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Membrane Structure and Function, Exams of Biology

Liberty University (LU)Biology

A detailed overview of the fluid mosaic model of cell membranes, including the properties and functions of different membrane components such as proteins, lipids, and ion pumps. It covers topics like membrane fluidity, selective permeability, diffusion, osmosis, and various transport mechanisms across the membrane, including facilitated diffusion, channel proteins, and carrier proteins. The document also discusses the role of membrane proteins in depression medications and the sodium-potassium pump as an example of an electrogenic ion pump. This comprehensive information on cell membrane structure and function would be highly relevant for students studying biology, biochemistry, or related fields.

Typology: Exams

2024/2025

Available from 10/12/2024

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LSU Biology 1201 Exam 2 Chapter 7
solution update
SJ Singer and G Nicolson - 1972- proposed that membrane proteins are dispersed,
individually inserted into phospholipid bilayer with their hydrophilic regions
protruding
Fluid Mosaic Model - -behaves like liquid
-contains numerous diff. types of proteins
-not held in one place, constantly moving
Proteins - embedded in the membrane need to have amino acids that interact
with water/ repel water to be inside the membrane
Membrane Fluidity - -membranes are locked in place
-held together by hydrophobic interactions which are much weaker than covalent
bonds
-whenever bloods goes through the vessels, its fluid and could burst
--anemia due to blood lost
--no iron=no oxygen
Membrane Proteins - 2 major populations:
integral proteins- inserted in the membrane
(shape-like: =O=)
peripheral proteins- located on the side of the membrane but NOT embedded
Integral proteins - -penetrate the hydrophobic core
- some embedded in the membrane
-many are trans-membrane proteins, spanning the entire membrane
-hydrophobic regions- made of nonpolar amino acids coiled into HELICES
-hydrophilic regions are exposed to aq environments on both sides of membrane
Channel and Carrier Proteins - -primarily need proteins to transport
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LSU Biology 1201 Exam 2 Chapter 7

solution update

SJ Singer and G Nicolson - 1972 - proposed that membrane proteins are dispersed, individually inserted into phospholipid bilayer with their hydrophilic regions protruding Fluid Mosaic Model - - behaves like liquid

  • contains numerous diff. types of proteins
  • not held in one place, constantly moving Proteins - embedded in the membrane need to have amino acids that interact with water/ repel water to be inside the membrane Membrane Fluidity - - membranes are locked in place
  • held together by hydrophobic interactions which are much weaker than covalent bonds
  • whenever bloods goes through the vessels, its fluid and could burst --anemia due to blood lost --no iron=no oxygen Membrane Proteins - 2 major populations: integral proteins- inserted in the membrane (shape-like: =O=) peripheral proteins- located on the side of the membrane but NOT embedded Integral proteins - - penetrate the hydrophobic core
  • some embedded in the membrane
  • many are trans-membrane proteins, spanning the entire membrane
  • hydrophobic regions- made of nonpolar amino acids coiled into HELICES
  • hydrophilic regions are exposed to aq environments on both sides of membrane Channel and Carrier Proteins - - primarily need proteins to transport

Channel protein - acts like a straw Carrier Protein - changes shape using ATP to scatter it across the membrane Facilitated Diffusion - diffusion across a membrane with the help of transport proteins

  • moving from high to low concentration Bind and release - allows it to be transported across Aquaporins - facilitate the movement of water across membranes
  • cannot cross easily
  • channels that have amino acids let water in and out --common in kidney cells ---allows them to reclaim water from urine before it is excreted from the body Gated Channels - open or close in response to a stimulus
  • 2 forms: ligand-gated- activated by chemical messengers such as hormones and neurotransmitters voltage-gated- activated by changes in electrical membrane potential selective permeability - property of biological membranes which allows some substances to cross more easily than others nonpolar molecules (hydrocarbons, CO2, and O are hydrophobic) - can be dissolved in the lipid bilayer of the membrane and cross it easily hydrophobic core - prevents charged or polar substances from crossing directly diffusion - process where a substance moves from an area of greater conc to an are of lesser conc
  • essentially a process of spreading molecules out evenly into the available space Diffusion - - dissolved oxygen will continue to diffuse across a membrane while a cellular respiration is taking place
  • due to 2 key factors:

depression medications - - most meds are SSRI's= Selective Serotonin Re-Uptake Inhibitors Serotonin - neurotransmitter in the central nervous system, produces a feeling of pleasure, euphoria, and general well-being SSRI's - block receptor mediated endocytosis

  • so instead of binding the receptor and being taken back up into Neuron A and stopping its effect, it is allowed to keep binding the serotonin receptor, producing a constant feeling of well being Ion pumps - can generate or maintain voltage across membranes Membrane potential - charge difference across a membrane due to an unequal distributive of ions
  • most cells are slightly negative on the inside relative to the outside Sodium-Potassium Pump (Na/K ATPase pump) - is an electrogenic pump in animals that moves 3 Na+ ions out of the cell, for every 2 K+ ions into the cell
  • pump is in the initial conformation-very high affinity for Na+ --phosphate group from ATP molecule is added to the pump (how ATP is used for energy) ---pump undergoes conformational change and loses its affinity for Na+ ----new conformation = high affinity for K+. Binds fro the extracellular side/ induces release of phosphate -----returns to original conformation ------pump now has low affinity for K+ and high affinity for Na+