Week 5 eukaryotic and prokaryotic cells Flashcards
Cells intro
All living things = organisms
Made of cells -> smallest and fundamental units of life
New cells are made from pre-existing cells
Unicellular organisms
-Simpler organisms
-One cell exerting all life functions
-Bacteria
-Protozoa
-Unicellular Fungi
Multicellular organisms
-More evolute organisms
-Multiple cells with specialised functions
-Pluricellular Fungi
-Plants
-Animals/humans
Cell specialisation
-The human body is made up of ~1013 cells, with 200 types of specialised cells
-Distinct cell types vary in size,
shape, functions
-Cell shape and size determine a
particular specialisation
-Cooperation of different specialised cells allows complex organisms to perform a wide range of functions
Red blood cells
Main function:
O2 / CO2 transport
-Biconcave shape
-No nucleus
-Contain haemoglobin
-Small and flexible
Neurons
Propagation of nerve impulse
(action potential)
-Thin and long cells
-Branched at their ends
-Different subcellular parts
-Release of neurotransmitter signals
Organisation in the human body
The human body is organised into levels of increasing complexity;
Cell -> Tissue -> Organ -> Organ system -> Organism
Light microscope or optical microscope
The light microscope:
-Is used to observe living cells in a tissue
-Its resolution limit is ~ 0.2μm (not suitable for organelles)
Properties of microscopes
Magnification – the ratio of an object’s image to its real
size (up to 1000 times)
Resolution – it is the ability to distinguish between two very closely positioned objects
Fluorescence microscope
A technique to make specific parts of a cell or tissue that uses fluorophore proteins or dyes under a special light causing the fluorescent molecules to absorb this light and emit visible light, which makes them glow
-Used to monitor the localisation of target labelled molecules within a cell / tissue
Electron microscope (EM)
EM use:
-High resolution images of cell
structures (e.g. organelles)
-Living cells cannot be observed
-Resolution limit is ≈ 2 nm (nanometres)
Two main EM biomedical applications:
->Transmission EM (TEM) - to study organelles
->Scanning EM (SEM) - to study the cell surface
Two distinct type of cells:
-Prokaryotic cell
-Eukaryotic
Prokaryotic cell
-Without nucleus
-No internal compartments
-No organelles
-Simple internal organisation
Eukaryotic cell
-With nucleus
-Internal membranes that enclose the organelles
-Complex organisation
Basic components of a cell
-Plasma membrane
-Cytosol, a concentrated aqueous solution of chemicals
-Ribosomes
-GENOME -> genetic information of a cell represented by DNA
that carry hereditary information and define each species
-Biological macromolecules
Macromolecules in cells
Cells of all organisms contain 4 major organic (carbon atoms) macromolecules;
-Carbohydrates/Polysaccharides
-Proteins
-Lipids
-Nucleic acids
Macromolecules are polymers made by specific repeating molecular units, monomers
Monomers
mono- (one) and -mer (part)
-Building blocks or subunits
-Smallest units of molecules that can join with each other to form larger molecules, polymers
Anabolism
Cells link monomers together to form a polymer through polymerisation / condensation reactions (requiring energy)
Catabolism
Polymers are broken down into smaller molecules by hydrolysis (realising energy)
Metabolism
Catabolism + Anabolism
Prokaryotic cell overview
Smaller (0.1-5 μm) and simpler cells
Intracellular compartment;
-Cytoplasm, nucleoid, ribosomes, plasmids, inclusion bodies
-Lack of nucleus and organelles
Internal boundary/ coating layers;
-Plasma membrane (internal boundary)
-Cell wall
-Glycocalyx/capsule
External appendages;
-Flagella, fimbriae, sex pili
Prokaryotic cell – Intracellular composition
-Cytoplasm
-Ribosomes
-Bacterial DNA chromosome
-Inclusion bodies
-Plasmids
Cytoplasm
Internal content of the cell - site of many reactions
Ribosomes
Composed of a large (50S) and a small subunit (30S)
-Each subunit is made of rRNA and proteins
-Involved in protein synthesis, translating mRNA code
Bacterial DNA chromosome
-Dispersed in a central cytoplasmic space - Nucleoid
-Single circular DNA - not linked to histone proteins
Inclusion bodies
Aggregates of reserve material (Storing function)
Plasmids
Additional/accessory circular DNA
-Confer new ability, such as degradative ability of antibiotics -> drug resistance
Prokaryotic cell – surface layers
-Plasma membrane
