Cell Biology: Cell Membrane
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Questions and Answers

What is the primary function of facilitated diffusion?

  • To allow selective transport of substances with the help of transport proteins (correct)
  • To maintain equilibrium across the cell membrane
  • To move molecules against their concentration gradient
  • To regulate cell growth and division

    • In which direction does the net movement of water molecules occur during osmosis?

  • From an area of higher water potential to an area of lower water potential (correct)
  • Across the cell membrane, regardless of water potential
  • Only through facilitated diffusion
  • From an area of lower water potential to an area of higher water potential

    • What is the primary difference between active transport and passive transport?

  • The type of molecules transported
  • The direction of molecular movement
  • The involvement of transport proteins
  • The requirement of energy expenditure (correct)

    • Which type of transport involves the engulfment of foreign substances from outside the cell to inside the cell?

    <p>Phagocytosis</p> Signup and view all the answers

    What is the primary function of carrier proteins in active transport?

    <p>To selectively transport molecules against their concentration gradient</p> Signup and view all the answers

    In which type of transport is energy required to move molecules from a higher concentration to a lower concentration?

    <p>Active transport</p> Signup and view all the answers

    What is the primary function of vesicles formed during endocytosis?

    <p>To engulf and internalize foreign substances</p> Signup and view all the answers

    Which type of transport is involved in the movement of CO₂ into plant leaves?

    <p>Simple diffusion</p> Signup and view all the answers

    What is the primary function of receptor-mediated endocytosis?

    <p>To facilitate the uptake of specific molecules</p> Signup and view all the answers

    Which type of transport is involved in the movement of amino acids from the intestine to the blood?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What is the main function of the cristae in the inner membrane of mitochondria?

    <p>To increase the surface area for ATP production</p> Signup and view all the answers

    What is the purpose of the proton pumps in lysosomes?

    <p>To maintain a low pH optimal for enzyme activity</p> Signup and view all the answers

    What is the role of mitochondrial DNA?

    <p>To encode some of the proteins essential for mitochondrial function</p> Signup and view all the answers

    What is the primary function of lysosomes?

    <p>To break down macromolecules into smaller components</p> Signup and view all the answers

    What is the purpose of peroxisomes in metabolic processes?

    <p>To detoxify harmful substances and break down fatty acids</p> Signup and view all the answers

    What is the role of peroxisomes in photorespiration?

    <p>To help plants manage excess oxygen and convert glycolate into carbon dioxide</p> Signup and view all the answers

    What is the result of disrupted peroxisome function in genetic disorders like Zellweger syndrome?

    <p>Neurological challenges</p> Signup and view all the answers

    What is the location of the enzymes involved in the citric acid cycle and fatty acid oxidation?

    <p>Matrix of mitochondria</p> Signup and view all the answers

    What is the main function of the Smooth ER?

    <p>Lipid synthesis and detoxification of drugs and toxins</p> Signup and view all the answers

    What is the cis-Golgi Network responsible for?

    <p>Receiving proteins and lipids from the ER</p> Signup and view all the answers

    What is the primary function of Mitochondria?

    <p>Generating ATP through cellular respiration</p> Signup and view all the answers

    What is the outer membrane of Mitochondria like?

    <p>Smooth and covers the entire organelle</p> Signup and view all the answers

    Where is the Golgi apparatus developed from?

    <p>The plasma membrane and the nuclear envelope</p> Signup and view all the answers

    Which organelle is responsible for protein synthesis, folding, and modification?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    What is the trans-Golgi Network responsible for?

    <p>Final processing, sorting, and packaging of molecules</p> Signup and view all the answers

    What is unique about the DNA in Mitochondria?

    <p>It is mitochondrial DNA</p> Signup and view all the answers

    What is the function of flagella in prokaryotic cells?

    <p>Locomotion</p> Signup and view all the answers

    What is a characteristic of eukaryotic cells?

    <p>Possession of a true nucleus</p> Signup and view all the answers

    How do prokaryotic cells reproduce?

    <p>Binary fission</p> Signup and view all the answers

    What contributes to the adaptability and survival of prokaryotic cells?

    <p>Genetic diversity</p> Signup and view all the answers

    What is the function of the nuclear envelope?

    <p>To regulate the movement of molecules</p> Signup and view all the answers

    What is the purpose of the rough endoplasmic reticulum?

    <p>Protein synthesis</p> Signup and view all the answers

    What is the function of the nucleolus?

    <p>RNA synthesis</p> Signup and view all the answers

    What is a characteristic of eukaryotic cells?

    <p>Presence of membrane-bound organelles</p> Signup and view all the answers

    Study Notes

    Cell Membrane

    • The cell membrane is also known as the plasma membrane or plasmalemma, forming the outer protective layer of the cell.
    • It maintains the cell's shape and size, and regulates exchange between the cell's interior and exterior.

    Cell Membrane Structure

    • The cell membrane is very thin (about 10 nm) and pliable.
    • Its main constituents are lipids (40%), proteins (55%), and carbohydrates (5%).
    • Lipids are arranged in a lipid bilayer, with two types: phospholipids and cholesterol.
    • Phospholipids have a phosphate head (hydrophilic) and a lipid tail (hydrophobic), and are freely moving along the plane of the layer, making the membrane fluid.

