Topic 5: Membranes Flashcards
Describe the lipids used in cells and explain how their properties relate to the structure.
- Lipids are a diverse group of hydrophobic (water-hating) molecules that play a crucial role in cellular structure and function.
1. triglycerides or triaclylglycerols
structure: consist of one glycerol molecule linked to three fatty acid chains through ester bonds
Properties and functions:
Energy storage: Triglycerides serve as the primary energy storage molecules in animals. Due to their highly reduced state, they provide more than double the energy per gram compared to carbohydrates
Insulation: in adipose tissue they helps insulate the body, protecting it from temperature changes
Protection: they provide cushioning around vital organs
2. Phospholipids
structure: these are similar to triglycerides, but one of the fatty acid chains is replaced by a phosphate group. The phosphate group often has other polar molecules attached to it
Properties and functions : - amphipathic nature: they have both hydrophilic (water-loving) and hydrophobic (water-repelling) parts. This makes them ideal for forming biological membranes
- Bilayer formation: in aqueous ( in water), phospholipids spontaneously form bilayers with the hydrophilic heads facing outward and the hydrophobic tails facing inward. This bilayer structure forms the basis of the cellular membrane.
3. STEROIDS:
Structure
: steroids have a basic structure of our linked carbon rings
Properties and functions:
Hormones: some steroids like testosterone and estrogen act as hormones and play vital roles in regulating function
Cell membrane component: Cholesterol, a type of steroid is embedded in animal cell membranes, helping maintain fluidity and integrity
How Properties Relate to Structure:
Chain Length and Saturation: The length and saturation level of fatty acid chains in lipids influence their properties. For example, longer chains and more saturation (fewer double bonds) raise the melting point, making the lipid more solid at room temperature (like butter).
Amphipathic Nature: The dual nature of phospholipids, being both hydrophilic and hydrophobic, arises from their structure and allows them to form the basic structure of cell membranes.
Ringed Structure of Steroids: The four-ring structure of steroids imparts rigidity, and slight modifications to this structure can greatly change its function, as seen in the various steroid hormones.
Please explain how the structure of phospholipids allows them to form membranes and why phospholipids confer selective permeability on membranes.
Imagine phospholipids as tiny “Tadpole” shaped creatures. The head of the tadpole is attracted to water (hydrophilic), and the tail dislikes water (hydrophobic)
FORMATION OF MEMBRANES:
1. Bilayer formation: if you place these tadpoles in water, they would arrange themselves with their heads facing the water and their tails facing away, trying to avoid the water. The result is a double layer or “bilayer”, where the tails of two layers of tadpoles face each other, and the heads face outwards. The self-organized structure is the basic form of cell membranes
2. protective barrier: This bilayer creates a barrier between two aqueous ( water-containing) environments, like the inside and outside of a cell. it acts like a wall, separating the cell’s interior from its external environment.
SELECTIVE PERMEABILITY:
1. small charged and non-polar molecules:
Small gases like oxygen and carbon dioxide can slip between tadpoles without any problem. Similarly, molecules that are also “Water-disliking” or non-polar, like the tadpoles’ tails, can pass through easily. These molecules speak the same “language” as the tails
ex. O2, C02, N2
Small, uncharged polar molecules:
H2O, indole, glycerol, and polar molecules are slower to pass through the bilayer
2. Charged or Large polar molecules: These have a hard time passing through the wall of tadpoles because they are attracted to water and don’t mesh well with the water-disliking tails of the tadpoles. Examples include ions (like sodium or potassium) and large sugars.
- WATER: while water is polar and attracted to the tadpole heads, it’s small enough to slip through but not as quickly as the non-polar molecules.
IONS: CL-, K+. Na+ cannot pass through the bilayer.
Describe membrane structure according to the fluid mosaic model of membrane structure and explain the roles of proteins and sterols in membrane function.
