Cell Biology
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Transcript of Cell Biology
Introduction to the Study of Cell Biology
ObjectivesA brief outline of the early history of cell biology.Principle of microscopyFamiliarize with the basic properties of all cells.Describe the differences between prokaryotic and eukaryotic cells.
Biology = science of lifeCharacteristics, classification and behaviors
of organisms, how species and individuals come into
existence, and the interactions they have with each other
and with their environment.
Modern biology is divided into 2 categories based on primary level of focus:Organismic biology ~ emphasize on
biodiversity, evolutionary relationships,adaptations,and ecology of plants & animals.
Molecular & cellular biology MB – concerns with interactions between the various
systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and how these interactions are regulated.
CB –studies the physiological properties of cells, as well as their behaviors, interactions, and environment.
Cellular and molecular biology is reductionist; i.e.
The knowledge of the parts of the whole can explain the character of the whole
Create the need to explain the mechanisms of the living system cellular activity
Modern Cell Biology
Involve interweaving of 3 historically distinct disciplines
1. Cytology (the study of cells) Microscopic study of cell structure organization
2. Biochemistry chemistry of biological structure &
function/cellular function
3. Genetics Information flow
The Cell Biology Time Line
The Discovery of Cells - The cell theory
The term cell was first used by the English scientist Robert Hooke (1635-1703), who, in the mid-seventeenth century, used the term to describe the structure of cork.
The Dutch scientist Anton van Leeuwenhoek (1632-1723) made the first recorded observations of bacterial cells (termed "animalcules") from pond water & tooth scrapings.
1830s –importance of cells realised 1838 - German botanist Matthias Schleiden (1804-1881)
observed that despite differences in tissue structure, all plants tissues were made of cells.
1839 - German zoologist Theodor Schwann (1810-1882) realized animals were also composed of fundamental cellular units or cells.
Schwann proposed first 2 principles of Cell Theory: All organisms consist of 1 or more cells The cell is the structural unit of life
Schleiden-Schwann view of cell origin was less insightful – i.e. cells could arise from noncellular materials
German physician Rudolph Virchow (1821-1902) demonstrated that living cells could arise only from other living cells (biogenesis), and not from inanimate matter (abiogenesis).
Size – pose challenge to understand cellular structure & organization
Most cells and their organelles cannot be seen by the unaided eye
Size measured in micrometers (m, where 1000m = 1mm ), nanometers (nm, 10-9 m)
Principles of microscopy
Cells are mostly microscopic in sizeMost eukaryotic cells have single nucleus
with only 2 copies of most genesAs a cell in size, the surface area/vol.
ratio Ability of a cell to exchange substances with its
environment is proportional to its surface.Cells depend to a large degree on random
movement of molecules (diffusion)
Resolving Power of the Human Eye, the Light Microscope, and the Electron Microscope
MicroscopeMake small objects appear biggerMagnification is only better when more
details are revealed
Light microscopeHas a series of lenses and uses light as its
source of illumination Condenser lenses Objective lens Projector lens/eyepiece
Components and their function (refer handout)
Resolution: resolving power
Ability to distinguish fine detail and structures
i.e: to distinguish between 2 points at a specified distance
Limit of resolution , resolving power Limit of resolution imposed by the wavelengths
of illumination source e.g. visible light (400-700 nm)
Wavelength shorter, resolution (resolution = /2)
Magnification Ability of the lens to enlarge or magnify the
objectTotal magnification = magnification of the
objective lens x magnification of the ocular (eyepiece) lens
To achieve high magnification with good resolution – immersion oil between slide and objective lens
Reduce lost of light rays after passed through the specimen
Same refractive index as glass – same effect as increasing the diameter of objective lens
Visibility / contrast
Features that allen a object actually to ….,larger determined by contrast
Difference between adjacent parts of an object or an object and its background
Staining with dye (mostly is metaline blue) Stained object to appear coloured Disadvantage: cannot be used with living cells
because it will kill the cell and can’t see the cell movement
Different types of light microscopy• Brightfield• Phase contrast• Differential interference contrast• Fluorescense• Confocal
Table 1-1 Different Types of Light Microscopy: A Comparison
The paths taken by light rays that form the image of the specimen & those that form the background light of the field
A comparison of cells seen with different types of light microscope: brightfield, phase contrast, diffrential interference contrast (DIC)
The light paths in a fluorescence confocal scanning light microscope
Confocal scanning micrographs of 3 optical sections 0.3 mm thick of a yeast nucleus stained with 2 different fluorescently labeled antibodies
Electron microscopy Types of electron microscopy:~transmission electron microscopy (TEM)~scanning electron microscopy (SEM) Has a limit of resolution of about 0.2 – 0.5nm. Looks at replicas of dead cells, after fixation and
heavy metal ion staining
1. Transmission electron microscopes (TEMs) Electron are scattered as they pass through a thin
section of the specimen, and then detected and projected
2. Scanning electron microscopes (SEMs)
A comparison of the lens systems of a light and electron microscope
Streptococcus pyogenes
SEM
TEM
Scanning Electron Microscopy
Basic properties of cells
1. Life – most basic property of cells
• Smallest unit to exhibit this properties
• Can be removed from organism and cultured in lab
2. Cells are highly complex and organized
Each level of structure in cells has a great level of consistency from cell to cell Organelles have a particular shape & location in
all individuals of species consistent appearance in the electron microscope
Organelles have consistent macromolecules composition arranged in a predictable patternCell structure is similar from organism to organism despite differences in higher anatomical features
3. The information to build a cell is encoded in its genes
Genes - blueprints for constructing cellular structures
• Give direction for running cellular activities program for cell reproduction
Changes in genetic information from generation to generation lead variation
4. Cells capable of producing more of themselves – mitosis & meiosis
Cell reproduce by divisionThe content of a ‘mother’ cell are
distributed into 2 ‘daughter’ cells.
