The CellThe CellThe CellThe CellThe Organism’s Basic Unit of Structure and Function

ProkaryoticProkaryoticProkaryoticProkaryotic EukaryoticEukaryoticEukaryoticEukaryotic

TypesTypes of cellsof cells

Micro-organisms All other forms of life

Cellulae (Small room)

2

Cell Theory Cell Theory Cell Theory Cell Theory

1- All organisms are composed of one or1- All organisms are composed of one or more of cells. more of cells.

2- Cell is the basic unit of life.2- Cell is the basic unit of life.

3- The new cell arises only from pre-3- The new cell arises only from pre- existing cell. existing cell.

• All cells are surrounded by a All cells are surrounded by a plasma membraneplasma membrane..

• The semi-fluid substance within the cell is called The semi-fluid substance within the cell is called “cytosol”“cytosol”, ,

containing the cell organelles.containing the cell organelles.

• All cells contain chromosomes which have genes in the form of DNA.All cells contain chromosomes which have genes in the form of DNA.

• All cells have tiny organelles called All cells have tiny organelles called ““Ribosomes”Ribosomes” that make proteins. that make proteins.

1). 1). ProkaryoticProkaryotic and and eukaryoticeukaryotic cells cells differ in size and complexity differ in size and complexity

SimilaritiesSimilaritiesSimilaritiesSimilarities

• A major difference between prokaryotic and eukaryotic A major difference between prokaryotic and eukaryotic

cells is the cells is the location of chromosomeslocation of chromosomes..

– In an eukaryotic cell, chromosomes are contained in a true In an eukaryotic cell, chromosomes are contained in a true nucleus nucleus ))..

– In a prokaryotic cell, the DNA is concentrated in the In a prokaryotic cell, the DNA is concentrated in the nucleoidnucleoid) without a ) without a

membrane separating it from the rest of the cell. membrane separating it from the rest of the cell.

– In prokaryotic cell, DNA is a single strand or double strand DNA. But in In prokaryotic cell, DNA is a single strand or double strand DNA. But in

eukaryotic cell, DNA is double strand.eukaryotic cell, DNA is double strand.

1). 1). ProkaryoticProkaryotic and and eukaryoticeukaryotic cells cells differ in size and complexity differ in size and complexity

DifferencesDifferences

A)- ProkaryotesA)- Prokaryotes

What are Prokaryotes?What are Prokaryotes?

• It includes two Major Domains: Archaea and BacteriaIt includes two Major Domains: Archaea and Bacteria

• Prokaryotes are single-celled organisms that do not Prokaryotes are single-celled organisms that do not have a membrane-bound nucleus, and can live in have a membrane-bound nucleus, and can live in nearly every environment on Earth.nearly every environment on Earth.

• Although tiny, prokaryotes differ greatly in their Although tiny, prokaryotes differ greatly in their genetic traits, their modes of nutritiongenetic traits, their modes of nutrition, however,, however, their habitats are similar.their habitats are similar.

• Based on genetic differences, prokaryotes are Based on genetic differences, prokaryotes are grouped in two domains: Domain Archaea and grouped in two domains: Domain Archaea and Domain Bacteria.Domain Bacteria.

– “Prokaryote” means “before a nucleus”– No internal membrane-bound organelles –

just one little bag of cytoplasm– No nucleus – Usually single-celled (may form simple

colonies)– May or may not require oxygen for survival.– Earliest types of cells on Earth– Cell type of all bacteria and Archaea

Prokaryotes

Much tougher than eukaryotesCan survive almost anywhere – and do!

Have much greater genetic diversity than eukaryotesHave a cell wall surrounding the cell membrane (different chemistry from plant cell wall)

ProkaryotesProkaryotes

BacteriaBacteriaBacteriaBacteria ArchaeaArchaeaArchaeaArchaea

- Exist in extreme environments - Exist in extreme environments (hot and salty) (hot and salty)

- Exist in most - Exist in most environments environments

They are differing in some other They are differing in some other structuralstructural,, biochemical biochemical andand physiological physiological characteristics characteristics

Types of ProkaryotesTypes of Prokaryotes

1. Domain: 1. Domain: ArchaeaArchaea

• Archaea are extremophiles, “ حب ُمالقاسية of extreme ”للظروف

environments and can be classified into:

a)- Extreme halophiles للملوحة : ُم حب• live in such saline places as the Great

Salt Lake and the Dead Sea.

• Some species require an extremely salty الملوحة environment to شديدةgrow.

b)- Extreme thermophiles للحرارة live ُم حبin hot environments.

