Cell Structure and Cellular Process

MPharm Programme - Cell Science

• Course title: Cell Science - Introduction to Cellular Structure 1 & 2
• Lecturer: Dr Praveen Bhugra
• Course code: PHA115

Learning Objectives

• Students will be able to explain cell theory in detail
• Students will be able to detail stem cells
• Students will be able to differentiate between prokaryotic and eukaryotic cells
• Students will be able to differentiate between plant cell, animal cell and bacteria
• Students will be able to explain the structure and function of the three main parts of a cell (plasma membrane, cytoplasm & nucleus)

Cells Theory

• Cells are the building blocks of all plants and animals
• All cells come from the division of pre-existing cells
• Cells are the smallest units that perform all vital physiological functions.
• Each cell maintains homeostasis at the cellular level

Cells in the human body

• All body parts are made up of cells
• An estimated 3.72 x 10^13 cells in the human body
• There is no such thing as a typical cell
• The human body has many different types of cells - over 200 + 20 different organelles
• Chemical and structural features are shared by most cells

Diversity of Human Cells

• Adult humans consist of more than 200 different types of cells
• These types include nerve, muscle, skin, blood (red, monocytes, lymphocytes), bone, and cartilage cells
• Cells essential for embryonic development but not incorporated into the embryo's body include extra-embryonic tissues, placenta, and umbilical cord.
• These cells all derive from a single totipotent cell, the zygote

Diversity of Human Cells Examples

• Epithelial cells are cells that form linings or transport gases
• Fibroblasts connect body parts
• Erythrocytes are red blood cells
• Nerve cells gather information and control body functions
• Muscle cells move organs
• Macrophages fight disease
• Fat cells store nutrients
• Sperm is cells of reproduction

Stem Cells

• Stem cells are undifferentiated biological cells that can differentiate into specialized cells and divide further through mitosis to produce more stem cells
• In mammals, there are two broad types of stem cells:
  • Embryonic stem cells which are isolated from the inner cell mass of blastocysts
  • Adult stem cells which are found in various tissues
• In a developing embryo, stem cells can differentiate into all the specialized cells - ectoderm, endoderm, and mesoderm. These layers give rise to all the body tissues and organs

Stem cells potency

• Totipotent stem cells can differentiate into embryonic and extraembryonic cell types and form a complete, viable organism
• These cells result from an egg and sperm cell fusion
• Pluripotent stem cells are descendants of totipotent cells and can differentiate into nearly all cell types derived from any of the three germ layers
• Multipotent stem cells differentiate into a number of cell types, but only those in a related family (e.g. lymphoid or myeloid stem cells),
• Unipotent cells can produce only one cell type and have the property of self-renewal, which distinguishes them from non-stem cells

Stem cell division and differentiation

• Steps in stem cell division and differentiation
  • Symmetric division of a stem cell produces two identical stem cells
  • Asymmetric division of a stem cell produces one stem cell and one progenitor cell that can differentiate
  • Progenitor cells divide and differentiate into specialized cells

Potential uses of stem cells

• Potential therapeutic applications:
  • Stroke
  • Traumatic Brain Injury
  • Learning defects
  • Alzheimer's Disease
  • Parkinson's Disease, and more.
  • Bone marrow transplantation
  • Spinal cord injury
  • Osteoarthritis and rheumatoid arthritis.
  • Crohn's disease
• Potential uses include treating muscle dystrophy, diabetes, and many types of cancer.

Stem cell potency and source development

• Totipotent embryonic stem cells can become an entire organism
  • Human embryonic stem cells = harmonic
• Pluripotent embryonic stem cells can become an entire organism
  • Some give rise to blood cells
• Multipotent stem cells can become many cells of one type
  • Example adult bone marrow, skin, and deciduous teeth (baby teeth)

Hierarchy of haematopoiesis differentiation

• Diagram showing lineage of differentiation A lineage diagram illustrating stem cells leading to progenitor cells and mature cells
• Illustrates haemopoiesis, the process that gives rise to blood cells and platelets

Characteristics of all cell types

• All types of cells have a surrounding membrane, protoplasm, organelles and a control centre with DNA
• Two major categories of cells include prokaryotic and eukaryotic

Prokaryotic Cells

• Lack a nucleus or membrane-bound organelles
• Simplest cell type
• Single circular chromosome
• Nucleoid region (central)
• Surrounded by cell membrane and a cell wall (peptidoglycan)
• Contain ribosomes in their cytoplasm to make proteins
• Examples: Bacteria

Prokaryotic Cells (Bacteria)

• Cell walls protect the cell and maintain cell shape

• Bacterial cell walls are composed of peptidoglycan

• Archaean cell walls lack peptidoglycan

• Flagella are present in some prokaryotic cells and are used for locomotion and rotary motion

• Gram-positive bacteria: thick peptidoglycan layer, stains purple, high susceptibility to penicillin.

