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.

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).

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.

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.

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.

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.

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