• The optimum temperatures for most thermophiles are 60 - 80°C.

بالزمى بالزمى غشاء غشاء

الخلوى الخلوى الجدار الجدار

شبه شبه نواةنواةالريبوزوماتالريبوزومات

الكبسالكبساألسوااألسواولةولة

طط

Bacteria occur in many shapes and sizes. Bacteria of four shapes: rod-Bacteria occur in many shapes and sizes. Bacteria of four shapes: rod-shaped, sphere-shaped, spiral-shaped, or filamentous-shaped.shaped, sphere-shaped, spiral-shaped, or filamentous-shaped.

2. Domain: Bacteria2. Domain: Bacteria

األهدااألهدابب

Prokaryotic CellProkaryotic Cell

CapsuleCapsuleCell WallCell WallPlasma Plasma membranemembrane

Cytoplasm Cytoplasm ((CytosolCytosol))

NucleoidNucleoidRibosomesRibosomes

• Bacteria occur in many shapes and sizes. Most bacteria have one of three basic shapes: rod-shaped, sphere-shaped, or spiral-shaped.

• Spiral shaped bacteria in the form of spirilla (singular, spirillum) or vibrio (comma like).

• Sphere-shaped bacteria are called cocci (singular, coccus). An example of cocci is Micrococcus luteus. Cocci are single or aggregate cells in different shapes.

• Rod-shaped bacteria are called bacilli (singular, bacillus). An example of bacilli is Escherichia coli. Bacilli are single or aggregate cells in different shapes also.

Shapes of BacteriaShapes of Bacteria

• It is a tool for identifying تعريف bacteria, based on differences in their cell walls.

• A)- Gram-positive (Gram +ve) bacteria:

• Their cell walls have large amounts كبيرة of peptidoglycans كميةthat react with Gram’s stain (appear violet-stained بنفسجيا .(تُـصبغ

The Gram’s stain: The Gram’s stain: جرام جرام صبغة صبغة

• B)- Gram-negative (Gram -ve) bacteria:

• their cell walls have no or small amount of peptidoglycan. So, do not react or very weakly react with Gram’s stain (appear red-stained باألحمر (تصبغ

The Gram’s stain: The Gram’s stain: جرام جرام صبغة صبغة

• Gram StainGram Stain

– Most species of bacteria are classified into two categories based on the structure of their cell walls as determined by a technique called the Gram stain.

– Gram-positive bacteriaGram-positive bacteria have a thick layer of

peptidoglycan in their cell wall, and they appear violet under a microscope after the Gram-staining procedure.

– Gram-negative bacteriaGram-negative bacteria have a thin layer of peptidoglycan in their cell wall, and they appear reddish-pink under a microscope after the Gram-staining procedure.

Summary of Gram’s stain: جرام صبغة

• Gram +ve bacteria: Gram +ve bacteria: have Large amount of peptidoglycan that stained violet.

• Gram –ve bacteria: Gram –ve bacteria: Have small amount or no peptidoglycan stained red.

Most Gram-negative species are pathogenic (ُممرضة ) more threatening ( خطورة .than gram-positive species (أكثر

Gram-negative bacteria are commonly more resistant ( ُممانعة (أكثرthan gram-positive species to antibiotics الحيويةللمضادات .

Summary of Gram’s stain: جرام صبغة

• Many prokaryotes (bacteria) secrete a sticky protective layer called capsule outside the cell wall.

• Capsule has the following functions وظائف:

Adhere تثبيت bacterial cells to their substratum السطح. Increase bacterial resistance المقاوُمة to host defenses ُمناعة

.العائل Stickتلصق) ) bacterial cells together when live in colonies. Protect تحمى bacterial cell.

I - the bacterial capsuleI - the bacterial capsule

• In all prokaryotes, the functions of the cell wall are as

following:

1. maintains تحافظ the shape of the cell,

2. affords physical protection الطبيعية توفر الحماية

3. prevents the cell from bursting ((إنفجار) ) in a hypotonic

environment ذات المنخفض التركيزالبيئة األسموزى .

• Most bacterial cell walls contain peptidoglycan

(a polymer of modified sugars cross-linked by short

polypeptides).

• The walls of Archaea lack ((تـفـتـقـد) ) peptidoglycan.

II - The bacterial cell wallII - The bacterial cell wall

Structural Characteristics of a Bacterial Cell

Nutritional and metabolic diversity 

All prokaryotes (and eukaryotes too) are grouped into four (4) categories according to how they obtain energy and carbon . 1.  Photoautotrophs                                    - Photosynthetic use light as the energy source                                    - CO2 is the carbon source

                                    Example:  Cyanobacteria; plants (eukaryotic).

