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Questions and Answers
What structure forms the basis of the cell membrane?
What type of molecules are phospholipids classified as?
Which type of ion channel requires a signaling molecule to open?
What is the role of carrier proteins in the cell membrane?
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What type of transport is exemplified by the NA+-K+ pump?
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Which of the following best describes gated ion channels?
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What type of lipids form the primary structure of the cell membrane?
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What distinguishes ungated channels from gated channels?
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What is facilitated diffusion primarily characterized by?
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In which type of transport does a vesicle eject out substances?
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What percentage of the body weight of a hypothetical adult female is composed of water?
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What is the primary component of extracellular fluid?
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Which feedback mechanism inhibits a function to maintain homeostasis?
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Which form of transport can occur with the aid of carrier proteins but does not require energy?
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What defines intracellular fluid?
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How is homeostasis primarily regulated in the body?
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Study Notes
Cell Membrane
- The cell membrane is a selectively permeable barrier between the cytoplasm and the external environment.
- It plays a dynamic role in cellular activity.
- Composed of a trilaminar structure (bi-lipid layers with an intermediate clear thin layer).
- Double Layered (bi-layer) of lipids with imbedded proteins.
- The bi-layer consists of phospholipids, cholesterol, and glycolipids.
- Glycolipids are lipids with bound carbohydrates.
- Phospholipids have hydrophobic and hydrophilic portions.
- The phospholipid molecule of the lipid bilayer is composed of a polar head, located at the surface of the membrane, and two long nonpolar tails projecting into the center of the plasmalemma.
- Because the phospholipid molecule is composed of a hydrophilic head and a hydrophobic tail, the molecule is said to be amphipathic.
- Philic = Love
- Phobic = Hate
Transmembrane Proteins
- Transmembrane proteins form channel proteins and carrier proteins.
- Channel proteins participate in the formation of hydrophilic pores, called ion channels.
- The hydrophobic amino acids are positioned peripherally.
- Most channels are gated channels; only a few are ungated.
- Gated channels are classified according to the control mechanism required to open the gate.
- Voltage-Gated Channels: The most common example is during the transmission of nerve impulses, such as Na+ channels.
- Ligand-Gated Channels: Channels that require the binding of a ligand (signaling molecule) to the channel protein to open their gate.
- G-Protein-Gated Ion Channels: Channels require the interaction between a receptor molecule and a G-protein complex with the resultant the activated G protein interacts with the channel protein to open or close it.
- Ungated Channels: Like potassium (K+) channel and these types of channels not under the cell's control.
- Carrier Proteins: Primary Active Transport “NA+- K+ Pump” and Secondary Active Transport “NA+- Glucose”.
- Carrier proteins are multipass membrane transport proteins, when a solute binds to the binding site, the carrier protein undergoes reversible conformational changes; as the molecule is released on the other side of the membrane, the carrier protein returns to its previous conformation.
Passive and Active Transport Across the Cell Membrane
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Facilitated Diffusion:
- Carrier mediated transport: can be passive or active
- Uniport: Carries one molecule at a time in one direction
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Cotransport: Carries two molecules at a time
- Symport: Carries both molecules in the same direction
- Antiport: Carries two molecules in opposite directions
- Active transport: Requires energy to move molecules against the concentration gradient
- Simple Diffusion: Movement of molecules from an area of high concentration to low concentration.
- Facilitated Diffusion: Movement of molecules across a membrane with the help of a carrier protein.
- Active Transport: Movement of molecules across a membrane against their concentration gradient, requiring energy.
- Osmosis: Movement of water across a semipermeable membrane from a region of high water concentration to a region of low water concentration.
Cell/Material Movement
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Large objects:
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Endocytosis: Taking in substances from the external environment
- Phagocytosis: Cell engulfs large particles
- Pinocytosis: Cell engulfs fluid
- Exocytosis: Ejecting out substances from the cell (secretion - wastes) by vesicles.
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Endocytosis: Taking in substances from the external environment
Body Water
- The 70 kg 'standard male' contains 42 liters of water - 60% of his body weight.
- The hypothetical adult female contains 55% of her body weight as water: this lower percent being due to a higher fat content.
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Variations in Water Content:
- Variation due to Age (Neonates contain more water then adults: 75-80% water)
- Variation between Tissues (Plasma: 93% water, Fat: 10-15% water and Bone: 20% water)
- Variation between Individuals
Compartments
- The water in the body is distributed in 2 compartments.
- The major division is into Intracellular Fluid (ICF: about 23 liters; 55%) and Extracellular Fluid (ECF: about 19 liters; 45%) based on which side of the cell membrane the fluid lies.
- Intracellular fluid (ICF): the fluid (water) present inside the cell.
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Extracellular fluid (ECF): the fluid present outside the cell.
- Interstitial fluid (ISF): present between cells.
- Intravascular fluid (plasma): present inside the blood vessels.
Homeostasis
- Definition: Keeping the internal environment of the body (ECF) constant [Volume (water content) / Ions concentration / Temperature / PH] to make it optimum for cellular function.
- Homeostasis is regulated by rapid control systems (nervous system) and slow control systems (endocrine system) as homeostatic control systems.
Feedback Control in Homeostasis
- Negative feedback: The resultant effect of a function inhibits that function (Negative feedback mechanisms consist of reducing the output or activity of any organ or system back to its normal range of functioning).
- Positive feedback: The resultant effect of a function stimulates that function. One example is the onset of contractions in childbirth.
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Description
This quiz covers the structure and function of the cell membrane, emphasizing its selectively permeable nature and the composition of phospholipids and proteins. It also explores the roles of transmembrane proteins in cellular activities. Test your knowledge on these foundational concepts in cell biology.
