Biology – Premed 1 Windsor University School

of Medicine

Dr. VeipuSeptember 2015

All organisms are made up of cells which are rather minute in size and cannot be seen with the naked eye

Robert Hooke (1665) was the first to use a primitive microscope to observe “cells”

• Microscopy --- Use of microscopes for studying cells

• Light Microscope, also called “Optical microscope”• Uses light source to magnify image of sample• 1. Simple Microscope• 2. Compound Microscope – Combination of lens,

enhances the magnifying power

Variations in the optical microscope:

Dark Field Microscopy (Image illuminated against dark background, used in studying nuclei, mitochondria and cell vacuoles)

Fluorescent Microscopy (Image illuminated with UV Radiations instead of light source, used in identifying infection agents such as bacteria and viruses)

Phase Contrast Microscopy (Study of internal structures with different densities, such as chromosomes during mitosis or meiosis)

Electron Microcopy ( Image formed with a beam of electrons that travel in a wave-like pattern, and enlarged image produced on fluorescent screen) - Able to image organelles Two Types: Transmission Electron Microscope (Cut section) & Scanning Electron Microscope (3D Image)

CELL

“BASIC UNIT OF LIFE”

All organisms are composed of cells! All cells come from pre-existing cells!

Unicellular --- Organisms are made up of a single cell Multicellular --- Organisms are made up of many cells

Cells having a common origin and perform a similar or specific function is called a “Tissue”

Several tissues constitute an “Organ”

• Life of every organism begins as a single cell• All cells of our body come from a single cell, the “Zygote”

• Zygote divides continuously to form our multicellular body• *In a multicellular organism, a number of different types

of cells may coexist

• All cells have similar genetic material• Mature cells become specialized to perform a specific

function• This capability to divide and differentiate to give rise to a

new individual is called “Totipotency”

• Cells can be divided into two main types:-

• 1. Prokaryotic Cells ----Simplest Organization• Without True Nucleus

• 2. Eukaryotic Cells ---- High degree of differentiation• True Nucleus

Prokaryotic Cell• Bacteria, blue-green algae, mycoplasma• Generally, smaller than eukaryotes• Multiply more rapidly than eukaryotes

• High variation in shape and size– Bacillus (most common shape of rod-like)– Coccus or Spherical– Vibrios or Rod-shaped bacteria that are slightly curved

or comma-shaped– Spirilla or long, twisted spiral resembling a cork-screw

Prokaryotic Cell Every prokaryotic cell is bounded by a complex cell wall Structure and thickness of the Cell Wall will differ into Gram

(+) and Gram (-) cells

Inside the cell wall is the Periplasmic space and beneath lies the plasma membrane

Plasma membrane invaginates to form internal membrane structures

Genetic material is localized within a region called Nucleoid which is not separated from the surrounding cytoplasm by any membrane

Prokaryotic Cell

Cell Envelope:-

Bacterial cells have a complex cell envelope, the layers of this envelope are bonded together tightly

3 basic layers

1. Glycocalyx --- Outermost layer that protects the cell and helps in adhesion (slimy layer or capsule)

2. Cell wall – Second layer of cell envelope below glycocalyx, determines the shape of the cell and provides a structural support by preventing cell from bursting. The layer is made of “Peptidoglycan”, a macromolecule. Peptidoglycan composed of long glycan strands that are cross-linked by short

peptide chains

3. Cell Membrane (Plasma Membrane)

Glycocalyx

Gram Staining• Technique used to classify bacteria into two groups: Gram (+) and Gram

(-)• Staining done with weak alkaline solution of crystal violet or gentian

violet• Stained slide of bacteria is then treated with 0.5% of iodine solution • Followed by washing with water, then alcohol or acetone• Final stain with Red safranin

• Identification ---• Gram (+), the cell wall is thick and primarily made of peptidoglycan

• Gram (-) cell envelop shows three layers; the outer membrane, thin layer of peptidoglycan, and the plasma membrane– Outer membrane contains “Lipopolysaccharides” and protein channels called

“Porins”– Inner membrane contains proteins anchored into the petidoglycan

Gram – Positive Gram - Negative

Bacteria remain colored blue or purple with Gram staining even after washing with alcohol

