from the inside of a cell into the extracellular fluid via the fusion of a vesicle with the membrane
- Endocytosis is used by cells to take in materials from their surrounding environment by forming a vesicle around them.
- There are three types of endocytosis: phagocytosis, pinocytosis and receptor-mediated endocytosis.
Chapter 5.6
- Cell signalling is important for cells to detect changes in their environment, including the presence of specific chemical signals called ligands.
- The four main steps of cell signalling are signal reception, signal transduction, cellular response, and termination of the signal cascade.
- Hydrophobic ligands can enter cells and bind to intracellular receptor proteins.
- Hydrophilic and/or large ligands cannot cross the cell membrane and must bind to cell surface receptor proteins.
- Signal transduction often involves the use of secondary messenger molecules like cyclic AMP, inositol triphosphate (IP3), diacylglyercol (DAG), and calcium ions (Ca2+).
- Cellular responses can involve changes in protein abundance (e.g. by changing gene expression) or protein activity, influencing many cell functions.
- In multicellular organisms, signalling can be classified as autocrine, paracrine, direct, or endocrine.