Introduction to Eukaryotic cell structure Eukaryotic cell structure Function of cell organelles...
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Introduction to Eukaryotic cell 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 cellsThe eukaryotic cell structure is found in all plants, animals, fungi and protoctistsThe complex structure allows for the specialisation of cells to perform certain functionsWith the specialisation of function, cells can form tissues which can work together to form an organHence eukaryotic cells can form complex multicellular organisms
The animal cell
A eukaryotic animal cellMitochondriaNucleusLysosomeRough ERRibosomesSmooth ERVacuole
The plant cell
A eukaryotic plant cell
Eukaryotic cellular organelles and structureOrganelles Nucleus MitochondriaEndoplasmic reticulumRibosomesGolgi bodyLysosomesCentriolesChloroplastsVacuole
The detailed organisation of the cell is called the cell ultrastructure
The ultrastructure of a cell can only be seen using an electron microscope
Nuclear envelopeNuclear poreNucleolusChromatinMitochondrionRough ER
NucleusThe nucleus controls the cells activities It contains chromatin which are coils of DNA bound to protein. During cell division the chromatin condenses to form the chromosomes.The nucleus is surrounded by a nuclear envelope (double membrane) continuous with Rough ER. Pores allow transport of mRNA and nucleotides from the nucleus to the cytoplasm. The cytoplasm like material in the nucleus is called nucleoplasmA region called the nucleolus synthesises ribosomes.
DNA and histone proteins form chromatin. During cell division chromatin condenses to form visible chromosomes (prophase)
The MitochondriaMitochondria (pleural) mitochondrion (single) are sites isolated from the rest of the cytoplasm where enzyme-catalysed reactions of respiration take place.
Their main function is to synthesis ATP (adenosine tri-phosphate)The organelle has a double unit membrane the inner one being highly folded to increase surface area called the cristae.The inner and outer membrane are separated by a narrow fluid filled inter membrane spaceThe interior of the mitochondria contains a fluid called the matrixSome of the reactions of aerobic respiration takes place in the matrix while others on the inner membraneMitochondria have their own DNA (the genes code for respiratory enzymes)
Rough and smooth Endoplasmic Reticulum
Rough and smooth Endoplasmic ReticulumRough ER
Rough and smooth Endoplasmic ReticulumThere is a system of flattened membranes which form sacs in the cytoplasm of all eukaryotic cells called Endoplasmic Reticulum. It is continuous with the nuclear membrane and can link to the Golgi bodyIts function is to transport substances throughout the cellThe fluid filled spaces between the membranes are called cisternaeER encrusted with ribosomes is called Rough ER, whilst that devoid of ribosomes is smooth ER. Smooth ER is concerned with lipid metabolism and the manufacture of steroids. Rough ER transports proteins made by the ribosomes
RibosomesThese are the sites of protein synthesis within cells and are composed of ribosomal RNA and protein. Ribosomes are synthesised in a region of the nucleus called the nucleolus. They can be attached to the ER or free-floating in eukaryotic cells but only free-floating in prokaryotic cells. Attached ribosomes make proteins used outside the cell. Free-floating ribosomes make protein for use inside the cell.
Action of Lysosomes
LysosomesLarger vesicles surrounded by a single unit membrane - formed from the Golgi body. They contain hydrolytic enzymes (proteases and lipases) to digest the contents of food vacuoles with which they fuse. (Phagocytosis)They can also fuse with and digest worn out cellular organelles. The entire cell can be destroyed on occasions when the lysosomes break down (suicide bags).
CentriolesCentrioles are found in all animal cells, protoctists but not in higher plants.They are found outside the nucleus in a region of the cytoplasm called the centrosome.These have a 9 + 2 microtubular arrangement when viewed in cross-section. They consist of two hollow cylinders positioned at right angles to each other.They are the regions from which the spindle fibres emerge during cell division. Centrioles migrate to opposite ends of the nucleus and molecules of tubulin (a dimer protein with a large molecular weight) polymerise to form the spindle.
Chloroplast (Plants only)
Chloroplast (Plants only)Sites isolated from the rest of the cytoplasm in eukaryotic plant cells where reactions of photosynthesis occur. They consist of a double membrane with a fluid filled stroma.The stroma contains ribosomes, lipid, circular DNA and starchThe thylakoids (stack of pennies) form the granum and house the photosynthetic pigmentsThe thylakoids are adapted to form a large surface area to trap light Main function is to manufacture reduced nicotinamide adenine dinucleotide phosphate (NADP.H2) and ATP in the light dependent reactions, to use in the light independent reactions to fix CO2 into a storage carbohydrate (Starch).
Permanent VacuoleThese include numerous small vesicles found in animal cells (food vacuoles) and a large central cavity surrounded by a single membrane called the tonoplast, in plant cells.In animal cells vacuoles are a temporary store of food and secretions In plants the permanent vacuole is a store of amino acids, carbohydrates and lipids (mainly oils). They also store tannins and other substances that comprise cell sap.The cell sap provides an osmotic system which plants can alter to move water in and out
Structural components of the cellThese are the structural elements of the cell required for protection, shape, boundary layers and movement
Cellulose cell wallCytoskeletonFlagella and ciliaPlasma membraneCytoplasm
Cellulose cell wallThe cell wall consists of cellulose microfibrils embedded in a polysaccharide matrix.The cell wall provides strength and support and also permits the movement of water from cell to cell via the plasmodesmata.
PlasmodesmataThere are gaps in the cell wall that allow neighbouring cells to link togetherThere is a continuation of cytoplasm from cell to cell and the endoplasmic reticulum can also be linked
CytoskeletonThe cytoskeleton is an internal network of protein fibres which helps to keep the cell shape. There are three types:The actin filaments are able to move against each other and can cause the cell to move (WBC) or move organelles aroundIntermediate filaments help provide structureMicrotubules are cylinders made from a protein called tubulin. Microtubule motors on the tubulin use ATP for movementMove chromosomes during mitosisMove vesicles from ER to golgi body
Flagella and ciliaBoth have the same structure but cilia are shorter and tend to occur in greater numbers (flagella 1-2)Flagella also tend to move the entire cell (sperm) cilia tend to sweep substances and mucusEach consists of a cylinder with a 9 + 2 arrangement of microtubules which use ATP as a source of energy
Cell membraneFunction of the plasma membranes:Occur around the cell and determine what enters and leaves the cellOccur around organelles isolating enzymes within the organelleWithin organelles providing a large surface area for the attachment of enzymesProvide a transport system within the cell. e.g vesiclesThe structure of the plasma cell membrane will be studied in section 1.3
CytoplasmThe cytoplasm outside the organelles is called the cytosolThe cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is the site of glycolysis (respiration)
Plant and animal cells are eukaryotic cellsBoth types of cell possess characteristic organelles;NucleusRough endoplasmic reticulumSmooth endoplasmic reticulumMitochondriaGolgi apparatusMicrotubulesDifferences between mature plant and animal cells include:
Division of labourThe relationship between organellesThe DNA in the nucleus contains the code to produce the protein. A gene on the DNA will be copiedThe code will be transcibed by mRNAThe mRNA attaches to the ribosome (free or on RER)The protein will be made using tRNAThe assembled protein inside the RER will be pinched off into a vesicle and transported to the golgi bodyThe golgi will package the protein and maybe modifyAnother vesicle will be pinched off the golgi and moved to cell surface for exocytosis
Division of labourHow organelles work together