• Gram-negative bacteria: thinner peptidoglycan layer, stains pink, low susceptibility to penicillin

Eukaryotic Cells

• Possess a membrane-bound nucleus
• More complex than prokaryotic cells in structure
• Organelles and the endomembrane system compartmentalize many cellular functions
• Contain a cytoskeleton for support and maintaining cellular structures
• Examples include fungi, protozoa, plant cells and animal cells

Eukaryotic cells - Animal cell

• Typical size of 1/100mm
• Two main parts: nucleus and cytoplasm
• Nucleus = DNA storage
• Cytoplasm = fluid inside the cell that contains organelles

Eukaryotic cells - Plant cell

• 40 times bigger than animal cells
• Main parts: nucleus and cytoplasm
• Plant cell wall = cellulose
• Vacuole
• Chloroplast

Cell Structure

• Three main parts:
  • Plasma membrane
  • Cytoplasm: cytosol + organelles
  • Nucleus

Plasma Membrane

• Major structural element in cells
• Phospholipid bilayer
• Cholesterol
• Proteins (integral and peripheral)
• Attached carbohydrates (glycolipids and glycoproteins)

Plasma Membrane (Functions)

• Barrier between inside and outside of the cell
• Controls entry of materials (transport)
• Receives chemical and mechanical signals
• Transmits signals between intracellular and extracellular spaces

Plasma Membrane (Phospholipids)

• Amphipathic
• Non-polar fatty acid chains are in the middle
• Polar regions oriented toward the water in the extracellular fluid and cytosol

Plasma Membrane (Cholesterol)

• Intracellular membranes have less cholesterol
• Associates with membrane phospholipids and proteins
• Forms organized clusters that pinch off portions of the plasma membrane to form vesicles

Plasma Membrane (Glycolipids)

• Forms a polar "head", tails are nonpolar
• Located on the extracellular surface of the membrane.

Plasma Membrane (Protein)

• Integral and peripheral membrane proteins
• Integral proteins are closely associated with membrane lipids
• Peripheral proteins are not amphipathic

Plasma Membrane (Protein) - Functions

• Classify proteins by their position and function:
  • Anchoring proteins
  • Recognition proteins
  • Enzymes
  • Receptor proteins
  • Carrier proteins
  • Leak channels
  • Gated channels

Plasma Membrane (Junctions)

• Cells can be physically joined by types of junctions:
  • Desmosomes
  • Tight junctions
  • Gap junctions
• Integrate transmembrane proteins in the plasma membrane to link to specific proteins in the extracellular matrix

Cell Organelles

• Cytoskeleton
• Flagella, cilia, and centrioles
• Endoplasmic reticulum
• Golgi apparatus
• Mitochondrion
• Nucleus, nucleolus, nuclear envelope
• Vesicles (e.g., lysosome)

Cell Organelles (Cytoskeleton)

• Maintains cell shape and organelle positioning.
• Includes microfilaments, intermediate filaments, and microtubules

Cell Organelles (Centrosome)

• Composed of two centrioles
• Composed of microtubules, in 9 clusters of 3 (triplets)
• Pericentriolar material composed of tubulin that grows the mitotic spindle.
• Moves chromosomes during cell division

Cell Organelles (Cilia and Flagella)

• Specialized for motion
• Flagellum: Single tail-like structure on sperm, propels the sperm
• Cilia: Occur in groups, found in the respiratory system, moves mucus

Cell Organelles (Ribosomes)

• Made within the nucleus
• Sites of protein synthesis
• Consist of rRNA and proteins
• Can be attached to endoplasmic reticulum or free in cytosol

Cell Organelles (Endoplasmic Reticulum) (ER)

• Network of folded membranes
• Functions include synthesis and intracellular transport
• Rough ER is studded with ribosomes and is responsible for protein synthesis
• Smooth ER lacks ribosomes and has functions such as lipid synthesis, detoxification, and storage/release of calcium ions

Cell Organelles (Golgi Complex)

• Flattened membranes or cisterns
• Modifies proteins and glycoproteins
• Packages and exports protein or stored in lysosomes

