Cell Biology: Structure and Functions
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Questions and Answers

What is the primary function of organelles within a cell?

  • Facilitate the transportation of materials outside
  • Perform specific functions vital for cell survival (correct)
  • Maintain the structural integrity of the cell
  • Generate energy through cellular respiration

    • Which statement accurately describes the cell membrane?

  • It serves as a selective barrier between the intracellular and extracellular environments. (correct)
  • It is composed solely of proteins and carbohydrates.
  • It is impermeable to any substances.
  • It has a rigid structure that does not allow movement.

    • What property of phospholipids is crucial for cell membrane formation?

  • Amphipathic nature with hydrophilic heads and hydrophobic tails (correct)
  • Presence of multiple layers of phospholipids
  • Hydrophobic nature of the polar head regions
  • Oiliness of the nonpolar tail regions

    • How do small nonpolar molecules like O2 and CO2 pass through the cell membrane?

    <p>Directly through the phospholipid bilayer</p> Signup and view all the answers

    Which substances typically have higher concentrations inside the cell?

    <p>Enzymes and glycogen</p> Signup and view all the answers

    What does the term 'selective permeability' refer to in context of the cell membrane?

    <p>The selective limitation on certain substances entering or exiting the cell</p> Signup and view all the answers

    Which component is NOT found in the structure of the cell membrane?

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

    What roles do transmembrane proteins play in the cell membrane?

    <p>They facilitate the selective transport of certain ions and molecules.</p> Signup and view all the answers

    What are mitochondria primarily responsible for producing?

    <p>ATP through aerobic metabolism</p> Signup and view all the answers

    What is the primary function of the cytoskeleton in a cell?

    <p>Providing internal support and shape</p> Signup and view all the answers

    Which of the following molecules in mitochondria contains mitochondrial DNA?

    <p>The mitochondrial matrix</p> Signup and view all the answers

    What structural component forms the basis of microtubules?

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

    What type of protein structure contributes to muscle cell contraction?

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

    Which type of cytoskeletal element has the largest diameter?

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

    What substance is broken down by enzymes in peroxisomes?

    <p>Hydrogen peroxide</p> Signup and view all the answers

    What distinguishes the inner membrane of mitochondria from the outer membrane?

    <p>It contains folds called cristae.</p> Signup and view all the answers

    What is the primary function of the nucleolus within the nucleus?

    <p>Formation of ribosomal subunits</p> Signup and view all the answers

    During which phase do chromosomes become tightly coiled and visible under a microscope?

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

    What distinguishes rough endoplasmic reticulum (ER) from smooth ER?

    <p>Presence of ribosomes</p> Signup and view all the answers

    What type of vesicles are formed by the Golgi apparatus?

    <p>Secretory vesicles and lysosomes</p> Signup and view all the answers

    Lysosomes serve primarily as what type of system within the cell?

    <p>Intracellular digestion system</p> Signup and view all the answers

    What do peroxisomes primarily break down within the cell?

    <p>Fatty acids and hydrogen peroxide</p> Signup and view all the answers

    Which of the following statements is true regarding ribosomes?

    <p>They can be free or bound to other organelles.</p> Signup and view all the answers

    What is one of the functions of the smooth endoplasmic reticulum?

    <p>Storage of calcium ions</p> Signup and view all the answers

    What is the role of centrioles in a cell?

    <p>They assist in the process of mitosis.</p> Signup and view all the answers

    What is the primary component that makes up the structure of DNA?

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

    Which nitrogenous base is found in RNA but not in DNA?

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

    Where does transcription occur in the cell?

    <p>In the nucleus</p> Signup and view all the answers

    What connects the two strands of a DNA molecule?

    <p>Hydrogen bonds between bases</p> Signup and view all the answers

    During the process of gene expression, which step involves the creation of mRNA?

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

    Which of the following best describes keratin?

    <p>An intermediate filament protein</p> Signup and view all the answers

    What are the products of transcription?

    <p>mRNA and tRNA</p> Signup and view all the answers

    What is the primary outcome of mitosis?

    <p>Formation of two daughter cells</p> Signup and view all the answers

    During which phase of mitosis do the chromosomes become organized into two separate nuclei?

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

    What is the role of spindle fibers during mitosis?

    <p>To move chromosomes to opposite sides of the cell</p> Signup and view all the answers

    What term describes the process by which cells develop specialized structures and functions?

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

    What is apoptosis commonly referred to as?

    <p>Programmed cell death</p> Signup and view all the answers

    What phenomenon occurs during the differentiation of a cell?

