Introduction to Eukaryotic Introduction to Eukaryotic cell structurecell structure

• Eukaryotic cell structure• Function of cell organelles• Function of cell structural components• Differences between plant and animal cells• Division of labour within a cell

Eukaryotic cellsEukaryotic cells

The eukaryotic cell structure is found in all The eukaryotic cell structure is found in all plants, animals, fungi and protoctistsplants, animals, fungi and protoctists

The complex structure allows for the The complex structure allows for the specialisation of cells to perform certain specialisation of cells to perform certain functionsfunctions

With the specialisation of function, cells With the specialisation of function, cells can form tissues which can work together can form tissues which can work together to form an organto form an organ

Hence eukaryotic cells can form complex Hence eukaryotic cells can form complex multicellular organismsmulticellular organisms

The animal cell

A eukaryotic animal cell

Mitochondria

Nucleus

Lysosome

Rough ER

Ribosomes

Smooth ER

Vacuole

The plant cell

A eukaryotic plant cell

Eukaryotic cellular organelles and Eukaryotic cellular organelles and structurestructure

Organelles Organelles Nucleus Nucleus MitochondriaMitochondria Endoplasmic Endoplasmic

reticulumreticulum RibosomesRibosomes Golgi bodyGolgi body LysosomesLysosomes CentriolesCentrioles ChloroplastsChloroplasts VacuoleVacuole

The detailed The detailed organisation of organisation of the cell is called the cell is called the cell the cell ultrastructureultrastructure

The ultrastructure The ultrastructure of a cell can only of a cell can only be seen using an be seen using an electron electron microscopemicroscope

Nuclear envelope

Nuclear pore

Nucleolus

Chromatin

MitochondrionRough ER

NucleusNucleus The nucleus controls the cells activities The nucleus controls the cells activities It contains chromatin which are coils of DNA It contains chromatin which are coils of DNA

bound to protein. During cell division the bound to protein. During cell division the chromatin condenses to form the chromatin condenses to form the chromosomes.chromosomes.

The nucleus is surrounded by a nuclear The nucleus is surrounded by a nuclear envelope (double membrane) continuous with envelope (double membrane) continuous with Rough ER. Pores allow transport of mRNA and Rough ER. Pores allow transport of mRNA and nucleotides from the nucleus to the cytoplasm. nucleotides from the nucleus to the cytoplasm.

The cytoplasm like material in the nucleus is The cytoplasm like material in the nucleus is called nucleoplasmcalled nucleoplasm

A region called the nucleolus synthesises A region called the nucleolus synthesises ribosomes. ribosomes.

DNA and histone proteins form DNA and histone proteins form chromatin. During cell division chromatin. During cell division

chromatin condenses to form visible chromatin condenses to form visible chromosomes (prophase)chromosomes (prophase)

The MitochondriaThe Mitochondria

The MitochondriaThe Mitochondria

The MitochondriaThe MitochondriaMitochondriaMitochondria (pleural) (pleural) mitochondrionmitochondrion (single) are (single) are

sites isolated from the rest of the cytoplasm where sites isolated from the rest of the cytoplasm where enzyme-catalysed reactions of respiration take enzyme-catalysed reactions of respiration take place.place.

Their main function is to synthesis ATP (adenosine tri-Their main function is to synthesis ATP (adenosine tri-phosphate)phosphate)

The organelle has a double unit membrane – the inner one The organelle has a double unit membrane – the inner one being highly folded to increase surface area called the cristae.being highly folded to increase surface area called the cristae.

The inner and outer membrane are separated by a narrow The inner and outer membrane are separated by a narrow fluid filled inter membrane spacefluid filled inter membrane space

The interior of the mitochondria contains a fluid called the The interior of the mitochondria contains a fluid called the matrixmatrix

Some of the reactions of aerobic respiration takes place in the Some of the reactions of aerobic respiration takes place in the matrix while others on the inner membranematrix while others on the inner membrane

Mitochondria have their own DNA (the genes code for Mitochondria have their own DNA (the genes code for respiratory enzymes)respiratory enzymes)

Smooth Endoplasmic ReticulumNucleus

Nuclear envelope

Rough endoplasmic

reticulum

Transitional elements

Golgi body

Rough and smoothRough and smooth Endoplasmic Reticulum Endoplasmic Reticulum

Rough and smoothRough and smooth Endoplasmic Reticulum Endoplasmic Reticulum

Rough ER

Rough and smoothRough and smooth Endoplasmic Reticulum Endoplasmic Reticulum

There is a system of flattened membranes There is a system of flattened membranes which form sacs in the cytoplasm of all which form sacs in the cytoplasm of all eukaryotic cells called Endoplasmic eukaryotic cells called Endoplasmic Reticulum. Reticulum.

It is continuous with the nuclear It is continuous with the nuclear membrane and can link to the Golgi bodymembrane and can link to the Golgi body

ItIt’’s function is to transport substances s function is to transport substances throughout the cellthroughout the cell

The fluid filled spaces between the The fluid filled spaces between the membranes are called cisternaemembranes are called cisternae

ER encrusted with ribosomes is called ER encrusted with ribosomes is called Rough ER, whilst that devoid of ribosomes Rough ER, whilst that devoid of ribosomes is smooth ER. is smooth ER.

