Themes and Concepts of Biology

Chapter 3 | Cell Structure and Function

• Figure 3.1 shows nasal sinus cells, onion cells, and Vibrio tasmaniensis bacterial cells all share basic cell structure characteristics, despite coming from different organisms.

Introduction

• The body consists of many cell types, each specialized for a specific function.

Microscopy

• Cells vary in size, and microscopes are essential for studying them due to their small size.
• Most cell images are taken with a microscope and are called micrographs.

Light Microscopes

• A typical human red blood cell is about eight micrometers in diameter.
• Approximately 250 red blood cells could fit on the head of a pin.
• The lenses of a light microscope alter the image orientation, inverting and reversing the image.
• Microscopes use two sets of lenses to magnify the image.
• Student light microscopes can magnify up to 400 times.
• Key microscopy parameters include magnification and resolving power.
  • Magnification constitutes the degree of enlargement,
  • Resolving power signifies the ability to distinguish adjacent structures as separate entities to improve image clarity and detail.
• With oil immersion lenses, magnification increases to 1,000 times. Samples must be thin or translucent for light to pass through in light microscopy.
• Dissecting microscopes offer lower magnification (20-80x) than light microscopes and provide a three-dimensional view.
• Dissecting microscopes are binocular for each eye, and have optics that correct the image.

Electron Microscopes

• Electron microscopes use electron beams for higher magnification and resolving power.
• Electron microscope sample preparation kills the specimen making it impossible to view live cells.
• The electron beam's vacuum requirement also prevents viewing living materials.
• Scanning electron microscopy (SEM) involves scanning across a cell's surface, where cells are coated with metal, to provide details on cell surface characteristics by reflection.
• Transmission electron microscopy (TEM) transmits the electron beam gives insight into a cell's internal structures.
• Electron microscopes are more expensive than light microscopes.

Careers in Action: Cytotechnologist

• Cytotechnologists examine stained cells for changes indicating cancer or microbial infections in medical labs, and determine if cellular changes are normal or abnormal.
• Cytotechnologists examine cellular specimens from all organs and consult with pathologists upon noticing abnormalitites.
• Early discovery of abnormalities by cytotechnologists increases treatment and successful treatment chances.
• An example of a test is called a Pap smear, in which a doctor takes a small sample of cells from the uterine cervix of a patient and sends it to a medical lab where a cytotechnologist stains the cells and examines them for any changes that could indicate cervical cancer or a microbial infection.

Cell Theory

• Antony van Leeuwenhoek observed protist movements to view cells under a microscope.
• Robert Hooke coined the term "cell" for box-like structures when viewing tissue through a lens.
• The unified cell theory which states that:
  • all living things are composed of one or more cells
  • the cell is the basic unit of life
  • all new cells arise from existing cells, applies today.

Comparing Prokaryotic and Eukaryotic Cells

• Cells fall into prokaryotic and eukaryotic categories.
  • Prokaryotes comprise Bacteria and Archaea domains which makes organisms predominantly single-celled.
  • Eukaryotes include animal, plant, fungi, and protist cells which make up true cells.

Components of Prokaryotic Cells

• All cells share four components:
  • Plasma membrane
  • Cytoplasm
  • DNA
  • Ribosomes
• Prokaryotic cells are simple, unicellular organisms lacking a nucleus or membrane-bound organelles.
• Prokaryotic DNA resides in a central darkened region called the nucleoid.
• Bacteria unlike Archaea and eukaryotes have peptidoglycan.
• The polysaccharide capsule enables the cell to attach to surfaces.
• Some prokaryotes have:
  • Flagella for locomotion
  • Pili to exchange genetic material during conjugation.

Eukaryotic Cells

• Eukaryotic cells have a membrane-bound nucleus and organelles.
• "Form follows function" means that structure can give clues to function which is apparent at all levels, including the level of the cell.
• Eukaryotic cells are 10-100 µm in diameter versus prokaryotic cells which are 0.1-5.0 µm.
• The small size of prokaryotes allows efficient ion and molecule spread.
• Larger eukaryotic cells require structural adaptations for cellular transport.
• Cell size is limited by the need for sufficient material acquisition relative to their surface area.

Eukaryotic Cells

• Eukaryotic cells have organelles that allow various functions to occur in the cell at the same time.
• Two important components include the plasma membrane and the cytoplasm.

The Plasma Membrane

• Eukaryotic cells contain similar plasma membranes as prokaryotic cells.
• Consists of a phospholipid bilayer with embedded proteins that separates cell contents from the external environment where a phospholipid contains:
  • Two fatty acid chains
  • Glycerol backbone
  • Phosphate group
• The plasma membrane regulates substance passage and maintains internal conditions through active transport..
• Cells specializing in absorption have microvilli, or fingerlike projections, that increase surface area.
• People with celiac disease have damaged microvilli and individuals cannot absorb nutrients as a result and must follow a gluten-free diet.

