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BIOSCI 101 Note Complete Set
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Cell and Molecular Biology - Lecture 1: Cells and OrganellesCell theory
Three tenets of the cell theory:
1. All living organisms are composed of one or more cells
2. The cell is the basic unit of structure and organization in organisms
3. Cells arise from pre-existing cells
Generalized properties of cells:
Genetic information: genetic information is stored as DNA
Protein synthesis: proteins are stored on ribosome
Plasma membrane: a selectively permeable plasma membrane encloses every cells
Units of measurement used in microscopy
Name Unit Magnitude (in metres)
Centimetre cm 10-2 m
Millimetre mm 10-3 m
Micrometre μm 10-6 m
Nanometre nm 10-9 m
Picometre pm 10-12 m
Microscopy
3 important parameters in microscopy:
Magnification: enlargement of the image
Resolution: measure of the clarity of the image
Contrast: enables you to distinguish between different parts of the cell
Types of microscope
Light microscope Electron microscope
Fluorescence microscope Scanning EM Transmission EM
Maximum resolution (nm) 200 nm 10 nm 2 nm
Function Used to visualize whole cells and Used to study cell surface and Used to study internal cell
large subcellular organelles generate 3D images structure, organelles, proteins
Characteristics of view Cells/organelles cannot be
distinguished without aid; require
fluorescence staining for contrast
Mechanism Light is shined through a specimen SET focuses a beam of TEM focuses a beam of
into the objective lens and eyepiece electrons onto the surface of electrons through the specimen
lens for magnification the specimen
Bright-field microscopy (light): only white light is used for illumination
Fluorescence microscopy (light): fluorescence dies are used for resolution
Light microscopes are limited by the wavelength of light (400-700 nm), and therefore is difficult to resolve smaller objects
Beams of electrons have a much smaller wavelength so electron microscopes have a much higher resolution
Prokaryotic cells
Prokaryotic cells: cells that do not have compartmentalized structure (cell contain membrane-bound organelles)
Central prokaryotic organelles
Nucleoid DNA concentrated regions not enclosed by a membrane
Cell wall Rigid structure that protects the cell and maintain the shape to prevent
excessive swelling and bursting
Plasma membrane Allows for passive and active transport of molecules
Capsule Jelly-like coating covering the cell wall
Cytoplasm Present in one uninterrupted chamber and contains many enzymes for
metabolism
70s ribosome Smaller than those of eukaryotes; fundamental for RNA translation
Circular DNA Only one is present in a circular model; does not contain introns
Additional prokaryotic organelles
Flagellum Used for locomotion
Fimbriae Used for attachment to other cells or surface
Mesosomes Infolding of plasma membrane during cell division
Plasmids Small circle of DNA that contains additional information
Notable characteristics of a prokaryotic cell:
Lack of membrane bound organelles: there are little or no internal structure or organelles
Circular DNA: has one circular DNA with no introns
,Eukaryotic cells
Eukaryotic cells: cells that have compartmentalized structure (cell contain membrane-bound organelles)
Comparing plant to animal cells:
Cell wall: plant cells have cell walls, animal cells do not
Central vacuole: plants have large central vacuole, animal cells do not
Chloroplasts: plant cells have chloroplasts for photosynthesis, animal cells do not
Cell organelles
Endomembrane system: collection of organelles that are membrane-bound (e.g. GA, ER, nucleus, lysosome)
Endoplasmic reticulum (ER)
Diagram Parts Description
Cisterna Flattened double membrane-enclosed sacs or tubes
These buds off to form transport vesicles sent to the Golgi apparatus
Ribosome (80S) Only found in rough ER; attached to the outside of cisterna and produces protein
Function
Smooth ER Synthesis of lipids and steroids, metabolism of carbohydrates
Rough ER Production and packaging of proteins that are not for internal cell use (mainly for
packaging and processing in GA)
Note
Endoplasmic reticulum form an extensive transport system throughout the cell.