Bacteria do not retain the stain when washed with alcohol

Outer membrane is absent Outer membrane is present

Cell wall is 20 -80 nm thick Cell wall is 8-12 nm thick

Murein content is 70-80% Murein content is 10-20%

Mesosomes are prominent Mesosomes are less prominent

Few bacteria below to Gram + Most bacteria belong to Gram -

Plasma Membrane

PLASMA MEMBRANE

• Membrane forms the boundary of the cytoplasm• Composed of lipids, proteins, oligosaccharides

and water• “Semi-permeable” • Permeable to some substances E.g. ions,

molecules;• Carrier molecules embedded within the

membrane that bind to specific molecules;• Transport these molecules in a specific direction

PLASMA MEMBRANE

• Lipid components – Phospholipids, glycolipids, and cholesterol

• “Amphipathic” contain both hydrophillic and hydrophobic regions

• Hydrophobic ends are buried in the interior away from surrounding water

• “Fluid-mosaic model”

PLASMA MEMBRANE

• Prevents loss of essential components through leakage and aids in movement of molecules

• Transport system for nutrient uptake, waste secretion, protein secretion, etc.

• Bacterial plasma membrane is location of critical metabolic processes like respiration, photosynthesis, and synthesis of lipids and cell wall constituents

Mesosomes

• Extensions or infoldings of the plasma membrane into the cell, in the form of vesicles

• Commonly seen in Gram (-) bacteria

• Unknown function

Inclusion Bodies• Contents of bacteria are stored in the cytoplasm as

inclusion bodies

• Storage granules (E.g. phosphate granules, cyanophycean granules, glycogen granules)

• Not bounded by any membrane, lie freely in the cytoplasm

• Gas Vacuoles E.g. Cyanobacteria allows to float on surface of water and trap sunlight for photosynthesis

• Phosphate and sulfur granules

PM = plasma membrane R = ribosomeCW = cell wall

N = nucleoidM = mesosome PHB = inclusion body

Ribosomes

• Site of protein synthesis• Plasma membrane ribosomes make proteins that are

transported outside• Matrix ribosomes sythesize proteins that remain within the

cell• In prokaryotes, they are composed of two subunits -30S

and 50S, that make up a 70S (S =Svedberg unit)

• Several ribosomes attached to a single messenger RNA (mRNA) function in “translation” of the message in mRNA into proteins

Nucleoid• *Prokaryotes do not have a membrane bound, well defined

nucleus

• Genetic material (DNA) is not complexed with other molecules nor packed in chromosomes

• Genetic material is composed of a “single circular DNA” packed in a Nucleoid

• DNA is looped and coiled with help of nucleoid proteins

• DNA is therefore said to be attached to cell membrane, and the membrane involves in separation of duplicated DNA into daughter cells during division

Flagellum

FLAGELLUM• Motility by rotation, spins the body in the opposite direction and

pushes bacterium in the forward direction

• Composed of 3 parts:

• 1. Filament --- Longest and most obvious portion of the flagellum, cylindrical and hollow structure made of protein flagellin. Filament rotates 360⁰

• 2. Hook

• 3. Basal body (Complex part of flagellum, has 4 rings connected to a central rod in Gram negative bacteria. Gram positive cells have only 2 rings connecting to plasma membrane and peptidoglycan membrane)

Pilus and Fimbriae• Bacterial surface appendages not involved with motility• Both terms are used interchangeably

• Pili:• Elongated tubular structures in Gram (- ) bacteria• Participate in mating process by transfer of DNA from one

cell to another - “Conjugation”

• Fimbriae:• Small, bristle-like fibers sprouting out of the cell• Allows attaching of bacteria to solid surfaces such as rocks,

host tissues, clinging of cells forming a film

Eukaryotes

Eukaryotes

• Cell Wall ( Absent in animal cells and some protists)

• Plasma Membrane

• Cytoplasm – Highly complex organization

• Additional appendages for locomotion

Cell Wall

• Plant cells have a fixed shape and size • Thick, strong and rigid• Composition and appearance differ according to cell

type and function

• In higher plants, cell wall fibers are made of polysaccharide cellulose and embedded in cross-linked matrix of polysaccharides

• In young and small cell, the cellulose fibers are loosely packed

Cytoskeleton

• Ability of eukaryotic cells to adopt a variety of shapes and carry out directed movements depend on the cytoskeleton.