The basic structure of the fluid mosaic model:
a. phospholipid bilayer: The fundamental structural component of all cell membranes is a layer of lipid molecules. In most cases, these are phospholipids, which consist of hydrophilic and two hydrophobic tails. The phospholipids organize themselves in a bilayer, with the hydrophobic tails facing inward, away from the watery environment inside and outside the cell, and the hydrophilic heads facing inward.
b. scattered within the lipid bilayer are various proteins. These can be peripheral (on the surface of the bilayer) or integral (spanning the bilayer). The pattern isn’t static; instead, proteins and lipids can drift around, like boats on the surface of the calm ocean, hence the term fluid
c. carbohydrates: often bound to proteins (glycoproteins) or lipids (glycolipids) in the cell’s exterior surface. They play a role in cell recognition and signalling
d. Cholesterol and sterols: embedded within the phospholipid bilayer are cholesterol molecules or other sterols. They help modulate the fluidity and stability of the membrane
ROLES OF PROTEINS AND STEROLS IN MEMBRANE FUNCTION:
A. PROTEINS:
Transport: some proteins form channels or pumps to help substances move across the membrane/ These can be selective, allowing specific ions or molecules to pass through
Receptors: Proteins on the cell surface can act as receptors, binding to specific molecules (like hormones) and triggering a response inside the cell
Enzymatic activity: Some membrane proteins are enzymes that catalyze specific chemical reactions
STEROLS (like cholesterol)
- fluidity regulator: cholesterol plays a crucial role in modulating the membrane’s fluidity. At high temperatures, cholesterol makes the membrane less fluid and prevents the fatty acid chains of phospholipids from packing closely together. At low temperatures, it prevents the membrane from becoming too rigid.
- membrane stability: Cholesterol helps maintain the stability of the membrane without making it too rigid
The fluid mosaic model highlights the dynamic and versatile nature of the cell membrane. It’s not rigid or static structure; its a made of various biological processes.
Compare and contrast passive discussion, facilitated diffuson and active transport in terms of which tpes of transport involve integral membrane proteins, which require input of cellular energy, and type of molecules that move by each means
ChatGPT
Certainly! Let’s compare and contrast passive diffusion, facilitated diffusion, and active transport based on the criteria you mentioned:
Involvement of Integral Membrane Proteins:
Passive Diffusion (Simple Diffusion): Does not generally involve integral membrane proteins. Molecules move directly through the lipid bilayer.
Facilitated Diffusion: Involves integral membrane proteins. These proteins provide channels or carrier mechanisms that allow certain molecules to move across the membrane.
Active Transport: Involves integral membrane proteins known as pumps, which move molecules against their concentration gradients.
Requirement of Cellular Energy:
Passive Diffusion (Simple Diffusion): Does not require energy. Molecules move down their concentration gradient (from high to low concentration).
Facilitated Diffusion: Does not require cellular energy. Even though it involves proteins, the molecules still move down their concentration gradient.
Active Transport: Requires energy, usually derived from ATP. This is because molecules are often moved against their concentration gradient (from low to high concentration).
Type of Molecules Moved:
Passive Diffusion (Simple Diffusion): Typically non-polar and small polar molecules like oxygen (O₂), carbon dioxide (CO₂), and some lipids. These molecules can easily pass through the lipid bilayer without assistance.
Facilitated Diffusion: Polar or charged molecules that cannot easily pass through the lipid bilayer by simple diffusion. This includes ions like potassium (K⁺) or chloride (Cl⁻), and larger molecules like glucose. They require the assistance of channel or carrier proteins.
Active Transport: Can transport a variety of molecules, including ions and larger molecules. What characterizes this mode of transport is not the type of molecule but the fact that the molecules are moved against their concentration gradient. Examples include the sodium-potassium pump (Na⁺/K⁺ pump) which maintains cellular ion concentrations.
In summary, while both facilitated diffusion and active transport involve integral membrane proteins, only active transport requires an input of energy. The type of molecule transported can vary across all three mechanisms, but it’s determined by the molecule’s properties and concentration gradients in the case of passive and facilitated diffusion. In contrast, active transport is characterized by movement against the concentration gradient.