Before division, genetic material is copied each daughter cell get complete and equal share of genetic information. (preexisting theory)
5. Cells acquire & use energy to develop & maintain complexity – photosynthesis, respiration
Virtually all energy needed by life on Earth comes from sunLight energy is turned to chemical energy by photosynthesis; stored in energy-rich CHO i.e. sucrose, starchMost animal cells get energy prepackaged, often as glucoseOnce in cell, glucose disassembled; energy is stored as ATP & use to run cell activities
6. Cells carry out a variety of chemical reactions
Sum total of the chemical reaction in a cell represents that cell’s metabolism
Chemical changes that take place in cells require enzymes (increase rate of chemical reactions)
7. Cells engage in numerous mechanical activities
Based on dynamic, mechanical changed in cellMostly initiated in the shape of ‘motor’ proteins (require constant energy to keep working) Materials are transported from place to place Structures are assembled and then rapidly
disassembled The entire cell moves itself from one site to
another
8. Cells able to respond to stimuli
Most cells have receptors that sense environment & initiate responses
Cells posses receptors to bind• Hormones• growth factors• extracellular materials• surfaces of others cells
Cells respond to specific stimuli• Altering metabolic activities• Preparing for cell division• Moving from 1 place to another• Committing suicide
9. Cells are capable of self-regulation
Cell processes are a series of ordered steps
The importance of a cell’s regulatory mechanisms becomes most evident when they break down
Examples Failure of a cell to correct error in DNA replication
mutation Breakdown in growth control may lead to cancer
cell (unable to control)
Classification of cells
Cells are classified by fundamental units of structure and by the way they obtain energy.
1. Cells are either Prokaryotic~archaebacteria and
eubacteria Eukaryotic~protists, fungi, plants and
animalsDistinguish by their size and the types of internal structures (organelles)
2. Cells are also defined according the need for energy.
Autotrophs are ‘self feeders’ that use light or chemical energy to make food, e.g : plant
In contrast, heterotrophs ("other feeders") obtain energy from other autotrophs or heterotrophs
e.g : many bacteria and animals
Prokaryotic prokaryotes are surrounded by a membrane and
cell wall. cells lack characteristic eukaryotic subcellular
membrane enclosed "organelles," but may contain membrane systems inside a cell wall.
Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria ("blue bacteria").
Some prokaryotic cells have external whip-like flagella for locomotion or hair like pili for adhesion.
Prokaryotic cells come in multiple shapes: cocci (round), baccilli (roots) and spirilla or
spirochetes (helical shapes).
baccillus
Structure of animals cell
Plant
Cell
Differences between prokaryotic and eukaryotic cellsProkaryotes Eukaryotes
Size Usually 1-2 m 5-100 m
Nucleus Absent Presence, bounded by nuclear envelope
DNA Usually a single, circular molecule (chromosome)
Multiple molecules, linear, associated with protein
Cell division Simple fission Mitosis & meiosis
Internal membranes
Rare Complex (nuclear envelope, Golgi apparatus, endoplasmic reticulum, etc)
Ribosome 70S 80S (70S in mitochondria & chloroplasts)
Cytoskeleton Absent Microtubules, microfilaments, intermediate filaments
Motility Rotary motor (drives bacterial flagelum)
Dynein (drives cilia & eukaryote flagellum), kinesin, myosin
Types of prokaryotic cells
Divided into 2 major taxonomic groups/domains
A. The Archaea/archaebacteria Live in extremely inhospitable environment/extremophiles
1. Methanogens, convert CO2 and H2 into CH3 methane gas
2. Halophiles, extreme salty environment
3. Acidophiles, acid loving
4. Thermophiles, extreme high temperature
B. The bacteria/eubacteria Present in every conceivable habitat on Earth
Types of eukaryotic cells
Protists (single-cell) – do everything an organism must do to survive in single cell
Multicellular organisms (fungi, plants, animals) exhibit differentiation – different activities conducted by different types of specialized cells
Differentiation – process by which a relatively unspecialized cell become highly specializedCells specialized for varied functions, have distinctive appearance, carry unique materials
E.g. skeletal muscle, cartilage cells, red blood cells
Cells have similar organelles but their no., appearance & location may differ and correlate with cell activities
Viruses Common virus properties – not considered living since need host to reproduce and metabolize, etc
All are obligatory intracellular parasitesOutside the living cell, it exists as particle or virionGenetic material is surrounded by protein capsule or coat (capsid)
Tobacco mosaic virus
Bacteriophage
Have surface proteins that bind to particular host cell surface component
In the viral life cycle, a virus infects a cell, allowing the viral genetic information to direct the synthesis of new virus particles by the cell.
Conclusion
“Long ago it became evident that the key to every biological problem must be finally sought in the cell; for every living organism is, or at some time, has been a cell”
(Wilson, E.B)