BSC1010C: General Biology 1 - Cell Structure Study Notes

BSC1010C: General Biology 1

CELL STRUCTURE (Chapter 4 B2E) MODULE 4 - PART 1

LEARNING OBJECTIVES

  • Role of Cells in Organisms:

    • Cells serve as the fundamental units of life.

  • Microscopy:

    • Comparison of light microscopy and electron microscopy.

  • Cell Theory:

    • Importance and summary of cell theory.

  • Cell Types:

    • Distinction between prokaryotic and eukaryotic cells.

  • Cell Structure:

    • Detailed structures of prokaryotic and eukaryotic cells.

  • Comparison of Animal and Plant Cells:

  • Understanding Cell Parts:

    • The interrelation of different cell components.

  • Plasma Membrane and Organelles:

    • Functions of the plasma membrane and major organelles.

FUNDAMENTAL UNITS OF LIFE

  • Cells are the building blocks of all organisms.

  • In single-celled organisms, the cell fulfills all life functions.

CELL THEORY

  • The foundational principle of biology formulated by Theodor Schwann, Matthias Schleiden, and Rudolf Virchow:

    1. Cells are the basic units of life.

    2. All living organisms consist of cells.

    3. All cells arise from preexisting cells.

  • It states that all organisms are composed of cells.

  • All cells contain:

    1. Proteins: Perform cellular functions.

    2. Nucleic Acids: Store, transmit, and process information.

    3. Carbohydrates: Provide energy, carbon, structural support, and identity.

    4. Plasma Membrane: A selectively permeable barrier.

    5. Ribosomes: Sites of protein synthesis.

    6. Chromosomes: Structures of nucleic acids that transmit hereditary information.

    7. Cytoplasm: The internal fluid of the cell (cytosol).

TYPES OF CELLS

  • Cells categorized by morphology:

    1. Eukaryotes:

    • Contain a membrane-bound nucleus.

    1. Prokaryotes:

    • Lack a membrane-bound nucleus.

  • Organisms classified into three domains based on phylogeny:

    1. Bacteria: Prokaryotic organisms.

    2. Archaea: Prokaryotic organisms.

    3. Eukarya: Eukaryotic organisms.

TREE OF LIFE

Example Organisms:

  • Bacteria:

    • Includes spirochetes, green filamentous bacteria, and others.

  • Archaea:

    • Includes methanogens, halophiles, etc.

  • Eukaryota:

    • Includes animals, fungi, plants (e.g. Entamoebae, slime molds).

BACTERIAL AND ARCHAEAL CELL STRUCTURES AND THEIR FUNCTIONS

  • Advancements in prokaryotic cell study due to transmission electron microscopy (TEM) reveal complexity.

CELL SIZE VARIATION

  • Most cells are too small to be seen with the naked eye.

  • Microscopes enhance visibility of small cells.

MICROSCOPY

  • Types of Microscopes:

    • Light Microscopes: Use light to focus on specimen.

    • Electron Microscopes: Use electron beams.

    • Types:

      1. Scanning Electron Microscope (SEM): Views surface structures.

      2. Transmission Electron Microscope (TEM): Views internal structure (ultrastructure).

  • Parameters of Microscopy:

    1. Magnification: Ratio of image size to actual size.

    2. Resolution: Clarity; minimum distance where two points are distinguishable.

    • Light microscope resolution: ~200 nm.

    • Electron microscope resolution: ~2 nm.

    • Can image live specimens with light microscopy; fixed specimens with electron microscopy.

DIFFERENCES BETWEEN LIGHT AND ELECTRON MICROSCOPES

Factor

Light Microscope

Electron Microscope

Illuminating source

Light

Beam of electrons

Specimen preparation

Minutes to hours

Days

Live specimens

Yes

No

Resolving power

0.25-0.3 µm

~250 times higher than light microscope

Magnification

500X to 1500X

100,000X to 300,000X

Image color

Colored

Black and White

Specimen treatment

Colored dyes

Coated with heavy metals

EVALUATING CELLS: COMMON COMPONENTS

  1. Plasma Membrane: Encloses the cell’s interior.

  2. Cytoplasm: Composed of cytosol where other components reside.

  3. DNA: Genetic material.

  4. Ribosomes: Synthesize proteins.

PROKARYOTIC CELL STRUCTURES: PARTS LIST

  • Prokaryotic cells possess distinctive structures:

    • At least one chromosome.

    • Numerous ribosomes for protein synthesis.

    • Distinct phospholipid components:

    • Bacterial phospholipids consist of fatty acids bound to glycerol.

    • Archaeal phospholipids consist of branched isoprenoid chains bound to glycerol.

- Cytoplasm: All contents located inside the membrane.

OVERVIEW OF A PROKARYOTIC CELL

  • Key Structures:

    • Plasmid, Ribosomes, Cell Wall, Plasma Membrane, Cytoplasm, Chromosome.

CHARACTERISTICS OF PROKARYOTES

  • Prokaryotes resemble the first cells.

  • Organisms in domains Archaea & Bacteria are classified as prokaryotes.

THE CHROMOSOME IN PROKARYOTES

  • Nucleoid:

    • Chromosome is the most prominent structure within prokaryotic cells consisting of a single circular DNA associated with proteins that provide structural support.

  • Prokaryotic DNA can also exist as supercoiled plasmids.

RIBOSOMES IN PROKARYOTES

  • Ribosomes are macromolecular machines made of RNA and proteins, crucial for protein synthesis.

  • Bacterial and archaeal ribosomes, though similar in size, differ in primary structure of RNA and protein components.

CYTOSKELETON IN PROKARYOTES

  • Prokaryotes contain protein filaments that form the cytoskeleton, fulfilling various roles such as maintaining cell shape and aiding in cell division.