    Lipid Components

    • Cholesterol molecules are dissolved in the lipid bilayer, controlling the membrane's fluidity.
    • At modest concentrations, cholesterol decreases fluidity, while at high concentrations, it increases fluidity.

    Permeability of Lipid Bilayer

    • The lipid bilayer is semi-permeable, allowing lipid-soluble substances to pass through.
    • Water, water-soluble substances, and large molecules cannot pass through.

    Protein Components

    • Proteins are mostly in the form of glycoproteins.
    • There are two types of membrane proteins: integral membrane proteins (tightly integrated with lipid bilayer) and peripheral membrane proteins (loosely attached to lipids).
    • Membrane proteins serve as transport proteins, allowing passage of water and water-soluble substances.
    • Other functions of membrane proteins include:
      • Receiving signals (receptor proteins)
      • Intracellular signaling (second messenger)
      • Enzyme functions
      • Adhesion molecules for cell attachment or cell-to-cell contact
      • Submembrane cytoskeleton for strength and resilience
      • Antigen functions

    Carbohydrate Components

    • Most carbohydrates are in combination with proteins and lipids in the form of glycoproteins and glycolipids.
    • Carbohydrates are usually found on the outer side of the cell, forming a glycocalyx.
    • Functions of carbohydrates include:
      • Making the outer surface of the cell electronegative
      • Allowing neighbor cells to attach to each other through glycocalyx
      • Involvement in immune reactions

    Cell Membrane Transport

    Passive Transport / Diffusion

    • Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
    • Examples: amino acid movement from intestine to blood, and CO₂ into plant leaves.
    • There are two types of diffusion:
      • Simple diffusion: molecules pass through the concentration gradient in a solution across a semipermeable membrane.
      • Facilitated diffusion: transport of substances with the help of a transport protein molecule.

    Passive Transport / Osmosis

    • Osmosis is the net movement of water molecules through the cell membrane from an area of higher water potential to an area of lower water potential.
    • Examples: absorption in plant roots and small intestine in animals.

    Active Transport / Carrier Protein

    • Active transport is the movement of molecules from low concentration to high concentration, requiring energy.
    • It is carried out by selective protein carriers, such as the sodium-potassium ion pump.

    Active Transport / Vesicular Transport

    • There are two types of vesicular transport:
      • Endocytosis: engulfing foreign substances from outside the cell to inside the cell, requiring energy.
        • Pinocytosis: engulfing small particles or molecules (e.g. protein, Vitamin B12, glycoprotein).
        • Phagocytosis: engulfing large particles or cells (e.g. bacteria, degenerating tissue).
        • Receptor-mediated endocytosis (clathrin-mediated).
      • Exocytosis: expelling material into the extracellular space, such as hormonal secretion by endocrine glands.

    Endoplasmic Reticulum

    • Involved in protein synthesis, folding, and modification
    • Rough ER has ribosomes, involved in protein synthesis
    • Smooth ER lacks ribosomes, involved in lipid synthesis, detoxification, and calcium ion storage
    • ER dysfunction linked to various neurological disorders (e.g., Alzheimer's, multiple sclerosis)

    Golgi Apparatus

    • A stack of flattened membrane sacs called cisternae
    • Involved in processing, sorting, and packaging of proteins and lipids from the ER
    • Has three main regions: cis-Golgi network, medial Golgi, and trans-Golgi network

    Mitochondria

    • Powerhouses of the cell, generating ATP through cellular respiration
    • Double membrane structure with inner membrane folded into cristae, increasing surface area for ATP production
    • Contain their own DNA (mitochondrial DNA)
    • Matrix contains enzymes involved in citric acid cycle and fatty acid oxidation

    Lysosomes

    • Membrane-bound organelles containing digestive enzymes
    • Involved in intracellular digestion and recycling of cellular components
    • Acidic interior optimal for enzyme activity
    • Break down macromolecules into smaller components

    Peroxisomes

    • Involved in fatty acid breakdown, detoxification, and photorespiration in plants
    • Generate hydrogen peroxide, maintaining a delicate balance to prevent cellular damage
    • Dysfunction linked to genetic disorders like Zellweger syndrome

    Eukaryotic Characteristics

    • Possess a true nucleus and membrane-bound organelles
    • Found in plants, animals, fungi, and protists (e.g., paramecium, chlamydia, red algae)
    • More complex than prokaryotic cells

    Nucleus

    • Well-defined nucleus housing genetic material
    • Enclosed by a double membrane (nuclear envelope) with nuclear pores
    • Genetic material organized into linear chromosomes made up of DNA and proteins

    Nucleus Components

    • Nuclear envelope separates nucleus from cytoplasm
    • Nucleoplasm contains chromatin, nucleolus, and proteins involved in DNA replication and RNA processing
    • Chromatin is a complex of DNA, histone proteins, and other proteins that make up chromosomes
    • Nucleolus is a region for rRNA synthesis and ribosome assembly

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    Description

    Learn about the cell membrane, also known as the plasma membrane, which serves as the outer protective layer of a cell. Discover its structure, constituents, and functions.

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