• A network of fibers extending throughout the cytoplasm;

• 3 types of protein filaments:• Microfilaments, Microtubules, Intermediate

filaments

• Microtubules -- hollow tubules with 2 subunits of alpha-tubulin and beta-tubulin arranged in a helical manner to form a cylinder– Role in movement of organelles, movement of chromosomes

during cell division

• Microfilaments -- made up of actin like protein• Bear tension

• Intermediate Filaments – Cell to cell junctions• Bear tension

Endoplasmic Reticulum

• Irregular network of membranous tubules

• Continous sheet enclosing a single internal space

• When studded with ribosomes, its appearance gives its name “Rough endoplasmic reticulum” (RER)

• When not studded with ribosomes, called “Smooth endoplasmic reticulum” (SER)

Endoplasmic Reticulum

• Biosynthetic Factory

• Smooth ER• Synthesis of lipids (steroids)• Detoxification of drugs• Muscle contraction by release and uptake of Ca2+ ions

• Rough ER: • Synthesis of secretory lysosomal or membrane proteins

and its transport through ER lumen

Golgi Apparatus

• Flattened sac-like cisternae stacked on one another

• Resemble ER but “ a stack of pita bread”

• Package the material (products of ER e.g. protein) and prepare for secretions Golgi packaged and into vesicles that bud off and fuse with plasma membrane

Golgi Apparatus

• Cis to trans face (Materials are transported from cis to trans face by vesicles that bud off from the cisternal edge)

• Cis = Receiving End Trans = Shipping End*Cis face located near ER

• Identification tags (Zip codes) E.g phosphate groups are added to the golgi products

Lysosomes• Budding off vesicles from golgi apparatus

• Involved in intracelular digestion and contain hydrolytic enzymes to digest all types of macromolecules

• Hydrolases enzymes present in the vesicles

• 1. Phagocytosis – Engulfing smaller food particles (e.g. amoeba)• In humans, Macrophages and white blood cellsdestroy bacteria by

engulfing

• 2. Autophagy – Lysosomes use hydrolytic enzymes to recycle cell’s own material

• Eg. Damaged organelle contained in vesicle to which lysosome fuses

Ribosomes

• Can be either free or bound with ER• 80S (60S and 40S subunits)

• Free ribosomes synthesize proteins (function within cytosol)

• ER associated ribosomes synthesize secretory membrane and lysosomal proteins, and for export from cell

• Synthesized proteins are transported to organelles such as nucleus, mitochondria and chloroplasts

• Proper folding of synthesized proteins are assisted by proteins called “Chaperones”

• Ribosomes attached to messenger RNA are called “Polysomes”

Mitochondria• Powerhouse of the cell (Site of cellular respiration)

• Generation of ATP (Energy!!) – “Metabolic process using oxygen to drive generation of ATP by extracting

energy from sugars, fats and other fuels”

**In plants, Chloroplasts are sites of photosynthesis (solar energy to chemical energy)

• Bound by Double Membrane, an intermembrane space exists between the outer and inner membrane

• Inner membrane forms folds called “Cristae” to increase the surface area

• Contains ribosomes, DNA, and calcium phosphate granules

• Mitochondrial DNA is a closed circular DNA• Multiple circular DNA molecules are found in Mitochondria

inner membrane

• Enzymes and electron carriers for formation of ATP are located in the inner membrane

• Endosymbiont Theory: Early ancestor of eukaryotic cell engulfed an oxygen-using non-photosythetic prokaryotic cell resulting in a mitochondrion organelle in a euk.. cell!

