CELL CELL

TopicsTopics Cell structureCell structure Cell functionCell function Cellular organizationCellular organization Cellular metabolismCellular metabolism

(by Dr. Amjad Ali Khan)(by Dr. Amjad Ali Khan)

Introduction

The cell is the structural and functional The cell is the structural and functional basic basic unitunit of life. of life.

It was discovered by It was discovered by Robert HookeRobert Hooke and is and is the functional unit of all known living the functional unit of all known living organisms. organisms.

It is the It is the smallest unit of life smallest unit of life that is that is classified as a living thing, and is often classified as a living thing, and is often called the called the building block building block of life.of life.

Introduction

Some organisms, such as most bacteria, Some organisms, such as most bacteria, are are unicellularunicellular (consist of a single cell). (consist of a single cell).

Other organisms, such as humans, are Other organisms, such as humans, are multicellularmulticellular. .

Humans have about 100 trillion or 10Humans have about 100 trillion or 101414 cells; a typical cell size is cells; a typical cell size is 10 µm 10 µm (micrometer) and a typical cell mass is (micrometer) and a typical cell mass is 1 nanogram1 nanogram. .

Types of Cells

There are two types of cells: There are two types of cells:

prokaryotic prokaryotic and and

eukaryoticeukaryotic

Prokaryotic cells are usually Prokaryotic cells are usually independentindependent, while eukaryotic cells , while eukaryotic cells are often found in multicellular are often found in multicellular organisms.organisms.

Prokaryotic Cell

The prokaryote cell is The prokaryote cell is simplersimpler, and , and therefore therefore smallersmaller, than a eukaryote cell, , than a eukaryote cell, lacking a nucleus lacking a nucleus and most of the other and most of the other organelles of eukaryotes.organelles of eukaryotes.

Nuclear material of prokaryotic cell consist Nuclear material of prokaryotic cell consist of a of a single chromosome single chromosome which is in direct which is in direct contact with cytoplasm. Here the contact with cytoplasm. Here the undefined nuclear region in the cytoplasm undefined nuclear region in the cytoplasm is called is called nucleoidnucleoid..

On the outside, On the outside, flagella and pili flagella and pili may may be present. These facilitate the be present. These facilitate the movementmovement and and communicationcommunication between cells.between cells.

Enclosing the cell is the cell Enclosing the cell is the cell envelope envelope – generally consisting of a – generally consisting of a cell wall cell wall covering a plasma membranecovering a plasma membrane

General structure of a Prokaryotic cell

Eukaryotic Cell Cell

Eukaryotic cells are far Eukaryotic cells are far more advanced more advanced and and complexcomplex than a Prokaryotic cell. than a Prokaryotic cell.

Eukaryotic cell can be as much as Eukaryotic cell can be as much as 1000 1000 times bigger times bigger in size than a prokaryotic cell. in size than a prokaryotic cell.

eukaryotic cells contain membrane-bound eukaryotic cells contain membrane-bound compartments (compartments (organellesorganelles) in which ) in which specific metabolic activities take place.specific metabolic activities take place.

Most important among these is a Most important among these is a nucleusnucleus, a , a membrane bound compartment that membrane bound compartment that contains contains DNADNA. This nucleus gives the . This nucleus gives the eukaryote its name, which means "eukaryote its name, which means "truetrue nucleus.nucleus.

There are some differences in the structure There are some differences in the structure and function of animal and plant cells. and function of animal and plant cells. Though both cells are eukaryotic.Though both cells are eukaryotic.

In the cytoplasm the eukaryotic cell In the cytoplasm the eukaryotic cell contains many organelles such as:contains many organelles such as:

MitochondriaMitochondria Endoplasmic reticulum (rough and smooth)Endoplasmic reticulum (rough and smooth) Golgi bodiesGolgi bodies LysosomesLysosomes PeroxisomesPeroxisomes RibosomesRibosomes Chloroplast (found in plant cells)Chloroplast (found in plant cells) VacuoleVacuole centriolecentriole

Simple structure of a eukaryotic cell

Eukaryotic cell organelles

There are several types of organelles in a There are several types of organelles in a cell. cell.

Some (such as the nucleus and golg Some (such as the nucleus and golg apparatus) are typically apparatus) are typically solitarysolitary, while , while others (such as mitochondria, peroxisomes others (such as mitochondria, peroxisomes and lysosomes) can be and lysosomes) can be numerousnumerous (hundreds to thousands). (hundreds to thousands).