Cell Organelles (Lysosomes)

• Spherical or oval structures
• Contains digestive enzymes for digestion of worn-out parts of the cell
• Tay-Sachs disease (hereditary disorder) - a missing lysosomal enzyme leads to nerve destruction

Cell Organelles (Peroxisomes)

• Moderately dense oval bodies enclosed by a single membrane
• Consume molecular oxygen to remove hydrogen from organic molecules
• Abundant in liver for detoxification

Cell Organelles (Proteasomes)

• Tiny barrel-shaped structure containing proteases
• Digest unneeded or faulty proteins
• Examples include the accumulation of faulty proteins in those with Alzheimer's Disease or Parkinson's

Cell Organelles (Mitochondria)

• Sausage-shaped with many folded membranes (cristae) and a liquid matrix containing enzymes.
• Have some DNA and ribosomes (can make proteins) - Major site of ATP production, O₂ utilization and CO₂ formation Contains enzymes active in Kreb's cycle and oxidative phosphorylation

Nucleus

• Round or oval structure surrounded by a nuclear envelope with nuclear pores.
• Contains nucleolus (makes ribosomes).
• DNA/proteins form a fine network known as chromatin

Nucleus - Characteristics

• The most prominent structure in the nucleus is the nucleolus (small dense region without membrane).
• Associated with DNA regions containing genes which code for the particular types of RNA that is used to build ribosomes.
• Contains DNA in 46 chromosomes, storing genetic material for protein synthesis and in the new cells formed during reproduction.

Comparison of Bacteria, Animal, and Plant Cells

Cellular Processes 1&2

Learning Objectives

• Understand the different transport processes (passive and active) and transport in vesicles into and out of cells.
• Understand how substances are transported across membranes
• Apply the transport processes to the functioning of cells and the nervous system / neurotransmission
• Terminology: Body Fluid Pools*
• Intracellular Fluid (ICF) - Inside cells
• Extracellular Fluid (ECF) - Outside cells
  • Interstitial fluid - ECF between cells
  • Plasma - ECF within blood vessels
  • Lymphatic fluid (lymph) - ECF in lymphatic vessels
  • Cerebrospinal fluid - ECF in the brain and spinal cord

Terminology: Solutions

• Solvent: Liquid doing the dissolving (usually water)
• Solute: Dissolved material
• Concentration: Amount of solute in a given amount of solvent
• Concentration gradient: Difference in concentration between two areas.

Molecule movement across membranes

• Selective Permeability: the cell membrane allows some substances to cross while restricting others
• Concentration Gradient: a difference in the concentration of a substance across a membrane
• Electrical Gradient: a difference in electrical charge across a membrane (membrane potential).
• Electrochemical Gradient: Combined influence of concentration and electrical gradients on the movement of a molecule

Transport Methods (Passive)

• Simple Diffusion: Substances cross the membrane from high to low concentration.
• Facilitated Diffusion: Substances cross the membrane with the help of proteins (channels or carriers) from high to low concentration.
• Osmosis: Water movement across the membrane from high water concentration to low water concentration.
• Important: Osmolarity (total solute concentration) influences water concentration.
• Tonicity: The ability of a solution to cause a cell to gain or lose water (isotonic, hypertonic, hypotonic)

Transport Methods (Active)

• Active transport: Substances are moved across the membrane against their concentration gradient, requiring energy (ATP).
• Primary Active Transport: Directly uses ATP to move substances. Examples include Na+/K+-ATPase, Ca2+-ATPase, and H+/K+-ATPase.
• Secondary Active Transport: Uses the energy stored in an electrochemical gradient established by primary active transport to move other substances across the membrane.
• Symporters: Move substances in the same direction
• Antiporters: (or exchangers) Move substances in opposite directions

Vesicular Transport

• Endocytosis: Brings substances into the cell.

  • Receptor-mediated endocytosis: Selective uptake of specific substances bound to receptors on the cell surface
  • Pinocytosis: ("cell drinking") Non-selective uptake of extracellular fluid.
  • Phagocytosis: ("cell eating") Engulfing large particles like bacteria.

• Exocytosis: Moves substances out of the cell.

Summary of Transport Processes

• Refer to details in the information above.

Test your knowledge on the key principles of cell theory and the various types of human cells. This quiz covers topics such as prokaryotic vs eukaryotic cells, the roles of stem cells, and their differentiation capabilities. Perfect for students looking to solidify their understanding of cellular biology.