- involvement of integral membrane proteins:
- passive diffusion (simple diffusion): does not generally involve integral membrane proteins. Molecules move directly through the lipid bilayer.
- facilitated diffusion: involves integral membrane proteins. These proteins provide channels or carrier mechanisms that allow specific molecules to move across the membrane. GOES FROM HIGH (outside) concentration to LOW (inside)
- active transport: Involves integral membrane proteins known as pumps, which move molecules against their concentration gradients
REQUIREMENT OF CELLULAR ENERGY:
- passive diffusion: does not require energy. Molecules move down their concentration gradient from high to low concentration
- facilitated diffusion: does not require cellular energy. Even though it involves proteins, the molecules still move down their concentration gradient
- active transport: requires energy, usually derived from ATP. This is because molecules often move against their gradient from low to high concentration
TYPES OF MOLECULES MOVED:
- passive diffusion ( simple diffusion): typically non-polar small polar molecules like oxygen, carbon dioxide and some lipids. These molecules can easily pass through the lipid bilayer without assistance
- facilitated diffusion: polar or charged molecules that cannot easily pass through the lipid bilayer by simple diffusion. This includes ions like potassium (k+) or chloride (CL-), and larger molecules like glucose. THEY REQUIRE THE ASSISTANCE OF CHANNEL OR CARRIER PROTEINS.
- ACTIVE TRANSPORT: can transport a variety of molecules, including ions and larger molecules. What characterizes this mode of transport is not the type of molecule but the fact that the molecules are moved against the concentration gradient. Examples include the sodium-potassium pump (Na+/k+), which maintains cellular ion concentrations.
Compare and contrast primary and secondary. active transport
PRIMARY ACTIVE TRANSPORT:
1. energy source: in primary active transport, energy is directly utilized from ATP to transport molecules against their concentration gradient. The energy is often used to change the conformation of the transport protein.
2. Example: The most classic example of primary active transport is the sodium-potassium pump (Na+/K+-ATPase), which moves sodium ions out of the cell and potassium ions into the cell against their concentration gradients.
3. Direct Involvement of ATP: ATP is hydrolyzed directly by the transport protein, which leads to a direct change in the protein’s structure and the movement of substances.
- One Substance Movement: Typically, primary active transport moves only one type of substance at a time, either into or out of the cell.
SECONDARY ACTIVE TRANSPORT:
1. ENERGY SOURCE: Secondary active transport does not directly use ATP. Instead, it relies on the electrochemical gradient created by primary active transport as its energy source.
2. Example: An example is the sodium-glucose cotransporter, which uses the sodium gradient established by the sodium-potassium pump to bring glucose into the cell against its concentration gradient.
3. Indirect Use of ATP: The energy used in secondary active transport is derived indirectly from ATP, used initially by a primary active transport mechanism to create the gradient.
4. Cotransport of Substances: Secondary active transport often involves the movement of two substances simultaneously through a cotransport mechanism (symport or antiport). In symport, both substances move in the same direction, while in antiport, they move in opposite directions.
Contrasts
Energy Utilization: Primary active transport directly uses ATP, while secondary active transport uses the energy from the ionic gradients created by primary active transport.
Types of Molecules Transported: Primary active transport usually works with ions, while secondary active transport can move ions and other molecules like sugars and amino acids.
Reliance on Protein Conformation: While both mechanisms involve a change in protein conformation, primary active transport relies directly on energy from ATP to drive this change.
Number of Substances Moved: Primary often moves one substance, while secondary typically involves the movement of two substances at the same time.
Similarities
Both transport mechanisms move substances against their concentration gradients (from low to high concentration).
Both require specific carrier proteins or transporters embedded in the cell membrane.
Both are critical for maintaining essential cellular functions, such as the regulation of pH, the volume of cells, and the concentration of key metabolites and ions.