2.  Chemoautotrophs     - Energy from oxidation of inorganic substances (e.g. NH4,

and S)     - CO2 is the carbon source

        Example:  Sulfolobus, Beggiatoa (shown on slide)                                                               

3.  Photoheterotrophs

     - Light as energy source

     - Organic compounds are source of carbon

 

4.  Chemoheterotrophs

      - Organic compounds are energy source and source of carbon (this includes humans)

 

Examples:  Many prokaryotes; animals (eukaryotic); fungi (eukaryotic)

• Cell division involves inward growth of the plasma membrane, dividing the parent cell into two daughter cells, each with a complete genome.

binary fission in bacteria

26

B- Eukaryotic CellB- Eukaryotic Cell

• In eukaryote cells, the chromosomes are contained within a membranous nuclear envelope.

• The region between the nucleus and the plasma membrane is the cytoplasm.– All the material within the plasma membrane of

a prokaryotic cell is cytoplasm.

• Within the cytoplasm of a eukaryotic cell is a variety of membrane-bounded organelles of specialized form and function.– These membrane-bounded organelles are

absent in prokaryotes.

• Eukaryotic cells are generally much bigger than prokaryotic cells.

• The logistics of carrying out metabolism set limits on cell size.– At the lower limit, the smallest bacteria,

mycoplasmas, are between 0.1 to 1.0 micron.– Most bacteria are 1-10 microns in diameter.– Eukaryotic cells are typically 10-100 microns in

diameter.

• An eukaryotic cell has internal membranes, which partition the cell into compartments .

• These membranes also participate in metabolism as many enzymes are built into membranes.

• The general structure of a biological membrane is a double layer of phospholipids and diverse proteins.

• Each type of membrane has a unique combination of lipids and proteins for its specific functions.

– For example, those in the membranes of mitochondria function in cellular respiration.

Internal membranes compartmentalize the Internal membranes compartmentalize the functions of a eukaryotic cellfunctions of a eukaryotic cell

Eu: True

Karyon: Nucleus

B- Eukaryotic CellB- Eukaryotic Cell

Animal CellAnimal Cell Plant CellPlant Cell

Compare between Animal and Plant Compare between Animal and Plant cell?cell?

What are the functions of cell organelles What are the functions of cell organelles ??

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.8

•Euokaryotes: Euo = true karyot = nucleus . Plant and animals have real nucleus, surrounded with nuclear membrane.

•-The Bacteria and the virus’s have no real nucleus they contain nucleiod region (no nuclear membrane) were the very simple genetic material (DNA or chromosome)

•-The prokaryotic cells (bacteria and viruses) also have a very simples cell structure cell wall, cell membrane, cytoplasm, ribosome’s and nucleiod area for a very simple genetic material (DNA or RNA) and cilia or flagella.

• The euokayotic cells have a very complex structure and many cell organelles (Look at the book page 112. 6th ed.)

33

ميتوكوندريميتوكوندرياا

غشاء غشاء بالزمىبالزمى

حهاز حهاز جولـچـىجولـچـى

ريبوسوريبوسومم

الهيكل الهيكل الخلوىالخلوى

مWحلل مWحلل جسم جسم

جسم جسم مركزىمركزى

سوط سوط حركىحركى

الشبكة الشبكة اإلندوبالزميةاإلندوبالزمية

النواةالنواة

المادة المادة الوراثيةالوراثية

نويةنوية

الجدار الجدار النووىالنووى

حلمات حلمات دقيقةدقيقة

34

فجوة فجوة مركزيةمركزية

بالستيدة بالستيدة خضراءخضراء

بينية بينية ثقوب ثقوب

الجدار الجدار الخلوىالخلوى

• Cytokinesis, division of the cytoplasm, typically follows mitosis.

• In animals, the first sign of cytokinesis (cleavage) is the appearance of a cleavage furrow in the cell surface near the old metaphase plate.

Cytokinesis in animal cell:

• Cytokinesis in plants, which have cell walls, involves a completely different mechanism.

• During telophase, vesicles from the Golgi coalesce at the metaphase plate, forming a cell plate.– The plate enlarges until its

membranes fuse with the plasma membrane at the perimeter, with the contents of the vesicles forming new wall material in between.

37

Prokaryotic vs. eukaryotic gene structure

prokaryotes:polycistronic transcripts

eukaryotes:monocistronic transcripts