CELL WALL IN PROKARYOTES

  • Prokaryotic cell walls form an exoskeleton and provide structural support.

    • In bacteria, the primary structure consists of peptidoglycan which can include an outer membrane of glycolipids.

PHOTOSYNTHETIC SPECIES IN PROKARYOTES

  • Some prokaryotes possess internal membrane complexes for photosynthesis, which are derived from infoldings of the plasma membrane to increase surface area and contain enzymes and pigments necessary for energy conversion.

SPECIALIZED ORGANELLES IN PROKARYOTIC CELLS

  • Certain bacteria contain internal organelles for specialized functions such as storing calcium ions or concentrating enzymes for organic compound synthesis.

EXTERNAL STRUCTURES FOR MOVEMENT IN PROKARYOTES

  • Structures like flagella and fimbriae on bacterial surfaces facilitate mobility and attachment.

    • Flagella: Long filaments for propulsion.

    • Fimbriae: Needle-like projections for cellular attachment.

SIZE DIFFERENCES IN CELL TYPES

  • Prokaryotic cells generally range from 0.1 to 5.0 μm while eukaryotic cells measure from 10 to 100 μm.

  • The small size of prokaryotes facilitates a favorable surface area to volume ratio for efficient material transport.

FACTORS LIMITING CELL SIZE

  • Cell size is constrained by the surface area-to-volume ratio.

    • As cells grow, volume increases faster than surface area, which decreases the efficiency of material transport.

EUKARYOTIC CELL STRUCTURES AND FUNCTIONS

  • Organelles: Allow compartmentalization within eukaryotic cells, offering advantages such as separating incompatible reactions, increasing efficiency, and maximizing surface area to volume ratio.

EUROKARYOTIC CELL COMPONENTS

Animal Cell Overview:

  • Structures include plasma membrane, extracellular matrix, centrioles, lysosomes, cytoskeletal elements, nucleus, mitochondria, Golgi apparatus, and endoplasmic reticulum types.

  • Eukaryotes can be around 10 times larger in diameter and 1000 times larger in volume than prokaryotes.

STRUCTURE OF THE NUCLEUS

  • The nucleus is a large, organized membrane-bound compartment surrounded by a double membrane nuclear envelope with pore-like openings.

    • Nucleoplasm: Aqueous fluid within the nucleus.

    • Nucleolus: Region for ribosomal RNA synthesis and subunit assembly, non-membrane-bound.

    • Chromosomes: DNA units containing genetic information, composed of chromatin (DNA + proteins).

RIBOSOMES IN EUKARYOTIC CELLS

  • Ribosome Structure: Composed of a large and small subunit, lacks a membrane.

    • Free ribosomes manufacture cytosolic proteins, while bound ribosomes on the endoplasmic reticulum synthesize proteins destined for membranes or export.

ENDOPLASMIC RETICULUM (ER)

  • Comprises a vast membrane-enclosed factory continuous with the nuclear envelope, divided into two regions:

    1. Rough Endoplasmic Reticulum (RER): Studded with ribosomes for protein synthesis, consists of flat membranous sacs (cisternae).

    2. Smooth Endoplasmic Reticulum (SER): Lacks ribosomes, synthesizes lipids, detoxifies, and serves as a reservoir for calcium ions.

GOLGI APPARATUS

  • Comprised of stacked, flat membranous sacs (cisternae); functions in processing, sorting, and shipping proteins synthesized in the RER.

    • Distinct polarity:

    • Cis (nearest nucleus) and Trans (towards membrane) sides.

    • Undergoes cisternal maturation for protein modification throughout movement.

LYSOSOMES

  • Recycling centers exclusive to animal cells, housing around 40 types of hydrolytic enzymes (acid hydrolases) active at pH 5.0.

  • Proton pumps maintain low internal pH critical for enzyme function.

VACUOLES

  • Prominent organelles found in plant and fungal cells, involved in storage, digestion, and recycling.

    • Central Vacuole: Takes up significant volume in plant cells; surrounded by Tonoplast membrane, part of the endomembrane system.

PEROXISOMES

  • Globular organelles in eukaryotic cells originating from ER vesicles loaded with specific enzymes.

  • Catalyze oxidation reactions; specialized plant peroxisomes (glyoxysomes) convert fats to energy-storage compounds, managing toxic byproducts like hydrogen peroxide via catalase.

MITOCHONDRIA

  • Powerhouses of the cell where ATP production occurs.

  • Enclosed by two membranes, the inner one folded into cristae to increase surface area.

  • Mitochondrial Morphology: Dynamic in cells, undergoing fusion and fission.

  • Contain mtDNA and can grow independently.

CHLOROPLASTS

  • Present in plant and algal cells, pivotal for photosynthesis.

  • Composed of three membranes with thylakoids arranged in stacks (grana) and surrounded by stroma where sugar synthesis occurs.

  • Contain their own DNA and ribosomes, grow independently of the cell cycle.

ENDOSYMBIOSIS THEORY

  • Proposed by Lynn Margulis in 1960, suggesting that mitochondria and chloroplasts originated from engulfed free-living bacteria, leading to a mutualistic relationship.

CYTOSKELETON IN EUKARYOTIC CELLS

  • An elaborate system of protein fibers providing structural integrity, stability, and organized transport of materials.

    • Types:

    1. Microfilaments: Support and movement.

    2. Microtubules: Structural framework, involved in transport.

    3. Intermediate Filaments: Provide structural support.

CELL WALL AND EXTRACELLULAR MATRIX

  • Present in fungi, algae, and plants; provides protection and structural support.

  • In animals, the extracellular matrix (ECM) offers support lacking a cell wall, consisting of secreted proteins and polysaccharides.