ER constitutes for more than half the total membrane in many eukaryotic cells
Golgi apparatus (GA)
Diagram Parts Description
Cisterna Flattened double membrane-enclosed sacs or tubes
4-8 Cisternae are usually staked together
Lumen Inside space of the cisterna that contains enzymes that modifies proteins
Vesicles Cisterna buds off to form transport vesicles
Transports proteins into (cis face) and out of (trans face) the Golgi apparatus
Function
Storage Transports and stores lipid
Modification Receives and modifies molecules (such as proteins) from ER as required
Synthesis Produces digestive enzymes, lysosomes and glycoproteins much as mucin
Transportation Directs molecules synthesised or received to correct cellular compartment or to plasma membrane
Note
Any cells that secretes (such as glands) have large Golgi apparatus
Mechanism of ER to GA transport and progression
Cis golgi receives cargo: cis golgi comes to ER to receive cargo (Hug and Kiss model)
Protein modification: proteins from rough ER undergo modification
Golgi matures from cis to trans: golgi matures from cis → medial → trans
Retrograte transportation: proteins (not from ER) used at later stage of Golgi will be
transported back to the earlier golgi by vesicles (COPI)
Vesicle transport to different destination: proteins are sorted towards different destination
by the trans Golgi network
Nucleus
Diagram Parts Description
Chromatin Uncoiled chromosomes spread through the nucleus
(often densely staining around the edge of nucleus)
Neucleoplasm Supports the structure of chromosomes and nucleoli
Nuclear pores Regulate passage of materials in to/out of the nucleus
(pore complex)
Nuclear envelope Lipid membrane that separates the nucleus and its contents from the cytoplasm
and prevents the DNA from escaping
Outer layer is continuous with the endoplasmic reticulum
Nucleolus Site of rRNA synthesis and ribosome assembly
Not surrounded by a membrane
Function
DNA replication DNA is replicated during interphase before cell division occurs
DNA transcription DNA is transcribed to form mRNA which is exported to the cytoplasm
Note
The nucleus is the largest organelle in the cell of 10µm diameter
Spliceosomes are found attached to the nuclear membrane – prokaryotes do not have introns for this reason
The nuclear envelope is connected to the endoplasmic reticulum
,Lysosomes
Function
Autolysis Self-destruction of the cell by
releasing enzymes
Phagocytosis Digestion of material that has been
taken into the cell by engulfment
Exocytosis Lysosomes are docked to the cell
surface and fuse with the plasma
membrane to release their content
Note
Lysosome contain hydrolytic enzymes that digest materials
As the constituents of lysosomal membrane does not fit to the
active site of the enzyme, they do not become hydrolysed
Mitochondria
Diagram Parts Description
Outer membrane Semi-porous membrane and is permeable to small molecules and ions
Inner membrane Contains folds which increases surface area
Surface of crista is covered in cytochromes that enables ATP synthesis
Intermembrane Stores proteins that allows cellular respiration
space Narrow space enables quick accumulation of protons
Strictly permeable only to oxygen and ATP
Matrix Contains enzymes that allows ATP production
Contains ribosomes and DNA which enables mitochondrion replication
Function
Aerobic respiration Generates the cell’s supply of energy through production of adenosine triphosphate (ATP)
Maintenance of calcium Maintain proper concentration of calcium ions within the compartments of the cell
Note
Fat is digested here if is being used as an energy source
Contains its own DNA and ribosomes
Plasma membrane
Diagram Parts Description
Phospholipid Semi-permeable; phospholipids have hydrophobic tails and hydrophilic heads
bilayer
Cholesterol Embedded within the phospholipid bilayer to enhance rigidity
Proteins Transport: allow certain necessary molecules to pass through the membrane
Receptor: helps communication of the cell with the external environment
Glycoprotein: allows cell communication and molecule transport
Function
Cell enclosure Separates the contents of the cell from its outside environment
Control of cell environment Protects the integrity of the interior by allowing only selected substances in the cell
Chloroplast
Diagram Parts Description
Outer membrane Semi-porous membrane and is permeable to small molecules and ions
Inner membrane Forms a border to the stroma and regulates molecule transport
Fatty acids, lipids and carotenoids are synthesised here
Stroma Alkaline, aqueous fluid which is protein rich
Chloroplast DNA, ribosomes, start and thylakoids are floating around the stroma
Lumen Internal space of thylakoids
Often contain a high proton gradient for photosynthesis
Thylakoids Thylakoid contains chlorophyll for the light reactions of photosynthesis
A thylakoid stack of 10-20 thylakoid is called a granum
Function
Production of sugars During photosynthesis sugar and oxygen are made using light energy, water and carbon dioxide
Note
Most important plastid found in plant cells
Vacuoles
Function
Storage Stores water, protein, inorganic ions, waste and harmful products
Support Provides support for plants through water pressure for minimal investment in cytoplasm
Homeostasis Vacuoles regulate internal pH and water levels to ensure an optimum condition
, Note
Vesicles are small vacuoles are used to transport materials within a cell
Large central vacuole develops from small vacuoles coming together
Cytoskeleton
Microtubules Microfilaments Intermediate filaments
Protein subunits Tubulin ( and ) Actin Different proteins (e.g. keratin)
Structure Hollow tubes; walls consists of 13 Two interwined strands of actin Fibrous proteins supercoiled into
columns of tubulin molecules thick cables
Diameter 25nm (15nm lumen) 7 nm 8-12 nm
Main functions Structure: maintains cell shape Structure: maintains and changes Structure: maintains and changes
cell shape cell shape
Motility: part of cilia or flagella that Cell motility: forms pseudopodia Anchorage: anchors nucleus and
is moved by dynein certain other organelles in place
Cell division: involved in Cell division: involved in Nuclear lamina formation: forms
chromosome movements in CD cytokinesis in CD nuclear lamina in nucleus
Network for intracellular transport: Movement: involved in muscle
provides network for vesicles to contraction
move along in cells
Comparison of examples of microtubules in cellular structure
Cytoskeleton Cilia and flagella Centrioles/centrosomes Basal body
Diagram
Structure Vesicles connected to nine doublets of a centrosome is a pair of nine set of triplet
the microtubule of microtubules arranged centrioles, each composed microtubules in a ring
cytoskeleton by in a ring with two of nine set of triplet
proteins microtubules in centre microtubules in a ring
covered by a layer of
plasma membrane
Microscope
Function Transport vesicles Motility of the cell Compression-resisting Anchors cilia/flagella to
girders of cytoskeleton the cell
Help in the formation of becomes a centriole
the spindle fibres (e.g. of sperm)
Location Cytoskeleton of Connected to the Near the nucleus of animal Where flagella is
eukaryotic cells exterior of cell cell (most often) present
Flagella and cilia in prokaryotes and eukaryotes:
Prokaryotic cells: flagella are anchored in the cell membrane by a motor, which rotates the flagella
Eukaryotic cells: dynein is anchored to one pair of microtubules and they “walk” along the neighbouring microtubules
Endomembrane system: composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell
Components: nucleus, endoplasmic reticulum, goli apparatus, lysosomes
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