The Cytoplasm

• The cytoplasm constitutes the cell between the plasma membrane and the nuclear envelope.
• It contains:
  • Organelles in gel-like cytosol
  • The cytoskeleton
  • Various chemicals
• Cytoplasm having 70 to 80 percent water gives it a semi-solid consistency.
• The cytoplasm contains:
  • Glucose
  • Simple Sugars
  • Polysaccharides
  • Amino Acids
  • Nucleic Acids
  • Fatty Acids
  • Derivatives of Glycerol
  • Ions of Sodium -Postassium -Calcium
• Metabolic reactions, which take place in the cytoplasm, include protein synthesis.

The Cytoskeleton

• Within the cytoplasm exists ions, organic molecules, and a protein fiber network called the cytoskeleton that:
  • Maintains cell shape
  • Secures organelle positioning
  • Moves cytoplasm and vesicles
  • Enables unicellular organism movement
• There are three cytoskeleton fiber types:
  • Microfilaments (actin filaments) are the thinnest that enables cellular component movement, maintain microvilli structure, and cause muscle cell contraction.
  • Intermediate filaments have structural shape, anchor organelles, and strengthen hair and nails with keratin.
  • Microtubules, being the thickest elements, dissolve and reform quickly to allow organelle movement, pull chromosomes during cell division, and form flagella and cilia structural components as a circle of nine double microtubules and two in the center.
• Centrosomes organize microtubules near the animal cell nucleus, containing two perpendicular centrioles which replicate before cell division to pull chromosomes.
• Flagella refers to long, hair-like structures that move an entire cell.
  • A cell has one or few flagella used to move cells, like sperm / Euglena .
• Cilia include short, hair-like structures to move entire cells and substances along plasma membrane.
  • The epithelia lining and cells lining the respiratory tract.

The Endomembrane System

• The endomembrane system consists of the following:
  • Nuclear envelope
  • Lysosomes
  • Vesicles
  • Endoplasmic reticulum
  • Golgi apparatus
• These membranes function together to modify, package, and transport lipids / proteins with the plasma membrane included due to its interactions elsewhere in organelles.

The Nucleus

• The nucleus is the most prominent cell organelle, containing DNA in chromatin form and directs ribosome / protein synthesis.
• The nuclear envelope which makes us the outermost parts of the nucleus, consists of two phospholipid bilayers, inner and outer membranes, and includes pores to control molecule passage. Chromosomes which are visible when the cell prepares to and during the process of divide contains DNA and proteins called chromatin.
• The nucleolus stains darkly and codes for ribosomal RNA.

The Endoplasmic Reticulum

• The endoplasmic reticulum (ER) includes interconnected tubules modifying proteins and synthesize lipids.
• The hollow ER tubule portion is the lumen (cisternal space) where the membrane is phospholipid bilayer with proteins and connects to the nuclear envelope.
• Ribosomes give the rough endoplasmic reticulum (RER) so named this structure in order to synthesize proteins The lumen receives proteins for modification/ folding while also creating phospholipids for cell membranes.
• Vesicles transport non-RER destined phospholipids or modified proteins.
• The RER helps secreted proteins and resides abundantly in the liver.
• The smooth endoplasmic reticulum (SER) continuous with the RER but contains very few ribosomes, creates carbohydrates, lipids, and steroid hormones, detoxifies medications/poisons, metabolizes alcohol, and stores calcium ions.

The Golgi Apparatus

• Vesicles bud from the ER for sorting, packaging, and distribution of lipids / proteins in a process that happens in the Golgi apparatus which have flattened membrane sacs with a receiving cis face near the ER and a releasing trans face away from the ER toward the cell membrane.
• Transport vesicles from the ER fuse to empty contents and modifies traveling proteins/lipids where adding of sugar molecule chains stands as the most frequent change.
• Newly modified proteins and lipids are tagged with small molecular groups for proper destination routing that get packaged into transport vesicles.
• Amount of Golgi in different cell types suggests that they function in cells engages in secretion in the salivary glands, digestive enzymes, and immune system.

Lysosomes

• Animal cells contain lysosomes that serve as the cells garbage disposal.
• These digestive enzymes use the breakdown of proteins, polysaccharides, lipids, nucleic acids, and worn-out organelles in single-celled eukaryotes.
• They are in the form of enzymes that function at low acidic pH.
• There hydrolytic enzymes serve to destroy foreign organisms such part in body's immune system: Macrophages, or white blood cells, which digest pathogens through phagocytosis.

Vesicles and Vacuoles

• Vesicles and vacuoles have a function for transport or storage and contain membrane-bound sacs.
• Vacuoles are larger than vesicles and lack vacuoles from membranes to other compartments.
• Enzymes in plant vacuoles break down macromolecules.