The The cytosolcytosol is the gelatinous fluid that fills is the gelatinous fluid that fills the cell and surrounds the organelles.the cell and surrounds the organelles.

Nucleus The cell The cell nucleusnucleus is the most conspicuous is the most conspicuous

organelle found in a eukaryotic cell. It organelle found in a eukaryotic cell. It contains the contains the chromosomeschromosomes, ,

The nucleus is The nucleus is sphericalspherical and separated and separated from the cytoplasm by a from the cytoplasm by a double double membranemembrane called the called the nuclear envelopenuclear envelope..

The nuclear envelope isolates and protects The nuclear envelope isolates and protects a cell's DNAa cell's DNA

The nucleolus is a specialized region The nucleolus is a specialized region within the nucleus where ribosome within the nucleus where ribosome subunits are assembled. subunits are assembled.

In prokaryotes, DNA processing takes In prokaryotes, DNA processing takes place in theplace in the

cytoplasm. cytoplasm.

Mitochondria Mitochondria play a critical role in Mitochondria play a critical role in

generating energy generating energy in the eukaryotic cell so in the eukaryotic cell so it is also called “it is also called “power house of a cellpower house of a cell. .

Mitochondria are Mitochondria are self-replicating self-replicating organelles that occur in various numbers, organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all shapes, and sizes in the cytoplasm of all eukaryotic cells. eukaryotic cells.

Mitochondria multiply by splitting in two.Mitochondria multiply by splitting in two. Respiration occurs in the cell Respiration occurs in the cell

mitochondria. mitochondria.

General structure of MitochondriaGeneral structure of Mitochondria

Endoplasmic reticulum The The endoplasmic reticulum (ER) endoplasmic reticulum (ER) is the is the

transporttransport network for molecules targeted network for molecules targeted for certain for certain modifications modifications and specific and specific destinations.destinations.

The ER has two forms: the The ER has two forms: the rough ERrough ER, which , which has has ribosomes on its surfaceribosomes on its surface and secretes and secretes proteins into the cytoplasm, and the proteins into the cytoplasm, and the smooth ERsmooth ER, which lacks them, which lacks them. .

Endoplasmic ReticulumEndoplasmic Reticulum

Golgi apparatus

The primary function of the Golgi The primary function of the Golgi apparatus is to process and apparatus is to process and packagepackage the the macromolecules such as proteins and macromolecules such as proteins and lipids that are synthesized by the cell.lipids that are synthesized by the cell.

It is particularly important in the It is particularly important in the

processing of proteins for processing of proteins for secretionsecretion..

It consists of It consists of -cis and -trans faces-cis and -trans faces

Golgi apparatus

Ribosomes

The ribosome is a large The ribosome is a large complex of complex of RNA and protein molecules. RNA and protein molecules.

They each consist of two subunits, They each consist of two subunits, and act as an assembly line where and act as an assembly line where RNA from the nucleus is used to RNA from the nucleus is used to synthesize proteins from amino synthesize proteins from amino acids. acids.

Ribosomes

Ribosomes can be found either Ribosomes can be found either floating freely or bound to endoplas-floating freely or bound to endoplas-mic reticulum in eukaryotes, or the mic reticulum in eukaryotes, or the cell membrane in prokaryotes).cell membrane in prokaryotes).

In prokaryotic cells In prokaryotic cells 70S70S ribosomes ribosomes are present while in eukaryotic cells are present while in eukaryotic cells 80S80S ribosomes are present ribosomes are present

Lysosomes

Lysosomes contain Lysosomes contain digestive digestive enzymesenzymes. They digest excess or . They digest excess or worn-out organellesworn-out organelles,, food particles food particles,, andand engulfed viruses engulfed viruses oror bacteria. bacteria.

These organelles (lysosomes and These organelles (lysosomes and peroxisomes) are often called a peroxisomes) are often called a ""suicide bagsuicide bag" because of their ability " because of their ability to detonate and destroy the cell.to detonate and destroy the cell.

Vacuoles

Vacuoles Vacuoles store food and wastestore food and waste. Some . Some vacuoles store extra water. vacuoles store extra water.

The vacuoles of eukaryotic cells are The vacuoles of eukaryotic cells are usually larger in those of plants than usually larger in those of plants than animals.animals.