    <p>Some portions of DNA are inactive</p> Signup and view all the answers

    Which factor is NOT a cause of cellular aging?

    <p>Increased mitotic divisions</p> Signup and view all the answers

    What defines a tumor in biological terms?

    <p>An abnormal proliferation of cells</p> Signup and view all the answers

    Study Notes

    ### Cell Structure

    • Specialized structures within cells that perform specific functions are called organelles
    • Examples of organelles: nucleus, mitochondria, Golgi apparatus
    • Jelly-like substance that holds organelles is called cytoplasm
    • The cell membrane (plasma membrane) encloses the cytoplasm.

    Functions of the Cell

    • The smallest units of life
    • Cell metabolism and energy use
    • Synthesis of molecules
    • Communication
    • Reproduction and inheritance

    Cell Membrane

    • The outermost component of a cell
    • Forms a boundary between materials inside and outside the cell.
    • Intracellular: refers to materials inside the cell.
    • Extracellular: refers to materials outside the cell
    • Acts as a selective barrier regulating what enters and exits the cell.

    Cell Membrane Structure

    • Described by the fluid-mosaic model.
    • Composed of phospholipids, cholesterol, proteins, and carbohydrates.
    • Phospholipids form a bilayer.
    • Each phospholipid has two regions: a polar head and a nonpolar tail.
    • The polar head is hydrophilic (attracted to water) and faces the water surrounding the membrane.
    • The nonpolar tail is hydrophobic (repels water) and faces the interior of the membrane.

    Movement through the Cell Membrane

    • The cell membrane exhibits selective permeability, allowing only certain substances to pass through.
    • Enzymes, glycogen, and potassium are found in higher concentrations inside the cell.
    • Sodium, calcium, and chloride are found in higher concentrations outside the cell.

    Cell Membrane Passage

    • Some substances, like oxygen (O2) and carbon dioxide (CO2), can pass directly through the cell membrane's phospholipid bilayer.
    • Other substances require transmembrane protein channels for passage, such as sodium ions (Na+) moving through their specific channels.
    • The route of transport (direct or channel mediated) depends on the size, shape, and charge of the substance.

    Cell Nucleus

    • Contains nucleoli, which are bodies without surrounding membranes.
    • One to several nucleoli are typically present in the nucleus.
    • The subunits of ribosomes, a type of cytoplasmic organelle, are formed within a nucleolus.
    • Ribosomal components exit the nucleus through nuclear pores

    Cell Nucleus

    • Human cell nuclei contain 23 pairs of chromosomes composed of DNA and proteins.
    • During most of a cell's life, chromosomes are loosely coiled and collectively called chromatin.
    • When a cell prepares to divide, chromosomes become more tightly coiled and visible under a microscope.

    Ribosomes

    • Components are produced in the nucleolus.
    • Organelles where proteins are produced.
    • Can be attached to other organelles, such as the endoplasmic reticulum (ER).
    • Free ribosomes are not attached to any other organelle

    Endoplasmic Reticulum (ER)

    • A series of membranes forming sacs and tubules that extend from the outer nuclear membrane into the cytoplasm.
    • Rough ER is involved in protein synthesis and has attached ribosomes, giving it a rough appearance.
    • Smooth ER has no attached ribosomes and plays a role in lipid synthesis, cellular detoxification, and calcium ion storage in skeletal muscle cells.

    Golgi Apparatus

    • Also called the Golgi complex.
    • Consists of closely packed stacks of curved, membrane-bound sacs.
    • Collects, modifies, packages, and distributes proteins and lipids manufactured by the ER.
    • Forms vesicles, including secretory vesicles, lysosomes, and other vesicles.

    Lysosomes

    • Membrane-bound vesicles formed from the Golgi apparatus.
    • Contain various enzymes that function as intracellular digestive systems
    • Vesicles formed by endocytosis (taking in material from outside the cell) may fuse with lysosomes to break down materials within those vesicles.
    • Example: White blood cells engulfing (phagocytizing) bacteria.

    Peroxisomes

    • Small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2).
    • Hydrogen peroxide is toxic to cells, but peroxisome enzymes break it down.

    Mitochondria

    • Small organelles responsible for producing a significant amount of ATP (energy) through aerobic (with oxygen) metabolism.
    • Have inner and outer membranes separated by a space.
    • The outer membrane has a smooth contour, while the inner membrane has numerous folds called cristae projecting into the interior.
    • The space within the inner membrane is the mitochondrial matrix, containing enzymes and mitochondrial DNA (mtDNA).
    • Cells with a high energy requirement have more mitochondria than cells with lower energy needs.

