Transport Across Cell Membrane 2024-2025 PDF

10/21/2024 Transport Across Cell Membrane Dr. Rasha Mohammed Atta...

10/21/2024 Transport Across Cell Membrane Dr. Rasha Mohammed Atta Lecturer of physiology FOM-SCU 2024-2025 1 Plasma membrane Plasma (cell) membranes are formed from lipid bilayers. The cell membrane is selectively permeable in that it permits some particles to pass through while excluding others. 2 1  10/21/2024 What determines whether a given substance can cross the plasma membrane? 1. Lipid solubility: The more lipid soluble, the more readily it will diffuse across. 1. Size: The smaller the molecule, the more readily it will diffuse across. 3 -Highly lipid soluble: can dissolve in the lipid bilayer and pass through the membrane Example: O2, CO2, and fatty acids - Low lipid soluble: Na+ , K+ , glucose and proteins. Pass through Protein channels or carrier 4 2  10/21/2024 Transport across cell membrane Two types of basic mechanisms are involved in the transport of substances across the cell membrane: 1. Passive transport mechanism 2. Active transport mechanism. 5 1. Passive transport Is the transport of substances across the plasma membrane along the concentration gradient or electrical gradient. It is also known as diffusion or downhill movement. It does not need energy 6 3  10/21/2024 Passive transport Facilitated diffusion Simple diffusion (concentration gradient) Ion channels Protein mediated (electrochemical gradient) Aquaporins(osmosis) 7 8 4  10/21/2024 A. Simple diffusion Substances diffuse directly through the cell membrane. Examples: a. Gases (such as oxygen and carbon dioxide) b. Steroid hormones c. Fatty acids. 9 B. Protein mediated Glucose, some amino acids, and ions are not lipid soluble Types: 1. Carrier 2. Channel 3. Aquaporins 10 5  10/21/2024 Carrier proteins 11 I. Carrier: Facilitated diffusion Carriers never form an open channel between the two sides of the membrane. Alterations in the shape of the carrier allow it to first envelop and then release the transported substance on the opposite side of the membrane. Example: glucose transport 12 6  10/21/2024 II. Ion channels Channels are selective Types: 1. Leaky channels are always open and simply allow ions to move according to concentration gradients. 2. Gated channels opened or closed only when required, are controlled usually by chemical or electrical signals 13 Diffusion through Diffusion through Example: K+ leaky Example: voltage gated Na + channels channels 14 7  10/21/2024 Ungated Voltage gated Mechanical Ligand gated channels channels gated channels channels 15 Gated ion channels Voltage-gated channels open and close when the electrical state of the cell changes. Mechanically gated channels respond to physical forces, such as increased temperature or pressure that puts tension on the membrane. Chemical (ligand) gated channels: messenger molecules binds to channel protein. 16 8  10/21/2024 17 18 9  10/21/2024 III. Osmosis Osmosis is the net diffusion of water across the membrane Water molecules can diffuse through the plasma membrane because of their small size and lack of net charge. Or pass through specific water channels (called aquaporins) 19 2. ACTIVE TRANSPORT Is the movement of substances against the chemical or electrical or electrochemical gradient. It is also called uphill transport. 20 10  10/21/2024 Active transport Vesicular transport Secondary active transport Protein mediated Primary active transport) 21 Primary active transport Active transport requires energy, which is obtained mainly by breakdown of high energy compounds like adenosine triphosphate (ATP) Example: Na+/K+ ATPase 22 11  10/21/2024 23 24 12  10/21/2024 Secondary active transport Secondary active transport uses the kinetic energy of one molecule moving down its concentration gradient to push other molecules against their concentration gradient Example: Sodium-glucose cotransport 25 Vesicular transport Polypeptides and proteins, as well as many other molecules, are too large to be transported through a membrane by the carriers and so transported by vesicular transport. a. Exocytosis: Transport out of the cell. b. Endocytosis: Transport into the cell. Together provide bulk transport (The term bulk: many molecules are moved at the same time). Example: Secretion of hormones or neurotransmitters 26 13  10/21/2024 Endocytosis and Exocytosis 27 If a poison stopped the production of ATP, which of the following transport processes would cease? a. The movement of Na+ out of a cell b. Osmosis c. The movement of K+ out of a cell d. All of these Which of these statements about the facilitated diffusion of glucose is true? a. There is a net movement from the region of lower to the region of higher concentration. b. Carrier proteins in the cell membrane are required for this transport. c. This transport requires energy obtained from ATP. d. It is an example of cotransport. The movement of water across a plasma membrane occurs by a. an active transport water pump. b. a facilitated diffusion carrier. c. simple diffusion through membrane channels. d. all of these. 28 14  10/21/2024 29 15