Smooth ER is concerned with lipid Smooth ER is concerned with lipid metabolism and the manufacture of metabolism and the manufacture of steroids. steroids.

Rough ER transports proteins made by the Rough ER transports proteins made by the ribosomesribosomes

RibosomesRibosomes

RibosomesRibosomes

RibosomesRibosomes These are the sites of protein synthesis These are the sites of protein synthesis

within cells and are composed of within cells and are composed of ribosomal RNAribosomal RNA and and proteinprotein. .

Ribosomes are synthesised in a region of Ribosomes are synthesised in a region of the nucleus called the the nucleus called the nucleolusnucleolus. .

They can be attached to the ER or free-They can be attached to the ER or free-floating in eukaryotic cells but only free-floating in eukaryotic cells but only free-floating in prokaryotic cells. floating in prokaryotic cells.

Attached ribosomes make proteins used Attached ribosomes make proteins used outside the cell. outside the cell.

Free-floating ribosomes make protein for Free-floating ribosomes make protein for use inside the cell.use inside the cell.

Golgi BodyGolgi Body

Golgi BodyGolgi Body

Action of Lysosomes

LysosomesLysosomes

LysosomesLysosomes

Larger vesicles surrounded by a single unit Larger vesicles surrounded by a single unit membrane - formed from the Golgi body. membrane - formed from the Golgi body.

They contain hydrolytic enzymes (proteases They contain hydrolytic enzymes (proteases and lipases) to digest the contents of food and lipases) to digest the contents of food vacuoles with which they fuse. vacuoles with which they fuse. (Phagocytosis)(Phagocytosis)

They can also fuse with and digest worn out They can also fuse with and digest worn out cellular organelles. The entire cell can be cellular organelles. The entire cell can be destroyed on occasions when the lysosomes destroyed on occasions when the lysosomes break down (break down (suicide bagssuicide bags).).

CentriolesCentrioles Centrioles are found in all animal cells, protoctists but Centrioles are found in all animal cells, protoctists but

not in higher plantsnot in higher plants.. They are found outside the nucleus in a region of the They are found outside the nucleus in a region of the

cytoplasm called the centrosome.cytoplasm called the centrosome. These have a 9 + 2 microtubular arrangement when These have a 9 + 2 microtubular arrangement when

viewed in cross-section. viewed in cross-section. They consist of two hollow cylinders positioned at right They consist of two hollow cylinders positioned at right

angles to each other.angles to each other. They are the regions from which the spindle fibres They are the regions from which the spindle fibres

emerge during cell division. Centrioles migrate to emerge during cell division. Centrioles migrate to opposite ends of the nucleus and molecules of tubulin (a opposite ends of the nucleus and molecules of tubulin (a

dimer protein with a largedimer protein with a large molecular weight) polymerise molecular weight) polymerise to form the spindle.to form the spindle.

Chloroplast (Plants only)Chloroplast (Plants only)

Chloroplast (Plants only)Chloroplast (Plants only) Sites isolated from the rest of the cytoplasm Sites isolated from the rest of the cytoplasm in in

eukaryotic plant cellseukaryotic plant cells where reactions of where reactions of photosynthesis occur. photosynthesis occur.

They consist of a double membrane with a fluid They consist of a double membrane with a fluid filled stroma.filled stroma.

The stroma contains ribosomes, lipid, circular The stroma contains ribosomes, lipid, circular DNA and starchDNA and starch

The thylakoids (stack of pennies) form the The thylakoids (stack of pennies) form the granum and house the photosynthetic pigmentsgranum and house the photosynthetic pigments

The thylakoids are adapted to form a large The thylakoids are adapted to form a large surface area to trap light surface area to trap light

Main function is to manufacture reduced Main function is to manufacture reduced nicotinamide adenine dinucleotide phosphate nicotinamide adenine dinucleotide phosphate (NADP.H(NADP.H22) and ATP in the light dependent ) and ATP in the light dependent reactions, to use in the light independent reactions, to use in the light independent reactions to fix COreactions to fix CO22 into a storage carbohydrate into a storage carbohydrate (Starch).(Starch).

Permanent VacuolePermanent Vacuole

Permanent VacuolePermanent Vacuole These include numerous small vesicles found in These include numerous small vesicles found in

animal cells (food vacuoles) and a large central animal cells (food vacuoles) and a large central cavity surrounded by a single membrane called cavity surrounded by a single membrane called the tonoplastthe tonoplast, in plant cells., in plant cells.

In animal cells vacuoles are a temporary store of In animal cells vacuoles are a temporary store of food and secretions food and secretions

In plants the permanent vacuole is a store of In plants the permanent vacuole is a store of amino acids, carbohydrates and lipids (mainly amino acids, carbohydrates and lipids (mainly oils). They also store tannins and other substances oils). They also store tannins and other substances that comprise cell sap.that comprise cell sap.