    The Cytoskeleton

    • Provides an internal framework for the cell.
    • Composed of protein structures that support the cell, hold organelles in place, and enable cell shape changes.
    • These protein structures include microtubules, microfilaments, and intermediate filaments.

    Microtubules

    • Hollow structures formed from protein subunits.
    • Play various roles:
    • Support the cytoplasm of cells.
    • Assist in cell division.
    • Form essential components of certain organelles, such as cilia and flagella.

    Microfilaments

    • Small fibrils formed from protein subunits.
    • Structurally support the cytoplasm, determining cell shape.
    • Microfilaments in muscle cells enable contraction or shortening.

    Intermediate Filaments

    • Fibrils formed from protein subunits, smaller in diameter than microtubules but larger than microfilaments.
    • Provide mechanical support to the cell
    • Example: Keratin, a protein associated with skin cells.

    Centrioles

    • The centrosome is a specialized area of cytoplasm near the nucleus where microtubule formation occurs.
    • Contains two centrioles, typically oriented perpendicular to each other.
    • Each centriole is a small, cylindrical organelle composed of microtubules.
    • Involved in the process of mitosis (cell division).

    Cell Activity

    • A cell's characteristics are determined by the proteins it produces.
    • The proteins produced are dictated by the genetic information in the nucleus.
    • Information in DNA provides the cell with instructions for its cellular processes.

    DNA

    • Contains the information that directs protein synthesis, a process called gene expression.
    • A DNA molecule consists of nucleotides joined together to form two nucleotide strands.
    • The strands are connected and resemble a twisted ladder.
    • Each nucleotide consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

    DNA

    • Each nucleotide on one strand pairs specifically with another nucleotide on the opposite strand.
    • A gene is a sequence of nucleotides providing instructions for making a specific protein.

    Gene Expression

    • Gene expression, which is protein synthesis, involves transcription and translation.
    • Transcription is copying DNA into messenger RNA (mRNA).
    • Translation is using mRNA to produce a protein.

    Transcription

    • Occurs in the cell's nucleus.
    • DNA (template) determines the structure of mRNA through transcription.
    • The double strands of a DNA segment separate, and DNA nucleotides pair with RNA nucleotides forming the mRNA.
    • DNA contains thymine, adenine, cytosine, or guanine.
    • mRNA contains uracil, adenine, cytosine, or guanine.
    • DNA's thymine pairs with RNA's adenine.

    Mitosis

    • Involves the formation of two daughter cells from a single parent cell
    • Divided into four phases: prophase, metaphase, anaphase, and telophase

    Prophase

    • Chromatin condenses to form visible chromosomes.
    • Microtubules, termed spindle fibers, form to assist in breaking the centromere between chromatids and move chromosomes to opposite sides of the cell.
    • The nuclear membrane dissolves.

    Metaphase

    • Chromosomes align near the center of the cell.
    • Movement of chromosomes is regulated by the attached spindle fibers.

    Anaphase

    • Chromatids separate, and each is now called a chromosome.
    • Spindle fibers move the two sets of 46 chromosomes towards the centrioles at opposite cell poles.
    • Cytoplasm begins to divide.

    Telophase

    • Chromosomes in each daughter cell become organized into two separate nuclei, one in each newly formed cell.
    • Chromosomes unravel and resemble genetic material during interphase.
    • Cytoplasmic division is completed, producing two separate daughter cells.

    The Cell Cycle

    • A continuous process of cell growth and division.

    Differentiation

    • A sperm cell and an oocyte unite to form a single cell.
    • Many mitotic divisions occur to give rise to the trillions of cells of the body.
    • The process of cells developing specialized structures and functions is called differentiation.
    • During this process, some portions of DNA become active, while others become inactive.

    Apoptosis

    • Programmed cell death.
    • A normal process adjusting and controlling cell numbers in tissues.
    • Removes extra tissue during fetal development, such as between developing fingers and toes.
    • Eliminates excess cells in certain adult tissues to maintain constant cell numbers.

    Cellular Aspects of Aging

    • Various causes of cellular aging include:
    • Existence of a cellular clock
    • Presence of death genes
    • DNA damage
    • Formation of free radicals
    • Mitochondrial damage

    Tumors

    • Abnormal proliferations of cells

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    Description

    Explore the fascinating world of cell biology with this quiz focused on cell structure, functions, and the intricacies of the cell membrane. Learn about organelles, cell metabolism, and the fluid-mosaic model. Test your knowledge of the smallest units of life and their critical roles.

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