CentrioleCentriole In animal cells, centrioles are short In animal cells, centrioles are short

cylinders present near the nucleus.cylinders present near the nucleus. There is always one pair of centrioles There is always one pair of centrioles

near the nucleus.near the nucleus. Before a cell divides, the centrioles Before a cell divides, the centrioles

duplicate.duplicate. During cell division, the pair of During cell division, the pair of

centrioles separate so that each cell centrioles separate so that each cell gets one pair of centrioles.gets one pair of centrioles.

The cytoskeletonThe cytoskeleton

Several types of Several types of filamentousfilamentous proteins proteins form a cytoskeleton that helps form a cytoskeleton that helps maintain the maintain the cell’s shape cell’s shape and either and either anchors the organelles anchors the organelles or or assists assists their movementtheir movement..

The cytoskeleton includes The cytoskeleton includes microtub-microtub-ulesules and and actinactin filaments. filaments.

MICROTUBULESMICROTUBULES Microtubules are shaped like thin Microtubules are shaped like thin

cylinders and are several times cylinders and are several times larger than actin filaments.larger than actin filaments.

Microtubules are made up of Microtubules are made up of tubulintubulin.. Microtubules Microtubules can assemble and dis-can assemble and dis-

assembleassemble. . It is well known that during cell It is well known that during cell

division, division, microtubules form spindle microtubules form spindle fibresfibres, which assist the movement of , which assist the movement of chromosomeschromosomes

Cilia and FlagellaCilia and Flagella Cilia and flagella are projections of Cilia and flagella are projections of

cells that can move. cells that can move.

Cilia are shortCilia are short (2-10µm) while (2-10µm) while flagella flagella are longerare longer about 200 µm. about 200 µm.

Cells that have these organelles are Cells that have these organelles are capable of capable of self movement self movement or moving or moving material along the surface of the cell.material along the surface of the cell.

Cellular metabolismCellular metabolism

Cellular metabolism includes all the Cellular metabolism includes all the chemical reactions chemical reactions that occur in a that occur in a cell. cell.

Quite often these reactions are Quite often these reactions are organized in a organized in a metabolic pathwaysmetabolic pathways, , which can be shown as:which can be shown as:

AA BB CC DD

11 2 2 33

AA BB CC DD

11 2 2 33 The letters The letters A,B,C,D are the reactants A,B,C,D are the reactants

and productsand products whereas whereas 1,2,3 are the 1,2,3 are the enzymesenzymes which take part in the which take part in the reactions.reactions.

Every reaction in a cell requires a Every reaction in a cell requires a specific enzymespecific enzyme

Different types of enzymes present in Different types of enzymes present in a cell which act on different a cell which act on different substrates are:substrates are:

SubstrateSubstrate EnzymeEnzyme•LipidLipid lipaseslipases•ProteinProtein proteaseprotease•UreaUrea ureaseurease•MaltoseMaltose maltasemaltase•LactoseLactose lactaselactase

General structure of a Plant cell

Difference between prokaryotic Difference between prokaryotic and eukaryotic celland eukaryotic cell

Prokaryotic Eukaryotic

Typical organisms bacteria, archaea plants, animals, fungi

Size of cell 1 – 10 µm 10 – 100 µm

Type of nucleus No real nucleus True nucleus

Cell organelles (mitochnodria, chloroplast, ER, golgi bodies, lysosomes etc) Absent present

Ribosomes 70S 80S

Cell division Binary fission Mitosis and meiosis

DNA Circular , in cytoplasm In chromosomes, in nucleus

Difference and common between animal cell and plant cellDifference and common between animal cell and plant cell

Structure Animal Cell Plant cell

Cell membrane yes Yes

nucleus Yes yes

Nucleolus Yes yes

Ribosomes Yes yes

ER Yes yes

Golgi bodies Yes yes

Centrioles yes No

Cell wall No Yes

Mitochnondria yes Yes

Chloroplast No Yes

One big vacuole No Yes

cytoskeleton Yes Yes

Cell theory

The The cell theorycell theory, first developed in 1839 by , first developed in 1839 by Schleiden and SchwannSchleiden and Schwann, states that , states that

all organisms are composed of one or all organisms are composed of one or more cells, more cells,

that all cells come from pre-existing cells,that all cells come from pre-existing cells, that vital functions of an organism occur that vital functions of an organism occur

within cells, within cells,

Cell theory

and that all cells contain the and that all cells contain the hereditary information hereditary information necessary for necessary for regulating cell functions and for regulating cell functions and for transmitting information to the next transmitting information to the next generation of cells.generation of cells.

The word “Cell” was first coined by The word “Cell” was first coined by Robert Hooke in 1665Robert Hooke in 1665

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