The cell sap provides an osmotic system which The cell sap provides an osmotic system which plants can alter to move water in and outplants can alter to move water in and out

Structural components of the Structural components of the cellcell

These are the structural elements of the cell These are the structural elements of the cell required for protection, shape, boundary required for protection, shape, boundary layers and movementlayers and movement

Cellulose cell wallCellulose cell wall CytoskeletonCytoskeleton Flagella and ciliaFlagella and cilia Plasma membranePlasma membrane CytoplasmCytoplasm

Cellulose cell wallCellulose cell wall

The cell wall consists The cell wall consists of cellulose of cellulose microfibrils embedded microfibrils embedded in a polysaccharide in a polysaccharide matrix.matrix.

The cell wall provides The cell wall provides strength and support strength and support and also permits the and also permits the movement of water movement of water from cell to cell via from cell to cell via the plasmodesmata.the plasmodesmata.

Plasmodesmata

There are gaps in the cell wall that allow neighbouring cells to link together

There is a continuation of cytoplasm from cell to cell and the endoplasmic reticulum can also be linked

CytoskeletoCytoskeletonn

CytoskeletonCytoskeleton

The cytoskeleton is an internal network of The cytoskeleton is an internal network of protein fibres which helps to keep the cell protein fibres which helps to keep the cell shape. There are three types:shape. There are three types: The actin filaments are able to move against The actin filaments are able to move against

each other and can cause the cell to move (WBC) each other and can cause the cell to move (WBC) or move organelles aroundor move organelles around

Intermediate filaments help provide structureIntermediate filaments help provide structure Microtubules are cylinders made from a protein Microtubules are cylinders made from a protein

called tubulin. Microtubule motors on the tubulin called tubulin. Microtubule motors on the tubulin use ATP for movementuse ATP for movement

Move chromosomes during mitosisMove chromosomes during mitosis Move vesicles from ER to golgi bodyMove vesicles from ER to golgi body

Flagella and ciliaFlagella and cilia Both have the same Both have the same

structure but cilia are structure but cilia are shorter and tend to occur shorter and tend to occur in greater numbers in greater numbers (flagella 1-2)(flagella 1-2)

Flagella also tend to move Flagella also tend to move the entire cell (sperm) the entire cell (sperm) cilia tend to cilia tend to ‘‘sweepsweep’’ substances and mucussubstances and mucus

Each consists of a cylinder Each consists of a cylinder with a 9 + 2 arrangement with a 9 + 2 arrangement of microtubules which use of microtubules which use ATP as a source of energyATP as a source of energy

Cell membraneCell membrane

Function of the plasma membranes:Function of the plasma membranes: Occur around the cell and determine what Occur around the cell and determine what

enters and leaves the cellenters and leaves the cell Occur around organelles isolating enzymes Occur around organelles isolating enzymes

within the organellewithin the organelle Within organelles providing a large surface Within organelles providing a large surface

area for the attachment of enzymesarea for the attachment of enzymes Provide a transport system within the cell. Provide a transport system within the cell.

e.g vesiclese.g vesiclesThe structure of the plasma cell membrane will be studied in section 1.3

CytoplasmCytoplasm

The cytoplasm outside the organelles The cytoplasm outside the organelles is called the cytosolis called the cytosol

The cytosol is a complex mixture of The cytosol is a complex mixture of cytoskeleton filaments, dissolved filaments, dissolved molecules, and water that fills much molecules, and water that fills much of the volume of a cell. of the volume of a cell.

The cytosol is the site of glycolysis The cytosol is the site of glycolysis (respiration)(respiration)

ANIMAL CELL PLANT CELLCourtesy of Dr. Julian

Thorpe – EM & FACS Lab, Biological Sciences

University Of Sussex

Plant and animal cells are eukaryotic cells

Both types of cell possess characteristic organelles;•Nucleus•Rough endoplasmic reticulum•Smooth endoplasmic reticulum•Mitochondria•Golgi apparatus•Microtubules

Differences between mature plant and animal cells include:

PLANT CELLS•Cellulose cell wall•Large vacuoles that store cell sap•Chloroplasts in photosynthetic cells

ANIMAL CELLS•Microvilli•Centrioles

Division of labourDivision of labour The relationship between organellesThe relationship between organelles

The DNA in the nucleus contains the code to The DNA in the nucleus contains the code to produce the protein. A gene on the DNA will be produce the protein. A gene on the DNA will be copiedcopied

The code will be The code will be ‘‘transcibedtranscibed’’ by mRNA by mRNA The mRNA attaches to the ribosome (free or on The mRNA attaches to the ribosome (free or on

RER)RER) The protein will be made using tRNAThe protein will be made using tRNA The assembled protein inside the RER will be The assembled protein inside the RER will be

pinched off into a vesicle and transported to the pinched off into a vesicle and transported to the golgi bodygolgi body

The golgi will package the protein and maybe The golgi will package the protein and maybe modifymodify

Another vesicle will be pinched off the golgi and Another vesicle will be pinched off the golgi and moved to cell surface for exocytosismoved to cell surface for exocytosis

Division of labourDivision of labourHow organelles work How organelles work

togethertogether