Plastids

Organelles that are found only in Plant cells and some unicellular organisms (Euglena)

1. Chloroplasts --- Contain chlorophyll pigment 2. Chromoplasts --- Other pigments such as carotenoids

responsible for yellow, orange, or red coloration of plants 3. Leucoplasts --- Devoid of pigments, but have capacity to

develop pigments when required

These organelles are bound by two membranes, contain own DNA, RNA, and ribosomes

Plastids• Chlorophyll --- Green colored pigment present in the chloroplast• Performs function of trapping light energy required for the

formation of two products ---- ATP and NADPH

• The inner membrane of chloroplast folds inward forming a series of sheets called “Lamellae” suspended in a fluid-like matrix called stroma

• Lamellae in the chloroplasts are organized to form sac-like structures called Thylakoids

• Various components involved in the process of photosynthesis are present in Thylakoids

Nucleus

• Relatively large organelle controlling all the activities of the eukaryotic cells

• “Store house of hereditary information”• Binucleate (paramecium protozoa),

multinucleate, anucleate (lack nucleus)

• RBC? White blood cells?

Nucleus Enclosed by two membranes, which form a “Nuclear

envelope” Outer membrane remains in continuation with

Endoplasmic reticulum and the inner membrane surrounds the nuclear contents

At certain areas, the nuclear envelope is interrupted by the presence of Pores

Pores help in exchange of material between the nucleoplasm (fluid within nucleus) and cytoplasm

RNA and ribosomes leave the nucleus through these pores

Nucleus Nucleoplasm contains “Nucleolus” (spherical

structure that is Non-membrane bound) Nucleolus is the site for ribosomal RNA

synthesis (rRNA)

Within nucleus, chromosomes are uncoiled in a loose, indistinct network called “Chromatin” (DNA, RNA & Protein)

Types of protein present and associated with DNA are histone & non-histone proteins

Nucleus

During Interphase stage of the cell cycle ( See Picture in next slide), chromosomes are uncoiled and loose

During cell division or Mitosis, the chromosomes become more visible under microscope

Most observable at metaphase and anaphase

Cilia and Flagella

• Membrane bound cylinders• Organelles are complex structure made up of basal body, rootlets,

basal plate and shaft• The shaft consists of nine pairs of microtubule doublets in a circle

around two central tubules• A “9+2” pattern of microtubules

• Each doublet has pairs of arms projecting outward (See image in next slide)

• A radial spoke also extends towards the internal pair of microtubules

• Cilia and flagella bend because adjacent microtubule doublets slide along one another

• Doublet arms are made of the protein “Dynein”

Prokaryotic Cell Eukaryotic CellLack of organized nucleus, the genetic material present in the form of nucleoid

Nucleus well organized

Nuclear membrane absent Nuclear membrane present

DNA not complexed with histones DNA complexed with histones to make a chromatin

DNA in a circular form; not packed into chromosomes

Linear DNA packed into well defined chromosomes

Membrane-bound organelles absent Membrane-bound organelles like ER, golgi, lysosomes, etc. present

Mitochondria absent Mitochondria present

Chloroplast absent, photosynthetic lamella may be present in photosynthetic bacteria

Chloroplast present in plant cells

Ribsomes only of 70 S type Ribosomes of 80S (in cytoplasm) and 70S (in organelles) types in plants cells and 80S and 55S types in animal cells

Cell wall made up of murein Cell wall absent in animal cells; present in plant cells made up of cellulose

Flagella simple, made up of flagellin and 9+2 organization is absent

Flagella specialized and show 9+2 organization

Microtubules absent Microtubules forming cytoskeleton

Different kinds of pili present Pili absent

RespirationOsmosisDiffusionPhotosynthesis

Cellular processes

Cells break down carbohydrates and other molecules to produce energy

Oxidation of glucose is one of most common forms

Breaking down of sugar into water, carbon dioxide, and energy

Energy is used to do the work of the cell

Respiration

Transport of raw materials, wastes, and synthesized materials out of the cell

Osmosis & Diffusion

Movement of molecules, especially gases and liquids from areas of high concentration to areas of low concentration

Diffusion

Specific type of diffusionMovement of water through a

membrane from areas of high concentration to areas of low concentration

Osmosis

Osmosis

• A solution that is separated from another solution by a semi-permeable membrane can have three osmotic states:

• In an isotonic solution is the pressure at both sides of the membrane the same.

• A hypotonic solution has a lesser number of solute particles than the solution to which it is compared, while

• a hypertonic solution has a higher number of solute particles. At equilibrium is a solution always isotonic.

Diffusion and osmosis happen to enable a cell to reach equilibrium

Equilibrium