Ribosomes

• Ribosomes which are found in nearly every cells and appear smaller in prokaryotic cells make up both structure inside cells, responsible for protein synthesis.
• Are found attached to the cytoplasmic side of the plasma membrane.
• Ribosomes are enzyme complexes and have large and smal subunits, crucial are protein synthesis.
• Immature red blood cells have abundant stores of transport hemoglobin.

Mitochondria

• Singular of mitochondria represent called powerhouses / energy factories.
• Mitochondria is responsible for making adenosine triphosphate known are ATP which is its cellular version of energy made from glucouse known are ATP.
• Mitochondria contain ribosomes and oval-shaped, membrane-bound organelles with ribosomes and their own separate DNA.
• A phospholipid bilayer has each membrane embedded with cristae and the folds have different cellular functions. Muscle cells need plenty of energy as a theme of our function from this form.

Peroxisomes

• Peroxisomes is have single membranes and are known are carriers of small/round organelles that are the closure that form by reactions that break organic acids along with amino acids.
• Alchol is detoxified and comes with the result of hydrogen peroxide is produced within perox.
• Peroxide is safely broken down by H2.

Animal Cells versus Plant Cells

• Plants don't have the same components, but cells have different structures such are walls for plant cells, plastic and large central vacuoles.

The Cell Wall

• The cell wall has a rigid covering and protects the plant cell while providing shapes. Fungal cells consist of cell walls and the element is made from non rigid components as chitin of polysaccharide which have glucose.

Chloroplasts

• Chloroplasts have DNA ribosomes like mitochondria cells and photosyntesize for eukaryotic cells.
• Photosynsethesis, water and light energy are used for glucose and oxygen to make organic compounds our food source.
• Outer/ inner are used in the enclosed chloroplast.
• Grana is also part of fluid enclosing.

Endosymbiosis

• Mitochondria and chloroplasts make endosymbiosis to provide clear indication of a connection in which two separate species in organisms share mutual close adaptations in terms of beneficial relationship.
• Endosymbiotic relationship occurs the process of an organism existing inside cell by getting food.
• Endosymbiotes which produce the vitamin K and get food.

The Central Vacuole

• The central vacuole exist within the cell to change conditions of water in plants that has a liquid which will add an additional of water to the force and it will wilt if not watered.

Extracellular Matrix of Animal Cells

• Extracellular matrixes is the matrix that is not holding cells in each tissue it is also communicating for function.

Intercellular Junctions

• Junctions have difference of contacting and that has various forms such are gap, plasmodesmata, junctions and desosomes. Plasmodal Junctions have transport with them within the cell that transfers cell energy.

3.4 | The Cell Membrane

• A cell’s plasma membrane defines the boundary of the cell and determines the nature of its contact with the environment.
• The plasma membrane also carries receptors, receptor also has the function to provide changes for interior and energy for cell to have enough power.
• Some recognition sites are used by viruses as attachment points.
• The fluid mosaic model, a proposed new model of the plasma membrane better explained microscopic observations, as a mosaic of flow and structure of materials, while maintaining the basic integrity of the membrane

Fluid Mosaic Model

• S. J. Singer and Garth L. Nicolson proposed the fluid mosaic model to show:
  • Phospholipds
  • Cholestoral
  • Carbohydrates
  • All the membranes components
• Plasma membranes have cholesterol and the amount depends are environment weather.

3.5 | Passive Transport

• Plasma membranes must allow certain substances to enter and leave a cell, passively and selectively.
• Different concentrations in different areas are a form of potential energy, and diffusion is the dissipation of that potential energy as materials move down their concentration gradients.
• Some ions need means of penetrating membranes while amino acids are sugar and needed for transport.

Facilitated Transport

• In facilitated transport, also called facilitated diffusion, material moves across the plasma membrane with the assistance of transmembrane protein.
• Polar substances are made by proteins, and it creates substances for protein membrane surface in the interior.
• In particular substances it facilitates passage and creates help that are specifically for integral proteins, by membrane creation.

Osmosis

• Osmosis is the diffusion of water through a semipermeable membrane according to the concentration gradient of water and transports is only limited into water diffusion that are all in special.
• A principle of diffusion molecules move around evenly, while diffusing, water crosses and follows direction of cell's area.

Tonicity

• Tonicity show the amount concentration and the total in specific solutes to determine water with terms -Hypotonic:
  • Hypertonic
  • Istontonic

Active Transport

• Active transport mechanisms require the direct use of ATP to fuel the transport and electrochemical gradients .

Electrochemical Gradient

• There is a movement of electrochemical gradient and they are all in living cells such are charge to the membrane including potassium.

Moving Against a Gradient

• To move substances and requires metabolism for energy. The small membranes come from passive changes.

Andocytosis

• Endoytosis is a transport of movement known from the cell that varies but the invadation comes as particle for cell. Variations include phagocytosis, the ingestion of large particles by cell. In pinocytosis, the cell ingests small amount extracellular fluid. Receptor-mediated endocytosis involves specifically binding molecules to the plasma membrane.