-Cell wall
-Glycocalyx
Plasma membrane
Internal boundary;
-Flexible lipid bilayer, as in eukaryotic cells (with no sterols)
-Controls the movement of molecules (nutrients/waste)
-Sometimes, site of reactions (respiration/photosynthesis)
Cell wall
(Different composition in Gram+ve and –ve)
-Rigid structure to preserve cell shape & integrity
Glycocalyx
Not always
->Polysaccharides layer: Capsule (organised and stable) or Slime layer (loosely attached)
->Protection against dehydration, immune system (phagocytosis) and antibiotics
->Adherence factor
Prokaryotic cell – Appendages
-Flagellum
-Fimbriae / pili
-Sex pilus (pl. pili)
Flagellum
-Long and whip-like appendages
-Used for cell motility (movement)
-It is also a sensory structure to detect nutrients
Fimbriae / pili
-Short and thin projections
-Used for attachment to a surface or other cells
Sex pilus (pl. pili)
-Rigid hair-like tubular structures (longer than fimbriae)
-Use to facilitate genetic material transfer between two bacteria (through the conjugation
process)
Eukaryotic cell overview
-Cell wall is NOT present in human cells -> but present in plant and fungal eukaryotic cells
-Contain a nucleus (or more nuclei)
-Many membrane-enclosed organelles
->have specialised functions (like organs)
Organelles system
-Nucleus
-Endoplasmic reticulum
-Mitochondria
-Golgi apparatus
-Lysosomes
-Peroxisomes
General usefulness of organelles
-Membrane-bound intracellular components allowing
compartmentalisation
-Different enzymatic composition -> occurrence of
diverse metabolic reactions -> specialised functions
-Distinct eukaryotic organisms have different organelles
->Lysosomes are only in animals and chloroplasts are only found in plants
Cytoplasm
Content inside the plasma membrane excluding the nucleus
-Highly organised and dynamic
-It includes:
-Cytosol
-Distinct cell organelles
Cytosol
Gel-like fluid (pH 7.2) to support organelles
-It includes ribosomes, cytoskeleton, enzymes, etc
-It is the site of many cellular activities:
-Protein synthesis and degradation
-Metabolic reactions (e.g. glycolysis)
-Cell signalling pathways
Distinct cell organelles
-Enclosed by membranes (separated by the cytosol)
Ribosomes
Function: Cell machinery for protein synthesis
Structure:
Made by 2 subunits: large (60S) & small (40S) forming 80S -> bigger than the prokaryotic ones (50s and 30S 70S)
Both subunits are combinations of : Ribosomal proteins + ribosomal RNA (rRNAs)
Types: Free floating in the cytosol or bound to the rough endoplasmic reticulum
Cytoskeleton
A network of protein filaments and tubules that provides structural support
Cytoskeleton functions
-Structural support: cell shape & resists mechanical stress
-Intracellular transport: facilitates movement of
organelles, vesicles, and molecules
-Regulates cellular processes (eg cell division & motality)
Cytoskeleton structures - Composition
3 types of filamentous protein polymers (long repetitions of 1 or more proteins):
-Microfilaments (7 nm in diameter)
-Intermediate filaments (10 nm in diameter)
-Microtubules (25 nm in diameter)
Cytoskeleton - microfilaments
-Actin filaments
-Long, thread-like filaments of 2 helical strands of actin protein repetitions - (7nm in ⌀)
-Depending on interaction with actin binding proteins (e.g. myosin).
Very dynamic- Rapid assembly and disassembly for quick rearrangements;
-Muscle contraction
-Assist with cell movement
-Support cell’s shape (e.g. microvilli in intestinal cells)
-Cell division: formation of contractile ring in cytokinesis
Cytoskeleton - Intermediate filaments
Structure;
Rope-like fibres formed by many long strands of several types of proteins twisted together - (10nm in ⌀)
Function;
-Provide mechanical strength and stability to cells and tissues (abundant in muscle cells)
-Anchor cells in extracellular matrix
-No effect in cell motility (not bound to motor proteins). More stable
Cytoskeleton - Microtubules
Structure;
-Long and rigid hollow cylinders made by repetitions of two
tubulin protein subunits (α & β) - (25nm in ⌀)
Major;
-Cell structural support
-Intracellular transport linked to motor proteins
-Generate force and cell movement (cilia and flagella)
-Cell divisions ->forming Centrioles -> DNA segregation
Cytoskeleton defects
-Cytoskeleton defects can lead to cardiomyopathies, cancer
-Some anti-cancer drugs interfere with microtubule formation to block the uncontrolled cancer cell divisions
