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)